Recovery of phosphorus and nitrogen from domestic wastewater by using dolomite rock through struvite precipitation

Recovery of phosphorus and nitrogen from domestic wastewater by using dolomite rock through struvite precipitation | 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 Recovery of phosphorus and nitrogen from domestic wastewater by using dolomite rock through struvite precipitation Melsew Endalew Berihun, knife Kassa, Assen Yimam Mohammed This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7322931/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 16 You are reading this latest preprint version Abstract Recovering essential nutrients like phosphorus (P) and nitrogen (N) from domestic wastewater is not only feasible but also required for sustainable nutrient management. This study investigated the potential of dolomite rock, a low-cost and environmentally friendly resource abundant in Ethiopia, to facilitate nutrient recovery through struvite precipitation. Dolomite was dissolved in 2M hydrochloric acid at a solid-to-liquid ratio of 25% to release magnesium ions, which were then mixed with wastewater in varying ratios at a controlled pH of 8. The initial wastewater composition contained the following elements: calcium (Ca²⁺) 32.1 mg/L, magnesium (Mg²⁺) 21.9 mg/L, sodium (Na⁺) 66.2 mg/L, potassium (K⁺) 11.8 mg/L, phosphate (PO₄³⁻-P) 1.65 mg/L, and ammonium nitrogen (NH₄-N) 19.4 mg/L. The composition of the filtrate changed dramatically when struvite precipitation was carried out with a wastewater-to-dolomite ratio of 50:70 mL. Following precipitation, the levels of calcium (Ca²⁺) rising to 748 mg/L, magnesium (Mg²⁺) falling to 0.61 mg/L, sodium (Na⁺) rising to 195.8 mg/L, and potassium (K⁺) falling to 1.9 mg/L. In contrast to ammonium nitrogen (NH₄-N), which was successfully reduced to 2.18 mg/L with a recovery rate of 88.75%, phosphate (PO₄³⁻-P) was surprisingly totally eliminated (100% recovery). The result shows that dolomite-induced struvite precipitation is an effective method for recovering nutrients from wastewater offering an alternative to conventional synthetic fertilizers. This approach not only mitigates environmental pollution caused by nutrient-rich wastewater but also provides a pathway for producing eco-friendly fertilizers. By utilizing locally available resources, this research contributes to cost-effective nutrient management and promotes sustainable agricultural practices. Dolomite rock Eco-friendly fertilizers Nutrient Recovery Struvite Precipitation Figures Figure 1 Figure 2 1 Introduction Domestic wastewater, with its complex composition of organic and inorganic substances, presents a tremendous opportunity: it serves as a rich reservoir of essential nutrients, particularly nitrogen (N) and phosphorus (P), that can be recovered and repurposed for sustainable applications (Darwish et al., 2016 ; Rahman et al., 2014 ; Ronteltap, 2009 ; Suzuki et al., 2002 ). The eutrophication of aquatic habitats is one of the major environmental issues caused by poor management of these nutrients(Iamsomboon et al., 2024 ; Warmadewanthi & Liu, 2009 ). It causes excessive algal blooms that are not natural, lowers dissolved oxygen levels, and worsens aquatic life(Smith et al., 1999 ). Recovering nutrients from wastewater resources is crucial to promote environmental sustainability and enhancing agricultural productivity while also mitigating nutrient pollution(Cordell et al., 2009 ; Darwish et al., 2016 ). Phosphorus and nitrogen are vital nutrients for plant growth and are integral components of fertilizers (Saleem et al., 2020 ). However, the global reserves of phosphate rock are finite, and the overuse of synthetic fertilizers has resulted in environmental degradation(Ahmad et al.,2022; Cordell et al., 2009 ). As a result, recovering these nutrients from wastewater offers a sustainable approach to address nutrient pollution, reduce dependence on nonrenewable resources, and meet the increasing demand for fertilizers( Saleem et al., 2022 ; Batstone et al., 2015 ). Struvite precipitation is a growing technique for recovering nutrients from wastewater(Etter et al., 2011 ) that depends on the crystallization of phosphate, magnesium, and ammonium ions in an alkaline environment (Le Corre et al., 2009 ). The resulting product, MgNH₄PO₄·6H₂O, is a helpful slow-release fertilizer that offers a more environmentally friendly substitute for synthetic fertilizers(Darwish et al., 2016 ; Rahman et al., 2014 ). Because of their great solubility and efficiency in supplying magnesium ions, a variety of artificial magnesium sources, including magnesium chloride (MgCl₂) and magnesium sulfate (MgSO₄), have been extensively employed in struvite precipitation(Etter et al., 2011 ; Rahman et al., 2014 ). However, these chemical sources can be expensive and cause treated water to accumulate sulfate or chloride. In contrast, natural magnesium sources including magnesite (MgCO₃) and dolomite (CaMg(CO₃)₂) have drawn interest as more affordable choices(Darwish et al., 2016 ). Although dolomite is a common and naturally occurring rock, its limited solubility may limit its ability to create struvite quickly(Saldi et al., 2021 ). Magnesite is another intriguing natural source, although it dissolves slowly and needs acidic conditions to release magnesium as best it can. To increase the struvite precipitation process's economic viability, research is not still being done to choose a suitable magnesium source based on factors including cost, solubility, and environmental impact. Dolomite rock primarily composed of CaMg(CO₃)₂(Singurindy & Berkowitz, 2003 ), has the potential to be an inexpensive and sustainable source of magnesium(Piol et al., 2019 ). When dolomite is dissolved in acid, magnesium ions are released(Saldi et al., 2021 ), allowing struvite to precipitate. Still, not much research has been done on the application of dolomite in nutrient recovery processes. This research aims to evaluate the efficiency of dolomite as a magnesium source for the recovery of (PO 4 3- -p) and (NH 4 -N) from domestic wastewater. 2 Materials and Methodology 2.1 Description of the study area The study was conducted in the South Ethiopian Regional State's city of Arba Minch. With its network of springs and close vicinity to Lake Abaya and Lake Chamo, Arba Minch, which translates to "Forty Springs," is well-known for its plentiful natural water resources. According to National Meteorology Agency of Ethiopia the area is situated geographically at 6° 2˝ N 37° 33˝ E, and its elevation is 1,390 meters above sea level. The minimum monthly temperature is 17.36°C and the mean maximum temperature is 30.30°C. December saw the lowest recorded mean minimum temperature of 15.13°C and the highest recorded at 32°C. 2.2 Collection of dolomite rock The dolomite used for this study was obtained from the Bahir Dar Paint and Gypsum Factory. The factory uses a raw dolomite that originates from metamorphic rock outcrops in Abbay Valley, locally called Abbay Bereha, for its rich geological deposit areas. The collected dolomite rock is then processed into a fine powder form. It is a fine powder that acts as a versatile raw material and finds wide application in several industrial sectors, including ceramics, gypsum, and paints. The quality and availability of the rock, make it a resource for both industrial applications and research. 2.3 Preparation of Dolomite Solution For struvite precipitation, dolomite rock served as a supply of magnesium(Rahman et al., 2014 ). Due to its availability and easy to handle in laboratory settings 2M hydrochloric acid (HCl) was selected to dissolve the crushed and dried dolomite in a 25% solid-to-liquid ratio after it had been sieved through a 425µm sieve. As it is studied by(Yildirim & Akarsu, 2010 ) a stirring speed of 200 rpm ensures proper mixing and reduces the formation of a stagnant boundary layer around dolomite particles. For ten minutes, the dissolution process was conducted with continuous stirring at a speed of 200 rpm to guarantee that the dolomite was completely dissolved(Yildirim, 2008 ). The solution was then placed in a thermostatically controlled water bath (KOTTER MANN) for 30 minutes at 80 degrees Celsius because Dolomite (CaMg (CO₃)₂) dissolves more efficiently at higher temperatures because temperature increases the solubility of minerals and enhances the diffusion of reactants and products. At 80°C, the dissolution of dolomite is significantly accelerated compared to lower temperatures, facilitating the release of Ca²⁺ and Mg²⁺ ions into solution. After cooling, any remaining particles were filtered out of the resultant solution using a 0.45µm pore size WHAT-MAN filter paper, and stored for subsequent experiments. As illustrated by(Yildirim, 2008 ), the stoichiometric reaction of dolomite dissolution in hydrochloric acid is represented as follows: CaMg (CO 3 ) 2 + 2H + → Ca 2+ + MgCO 3 + H 2 O + CO 2 ↑ MgCO 3 + 2H + → Mg 2+ + H 2 O + CO 2 ↑ 2.4 Collection and Analysis of Wastewater Sample Domestic wastewater was collected in the septic tank from the Arba minch university teachers’ residential area of “Limate Condominium”. After collection, the sample was kept at 4°C to avoid biological deterioration before analysis then transferred to the water quality laboratory in the university. A calibrated HQ40D multi-meter was used to measure the pH, electrical conductivity (EC), and total dissolved solids (TDS). The argentometric method (titration) was used to analyze the chloride (Cl⁻).The ascorbic acid method was used to determine the (PO₄³⁻-P) spectrophotometrically at a wave length of 880nm. And the Nesslerization (Kejeldah) method was used to measure ammonium nitrogen (NH₄⁺-N). Additionally, the ions of calcium (Ca²⁺) and magnesium (Mg²⁺) were analyzed using atomic absorption spectrophotometry (AAS)(Basson & Van Staden, 1980 ), while potassium (K⁺) and sodium (Na⁺) were analyzed by using flame photometer . 2.5 Precipitation of struvite The dolomite solution prepared earlier was mixed with the wastewater in varying ratios to investigate its efficiency in nutrient recovery through struvite precipitation. The pH of the mixtures was adjusted to 8.0(Darwish et al., 2016 ; Le Corre et al., 2009 ; Zhou et al., 2023 ) using 1M sodium hydroxide (NaOH) to create optimal conditions for struvite formation. This pH level is crucial because it promotes the precipitation of struvite by ensuring the proper chemical environment for the magnesium, ammonium, and phosphate ions to combine and form struvite crystals. The mixture was stirred continuously by using orbital shaker at a stirring speed of 76rpm(Darwish et al., 2016 ; Ohlinger, 2018 ) for 25 minutes(Darwish et al., 2016 ) to allow for sufficient interaction between the dolomite solution and the wastewater. Researchers(Darwish et al., 2016 ; Le Corre et al., 2005 ; Rahman et al., 2014 ) have noted that under alkaline conditions, the combination of magnesium (Mg²⁺), ammonium (NH₄⁺), and phosphate (PO₄³⁻) ions leads to the formation of solid struvite, which precipitates out of the solution. This reaction is represented by the following chemical equation: Mg 2+ + NH 4 + ​+ PO 4 3− + 6H 2 ​O→MgNH 4 ​PO 4 ​⋅6H 2 ​O↓ In order to separate the solid precipitates, the mixtures were filtered through a 0.45µm pore size WHAT-MAN filter paper after the reaction had been allowed to settle for six hours(Etter et al., 2011 ). Nutrient recovery percentages were computed by analyzing the filtrate for residual amounts of (NH₄⁺-N). and (PO 4 3− -p). The production of the solid precipitate (struvite) was measured by weighing it after it had been dried in the sunlight(Etter et al., 2011 ). 2.6 Characterization of the struvite Following air drying and sieving, one gram of the struvite sample was precisely weighed and put into a 200 mL conical flask. The flask was then gradually filled with 20 mL of aqua regia. Nitric acid (HNO₃) and concentrated hydrochloric acid (HCl) in a normal 3:1 ratio make up the highly caustic mixture known as aqua regia. Due to its potent oxidizing qualities, this acidic combination is frequently utilized for the digestion of mineral samples. Following that, the conical flask holding the sample and aqua regia was heated to 150°C and kept there for an hour. To guarantee that the struvite material was completely broken down and that the constituent elements could be released into the solution, this digesting stage was carried out. Following digestion, the sample was given a little time to cool before 100 milliliters of distilled water were added to the flask. Reducing the acidity and preparing the solution for filtering and further analysis required this dilution step. A 0.45 µm-pore-size Whatman filter paper (model: WHA7404004) was then used to filter the resultant combination. Any solid particles that remained were eliminated by this filtration procedure, guaranteeing a clear solution for analysis. Finally, an Atomic Absorption Spectrophotometer (AAS) was used to evaluate the filtered extract. Concentrations of the principal cations calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), and potassium (K⁺) as well as specific heavy metals, such as arsenic (As), nickel (Ni), chromium (Cr), zinc (Zn), and copper (Cu), were the main focus of the analysis. 