Mitigation of Cyanide From Coke Plant Wastewater Using Chemical Oxidation Process

Mitigation of Cyanide From Coke Plant Wastewater Using Chemical Oxidation Process | 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 Mitigation of Cyanide From Coke Plant Wastewater Using Chemical Oxidation Process Amit Mondal, Priyanka Saha, Supriya Sarkar, Udayabhanu G Nair This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-727204/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Biological treatment with a stable activated sludge process, followed by chemical treatment is one of the potential and accepted cyanide treatment process for coke plant waste water treatment. Biologically treated coke plant wastewater contains free cyanide above permissible limit. Presently chemical treatment with NaOCl is being used to attenuate free cyanide below permissible limit in biologically treated water. This process increases the TDS and colour content in discharge water. Ca(OCl) 2 can be used as an alternative to NaOCl for cyanide remediation in biologically treated coke plant waste water without increasing TDS. In the present work, cyanide removal efficiency of NaOCl and Ca(OCl) 2 for real coke plant waste water after biological treatment has been studied. Optimisation of chemical dosage, treatment time and pH has been done for Ca(OCl) 2 and NaOCl treatment. It was found that up to 90% of free cyanide removal could be achieved through Ca(OCl) 2 treatment without increasing the TDS value. In addition, more than 50% colour of the waste water has been removed. pH elevation step required in NaOCl treatment can be eliminated in Ca(OCl) 2 treatment, thereby reducing caustic consumption. In conclusion, use of Ca(OCl) 2 is economically more viable than that of NaOCl in cyanide treatment. Environmental Chemistry Toxicology Biological treatment Chemical oxidation Coking wastewater Free cyanide Cyanide treatment Hypochlorite. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Integrated Steel Plant is a water intensive industry, where almost every process consumes a huge amount of water. Waste water from steel industry operation transport various organic, inorganic pollutants and toxic substances that have adverse effects on the environment (Park et al. 2008 ). Due to the toxic effects, discharge of this polluted water without detoxification cause severe damage to the environment. Coke plant is one of the major contributors for generation of waste water in an integrated steel plant. Nearly 4 m 3 of water is used to produce 1 ton of coke and the process generates a large volume of heavily polluted wastewater (Pal and kumar 2014). Coke plant waste water is generated during quenching, cleaning and recovery of valuable by-product of coke oven gas produced during carbonisation of coal in the coke oven batteries. The waste water generated during these processes contains various organic and inorganic toxic compounds like ammonia, thiocyanate, cyanides, sulphides, pyridine, phenols and other poly aromatic hydrocarbons (PAH) (Mondal et al. 2021 ; Dhoble et al. 2019). Cyanide is the most toxic chemical present in the coke plant discharge water among those pollutants (Ozyonar and Karagozogly 2015 ; Maranon et al. 2008 ). The wastewater from the coke plant and blast furnace blow down have been identified as the major contributors of aqueous cyanide emissions in the iron and steel industries (Saha et al. 2018 ; Singha et al. 2018 ). Thus, steel industry is coming under increasing scrutiny of environmental regulators to meet more stringent water discharge limits. Metal-complexed cyanides are classified according to the strength of the metal cyanide bond. Cyanide in waste water are classified into three types; a. free cyanide (CN F ), which include CN- and HCN, b. weak-acid dissociable (CN WAD ) indicate weak cyanide complexes with metals such as copper, nickel, cadmium and zinc, c. strong-acid dissociable (CN SAD ) refer to strong cyanide-complexes with metals such as gold, cobalt, iron and silver. Toxicity of these cyanides are in the order of CN F > CN WAD > CN SAD (Johnson 2015 ). All cyanides are classified as hazardous to the characteristics of acute and chronic toxicity (Deveci et al. 2006 ). But the legislation of the Government for the cyanide discharge deals with only CN F as it is the most toxic to living elements and sometimes is deadly in nature. The discharge limit of CN F to the environment is up to 0.2 ppm (Mondal et al. 2019 ) as guided by Central Pollution Control Board. Because of the environmental concerns and potential hazards due to the toxic effects, control and remediation of cyanide containing industrial waste water is essential. There are several physical, chemical, and biological treatment methodologies available for cyanide removal in coke plant wastewater. But, all the processes have some limitations for implementation in the plant scale. Table 1 presents some of the commonly adopted cyanide treatment technologies and their limitations. It also shows the fate of cyanide after the treatment and the reagents used in each process. Table 1 Cyanide treatment technologies and their limitations. Treatment method Fate of cyanide Reagent/ Chemical Limitations Ozonation. Chegini et al. 2020 , Pueyo et al. 2016, Chang et al. 2008 . Oxidation to CO 3 2− and N 2 with O 3 O 3 Costly process. Adds ammonia to discharge water Photocatalytic oxidation. Biswas et al. 2020 , Chegini et al. 2020 , Saravi et al. 2015 , Dash et al. 2009 . Oxidation to CNO − Nano particle, UV source, TiO2 Energy intensive and costly process. Biological oxidation/biodegradation. Das et al. 2020 , Dwivedi et al. 2011 , Kumar et al.2011, Dash et al. 2009 , Woo et al. 2009 , Kim et al. 2007 . Oxidation to CO 3 2− and NH 4 + and then NO 3 − using microorganisms. Na 2 CO 3 , H 3 PO 4 Treatment of high concentrations create problem. Cannot reach the discharge standards of cyanide. Alkaline chlorination by Hypochlorite/Perchlorate. Das et al. 2020 , Khodadad et al. 2008 , Dash et al. 2009 , Reed et al. 2013 . Oxidation to CNO − and then N 2 and CO 3 2− . Cl 2 , NaOCl, NaOH Increase in TDS content. Requires high caustic to maintain pH SO 2 /Air (INCO) process. Dash et al. 2009 , Kumar et al.2011. Oxidation to CNO − with SO 2 & air and soluble Cu catalyst. SO 2 , air, Cu catalyst Partial removal of cyanide. Process adds sulphate to the treated water. Hydrogen peroxide. Singh et al. 2018, Pueyo et al. 2016, Dash et al. 2009 Oxidation to CNO − with H 2 O 2 & Cu catalyst: Degussa process H 2 O 2 Reagent is costly, accurate measurement of chemical dose is required. Caro’s acid. Cesar et al. 2013, Pueyo et al. 2016, Dash et al. 2009 , Oxidation to CNO − with H 2 SO 5 H 2 SO 5 Increase in TDS content. Difficult to handle due to decomposition to oxygen and sulfuric acid. Iron cyanide precipitation. Arbabi et al. 2015 , Dash et al. 2009 , Precipitated as Fe(CN) 6 FeSO 4 Works only with low concentration of cyanide. Maintaining pH and disposal of precipitate is difficult. AVR process. Munive et al. 2015 , Yilmaz et al. 2017 , Dash et al. 2009 Acidification to HCN and neutralisation. H 2 SO 4 , NaOH High acid consumption. Complex process. Activated carbon. Adhoum et al. 2002, Dash et al. 2009 Oxidation to CNO − and partially to CO 3 2− and NH4 + Activated carbon, air/O 2 , Cu catalyst Expensive method. Used only for low concentration of CN Catalytic oxidation. Kumar et al. 2011 , Dash et al. 2009 , Chiang et al. 2002 . Larry et al. 1982 . Oxidation to CO 2 , N 2 & NH 4 + with air and catalyst. Catalyst Restriction in treating very low concentration. Costly process. Anodic oxidation. Pillai et al. 2016, Dash et al. 2009 Oxidation to CNO − and then CO 2 and N 2 NaCl Partial removal of cyanide. Reverse osmosis. Pal et al. 2014 , Dash et al. 2009 , Gude 2012 . Uses a partially permeable membrane to separate ions. - Energy intensive and costly process. To overcome these limitations, different combined treatment methodologies are being used for the remediation of cyanide in coke plant waste water. Combined treatment of biological, followed by chemical treatment is one of the potential and accepted cyanide treatment process for coke plant waste water (Pal and Kumar 2014 ). Present process, uses the biological treatment through a stable activated sludge process followed by chemical treatment with sodium hypochlorite. The treatment process is schematically represented in Fig. 1 . After biological treatment, the discharge water contains high amount of CN F which is taken care of by sodium hypochlorite (NaOCl) treatment. In this chemical treatment, oxidation transforms CN F to cyanate (CNO − ), which has an environmental hazard 1,000 times lower than cyanide (Mosher and Figueroa 1996 ). But this popular treatment method has the major disadvantage of increasing TDS content in the discharge water (Ghosh et al. 2020 and Das et al. 2019) and is also expensive due to the extraneous dosing of sodium hydroxide (Tyagi et al. 2018 ). Moreover, biologically treated water gets more intense dark brown color than the untreated water due to the presence of degraded phenolic compounds (Mijangos et al. 2006 ). This acute colour could not be taken care by NaOCl treatment. Calcium hypochlorite [Ca(OCl) 2 ] can be used as an alternative chemical for reduction of cyanide in biologically treated coke plant wastewater (BTCPW), which decrease TDS and colour along with CN F content. Ca(OCl) 2 is more stable and potentially more efficient for cyanide removal as compared to the NaOCl due to having higher available chlorine (Hasab et al. 2013 ). Powdered Ca(OCl) 2 has the highest oxidation power among other chemicals used for chlorination (Parekh and Ban 2018 ). Moreover, removal of cyanide through Ca(OCl) 2 treatment is more effective considering the dosage and cost (Sinbuathong et al. 2000 ). However, very few studies have been reported on the application of this method to biologically treated coke plant effluent. Present research aims to develop a continuous, effective and economical process with the use of Ca(OCl) 2 in cyanide treatment process of BTCPW. Comparative study of cyanide removal efficiency in BTCPW