Saeed Rajabi, Fahimeh Ahmadian, Sobhan Maleky, Hassan Hashemi
Abstract Oily wastewater from machining processes poses significant environmental challenges due to its high organic load and stable emulsions, rendering conventional treatment methods ineffective. This study investigated the optimization of the coagulation/flocculation process for treating machining oily effluent using response surface methodology (RSM). Systematic optimization of the impact of critical parameters, including FeCl 3 dosage, pH, temperature, and reaction time, was conducted to achieve the optimum chemical oxygen demand (COD) removal efficiency. Under 2.5 g/L FeCl 3 , pH of 7, 25 °C temperature, and 30 min reaction time, optimal conditions, a maximum 80.42% COD reduction was achieved. The RSM model demonstrated good prediction ability, reflecting strong interactions between the process variables and predicting the efficiency of the treatment. Unlike conventional coagulation procedures, this optimized approach raises the pollutant removal rate while reducing chemical consumption and sludge generation, making it a greener industrial option. The general study also indicated the influence of wastewater components on defining coagulation efficiency, requiring process versatility in different industrial settings. Such findings form part of developing cost-effective, environmentally friendly wastewater treatment technologies consistent with legislative discharge requirements. Future research must focus on further integrating this method with advanced treatment technologies to improve overall efficiency and sludge management.