Decomposition of Biological Waste Sludge by Thermophilic Bacteria

Abstract

Conventional activated sludge (AS) process is an economical and effective biooxidation process although a large amount of excess sludge is necessarily generated. We have developed a sludge decomposing process formed by combining the conventional AS process with thermophilic aerobic sludge digester where the excess sludge is solubilized by thermophilic enzyme (S-TE reactor) secreted by thermophilic bacteria The excess sludge withdrawn from the AS process is subjected to S-TE reactor, followed by its circulation to an aeration tank. Remarkable decomposition of the excess sludge is carried out when the sludge is solubilized by thermophilic bacteria (e. g. Bacillus sp.) and mineralized by mesophilic bacteria. Bench-scale test using artificial wastewater for over 100 days showed that no excess sludge was generated when 3-fold amounts of the excess sludge generated in the conventional AS proc- ess was subjected to the S-TE reactor. A pilot-scale facility of the process has been operated with a petrochemical plant wastewater for a year. It was demonstrated that excess sludge generation was completely reduced in the new process. According to our estimates, total operating costs for the new process is reduced to 40-50% of those of conventional wastewater dewatering process.