Mechanism of high contaminant removal performance in the expanded granular sludge blanket (EGSB) reactor involved with granular activated carbon for low-strength wastewater treatment

The sludge granulation in an anaerobic bioreactor is rather difficult for treating low-strength wastewater. In this study, an expanded granular sludge blanket (EGSB) reactor involved with granular activated carbon (GAC) was employed to treat wastewater at different operational conditions. In general, a stable COD removal performance was operated at the HRT condition of 8, 6, 5, and 4 h, and Vup ranges from 1.09 to 2.44 m h−1. However, the NH3-N removal efficiency was at a relatively low level resulted from the nitrification efficiency was limited to the low dissolved oxygen concentration in anaerobic bioreactor. Adding GAC to the raw sludge, the average size of granular sludge and enzymatic [dehydrogenase activity (DHA) and specific methanogenic activity (SMA)] activities presented an increase trend with the experiment grows. In addition, the promotion of organic load rate (OLR) and Vup might stimulate the external mass transfer effect in EGSB reactor, which resulted in the increase of extracellular polymeric substances (EPS) content. DNA sequencing analysis demonstrated that the growth of Aeromonas genus was the main reason for the unstable distribution of acetoclastic and hydrogenotrophic methanogens in HRT condition of 4 h.