2.7 Phosphate phosphorus (PO₄³⁻-P) determination After being sieved and allowed to air dry, one gram of the struvite sample was weighed and put into a 50 mL volumetric flask. The struvite-containing flask was filled with 25 milliliters (25 mL) of phosphate extraction reagent (Olsen). A Stuart SSL1 orbital shaker (model: 51091-00) was then used to shake the mixture vigorously for five minutes in order to guarantee that all of the available phosphate was properly extracted. A 0.45 µm pore-size Whatman filter paper (model: WHA7404004) was used to filter the suspension. For the purpose of phosphate analysis, the clear extract was gathered. A working reagent solution, usually the ascorbic acid reagent, which comprises ammonium molybdate, antimony potassium tartrate, and ascorbic acid in an acidic medium, was used to pipette two milliliters (2 mL) of the extract and dilute it to 25 mL. In order to properly produce the blue color complex (molybdenum blue), the mixture was vigorously stirred and left to stand for 20 minutes. The UV-VIS spectrophotometer (model no: S-925 India) was used to measure the absorbance of the generated blue hue at 880 nm. To zero the device, a reagent blank (made with the extraction reagent without struvite) was utilized. The absorbance of the struvite sample was compared to a standard calibration curve made from known phosphate standard solutions (using KH₂PO₄) in order to ascertain the phosphate concentration in the sample. The sample concentration was extrapolated from the calibration curve and displayed against the phosphate content on an absorbance graph. 2.8 Total Kjeldahl Nitrogen (TKN) Using the Ascorbic Acid Method After being carefully weighed, 1g of the air-dried and sieved struvite sample was put into Kjeldahl digestion tubes. For reference, a blank sample with just 10 milliliters of distilled water was also made. 25 milliliters of the digesting reagent a combination of potassium sulfate, concentrated sulfuric acid, and a copper and selenium catalyst were added to each tube. After that, the tubes were heated gradually at first, then more quickly, until the liquid turned transparent and the volume was greatly decreased. The digestion process was carried out until a pale green, light-colored solution was produced, signifying that the organic nitrogen had been fully broken down into ammonium ions (NH₄⁺). To neutralize the acid and turn ammonium ions into ammonia gas, 25 milliliters of an alkaline solution a combination of sodium hydroxide and sodium thiosulfate was carefully added to each digestive tube after it had cooled. The tubes were then attached to a distillation equipment, and 150 milliliters of distilled water was added to dilute the mixture. At the same time, a 100 ml Erlenmeyer flask was filled with a mixed indicator (such as methyl red and bromocresol green) and 25 ml of a 4% boric acid solution. The reception flask was set up to catch the ammonia that had been distilled. Until the distillate volume in the receiving flask reached roughly 50–75 ml, the distillation process was continued. This phase involved the sample's ammonia gas being trapped in the boric acid solution to produce ammonium borate, which turned the solution a light green. Following that, the distillate was titrated with standardized 0.02 N sulfuric acid until the green tint turned pink, signifying neutralization. By comparing the absorbance values with a calibration curve made from standard nitrogen solutions and calculating the volume of acid used during titration, the total Kjeldahl nitrogen concentration in the struvite sample was determined 3 Results and Discussion 3.1 Dolomite Characterization Dolomite [CaMg(CO₃)₂], a naturally occurring sedimentary carbonate mineral, is widely recognized for its richness in calcium and magnesium ions. The mineral's stoichiometric composition ideally consists of equal molar amounts of calcium and magnesium; however, natural variations often result in deviations due to geological formation conditions and associated impurities(Manche & Kaczmarek, 2021 ). Similarly (Sdiri, 2018 )performed chemical and mineralogical analysis of dolomite samples and noted that the Mg:Ca ratio can vary significantly depending on mineral purity and associated gangue materials such as silica, alumina, and iron oxides. Their work confirmed that high-purity dolomite samples are capable of releasing sufficient quantities of both Ca²⁺ and Mg²⁺ for environmental and industrial applications. The characterization of dolomite revealed its high magnesium content (453.6 ± 28 mg/L) and significant calcium concentration (3128 ± 62 mg/L) as shown in (Table 1 ). These values indicate its suitability as a magnesium source for struvite precipitation. Magnesium ions play a critical role in the crystallization of struvite(Darwish et al., 2016 ; Etter et al., 2011 ), while the presence of calcium could affect struvite formation by promoting competing reactions(Bhuiyan et al., 2008 ). The low concentrations of sodium (3.13 ± 0.38 mg/L) and potassium (3.03 ± 0.06 mg/L) in dolomite further support its potential as an eco-friendly and low-cost resource for nutrient recovery. These findings align with previous studies that emphasize the importance of magnesium sources in struvite precipitation (Uysal et al., 2010 ). Table 1 the measured ion concentrations in the Dolomite sample Ions Concentration in (mg/l) magnesium (Mg 2+ ) 453.6 ± 28 calcium (Ca 2+ ) 3128 ± 62 sodium (Na + ) 3.13 ± 0.38 potassium (K + ) 3.03 ± 0.06 3.2 Wastewater Sample Characterization The physicochemical characteristics of the wastewater sample were examined as shown in (Table 2 ). Because the wastewater has significant amounts of important nutrients including (PO 4 3− -P) and (NH₄⁺-N), it was shown to be appropriate for nutrient recovery. The measured pH of the wastewater was 7.8 ± 0.1, which is somewhat alkaline and, when properly corrected to the ideal pH range of 8–9, conducive to struvite precipitation(Le Corre et al., 2009 ; Unyimadu et al., 2018 ; Zhou et al., 2023 ). According to the studies, pH has a significant impact on the solubility and crystallization of the three primary components of struvite Mg²⁺, (NH₄⁺-N), and (PO 4 3− -P) and is a key element in the effectiveness of nutrient recovery. The conductivity range of 625.6 ± 0.5 µS/cm and the total dissolved solids range of 292.7 ± 1.5 mg/L suggest a moderate ionic strength, which could have an impact on the precipitation process. Although they are present (24.9 ± 0.2 mg/L), chloride ions are less likely to prevent struvite production in controlled settings(Rahman et al., 2014 ). The amounts of magnesium (21.9 ± 0.3 mg/L) and calcium (32.1 ± 0.1 mg/L) are particularly significant. Dolomite dissolving can be used to supply magnesium, which is essential for struvite precipitation. The purity of struvite may be lowered, though, if excessive calcium competes with magnesium for precipitation, producing precipitates of calcium based minerals such calcium phosphates(Bhuiyan et al., 2008 ). Although the potassium and sodium concentrations are very low 11.8 ± 0.7 mg/L and 66.2/L, respectively, they should be taken into account since too much sodium can affect soil permeability if the recovered struvite is utilized as fertilizer(Rahman et al., 2014 ). Significant levels of (NH₄⁺-N) (19.4 ± 0.5 mg/L) and (PO 4 3− -P) (1.65 ± 0.2 mg/L) indicate the potential the wastewater for (NH₄⁺-N) and (PO 4 3− -P) recovery. In aquatic systems, phosphate concentration above 1 mg/L is regarded as critical for nutrient pollution and eutrophication hazards(Smith et al., 1999 ). In addition to meeting the demand for agricultural fertilizer, recovering these minerals through precipitation offers an environmentally friendly approach(Scholz et al., 2013 ). Table 2 the physicochemical analysis of the wastewater sample no parameters unit concentration 1 pH. - 7.8 ± 0.1 2 Electrical conductivity \(\:\mu\:s/cm\) 625.6 ± 0.5 3 Total dissolved solids mg/l 292.7 ± 1.5 4 Chloride(Cl − ) mg/l 24.9 ± 0.2 5 Calcium(Ca 2+ ) mg/l 32.1 ± 0.1 6 Magnesium(Mg 2+ ) mg/l 21.9 ± 0.3 7 Sodium (Na + ) mg/l 66.2 ± 0.13 8 Potassium ( K + ) mg/l 11.8 ± 0.7 9 Phosphate(PO 4 3− -P) mg/l 1.65 ± 0.2 10 Ammonium nitrogen (NH₄⁺-N) mg/l 19.4 ± 0.5 3.3 Phosphate Phosphorus Recovery Phosphorus is very critical element especially for agriculture and different industries(Song et al., 2007 ). But when it is released to natural water bodies it causes eutrophication (Lu et al., 2025 ). On the other hand, Phosphorus is very scarce resource all over the world. Due to this reason P recovery and reuse is critical for sustainable utilization ( Saleem et al., 2020 ; J. Driver, 1999 ). The best phosphorus recovery occurs at pH 8, which is in line with several studies that highlight how important pH is for phosphate precipitation and struvite (MgNH₄PO₄·6H₂O) crystallization (Le Corre et al., 2009 ). Achieving the proper molar ratios of magnesium, ammonium, and phosphate as well as preserving a favorable pH are crucial for the formation of struvite. Using magnesium chloride (MgCl₂) as the magnesium source, (Sengupta et al., 2015 ) showed that struvite precipitation could effectively recover 80–99% of phosphorus from wastewater, indicating the potential of struvite as a slow-release fertilizer. Similarly, by modifying the pH and increasing the dosage of magnesium oxide (MgO), which improves the crystallization effectiveness of MAP (magnesium ammonium phosphate),(Martí et al., 2010 )claimed that up to 97% phosphorus removal may be obtained. According to (Darwish et al., 2016 ), struvite precipitation employing magnesium sulfate (MgSO₄) as the Mg source can achieve phosphorus recovery rates of above 95%. Furthermore, (Wang et al., 2016 ) discovered that magnesium hydroxide (Mg (OH) ₂) may reach removal efficiencies of over 90% and be utilized successfully for struvite crystallization, especially in systems with high ammonium concentrations. Furthermore, with encouraging recovery rates exceeding 85%, (Yetilmezsoy et al., 2017 ) looked into the use of bittern, a magnesium-rich byproduct of salt manufacturing, as an affordable and sustainable alternative Mg source for struvite precipitation. Wu et al. (2001) also highlighted that the selection of magnesium source influences the crystal size and purity of struvite, which are important factors for its repurposing as fertilizer, in addition to recovery efficiency. In the treatment of municipal wastewater, (Achilleos et al., 2022 ) also reported successful struvite production using MgCl₂, with phosphate removal efficiencies above 90% under regulated pH and molar ratios. All of these results highlight the need of keeping pH at an ideal level and choosing magnesium sources (MgCl₂, MgO, Mg (OH) ₂, MgSO₄, and bittern) carefully in order to maximize phosphorus recovery from wastewater by struvite crystallization. In Fig. 1 , the experimental results demonstrate a progressive increase in phosphate removal efficiency with an increasing waste-to-dolomite ratio. Initially, at a dolomite volume of 10 mL was added to 50ml of wastewater, the phosphate recovery was 60.79%, indicating a moderate reduction in phosphate concentration. As the dolomite dosage increased, the phosphate recovery continued to improve, reaching 88.71% at 40 mL. The complete phosphate removal (100% recovery) was achieved at dolomite volumes of 70 mL and higher, as evidenced by the absence of detectable phosphate in the filtrate. This suggests that at a waste-to-dolomite ratio of 50:70, all available phosphate ions were effectively precipitated, indicating optimal conditions for phosphate recovery. Further increasing the dolomite volume beyond 70 mL did not yield additional benefits, as complete phosphate removal had already been attained. These findings highlight the effectiveness of dolomite as a natural magnesium source for struvite precipitation, particularly at higher dosages, making it a viable option for nutrient recovery from wastewater. Therefore according to the above mentioned literatures the recovery results of this research (100%) is acceptable. 