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Low-energy cost wastewater treatment is required to change its current energy-intensive status. Although promising, the direct anaerobic digestion of municipal wastewater treatment faces challenges such as low organic content and low temperature, which require further development. The hydrolysis-aerobic system investigated in this study utilized the two well-proven processes of hydrolysis and aerobic oxidation. These have the advantages of efficient COD removal and biodegradability improvement with limited energy cost due to their avoidance of aeration. A pilot-scale hydrolysis-aerobic system was built for performance evaluation with actual municipal wastewater as feed. Results indicated that as high as 39–47% COD removal was achieved with a maximum COD load of 1.10 kg/m3·d. The dominant bacteria phyla included Proteobacteria (36.0%), Planctomycetes (15.4%), Chloroflexi (9.7%), Bacteroidetes (7.7%), Firmicutes (4.4%), Acidobacteria (2.5%), Actinobacteria (1.8%) and Synergistetes (1.3%), while the dominant genera included Thauera (3.42%) and Dechloromonas (3.04%). The absence of methanogens indicates that the microbial community was perfectly retained in the hydrolysis stage instead of in the methane-producing stage.

Chemical companies, food industries usually produce wastewaters with high salinity. In consideration of economy, biological methods are preferred to physicochemical methods to remove organic matters. When sequence batching reactors are applied, aeration rate is of great importance to the COD removal efficiency. In this bench scale experiment, the aeration rate of 0.40 m3/m3.min led to sludge disintegration, poor COD removal efficiency and superfluous foam. After sludge conditioner addition, the aeration rate of 0.19 m3/m3.min led to good sludge flocs, satisfactory COD removal efficiency and few foam. It is the oxidizing environment caused by the high dissolved oxygen that harmed the sludge and made it work with low efficiency.