Survey on Chlorine Application in Sequencing Batch Reactor Waste Sludge in Order to Sludge Minimization

Abstract

The ultimate disposal of excess sludge generated from activated sludge processes has been one the most challenging problems for waste water treatment utilities. To solve the problem of excess sludge production, oxidizing the excess sludge by chlorine, thus reducing the biomass coefficient as well as the sewage sludge disposal is a fine idea. In this study, two sequencing batch reactors, each with 20 L volume were continuously operated with synthetic wastewater under the same conditions. After providing the steady state conditions in the reactors, sampling and testing of parameters were done for several months. During this period, one pilot unit was used as the reference system without chlorination of excess sludge, while another served as a testing unit. The results showed that during the solid retention time of 10 days the kinetic coefficient of Y and Kd were 0.60 mg biomass/mg COD and 0.068/day, respectively. At the next stage, different concentrations of chlorine were used in excess sludge and the chlorinated liquor was then returned to the aeration tank. Results showed that 0.26 g chlorine/g MLSS in return excess sludge to the reactor was able to reduce the yield coefficient from 0.60 to 0.3 mg biomass/mg COD. In other words, the biological excess sludge was reduced ca. 50 %. But the soluble chemical oxygen demand increased slightly in the effluent and the removal percentage decreased from 95 % in the blank reactor to 56 % in the test reactor.