3.4 Ammonium Nitrogen Recovery The recovery of (NH₄⁺-N) from domestic wastewater using dolomite was evaluated by varying the ratio of wastewater to dolomite (Fig. 2 ).The results indicate that the ammonium nitrogen recovery increases progressively with the volume of dolomite solution added. As the dolomite volume increased, the percentage recovery improved significantly, reaching 93.47% at a wastewater-to-dolomite ratio of 50:100ml. Interestingly, the recovery rate showed a steep increase beyond the 50:40 mL ratio, with significant improvement observed at 50:70 mL and higher. After this ratio the precipitated product may not be struvite because all of the (PO 4 3− -p) was recovered at a wastewater to dolomite solution of 50:70ml. The efficiency of struvite crystallization in recovering ammonium nitrogen (NH₄⁺-N) from wastewater utilizing a variety of magnesium sources has been shown in numerous research. When magnesium chloride (MgCl₂) was utilized as the magnesium source,(Darwish et al., 2016 ) found that struvite precipitation could recover over 95% of NH₄⁺-N. According to (Uysal et al., 2010 ), soluble magnesium salts promote the synthesis of struvite, as evidenced by their high removal efficiencies of NH₄⁺-N using MgCl₂·6H₂O. The inhibitory effect of calcium ions on struvite crystallization was highlighted by (Huang et al., 2011 ), who employed magnesium oxide (MgO) as the Mg source. They found that increasing the calcium-to-magnesium (Ca:Mg) molar ratio from 0 to 0.75 resulted in a significant reduction in NH₄⁺-N removal efficiency from 87.7–58%. Rahman et al. ( 2014 ) also found that the type of magnesium source employed affects the effectiveness of struvite precipitation. After comparing MgCl₂, MgSO₄, and MgO, they found that MgO was less effective because of its slower rate of dissolution, but MgCl₂ and MgSO₄ offered faster reaction kinetics because of their high solubility. The potential of struvite crystallization as a sustainable nutrient recovery approach was further supported by(Yetilmezsoy & Sapci-Zengin, 2009 ) demonstration that employing MgCl₂ in a molar ratio of 1:1:1 (Mg²⁺:NH₄⁺:PO₄³⁻) produced over 90% removal of NH₄⁺-N and phosphorus simultaneously. In the case of this research the calcium concentration is much higher than that of magnesium concentration both in the wastewater sample and in the dolomite solution: this makes the percentage of NH₄⁺-N recovery 88.75%. Therefore according to (Huang et al., 2011 )the recovery results of this research was reasonable. 3.5 Quantification of Struvite Production The mass of struvite precipitated M(s) was determined by subtracting the mass of the filter paper M(f) from the combined mass of the filter paper and struvite M(f + s). The results demonstrate a clear relationship between the dolomite volume and the amount of struvite formed. As it is presented in (Table 3 ) when the dolomite volume increased, the mass of struvite precipitated also increased. At a wastewater to dolomite ratio of 50ml: 70ml the mass of struvite produced reached 0.123g. Beyond this dolomite volume the mass of struvite formed begins to plateau. This suggests that the system may reach a saturation point where all available phosphate ions in the wastewater are precipitated as struvite, and additional magnesium does not significantly enhance struvite production. Table 3 Quantification of struvite production no V(ww)(ml) V(Dolomite)(ml) M(F)(gram) M(F + S) (gram) M(s) (gram) 1 50 10 0.798 0.853 0.055 2 50 20 0.803 0.881 0.078 3 50 30 0.786 0.885 0.099 4 50 40 0.822 0.931 0.109 5 50 50 0.77 0.882 0.112 6 50 60 0.804 0.919 0.115 7 50 70 0.755 0.878 0.123 8 50 80 0.793 0.914 0.121 9 50 90 0.782 0.904 0.122 10 50 100 0.798 0.919 0.121 3.6 Filtrate Sample Characterization Post-precipitation filtrate analysis revealed significant reductions in phosphate phosphorus and ammonia nitrogen concentrations, confirming successful nutrient removal (Table 4 ). Table 4 Physio-chemical parameters of filtrate sample no parameters unit concentration 1 pH. - 9.1 ± 0.2 2 Electrical conductivity \(\:\mu\:s/cm\) 2190.1 ± 0.1 3 Total dissolved solids mg/l 31843.3 ± 60.3 4 chloride mg/l 32147 ± 6.3 5 Calcium(Ca 2+ ) mg/l 748 ± 6.8 6 Magnesium(Mg 2+ ) mg/l 0.61 ± 0.1 7 Sodium (Na + ) mg/l 195.8 ± 0.3 8 Potassium ( K + ) mg/l 1.9 ± 0.3 9 Phosphate(PO 4 3− -p) mg/l 0.0 10 Ammonia nitrogen mg/l 2.18 ± 0.12 Magnesium and calcium concentrations also decreased, indicating their incorporation into the struvite structure. The low concentrations of sodium and potassium in the filtrate suggest that these ions did not interfere significantly with the precipitation process. This outcome highlights the recovery potential of struvite precipitation when dolomite is used as the magnesium source. 3.7 Chemical composition of struvite The chemical composition of the produced struvite was analyzed, and the results are shown in the Table 5 . Table 5 chemical composition of the produced struvite no parameters concentration mg/l Concentration (%) 1 Magnesium(Mg 2+ ) 234.9 2.58 2 Calcium(Ca 2+ ) 29685.4 11.77 3 Sodium(Na + ) 0.061 0.05 4 Potassium( K + ) 0.073 0.06 5 Phosphate(PO 4 3− -p) 245.7 2.66 6 Ammonium nitrogen 121.3 1.01 The findings highlight the elemental concentrations of key components, including magnesium (Mg²⁺), calcium (Ca²⁺), phosphate (PO₄³⁻-P), ammonium nitrogen (NH₄⁺-N), sodium (Na⁺), and potassium (K⁺). These values provide insight into the composition and potential utility of the struvite as a slow-release fertilizer. Magnesium (Mg²⁺) The concentration of magnesium in the produced struvite was 234.9 mg/L, contributing to 2.58% of the total composition. Magnesium is an essential component of struvite and plays a crucial role in its crystallization process. This concentration indicates that magnesium from dolomite was effectively utilized in the precipitation reaction. Studies have shown that sufficient magnesium is critical for efficient struvite formation, as it reacts with ammonium and phosphate to form the crystal lattice(Le Corre et al., 2009 ). Calcium (Ca²⁺) Calcium was present at a significantly higher concentration of 29685.4 mg/L, constituting 11.77% of the total composition. This high calcium content strongly suggests that calcium-based molecules, including calcium phosphate ( \(\:{Ca}_{3}\) (PO₄)₂) and struvite (MgNH₄PO₄·6H₂O), may co-precipitate. The effectiveness and purity of struvite recovery procedures can be greatly impacted by this co-precipitation, particularly in systems that use calcium-rich minerals, such as dolomite, as a magnesium source. Several investigations have demonstrated that by preferentially interacting with phosphate to generate calcium phosphate compounds, excess calcium ions can obstruct struvite crystallization. This can lead to decreased struvite production and purity in addition to competing with struvite formation. (Rahman et al., 2014 ) found that high calcium concentrations significantly reduced the recovery efficiency of struvite, especially when dolomite was utilized as a magnesium donor since it releases both Mg²⁺ and Ca²⁺ ions when acid is applied. Similar to this, (Le Corre et al., 2009 ) highlighted that calcium and magnesium compete with one another for phosphate binding, particularly in neutral to alkaline pH ranges, resulting in the development of either crystalline or amorphous calcium phosphates. Because these substances precipitate more quickly than struvite, there is less phosphate available for struvite crystallization. (Wu et al., 2016 ) also found that the production of hydroxyapatite and other calcium phosphates inhibited the precipitation of struvite when the molar ratio of Ca 2+ to Mg 2+ was high. Their results showed that competitive precipitation caused struvite purity and recovery to drastically decline in situations where the Ca:Mg molar ratio was greater than 1. Overall, it is abundantly evident from the literature that high calcium levels can prevent struvite precipitation through co-precipitation mechanisms, especially when they are delivered through calcium-rich precursors like dolomite. To improve the production and selectivity of struvite, especially in nutrient recovery applications from wastewater, calcium interference must be taken into account during process optimization. Phosphate (PO₄³⁻-P) The phosphate content of the struvite was 245.7 mg/L, representing 2.66% of the total composition. Phosphate is a critical nutrient in struvite and is responsible for its utility as a phosphorus-rich fertilizer. The recovery of phosphate in this study demonstrates the effectiveness of dolomite as a reagent for struvite precipitation. These findings align with previous research, which underscores the role of phosphate in the crystallization process and its recovery potential from wastewater(Song et al., 2007 ). Total Kjeldahl Nitrogen (TKN) The Total Kjeldahl Nitrogen (TKN) concentration in the struvite was 121.3 mg/L, making up 1.01% of the total composition. Ammonium ions are essential for the formation of struvite crystals, as they combine with magnesium and phosphate in stoichiometric proportions. The recovery of ammonium nitrogen indicates the dual nutrient recovery capability of this process, making struvite an attractive option for sustainable wastewater treatment. Sodium (Na⁺) and Potassium (K⁺) Sodium and potassium were present in trace amounts, with concentrations of 0.061 mg/L (0.05%) and 0.073 mg/L (0.06%), respectively. Their low concentrations suggest minimal interference with the struvite precipitation process. These elements may originate from the dolomite or wastewater but are not significant contributors to the struvite composition. Heavy metals (As, Ni, Cr, Zn, and Cu) The concentration of heavy metals in the produced struvite is the first and most crucial factor in determining whether or not it may be utilized as fertilizer(Uysal et al., 2010 ). According to this study, the concentration of heavy metals (As, Ni, Cr, Zn, and Cu) was below the AAS instrument's detection limit. It is therefore possible to use the struvite generated in this work as fertilizer. 3.8 The purity of the produced struvite According to several researchers (Korchef et al., 2011; Liu et al., 2013; Rahman et al., 2014 ; Yesigat et al., 2022), the ideal chemical composition of pure struvite is magnesium ammonium phosphate hexahydrate (MgNH₄PO₄·6H₂O), which appears as a white crystalline solid. This ideal form assumes a 1:1:1 molar ratio of magnesium, phosphorus, and nitrogen. However, the struvite recovered in this study deviates from this pure form both in appearance and chemical composition. The product obtained was brownish in color and contained 1.01% nitrogen, 2.66% phosphorus, 0.06% potassium, 2.58% magnesium, and a significantly high 11.77% calcium content. The presence of elevated calcium levels indicates substantial co-precipitation of metallic ions particularly calcium during the recovery process, which adversely affects the purity of the struvite. As a result, the final product cannot be classified as pure struvite. Nevertheless, it is worth noting that the recovered material is free from detectable concentrations of heavy metals, which are known to pose risks to plant and human health. This absence of toxic elements makes the product safe for further testing in agricultural applications. Despite its impurity, the product retains essential nutrients such as phosphorus, magnesium, and ammonium nitrogen which are key elements for plant growth. 