Techno-economic evaluation of soap production from waste cooking oil with additives derived from citrus peel waste.

Techno-economic evaluation of soap production from waste cooking oil with additives derived from citrus peel waste. | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Techno-economic evaluation of soap production from waste cooking oil with additives derived from citrus peel waste. Beatrice Walelu Mwamba, Mensah Sarpong Brobbey, Bianke Leodolff, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4017927/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In the pursuit of sustainable waste management practices, this study explores the technical and economic feasibility of soap production using waste cooking oil (WCO) combined with citrus peel waste (CPW), with a specific focus on extracting limonene as soap additives. The preliminary experimental investigations indicated that soaps produced from WCO have similar qualities if properly treated, compared to those produced from virgin oils. Also, including limonene effectively addresses WCO odours and demonstrates a promise of anti-microbial properties against E.coli . From the comprehensive techno-economic evaluation of WCO-based soap production, a focus on industrial symbiosis by integrating CPW-derived limonene is necessary. Results show that soap production with WCO and on-site additive in limonene (scenario 3) was competitive, with an IRR of 19% compared to 16% when the soap was produced using WCO and the additives were purchased (scenario 4). Also, the minimum selling prices of soaps were comparable for scenarios 3 (R 160.53/kg) and 4 (R 159.87/kg), further building on the economic viability of on-site limonene production. Hence, the environmental potential and economic viability of integrating WCO and CPW into soap production seem to be a profitable approach should on-site production be implemented. Waste recycling citrus peel waste process simulation soap production green chemistry Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Highlights A technoeconomic model for soap production from agricultural and municipal waste. A pre-treatment strategy for the waste cooking oil (WCO) scenario is necessary for soap quality. Soaps produced from WCO had similar properties to those produced from virgin oil. On-site production of additives resulted in an MSP of R160.53 per kg as compared to a R172 per kg market price. 1. Introduction Food waste is a significant problem in today's global economy, with a considerable amount being lost during the supply and consumption stages of food production [ 1 ]. This waste has a detrimental impact on the environment and the human life cycle, contributing to an increase in global greenhouse gas emissions, deforestation, loss of biodiversity, and depletion of natural resources [ 1 ]. To mitigate these effects, reducing food waste and utilizing food residue, such as waste cooking oil (WCO), for sustainable practices is crucial. Despite the versatility of WCO, its potential for sustainable chemical or product manufacture is yet to be fully realized. Therefore, exploring the long-term viability of WCO could be a promising approach towards sustainability [ 1 ] In a world estimate, over 41 million tonnes of WCO are produced annually, highlighting an urgent need for sustainable solutions to this waste problem [ 2 ]. In South Africa for example, approximately 2 million tonnes of vegetable and oilseed oil are consumed each year, with an estimated 32% wasted [ 2 , 3 ], which poses a threat to the environment, and violets the 2008 Waste Management Act [ 4 ]. While WCO is currently used to produce different products (e.g., biodiesel, energy, bio-lubricant, and animal feed [ 5 ]), more research is needed to explore its long-term viability through finding new and innovative ways for system sustainability. Conventional uses of WCO have inherent limitations when it comes to sustainability: biodiesel production requires large amounts of water and energy, direct burning leads to air pollution, while the application as animal feed may result in water pollution and possibly eutrophication [ 6 , 7 ]. In contrast, using WCO for soap production has not been extensively investigated, although it portrays the following benefits: Firstly, soap is a household product used daily, which means using WCO for soap production could create a sustainable way of recycling. Secondly, soap production could be a cost-effective way of using WCO feedstock, as it does not require the same level of pre-treatment, and refining, compared to biodiesel and bio-lubricants production. Lastly, using WCO for soap production could have a significant social impact, because soap is essential for sanitation and hygiene. Moreover, considering the simplicity of soap-making processes, it is easily transferable which could ultimately create employment opportunities [ 8 , 9 ]. Furthermore, soap production becomes more attractive when suitable soap additives are added. For example, the valorization of citrus peel waste (CPW) offers one such additive in the form of D-Limonene. D-Limonene is a monoterpene found in the peels of citrus fruits with known anti-microbial properties [ 10 , 11 ]. Apart from its anti-microbial properties, it is also a natural solvent, a degreaser and has a pleasant scent[ 12 ]. Adding D-Limonene could help to enhance the cleansing power and the consumer appeal of the soaps. Nevertheless, the presence of D-Limonene makes the CPW difficult to compost and unsuitable for animal feed or fermentation processes [ 13 , 14 ], as its high acidic content is challenging for biodegradation and fermentation, further exacerbating issues surrounding food waste management [ 13 ]. Therefore, extracting D-Limonene from CPW could offer a dual solution, both adding value to soap production technology and mitigating issues in food waste management. Fundamentally, soaps are produced by a reaction between triglyceride esters and a strong mineral base, which is either sodium hydroxide for hard soaps or potassium hydroxide for soft soaps [ 8 , 15 ]. The quality of the soaps produced depends on numerous factors, these include the type and quality of the oil or the fat used, temperature and the duration of the reaction, the concentration of the mineral base, pH, and water content [ 16 ]. Adequate stirring during soap making also plays an important role, as it ensures that the oils are exposed to the base [ 17 ]. Since the quality of the soaps is affected by the quality of the oil used, it is essential to compare soaps made from waste cooking oil to those made from unused, fresh oils, as a benchmark for potential system scalability and economic viability [ 18 ]. Therefore, this study initially investigated the experimental production of soap using WCO and CPW (results presented in the supplementary material), as a technique to evaluate the experimental feasibility and to understand the production steps that are necessary for developing a techno-economic model. Furthermore, the study investigated four different soap production scenarios to understand the economic potential of producing soap from a combination of WCO and CPW. Thus, permitted an understanding of the mass and energy balances, economic potential and the sensitivity prospects from input indicators using an Aspen Plus® simulations model. Overall, this study provides valuable insights into the feasibility of using WCO and CPW for sustainable soap production and highlights this approach's potential benefits and challenges for the industry. 2. Materials and Methods 2.1. Approach The work set out to evaluate techno-economics for soap production using WCO and CPW. The modelling was conducted through Aspen Plus® using data gathered from experimental feasibility studies (soap making) and existing literature. For the experiments, soaps were made using filtered waste cooking oil, treated waste cooking oil, and compared to virgin cooking oil (olive oil). In brief, WCO was pre-treated through a succession of filtration (using muslin cloth), brine washing and chemical bleaching. The WCO was washed twice with 10% brine solution (at a ratio of 1:1) at 50 ℃ for 1 minute under constant mixing. The mixture was transferred to a separatory funnel and allowed to stand for 2 hours for the brine and oil-organic phases to separate. After the brine had been decanted, the WCO was bleached at 70 ℃ for 30 minutes, under constant stirring using 3% H 2 O 2 solution, allowed to stand for 12 hours and then H 2 O 2 solution was then decanted. Soaps were then made using a blend of soft oils (WCO or olive oil) and hard oil (coconut oil) at varying soft oil compositions (78.4, 62.4, and 46.5% wt) at 20 ℃. 4% wt D-limonene from CPW was added once the ‘trace’ stage had been achieved. The soaps were allowed to air dry for 4 weeks, after which pH, moisture content and anti-microbial activities (against E. coli ) were tested (results presented in supplementary materials, Figures S1 – S5). The experimental pre-treatment experimental approach was therefore adopted for modelling, using the composition of the best performing soap composition for modelling. 2.2. Modelling Four process simulations were performed, with a feed rate of 64.2 kg/h of oil for all scenarios and 302 kg/h of citrus peel waste in Scenarios 1 and 3. This calculation basis was assumed based on typical production rates of citrus fruit processor ALG Estates in the Western Cape, South Africa, corresponding to 20,000 ton/yr citrus fruits processed of which 50–60% end up as CPW [ 19 , 20 ]. ALG Estates is situated in the Cederberg municipal area, with a population of 74,000, producing about 1.28 ton/yr of WCO [ 21 ]. 40% collection rate of the estimated mass of WCO from surrounding towns was assumed [ 3 , 22 ]. The compositions of waste cooking, olive, and coconut oils, and citrus peel waste are provided in the Supplementary Sheet (Tables S1 and S2). The Peng-Robinson property method was used in the Aspen Plus ® simulations. 2.2.1. Process description The scenarios developed were as follows: Scenario 1 – production of soap using olive oil with limonene production from CPW on-site; Scenario 2 – production of soap using olive oil with limonene purchased; Scenario 3 – production of soap using WCO with limonene production from CPW on-site; Scenario 4 – production of soap using WCO with limonene purchased. For olive oil scenarios (1 and 2), area 100 was excluded from the process. For scenarios (2 and 4) where limonene was purchased, area 500 was excluded from the process. In reference to the Aspen simulation, the process flow diagram is provided in a comprehensive diagram in the supplementary sheet (Figure S6), and the following process description is provided below: Area 100: Waste cooking oil treatment 64.2 kg/hr of untreated waste cooking oil enters the plant at 20°C and 1 bar and is stored in the oil storage tank (TK-103). Once enough oil has been collected for the plant to run continuously, the oil is withdrawn from TK-103 and filtered in rotary filter F-101 to remove gross solid impurities. The solid impurities are disposed of as non-hazardous waste while the filtered oil is mixed with a 10 wt% heated brine solution in a 1:1 volume ratio (mixer M-101). The mixture is then sent to decanter D-101 where two immiscible phases readily form. The aqueous phase contains the brine solution and polar compounds removed from the oil. This forms the bottom phase and is decanted, sent to treatment works and disposed of. The oil phase is decanted and washed with hot brine a second time in M-102 and decanted in D-102. Area 200: Oil hydrolysis and crude glycerol removal The washed and filtered oil is mixed with coconut oil stored in TK-201 using static mixer M-201. The oil blend, comprised of 78.4 wt% treated WCO, is pumped to 40 bar in P-202 A/B and sent to the bottom of the hydrolyser (T-201). 36.9 kg/hr of hot water is sent to the top of T-201 so that the oil hydrolysis takes place counter-currently. The hydrolysis takes place at 40 bar and 250°C. With a 2-hour residence time in the hydrolyser, the expected conversion of triglycerides to fatty acids at these conditions is 99%. The bottom product, sweet water, is 20.8 wt% glycerol, 79wt% water and the remainder trace amounts of impurities. The moisture is removed from this stream by flash evaporation in FL-201 at 10 bar and 202°C to produce an 80.1% crude glycerol stream. Area 300: Fatty acid drying and distillation. The distillate stream from T-201 contains the fatty acids produced in the oil hydrolysis reaction. This fatty acid stream, at a flow rate of 78.4 kg/hr, has a mass composition of 9.0% water, 87.7% fatty acids, 0.9% triglycerides, 1.3% glycerol, and 1.1% polar impurities from the raw feed. The fatty acid stream is flash dried in FL-301 and the water content is reduced to 1.4 wt%. The water vapour product from FL-301 is sent to wastewater treatment while the liquid product is sent to distillation tower T-301. T-301 operates at 0.0013 bar and separates the fatty acids from remaining impurities in the feed stream. This vacuum distillation tower contains a partial condenser and a kettle reboiler. There are 6 stages excluding the condenser and reboiler. At a distillate rate of 61.7 kg/h, the distillate product stream has a weight composition of 95.0% fatty acids, 1.6% glycerol, 1.7% moisture, 0.3% polar impurities and the balance triglycerides. Although the moisture and glycerol have not been completely removed, the purification steps in FL-301 and T-301 are not intensified because, for soap production, additional water and glycerol content are not disadvantageous to the process. The distillate stream is then compressed to 5 bar in C-301 and completely condensed in shell-and-tube condenser E-301. Area 400: Fatty acid neutralisation The liquid fatty acid stream is sent to static mixer M-401. Sodium hydroxide pellets, which are stored on the plant in TK-401, are mixed with deionised water to create a 33 wt% NaOH solution. The solution is stored in TK-402 and sent to M-401 to be mixed with the fatty acid stream before being sent to the neutralisation reactor (R-401). The reactor operates at 5 bar and 93°C. After a residence time of 30 minutes in the reactor, the conversion of fatty acids to soap is 98%. The neat soap exits the reactor at 93°C and 87.1 kg/h as a warm liquid. This product stream is sent to a dryer (FL-401) to reduce the moisture content from 25.0 wt% to 11.8 wt% through simultaneous cooling and drying. The cooled, dried soap is sent to amalgamator M-402 where it is mixed with D-Limonene extracted from citrus peel waste in Area 500. Citric acid is also added to reduce the soap's pH and to form sodium citrate, which acts as a chelator in the soap. This soap mixture is sent to finishing operations in Area 600 where the final steps are performed to produce the packaged soap product. Area 500: D-Limonene extraction from citrus peel waste Raw citrus peel waste (CPW) enters the process at varying rates and is crushed in a hammer mill (H-501) before being stored in TK-501, a hopper. The CPW remains in storage until the production process can take place in the continuous mode. H-501 reduces the size of the CPW from a mean size of 75 mm to 0.5 mm. The crushed CPW is flash-dried in FL-501 and the resulting solids residue can be used for animal fodder and/or compost on ALG Estates’ farm. The vapour product stream, with a composition of 95% D-Limonene and the remainder of water and other monoterpenes, is condensed in E-501 and decanted in D-501. Area 600: Soap finishing operations The neat soap, which now contains D-Limonene, is sent to the soap finishing line. An extruder gives the soap a new shape before it is cut into bars and stamped. 