has been carried out with Ca(OCl) 2 and NaOCl. TDS and colour of the treated solution were also compared in both the treatments. In addition to this, optimisation of Ca(OCl) 2 treatment process by changing chemical dosage, treatment time and pH of the treatment solution has been carried out. Lab scale trial of Ca(OCl) 2 treatment in BTCPW was also performed in optimum conditions and the results are presented. Materials & Methods Collection of water samples For the present study, water samples were collected from Biological Oxygen Treatment (BOT) plant of the coke plant in an integrated steel plant situated in the eastern part of India. This plant produces approximately 9 MT of coke per day and about 200 m 3 of waste water is generated daily by the process of coke making. Characterisation of coke plant wastewater The water samples collected from coke plant after biological treatment has the characteristics as shown in Table 2. Table 2: General characteristics of Coke plant waste water after biological treatment Parameter Coke plant waste water after biological treatment pH 7.5-8.5 TDS, ppm 2450-3350 Colour, (PtCo) 2550-2950 BOD, ppm 50-110 COD, ppm 220-550 Thiocyanate, ppm 10-30 Free cyanide, ppm 1.5-4.5 Ammonia, ppm 30-100 TKN, ppm 150-350 Experimental Set up and Procedure The experiment for optimisation study has been carried out in 1L biologically treated water from coke plant in a glass beaker. Water samples were taken in a beaker and the pH was adjusted with sodium hydroxide and dilute hydrochloric acid. For lab scale trial, 5 L of BTCPW was taken and treated with Ca(OCl) 2 at its optimised condition. After maintaining the pH, 4% Ca(OCl) 2 was added drop wise from the burette. The samples were kept in continuous stirring condition up to the end of the treatment. Cyanide content has been tested at every 10-min time interval after filtration through Whatman 1 paper. Each experiment was performed in duplicate and the average of the results have been reported. All parameters including CN F were tested in triplicate throughout the study and average value has been reported. Analysis of pH pH of the water samples was measured using the pH meter (Systronics, India, digital pH meter, model no: 335). Analysis of TDS TDS is a measure of the combined content of all inorganic and organic substances contained in a liquid in molecular, ionized or micro-granular suspended form (Hussain, 2019). During the study, TDS of the water samples has been measured by using TDS meter (Systronics, India, model no: 308). Determination of free cyanide concentration by ion selective method Free cyanide has been determined by filtering water sample through Whatman No. 1 filter paper and taking 10 mL of the filtered water for analysis. It was analysed potentiometrically using ion selective cyanide electrode (Thermo Scientific) according to the procedure given by manufacturer. Many tests can be done at a time through this method, due to the low analysis time (about 5 min). Determination of ammonia concentration using ion selective electrode Ammonia has been measured potentiometrically with ammonia ion selective electrode (Thermo Scientific) according to the procedure given by manufacturer. Determination of thiocyanate concentration spectrophotometrically Thiocyanate concentration in ppm was measured using spectrophotometer (Thermo Scientific, Genesys 10S UV-VIS spectrophotometer). The wavelength used was 460 nm. This was performed after a blood red colour was developed by using ferric nitrate [Fe(NO3) 3 . 9H 2 0 solution according to the standard procedure (APHA 2017). Measurement of colour Coke plant water gets more intense brown colour after biological treatment due to the presence of aromatic coloured compounds such as ortho- and para-benzoquinone, which form through the degradation of phenol (Mijangos et al. 2006). The color of the wastewater was measured by the color measuring instrument (Make: Lovibond) and expressed in PtCo unit. Results And Discussion Ca(OCl) 2 and NaOCl react to form hypochlorite and hydroxide ion when added to water NaOCl + H 2 O → OCl - + OH - + Na + (1) Ca(ClO) 2 + 2 H 2 O → 2 OCl - + 2 OH - + Ca +2 (2) Hypochlorite ion (OCl - ) oxidises CN - in BTCPW to cyanogen chloride (CNCl). More the addition of Ca(OCl) 2 , the greater the cyanide reacts to form CNCl, therefore the CN F content in the liquid waste is reduced. Further CNCl is oxidized into CNO and finally into CO 2 and N 2 (Johnson 2015). The oxidation reaction of cyanide and hypochlorite can be shown as follows CN - + HOCl → CNCl + OH - (3) CNCl + OH → CNO - + Cl + H 2 O (4) CNO - + OCl - + H 2 O → N 2 + Cl - + HCO 3 (5) In the present study, cyanide treatment by 4% NaOCl and 4% Ca(OCl) 2 solution was carried out in one litre BTCPW for 120 minutes. The residual CN F content was checked in every 10 minutes by ion selective electrode. No significant changes were observed in CN F concentration at the beginning of the treatment. But, significant decrease in CN F started after 20 minutes of NaOCl treatment and 30 minutes of Ca(OCl) 2 treatment Fig. 2. Up to 80 % of CN F was removed in 50 minutes of NaOCl treatment. Whereas Ca(OCl) 2 treatment took 60 minutes for the removal of 80% of CN F . This result is in line with that reported by Muntasir et al. 2016. In addition to CN F , significant changes were observed in TDS and colour (Fig. 3) of the treated water. It was found that TDS content was increased in NaOCl treatment and decreased in the case of Ca(OCl) 2 treatment. Similar trend has been observed in case of colour, where more than 55% colour was removed in Ca(OCl) 2 treatment against the increase in colour for NaOCl treatment. This is in accordance with the research work reported by Khandaker et al. 2020 and Massoudinejad et al. (2015). The colour removal and TDS decrease along with the CN F reduction shows scope of enhancement in Ca(OCl) 2 treatment efficiency by optimising treatment parameters like pH, treatment time and dosing rate, to get maximum efficiency compared to NaOCl treatment of BTCPW. Optimisation study Optimum condition of pH For optimisation study, BTCPW containing CN F 4.08 ppm, TDS 2970 ppm and colour 2780 PtCo was considered. Treatment of Ca(OCl) 2 and NaOCl were carried out in 1 L of BOT water at a constant treatment time of 60 minute. The experiment was done for three different dosing rates (20ml, 30ml and 50 ml) with 4% of NaOCl and 4% Ca(OCl) 2 solutions. pH of the solution was varied from 7.5 to 12. Colour and TDS of the solution at different pH were also checked before and after the treatment along with CN F . It has been found that cyanide removal efficiency of Ca(OCl) 2 increases with pH and reaches the maximum at pH 8.5. Further increase in pH has not shown any increase in removal efficiency of CN F with 50ml, 30ml and 20 ml of Ca(OCl) 2 solution as shown in Fig. 4a. However, for NaOCl, maximum CN F removal was achieved at pH 10.5 as shown in Fig. 4b. Maintaining proper pH allows calcium hypochlorite to react perfectly with CN F in wastewater (Cidu et al. 2011 and Muntasir et al. 2016). At optimum pH decrease in the levels of CN F ismaximum. This is in line with the research work reported by Lee and Tiwary (2009). Optimum pH for NaOCl and Ca(OCl) 2 treatment in BTCPW has been found as 10.5 and 8.5 respectively through this experiment. As the pH of the BTCPW lies around 7.5 to 8.5, elevation of solution pH up to 10.5 is required in NaOCl treatment to get maximum efficiency. Whereas Ca(OCl) 2 treatment does not require such elevation of pH. It was also found that during Ca(OCl) 2 treatment, colour and TDS content of the treated water were in lower range at pH 8.5 as shown in Fig. 5a and Fig. 5b. For NaOCl treatment colour (Fig. 5a) and TDS (Fig. 5b) content of the treated water varies throughout the pH range. This has again confirmed the optimum pH of Ca(OCl) 2 treatment at 8.5. Optimum condition of dosage and time Considering the oxidation reaction of CN - by chlorine compound, during which CN - has been changed to CNO - , hypochlorite ion (OCl - ) is the active chlorine group in the oxidation process. This reaction can be slow, from 30 minutes to 2 hours. The Ca(OCl) 2 has 2 groups of OCl - , hence more effective in oxidation than NaOCl. The optimum condition is achieved by the equilibrium between the volume of Ca(OCl) 2 solution added and the cyanide content in the waste water (Teixeira et al. 2013). To attain the best condition for maximum treatment efficiency with removal of CN F to its MPL and simultaneous removal of colour from BTCPW, different experiments were carried with NaOCl and Ca(OCl) 2 solutions. Condition was assumed to be optimum when the residual CN F concentration of the solution reached its MPL (0.2ppm) with minimum time and minimum doses of the hypochlorite solution. Treatment of NaOCl and Ca(OCl) 2 was done at their optimum pH (10.5 and 8.5 respectively) for 60-minute reaction time to find out the dosage at which both methods are at their maximum efficiency level. The results are as shown in Fig. 6. From the above experiment, it was found that cyanide removal efficiency increases as the volume of NaOCl and Ca(OCl) 2 solution is increased. The removal rate was faster up to addition of 30 ml of hypochlorite solution and then gets slower. No significant changes were observed after the addition of 40 ml of the solution. This may be due to the faster reaction of CN F with OCl - to form CNCl and thereby reducing the CN - at higher concentration of OCl - in the initial stage of the treatment. The reaction gets slower as the concentration of hypochlorite ion is decreased for both (NaOCl and Ca(OCl) 2 ) treatment (Teixeira et al. 2013). From the above treatment, it was clear that the maximum removal efficiency of CN F lies in between 30 and 40 ml of the NaOCl or Ca(OCl) 2 solution. To find out the exact dose and more precise condition, experiment has been carried out at 2 minutes interval with five different volume of doses between 20 ml and 40 ml (20ml, 25ml, 30ml, 35ml and 40 ml). pH was kept constant at 10.5 and 8.5 respectively for NaOCl and Ca(OCl) 2 . Result shows that, addition of 35 ml of Ca(OCl) 2 up to 62 