Coagulation/flocculation process in the treatment of abattoir wastewater

Abstract

The coagulation/flocculation process was used at laboratory bench scale for the removal of chemical oxygen demand (COD), total suspended solids (TSS) and total phosphorus (TP) in abattoir wastewater. The wastewater was allowed to settle for 24 h and TSS and TP removal efficiencies of 65% and 32% were achieved, respectively. Alum, ferric chloride and ferric sulfate were employed during the coagulation/flocculation process. Alum proved more effective in the reduction of TSS and TP present in the wastewater, whereas ferric sulfate was more effective in the reduction of COD. Increasing the dose of alum to 750 mg/l caused the removal efficiency of TP to reach 45%. The rate of removal of TP linearly increased with increasing doses of alum, resulting in a 98% removal efficiency of TP at 1000 mg/l dose of alum. At a 95% confidence interval, alum dose, coagulation velocity gradient/rapid mixing time (coagulation Gt) and flocculation velocity gradient/slow mixing time (flocculation Gt) were not significant for TSS removal efficiency, but alum dose was significant for TP removal. The addition of a polyelectrolyte to an inorganic coagulant proved effective in the reduction of COD, TSS and TP, cut the amount of coagulant used and reduced the cost of the coagulation/flocculation process. A significant degree of particle elimination by size was produced by using alum; this improved further with the addition the polyelectrolyte.