Comparative performance evaluation of chemical coagulants in dairy wastewater treatment: a multi-criteria...

This study evaluates the performance of an Effluent Treatment Plant (ETP) at a dairy industry in Bangladesh and investigates the potential of physicochemical pretreatment methods using chemical coagulants. Influent and effluent samples were collected three times over three seasons and analyzed for key parameters, including pH, BOD, COD, TDS, and TSS. The results confirmed that on all three occasions, the tested parameters were within the permissible discharge limits set by the Environmental Conservation Rules (ECR) 2023 of Bangladesh. ETP demonstrated high treatment efficiency, achieving maximum removal rates of 98.3% for BOD and 97.1% for COD. To assess the feasibility of pretreatment, experiments were conducted using three conventional chemical coagulants: FeSO₄, PAC, and FeCl₃ with lime as a coagulant aid. However, no single coagulant combination excelled in removing all pollutants simultaneously. To address this challenge, three Multi-Criteria Decision Making (MCDM) methods: AHP, TOPSIS, and PROMETHEE II were employed. These methods consistently identified Lime + FeSO₄ (100 mg/L + 100 mg/L) as the most effective dosage, achieving 93.51% BOD, 85.50% COD, 51.71% TDS, and 93.95% TSS removal. This study underscores the utility of MCDM in wastewater treatment optimization and highlights the potential of chemical pretreatment.