4 Conclusion This study demonstrates the effective recovery of phosphorus and nitrogen from domestic wastewater using dolomite rock as a low-cost and environmentally sustainable source of magnesium for struvite precipitation. Optimal nutrient recovery was achieved at a wastewater-to-dolomite ratio of 50:70 mL and a pH of 8.0, where phosphorus recovery reached 100% and nitrogen recovery was 88.75%. The production of struvite increased with the dolomite dosage, confirming its efficiency in precipitating nutrients. Post-recovery filtrate analysis revealed substantial reductions in phosphorus and nitrogen concentrations, highlighting the potential of this approach for wastewater treatment and nutrient recovery. Despite these promising results, certain limitations were encountered. The mineralogical composition of dolomite was not analyzed using XRD or FTIR due to limited instrument availability and financial constraints. Additionally, minimizing calcium interference from dolomite during struvite precipitation proved challenging. Sodium hydroxide was used for pH adjustment; however, the presence of sodium from NaOH and calcium from dolomite significantly affected the purity of the produced struvite. It is important to note, however, that the struvite recovered in this study deviates from the pure form both in appearance and chemical composition. The product was brownish in color and contained 1.01% Total Kjeldahl Nitrogen (TKN), 2.66% phosphorus, 0.06% potassium, 2.58% magnesium, and a notably high 11.77% calcium content. The elevated calcium concentration indicates substantial co-precipitation of metallic ions, particularly calcium, during the recovery process, which negatively impacts the purity of the struvite. Consequently, the final product cannot be classified as pure struvite. Despite this, the findings highlight the potential of recovered struvite, even in its impure form; can serve as a viable and sustainable alternative to chemical fertilizers, because it contains essential nutrients such as phosphorus, magnesium, and ammonium nitrogen which are key elements for plant growth. Declarations Ethics approval not applicable Consent to participate not applicable Consent for publication not applicable Funding There is no funding Conflict of interest : The authors have no relevant financial or non-financial interests to disclose Availability of data and materials: The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request Acknowledgment The authors are grateful to Arba Minch University for providing the chance and resources necessary to conduct this study. The Water Quality Professionals from Arba Minch University deserve a great deal of gratitude for their assistance, counsel, and knowledge throughout the experiment. Most importantly, the authors would like to express their gratitude to Bahir Dar Paint and Gypsum Factory for their kind donation of the dolomite sample, which was essential to the accomplishment of this study. References Achilleos P, Roberts KR, Williams ID. Struvite precipitation within wastewater treatment: A problem or a circular economy opportunity? Heliyon. 2022;8(7):e09862. https://doi.org/10.1016/j.heliyon.2022.e09862 . Basson WD, Van Staden JF. Simultaneous determination of sodium, potassium, magnesium and calcium in surface, ground and domestic water by flow-injection analysis. Fresenius’ Z Für Analytische Chemie. 1980;302(5):370–4. https://doi.org/10.1007/BF00470925 . Batstone DJ, Hülsen T, Mehta CM, Keller J. Platforms for energy and nutrient recovery from domestic wastewater: A review. 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Removal of phosphate, magnesium and calcium from swine wastewater through crystallization enhanced by aeration. Water Res. 2002;36(12):2991–8. https://doi.org/10.1016/S0043-1354(01)00536-X . Unyimadu JP, Osibanjo O, Babayemi JO. Selected persistent organic pollutants (POPs) in water of River Niger: occurrence and distribution. Environ Monit Assess. 2018;190(1). https://doi.org/10.1007/s10661-017-6378-4 . Uysal A, Yilmazel YD, Demirer GN. The determination of fertilizer quality of the formed struvite from effluent of a sewage sludge anaerobic digester. J Hazard Mater. 2010;181(1–3):248–54. https://doi.org/10.1016/j.jhazmat.2010.05.004 . Wang H, Wang XJ, Wang WS, Yan XB, Xia P, Chen J, Zhao JF. Modeling and optimization of struvite recovery from wastewater and reusing for heavy metals immobilization in contaminated soil. J Chem Technol Biotechnol. 2016;91(12):3045–52. https://doi.org/10.1002/jctb.4931 . Warmadewanthi, Liu JC. Recovery of phosphate and ammonium as struvite from semiconductor wastewater. Sep Purif Technol. 2009;64(3):368–73. https://doi.org/10.1016/j.seppur.2008.10.040 . Wu H, Zhang Y, Yuan Z, Gao L. A review of phosphorus management through the food system: Identifying the roadmap to ecological agriculture. J Clean Prod. 2016;114:45–54. https://doi.org/10.1016/j.jclepro.2015.07.073 . Yetilmezsoy K, Ilhan F, Kocak E, Akbin HM. Feasibility of struvite recovery process for fertilizer industry: A study of financial and economic analysis. J Clean Prod. 2017;152:88–102. https://doi.org/10.1016/j.jclepro.2017.03.106 . Yetilmezsoy K, Sapci-Zengin Z. Recovery of ammonium nitrogen from the effluent of UASB treating poultry manure wastewater by MAP precipitation as a slow release fertilizer. J Hazard Mater. 2009;166(1):260–9. https://doi.org/10.1016/j.jhazmat.2008.11.025 . Yildirim M. (2008). Dissolution Kinetics of Icel-Aydincik Dolomite in Hydrochloric Acid . 127–132. Yildirim M, Akarsu H. Preparation of magnesium oxide (mgo) from dolomite by leach-precipitation-pyrohydrolysis process. Physicochemical Probl Mineral Process. 2010;44:257–72. Zhou Y, Zhu Y, Zhu J, Li C, Chen G. A Comprehensive Review on Wastewater Nitrogen Removal and Its Recovery Processes. Int J Environ Res Public Health. 2023;20(4). https://doi.org/10.3390/ijerph20043429 . Ahmad M, Ishaq M, Shah WA, Adnan M, Fahad S, Saleem MH, Khan FU, Mussarat M, Khan S, Ali B, Mostafa YS. 2022. Managing phosphorus availability from organic and inorganic sources for optimum wheat production in calcareous soils. Sustainability, vol. 14, no. 13 [online] 10.3390/su14137669 Saleem MH, Zhu H, Liu L. Synergistic and sustainable impact of reducing nitrogen fertilizer on growth, yield, and quality of ramie (Boehmeria nivea L). Plant Prod Sci. 2022;25(3):289–97. https://doi.org/10.1080/1343943X.2022.2077223 . Saleem MH, Ali S, Rehman M, Rana MS, Rizwan M, Kamran M, Imran M, Riaz M, Soliman MH, Elkelish A, Liu L. 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Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Ronteltap, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Suzuki et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe eutrophication of aquatic habitats is one of the major environmental issues caused by poor management of these nutrients(Iamsomboon et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Warmadewanthi \u0026amp; Liu, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). It causes excessive algal blooms that are not natural, lowers dissolved oxygen levels, and worsens aquatic life(Smith et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Recovering nutrients from wastewater resources is crucial to promote environmental sustainability and enhancing agricultural productivity while also mitigating nutrient pollution(Cordell et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003cp\u003ePhosphorus and nitrogen are vital nutrients for plant growth and are integral components of fertilizers (Saleem et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, the global reserves of phosphate rock are finite, and the overuse of synthetic fertilizers has resulted in environmental degradation(Ahmad et al.,2022; Cordell et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). As a result, recovering these nutrients from wastewater offers a sustainable approach to address nutrient pollution, reduce dependence on nonrenewable resources, and meet the increasing demand for fertilizers( Saleem et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Batstone et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eStruvite precipitation is a growing technique for recovering nutrients from wastewater(Etter et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) that depends on the crystallization of phosphate, magnesium, and ammonium ions in an alkaline environment (Le Corre et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The resulting product, MgNH₄PO₄\u0026middot;6H₂O, is a helpful slow-release fertilizer that offers a more environmentally friendly substitute for synthetic fertilizers(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eBecause of their great solubility and efficiency in supplying magnesium ions, a variety of artificial magnesium sources, including magnesium chloride (MgCl₂) and magnesium sulfate (MgSO₄), have been extensively employed in struvite precipitation(Etter et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, these chemical sources can be expensive and cause treated water to accumulate sulfate or chloride. In contrast, natural magnesium sources including magnesite (MgCO₃) and dolomite (CaMg(CO₃)₂) have drawn interest as more affordable choices(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAlthough dolomite is a common and naturally occurring rock, its limited solubility may limit its ability to create struvite quickly(Saldi et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Magnesite is another intriguing natural source, although it dissolves slowly and needs acidic conditions to release magnesium as best it can. To increase the struvite precipitation process's economic viability, research is not still being done to choose a suitable magnesium source based on factors including cost, solubility, and environmental impact.\u003c/p\u003e\u003cp\u003eDolomite rock primarily composed of CaMg(CO₃)₂(Singurindy \u0026amp; Berkowitz, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), has the potential to be an inexpensive and sustainable source of magnesium(Piol et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). When dolomite is dissolved in acid, magnesium ions are released(Saldi et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), allowing struvite to precipitate. Still, not much research has been done on the application of dolomite in nutrient recovery processes. This research aims to evaluate the efficiency of dolomite as a magnesium source for the recovery of (PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3-\u003c/sup\u003e -p) and (NH\u003csub\u003e4\u003c/sub\u003e-N) from domestic wastewater.\u003c/p\u003e"},{"header":"2 Materials and Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Description of the study area\u003c/h2\u003e\u003cp\u003eThe study was conducted in the South Ethiopian Regional State's city of Arba Minch. With its network of springs and close vicinity to Lake Abaya and Lake Chamo, Arba Minch, which translates to \"Forty Springs,\" is well-known for its plentiful natural water resources. According to National Meteorology Agency of Ethiopia the area is situated geographically at 6\u0026deg; 2˝ N 37\u0026deg; 33˝ E, and its elevation is 1,390 meters above sea level. The minimum monthly temperature is 17.36\u0026deg;C and the mean maximum temperature is 30.30\u0026deg;C. December saw the lowest recorded mean minimum temperature of 15.13\u0026deg;C and the highest recorded at 32\u0026deg;C.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Collection of dolomite rock\u003c/h2\u003e\u003cp\u003eThe dolomite used for this study was obtained from the Bahir Dar Paint and Gypsum Factory. The factory uses a raw dolomite that originates from metamorphic rock outcrops in Abbay Valley, locally called Abbay Bereha, for its rich geological deposit areas. The collected dolomite rock is then processed into a fine powder form. It is a fine powder that acts as a versatile raw material and finds wide application in several industrial sectors, including ceramics, gypsum, and paints. The quality and availability of the rock, make it a resource for both industrial applications and research.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Preparation of Dolomite Solution\u003c/h2\u003e\u003cp\u003eFor struvite precipitation, dolomite rock served as a supply of magnesium(Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Due to its availability and easy to handle in laboratory settings 2M hydrochloric acid (HCl) was selected to dissolve the crushed and dried dolomite in a 25% solid-to-liquid ratio after it had been sieved through a 425\u0026micro;m sieve. As it is studied by(Yildirim \u0026amp; Akarsu, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) a stirring speed of 200 rpm ensures proper mixing and reduces the formation of a stagnant boundary layer around dolomite particles.