3 conveyor belts are used for the transportation of the soap within the finishing operations (Shreve and Austin, 1984). Finally, a small packing machine automates the packaging of the finished soaps. 2.2.2. Cost estimations, Profitability, and Sensitivity analysis 2.2.2.1. Capital cost estimation: A study estimate was used to determine the capital costs, as detailed in Turton (2018). Firstly, the equipment costs were found in one of three ways: cost correlations found in Turton (2018), equipment cost estimations mapped in Aspen Plus ®, or scaled from costs quoted by industry suppliers. For the costs estimated using correlations, the relevant capacity parameter (A) of each major piece of equipment was used to estimate the base case cost of the equipment (Cp°). This base cost was scaled to account for the pressure and material of construction of the equipment. The chemical engineering plant cost index (CEPCI) for 2022 was used to scale for time. This gave estimates of the capital cost of each unit (Cp). It was assumed that a 3% delivery levy was imposed on the total equipment capital cost. Finally, the delivered equipment cost was used to estimate the direct and indirect capital costs of the plant. 2.2.2.2. Operating cost estimation: To estimate the operating costs, the cost of raw materials, waste treatment, utilities, and operating labour was calculated explicitly, and the rest of the operating costs were calculated as factors of these as per the factor approach given in Turton (2018). For the waste cooking oil plant, the material requirements were calculated using the flow rates from the results of the Aspen Plus ® simulation and materials costs listed in the assumptions in overleaf. The cost of the waste cooking oil included a 10% transportation cost associated with collecting the material from nearby towns. Citric acid was not included in the Aspen Plus ® simulation but the mass of citric acid added was 2% of the oil mass as proposed in Burke (2005). For utilities, the costs mapped in Aspen Plus ® were used while operating labour costs were determined by estimating the number of plant operators required and an assumed annual salary of R299 000 for a chemical plant operator. 2.2.2.3. Economic evaluation and performance indicators: The fixed capital investment, cost of manufacturing without depreciation, soap, crude glycerol, and D-Limonene production rates and selling prices as well as the assumptions listed below were used to conduct the profitability analysis. The negative cash flows from capital investments and land purchases were accounted for over 2 years before plant operation. Once the operation began, the revenue and expenses were used to calculate yearly profit. The profit was then taxed, and depreciation was incorporated. The cash flows were then discounted; the sum of the discounted cash flow gives the net present value at a 10% discount rate. The present value ratio (PVR), discount payback period (DPBP), discounted cash flow rate of return (DCFROR), minimum selling price (MSP, calculated as the price at which the NPV is R 0 at a 10% discount rate) were calculated as key economic indicators. Table 1 Major assumptions made to perform the profitability analysis. Assumption Reference and/or justification Discount rate 10% Engineering judgement Cost Year 2022 Construction period 2 years: 60% and 40% completion in years 1 and 2, respectively Engineering judgement Plant life 10 years Engineering judgement Depreciation Straight-line method over 6 years (no salvage) Similar scenario; [ 23 ] Taxation rate 30% Company tax rate in South Africa is 27% as stated by SARS. 30% is chosen as a conservative approach Exchange rate 18.08 R/USD Exchange rate as of 28 Oct 2022 (Bloomberg, 2022) Yearly operating hours 8 000 Similar scenario; [ 23 ] Land R3 800 000 for additional land Typical price of land used for citrus farming in Citrusdal Buildings R2 808 000 for additional buildings Estimate of land area required for soap production plant based on O’live Soap Factory (PayFast, 2021) Cost of chemicals R109.99/kg of NaOH pellets (98.5% purity) Purchasing price at ChemLab Supplies R7.8/kg of NaCl pellets Purchasing price at ChemLab Supplies 4 USD/kg of coconut oil Purchasing price from Alibaba.com 120 USD/ton of WCO Purchasing price from Alibaba.com 1 200 USD/ton of olive oil Purchasing price from Alibaba.com 2.5 USD/kg of citric acid Purchasing price from Alibaba.com 14.5 USD/ton of deionised water (Turton et al., 2018) No cost involved for CPW CPW from fruit processing on the plant is used as raw feed Selling price of products R19.8/115 g of soap Selling price of similar soap type sold by Soap Factory (small business in South Africa) 10 USD/kg of 95% D-Limonene Purchasing price at ChemLab Supplies 0.09 USD/lb of 80% crude glycerol [ 25 ] Cost of utilities 1 0.0674 USD/kWh of electricity [ 26 ] 4.22 USD/ton of LPS [ 26 ] 15.7 USD/m 3 of cooling water [ 26 ] 1 Adjusted for the cost year of 2022 using inflation 2.2.2.4. Sensitivity and Monte Carlo Simulation All scenarios were subjected to a sensitivity analysis to determine how a 30% change in a few parameters would affect the NPV. The economic parameters considered for the analysis were exchange rate, soap selling price, WCO purchasing price, equipment cost, and crude glycerol price among others. For every parameter considered, all other parameters were kept constant to determine the effect on the NPV. Monte Carlo simulations were performed for simultaneous changes in the variables of up to 20%. The 20% range represents an optimistic case, where the variables do not deviate far from their original values. A total of 1,000 iterations were performed for all scenarios to determine the effect of the variability on the NPV. 3. Results and discussion 3.1. Material and energy balance results A summary of the mass and energy results is provided in Table 2 . As seen in this table, scenarios 1 and 2 used olive oil in the production process while scenarios 3 and 4 used WCO as the soft oil for soap production. After pretreatment procedures, a 10% loss in mass was seen in scenarios 3 and 4 leading to about 8% less product rate (84.5 kg/h for olive oil and 78 kg/h for WCO) compared to scenarios 1 and 2 (see Table 2 ). Also, in scenarios 1 and 3 where CPW was treated, excess limonene was obtained (Table 2 ) which was sold for income generation as a by-product. These changes will correspond to an economy of scale benefits for the olive oil scenarios which will be discussed in the profitability section. Scenarios 3 and 4 had the highest electricity demand per soap produced (see Table 2 ) which was due to the need to treat the WCO. As seen with the use of waste vegetable oil in green diesel production and other bioprocesses, the treatment of feedstock significantly increases energy demand and cost depending on the level of contamination [ 27 , 28 ]. Also, it can be observed that the production of limonene on-site (scenarios 1 and 3) resulted in less than a 1% increase in the electricity demand of the process when compared to Scenarios 2 and 4 respectively. The increase in electricity will result in an increase in the operating costs of the scenario and implies additional treatment strategies should be more beneficial and economically sustainable based on production scale-up potential. In terms of the heating demand, the WCO scenarios were also higher than the olive oil scenarios. This was partly due to the preheating requirement included based on experimental understanding of utilizing a brine solution in the pretreatment of the WCO which was avoided in Scenarios 1 and 2 (Table 2 ). The cooling demand of the scenarios indicates a higher demand (about 1%) for olive oil scenarios compared to WCO scenarios. This demand decreases by 5% when comparing Scenario 1 with Scenario 2. This is due to the contribution of cooling demand in the production of limonene from CPW which is excluded from Scenario 2 and 4. Table 2 Material and energy balance results Scenario Parameter 1 2 3 4 Mass of WCO, kg/h - - 64.2 64.2 Mass of treated WCO, kg/h - - 57.8 57.8 Mass of Olive oil, kg/h 64.2 64.2 - - Mass of Limonene used, kg/h 4.224 4.224 4.028 4.028 Mass of excess Limonene, kg/h 3.91 - 4.11 - Mass of excess glycerol, kg/h 8.45 8.45 7.53 7.53 Soap production rate, kg/h 84.5 84.5 78.0 78.0 Electricity demand, MJ/kg soap 2.06 2.04 2.13 2.11 Heating demand, MJ/kg soap 2.02 2.02 2.26 2.26 Cooling demand, MJ/kg soap 0.764 0.721 0.756 0.715 3.2. Economic assessment 3.2.1. Capital costs A breakdown of the equipment costs per plant area is illustrated with a summary of the economic parameters given in Table 3 . As seen in Fig. 2 , the hydrolysis and neutralisation areas (Areas 200 and 400, respectively) had high costs associated with them for all scenarios (i.e., about 20–40% cost for all scenarios). The equipment costs in Areas 200 and 400 are larger for the olive oil scenarios (1 and 2) i.e., 30% and 41% which corresponded to about R 5 million for both scenarios (Fig. 2 ). There is a high cost (about R5.6 million) associated with Area 100 (waste cooking oil pre-treatment) which accounts for 26% and 33% of the equipment cost for Scenario 3 and 4 respectively. This significantly increases the equipment cost for the WCO scenarios compared to the olive oil scenarios. From Scenario 1 and 3, it can be observed that the production of limonene accounted for 26% and 21% cost respectively (Fig. 2 ). This corresponds to an amount of R 4.6 million increase in the equipment cost for the scenarios when compared (scenario 1 vs. 2 and scenario 3 vs. 4). The total costs of equipment are R 21.6 million and R 17.0 million (Table 3 ) for the WCO scenarios and R 17.4 million and 12.8 million for the olive oil scenarios. Hence it can be observed that treatment of WCO significantly increases the equipment cost of the process (about 24%) whilst the production of limonene onsite also results in an increase of about 35% in the equipment costs of the process (see Fig. 1 ). The main capital costs for the plants are shown below. The WCO scenarios had a higher total cost of equipment which translates into all the capital costs for the scenarios as these are a function of equipment cost Table 3 . Table 3 Summary of economic results for all scenarios Parameter Scenario 1 2 3 4 Total Equipment Cost, Million R 17.43 12.85 21.35 16.79 Direct Cost, Million R 52.62 38.78 64.51 50.68 Indirect Costs, Million R 11.85 8.74 14.53 11.42 Working Capital, Million R 13.29 9.79 16.29 12.80 Fixed Capital, Million R 74.16 54.67 90.93 71.43 Direct Manufacturing Cost, Million R 61.70 65.88 51.19 55.08 Fixed Costs, Million R 16.74 14.95 18.48 16.70 General manufacturing expenses, Million R 11.87 8.75 14.55 11.43 Total Operating Cost, Million R 90.47 89.74 84.47 83.46 Minimum selling price, R/kg 150.61 150.40 160.53 159.87 NPV, Million R 62.66 64.44 31.23 33.01 IRR, % 25 30 19 16 Payback period, years 2.95 2.52 3.9 3.6 3.2.2. Operational costs Figure 3 below illustrates the raw material, waste treatment, utility, and labour costs for the four soap production scenarios investigated. A raw material cost of R33.6 million is required for Scenario 1 mainly due to the purchase of olive oil (which accounts for 45% of the raw materials cost). The cost further increases by 18% when limonene is purchased in Scenario 2 compared to Scenario 1 where it was produced onsite. Also, the raw materials cost from scenarios 1 and 2 were higher than those for the WCO scenarios (R 20.2 million for scenario 3 and R 26.0 million for scenario 4), and implies should WCO feedstock be purchased or even collected with incentives, its operability for soap production would increase should sufficient and proper treatment procedures be put in place for smooth operations. Looking at all scenarios, the cost of utilities was below R 760 000 although WCO scenarios are lower (16%) than for the olive oil scenarios (see Fig. 3 ). The waste treatment costs for Scenarios 3 and 4 are R 2.5 million compared to R 1.48 million for Scenarios 1 and 2. This was due to the disposal costs associated with the brine-contaminated water in the WCO treatment in Scenarios 3 and 4. The total operating costs were found to be higher when using olive oil as opposed to WCO and also higher when comparing the purchase of limonene as a raw material as opposed to producing it on-site Table 3 . This implies aside from the added environmental benefits of producing limonene from CPW, there exists an economic incentive as far as operating costs are concerned. The labour costs for the Scenarios were close without significant difference, there was a 2% increase in the labour cost for the WCO scenarios due to the increase in equipment at the pretreatment of the WCO. Similarly, the removal of the limonene production resulted in less than 1% reduction in labour costs when compared (see Fig. 3 ). Although the cost of labour and waste treatment are lower for the olive oil scenarios, the higher raw material cost increases its operating cost just above that of the WCO scenarios. The lower raw material cost highlights one advantage of the use of WCO in large-scale soap production, which should be capitalised upon in future iterations of this plant design. 