Chemical coagulation-flocculation shows effectiveness in reducing turbidity and COD in coffee processing mill effluent, indicating the importance of pH levels.
The effectiveness of chemical coagulation-flocculation for treating coffee processing mill effluent (CPME) was evaluated in this study using various commercial coagulants, such as ferric chloride, aluminium sulphate (alum), polyaluminum chloride, ferrous sulphate, chitosan, alum-lime, and ferric chloride-lime. Untreated CPME initially had a pH of 4.5, which increased to between 5 and 9 after pH adjustment with 0.25 M sodium hydroxide. Alum demonstrated the best performance, achieving 98% turbidity removal, 30% COD reduction, 85% NH₃-N removal, and complete iron removal at an optimal dosage of 1000 mg/L. The effect of pH on coagulation-flocculation effectiveness was also investigated, with alum being most effective at pH 7–8. While turbidity and iron were effectively removed using alum, its performance in reducing COD and color was limited. Additionally, NH₃-N removal efficiency varied with alum dosage, but residual nitrogen was consistently present in the effluent. As none of the treated samples met the Environmental Quality (Industrial Effluent) Regulation 2009 Standard B discharge limits, particularly for COD and color, post-treatment is necessary. Adsorption is suggested as a viable post-treatment technique to improve CPME treatment quality and ensure compliance with regulatory standards. Integrating coagulation-flocculation with adsorption may offer a more effective and environmentally friendly approach for CPME treatment.
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Hasan et al. (2025) studied this question.
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