Abstract
Characterization of organic matter in return flow from sludge treatment processes is essential for their effective to use nutrient removal process. This characterization showed that (1) the return flows from sludge thickening unit and dewatering unit contain higher percentage of readily biodegradable organic matter than sewage, and (2) it is not adequate to use the return flows from anaerobic digestion unit and sludge incineration process because of their low concentration ofbiodegradable organic matter, high nitrogen content, and high soluble inert organic matter. Simulation based on the Activated sludge model showed that (1) separate application of return flow in a two stepanoxic-aerobic nitrogen removal process is effective, such that sewage is fed to first anoxic zone whereas the return flow is fed to second anoxic zone; and (2) the centralized sludge treatment plant processing the sludge from 650, 000m3/day-sewage treatment is required to treat the nitrogen contained in 50, 000m3/day-sewage.