3.2.3. Profitability analysis Table 3 provides the performance parameters from the profitability analyses of the scenarios as well. The high product rate for the olive oil scenarios 1 and 2 seen in Table 2 , contributes to increasing the profitability compared to the WCO scenarios (3 and 4). At a discount rate of 10%, the positive net present values (NPVs) of all scenarios indicate economic feasibility, although the olive oil plants were observed to be more profitable (about 50% higher NPV for scenario 1 vs. 3). It may also be observed that the production of limonene on site further increases the NPV for the scenarios (about R 2 million), this was mainly due to the additional revenue from the excess limonene produced in the scenarios (Scenario 1 and 2). This shows that besides the environmental benefits of the production of limonene, it increases the profitability of the process as well. The WCO scenarios (Scenario 3 and 4) had a longer discounted payback period (DPBP). As shown in Table 3 . The WCO plant was found to recover its land and working capital costs after 3.6 and 3.9 years of plant life for Scenario 3 and 4 respectively. However, the olive oil case recovers these costs after 3.0 and 2.5 years of plant life for Scenario 1 and 2. Hence, it could be more beneficial if incentives such as cost reduction in obtaining the WCO are put in place to make them directly competitive in the production of soap and further drop its payback time than the Olive oil cases. The minimum selling price (MSP) of the soap was found to be lower than the market price of about R 172 per kg of soap. This indicates that the scenarios are profitable and translated to the positive NPVs obtained. The MSP of Scenarios 1 and 2 were lower than for Scenarios 3 and 4 which indicates a higher profitability for the olive oil scenarios (about 6%). The low difference (R 150 vs 160) in MSPs indicates that WCO scenarios are competitive and can be further made attractive to match up the MSP of the olive oil scenarios. From Scenarios 1 and 2 it can be observed that production of limonene onsite accounted for less than 1% decrease in the MSP of the soap (R 150.61 vs R 150.40, see Table 3 ). This was because of the reduction in the operating costs associated with limonene purchases. This can also be observed from Scenarios 3 and 4, indicating soaps can be competitive where the limonene is produced onsite and has the added advantage of using CPW making it an environmentally friendlier process. The IRR for the scenarios investigated ranged from 16–30% which is above the discount rate of 10% indicating all scenarios are profitable. The IRR for the WCO scenarios were lower than the olive oil scenarios by 9–12% for both scenarios. 3.2.4. Sensitivity analysis A sensitivity analysis was performed for the waste cooking oil case and the Strauss plots shown in Fig. 4 were generated. The plant profitability for all scenarios is highly sensitive to the selling price of the soap. The soap price used in the base case, R 172.17 per kg (R 19.8/115 g of soap), was selected based on typical prices of similar artisan soaps made from olive and coconut oil. A 30% decrease in the selling price results in a large decrease in NPV making all the scenarios unprofitable with a negative NPV. On the other hand, the NPV is resilient to changes in the crude glycerol selling price, taxation rate, and WCO price as seen in the relatively flat slope in Fig. 4 . The NPV is also significantly affected by the exchange rate in all scenarios which also translates to the equipment cost. A 30% increase in the exchange rate makes all scenarios end with a negative NPV, whilst a 30% decrease in the exchange rate significantly improves the profitability as well. The exchange rate is influential in the NPV calculations as the USDRand exchange rate is used in most of the calculations of equipment, utility, and raw material costs. The limonene price was observed to also have a slight impact on the NPV although not resulting in negative NPVs with a 30% increase in the price, the change was however experienced more in Scenario 2 (Fig. 4 b) and Scenario 4 (Fig. 4 d) where limonene was purchased. From the Monte Carlo simulation shown in Fig. 5 , it was found that the likelihood of plant profitability is higher than 80% for all scenarios. This gives reasonable motivation for the development of large-scale soap production from WCO as well. This is good motivation for the waste valorisation plant as it does not have well-documented precedence from previous plants. The Monte Carlo simulations were performed for simultaneous changes in the variables of up to 20%. As seen in Fig. 5 a and c, plant profitability (NPV > 0) is about 80% for Scenarios 1 and 3 where limonene is produced. This number increases to more than 95% for scenarios where limonene was purchased (Scenario 2 and 4). 3.3. Technical and eco-conscious evaluation Other important factors must be considered in addition to economic indicators for this proposed process. The rate of recovery of WCO is an important consideration. This factor has an impact on plant profitability because it determines production capacity and, as a result, plant revenue. According to a previous study, developing countries are expected to have a WCO valorisation rate of 23.3% (Teixeira et al., 2018). However, in the current study, a 40% collection rate was assumed based on a study that found that up to 53% collection is possible in a small enough control volume (De Feo et al., 2020). Furthermore, because this plant offers to pay for the oil, households will be incentivized to provide their WCO. WCO collection from households has another important consideration, environmental impact. Due to unconscious behaviours, WCO from households end up being disposed of in sinks or with solid food residues, ending up in water resources and landfills [ 6 , 29 ]. There are multiple issues associated with WCO ending up in wastewater, such as; increasing wastewater treatment costs, damage to infrastructure, and they cause odours. Additionally, the oil layer on water resources would affect aquatic life, by reducing oxygen levels as well as sunlight penetration, thereby negatively impacting the aquatic ecosystem [ 29 ]. It is apparent that WCO volarization would lead to less WCO entering wastewater treatment works, allowing communities to reduce their environmental impact, a sentiment not necessarily shared by the virgin olive oil scenario. Industrial symbiosis of soap production from WCO with on-site limonene extraction from CPW is also an important consideration. CPW are often dumped into landfills or burned, resulting in soil quality degradation and air pollution. Additionally, this waste finds its way into water resources, leading to reduced dissolved oxygen as well as increased acidity. The issues of CPW waste management by disposal are further exuberated by the presence of essential oils, more specifically limonene which limits biodegradability due to its anti-microbial properties. Therefore, extraction and utilization of limonene not only offer advantages in enhancing soap quality but also aid in the reduction of CPW waste management issues[ 14 ]. Finally, public perception and product marketability are essential considerations for soap production from the WCO plant. The profitability estimate assumed that all units produced in an operating year would be sold at market price during the course of the plant’s 10-year existence. This assumption does not take into account changes in demand, which have a direct impact on sales. As a result, the design and development of this plant will require market research to evaluate whether customers notice significant changes between WCO, and soaps made from wasted oils. This will indicate whether the market demand is high enough to justify the development of this plant. Such research is critical since the sensitivity study of this plant indicated that the NPV is extremely sensitive to the selling price of the soaps. 4. Conclusion Soap production from WCO, coupled with additives from CPW (limonene) is a promising means for reducing waste, whilst also being a profitable process. Experimental results showed that soaps produced from WCO had comparable quality while the addition of additives such as D-limonene did not only contribute to the reduction of odour from WCO but could also be a potential and promising anti-microbial agent. In terms of the comprehensive techno-economic evaluation of soap production from WCO in comparison to a traditional soap production oil (olive), key insights were developed and demonstrated below. On-site production of additives and utilisation of WCO : From Scenario 3, higher initial capital expenditures (CAPEX) due to additional equipment are required and should be compensated for in the 6% reduction in operating expenditures (OPEX) of obtaining the WCO and producing the limonene on site. The process could recoup its working investment in 3.9 years with an IRR of 1 9 %. This implies its recycling potential of both CPW and WCO for environmental sustainability is accompanied by investment prospects. Purchasing additives and utilisation of WCO : From scenario 4, with the lowest IRR of 1 6 % was reported with a payback period of 3.6 years. This scenario seems feasible should a plant require investment in this range; however, environmental benefits are primarily reliant on the WCO waste, and a lower NPV and an increased MSP should be expected thereby reducing potential investors and consumers purchasing power. Declarations Credit authorship contribution statement Beatrice Walelu Mwamba : Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing – original draft, Visualization. Mensah Sarpong Brobbey : Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing – original draft, Visualization, Bianke Leodolff : Methodology, Writing – editing, Supervision. Shaun Peters : Resources, Methodology, Writing – editing, Supervision. George Mbella Teke : Conceptualisation, Writing – review and editing, Project administration, Supervision. Zwonaka Mapholi : Resources, Conceptualization, Writing – review and editing, Project administration, Supervision. Data availability: The data generated and analysed during this study is available from the corresponding author upon reasonable request. Conflict of interest – The authors declare that they have no conflict of interest. Acknowledgements The authors would like to acknowledge the technical and financial support from the Department of Chemical Engineering, and the Institute of Plant Biotechnology (Department of Natural Sciences), Stellenbosch University (South Africa). The opinions and views expressed, and conclusions derived at, are those of the authors and not necessarily attributed to Stellenbosch University. References FAO: Food loss and waste - Framing the issues. The State of the World. 1–19 (2019) Orjuela, A., Clark, J.: Green chemicals from used cooking oils: Trends, challenges, and opportunities. Curr Opin Green Sustain Chem. 26, 100369 (2020). https://doi.org/10.1016/J.COGSC.2020.100369 Teixeira, M.R., Nogueira, R., Nunes, L.M.: Quantitative assessment of the valorisation of used cooking oils in 23 countries. Waste Management. 78, (2018). https://doi.org/10.1016/j.wasman.2018.06.039 Linganiso, E.C., Tlhaole, B., Magagula, L.P., Dziike, S., Linganiso, L.Z., Motaung, T.E., Moloto, N., Tetana, Z.N.: Biodiesel Production from Waste Oils: A South African Outlook. Sustainability 2022, Vol. 14, Page 1983. 14, 1983 (2022). https://doi.org/10.3390/SU14041983 Mannu, A., Vlahopoulou, G., Urgeghe, P., Ferro, M., Del Caro, A., Taras, A., Garroni, S., Rourke, J.P., Cabizza, R., Petretto, G.L.: Variation of the Chemical Composition of Waste Cooking Oils upon Bentonite Filtration. Resources 2019, Vol. 8, Page 108. 8, 108 (2019). https://doi.org/10.3390/RESOURCES8020108 Orjuela, A., Clark, J.: Green chemicals from used cooking oils: Trends, challenges, and opportunities. Curr Opin Green Sustain Chem. 26, 100369 (2020). https://doi.org/10.1016/J.COGSC.2020.100369 Liu, Y., Yang, X., Adamu, A., Zhu, Z.: Economic evaluation and production process simulation of biodiesel production from waste cooking oil. Current Research in Green and Sustainable Chemistry. 4, 100091 (2021). https://doi.org/10.1016/J.CRGSC.2021.100091 Félix, S., Araújo, J., Pires, A.M., Sousa, A.C.: Soap production: A green prospective. Waste Management. 