Comparative study of the efficacy of three coagulants in treating dairy factory waste water

The treatment of dairy factory waste water by coagulation and decantation has shown that calcium hydroxide at a weak dose of 0.49-0.63 g provides the highly efficient removal of suspended matter (SM) (94%) and total phosphorus (Tp-P) (89%) accompanied by an average elimination of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN-N), faecal coliforms (FC) and faecal streptococci (FS). This is within the Moroccan limits for the first two parameters (SM and TP-P). The dose necessary to obtain optimal removal is 0.8-1.2 g when using aluminium sulfate and 0.6-0.75 g with iron chloride and the percentage elimination of chemical and bacteriological pollutants is not substantial. However, coagulation by calcium hydroxide induced less sludge (0.93 g/L) than either aluminium sulfate (1.21 g/L) or iron chloride (1.38 g/L). In terms of cost, the price of treating 1 m(3) of dairy effluent by using calcium hydroxide is lower (approximately 25 times less expensive) than when using the other two coagulants.