Ecological study of activated sludge settling property in the completely mixed system

The bulking problem associated with both nitrogen-rich and nitrogen-deficient activated sludges was thoroughly investigated under a DO sufficient condition in the completely-mixed continuous flow system. The reactor temperature was controlled at 27 ± 1°C and the pH was maintained at nearly equal to 7.0. The activated sludge cultures were acclimated under various organic loadings and their settling characteristics were determined by sludge volume index and zone settling velocity. The contents of sludge protein and carbohydrate along with the cell surface charge were examined for understanding the correlation between sludge composition and sludge settleability. Also, the major types of long-length filaments existed in the bulky activated sludge were identified. Moreover, the effect of sludge settleability on effluent quality was determined.