\u003c/p\u003e\u003cp\u003eFor ten minutes, the dissolution process was conducted with continuous stirring at a speed of 200 rpm to guarantee that the dolomite was completely dissolved(Yildirim, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The solution was then placed in a thermostatically controlled water bath (KOTTER MANN) for 30 minutes at 80 degrees Celsius because Dolomite (CaMg (CO₃)₂) dissolves more efficiently at higher temperatures because temperature increases the solubility of minerals and enhances the diffusion of reactants and products. At 80\u0026deg;C, the dissolution of dolomite is significantly accelerated compared to lower temperatures, facilitating the release of Ca\u0026sup2;⁺ and Mg\u0026sup2;⁺ ions into solution. After cooling, any remaining particles were filtered out of the resultant solution using a 0.45\u0026micro;m pore size WHAT-MAN filter paper, and stored for subsequent experiments.\u003c/p\u003e\u003cp\u003eAs illustrated by(Yildirim, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), the stoichiometric reaction of dolomite dissolution in hydrochloric acid is represented as follows:\u003c/p\u003e\u003cp\u003eCaMg (CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e + 2H\u003csup\u003e+\u003c/sup\u003e \u0026rarr; Ca\u003csup\u003e2+\u003c/sup\u003e + MgCO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;CO\u003csub\u003e2\u003c/sub\u003e\u0026uarr;\u003c/p\u003e\u003cp\u003eMgCO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2H\u003csup\u003e+\u003c/sup\u003e \u0026rarr; Mg\u003csup\u003e2+\u003c/sup\u003e + H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;CO\u003csub\u003e2\u003c/sub\u003e\u0026uarr;\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Collection and Analysis of Wastewater Sample\u003c/h2\u003e\u003cp\u003eDomestic wastewater was collected in the septic tank from the Arba minch university teachers\u0026rsquo; residential area of \u0026ldquo;Limate Condominium\u0026rdquo;. After collection, the sample was kept at 4\u0026deg;C to avoid biological deterioration before analysis then transferred to the water quality laboratory in the university. A calibrated HQ40D multi-meter was used to measure the pH, electrical conductivity (EC), and total dissolved solids (TDS). The argentometric method (titration) was used to analyze the chloride (Cl⁻).The ascorbic acid method was used to determine the (PO₄\u0026sup3;⁻-P) spectrophotometrically at a wave length of 880nm. And the Nesslerization (Kejeldah) method was used to measure ammonium nitrogen (NH₄⁺-N). Additionally, the ions of calcium (Ca\u0026sup2;⁺) and magnesium (Mg\u0026sup2;⁺) were analyzed using atomic absorption spectrophotometry (AAS)(Basson \u0026amp; Van Staden, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1980\u003c/span\u003e), while potassium (K⁺) and sodium (Na⁺) were analyzed by using flame photometer .\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Precipitation of struvite\u003c/h2\u003e\u003cp\u003eThe dolomite solution prepared earlier was mixed with the wastewater in varying ratios to investigate its efficiency in nutrient recovery through struvite precipitation. The pH of the mixtures was adjusted to 8.0(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Le Corre et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Zhou et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) using 1M sodium hydroxide (NaOH) to create optimal conditions for struvite formation. This pH level is crucial because it promotes the precipitation of struvite by ensuring the proper chemical environment for the magnesium, ammonium, and phosphate ions to combine and form struvite crystals. The mixture was stirred continuously by using orbital shaker at a stirring speed of 76rpm(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Ohlinger, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) for 25 minutes(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) to allow for sufficient interaction between the dolomite solution and the wastewater.\u003c/p\u003e\u003cp\u003eResearchers(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Le Corre et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) have noted that under alkaline conditions, the combination of magnesium (Mg\u0026sup2;⁺), ammonium (NH₄⁺), and phosphate (PO₄\u0026sup3;⁻) ions leads to the formation of solid struvite, which precipitates out of the solution. This reaction is represented by the following chemical equation:\u003c/p\u003e\u003cp\u003eMg\u003csup\u003e2+\u003c/sup\u003e + NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e​+ PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e + 6H\u003csub\u003e2\u003c/sub\u003e​O\u0026rarr;MgNH\u003csub\u003e4\u003c/sub\u003e​PO\u003csub\u003e4\u003c/sub\u003e​\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003e​O\u0026darr;\u003c/p\u003e\u003cp\u003eIn order to separate the solid precipitates, the mixtures were filtered through a 0.45\u0026micro;m pore size WHAT-MAN filter paper after the reaction had been allowed to settle for six hours(Etter et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Nutrient recovery percentages were computed by analyzing the filtrate for residual amounts of (NH₄⁺-N). and (PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -p). The production of the solid precipitate (struvite) was measured by weighing it after it had been dried in the sunlight(Etter et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.6 Characterization of the struvite\u003c/h2\u003e\u003cp\u003eFollowing air drying and sieving, one gram of the struvite sample was precisely weighed and put into a 200 mL conical flask. The flask was then gradually filled with 20 mL of aqua regia. Nitric acid (HNO₃) and concentrated hydrochloric acid (HCl) in a normal 3:1 ratio make up the highly caustic mixture known as aqua regia.\u003c/p\u003e\u003cp\u003eDue to its potent oxidizing qualities, this acidic combination is frequently utilized for the digestion of mineral samples. Following that, the conical flask holding the sample and aqua regia was heated to 150\u0026deg;C and kept there for an hour. To guarantee that the struvite material was completely broken down and that the constituent elements could be released into the solution, this digesting stage was carried out.\u003c/p\u003e\u003cp\u003eFollowing digestion, the sample was given a little time to cool before 100 milliliters of distilled water were added to the flask. Reducing the acidity and preparing the solution for filtering and further analysis required this dilution step. A 0.45 \u0026micro;m-pore-size Whatman filter paper (model: WHA7404004) was then used to filter the resultant combination. Any solid particles that remained were eliminated by this filtration procedure, guaranteeing a clear solution for analysis.\u003c/p\u003e\u003cp\u003eFinally, an Atomic Absorption Spectrophotometer (AAS) was used to evaluate the filtered extract. Concentrations of the principal cations calcium (Ca\u0026sup2;⁺), magnesium (Mg\u0026sup2;⁺), sodium (Na⁺), and potassium (K⁺) as well as specific heavy metals, such as arsenic (As), nickel (Ni), chromium (Cr), zinc (Zn), and copper (Cu), were the main focus of the analysis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e2.7 Phosphate phosphorus (PO₄\u0026sup3;⁻-P) determination\u003c/h2\u003e\u003cp\u003eAfter being sieved and allowed to air dry, one gram of the struvite sample was weighed and put into a 50 mL volumetric flask. The struvite-containing flask was filled with 25 milliliters (25 mL) of phosphate extraction reagent (Olsen). A Stuart SSL1 orbital shaker (model: 51091-00) was then used to shake the mixture vigorously for five minutes in order to guarantee that all of the available phosphate was properly extracted.\u003c/p\u003e\u003cp\u003eA 0.45 \u0026micro;m pore-size Whatman filter paper (model: WHA7404004) was used to filter the suspension. For the purpose of phosphate analysis, the clear extract was gathered. A working reagent solution, usually the ascorbic acid reagent, which comprises ammonium molybdate, antimony potassium tartrate, and ascorbic acid in an acidic medium, was used to pipette two milliliters (2 mL) of the extract and dilute it to 25 mL. In order to properly produce the blue color complex (molybdenum blue), the mixture was vigorously stirred and left to stand for 20 minutes. The UV-VIS spectrophotometer (model no: S-925 India) was used to measure the absorbance of the generated blue hue at 880 nm.\u003c/p\u003e\u003cp\u003eTo zero the device, a reagent blank (made with the extraction reagent without struvite) was utilized. The absorbance of the struvite sample was compared to a standard calibration curve made from known phosphate standard solutions (using KH₂PO₄) in order to ascertain the phosphate concentration in the sample. The sample concentration was extrapolated from the calibration curve and displayed against the phosphate content on an absorbance graph.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e2.8 Total Kjeldahl Nitrogen (TKN) Using the Ascorbic Acid Method\u003c/h2\u003e\u003cp\u003eAfter being carefully weighed, 1g of the air-dried and sieved struvite sample was put into Kjeldahl digestion tubes. For reference, a blank sample with just 10 milliliters of distilled water was also made. 25 milliliters of the digesting reagent a combination of potassium sulfate, concentrated sulfuric acid, and a copper and selenium catalyst were added to each tube.\u003c/p\u003e\u003cp\u003eAfter that, the tubes were heated gradually at first, then more quickly, until the liquid turned transparent and the volume was greatly decreased. The digestion process was carried out until a pale green, light-colored solution was produced, signifying that the organic nitrogen had been fully broken down into ammonium ions (NH₄⁺).\u003c/p\u003e\u003cp\u003eTo neutralize the acid and turn ammonium ions into ammonia gas, 25 milliliters of an alkaline solution a combination of sodium hydroxide and sodium thiosulfate was carefully added to each digestive tube after it had cooled. The tubes were then attached to a distillation equipment, and 150 milliliters of distilled water was added to dilute the mixture. At the same time, a 100 ml Erlenmeyer flask was filled with a mixed indicator (such as methyl red and bromocresol green) and 25 ml of a 4% boric acid solution. The reception flask was set up to catch the ammonia that had been distilled.\u003c/p\u003e\u003cp\u003eUntil the distillate volume in the receiving flask reached roughly 50\u0026ndash;75 ml, the distillation process was continued. This phase involved the sample's ammonia gas being trapped in the boric acid solution to produce ammonium borate, which turned the solution a light green.\u003c/p\u003e\u003cp\u003eFollowing that, the distillate was titrated with standardized 0.02 N sulfuric acid until the green tint turned pink, signifying neutralization. By comparing the absorbance values with a calibration curve made from standard nitrogen solutions and calculating the volume of acid used during titration, the total Kjeldahl nitrogen concentration in the struvite sample was determined\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Dolomite Characterization\u003c/h2\u003e\u003cp\u003eDolomite [CaMg(CO₃)₂], a naturally occurring sedimentary carbonate mineral, is widely recognized for its richness in calcium and magnesium ions. The mineral's stoichiometric composition ideally consists of equal molar amounts of calcium and magnesium; however, natural variations often result in deviations due to geological formation conditions and associated impurities(Manche \u0026amp; Kaczmarek, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eSimilarly (Sdiri, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)performed chemical and mineralogical analysis of dolomite samples and noted that the Mg:Ca ratio can vary significantly depending on mineral purity and associated gangue materials such as silica, alumina, and iron oxides. Their work confirmed that high-purity dolomite samples are capable of releasing sufficient quantities of both Ca\u0026sup2;⁺ and Mg\u0026sup2;⁺ for environmental and industrial applications.\u003c/p\u003e\u003cp\u003eThe characterization of dolomite revealed its high magnesium content (453.6\u0026thinsp;\u0026plusmn;\u0026thinsp;28 mg/L) and significant calcium concentration (3128\u0026thinsp;\u0026plusmn;\u0026thinsp;62 mg/L) as shown in (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These values indicate its suitability as a magnesium source for struvite precipitation. Magnesium ions play a critical role in the crystallization of struvite(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Etter et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), while the presence of calcium could affect struvite formation by promoting competing reactions(Bhuiyan et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The low concentrations of sodium (3.