Upgrading activated sludge systems and reduction in excess sludge

► Optimum HRT for COD removal (about 80%) can be considered 4 h at 30 °C. ► Removal of COD is maximum in the organic loading range of 7.2-10.8 kg COD/m3 d. ► Such a system upgrading will increase treatment capacity by factor of 5. ► The excess sludge reduction was over 90% with overall SRT of 100 days. ► Filamentous bacteria about 100 have no adverse effects on membrane performance.