Nationwide Assessment of Sludge Production of Wastewater Treatment Plants in China

Sludge handling is becoming one of the bottlenecks in dealing with wastewater treatment plants (WWTPs) management issues. A comprehensive nationwide WWTPs investigation program was performed to analyze the key design parameters (scale, treatment process, and effluent standard), chemical oxygen demands (COD) reduction, and geographical distribution of WWTPs in terms of sludge production. It was found that integrated effects of key factors on sludge production should be given full consideration. To achieve the minimal unit sludge production, membrane bioreactor can be the best candidate (0.390 kg/m3). Besides MBR, biological filter is the best option for small- and large-scale WWTPs (<5 × 104 m3/day and 10-20 × 104 m3/day), whereas sequencing batch reactor is suitable for medium-scale and super large-scale WWTPs (5-10 × 104 m3/day and >20 × 104 m3/day) and oxidation ditch is not fit for large-scale WWTPs (10 × 104 m3/day to 20 × 104 m3/day). Comparatively, the effects of WWTP treatment process on unit sludge yield prevail over those of effluent discharge norm. In general, there was a marked positive correlation between COD reduction and sludge production. Additionally, unit WWTPs sludge production per COD reduction was summarized systematically. The present work will assist in understanding of how and to what extent key factors are incorporated in design guidelines and also help decision makers and engineers construct and upgrade WWTPs in the best possible way.