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38 mg/L) and potassium (3.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 mg/L) in dolomite further support its potential as an eco-friendly and low-cost resource for nutrient recovery. These findings align with previous studies that emphasize the importance of magnesium sources in struvite precipitation (Uysal et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\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\u003ethe measured ion concentrations in the Dolomite sample\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIons\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eConcentration in (mg/l)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003emagnesium (Mg\u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e453.6\u0026thinsp;\u0026plusmn;\u0026thinsp;28\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ecalcium (Ca\u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e3128\u0026thinsp;\u0026plusmn;\u0026thinsp;62\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003esodium (Na\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e3.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003epotassium (K\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e3.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\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 Wastewater Sample Characterization\u003c/h2\u003e\u003cp\u003eThe physicochemical characteristics of the wastewater sample were examined as shown in (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Because the wastewater has significant amounts of important nutrients including (PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -P) and (NH₄⁺-N), it was shown to be appropriate for nutrient recovery.\u003c/p\u003e\u003cp\u003eThe measured pH of the wastewater was 7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1, which is somewhat alkaline and, when properly corrected to the ideal pH range of 8\u0026ndash;9, conducive to struvite precipitation(Le Corre et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Unyimadu et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhou et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). According to the studies, pH has a significant impact on the solubility and crystallization of the three primary components of struvite Mg\u0026sup2;⁺, (NH₄⁺-N), and (PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -P) and is a key element in the effectiveness of nutrient recovery.\u003c/p\u003e\u003cp\u003eThe conductivity range of 625.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 \u0026micro;S/cm and the total dissolved solids range of 292.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 mg/L suggest a moderate ionic strength, which could have an impact on the precipitation process. Although they are present (24.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 mg/L), chloride ions are less likely to prevent struvite production in controlled settings(Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe amounts of magnesium (21.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 mg/L) and calcium (32.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 mg/L) are particularly significant. Dolomite dissolving can be used to supply magnesium, which is essential for struvite precipitation. The purity of struvite may be lowered, though, if excessive calcium competes with magnesium for precipitation, producing precipitates of calcium based minerals such calcium phosphates(Bhuiyan et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAlthough the potassium and sodium concentrations are very low 11.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 mg/L and 66.2/L, respectively, they should be taken into account since too much sodium can affect soil permeability if the recovered struvite is utilized as fertilizer(Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eSignificant levels of (NH₄⁺-N) (19.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 mg/L) and (PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -P) (1.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 mg/L) indicate the potential the wastewater for (NH₄⁺-N) and (PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -P) recovery. In aquatic systems, phosphate concentration above 1 mg/L is regarded as critical for nutrient pollution and eutrophication hazards(Smith et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). In addition to meeting the demand for agricultural fertilizer, recovering these minerals through precipitation offers an environmentally friendly approach(Scholz et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\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\u003ethe physicochemical analysis of the wastewater sample\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eparameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eunit\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003econcentration\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003epH.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eElectrical conductivity\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:s/cm\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e625.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTotal dissolved solids\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e292.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eChloride(Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e24.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCalcium(Ca\u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e32.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMagnesium(Mg\u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e21.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSodium (Na\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e66.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePotassium ( K\u003csup\u003e+\u003c/sup\u003e )\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e11.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePhosphate(PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -P)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e1.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmmonium nitrogen (NH₄⁺-N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e19.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\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=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Phosphate Phosphorus Recovery\u003c/h2\u003e\u003cp\u003ePhosphorus is very critical element especially for agriculture and different industries(Song et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). But when it is released to natural water bodies it causes eutrophication (Lu et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). On the other hand, Phosphorus is very scarce resource all over the world. Due to this reason P recovery and reuse is critical for sustainable utilization ( Saleem et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; J. Driver, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1999\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe best phosphorus recovery occurs at pH 8, which is in line with several studies that highlight how important pH is for phosphate precipitation and struvite (MgNH₄PO₄\u0026middot;6H₂O) crystallization (Le Corre et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Achieving the proper molar ratios of magnesium, ammonium, and phosphate as well as preserving a favorable pH are crucial for the formation of struvite. Using magnesium chloride (MgCl₂) as the magnesium source, (Sengupta et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) showed that struvite precipitation could effectively recover 80\u0026ndash;99% of phosphorus from wastewater, indicating the potential of struvite as a slow-release fertilizer. Similarly, by modifying the pH and increasing the dosage of magnesium oxide (MgO), which improves the crystallization effectiveness of MAP (magnesium ammonium phosphate),(Mart\u0026iacute; et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2010\u003c/span\u003e)claimed that up to 97% phosphorus removal may be obtained.\u003c/p\u003e\u003cp\u003eAccording to (Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), struvite precipitation employing magnesium sulfate (MgSO₄) as the Mg source can achieve phosphorus recovery rates of above 95%. Furthermore, (Wang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) discovered that magnesium hydroxide (Mg (OH) ₂) may reach removal efficiencies of over 90% and be utilized successfully for struvite crystallization, especially in systems with high ammonium concentrations. Furthermore, with encouraging recovery rates exceeding 85%, (Yetilmezsoy et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) looked into the use of bittern, a magnesium-rich byproduct of salt manufacturing, as an affordable and sustainable alternative Mg source for struvite precipitation.\u003c/p\u003e\u003cp\u003eWu et al. (2001) also highlighted that the selection of magnesium source influences the crystal size and purity of struvite, which are important factors for its repurposing as fertilizer, in addition to recovery efficiency.\u003c/p\u003e\u003cp\u003eIn the treatment of municipal wastewater, (Achilleos et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) also reported successful struvite production using MgCl₂, with phosphate removal efficiencies above 90% under regulated pH and molar ratios. All of these results highlight the need of keeping pH at an ideal level and choosing magnesium sources (MgCl₂, MgO, Mg (OH) ₂, MgSO₄, and bittern) carefully in order to maximize phosphorus recovery from wastewater by struvite crystallization.\u003c/p\u003e\u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the experimental results demonstrate a progressive increase in phosphate removal efficiency with an increasing waste-to-dolomite ratio. Initially, at a dolomite volume of 10 mL was added to 50ml of wastewater, the phosphate recovery was 60.79%, indicating a moderate reduction in phosphate concentration. As the dolomite dosage increased, the phosphate recovery continued to improve, reaching 88.71% at 40 mL. The complete phosphate removal (100% recovery) was achieved at dolomite volumes of 70 mL and higher, as evidenced by the absence of detectable phosphate in the filtrate. This suggests that at a waste-to-dolomite ratio of 50:70, all available phosphate ions were effectively precipitated, indicating optimal conditions for phosphate recovery. Further increasing the dolomite volume beyond 70 mL did not yield additional benefits, as complete phosphate removal had already been attained. These findings highlight the effectiveness of dolomite as a natural magnesium source for struvite precipitation, particularly at higher dosages, making it a viable option for nutrient recovery from wastewater. Therefore according to the above mentioned literatures the recovery results of this research (100%) is acceptable.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Ammonium Nitrogen Recovery\u003c/h2\u003e\u003cp\u003eThe recovery of (NH₄⁺-N) from domestic wastewater using dolomite was evaluated by varying the ratio of wastewater to dolomite (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).The results indicate that the ammonium nitrogen recovery increases progressively with the volume of dolomite solution added. As the dolomite volume increased, the percentage recovery improved significantly, reaching 93.47% at a wastewater-to-dolomite ratio of 50:100ml. Interestingly, the recovery rate showed a steep increase beyond the 50:40 mL ratio, with significant improvement observed at 50:70 mL and higher. After this ratio the precipitated product may not be struvite because all of the (PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -p) was recovered at a wastewater to dolomite solution of 50:70ml.\u003c/p\u003e\u003cp\u003eThe efficiency of struvite crystallization in recovering ammonium nitrogen (NH₄⁺-N) from wastewater utilizing a variety of magnesium sources has been shown in numerous research. When magnesium chloride (MgCl₂) was utilized as the magnesium source,(Darwish et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) found that struvite precipitation could recover over 95% of NH₄⁺-N. According to (Uysal et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), soluble magnesium salts promote the synthesis of struvite, as evidenced by their high removal efficiencies of NH₄⁺-N using MgCl₂\u0026middot;6H₂O.