minutes treatment reduces the residual CN F concentration to 0.2 ppm as shown in Fig. 7a. Which is the optimum condition for Ca(OCl) 2 treatment of BTCPW. Whereas, optimum condition for NaOCl reached at 58 minutes of treatment time and 35ml of NaOCl addition as in Fig. 7b. Lab scale trial After the completion of the optimisation study, 5 litre BTCPW water was treated with 4% Ca(OCl) 2 solution at its optimum dose of (35 ml or 1.4 gm per litre) and treatment time (62 min). Physico chemical parameters like pH, TDS, thiocyanate, ammonia and colour have been analysed along with CN F (Table 3), to know the changes in water characteristics before and after the treatment. Table 3: Characteristics of BOT wastewater before and after Ca(OCl) 2 treatment Parameters Before Treatment Mean ± SE* After Treatment Mean ± SE pH 8.26 ± 0.03 8.25 ± 0.03 TDS, ppm 2812 ± 15.4 2345 ± 11.8 Free cyanide, ppm 2.75 ± 0.04 0.22 ± 0.01 Thiocyanate, ppm 12.6 ± 0.08 3.34 ± 0.02 Ammonia, ppm 66 ± 1.3 56 ± 1.3 Colour, (PtCo) 2610 ± 3.0 1240 ± 3.4 *SE: In the table SE stands for standard error. In the table, data represents mean ±SE (Standard error) of n = 5. The results presented in Table 3 show 92% CN F removal by calcium hypochlorite with removal of more than 50% of colour and no increase in TDS content. In addition to this, no negative impact was observed in other important parameter like thiocyanate and ammonia content. Economic aspect of Ca(OCl) 2 use over NaOCl From the economic aspect of cyanide remediation from coke plant waste water, the cost can be calculated for optimum dose of the two treatment processes. Using the price of 1 gm NaOCl (Rs 0.55) and 1 gm Ca(OCl) 2 (Rs 0.27), the cost of cyanide removal for one litre of waste water can be computed as Rs 0.77 and Rs 0.38 for NaOCl and Ca(OCl) 2 respectively. In addition to this, cost of pH elevation step is required in NaOCl treatment where as it is not required in Ca(OCl) 2 treatment. Therefore, use of Ca(OCl) 2 of cyanide removal from coke plant waste water is economically more viable than that of NaOCl. Conclusion The removal of cyanide from steel industrial wastewater using either NaOCl or Ca(OCl) 2 can be achieved. The optimum condition for cyanide remediation in BTCPW with NaOCl or Ca(OCl) 2 treatment has been reported. Ca(OCl) 2 could be more effective than NaOCl considering the cost, TDS and colour removal from the coke plant wastewater. There is no requirement of pH adjustment in case of Ca(OCl) 2 treatment as the optimum condition is close to the original pH of the feed water, thereby reducing expensive caustic consumption. The experiment showed that more than 90% removal of CN F could be achieved along with more than 50% reduction of colour by optimising calcium hypochlorite treatment. Therefore, Ca(OCl) 2 can be one of the promising chemical treatment method for reduction of cyanide treatment without increasing the TDS value of the Coke plant water after biological treatment. Declarations Ethical Approval : Hereby, I /Amit Mondal/ consciously assure that for the manuscript / Mitigation of cyanide from coke plant wastewater using chemical oxidation process / the following is fulfilled: 1) This material is the authors' own original work, which has not been previously published elsewhere. 2) The paper is not currently being considered for publication elsewhere. 3) The paper reflects the authors' own research and analysis in a truthful and complete manner. 4) The paper properly credits the meaningful contributions of co-authors and co-researchers. 5) The results are appropriately placed in the context of prior and existing research. 6) All sources used are properly disclosed (correct citation). Literally copying of text must be indicated as such by using quotation marks and giving proper reference. 7) All authors have been personally and actively involved in substantial work leading to the paper, and will take responsibility for its content. Consent to Publish : The authors have been declared consent to publish this article in Environmental Science and Pollution Research. Authors Contributions: All authors have been actively involved in research work leading to the manuscript as follows: U. G. Nair and S. Sarkar designed and directed the project. U. G. Nair and S. Sarkar helped supervise the project. A. Mondal, P. Saha and S. Sarkar were involved in planning of experimental work. A. Mondal and P. Saha contributed to sample collection and sample preparation. A. Mondal, U. G. Nair and S. Sarkar verified the analytical methods. A. Mondal and P. Saha performed the measurements, A. Mondal and P. Saha compiled all data. A. Mondal and S. Sarkar verified the compiled data. A. Mondal, P. Saha and S. Sarkar contributed analysis of data. A. Mondal, U. G. Nair and S. Sarkar contributed in literature review. A. Mondal and P. Saha wrote the manuscript. All authors contributed to the interpretation of the results. All authors discussed the results and contributed to the final manuscript. All authors provided critical feedback and helped shape the research, analysis and manuscript. Conflicts of interest: The authors declare that they have no conflict of interest. Availability of data and material: The data that support the findings of this study are available with the corresponding author, upon reasonable request. Funding: There are no specific funding received by the authors for this work. Acknowledgement Authors are thankful to Research and Development department of Tata Steel Limited for providing necessary laboratory facilities in completing the research work. References Adams M D (1994) Removal of cyanide from solution using activated carbon. Miner Eng 7(9):1165–1177. Adhoum N, Monser L. (2002) Removal of cyanide from aqueous solution using impregnated activated carbon. Chem Eng Process. 41(1): 17-21. 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DOI: 10.1016/j.jwpe.2019.01.013. Mosher JB, Figueroa L (1996) Biological oxidation of cyanide: A viable treatment option for the minerals processing industry. Miner Eng 9(5):573-581. Munive GT, Coronado H, Encinas RM, Vazquez VV, Parga JR, (2015) Leaching of Sludge from the AVR Process with Ammonium Thiosulfate: Alternative Technology to the Cyanidation, Journal of Multidisciplinary Engineering Science and Technology (JMEST). 2(5): 1221-1225. Muntasir, Sjahrul M, Zakir M, Raya I (2016) Elimination Cyanide with Hydrogen Peroxide (H2O2) and Calcium Hypochlorite (Ca(OCl)2 on Gold Mine Waste from North Luwu, South Sulawesi. American Journal of Environmental Protection 5(4):97-102. Ozyonar F, Karagozogly B (2015) Treatment of pre-treated coke wastewater by electrocoagulation and electrochemical peroxidation processes. Sep Pur Tech 150:268-277. DOI:10.1016/j.seppur.2015.07.011. Pal P, Kumar R (2014) Treatment of coke wastewater: a critical review for developing sustainable management strategies. Sep Purif Rev 43(2):89–123. Pal P, Pamela Bhakta P, Kumar R (2014) Cyanide Removal from Industrial Wastewater by Cross-Flow Nanofiltration: Transport Modeling and Economic Evaluation. 86(6):698-706. Parekh F, Ban GH (2018) Reduction of COD from Secondary Effluent of CETP by Chlorination. International Journal of Latest Technology in Engineering, Management & Applied Science 7(2):155-157. Park D, Kim YM, Lee DS, Park, JM (2008) Chemical treatment for treating cyanides-containing effluent from biological cokes wastewater treatment process. Chem Eng J 143:141–146. Pillai IMS, Gupta AK (2016) Anodic oxidation of coke oven wastewater: Multiparameter optimization for simultaneous removal of cyanide, COD and phenol. Journal of Environmental Management 176: 45-53. Pueyo N, Miguel N, Ovelleiro JL and Ormad MP 2016 Limitations of the removal of cyanide from coking wastewater by ozonation and by the hydrogen peroxideozone process. Water Science & Technology 74(2):482-490. Reed BE, Islam AA, Bendick J (2013) Ferrate and Alkaline Chlorination Treatment of Cyanide-Heavy Metal Maritime Wastewater. Journal of Environmental Engineering 139(5): 661-666. Saha P, Mondal A, Sarkar S (2018) Phytoremediation of cyanide containing steel industrial wastewater by Eichhornia crassipes. International Journal of Phytoremediation 20(4):407–416. Sinbuathong N, Kongseri B, Plungklang P, Khun-anake R (2000) Cyanide Removal from Laboratory Wastewater Using Sodium Hypochlorite and Calcium Hypochlorite. Kasetsart J. (Nat. Sci.) 34:74-78. Saravi HI, Dehestaniathar S, Darban AK, Zolfaghari M & Saeedzadeh S (2015) Photocatalytic decomposition of cyanide in pure water by biphasic titanium dioxide nanoparticles. Desalination and Water Treatment 57(43): 20503-20510. Singh H and Mishra BK (2018) Degradation of cyanide, aniline and phenol in pre-treated coke oven wastewater by peroxide assisted electrooxidation process. Water Science & Technology 78(10) : 2214-2227. Singha U, Arora NK, Sachan P (2018) Simultaneous biodegradation of phenol and cyanide present in coke-oven effluent using immobilized Pseudomonas putida and Pseudomonas stutzeri. Brazilian Journal of Microbiology 49:38-44. https://doi.org/10.1016/j.bjm.2016.12.013. Teixeira LAC, Arellano MTC, Sarmiento CM, Yokoyama, L., Araujo, F. V da F. (2013) Oxidation of cyanide in water by singlet oxygen generated by the reaction between hydrogen peroxide and hypochlorite, Minerals Engineering, 50–51, 57-63. Tyagi M, Rana A, Kumari S, Jagadevan S (2018) Adsorptive removal of cyanide from coke oven wastewater onto zero-valent iron: Optimization through response surface methodology, isotherm and kinetic studies, Journal of Cleaner Production, 178, 398-407. Woo SH, Jeon CO, Yua YS, Choi CH, Lee CS, Lee DS (2009) On-line estimation of key process variables based on kernel partial least squares in an industrial coke wastewater treatment plant. J. Hazard Mater. 161(1):538-544. Yilmaz E, Ahlatci F, Yazici EY, Celep O, Deveci H (2017) Recovery of cyanide from effluents using carbon dioxide. Mugla Journal of Science and Technology, 3(2): 171-177. