Coagulation/flocculation optimization and sludge production for pre-treatment of paint industry wastewater

Abstract

This study examined the optimization of paint industry wastewater pre-treatment by means of coagulation and the quantity of produced sludge generated. In preliminary tests, high concentrations of alum, PACI, and FeCl₃ were used, and removal efficiencies were determined to be 86–88%, 100%, and 46–72% for chemical oxygen demand (COD), SS, and color, respectively. Actual studies were conducted by adding lower concentrations of coagulants to reduce the produced sludge quantity due to the addition of coagulants at high concentrations. In those studies, COD removal efficiency decreased by 10%, while suspended solids and color removal increased. The optimum removal efficiency was obtained by adding 250 mg/L alum and FeCl₃, and the optimum anionic polyelectrolyte dose was found to be 4 mg/L. When equal amounts of coagulants were dosed, the quantities of sludge were found to be FeCl₃ > PACl > FeSO₄ ≥ alum. Considering the treatment efficiency and quantity of sludge together, the most economical solution with 0.077 $/m³ wastewater was obtained by FeSO₄. The cost of sludge disposal in the wastewater treatment plant is remarkable. The amounts of sludge should also be considered along with the removal efficiency during the detection of suitable treatment alternatives.

Keywords:

• Optimization
• Coagulation–flocculation
• Paint industry
• Sludge volume