66, 190–195 (2017). https://doi.org/10.1016/J.WASMAN.2017.04.036 Azme, S.N.K., Yusoff, N.S.I.M., Chin, L.Y., Mohd, Y., Hamid, R.D., Jalil, M.N., Zaki, H.M., Saleh, S.H., Ahmat, N., Manan, M.A.F.A., Yury, N., Hum, N.N.F., Latif, F.A., Zain, Z.M.: Recycling waste cooking oil into soap: Knowledge transfer through community service learning. Cleaner Waste Systems. 4, 100084 (2023). https://doi.org/10.1016/J.CLWAS.2023.100084 Dosoky, N.S., Setzer, W.N.: Biological Activities and Safety of Citrus spp. Essential Oils. Int J Mol Sci. 19, (2018). https://doi.org/10.3390/IJMS19071966 Han, Y., Sun, Z., Chen, W.: Antimicrobial Susceptibility and Antibacterial Mechanism of Limonene against Listeria monocytogenes. Molecules. 25, (2020). https://doi.org/10.3390/MOLECULES25010033 Siddiqui, S.A., Pahmeyer, M.J., Assadpour, E., Jafari, S.M.: Extraction and purification of d-limonene from orange peel wastes: Recent advances. Ind Crops Prod. 177, 114484 (2022). https://doi.org/10.1016/J.INDCROP.2021.114484 Santiago, B., Moreira, M.T., Feijoo, G., González-García, S.: Identification of environmental aspects of citrus waste valorization into D-limonene from a biorefinery approach. Biomass Bioenergy. 143, (2020). https://doi.org/10.1016/J.BIOMBIOE.2020.105844 Mbella Teke, G., De Vos, L., Smith, · Isle, Kleyn, T., Mapholi, Z.: Development of an ultrasound-assisted pre-treatment strategy for the extraction of d-Limonene toward the production of bioethanol from citrus peel waste (CPW). Bioprocess and Biosystems Engineering 2023. 1, 1–11 (2023). https://doi.org/10.1007/S00449-023-02924-Y Hill, M.: Product and process design for structured products. AIChE Journal. 50, 1656–1661 (2004). https://doi.org/10.1002/AIC.10293 Rahayu, S., Pambudi, K.A., Afifah, A., Fitriani, S.R., Tasyari, S., Zaki, M., Djamahar, R.: Environmentally safe technology with the conversion of used cooking oil into soap. J Phys Conf Ser. 1869, 012044 (2021). https://doi.org/10.1088/1742-6596/1869/1/012044 Mabrouk, S.T.: Making usable, quality opaque or transparent soap. J Chem Educ. 82, 1534–1537 (2005). https://doi.org/10.1021/ED082P1534 Abera, B.H., Diro, A., Beyene, T.T.: The synergistic effect of waste cooking oil and endod (Phytolacca dodecandra) on the production of high-grade laundry soap. Heliyon. 9, e16889 (2023). https://doi.org/10.1016/j.heliyon.2023.e16889 Satari, B., Karimi, K.: Citrus processing wastes: Environmental impacts, recent advances, and future perspectives in total valorization. Resour Conserv Recycl. 129, 153–167 (2018). https://doi.org/10.1016/J.RESCONREC.2017.10.032 Anwar, F., Naseer, R., Bhanger, M.I., Ashraf, S., Talpur, F.N., Aladedunye, F.A.: Physico-Chemical Characteristics of Citrus Seeds and Seed Oils from Pakistan. Journal of the American Oil Chemists’ Society 2008 85:4. 85, 321–330 (2008). https://doi.org/10.1007/S11746-008-1204-3 WCG: Wastern Cape Integrated Waste Management Plant 2022 - 2027 (Draft_. , Cape Town (2022) Williams, J.B., Clarkson, C., Mant, C., Drinkwater, A., May, E.: Fat, oil and grease deposits in sewers: Characterisation of deposits and formation mechanisms. Water Res. 46, 6319–6328 (2012). https://doi.org/10.1016/J.WATRES.2012.09.002 Lohrasbi, M., Pourbafrani, M., Niklasson, C., Taherzadeh, M.J.: Process design and economic analysis of a citrus waste biorefinery with biofuels and limonene as products. Bioresour Technol. 101, 7382–7388 (2010). https://doi.org/10.1016/J.BIORTECH.2010.04.078 Bloomberg: USD to ZAR Exchange Rate, https://www.bloomberg.com/quote/USDZAR:CUR Abdul Raman, A.A., Tan, H.W., Buthiyappan, A.: Two-Step Purification of Glycerol as a Value Added by Product From the Biodiesel Production Process. Front Chem. 7, 439904 (2019). https://doi.org/10.3389/FCHEM.2019.00774/BIBTEX Turton, R., Bailie, R.C., Whiting, W.B., Shaeiwitz, J.A., Bhattacharyya, D.: Analysis, Synthesis, and Design of Chemical Processes Fourth Edition. (2018) Glisic, S.B., Pajnik, J.M., Orlović, A.M.: Process and techno-economic analysis of green diesel production from waste vegetable oil and the comparison with ester type biodiesel production. Appl Energy. 170, 176–185 (2016). https://doi.org/10.1016/J.APENERGY.2016.02.102 Okoro, O.V., Sun, Z., Birch, J.: Meat processing waste as a potential feedstock for biochemicals and biofuels – A review of possible conversion technologies. J Clean Prod. 142, 1583–1608 (2017). https://doi.org/10.1016/J.JCLEPRO.2016.11.141 Foo, W.H., Chia, W.Y., Tang, D.Y.Y., Koay, S.S.N., Lim, S.S., Chew, K.W.: The conundrum of waste cooking oil: Transforming hazard into energy. J Hazard Mater. 417, 126129 (2021). https://doi.org/10.1016/J.JHAZMAT.2021.126129 Supplementary Files Supplementarysheet.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4017927","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":280651396,"identity":"d9ce05ce-e73b-4e98-b9c0-5aa58e3bb9df","order_by":0,"name":"Beatrice Walelu Mwamba","email":"","orcid":"","institution":"Stellenbosch University","correspondingAuthor":false,"prefix":"","firstName":"Beatrice","middleName":"Walelu","lastName":"Mwamba","suffix":""},{"id":280651397,"identity":"9e4fdd7a-1112-48ab-bff0-ba681044a0b5","order_by":1,"name":"Mensah Sarpong Brobbey","email":"","orcid":"","institution":"Stellenbosch University","correspondingAuthor":false,"prefix":"","firstName":"Mensah","middleName":"Sarpong","lastName":"Brobbey","suffix":""},{"id":280651398,"identity":"d7447ccb-a900-49b7-aada-ac28d4f9b111","order_by":2,"name":"Bianke Leodolff","email":"","orcid":"","institution":"Stellenbosch University","correspondingAuthor":false,"prefix":"","firstName":"Bianke","middleName":"","lastName":"Leodolff","suffix":""},{"id":280651399,"identity":"774eed7e-18b0-4639-a51c-9699eeac6921","order_by":3,"name":"Shaun Peters","email":"","orcid":"","institution":"Stellenbosch University","correspondingAuthor":false,"prefix":"","firstName":"Shaun","middleName":"","lastName":"Peters","suffix":""},{"id":280651400,"identity":"2f4f07e8-cc85-49af-bf13-3e67c93143cc","order_by":4,"name":"George Mbella Teke","email":"","orcid":"","institution":"Stellenbosch University","correspondingAuthor":false,"prefix":"","firstName":"George","middleName":"Mbella","lastName":"Teke","suffix":""},{"id":280651401,"identity":"490747d8-079b-4bbd-9df2-89e8c1f2f310","order_by":5,"name":"Zwonaka Mapholi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzklEQVRIiWNgGAWjYJACZgYGCx5+UrVI8Eg2kKqFweAAscrlpx1+9rigQkLG+PwZswcMNXYM8u0ENDPOTjM3nnFGgsfsRo65AcOxZAbGngQCjpJOMJPmbQNp4TGTYGA7AHQmAS1s0unfwFqM+88Atfw7wMDG/wC/Fh7pHIgtBgw5ZhKMbQcYeCQI2CIhnVNuzAP0i8SNtDKJxL5kHgkJArbIz07f9pinwsaev//wNokP3+zk5PsJ2ALyDoIJVMxDUD2qllEwCkbBKBgF2AAALhgx+1q8NgMAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-5240-8233","institution":"Stellenbosch University","correspondingAuthor":true,"prefix":"","firstName":"Zwonaka","middleName":"","lastName":"Mapholi","suffix":""}],"badges":[],"createdAt":"2024-03-05 16:14:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4017927/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4017927/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":53073473,"identity":"7f659137-2cce-44b5-b886-26621584b9f0","added_by":"auto","created_at":"2024-03-20 09:10:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":152183,"visible":true,"origin":"","legend":"\u003cp\u003eProcess flow diagram of soap production plant using WCO and CPW as raw feed. Area 100 - WCO oil treatment, Area 200 – Oil hydrolysis and crude glycerol removal, Area 300 – Fatty acid drying and distillation, Area 400 – Fatty acid neutralisation and Area 500 – D-Limonene extraction from CPW.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4017927/v1/ab0f467f60efe64498c72141.png"},{"id":53073472,"identity":"69520faa-90fc-49d5-ab13-c73535553a87","added_by":"auto","created_at":"2024-03-20 09:10:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":7547,"visible":true,"origin":"","legend":"\u003cp\u003eBreakdown of equipment cost per plant area for the four scenarios of soap production.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4017927/v1/5997c3a91de87c12bd2ad1f8.png"},{"id":53073475,"identity":"b2cc25f8-1314-4dea-9181-18af01324298","added_by":"auto","created_at":"2024-03-20 09:10:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":27509,"visible":true,"origin":"","legend":"\u003cp\u003eBreakdown of raw material, waste treatment, utility, and labour costs for the four scenarios of soap production.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4017927/v1/83e0534d60c4e1a7e95083bb.png"},{"id":53073474,"identity":"ea8b4c65-b314-44e1-b054-2e542d36ba79","added_by":"auto","created_at":"2024-03-20 09:10:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":63110,"visible":true,"origin":"","legend":"\u003cp\u003eStrauss plot used for sensitivity analysis at a 10% discount rate for a) Scenario 1 b) Scenario 2 c) Scenario 3 d) Scenario 4.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4017927/v1/2bab6bc51ebb232bef6cc03a.png"},{"id":53073477,"identity":"2e726056-f754-47aa-9195-9e41d64afe69","added_by":"auto","created_at":"2024-03-20 09:10:08","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":17998,"visible":true,"origin":"","legend":"\u003cp\u003eNPV after 10 years of plant life analysis using 1000 iterations for a) Scenario 1 b) Scenario 2 c) Scenario 3 d) Scenario 4.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4017927/v1/97fe08feb647e6daf93ff109.png"},{"id":56315846,"identity":"20960367-d86a-4005-ae66-2e035b456a0a","added_by":"auto","created_at":"2024-05-11 20:10:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1120580,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4017927/v1/72e1e84b-74b2-4a73-9c2e-d7702667523d.pdf"},{"id":53073476,"identity":"26a3e6dd-ed8c-4b54-8ef1-52d322b1190b","added_by":"auto","created_at":"2024-03-20 09:10:08","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2277765,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarysheet.docx","url":"https://assets-eu.researchsquare.com/files/rs-4017927/v1/9f60d9b14f24531effdce53f.docx"}],"financialInterests":"","formattedTitle":"Techno-economic evaluation of soap production from waste cooking oil with additives derived from citrus peel waste.","fulltext":[{"header":"Highlights ","content":"\u003cul class=\"decimal_type\"\u003e\n \u003cli\u003eA technoeconomic model for soap production from agricultural and municipal waste.\u003c/li\u003e\n \u003cli\u003eA pre-treatment strategy for the waste cooking oil (WCO) scenario is necessary for soap quality.\u003c/li\u003e\n \u003cli\u003eSoaps produced from WCO had similar properties to those produced from virgin oil.\u003c/li\u003e\n \u003cli\u003eOn-site production of additives resulted in an MSP of R160.53 per kg as compared to a R172 per kg market price.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eFood waste is a significant problem in today's global economy, with a considerable amount being lost during the supply and consumption stages of food production [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. This waste has a detrimental impact on the environment and the human life cycle, contributing to an increase in global greenhouse gas emissions, deforestation, loss of biodiversity, and depletion of natural resources [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. To mitigate these effects, reducing food waste and utilizing food residue, such as waste cooking oil (WCO), for sustainable practices is crucial. Despite the versatility of WCO, its potential for sustainable chemical or product manufacture is yet to be fully realized. Therefore, exploring the long-term viability of WCO could be a promising approach towards sustainability [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eIn a world estimate, over 41\u0026nbsp;million tonnes of WCO are produced annually, highlighting an urgent need for sustainable solutions to this waste problem [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In South Africa for example, approximately 2\u0026nbsp;million tonnes of vegetable and oilseed oil are consumed each year, with an estimated 32% wasted [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], which poses a threat to the environment, and violets the 2008 Waste Management Act [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. While WCO is currently used to produce different products (e.g., biodiesel, energy, bio-lubricant, and animal feed [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]), more research is needed to explore its long-term viability through finding new and innovative ways for system sustainability.\u003c/p\u003e \u003cp\u003eConventional uses of WCO have inherent limitations when it comes to sustainability: biodiesel production requires large amounts of water and energy, direct burning leads to air pollution, while the application as animal feed may result in water pollution and possibly eutrophication [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In contrast, using WCO for soap production has not been extensively investigated, although it portrays the following benefits: Firstly, soap is a household product used daily, which means using WCO for soap production could create a sustainable way of recycling. Secondly, soap production could be a cost-effective way of using WCO feedstock, as it does not require the same level of pre-treatment, and refining, compared to biodiesel and bio-lubricants production. Lastly, using WCO for soap production could have a significant social impact, because soap is essential for sanitation and hygiene. Moreover, considering the simplicity of soap-making processes, it is easily transferable which could ultimately create employment opportunities [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFurthermore, soap production becomes more attractive when suitable soap additives are added. For example, the valorization of citrus peel waste (CPW) offers one such additive in the form of D-Limonene. D-Limonene is a monoterpene found in the peels of citrus fruits with known anti-microbial properties [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Apart from its anti-microbial properties, it is also a natural solvent, a degreaser and has a pleasant scent[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Adding D-Limonene could help to enhance the cleansing power and the consumer appeal of the soaps. Nevertheless, the presence of D-Limonene makes the CPW difficult to compost and unsuitable for animal feed or fermentation processes [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], as its high acidic content is challenging for biodegradation and fermentation, further exacerbating issues surrounding food waste management [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Therefore, extracting D-Limonene from CPW could offer a dual solution, both adding value to soap production technology and mitigating issues in food waste management.