Effect of Glucosuria on the Perfomance of Small-scale Onsite Wastewater Treatment Plants-II. Biotreatment Characteristics

Experimental investigations using the model reactors of both separation and aeration in the small-scale onsite wastewater treatment plant (SOWTP) was carried out in order to evaluate its malfunction for domestic use caused by glucosuria. When wastewater containing glucosuria was anaerobically digested, acid fermentation occurred, causing accumulation of volatile fatty acids (VFAs) at high concentrations. When the BOD loading was high, the VFAs generated were primarily malodorous propionic acid, butyric acid, and valeric acid. Therefore, the decreases in pH and the occurrence of a bad odor in the sedimentation-separation chamber (the primary treatment chamber) of SOWTPs are considered to be due to acid fermentation of glucosuria. Furthermore, when the anaerobic digestion effluent (the primary effluent) was treated with activated sludge at a BOD-SS loading of 0.31 kg/kg·day or less, the BOD removal efficiency was 93%or higher if DO was maintained at a high level. Therefore, the lack of air supply in the aeration chamber (the secondary treatment chamber) is considered to be a major cause of deterioration of the final effluent, and that quality of the final effluent is considered to be improved by a marked increase in the air supply.