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-727204","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":56839149,"identity":"9b5f534b-0046-4a54-90a5-c127a4420709","order_by":0,"name":"Amit Mondal","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAklEQVRIiWNgGAWjYFACxgYIfYC58QFc8AE2lQgtjRA9BxibDQ4wGDAwsAE5CURZc4CxTYIoLfzTDrc/YMyxyeM7frCt+kPNH3n5+c0HHyQw2MnpNmDXInE7sbGBcVtaseSZxLYbB44ZGG44xpZskMCQbGx2AIc1EC2HEzccAGlhM2DcwMZjJpHAcCBxGw4t8nAt5x+2FRz4Z2A/v43/+w98WgzgWm4ktjEcbDNIbDjGw8aAT4shUMuMxG1piTNvPGyWONtnnLzhWJqxRIIBbr/I3U5/8OHjNpvEvvPJBz9UfJOznd98+OGHDxV2cji9DwIJWByMR/koGAWjYBSMAoIAAIYpbGxdU9HNAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-2505-9776","institution":"Tata Steel Ltd Jamshedpur","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Amit","middleName":"","lastName":"Mondal","suffix":""},{"id":56839150,"identity":"d1376914-fc0a-4742-89cc-adcbd8689615","order_by":1,"name":"Priyanka Saha","email":"","orcid":"","institution":"Tata Steel Ltd Jamshedpur","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Priyanka","middleName":"","lastName":"Saha","suffix":""},{"id":56839151,"identity":"e1f03ca1-85b3-4cf9-8a8b-aaa47031e533","order_by":2,"name":"Supriya Sarkar","email":"","orcid":"","institution":"Tata Steel Ltd Jamshedpur","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Supriya","middleName":"","lastName":"Sarkar","suffix":""},{"id":56839152,"identity":"535e5969-9c39-4e6e-b754-b509bbc475bd","order_by":3,"name":"Udayabhanu G Nair","email":"","orcid":"","institution":"Indian Institute of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Udayabhanu","middleName":"G","lastName":"Nair","suffix":""}],"badges":[],"createdAt":"2021-07-17 06:31:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-727204/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-727204/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":14719484,"identity":"216de030-93b1-4d3d-b2ae-34f3d36de2f5","added_by":"auto","created_at":"2021-10-20 15:30:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":54478,"visible":true,"origin":"","legend":"Schematic diagram of coke plant effluent treatment through biological process","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/7020490ebfab85d65fa07bac.png"},{"id":14719490,"identity":"54ce6f91-5932-4a79-9eb6-94a9d7f09275","added_by":"auto","created_at":"2021-10-20 15:30:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":14385,"visible":true,"origin":"","legend":"Removal of cyanide by NaOCl and Ca(OCl)2","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/c6a5a1dd439e1b55791ad223.png"},{"id":14719485,"identity":"209326bd-7cce-47ea-adbe-c1cd11b8a7ae","added_by":"auto","created_at":"2021-10-20 15:30:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":8639,"visible":true,"origin":"","legend":"Removal of colour and TDS by NaOCl and Ca(OCl)","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/c573bef7bb90dd37fc4a1d2b.png"},{"id":14720045,"identity":"8e7c752d-cfe1-4b24-9dda-ae9f38fdf4ba","added_by":"auto","created_at":"2021-10-20 15:33:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":30673,"visible":true,"origin":"","legend":"a Effect of pH on cyanide removal by using different concentration of Ca(OCl)2\nb Effect of pH on cyanide removal by using different concentration of NaOCl","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/3378f6b44e5f56bae4268304.png"},{"id":14720330,"identity":"b770290d-6929-48d5-94c4-ebca3db561e2","added_by":"auto","created_at":"2021-10-20 15:36:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":41400,"visible":true,"origin":"","legend":"a Changes of colour at different pH during NaOCl and Ca(OCl)2 treatment\nb Changes of TDS at different pH during NaOCl and Ca(OCl)2 treatment","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/fff2eef025260eefb6eb02e1.png"},{"id":14719488,"identity":"9be1c8f5-4516-4103-bfcc-26f38c12f4a5","added_by":"auto","created_at":"2021-10-20 15:30:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":14496,"visible":true,"origin":"","legend":"Cyanide removal efficiency by different volume of NaOCl and Ca(OCl)2 at optimum pH","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/c1b452f721a6cc21598f2ec9.png"},{"id":14719489,"identity":"ad12cfa0-d94b-4fc8-8504-9b1f661800f4","added_by":"auto","created_at":"2021-10-20 15:30:21","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":49453,"visible":true,"origin":"","legend":"a Optimum condition for Ca(OCl)2 treatment\nb Optimum condition for NaOCl treatment","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/cb8e0acc52b78d25c4fcb13d.png"},{"id":15816747,"identity":"fff47f37-d950-4df4-b935-49d1a0b9d302","added_by":"auto","created_at":"2021-11-23 11:02:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":619547,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-727204/v1/6a4c5b65-0221-4a42-a83f-e61ddab7a4bd.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eMitigation of Cyanide From Coke Plant Wastewater Using Chemical Oxidation Process\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIntegrated Steel Plant is a water intensive industry, where almost every process consumes a huge amount of water. Waste water from steel industry operation transport various organic, inorganic pollutants and toxic substances that have adverse effects on the environment (Park et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Due to the toxic effects, discharge of this polluted water without detoxification cause severe damage to the environment. Coke plant is one of the major contributors for generation of waste water in an integrated steel plant. Nearly 4 m\u003csup\u003e3\u003c/sup\u003e of water is used to produce 1 ton of coke and the process generates a large volume of heavily polluted wastewater (Pal and kumar 2014). Coke plant waste water is generated during quenching, cleaning and recovery of valuable by-product of coke oven gas produced during carbonisation of coal in the coke oven batteries. The waste water generated during these processes contains various organic and inorganic toxic compounds like ammonia, thiocyanate, cyanides, sulphides, pyridine, phenols and other poly aromatic hydrocarbons (PAH) (Mondal et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Dhoble et al. 2019). Cyanide is the most toxic chemical present in the coke plant discharge water among those pollutants (Ozyonar and Karagozogly \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Maranon et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The wastewater from the coke plant and blast furnace blow down have been identified as the major contributors of aqueous cyanide emissions in the iron and steel industries (Saha et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Singha et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Thus, steel industry is coming under increasing scrutiny of environmental regulators to meet more stringent water discharge limits.\u003c/p\u003e \u003cp\u003eMetal-complexed cyanides are classified according to the strength of the metal cyanide bond. Cyanide in waste water are classified into three types; a. free cyanide (CN\u003csub\u003eF\u003c/sub\u003e), which include CN- and HCN, b. weak-acid dissociable (CN\u003csub\u003eWAD\u003c/sub\u003e) indicate weak cyanide complexes with metals such as copper, nickel, cadmium and zinc, c. strong-acid dissociable (CN\u003csub\u003eSAD\u003c/sub\u003e) refer to strong cyanide-complexes with metals such as gold, cobalt, iron and silver. Toxicity of these cyanides are in the order of CN\u003csub\u003eF\u003c/sub\u003e \u0026gt; CN\u003csub\u003eWAD\u003c/sub\u003e \u0026gt; CN\u003csub\u003eSAD\u003c/sub\u003e (Johnson \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). All cyanides are classified as hazardous to the characteristics of acute and chronic toxicity (Deveci et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). But the legislation of the Government for the cyanide discharge deals with only CN\u003csub\u003eF\u003c/sub\u003e as it is the most toxic to living elements and sometimes is deadly in nature. The discharge limit of CN\u003csub\u003eF\u003c/sub\u003e to the environment is up to 0.2 ppm (Mondal et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) as guided by Central Pollution Control Board.\u003c/p\u003e \u003cp\u003eBecause of the environmental concerns and potential hazards due to the toxic effects, control and remediation of cyanide containing industrial waste water is essential. There are several physical, chemical, and biological treatment methodologies available for cyanide removal in coke plant wastewater. But, all the processes have some limitations for implementation in the plant scale. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents some of the commonly adopted cyanide treatment technologies and their limitations. It also shows the fate of cyanide after the treatment and the reagents used in each process.\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\u003eCyanide treatment technologies and their limitations.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTreatment method\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFate of cyanide\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReagent/\u003c/p\u003e \u003cp\u003eChemical\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLimitations\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOzonation.\u003c/p\u003e \u003cp\u003eChegini et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Pueyo et al. 2016, Chang et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e and N\u003csub\u003e2\u003c/sub\u003e with O\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCostly process. Adds ammonia to discharge water\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhotocatalytic oxidation. Biswas et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Chegini et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Saravi et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CNO\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNano particle, UV source, TiO2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEnergy intensive and costly process.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiological oxidation/biodegradation.