\u003c/p\u003e \u003cp\u003eFundamentally, soaps are produced by a reaction between triglyceride esters and a strong mineral base, which is either sodium hydroxide for hard soaps or potassium hydroxide for soft soaps [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The quality of the soaps produced depends on numerous factors, these include the type and quality of the oil or the fat used, temperature and the duration of the reaction, the concentration of the mineral base, pH, and water content [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Adequate stirring during soap making also plays an important role, as it ensures that the oils are exposed to the base [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Since the quality of the soaps is affected by the quality of the oil used, it is essential to compare soaps made from waste cooking oil to those made from unused, fresh oils, as a benchmark for potential system scalability and economic viability [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTherefore, this study initially investigated the experimental production of soap using WCO and CPW (results presented in the supplementary material), as a technique to evaluate the experimental feasibility and to understand the production steps that are necessary for developing a techno-economic model. Furthermore, the study investigated four different soap production scenarios to understand the economic potential of producing soap from a combination of WCO and CPW. Thus, permitted an understanding of the mass and energy balances, economic potential and the sensitivity prospects from input indicators using an Aspen Plus\u0026reg; simulations model. Overall, this study provides valuable insights into the feasibility of using WCO and CPW for sustainable soap production and highlights this approach's potential benefits and challenges for the industry.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Approach\u003c/h2\u003e \u003cp\u003eThe work set out to evaluate techno-economics for soap production using WCO and CPW. The modelling was conducted through Aspen Plus\u0026reg; using data gathered from experimental feasibility studies (soap making) and existing literature. For the experiments, soaps were made using filtered waste cooking oil, treated waste cooking oil, and compared to virgin cooking oil (olive oil). In brief, WCO was pre-treated through a succession of filtration (using muslin cloth), brine washing and chemical bleaching. The WCO was washed twice with 10% brine solution (at a ratio of 1:1) at 50 ℃ for 1 minute under constant mixing. The mixture was transferred to a separatory funnel and allowed to stand for 2 hours for the brine and oil-organic phases to separate. After the brine had been decanted, the WCO was bleached at 70 ℃ for 30 minutes, under constant stirring using 3% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solution, allowed to stand for 12 hours and then H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solution was then decanted.\u003c/p\u003e \u003cp\u003eSoaps were then made using a blend of soft oils (WCO or olive oil) and hard oil (coconut oil) at varying soft oil compositions (78.4, 62.4, and 46.5% wt) at 20 ℃. 4% wt D-limonene from CPW was added once the \u0026lsquo;trace\u0026rsquo; stage had been achieved. The soaps were allowed to air dry for 4 weeks, after which pH, moisture content and anti-microbial activities (against \u003cem\u003eE. coli\u003c/em\u003e) were tested (results presented in supplementary materials, Figures S1 \u0026ndash; S5). The experimental pre-treatment experimental approach was therefore adopted for modelling, using the composition of the best performing soap composition for modelling.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Modelling\u003c/h2\u003e \u003cp\u003eFour process simulations were performed, with a feed rate of 64.2 kg/h of oil for all scenarios and 302 kg/h of citrus peel waste in Scenarios 1 and 3. This calculation basis was assumed based on typical production rates of citrus fruit processor ALG Estates in the Western Cape, South Africa, corresponding to 20,000 ton/yr citrus fruits processed of which 50\u0026ndash;60% end up as CPW [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. ALG Estates is situated in the Cederberg municipal area, with a population of 74,000, producing about 1.28 ton/yr of WCO [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. 40% collection rate of the estimated mass of WCO from surrounding towns was assumed [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The compositions of waste cooking, olive, and coconut oils, and citrus peel waste are provided in the Supplementary Sheet (Tables S1 and S2). The Peng-Robinson property method was used in the Aspen Plus \u0026reg; simulations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1. Process description\u003c/h2\u003e \u003cp\u003eThe scenarios developed were as follows: Scenario 1 \u0026ndash; production of soap using olive oil with limonene production from CPW on-site; Scenario 2 \u0026ndash; production of soap using olive oil with limonene purchased; Scenario 3 \u0026ndash; production of soap using WCO with limonene production from CPW on-site; Scenario 4 \u0026ndash; production of soap using WCO with limonene purchased. For olive oil scenarios (1 and 2), area 100 was excluded from the process. For scenarios (2 and 4) where limonene was purchased, area 500 was excluded from the process. In reference to the Aspen simulation, the process flow diagram is provided in a comprehensive diagram in the supplementary sheet (Figure S6), and the following process description is provided below:\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eArea 100: Waste cooking oil treatment\u003c/span\u003e \u003c/p\u003e \u003cp\u003e64.2 kg/hr of untreated waste cooking oil enters the plant at 20\u0026deg;C and 1 bar and is stored in the oil storage tank (TK-103). Once enough oil has been collected for the plant to run continuously, the oil is withdrawn from TK-103 and filtered in rotary filter F-101 to remove gross solid impurities. The solid impurities are disposed of as non-hazardous waste while the filtered oil is mixed with a 10 wt% heated brine solution in a 1:1 volume ratio (mixer M-101). The mixture is then sent to decanter D-101 where two immiscible phases readily form. The aqueous phase contains the brine solution and polar compounds removed from the oil. This forms the bottom phase and is decanted, sent to treatment works and disposed of. The oil phase is decanted and washed with hot brine a second time in M-102 and decanted in D-102.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eArea 200: Oil hydrolysis and crude glycerol removal\u003c/span\u003e \u003c/p\u003e \u003cp\u003eThe washed and filtered oil is mixed with coconut oil stored in TK-201 using static mixer M-201. The oil blend, comprised of 78.4 wt% treated WCO, is pumped to 40 bar in P-202 A/B and sent to the bottom of the hydrolyser (T-201). 36.9 kg/hr of hot water is sent to the top of T-201 so that the oil hydrolysis takes place counter-currently. The hydrolysis takes place at 40 bar and 250\u0026deg;C. With a 2-hour residence time in the hydrolyser, the expected conversion of triglycerides to fatty acids at these conditions is 99%. The bottom product, sweet water, is 20.8 wt% glycerol, 79wt% water and the remainder trace amounts of impurities. The moisture is removed from this stream by flash evaporation in FL-201 at 10 bar and 202\u0026deg;C to produce an 80.1% crude glycerol stream.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eArea 300: Fatty acid drying and distillation.\u003c/span\u003e \u003c/p\u003e \u003cp\u003eThe distillate stream from T-201 contains the fatty acids produced in the oil hydrolysis reaction. This fatty acid stream, at a flow rate of 78.4 kg/hr, has a mass composition of 9.0% water, 87.7% fatty acids, 0.9% triglycerides, 1.3% glycerol, and 1.1% polar impurities from the raw feed. The fatty acid stream is flash dried in FL-301 and the water content is reduced to 1.4 wt%. The water vapour product from FL-301 is sent to wastewater treatment while the liquid product is sent to distillation tower T-301.\u003c/p\u003e \u003cp\u003eT-301 operates at 0.0013 bar and separates the fatty acids from remaining impurities in the feed stream. This vacuum distillation tower contains a partial condenser and a kettle reboiler. There are 6 stages excluding the condenser and reboiler. At a distillate rate of 61.7 kg/h, the distillate product stream has a weight composition of 95.0% fatty acids, 1.6% glycerol, 1.7% moisture, 0.3% polar impurities and the balance triglycerides. Although the moisture and glycerol have not been completely removed, the purification steps in FL-301 and T-301 are not intensified because, for soap production, additional water and glycerol content are not disadvantageous to the process. The distillate stream is then compressed to 5 bar in C-301 and completely condensed in shell-and-tube condenser E-301.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eArea 400: Fatty acid neutralisation\u003c/span\u003e \u003c/p\u003e \u003cp\u003eThe liquid fatty acid stream is sent to static mixer M-401. Sodium hydroxide pellets, which are stored on the plant in TK-401, are mixed with deionised water to create a 33 wt% NaOH solution. The solution is stored in TK-402 and sent to M-401 to be mixed with the fatty acid stream before being sent to the neutralisation reactor (R-401). The reactor operates at 5 bar and 93\u0026deg;C. After a residence time of 30 minutes in the reactor, the conversion of fatty acids to soap is 98%.\u003c/p\u003e \u003cp\u003eThe neat soap exits the reactor at 93\u0026deg;C and 87.1 kg/h as a warm liquid. This product stream is sent to a dryer (FL-401) to reduce the moisture content from 25.0 wt% to 11.8 wt% through simultaneous cooling and drying. The cooled, dried soap is sent to amalgamator M-402 where it is mixed with D-Limonene extracted from citrus peel waste in Area 500. Citric acid is also added to reduce the soap's pH and to form sodium citrate, which acts as a chelator in the soap. This soap mixture is sent to finishing operations in Area 600 where the final steps are performed to produce the packaged soap product.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eArea 500: D-Limonene extraction from citrus peel waste\u003c/span\u003e \u003c/p\u003e \u003cp\u003eRaw citrus peel waste (CPW) enters the process at varying rates and is crushed in a hammer mill (H-501) before being stored in TK-501, a hopper. The CPW remains in storage until the production process can take place in the continuous mode. H-501 reduces the size of the CPW from a mean size of 75 mm to 0.5 mm. The crushed CPW is flash-dried in FL-501 and the resulting solids residue can be used for animal fodder and/or compost on ALG Estates\u0026rsquo; farm. The vapour product stream, with a composition of 95% D-Limonene and the remainder of water and other monoterpenes, is condensed in E-501 and decanted in D-501.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eArea 600: Soap finishing operations\u003c/span\u003e \u003c/p\u003e \u003cp\u003eThe neat soap, which now contains D-Limonene, is sent to the soap finishing line. An extruder gives the soap a new shape before it is cut into bars and stamped. 3 conveyor belts are used for the transportation of the soap within the finishing operations (Shreve and Austin, 1984). Finally, a small packing machine automates the packaging of the finished soaps.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2. Cost estimations, Profitability, and Sensitivity analysis\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section4\"\u003e \u003ch2\u003e2.2.2.1. Capital cost estimation:\u003c/h2\u003e \u003cp\u003eA study estimate was used to determine the capital costs, as detailed in Turton (2018). Firstly, the equipment costs were found in one of three ways: cost correlations found in Turton (2018), equipment cost estimations mapped in Aspen Plus \u0026reg;, or scaled from costs quoted by industry suppliers. For the costs estimated using correlations, the relevant capacity parameter (A) of each major piece of equipment was used to estimate the base case cost of the equipment (Cp\u0026deg;). This base cost was scaled to account for the pressure and material of construction of the equipment. The chemical engineering plant cost index (CEPCI) for 2022 was used to scale for time. This gave estimates of the capital cost of each unit (Cp). It was assumed that a 3% delivery levy was imposed on the total equipment capital cost. Finally, the delivered equipment cost was used to estimate the direct and indirect capital costs of the plant.