Treatment of animal waste through algal-daphnid-chemical coagulation system

Abstract

A type of animal waste, cow``s liquid manure, which is specially high in nitrogen and phosphorus components, was tried to be treated with a combined system including algal culture, $\mbox{\underline{Daphnia}}$ culture, and chemical coagulation in a continuous basis. The manure was first diluted with water to a proper concentration and algal cells of mixed species were cultured in it. The algae removed 58\% and 99\% of initial nitrogen and phosphorus in the manure, respectively. On the other hand, the COD content in the waste increased dramatically due to the increase of algae biomass. The algal cells were then fed to $\mbox{\underline{Daphnia}}$ in the second stage of the treatment system. $\mbox{\underline{Daphnia}}$ could remove about 71\% of the COD content in the secondary stage influent. $\mbox{\underline{Daphnia}}$ contained 75\% of protein and could be harvested easily using a screen of proper pore size. At the third stage, the contents of remaining COD, and phosphorus were removed by precipitating with aluminum sulfate. When the precipitation was proceeded under conditions of pH 8.5 and 20$^\circ$C, the amount of aluminum sulfate needed for optimum precipitation of COD was 100 mg/l, whereas 400 mg/l was needed for 95\% phosphorus removal. Through the whole continuous three-stage system, 95\% of the particulate COD and 98\% of the phosphorus could be removed, whereas the nitrogen removal was only 72\%.