Study on Activated Sludge Processes without Sludge Wasting for Wastewater Treatment

The operation without sludge wasting from activated sludge processes for wastewater was studied by increasing the solid retention time (SRT) as long as possible. Two sets of activated sludge processes were prepared: one was an usual activated process with 8 hours detention time. To another was added an anaerobic tank with 2 hour detention time, to observe the effects of an anaerobic condition on sludge production. Both processes treated the effluent from a primary settling tank of a municipal wastewater treatment plant in Fukui City, Japan, and were operated for about 160 days without withdrawing any excess sludge. After the MLSS was accumulated to around 10,000mg/L, both processes were suffered from the washout of sludge from the sedimentation tank, and the quality of effluent was not very bad. The anaerobic tank appeared to have little influence on sludge reduction. The experimental results implied that it was proper to maintain the MLSS below a certain concentration