\u003c/p\u003e\u003cp\u003eThe inhibitory effect of calcium ions on struvite crystallization was highlighted by (Huang et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), who employed magnesium oxide (MgO) as the Mg source. They found that increasing the calcium-to-magnesium (Ca:Mg) molar ratio from 0 to 0.75 resulted in a significant reduction in NH₄⁺-N removal efficiency from 87.7\u0026ndash;58%.\u003c/p\u003e\u003cp\u003eRahman et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) also found that the type of magnesium source employed affects the effectiveness of struvite precipitation. After comparing MgCl₂, MgSO₄, and MgO, they found that MgO was less effective because of its slower rate of dissolution, but MgCl₂ and MgSO₄ offered faster reaction kinetics because of their high solubility. The potential of struvite crystallization as a sustainable nutrient recovery approach was further supported by(Yetilmezsoy \u0026amp; Sapci-Zengin, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) demonstration that employing MgCl₂ in a molar ratio of 1:1:1 (Mg\u0026sup2;⁺:NH₄⁺:PO₄\u0026sup3;⁻) produced over 90% removal of NH₄⁺-N and phosphorus simultaneously.\u003c/p\u003e\u003cp\u003eIn the case of this research the calcium concentration is much higher than that of magnesium concentration both in the wastewater sample and in the dolomite solution: this makes the percentage of NH₄⁺-N recovery 88.75%. Therefore according to (Huang et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2011\u003c/span\u003e)the recovery results of this research was reasonable.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Quantification of Struvite Production\u003c/h2\u003e\u003cp\u003eThe mass of struvite precipitated M(s) was determined by subtracting the mass of the filter paper M(f) from the combined mass of the filter paper and struvite M(f\u0026thinsp;+\u0026thinsp;s). The results demonstrate a clear relationship between the dolomite volume and the amount of struvite formed. As it is presented in (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) when the dolomite volume increased, the mass of struvite precipitated also increased. At a wastewater to dolomite ratio of 50ml: 70ml the mass of struvite produced reached 0.123g. Beyond this dolomite volume the mass of struvite formed begins to plateau. This suggests that the system may reach a saturation point where all available phosphate ions in the wastewater are precipitated as struvite, and additional magnesium does not significantly enhance struvite production.\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\u003eQuantification of struvite production\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eV(ww)(ml)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eV(Dolomite)(ml)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eM(F)(gram)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eM(F\u0026thinsp;+\u0026thinsp;S) (gram)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eM(s) (gram)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.798\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.853\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.055\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.803\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.881\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.078\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.786\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.885\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.099\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.822\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.931\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.109\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.882\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.112\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.804\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.919\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.115\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.755\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.878\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.123\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.793\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.914\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.121\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.782\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.904\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.122\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.798\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.919\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.121\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=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.6 Filtrate Sample Characterization\u003c/h2\u003e\u003cp\u003ePost-precipitation filtrate analysis revealed significant reductions in phosphate phosphorus and ammonia nitrogen concentrations, confirming successful nutrient removal (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePhysio-chemical parameters of filtrate sample\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eparameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eunit\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003econcentration\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003epH.\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\u003e9.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eElectrical conductivity\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:s/cm\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2190.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTotal dissolved solids\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e31843.3\u0026thinsp;\u0026plusmn;\u0026thinsp;60.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003echloride\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e32147\u0026thinsp;\u0026plusmn;\u0026thinsp;6.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCalcium(Ca\u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e748\u0026thinsp;\u0026plusmn;\u0026thinsp;6.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMagnesium(Mg\u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSodium (Na\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e195.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePotassium ( K\u003csup\u003e+\u003c/sup\u003e )\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePhosphate(PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -p)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmmonia nitrogen\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emg/l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\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\u003eMagnesium and calcium concentrations also decreased, indicating their incorporation into the struvite structure. The low concentrations of sodium and potassium in the filtrate suggest that these ions did not interfere significantly with the precipitation process. This outcome highlights the recovery potential of struvite precipitation when dolomite is used as the magnesium source.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e3.7 Chemical composition of struvite\u003c/h2\u003e\u003cp\u003eThe chemical composition of the produced struvite was analyzed, and the results are shown in the Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003echemical composition of the produced struvite\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eparameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003econcentration mg/l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eConcentration (%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMagnesium(Mg \u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e234.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.58\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCalcium(Ca \u003csup\u003e2+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e29685.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e11.77\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSodium(Na\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.061\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.05\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePotassium( K\u003csup\u003e+\u003c/sup\u003e )\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.073\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.06\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePhosphate(PO\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e3\u0026minus;\u003c/sup\u003e -p)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e245.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.66\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmmonium nitrogen\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e121.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.01\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\u003eThe findings highlight the elemental concentrations of key components, including magnesium (Mg\u0026sup2;⁺), calcium (Ca\u0026sup2;⁺), phosphate (PO₄\u0026sup3;⁻-P), ammonium nitrogen (NH₄⁺-N), sodium (Na⁺), and potassium (K⁺). These values provide insight into the composition and potential utility of the struvite as a slow-release fertilizer.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eMagnesium (Mg\u0026sup2;⁺)\u003c/b\u003e\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThe concentration of magnesium in the produced struvite was 234.9 mg/L, contributing to 2.58% of the total composition. Magnesium is an essential component of struvite and plays a crucial role in its crystallization process. This concentration indicates that magnesium from dolomite was effectively utilized in the precipitation reaction. Studies have shown that sufficient magnesium is critical for efficient struvite formation, as it reacts with ammonium and phosphate to form the crystal lattice(Le Corre et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eCalcium (Ca\u0026sup2;⁺)\u003c/b\u003e\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eCalcium was present at a significantly higher concentration of 29685.4 mg/L, constituting 11.77% of the total composition. This high calcium content strongly suggests that calcium-based molecules, including calcium phosphate (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{Ca}_{3}\\)\u003c/span\u003e\u003c/span\u003e(PO₄)₂) and struvite (MgNH₄PO₄\u0026middot;6H₂O), may co-precipitate. The effectiveness and purity of struvite recovery procedures can be greatly impacted by this co-precipitation, particularly in systems that use calcium-rich minerals, such as dolomite, as a magnesium source.\u003c/p\u003e\u003cp\u003eSeveral investigations have demonstrated that by preferentially interacting with phosphate to generate calcium phosphate compounds, excess calcium ions can obstruct struvite crystallization. This can lead to decreased struvite production and purity in addition to competing with struvite formation. (Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) found that high calcium concentrations significantly reduced the recovery efficiency of struvite, especially when dolomite was utilized as a magnesium donor since it releases both Mg\u0026sup2;⁺ and Ca\u0026sup2;⁺ ions when acid is applied.\u003c/p\u003e\u003cp\u003eSimilar to this, (Le Corre et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) highlighted that calcium and magnesium compete with one another for phosphate binding, particularly in neutral to alkaline pH ranges, resulting in the development of either crystalline or amorphous calcium phosphates. Because these substances precipitate more quickly than struvite, there is less phosphate available for struvite crystallization.\u003c/p\u003e\u003cp\u003e(Wu et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) also found that the production of hydroxyapatite and other calcium phosphates inhibited the precipitation of struvite when the molar ratio of Ca\u003csup\u003e2+\u003c/sup\u003e to Mg\u003csup\u003e2+\u003c/sup\u003e was high. Their results showed that competitive precipitation caused struvite purity and recovery to drastically decline in situations where the Ca:Mg molar ratio was greater than 1.\u003c/p\u003e\u003cp\u003eOverall, it is abundantly evident from the literature that high calcium levels can prevent struvite precipitation through co-precipitation mechanisms, especially when they are delivered through calcium-rich precursors like dolomite. To improve the production and selectivity of struvite, especially in nutrient recovery applications from wastewater, calcium interference must be taken into account during process optimization.