Abstract
To reuse the coagulant contained in water supply sludge, the coagulant was extracted using H2SO4 and its removal ratios for 117 types of pesticide and 14 types of metal on coagulation and sedimentation were studied compared with those of Al2(SO4)3 and polyaluminum chloride (PAC). For inflow (pH 6.0) at a sewage treatment plant using 2 μl · ml-1 (11.6 μg · ml-1 as Al) recovered coagulant, the removal ratios were as follows: organochlorine pesticides, 13.1-100%; organophosphorus pesticides, 10.8-100%; carbamate pesticides, 5.1-67.7%; nitrogen-containing pesticides, 0-100%; pyrethroid pesticides, 39.1-100%; other pesticides, 5.5-100%; and decomposition products of pesticides, 0-100%. The removal ratios of the recovered coagulant for 93 pesticides were higher than or the same as those of Al2(SO4)3 [50 μg · ml-1 (7.9 μg · ml-1 as Al)] and PAC [50 μg · ml-1 (3.2 μg · ml-1 as Al)]. On the other hand, the removal ratios of the recovered coagulant for metals were —106-100% and the remaining ratios for six metals including Al and Mn were more than 100% because those metals were contained in the recovered coagulant.
