Treatment of Slaughterhouse Plant Wastewater by Sequential Chemical Coagulation-Continuous Flow Electrooxidation Process Nawid Ahmad Akhtar, 1 Erhan Gengec, 2,z and Mehmet Kobya 1,3 1 Kyrgyz-Turkish Manas University, Faculty of Engineering, Department of Environmental Engineering, 720038, Bishkek- Kyrgyzstan 2 Kocaeli University, Department of Environmental Protection Technology, 41285 Kartepe, Kocaeli-Turkey 3 Gebze Technical University, Faculty of Engineering, Department of Environmental Engineering, 41400, Gebze-Turkey Wastewater from a small animal slaughterhouse (SWW) was treated by a two-step process: coagulation/flocculation (CF) followed by continuous flow electrooxidation (CFEO). Initially, a coagulant dose of 0.8 kg m −3 in the CF process, using FeCl 3 at pH 8.5, achieved 52% COD and 63% turbidity removal (effluent: 2000 mg l −1 and 65.2 NTU). Alum, (optimum pH = 6.5), yielded 50% COD and 55% turbidity removal (effluent of 2100 mg l −1 and 78.5 NTU). Subsequently, when employing the CFEO process following the CF process with FeCl 3 , the study achieved highly efficient results. Specifically, under optimum conditions (residence time in the CFEO reactor, τ = 240 min, wastewater feed rate to the reactor = 15 ml min −1 , and current density = 300 A m −2 ), the COD and turbidity removal efficiencies reached 99.60% (resulting in an effluent of 8 mg l −1 ) and 99.9% (resulting in an effluent of <0.10 NTU), respectively. In conclusion, the CF + CFEO consecutive treatment process demonstrated remarkable treatment efficiencies, with COD and turbidity removal rates of 99.9% and 99.9%, respectively. Moreover, the total operating cost of this treatment process was found to be 3.60 US $/m 3 . © 2024 The Electrochemical Society (“ECS”). Published on behalf of ECS by IOP Publishing Limited. [DOI: 10.1149/1945-7111/ ad6192] Manuscript submitted December 25, 2023; revised manuscript received July 3, 2024. Published July 24, 2024. In recent years, it has become critical to build and secure the environment against population growth and rapid industrialization. 1 Wastewater from the industrial sectors consists of a mixture of many different chemicals that can be classified as non-biodegradable, hardly biodegradable, and easily biodegradable components. Waste generated from industrial processes has increasingly become a major environmental problem in recent times. 2 Industrial wastewater needs to be treated and reused in different industrial processes; therefore, it is necessary to use treatment approaches that facilitate the reuse of this water. 3 Slaughterhouses are a large industry because meat is a major component of the diet of billions of people in nations across the world. Meat production and consumption have surged globally over the years. According to the Organization for Economic Co-operation and Development estimates, annual meat production is expected to reach 366 Mt by 2029. The average water requirement to produce a tonne of meat is estimated at 15,500 m 3 , 4800 m 3 , 6100 m 3 , and 4000 m 3 for cattle, pigs, sheep, and poultry, respectively. 4 Consequently, an overwhelming 1.5–18 m 3 of effluent is generated for each tonne of meat produced, which significantly impacts the global water balance. More specifically, the slaughter of cattle and pigs generally produces 1.6–9m 3 of wastewater per tonne of meat, while sheep and poultry slaughtering generate 5–8.3 and 5–15 m 3 of wastewater, respectively. 5 Slaughterhouse wastewater (SWW) is one of the most critical environmental problems because of the consumption of copious volumes of water during slaughter, meat processing, cleaning, and disinfection. 6 Waste from meat processing can be categorized into solid (15%) and liquid (85%) wastes. The SWW is characterized by a wide pH range of 4.8 to 8.10, turbidity of 200–300 NTU, total dissolved solids (TDS) measuring between 870 and 1010 mg l −1 , color intensity levels of 4500–6100 mg l −1 Pt-Co units, total suspended solids (TSS) between 270 and 6400 mg l −1 , and chemical oxygen demand (COD) levels between 500 and 15900 mg l −1 . 7,8 Meat processing produces substantial volumes of wastewater, characterized by a high biochemical oxygen demand (BOD) that can reach 8,000 mg l −1 , or 10–20 kilograms per metric ton (kg/t) of processed animal. Notably, among the various liquid effluents originating from slaughterhouses, blood exhibits the highest chemical oxygen demand (COD) levels, reaching up to 375,000 mg l −1 . 9 Physicochemical, biological, and advanced wastewater treatment processes are used for the treatment of SWW. 10 Biological treatment approaches (aerobic and anaerobic) for SWW have proven particu- larly difficult and generally infeasible, as these processes require a large area, the sensitivity of the microorganisms to chemical complexes, high operating costs, long residence times, and can leave floating oils in the rector. 11 Pretreatments such as coagulation/ floatation and filtrations are required before applying biological treatments. 12 Treatment by coagulation/flocculation of the SWW is cost-effective and efficient. 13 In the coagulation/flocculation process, the first stage aims to electrically destabilize the pollutant particles in wastewater; the second stage allows the destabilized particles to aggregate and form flakes, which are finally separated from the wastewater by sedimentation or flotation. 14,15 Cationic inorganic metal salts and long-chain non-ionic or anionic polymers are used mostly as coagulant dosages in the process. 16 However, this process has the disadvantage of generating a high amount of sludge due to high dosages of coagulants and chemicals. 17 In a study by Bazrafsan et al. 18 some pollutant removal efficiency from SWW by chemical coagulation was reported as 58.5%, COD, 44.9%, BOD 5 , 60% TSS, and 40% TKN under optimum conditions (polyaluminum chloride (PACl) coagulant dosage of 100 m l −1 and pH of 7). In another study by Amuda and Alade, 19 the removal efficiencies of COD, TSS, and TP by CC process under optimum conditions (alum coagulant dosage of 750 mg l −1 and pH of 8.5) were found to be 65, 34, and 45%, respectively. A study conducted by Gökçek and Özdemir 17 using the CC process for slaughterhouse wastewater treatment reported COD, TSS, and turbidity removal efficiencies of 75.2, 90.2, and 91.2%, respectively, and optimum alum coagulant dosage of 1000 mg l −1 and pH of 6.5. In another study by Tariq et al. 20 under optimum conditions (alum coagulant dosage of 2500 mg l −1 and pH of 6.5) COD, BOD 5 , and TSS removal efficiencies were found to be 85, 98, and 77%, respectively. These results concluded that the pollutant concentration in the effluent of the coagulation-flocculation process does not meet the effluent discharge standards for the environment. Therefore, the wastewater from conventional coagulation needs to be preceded by another treatment process to complete the treatment. Advanced methods or integrated physicochemical and biological approaches have proven efficient in SWW treatment because of relatively lower time demand and reduced sludge formation. 21,22 In recent years, electrochemical technologies have played a major role in the treatment of wastewater. 23–28 Electrochemical technologies z E-mail: erhan.gengec@kocaeli.edu.tr Journal of The Electrochemical Society, 2024 171 073505 1945-7111/2024/171(7)/073505/15/$40.00 © 2024 The Electrochemical Society (“ECS”). Published on behalf of ECS by IOP Publishing Limited