\u003c/p\u003e \u003cp\u003eDas et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Dwivedi et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, Kumar et al.2011, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, Woo et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, Kim et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2007\u003c/span\u003e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003eand NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e and then NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003eusing microorganisms.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTreatment of high concentrations create problem. Cannot reach the discharge standards of cyanide.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAlkaline chlorination by Hypochlorite/Perchlorate. Das et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Khodadad et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2008\u003c/span\u003e, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, Reed et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2013\u003c/span\u003e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CNO\u003csup\u003e\u0026minus;\u003c/sup\u003e and then N\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCl\u003csub\u003e2\u003c/sub\u003e, NaOCl,\u003c/p\u003e \u003cp\u003eNaOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncrease in TDS content.\u003c/p\u003e \u003cp\u003eRequires high caustic to maintain pH\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSO\u003csub\u003e2\u003c/sub\u003e/Air (INCO) process.\u003c/p\u003e \u003cp\u003eDash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, Kumar et al.2011.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CNO\u003csup\u003e\u0026minus;\u003c/sup\u003e with SO\u003csub\u003e2\u003c/sub\u003e \u0026amp; air and soluble Cu catalyst.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSO\u003csub\u003e2\u003c/sub\u003e, air, Cu catalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePartial removal of cyanide.\u003c/p\u003e \u003cp\u003eProcess adds sulphate to the treated water.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHydrogen peroxide.\u003c/p\u003e \u003cp\u003eSingh et al. 2018, Pueyo et al. 2016, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CNO\u003csup\u003e\u0026minus;\u003c/sup\u003e with\u003c/p\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026amp; Cu catalyst: Degussa process\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eReagent is costly, accurate measurement of chemical dose is required.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaro\u0026rsquo;s acid. Cesar et al. 2013, Pueyo et al. 2016, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e,\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CNO\u003csup\u003e\u0026minus;\u003c/sup\u003e with H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncrease in TDS content.\u003c/p\u003e \u003cp\u003eDifficult to handle due to decomposition to\u003c/p\u003e \u003cp\u003eoxygen and sulfuric acid.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIron cyanide precipitation. Arbabi et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e,\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePrecipitated as Fe(CN)\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFeSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWorks only with low concentration of cyanide. Maintaining pH and disposal of precipitate is difficult.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAVR process.\u003c/p\u003e \u003cp\u003eMunive et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Yilmaz et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAcidification to HCN and neutralisation.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, NaOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHigh acid consumption. Complex process.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActivated carbon.\u003c/p\u003e \u003cp\u003eAdhoum et al. 2002, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CNO\u003csup\u003e\u0026minus;\u003c/sup\u003eand partially to CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e and NH4\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eActivated carbon, air/O\u003csub\u003e2\u003c/sub\u003e, Cu catalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eExpensive method.\u003c/p\u003e \u003cp\u003eUsed only for low concentration of CN\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCatalytic oxidation.\u003c/p\u003e \u003cp\u003eKumar et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, Chiang et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2002\u003c/span\u003e. Larry et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1982\u003c/span\u003e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CO\u003csub\u003e2\u003c/sub\u003e, N\u003csub\u003e2\u003c/sub\u003e \u0026amp; NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003ewith air and catalyst.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCatalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRestriction in treating very low concentration. Costly process.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnodic oxidation.\u003c/p\u003e \u003cp\u003ePillai et al. 2016, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOxidation to CNO\u003csup\u003e\u0026minus;\u003c/sup\u003eand then CO\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNaCl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePartial removal of cyanide.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReverse osmosis. Pal et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, Dash et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, Gude \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2012\u003c/span\u003e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUses a partially permeable membrane to separate ions.\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\u003eEnergy intensive and costly process.\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\u003eTo overcome these limitations, different combined treatment methodologies are being used for the remediation of cyanide in coke plant waste water. Combined treatment of biological, followed by chemical treatment is one of the potential and accepted cyanide treatment process for coke plant waste water (Pal and Kumar \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePresent process, uses the biological treatment through a stable activated sludge process followed by chemical treatment with sodium hypochlorite. The treatment process is schematically represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAfter biological treatment, the discharge water contains high amount of CN\u003csub\u003eF\u003c/sub\u003e which is taken care of by sodium hypochlorite (NaOCl) treatment. In this chemical treatment, oxidation transforms CN\u003csub\u003eF\u003c/sub\u003e to cyanate (CNO\u003csup\u003e\u0026minus;\u003c/sup\u003e), which has an environmental hazard 1,000 times lower than cyanide (Mosher and Figueroa \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). But this popular treatment method has the major disadvantage of increasing TDS content in the discharge water (Ghosh et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e and Das et al. 2019) and is also expensive due to the extraneous dosing of sodium hydroxide (Tyagi et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Moreover, biologically treated water gets more intense dark brown color than the untreated water due to the presence of degraded phenolic compounds (Mijangos et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). This acute colour could not be taken care by NaOCl treatment. Calcium hypochlorite [Ca(OCl)\u003csub\u003e2\u003c/sub\u003e] can be used as an alternative chemical for reduction of cyanide in biologically treated coke plant wastewater (BTCPW), which decrease TDS and colour along with CN\u003csub\u003eF\u003c/sub\u003e content. Ca(OCl)\u003csub\u003e2\u003c/sub\u003e is more stable and potentially more efficient for cyanide removal as compared to the NaOCl due to having higher available chlorine (Hasab et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Powdered Ca(OCl)\u003csub\u003e2\u003c/sub\u003e has the highest oxidation power among other chemicals used for chlorination (Parekh and Ban \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Moreover, removal of cyanide through Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment is more effective considering the dosage and cost (Sinbuathong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). However, very few studies have been reported on the application of this method to biologically treated coke plant effluent.\u003c/p\u003e \u003cp\u003ePresent research aims to develop a continuous, effective and economical process with the use of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e in cyanide treatment process of BTCPW. Comparative study of cyanide removal efficiency in BTCPW has been carried out with Ca(OCl)\u003csub\u003e2\u003c/sub\u003e and NaOCl. TDS and colour of the treated solution were also compared in both the treatments. In addition to this, optimisation of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment process by changing chemical dosage, treatment time and pH of the treatment solution has been carried out. Lab scale trial of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment in BTCPW was also performed in optimum conditions and the results are presented.\u003c/p\u003e"},{"header":"Materials \u0026 Methods","content":"\u003cp\u003e\u003cstrong\u003eCollection of water samples\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor the present study, water samples were collected from Biological Oxygen Treatment (BOT) plant of the coke plant in an integrated steel plant situated in the eastern part of India. This plant produces approximately 9 MT of coke per day and about 200 m\u003csup\u003e3\u003c/sup\u003e of waste water is generated daily by the process of coke making.