Performance Evaluation of the Coagulation and Flocculation Process in Removing Pollutants from textile Dyeing Factory Wastewater

Background and Objective: In this research, the performance of coagulation and flocculation process for the removal of pollutants from raw wastewater as well as anaerobic unit effluent of biological treatment of textile dyeing factory wastewater treatment plant was investigated. Methods: For this purpose, the Jar test unit as a batch reactor, FeCl3, PAC, and Alum as coagulants, and two polyelectrolytes, namely, Zetafloc 7563 and Megafloc 3045PWG as cationic and anionic flocculants were used and the effect of coagulant dosage and type as well as flocculant type on removal of COD, turbidity and color were investigated in two stages. Findings: The results of coagulation and flocculation experiments on raw wastewater showed that Alum at concentration of 40 mg/L was the most effective coagulant with COD, turbidity and color removal efficiency of 73.1±1.5%, 93.7% and 71.7%, respectively. However, the results of coagulation and flocculation experiments on the effluent from biological anaerobic treatment unit showed that the highest percentage of COD and turbidity removal were 52.2±2.6% and 99.1%, respectively that corresponds to PAC with concentration of 2000 mg/L. Additionally, the COD removal efficiency of FeCl3 coagulant at concentration of 400 mg/L was 52.2±3.5%. The difference in the results of the two stages was due to the change in the nature of the pollutants after exposure to biological treatment and different pH of the wastewater used in these stages. Discussion and Conclusion: A general review of the results showed that use of physicochemical treatment applying only coagulation and flocculation process could not reduce the pollutants present in the dyeing wastewater for reuse, while this method could be considered as a pretreatment or one of the secondary treatment steps and post treatment.