Behavior of Nitrogen and Phosphorus during Batch Aerobic Digestion of Waste Activated Sludge. Continuous aeration and intermittent aeration by control of ORP

Abstract

Waste activated sludge samples from a municipal wastewater treatment plant were digested under 40-50 days batch operation, aerating continuously and intermittently, in order to find economical aeration systems. The cycle time of intermittent aeration was decided so that the ORP of the digestion liquid did not fall below 0 mV or 150 mV. Although the reduction rates of sludge solids were lower than in continuous aeration because of the extreme shortening of the aeration period, no odor problem was created and the digested sludge was completely stabilized. It was found that the percentage of liquid-phase nitrogen (phosphorus) in the initial total nitrogen (phosphous) decreased under intermittent aeration controlled by ORP. Also, the change of content of nitrogen and phosphorus in sludge solids suggested that biomass with low nitrogen content was decomposed in the first stage of aerobic digestion and that with high nitrogen content was decomposed thereafter. Operation by ORP control did not generate any froth in the digestion tank. © 1989, The Society of Chemical Engineers, Japan. All rights reserved.