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section4\"\u003e \u003ch2\u003e2.2.2.2. Operating cost estimation:\u003c/h2\u003e \u003cp\u003eTo estimate the operating costs, the cost of raw materials, waste treatment, utilities, and operating labour was calculated explicitly, and the rest of the operating costs were calculated as factors of these as per the factor approach given in Turton (2018). For the waste cooking oil plant, the material requirements were calculated using the flow rates from the results of the Aspen Plus \u0026reg; simulation and materials costs listed in the assumptions in overleaf. The cost of the waste cooking oil included a 10% transportation cost associated with collecting the material from nearby towns. Citric acid was not included in the Aspen Plus \u0026reg; simulation but the mass of citric acid added was 2% of the oil mass as proposed in Burke (2005). For utilities, the costs mapped in Aspen Plus \u0026reg; were used while operating labour costs were determined by estimating the number of plant operators required and an assumed annual salary of R299 000 for a chemical plant operator.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section4\"\u003e \u003ch2\u003e2.2.2.3. Economic evaluation and performance indicators:\u003c/h2\u003e \u003cp\u003eThe fixed capital investment, cost of manufacturing without depreciation, soap, crude glycerol, and D-Limonene production rates and selling prices as well as the assumptions listed below were used to conduct the profitability analysis. The negative cash flows from capital investments and land purchases were accounted for over 2 years before plant operation. Once the operation began, the revenue and expenses were used to calculate yearly profit. The profit was then taxed, and depreciation was incorporated. The cash flows were then discounted; the sum of the discounted cash flow gives the net present value at a 10% discount rate. The present value ratio (PVR), discount payback period (DPBP), discounted cash flow rate of return (DCFROR), minimum selling price (MSP, calculated as the price at which the NPV is R 0 at a 10% discount rate) were calculated as key economic indicators.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMajor assumptions made to perform the profitability analysis.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAssumption\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReference and/or justification\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiscount rate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEngineering judgement\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCost Year\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConstruction period\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 years: 60% and 40% completion in years 1 and 2, respectively\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEngineering judgement\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlant life\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10 years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEngineering judgement\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDepreciation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraight-line method over 6 years (no salvage)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSimilar scenario; [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTaxation rate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCompany tax rate in South Africa is 27% as stated by SARS. 30% is chosen as a conservative approach\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExchange rate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.08 R/USD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eExchange rate as of 28 Oct 2022 (Bloomberg, 2022)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYearly operating hours\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8 000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSimilar scenario; [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLand\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR3 800 000 for additional land\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTypical price of land used for citrus farming in Citrusdal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBuildings\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR2 808 000 for additional buildings\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEstimate of land area required for soap production plant based on O\u0026rsquo;live Soap Factory (PayFast, 2021)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"7\" rowspan=\"8\"\u003e \u003cp\u003eCost of chemicals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR109.99/kg of NaOH pellets (98.5% purity)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurchasing price at ChemLab Supplies\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR7.8/kg of NaCl pellets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurchasing price at ChemLab Supplies\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4 USD/kg of coconut oil\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurchasing price from Alibaba.com\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e120 USD/ton of WCO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurchasing price from Alibaba.com\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 200 USD/ton of olive oil\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurchasing price from Alibaba.com\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.5 USD/kg of citric acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurchasing price from Alibaba.com\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.5 USD/ton of deionised water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(Turton et al., 2018)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNo cost involved for CPW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCPW from fruit processing on the plant is used as raw feed\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSelling price of products\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR19.8/115 g of soap\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSelling price of similar soap type sold by Soap Factory (small business in South Africa)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10 USD/kg of 95% D-Limonene\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurchasing price at ChemLab Supplies\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.09 USD/lb of 80% crude glycerol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eCost of utilities\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0674 USD/kWh of electricity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.22 USD/ton of LPS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15.7 USD/m\u003csup\u003e3\u003c/sup\u003e of cooling water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003e Adjusted for the cost year of 2022 using inflation\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section4\"\u003e \u003ch2\u003e2.2.2.4. Sensitivity and Monte Carlo Simulation\u003c/h2\u003e \u003cp\u003eAll scenarios were subjected to a sensitivity analysis to determine how a 30% change in a few parameters would affect the NPV. The economic parameters considered for the analysis were exchange rate, soap selling price, WCO purchasing price, equipment cost, and crude glycerol price among others. For every parameter considered, all other parameters were kept constant to determine the effect on the NPV. Monte Carlo simulations were performed for simultaneous changes in the variables of up to 20%. The 20% range represents an optimistic case, where the variables do not deviate far from their original values. A total of 1,000 iterations were performed for all scenarios to determine the effect of the variability on the NPV.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Material and energy balance results\u003c/h2\u003e \u003cp\u003eA summary of the mass and energy results is provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. As seen in this table, scenarios 1 and 2 used olive oil in the production process while scenarios 3 and 4 used WCO as the soft oil for soap production. After pretreatment procedures, a 10% loss in mass was seen in scenarios 3 and 4 leading to about 8% less product rate (84.5 kg/h for olive oil and 78 kg/h for WCO) compared to scenarios 1 and 2 (see Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Also, in scenarios 1 and 3 where CPW was treated, excess limonene was obtained (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) which was sold for income generation as a by-product. These changes will correspond to an economy of scale benefits for the olive oil scenarios which will be discussed in the profitability section.\u003c/p\u003e \u003cp\u003eScenarios 3 and 4 had the highest electricity demand per soap produced (see Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) which was due to the need to treat the WCO. As seen with the use of waste vegetable oil in green diesel production and other bioprocesses, the treatment of feedstock significantly increases energy demand and cost depending on the level of contamination [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Also, it can be observed that the production of limonene on-site (scenarios 1 and 3) resulted in less than a 1% increase in the electricity demand of the process when compared to Scenarios 2 and 4 respectively. The increase in electricity will result in an increase in the operating costs of the scenario and implies additional treatment strategies should be more beneficial and economically sustainable based on production scale-up potential.\u003c/p\u003e \u003cp\u003eIn terms of the heating demand, the WCO scenarios were also higher than the olive oil scenarios. This was partly due to the preheating requirement included based on experimental understanding of utilizing a brine solution in the pretreatment of the WCO which was avoided in Scenarios 1 and 2 (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The cooling demand of the scenarios indicates a higher demand (about 1%) for olive oil scenarios compared to WCO scenarios. This demand decreases by 5% when comparing Scenario 1 with Scenario 2. This is due to the contribution of cooling demand in the production of limonene from CPW which is excluded from Scenario 2 and 4.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMaterial and energy balance results\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eScenario\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass of WCO, kg/h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e64.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e64.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass of treated WCO, kg/h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e57.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e57.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass of Olive oil, kg/h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass of Limonene used, kg/h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.224\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.224\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.028\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.028\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass of excess Limonene, kg/h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass of excess glycerol, kg/h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoap production rate, kg/h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e84.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e78.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e78.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectricity demand, MJ/kg soap\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeating demand, MJ/kg soap\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.26\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCooling demand, MJ/kg soap\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.764\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.721\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.756\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.715\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Economic assessment\u003c/h2\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. Capital costs\u003c/h2\u003e \u003cp\u003eA breakdown of the equipment costs per plant area is illustrated with a summary of the economic parameters given in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. As seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the hydrolysis and neutralisation areas (Areas 200 and 400, respectively) had high costs associated with them for all scenarios (i.e., about 20\u0026ndash;40% cost for all scenarios). The equipment costs in Areas 200 and 400 are larger for the olive oil scenarios (1 and 2) i.e., 30% and 41% which corresponded to about R 5\u0026nbsp;million for both scenarios (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). There is a high cost (about R5.6\u0026nbsp;million) associated with Area 100 (waste cooking oil pre-treatment) which accounts for 26% and 33% of the equipment cost for Scenario 3 and 4 respectively. This significantly increases the equipment cost for the WCO scenarios compared to the olive oil scenarios. From Scenario 1 and 3, it can be observed that the production of limonene accounted for 26% and 21% cost respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This corresponds to an amount of R 4.6\u0026nbsp;million increase in the equipment cost for the scenarios when compared (scenario 1 vs. 2 and scenario 3 vs. 4). The total costs of equipment are R 21.6\u0026nbsp;million and R 17.0\u0026nbsp;million (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) for the WCO scenarios and R 17.4\u0026nbsp;million and 12.8\u0026nbsp;million for the olive oil scenarios. Hence it can be observed that treatment of WCO significantly increases the equipment cost of the process (about 24%) whilst the production of limonene onsite also results in an increase of about 35% in the equipment costs of the process (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe main capital costs for the plants are shown below. The WCO scenarios had a higher total cost of equipment which translates into all the capital costs for the scenarios as these are a function of equipment cost Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of economic results for all scenarios\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eScenario\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Equipment Cost, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16.79\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDirect Cost, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e52.