Optimization of chemical dosing for enhanced treatment of textile industrial wastewater

The textile industry, mainly denim washing operations, produce large quantities of complex wastewater with high turbidity, intense colour, high chemical oxygen demand (COD) and high suspended solids due to the presence of dyes, surfactants and processing chemicals. In this study, wastewater samples were collected from the equalization tank inlet of Fabricraft Impex Pvt. Ltd. (Wanjra Industrial Layout, Kamptee Road, Nagpur, India) in order to evaluate and improve the chemical dosing strategy in primary treatment using coagulation–flocculation. The raw wastewater is highly pollutant with COD 1850 mg/L, BOD 620 mg/L, TSS 480 mg/L, turbidity 850 NTU and color 1250 Pt-Co units and needs to be treated correctly before discharge or further biological processing. As coagulants, three commonly used coagulants—alum, ferric chloride and polyaluminum chloride (PAC)—were studied together with polymer as coagulant aid. The pH of the jar test experiments was carried out to determine the best coagulant dosage, pH and settling time. The optimization study revealed that PAC with polymer works better than other coagulants. At a dosage of 60 mg/L PAC and 2.0 mg/L polymer with pH 7.2, they have the highest removal efficiency (88.2 % for COD, 84.5 % for BOD, 93.5 % for TSS, 96.1 % for turbidity and 93.5 % for colour). The better results can be attributed to charge neutralization, fast formation of flocs and settling time of the solution. The optimized dosing can also reduce the chemical consumption and sludge generation compared to traditional dosing. The importance of the coagulation parameters in textile wastewater treatment plants in order to improve treatment efficiency and sustainable operation is also highlighted in the present paper. The study developed methodology is practical and scalable for industrial use and meets discharge requirements and has minimal operational costs.