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterisation of coke plant wastewater\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe water samples collected from coke plant after biological treatment has the characteristics as shown in Table 2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2:\u0026nbsp;\u003c/strong\u003eGeneral characteristics of Coke plant waste water after biological treatment\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"0\" cellpadding=\"0\" cellspacing=\"0\" width=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003eCoke plant waste water after biological treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e7.5-8.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eTDS, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e2450-3350\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eColour, (PtCo)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e2550-2950\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eBOD, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e50-110\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eCOD, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e220-550\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eThiocyanate, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e10-30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eFree cyanide, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e1.5-4.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eAmmonia, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e30-100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"45.15151515151515%\"\u003e\n \u003cp\u003eTKN, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"54.84848484848485%\"\u003e\n \u003cp\u003e150-350\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eExperimental Set up and Procedure\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe experiment for optimisation study has been carried out in 1L biologically treated water from coke plant in a glass beaker. Water samples were taken in a beaker and the pH was adjusted with sodium hydroxide and dilute hydrochloric acid. \u0026nbsp;For lab scale trial, 5 L of BTCPW was taken and treated with Ca(OCl)\u003csub\u003e2\u003c/sub\u003e at its optimised condition. After maintaining the pH, 4% Ca(OCl)\u003csub\u003e2\u003c/sub\u003e was added drop wise from the burette. The samples were kept in continuous stirring condition up to the end of the treatment. Cyanide content has been tested at every 10-min time interval after filtration through Whatman 1 paper. Each experiment was performed in duplicate and the average of the results have been reported. All parameters including CN\u003csub\u003eF\u003c/sub\u003e were tested in triplicate throughout the study and average value has been reported.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalysis of pH\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003epH of the water samples was measured using the pH meter (Systronics, India, digital pH meter, model no: 335).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalysis of TDS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTDS is a measure of the combined content of all inorganic and organic substances contained in a liquid in molecular, ionized or micro-granular suspended form (Hussain, 2019). During the study, TDS of the water samples has been measured by using TDS meter (Systronics, India, model no: 308).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDetermination of free cyanide concentration by ion selective method\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFree cyanide has been determined by filtering water sample through Whatman No. 1 filter paper and taking 10 mL of the filtered water for analysis. It was analysed potentiometrically using ion selective cyanide electrode (Thermo Scientific) according to the procedure given by manufacturer. Many tests can be done at a time through this method, due to the low analysis time (about 5 min).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDetermination of ammonia concentration using ion selective electrode\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAmmonia has been measured potentiometrically with ammonia ion selective electrode (Thermo Scientific) according to the procedure given by manufacturer.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDetermination of thiocyanate concentration spectrophotometrically\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThiocyanate concentration in ppm was measured using spectrophotometer (Thermo Scientific, Genesys 10S UV-VIS spectrophotometer). The wavelength used was 460 nm. This was performed after a blood red colour was developed by using ferric nitrate [Fe(NO3)\u003csub\u003e3\u003c/sub\u003e. 9H\u003csub\u003e2\u003c/sub\u003e0 solution according to the standard procedure (APHA 2017).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMeasurement of colour\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCoke plant water gets more intense brown colour after biological treatment due to the presence of aromatic coloured compounds such as ortho- and para-benzoquinone, which form through the degradation of phenol (Mijangos et al. 2006). The color of the wastewater was measured by the color measuring instrument (Make: Lovibond) and expressed in PtCo unit.\u0026nbsp;\u003c/p\u003e"},{"header":"Results And Discussion","content":"\u003cp\u003eCa(OCl)\u003csub\u003e2\u003c/sub\u003e and\u0026nbsp;NaOCl react to form hypochlorite and hydroxide ion when added to water\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNaOCl + H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; OCl\u003csup\u003e-\u0026nbsp;\u003c/sup\u003e+ OH\u003csup\u003e-\u0026nbsp;\u003c/sup\u003e + Na\u003csup\u003e+\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; (1)\u003c/p\u003e\n\u003cp\u003eCa(ClO)\u003csub\u003e2\u003c/sub\u003e + 2 H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; 2 OCl\u003csup\u003e-\u003c/sup\u003e + 2 OH\u003csup\u003e-\u003c/sup\u003e + Ca\u003csup\u003e+2\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(2)\u003c/p\u003e\n\u003cp\u003eHypochlorite ion (OCl\u003csup\u003e-\u003c/sup\u003e)\u0026nbsp;oxidises CN\u003csup\u003e-\u003c/sup\u003e in BTCPW to cyanogen chloride (CNCl).\u0026nbsp;More the addition of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e, the greater the cyanide reacts to form CNCl, therefore the\u0026nbsp;CN\u003csub\u003eF\u003c/sub\u003e content in the liquid waste is reduced. Further\u0026nbsp;CNCl\u0026nbsp;is oxidized into CNO and finally into CO\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e(Johnson 2015).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe oxidation reaction of cyanide and hypochlorite can be shown as follows\u003c/p\u003e\n\u003cp\u003eCN\u003csup\u003e-\u0026nbsp;\u003c/sup\u003e+ HOCl \u0026rarr; CNCl + OH\u003csup\u003e-\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(3)\u003c/p\u003e\n\u003cp\u003eCNCl + OH \u0026rarr; CNO\u003csup\u003e-\u003c/sup\u003e + Cl + H\u003csub\u003e2\u003c/sub\u003eO \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(4)\u003c/p\u003e\n\u003cp\u003eCNO\u003csup\u003e-\u003c/sup\u003e + OCl\u003csup\u003e-\u003c/sup\u003e + H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; N\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e+ Cl\u003csup\u003e-\u003c/sup\u003e + HCO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(5)\u003c/p\u003e\n\u003cp\u003eIn the present study, cyanide treatment by 4% NaOCl and 4% Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solution was carried out in one litre BTCPW for 120 minutes. The residual CN\u003csub\u003eF\u003c/sub\u003e content was checked in every 10 minutes by ion selective electrode. No significant changes were observed in CN\u003csub\u003eF\u003c/sub\u003e concentration at the beginning of the treatment. But, significant decrease in CN\u003csub\u003eF\u003c/sub\u003e started after 20 minutes of NaOCl treatment and 30 minutes of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment Fig. 2.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUp to 80 % of CN\u003csub\u003eF\u003c/sub\u003e was removed in 50 minutes of NaOCl treatment. Whereas Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment took 60 minutes for the removal of 80% of CN\u003csub\u003eF\u003c/sub\u003e. This result is in line with that reported by\u0026nbsp;Muntasir et al. 2016.\u0026nbsp;In addition to CN\u003csub\u003eF\u003c/sub\u003e, significant changes were observed in TDS and colour\u0026nbsp;(Fig. 3)\u0026nbsp;of the treated water. It was found that TDS content was increased in\u0026nbsp;NaOCl treatment and\u0026nbsp;decreased in the case of\u0026nbsp;Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment. Similar trend has been observed in case of colour, where more than 55% colour was removed in Ca(OCl)\u003csub\u003e2\u0026nbsp;\u003c/sub\u003etreatment against the increase in colour for NaOCl treatment. This is in accordance with the research work reported by\u0026nbsp;Khandaker et al. 2020 and\u0026nbsp;Massoudinejad et al. (2015).\u003c/p\u003e\n\u003cp\u003eThe colour removal and TDS decrease along with the CN\u003csub\u003eF\u003c/sub\u003e reduction shows scope of enhancement in\u0026nbsp;Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment efficiency by optimising treatment parameters like pH, treatment time and dosing rate, to get maximum efficiency compared to NaOCl treatment of BTCPW.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOptimisation study\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eOptimum condition of pH\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFor optimisation study, BTCPW containing CN\u003csub\u003eF\u003c/sub\u003e 4.08 ppm, TDS 2970 ppm and colour 2780 PtCo was considered. Treatment of\u0026nbsp;Ca(OCl)\u003csub\u003e2\u003c/sub\u003e and\u0026nbsp;NaOCl were carried out in 1 L of BOT water at a constant treatment time of 60 minute.