\u003c/p\u003e\u003cp\u003e\u003cb\u003ePhosphate (PO₄\u0026sup3;⁻-P)\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe phosphate content of the struvite was 245.7 mg/L, representing 2.66% of the total composition. Phosphate is a critical nutrient in struvite and is responsible for its utility as a phosphorus-rich fertilizer. The recovery of phosphate in this study demonstrates the effectiveness of dolomite as a reagent for struvite precipitation. These findings align with previous research, which underscores the role of phosphate in the crystallization process and its recovery potential from wastewater(Song et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eTotal Kjeldahl Nitrogen (TKN)\u003c/b\u003e\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThe Total Kjeldahl Nitrogen (TKN) concentration in the struvite was 121.3 mg/L, making up 1.01% of the total composition. Ammonium ions are essential for the formation of struvite crystals, as they combine with magnesium and phosphate in stoichiometric proportions. The recovery of ammonium nitrogen indicates the dual nutrient recovery capability of this process, making struvite an attractive option for sustainable wastewater treatment.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eSodium (Na⁺) and Potassium (K⁺)\u003c/b\u003e\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eSodium and potassium were present in trace amounts, with concentrations of 0.061 mg/L (0.05%) and 0.073 mg/L (0.06%), respectively. Their low concentrations suggest minimal interference with the struvite precipitation process. These elements may originate from the dolomite or wastewater but are not significant contributors to the struvite composition.\u003c/p\u003e\u003cp\u003e\u003cb\u003eHeavy metals (As, Ni, Cr, Zn, and Cu)\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe concentration of heavy metals in the produced struvite is the first and most crucial factor in determining whether or not it may be utilized as fertilizer(Uysal et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). According to this study, the concentration of heavy metals (As, Ni, Cr, Zn, and Cu) was below the AAS instrument's detection limit. It is therefore possible to use the struvite generated in this work as fertilizer.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e3.8 The purity of the produced struvite\u003c/h2\u003e\u003cp\u003eAccording to several researchers (Korchef et al., 2011; Liu et al., 2013; Rahman et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Yesigat et al., 2022), the ideal chemical composition of pure struvite is magnesium ammonium phosphate hexahydrate (MgNH₄PO₄\u0026middot;6H₂O), which appears as a white crystalline solid. This ideal form assumes a 1:1:1 molar ratio of magnesium, phosphorus, and nitrogen. However, the struvite recovered in this study deviates from this pure form both in appearance and chemical composition. The product obtained was brownish in color and contained 1.01% nitrogen, 2.66% phosphorus, 0.06% potassium, 2.58% magnesium, and a significantly high 11.77% calcium content.\u003c/p\u003e\u003cp\u003eThe presence of elevated calcium levels indicates substantial co-precipitation of metallic ions particularly calcium during the recovery process, which adversely affects the purity of the struvite. As a result, the final product cannot be classified as pure struvite. Nevertheless, it is worth noting that the recovered material is free from detectable concentrations of heavy metals, which are known to pose risks to plant and human health. This absence of toxic elements makes the product safe for further testing in agricultural applications.\u003c/p\u003e\u003cp\u003eDespite its impurity, the product retains essential nutrients such as phosphorus, magnesium, and ammonium nitrogen which are key elements for plant growth.\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThis study demonstrates the effective recovery of phosphorus and nitrogen from domestic wastewater using dolomite rock as a low-cost and environmentally sustainable source of magnesium for struvite precipitation. Optimal nutrient recovery was achieved at a wastewater-to-dolomite ratio of 50:70 mL and a pH of 8.0, where phosphorus recovery reached 100% and nitrogen recovery was 88.75%. The production of struvite increased with the dolomite dosage, confirming its efficiency in precipitating nutrients. Post-recovery filtrate analysis revealed substantial reductions in phosphorus and nitrogen concentrations, highlighting the potential of this approach for wastewater treatment and nutrient recovery.\u003c/p\u003e\u003cp\u003eDespite these promising results, certain limitations were encountered. The mineralogical composition of dolomite was not analyzed using XRD or FTIR due to limited instrument availability and financial constraints. Additionally, minimizing calcium interference from dolomite during struvite precipitation proved challenging. Sodium hydroxide was used for pH adjustment; however, the presence of sodium from NaOH and calcium from dolomite significantly affected the purity of the produced struvite.\u003c/p\u003e\u003cp\u003eIt is important to note, however, that the struvite recovered in this study deviates from the pure form both in appearance and chemical composition. The product was brownish in color and contained 1.01% Total Kjeldahl Nitrogen (TKN), 2.66% phosphorus, 0.06% potassium, 2.58% magnesium, and a notably high 11.77% calcium content. The elevated calcium concentration indicates substantial co-precipitation of metallic ions, particularly calcium, during the recovery process, which negatively impacts the purity of the struvite. Consequently, the final product cannot be classified as pure struvite. Despite this, the findings highlight the potential of recovered struvite, even in its impure form; can serve as a viable and sustainable alternative to chemical fertilizers, because it contains essential nutrients such as phosphorus, magnesium, and ammonium nitrogen which are key elements for plant growth.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthics approval not applicable\u003c/p\u003e\n\u003cp\u003eConsent to participate \u0026nbsp; not applicable\u003c/p\u003e\n\u003cp\u003eConsent for publication\u0026nbsp;not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eThere is no funding\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e: The authors have no relevant financial or non-financial interests to disclose\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials:\u0026nbsp;\u003c/strong\u003eThe\u0026nbsp;datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgment\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors are grateful to Arba Minch University for providing the chance and resources necessary to conduct this study. The Water Quality Professionals from Arba Minch University deserve a great deal of gratitude for their assistance, counsel, and knowledge throughout the experiment.\u0026nbsp;\u003cbr\u003e\u0026nbsp;Most importantly, the authors would like to express their gratitude to Bahir Dar Paint and Gypsum Factory for their kind donation of the dolomite sample, which was essential to the accomplishment of this study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAchilleos P, Roberts KR, Williams ID. Struvite precipitation within wastewater treatment: A problem or a circular economy opportunity? 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In-situ synthesis of lanthanum-coated sludge biochar for advanced phosphorus adsorption. \u003cem\u003eJournal of Environmental Management\u003c/em\u003e, \u003cem\u003e373\u003c/em\u003e, p.123607.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Environment](https://www.springer.com/44274/)","snPcode":"44274","submissionUrl":"https://submission.nature.com/new-submission/44274/3","title":"Discover Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Dolomite rock, Eco-friendly fertilizers, Nutrient Recovery, Struvite Precipitation","lastPublishedDoi":"10.21203/rs.3.rs-7322931/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7322931/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRecovering essential nutrients like phosphorus (P) and nitrogen (N) from domestic wastewater is not only feasible but also required for sustainable nutrient management. This study investigated the potential of dolomite rock, a low-cost and environmentally friendly resource abundant in Ethiopia, to facilitate nutrient recovery through struvite precipitation. Dolomite was dissolved in 2M hydrochloric acid at a solid-to-liquid ratio of 25% to release magnesium ions, which were then mixed with wastewater in varying ratios at a controlled pH of 8.\u003c/p\u003e\u003cp\u003eThe initial wastewater composition contained the following elements: calcium (Ca\u0026sup2;⁺) 32.1 mg/L, magnesium (Mg\u0026sup2;⁺) 21.9 mg/L, sodium (Na⁺) 66.2 mg/L, potassium (K⁺) 11.8 mg/L, phosphate (PO₄\u0026sup3;⁻-P) 1.65 mg/L, and ammonium nitrogen (NH₄-N) 19.4 mg/L. The composition of the filtrate changed dramatically when struvite precipitation was carried out with a wastewater-to-dolomite ratio of 50:70 mL. Following precipitation, the levels of calcium (Ca\u0026sup2;⁺) rising to 748 mg/L, magnesium (Mg\u0026sup2;⁺) falling to 0.61 mg/L, sodium (Na⁺) rising to 195.8 mg/L, and potassium (K⁺) falling to 1.9 mg/L. In contrast to ammonium nitrogen (NH₄-N), which was successfully reduced to 2.18 mg/L with a recovery rate of 88.75%, phosphate (PO₄\u0026sup3;⁻-P) was surprisingly totally eliminated (100% recovery).\u003c/p\u003e\u003cp\u003eThe result shows that dolomite-induced struvite precipitation is an effective method for recovering nutrients from wastewater offering an alternative to conventional synthetic fertilizers. This approach not only mitigates environmental pollution caused by nutrient-rich wastewater but also provides a pathway for producing eco-friendly fertilizers. By utilizing locally available resources, this research contributes to cost-effective nutrient management and promotes sustainable agricultural practices.\u003c/p\u003e","manuscriptTitle":"Recovery of phosphorus and nitrogen from domestic wastewater by using dolomite rock through struvite precipitation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-03 18:53:06","doi":"10.21203/rs.3.rs-7322931/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-29T08:00:05+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-18T15:02:11+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-16T04:19:16+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-12T01:48:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"224428647032712046534912623287432806772","date":"2025-09-10T19:06:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"285928845465886649568373141675306905986","date":"2025-09-05T22:47:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"264150949636519316587247093762693781516","date":"2025-09-03T04:26:30+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-01T10:02:02+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-29T04:46:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"123352864106964973928320299204326707062","date":"2025-08-27T02:35:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"154840045178738363893756348977247736397","date":"2025-08-26T19:54:53+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-26T19:09:14+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-08-18T12:34:54+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-12T08:33:19+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-12T08:31:24+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Environment","date":"2025-08-08T03:01:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Environment](https://www.springer.com/44274/)","snPcode":"44274","submissionUrl":"https://submission.nature.com/new-submission/44274/3","title":"Discover Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2284ef02-01f2-407f-96aa-07ef1fca4e52","owner":[],"postedDate":"September 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-01-16T04:08:48+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-03 18:53:06","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7322931","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7322931","identity":"rs-7322931","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}