Optimization of Coagulants for Pretreatment of Printing Ink Wastewater

This study was aimed at the optimization of a coagulant agent for the treatment of printing ink wastewater generated from a currency printing press through flocculation studies. Coagulant agents, viz. ferric chloride and polyaluminum chloride, were evaluated to select the most suitable coagulant for effective treatment, and attain the optimum coagulant concentration in comparison to calcium chloride being presently used. Cationic polyelectrolyte, in conjunction with the most effective coagulant, was also studied to assess its effect on floc settleability. Polyaluminum chloride (PAC) was found to be the most efficient coagulant, achieving color, suspended solids (SS), biochemical oxygen demand (BOD), and chemical oxygen demand (COD) removals of 96, 97, 63, and 58%, respectively, at an optimum concentration of 1500 mg/L. Ferric chloride did not show substantial removals of color, BOD, and COD, except suspended solids in comparison to the performance of PAC. Cationic polyelectrolyte, in combination with PAC at an optimum concentration of 1,500 mg/L of PAC and 1.0 mg/L polyelectrolyte, further improved the removal efficiency of various parameters studied, in addition to improving the floc settling rate, and reduction in quantity of sludge generated. In comparison to calcium chloride presently in use at the currency printing press under study, performance efficiency of PAC in conjunction with cationic polyelectrolyte proved to be more effective. In addition, reduction in volume of sludge generation was 62.5% by using PAC and polyelectrolyte compared to calcium chloride. Cost analysis revealed that use of PAC and polyelectrolyte at optimum concentrations would result in a savings of around 56% in recurring cost of coagulant for a flow of 75 m³ per day.