\u0026nbsp;The experiment was done for three different dosing rates (20ml, 30ml and 50 ml) with 4% of NaOCl and 4% Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solutions. pH of the solution was varied from 7.5 to 12. Colour and TDS of the solution at different pH were also checked before and after the treatment along with CN\u003csub\u003eF\u003c/sub\u003e. \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIt has been found that cyanide removal efficiency of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e increases with pH and reaches the maximum at pH 8.5. Further increase in pH has not shown any increase in removal efficiency of CN\u003csub\u003eF\u003c/sub\u003e with 50ml, 30ml and 20 ml of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solution as shown in Fig. 4a. However, for NaOCl, maximum CN\u003csub\u003eF\u003c/sub\u003e removal was achieved at pH 10.5 as shown in Fig. 4b.\u003c/p\u003e\n\u003cp\u003eMaintaining proper pH allows calcium hypochlorite to react perfectly with\u0026nbsp;CN\u003csub\u003eF\u003c/sub\u003e in wastewater (Cidu et al. 2011 and Muntasir et al. 2016). At optimum pH decrease in the levels of\u0026nbsp;CN\u003csub\u003eF\u003c/sub\u003e ismaximum. This is in line with the research work reported by Lee and Tiwary (2009). \u0026nbsp;Optimum pH for NaOCl and\u0026nbsp;Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment in BTCPW has been found as 10.5 and 8.5 respectively through this experiment.\u0026nbsp;As the pH of the BTCPW lies around 7.5 to 8.5, elevation of solution pH up to 10.5 is required in NaOCl treatment to get maximum efficiency. Whereas Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment does not require such elevation of pH.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIt was also found that during Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment, colour and TDS content of the treated water were in lower range at pH 8.5 as shown in Fig. 5a and Fig. 5b. For NaOCl treatment colour (Fig. 5a) and TDS (Fig. 5b) content of the treated water varies throughout the pH range. This has again confirmed the optimum pH of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment at 8.5.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eOptimum condition of dosage and time\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; Considering the oxidation reaction of CN\u003csup\u003e-\u003c/sup\u003e by chlorine compound, during which CN\u003csup\u003e-\u003c/sup\u003e has been changed to CNO\u003csup\u003e-\u003c/sup\u003e, hypochlorite ion (OCl\u003csup\u003e-\u003c/sup\u003e) is the active chlorine group in the oxidation process. This reaction can be slow, from 30 minutes to 2 hours. The Ca(OCl)\u003csub\u003e2\u003c/sub\u003e has 2 groups of OCl\u003csup\u003e-\u003c/sup\u003e, hence more effective in oxidation than NaOCl.\u0026nbsp;The optimum condition is achieved by the equilibrium between the volume of\u0026nbsp;Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solution\u0026nbsp;added and the cyanide content in the waste water (Teixeira et al. 2013).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp;To attain the best condition for maximum treatment efficiency with removal of CN\u003csub\u003eF\u003c/sub\u003e to its MPL and simultaneous removal of colour from BTCPW,\u0026nbsp;different\u0026nbsp;experiments were carried with\u0026nbsp;NaOCl and Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solutions. Condition was assumed to be optimum when the residual CN\u003csub\u003eF\u003c/sub\u003e concentration of the solution reached its MPL (0.2ppm) with minimum time and minimum doses of the hypochlorite solution.\u003c/p\u003e\n\u003cp\u003eTreatment of\u0026nbsp;NaOCl and Ca(OCl)\u003csub\u003e2\u003c/sub\u003e was done at their optimum pH (10.5 and 8.5 respectively) for 60-minute reaction time to find out the dosage at which both methods are at their maximum efficiency level. The results are as shown in Fig. 6.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFrom the above experiment, it was found that cyanide removal efficiency increases as the volume of\u0026nbsp;NaOCl and Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solution is increased. The removal rate was faster up to addition of 30 ml of hypochlorite solution and then gets slower. No significant changes were observed after the addition of 40 ml of the solution. This may be due to the faster reaction of\u0026nbsp;CN\u003csub\u003eF\u003c/sub\u003e with OCl\u003csup\u003e-\u003c/sup\u003e\u0026nbsp; to form CNCl and thereby reducing the CN\u003csup\u003e-\u0026nbsp;\u003c/sup\u003eat higher concentration of OCl\u003csup\u003e-\u003c/sup\u003e in the initial stage of the treatment. The reaction gets slower as the concentration of hypochlorite ion is decreased for both (NaOCl and Ca(OCl)\u003csub\u003e2\u003c/sub\u003e) treatment (Teixeira et al. 2013).\u003c/p\u003e\n\u003cp\u003eFrom the above treatment, it was clear that the maximum removal efficiency of\u0026nbsp;CN\u003csub\u003eF\u003c/sub\u003e lies in between 30 and 40 ml of the NaOCl or Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solution. To find out the exact dose and more precise condition, experiment has been carried out at 2 minutes interval with five different volume of doses between 20 ml and 40 ml (20ml, 25ml, 30ml, 35ml and 40 ml). pH was kept constant at 10.5 and 8.5 respectively for NaOCl and Ca(OCl)\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eResult shows that, addition of 35 ml of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e up to 62 minutes treatment reduces the residual\u0026nbsp;CN\u003csub\u003eF\u003c/sub\u003e concentration to 0.2 ppm as shown in Fig. 7a. Which is the optimum condition for Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment of BTCPW. Whereas, optimum condition for NaOCl reached at 58 minutes of treatment time and 35ml of NaOCl addition as in Fig. 7b.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLab scale trial \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter the completion of the optimisation study, 5 litre BTCPW water was treated with 4%\u0026nbsp;Ca(OCl)\u003csub\u003e2\u003c/sub\u003e solution at its optimum dose of (35 ml or 1.4 gm per litre) and treatment time (62 min). Physico chemical parameters like pH, TDS, thiocyanate, ammonia and colour have been analysed along with CN\u003csub\u003eF\u003c/sub\u003e (Table 3), to know the changes in water characteristics before and after the treatment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3:\u0026nbsp;\u003c/strong\u003eCharacteristics of BOT wastewater before and after Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellpadding=\"0\" cellspacing=\"0\" width=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 26.8056%;\" width=\"26.08695652173913%\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameters\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.8889%;\" width=\"32.89224952741021%\"\u003e\n \u003cp\u003e\u003cstrong\u003eBefore Treatment \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Mean \u0026plusmn; SE*\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 39.3056%;\" width=\"41.02079395085066%\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Treatment \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Mean \u0026plusmn; SE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 26.8056%;\" width=\"26.08695652173913%\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.8889%;\" width=\"32.89224952741021%\"\u003e\n \u003cp\u003e8.26 \u0026plusmn; 0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 39.3056%;\" width=\"41.02079395085066%\"\u003e\n \u003cp\u003e8.25 \u0026plusmn; 0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 26.8056%;\" width=\"26.08695652173913%\"\u003e\n \u003cp\u003eTDS, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.8889%;\" width=\"32.89224952741021%\"\u003e\n \u003cp\u003e2812 \u0026plusmn; 15.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 39.3056%;\" width=\"41.02079395085066%\"\u003e\n \u003cp\u003e2345 \u0026plusmn; 11.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 26.8056%;\" width=\"26.08695652173913%\"\u003e\n \u003cp\u003eFree cyanide, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.8889%;\" width=\"32.89224952741021%\"\u003e\n \u003cp\u003e2.75 \u0026plusmn; 0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 39.3056%;\" width=\"41.02079395085066%\"\u003e\n \u003cp\u003e0.22 \u0026plusmn; 0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 26.8056%;\" width=\"26.08695652173913%\"\u003e\n \u003cp\u003eThiocyanate, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.8889%;\" width=\"32.89224952741021%\"\u003e\n \u003cp\u003e12.6 \u0026plusmn; 0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 39.3056%;\" width=\"41.02079395085066%\"\u003e\n \u003cp\u003e3.34 \u0026plusmn; 0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 26.8056%;\" width=\"26.08695652173913%\"\u003e\n \u003cp\u003eAmmonia, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.8889%;\" width=\"32.89224952741021%\"\u003e\n \u003cp\u003e66 \u0026plusmn; 1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 39.3056%;\" width=\"41.02079395085066%\"\u003e\n \u003cp\u003e56 \u0026plusmn; 1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 26.8056%;\" width=\"26.08695652173913%\"\u003e\n \u003cp\u003eColour, (PtCo)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.8889%;\" width=\"32.89224952741021%\"\u003e\n \u003cp\u003e2610 \u0026plusmn; 3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 39.3056%;\" width=\"41.02079395085066%\"\u003e\n \u003cp\u003e1240 \u0026plusmn; 3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e*SE: In the table SE stands for standard error.\u003c/p\u003e\n\u003cp\u003eIn the table, data represents mean\u0026nbsp;\u0026plusmn;SE (Standard error) of n\u0026nbsp;=\u0026nbsp;5.\u003c/p\u003e\n\u003cp\u003eThe results presented in Table 3 show 92% CN\u003csub\u003eF\u003c/sub\u003e removal by calcium hypochlorite with removal of more than 50% of colour and no increase in TDS content. In addition to this, no negative impact was observed in other important parameter like thiocyanate and ammonia content.