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e38.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e64.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e50.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndirect Costs, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWorking Capital, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e12.80\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFixed Capital, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e54.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e90.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e71.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDirect Manufacturing Cost, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e61.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e51.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e55.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFixed Costs, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16.70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGeneral manufacturing expenses, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Operating Cost, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e90.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e89.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e84.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e83.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimum selling price, R/kg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e150.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e150.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e160.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e159.87\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNPV, Million R\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e31.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e33.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIRR, %\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePayback period, years\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2. Operational costs\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e below illustrates the raw material, waste treatment, utility, and labour costs for the four soap production scenarios investigated. A raw material cost of R33.6\u0026nbsp;million is required for Scenario 1 mainly due to the purchase of olive oil (which accounts for 45% of the raw materials cost). The cost further increases by 18% when limonene is purchased in Scenario 2 compared to Scenario 1 where it was produced onsite. Also, the raw materials cost from scenarios 1 and 2 were higher than those for the WCO scenarios (R 20.2\u0026nbsp;million for scenario 3 and R 26.0\u0026nbsp;million for scenario 4), and implies should WCO feedstock be purchased or even collected with incentives, its operability for soap production would increase should sufficient and proper treatment procedures be put in place for smooth operations.\u003c/p\u003e \u003cp\u003eLooking at all scenarios, the cost of utilities was below R 760 000 although WCO scenarios are lower (16%) than for the olive oil scenarios (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The waste treatment costs for Scenarios 3 and 4 are R 2.5\u0026nbsp;million compared to R 1.48\u0026nbsp;million for Scenarios 1 and 2. This was due to the disposal costs associated with the brine-contaminated water in the WCO treatment in Scenarios 3 and 4. The total operating costs were found to be higher when using olive oil as opposed to WCO and also higher when comparing the purchase of limonene as a raw material as opposed to producing it on-site Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. This implies aside from the added environmental benefits of producing limonene from CPW, there exists an economic incentive as far as operating costs are concerned.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe labour costs for the Scenarios were close without significant difference, there was a 2% increase in the labour cost for the WCO scenarios due to the increase in equipment at the pretreatment of the WCO. Similarly, the removal of the limonene production resulted in less than 1% reduction in labour costs when compared (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Although the cost of labour and waste treatment are lower for the olive oil scenarios, the higher raw material cost increases its operating cost just above that of the WCO scenarios. The lower raw material cost highlights one advantage of the use of WCO in large-scale soap production, which should be capitalised upon in future iterations of this plant design.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3. Profitability analysis\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e provides the performance parameters from the profitability analyses of the scenarios as well. The high product rate for the olive oil scenarios 1 and 2 seen in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, contributes to increasing the profitability compared to the WCO scenarios (3 and 4). At a discount rate of 10%, the positive net present values (NPVs) of all scenarios indicate economic feasibility, although the olive oil plants were observed to be more profitable (about 50% higher NPV for scenario 1 vs. 3). It may also be observed that the production of limonene on site further increases the NPV for the scenarios (about R 2\u0026nbsp;million), this was mainly due to the additional revenue from the excess limonene produced in the scenarios (Scenario 1 and 2). This shows that besides the environmental benefits of the production of limonene, it increases the profitability of the process as well.\u003c/p\u003e \u003cp\u003eThe WCO scenarios (Scenario 3 and 4) had a longer discounted payback period (DPBP). As shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The WCO plant was found to recover its land and working capital costs after 3.6 and 3.9 years of plant life for Scenario 3 and 4 respectively. However, the olive oil case recovers these costs after 3.0 and 2.5 years of plant life for Scenario 1 and 2. Hence, it could be more beneficial if incentives such as cost reduction in obtaining the WCO are put in place to make them directly competitive in the production of soap and further drop its payback time than the Olive oil cases.\u003c/p\u003e \u003cp\u003eThe minimum selling price (MSP) of the soap was found to be lower than the market price of about R 172 per kg of soap. This indicates that the scenarios are profitable and translated to the positive NPVs obtained. The MSP of Scenarios 1 and 2 were lower than for Scenarios 3 and 4 which indicates a higher profitability for the olive oil scenarios (about 6%). The low difference (R 150 vs 160) in MSPs indicates that WCO scenarios are competitive and can be further made attractive to match up the MSP of the olive oil scenarios. From Scenarios 1 and 2 it can be observed that production of limonene onsite accounted for less than 1% decrease in the MSP of the soap (R 150.61 vs R 150.40, see Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This was because of the reduction in the operating costs associated with limonene purchases. This can also be observed from Scenarios 3 and 4, indicating soaps can be competitive where the limonene is produced onsite and has the added advantage of using CPW making it an environmentally friendlier process. The IRR for the scenarios investigated ranged from 16\u0026ndash;30% which is above the discount rate of 10% indicating all scenarios are profitable. The IRR for the WCO scenarios were lower than the olive oil scenarios by 9\u0026ndash;12% for both scenarios.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.2.4. Sensitivity analysis\u003c/h2\u003e \u003cp\u003eA sensitivity analysis was performed for the waste cooking oil case and the Strauss plots shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e were generated. The plant profitability for all scenarios is highly sensitive to the selling price of the soap. The soap price used in the base case, R 172.17 per kg (R 19.8/115 g of soap), was selected based on typical prices of similar artisan soaps made from olive and coconut oil. A 30% decrease in the selling price results in a large decrease in NPV making all the scenarios unprofitable with a negative NPV. On the other hand, the NPV is resilient to changes in the crude glycerol selling price, taxation rate, and WCO price as seen in the relatively flat slope in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The NPV is also significantly affected by the exchange rate in all scenarios which also translates to the equipment cost. A 30% increase in the exchange rate makes all scenarios end with a negative NPV, whilst a 30% decrease in the exchange rate significantly improves the profitability as well. The exchange rate is influential in the NPV calculations as the USDRand exchange rate is used in most of the calculations of equipment, utility, and raw material costs. The limonene price was observed to also have a slight impact on the NPV although not resulting in negative NPVs with a 30% increase in the price, the change was however experienced more in Scenario 2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) and Scenario 4 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) where limonene was purchased.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom the Monte Carlo simulation shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, it was found that the likelihood of plant profitability is higher than 80% for all scenarios. This gives reasonable motivation for the development of large-scale soap production from WCO as well. This is good motivation for the waste valorisation plant as it does not have well-documented precedence from previous plants. The Monte Carlo simulations were performed for simultaneous changes in the variables of up to 20%. As seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and c, plant profitability (NPV\u0026thinsp;\u0026gt;\u0026thinsp;0) is about 80% for Scenarios 1 and 3 where limonene is produced. This number increases to more than 95% for scenarios where limonene was purchased (Scenario 2 and 4).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Technical and eco-conscious evaluation\u003c/h2\u003e \u003cp\u003eOther important factors must be considered in addition to economic indicators for this proposed process. The rate of recovery of WCO is an important consideration. This factor has an impact on plant profitability because it determines production capacity and, as a result, plant revenue. According to a previous study, developing countries are expected to have a WCO valorisation rate of 23.3% (Teixeira et al., 2018). However, in the current study, a 40% collection rate was assumed based on a study that found that up to 53% collection is possible in a small enough control volume (De Feo et al., 2020). Furthermore, because this plant offers to pay for the oil, households will be incentivized to provide their WCO. WCO collection from households has another important consideration, environmental impact. Due to unconscious behaviours, WCO from households end up being disposed of in sinks or with solid food residues, ending up in water resources and landfills [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. There are multiple issues associated with WCO ending up in wastewater, such as; increasing wastewater treatment costs, damage to infrastructure, and they cause odours. Additionally, the oil layer on water resources would affect aquatic life, by reducing oxygen levels as well as sunlight penetration, thereby negatively impacting the aquatic ecosystem [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. It is apparent that WCO volarization would lead to less WCO entering wastewater treatment works, allowing communities to reduce their environmental impact, a sentiment not necessarily shared by the virgin olive oil scenario.\u003c/p\u003e \u003cp\u003eIndustrial symbiosis of soap production from WCO with on-site limonene extraction from CPW is also an important consideration. CPW are often dumped into landfills or burned, resulting in soil quality degradation and air pollution. Additionally, this waste finds its way into water resources, leading to reduced dissolved oxygen as well as increased acidity. The issues of CPW waste management by disposal are further exuberated by the presence of essential oils, more specifically limonene which limits biodegradability due to its anti-microbial properties. Therefore, extraction and utilization of limonene not only offer advantages in enhancing soap quality but also aid in the reduction of CPW waste management issues[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFinally, public perception and product marketability are essential considerations for soap production from the WCO plant. The profitability estimate assumed that all units produced in an operating year would be sold at market price during the course of the plant\u0026rsquo;s 10-year existence. This assumption does not take into account changes in demand, which have a direct impact on sales. As a result, the design and development of this plant will require market research to evaluate whether customers notice significant changes between WCO, and soaps made from wasted oils. This will indicate whether the market demand is high enough to justify the development of this plant. Such research is critical since the sensitivity study of this plant indicated that the NPV is extremely sensitive to the selling price of the soaps.