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEconomic aspect of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e use over NaOCl\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFrom the economic aspect of cyanide remediation from coke plant waste water, the cost can be calculated for optimum dose of the two treatment processes. Using the price of 1 gm NaOCl (Rs 0.55) and 1 gm Ca(OCl)\u003csub\u003e2\u003c/sub\u003e (Rs 0.27), the cost of cyanide removal for one litre of waste water can be computed as Rs 0.77 and Rs 0.38 for NaOCl and Ca(OCl)\u003csub\u003e2\u003c/sub\u003e respectively. In addition to this, cost of pH elevation step is required in NaOCl treatment where as it is not required in Ca(OCl)\u003csub\u003e2\u0026nbsp;\u003c/sub\u003etreatment. Therefore, use of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e of\u003csub\u003e\u0026nbsp;\u003c/sub\u003ecyanide removal from coke plant waste water is economically more viable than that of NaOCl.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe removal of cyanide from steel industrial wastewater using either NaOCl or Ca(OCl)\u003csub\u003e2\u003c/sub\u003e can be achieved. The optimum condition for cyanide remediation in BTCPW with NaOCl or Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment has been reported. Ca(OCl)\u003csub\u003e2\u003c/sub\u003e could be more effective than NaOCl considering the cost, TDS and colour removal from the coke plant wastewater. There is no requirement of pH adjustment in case of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment as the optimum condition is close to the original pH of the feed water, thereby reducing expensive caustic consumption. The experiment showed that more than 90% removal of CN\u003csub\u003eF\u003c/sub\u003e could be achieved along with more than 50% reduction of colour by optimising calcium hypochlorite treatment. Therefore, Ca(OCl)\u003csub\u003e2\u003c/sub\u003e can be one of the promising chemical treatment method for reduction of cyanide treatment without increasing the TDS value of the Coke plant water after biological treatment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHereby, I /Amit Mondal/ consciously assure that for the manuscript / Mitigation of cyanide from coke plant wastewater using chemical oxidation process / the following is fulfilled:\u003c/p\u003e\n\u003cp\u003e1) This material is the authors\u0026apos; own original work, which has not been previously published elsewhere.\u003c/p\u003e\n\u003cp\u003e2) The paper is not currently being considered for publication elsewhere.\u003c/p\u003e\n\u003cp\u003e3) The paper reflects the authors\u0026apos; own research and analysis in a truthful and complete manner.\u003c/p\u003e\n\u003cp\u003e4) The paper properly credits the meaningful contributions of co-authors and co-researchers.\u003c/p\u003e\n\u003cp\u003e5) The results are appropriately placed in the context of prior and existing research.\u003c/p\u003e\n\u003cp\u003e6) All sources used are properly disclosed (correct citation). Literally copying of text must be indicated as such by using quotation marks and giving proper reference.\u003c/p\u003e\n\u003cp\u003e7) All authors have been personally and actively involved in substantial work leading to the paper, and will take responsibility for its content.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e The authors have been declared consent to publish this article in Environmental Science and Pollution Research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors Contributions:\u003c/strong\u003e All authors have been actively involved in research work leading to the manuscript as follows:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eU. G. Nair and S. Sarkar designed and directed the project. U. G. Nair and S. Sarkar helped supervise the project. A. Mondal, P. Saha and S. Sarkar were involved in planning of experimental work. A. Mondal and P. Saha contributed to sample collection and sample preparation. A. Mondal, U. G. Nair and S. Sarkar verified the analytical methods. A. Mondal and P. Saha performed the measurements, A. Mondal and P. Saha compiled all data. A. Mondal and S. Sarkar verified the compiled data. A. Mondal, P. Saha and S. Sarkar contributed analysis of data. A. Mondal, U. G. Nair and S. Sarkar contributed in literature review. A. Mondal and P. Saha wrote the manuscript. All authors contributed to the interpretation of the results. All authors discussed the results and contributed to the final manuscript. All authors provided critical feedback and helped shape the research, analysis and manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest:\u003c/strong\u003e The authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material:\u003c/strong\u003e The data that support the findings of this study are available with the corresponding author, upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e There are no specific funding received by the authors for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthors are thankful to Research and Development department of Tata Steel Limited for providing necessary laboratory facilities in completing the research work.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAdams M D (1994)\u0026nbsp;Removal of cyanide from solution using activated carbon.\u0026nbsp;Miner Eng 7(9):1165\u0026ndash;1177.\u003c/li\u003e\n\u003cli\u003eAdhoum N, Monser L. 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DOI:\u0026nbsp;10.1016/j.jwpe.2019.01.013.\u003c/li\u003e\n\u003cli\u003eMosher JB,\u0026nbsp;Figueroa L (1996) Biological oxidation of cyanide: A viable treatment option for the minerals processing industry.\u0026nbsp;Miner Eng 9(5):573-581.\u003c/li\u003e\n\u003cli\u003eMunive GT, Coronado H, Encinas RM, Vazquez VV, Parga JR, (2015) Leaching of Sludge from the AVR Process with Ammonium Thiosulfate: Alternative Technology to the Cyanidation, Journal of Multidisciplinary Engineering Science and Technology (JMEST). 2(5): 1221-1225.\u003c/li\u003e\n\u003cli\u003eMuntasir, Sjahrul M, Zakir M, Raya I (2016) Elimination Cyanide with Hydrogen Peroxide (H2O2) and Calcium Hypochlorite (Ca(OCl)2 on Gold Mine Waste from North Luwu, South Sulawesi. American Journal of Environmental Protection 5(4):97-102.\u003c/li\u003e\n\u003cli\u003eOzyonar F, Karagozogly B (2015) Treatment of pre-treated coke wastewater by electrocoagulation and electrochemical peroxidation processes. 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Water Science \u0026amp; Technology 78(10) : 2214-2227.\u003c/li\u003e\n\u003cli\u003eSingha U, Arora NK, Sachan P (2018) Simultaneous biodegradation of phenol and cyanide present in coke-oven effluent using immobilized Pseudomonas putida and Pseudomonas stutzeri. Brazilian Journal of Microbiology 49:38-44.\u0026nbsp;https://doi.org/10.1016/j.bjm.2016.12.013.\u003c/li\u003e\n\u003cli\u003eTeixeira LAC, Arellano MTC, Sarmiento CM, Yokoyama, L., Araujo, F. V da F. (2013) Oxidation of cyanide in water by singlet oxygen generated by the reaction between hydrogen peroxide and hypochlorite, Minerals Engineering, 50\u0026ndash;51, 57-63.\u003c/li\u003e\n\u003cli\u003eTyagi M, Rana A, Kumari S, Jagadevan S (2018) Adsorptive removal of cyanide from coke oven wastewater onto zero-valent iron: Optimization through response surface methodology, isotherm and kinetic studies,\u0026nbsp;Journal of Cleaner Production, 178, 398-407.\u003c/li\u003e\n\u003cli\u003eWoo SH, Jeon CO, Yua YS, Choi CH, Lee CS, Lee DS (2009) On-line estimation of key process variables based on kernel partial least squares in an industrial coke wastewater treatment plant. J. Hazard Mater. 161(1):538-544.\u003c/li\u003e\n\u003cli\u003eYilmaz E, Ahlatci F, Yazici EY, Celep O, Deveci H (2017) Recovery of cyanide from effluents using carbon dioxide. Mugla Journal of Science and Technology, 3(2): 171-177.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Biological treatment, Chemical oxidation, Coking wastewater, Free cyanide, Cyanide treatment, Hypochlorite.","lastPublishedDoi":"10.21203/rs.3.rs-727204/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-727204/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBiological treatment with a stable activated sludge process, followed by chemical treatment is one of the potential and accepted cyanide treatment process for coke plant waste water treatment. Biologically treated coke plant wastewater contains free cyanide above permissible limit. Presently chemical treatment with NaOCl is being used to attenuate free cyanide below permissible limit in biologically treated water. This process increases the TDS and colour content in discharge water. Ca(OCl)\u003csub\u003e2\u003c/sub\u003e can be used as an alternative to NaOCl for cyanide remediation in biologically treated coke plant waste water without increasing TDS. In the present work, cyanide removal efficiency of NaOCl and Ca(OCl)\u003csub\u003e2\u003c/sub\u003e for real coke plant waste water after biological treatment has been studied. Optimisation of chemical dosage, treatment time and pH has been done for Ca(OCl)\u003csub\u003e2\u003c/sub\u003e and NaOCl treatment. It was found that up to 90% of free cyanide removal could be achieved through Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment without increasing the TDS value. In addition, more than 50% colour of the waste water has been removed. pH elevation step required in NaOCl treatment can be eliminated in Ca(OCl)\u003csub\u003e2\u003c/sub\u003e treatment, thereby reducing caustic consumption. In conclusion, use of Ca(OCl)\u003csub\u003e2\u003c/sub\u003e is economically more viable than that of NaOCl in cyanide treatment.\u003c/p\u003e","manuscriptTitle":"Mitigation of Cyanide From Coke Plant Wastewater Using Chemical Oxidation Process","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-10-20 15:30:19","doi":"10.21203/rs.3.rs-727204/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a975ff26-4a70-4cb7-ab33-49c2e43889e3","owner":[],"postedDate":"October 20th, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":7984754,"name":"Environmental Chemistry"},{"id":7984755,"name":"Toxicology"}],"tags":[],"updatedAt":"2021-11-23T11:02:44+00:00","versionOfRecord":[],"versionCreatedAt":"2021-10-20 15:30:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-727204","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-727204","identity":"rs-727204","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}