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eSoap production from WCO, coupled with additives from CPW (limonene) is a promising means for reducing waste, whilst also being a profitable process. Experimental results showed that soaps produced from WCO had comparable quality while the addition of additives such as D-limonene did not only contribute to the reduction of odour from WCO but could also be a potential and promising anti-microbial agent. In terms of the comprehensive techno-economic evaluation of soap production from WCO in comparison to a traditional soap production oil (olive), key insights were developed and demonstrated below.\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003eOn-site production of additives and utilisation of WCO\u003c/em\u003e: From Scenario 3, higher initial capital expenditures (CAPEX) due to additional equipment are required and should be compensated for in the 6% reduction in operating expenditures (OPEX) of obtaining the WCO and producing the limonene on site. The process could recoup its working investment in 3.9 years with \u003cem\u003ean\u003c/em\u003e IRR of 1\u003cem\u003e9\u003c/em\u003e%. This implies its recycling potential of both CPW and WCO for environmental sustainability is accompanied by investment prospects.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003ePurchasing additives and utilisation of WCO\u003c/em\u003e: From scenario 4, with the lowest IRR of 1\u003cem\u003e6\u003c/em\u003e% was reported with a payback period of 3.6 years. This scenario seems feasible should a plant require investment in this range; however, environmental benefits are primarily reliant on the WCO waste, and a lower NPV and an increased MSP should be expected thereby reducing potential investors and consumers purchasing power.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003eCredit authorship contribution statement\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBeatrice\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Walelu Mwamba\u003c/strong\u003e: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing \u0026ndash; original draft, Visualization. \u003cstrong\u003eMensah\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Sarpong Brobbey\u003c/strong\u003e: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing \u0026ndash; original draft, Visualization, \u003cstrong\u003eBianke\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Leodolff\u003c/strong\u003e: Methodology, Writing \u0026ndash; editing, Supervision. \u003cstrong\u003eShaun Peters\u003c/strong\u003e: Resources, Methodology, Writing \u0026ndash; editing, Supervision. \u003cstrong\u003eGeorge Mbella Teke\u003c/strong\u003e: Conceptualisation, Writing \u0026ndash; review and editing, Project administration, Supervision. \u003cstrong\u003eZwonaka\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Mapholi\u003c/strong\u003e: Resources, Conceptualization, Writing \u0026ndash; review and editing, Project administration, Supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u003c/strong\u003e The data generated and analysed during this study is available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003eConflict of interest \u0026ndash; The authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eThe authors would like to acknowledge the technical and financial support from the Department of Chemical Engineering, and the Institute of Plant Biotechnology (Department of Natural Sciences), Stellenbosch University (South Africa). The opinions and views expressed, and conclusions derived at, are those of the authors and not necessarily attributed to Stellenbosch University.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eFAO: Food loss and waste - Framing the issues. The State of the World. 1\u0026ndash;19 (2019)\u003c/li\u003e\n\u003cli\u003eOrjuela, A., Clark, J.: Green chemicals from used cooking oils: Trends, challenges, and opportunities. Curr Opin Green Sustain Chem. 26, 100369 (2020). https://doi.org/10.1016/J.COGSC.2020.100369\u003c/li\u003e\n\u003cli\u003eTeixeira, M.R., Nogueira, R., Nunes, L.M.: Quantitative assessment of the valorisation of used cooking oils in 23 countries. Waste Management. 78, (2018). https://doi.org/10.1016/j.wasman.2018.06.039\u003c/li\u003e\n\u003cli\u003eLinganiso, E.C., Tlhaole, B., Magagula, L.P., Dziike, S., Linganiso, L.Z., Motaung, T.E., Moloto, N., Tetana, Z.N.: Biodiesel Production from Waste Oils: A South African Outlook. Sustainability 2022, Vol. 14, Page 1983. 14, 1983 (2022). https://doi.org/10.3390/SU14041983\u003c/li\u003e\n\u003cli\u003eMannu, A., Vlahopoulou, G., Urgeghe, P., Ferro, M., Del Caro, A., Taras, A., Garroni, S., Rourke, J.P., Cabizza, R., Petretto, G.L.: Variation of the Chemical Composition of Waste Cooking Oils upon Bentonite Filtration. Resources 2019, Vol. 8, Page 108. 8, 108 (2019). https://doi.org/10.3390/RESOURCES8020108\u003c/li\u003e\n\u003cli\u003eOrjuela, A., Clark, J.: Green chemicals from used cooking oils: Trends, challenges, and opportunities. Curr Opin Green Sustain Chem. 26, 100369 (2020). https://doi.org/10.1016/J.COGSC.2020.100369\u003c/li\u003e\n\u003cli\u003eLiu, Y., Yang, X., Adamu, A., Zhu, Z.: Economic evaluation and production process simulation of biodiesel production from waste cooking oil. Current Research in Green and Sustainable Chemistry. 4, 100091 (2021). https://doi.org/10.1016/J.CRGSC.2021.100091\u003c/li\u003e\n\u003cli\u003eF\u0026eacute;lix, S., Ara\u0026uacute;jo, J., Pires, A.M., Sousa, A.C.: Soap production: A green prospective. Waste Management. 66, 190\u0026ndash;195 (2017). https://doi.org/10.1016/J.WASMAN.2017.04.036\u003c/li\u003e\n\u003cli\u003eAzme, S.N.K., Yusoff, N.S.I.M., Chin, L.Y., Mohd, Y., Hamid, R.D., Jalil, M.N., Zaki, H.M., Saleh, S.H., Ahmat, N., Manan, M.A.F.A., Yury, N., Hum, N.N.F., Latif, F.A., Zain, Z.M.: Recycling waste cooking oil into soap: Knowledge transfer through community service learning. Cleaner Waste Systems. 4, 100084 (2023). https://doi.org/10.1016/J.CLWAS.2023.100084\u003c/li\u003e\n\u003cli\u003eDosoky, N.S., Setzer, W.N.: Biological Activities and Safety of Citrus spp. Essential Oils. Int J Mol Sci. 19, (2018). https://doi.org/10.3390/IJMS19071966\u003c/li\u003e\n\u003cli\u003eHan, Y., Sun, Z., Chen, W.: Antimicrobial Susceptibility and Antibacterial Mechanism of Limonene against Listeria monocytogenes. Molecules. 25, (2020). https://doi.org/10.3390/MOLECULES25010033\u003c/li\u003e\n\u003cli\u003eSiddiqui, S.A., Pahmeyer, M.J., Assadpour, E., Jafari, S.M.: Extraction and purification of d-limonene from orange peel wastes: Recent advances. Ind Crops Prod. 177, 114484 (2022). https://doi.org/10.1016/J.INDCROP.2021.114484\u003c/li\u003e\n\u003cli\u003eSantiago, B., Moreira, M.T., Feijoo, G., Gonz\u0026aacute;lez-Garc\u0026iacute;a, S.: Identification of environmental aspects of citrus waste valorization into D-limonene from a biorefinery approach. Biomass Bioenergy. 143, (2020). https://doi.org/10.1016/J.BIOMBIOE.2020.105844\u003c/li\u003e\n\u003cli\u003eMbella Teke, G., De Vos, L., Smith, \u0026middot; Isle, Kleyn, T., Mapholi, Z.: Development of an ultrasound-assisted pre-treatment strategy for the extraction of d-Limonene toward the production of bioethanol from citrus peel waste (CPW). Bioprocess and Biosystems Engineering 2023. 1, 1\u0026ndash;11 (2023). https://doi.org/10.1007/S00449-023-02924-Y\u003c/li\u003e\n\u003cli\u003eHill, M.: Product and process design for structured products. AIChE Journal. 50, 1656\u0026ndash;1661 (2004). https://doi.org/10.1002/AIC.10293\u003c/li\u003e\n\u003cli\u003eRahayu, S., Pambudi, K.A., Afifah, A., Fitriani, S.R., Tasyari, S., Zaki, M., Djamahar, R.: Environmentally safe technology with the conversion of used cooking oil into soap. J Phys Conf Ser. 1869, 012044 (2021). https://doi.org/10.1088/1742-6596/1869/1/012044\u003c/li\u003e\n\u003cli\u003eMabrouk, S.T.: Making usable, quality opaque or transparent soap. J Chem Educ. 82, 1534\u0026ndash;1537 (2005). https://doi.org/10.1021/ED082P1534\u003c/li\u003e\n\u003cli\u003eAbera, B.H., Diro, A., Beyene, T.T.: The synergistic effect of waste cooking oil and endod (Phytolacca dodecandra) on the production of high-grade laundry soap. Heliyon. 9, e16889 (2023). https://doi.org/10.1016/j.heliyon.2023.e16889\u003c/li\u003e\n\u003cli\u003eSatari, B., Karimi, K.: Citrus processing wastes: Environmental impacts, recent advances, and future perspectives in total valorization. Resour Conserv Recycl. 129, 153\u0026ndash;167 (2018). https://doi.org/10.1016/J.RESCONREC.2017.10.032\u003c/li\u003e\n\u003cli\u003eAnwar, F., Naseer, R., Bhanger, M.I., Ashraf, S., Talpur, F.N., Aladedunye, F.A.: Physico-Chemical Characteristics of Citrus Seeds and Seed Oils from Pakistan. Journal of the American Oil Chemists\u0026rsquo; Society 2008 85:4. 85, 321\u0026ndash;330 (2008). https://doi.org/10.1007/S11746-008-1204-3\u003c/li\u003e\n\u003cli\u003eWCG: Wastern Cape Integrated Waste Management Plant 2022 - 2027 (Draft_. , Cape Town (2022)\u003c/li\u003e\n\u003cli\u003eWilliams, J.B., Clarkson, C., Mant, C., Drinkwater, A., May, E.: Fat, oil and grease deposits in sewers: Characterisation of deposits and formation mechanisms. Water Res. 46, 6319\u0026ndash;6328 (2012). https://doi.org/10.1016/J.WATRES.2012.09.002\u003c/li\u003e\n\u003cli\u003eLohrasbi, M., Pourbafrani, M., Niklasson, C., Taherzadeh, M.J.: Process design and economic analysis of a citrus waste biorefinery with biofuels and limonene as products. Bioresour Technol. 101, 7382\u0026ndash;7388 (2010). https://doi.org/10.1016/J.BIORTECH.2010.04.078\u003c/li\u003e\n\u003cli\u003eBloomberg: USD to ZAR Exchange Rate, https://www.bloomberg.com/quote/USDZAR:CUR\u003c/li\u003e\n\u003cli\u003eAbdul Raman, A.A., Tan, H.W., Buthiyappan, A.: Two-Step Purification of Glycerol as a Value Added by Product From the Biodiesel Production Process. Front Chem. 7, 439904 (2019). https://doi.org/10.3389/FCHEM.2019.00774/BIBTEX\u003c/li\u003e\n\u003cli\u003eTurton, R., Bailie, R.C., Whiting, W.B., Shaeiwitz, J.A., Bhattacharyya, D.: Analysis, Synthesis, and Design of Chemical Processes Fourth Edition. (2018)\u003c/li\u003e\n\u003cli\u003eGlisic, S.B., Pajnik, J.M., Orlović, A.M.: Process and techno-economic analysis of green diesel production from waste vegetable oil and the comparison with ester type biodiesel production. Appl Energy. 170, 176\u0026ndash;185 (2016). https://doi.org/10.1016/J.APENERGY.2016.02.102\u003c/li\u003e\n\u003cli\u003eOkoro, O.V., Sun, Z., Birch, J.: Meat processing waste as a potential feedstock for biochemicals and biofuels \u0026ndash; A review of possible conversion technologies. J Clean Prod. 142, 1583\u0026ndash;1608 (2017). https://doi.org/10.1016/J.JCLEPRO.2016.11.141\u003c/li\u003e\n\u003cli\u003eFoo, W.H., Chia, W.Y., Tang, D.Y.Y., Koay, S.S.N., Lim, S.S., Chew, K.W.: The conundrum of waste cooking oil: Transforming hazard into energy. J Hazard Mater. 417, 126129 (2021). https://doi.org/10.1016/J.JHAZMAT.2021.126129\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Waste recycling, citrus peel waste, process simulation, soap production, green chemistry","lastPublishedDoi":"10.21203/rs.3.rs-4017927/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4017927/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn the pursuit of sustainable waste management practices, this study explores the technical and economic feasibility of soap production using waste cooking oil (WCO) combined with citrus peel waste (CPW), with a specific focus on extracting limonene as soap additives. The preliminary experimental investigations indicated that soaps produced from WCO have similar qualities if properly treated, compared to those produced from virgin oils. Also, including limonene effectively addresses WCO odours and demonstrates a promise of anti-microbial properties against \u003cem\u003eE.coli\u003c/em\u003e. From the comprehensive techno-economic evaluation of WCO-based soap production, a focus on industrial symbiosis by integrating CPW-derived limonene is necessary. Results show that soap production with WCO and on-site additive in limonene (scenario 3) was competitive, with an IRR of 19% compared to 16% when the soap was produced using WCO and the additives were purchased (scenario 4). Also, the minimum selling prices of soaps were comparable for scenarios 3 (R 160.53/kg) and 4 (R 159.87/kg), further building on the economic viability of on-site limonene production. Hence, the environmental potential and economic viability of integrating WCO and CPW into soap production seem to be a profitable approach should on-site production be implemented.\u003c/p\u003e","manuscriptTitle":"Techno-economic evaluation of soap production from waste cooking oil with additives derived from citrus peel waste.","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-20 09:10:03","doi":"10.21203/rs.3.rs-4017927/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5ff59e64-6d3e-49de-ba71-7c3765e7d79c","owner":[],"postedDate":"March 20th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-05-11T20:02:04+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-20 09:10:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4017927","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4017927","identity":"rs-4017927","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}