Characteristics of Organics Transformation and Sludge Morphology in an ABR for Sewage Treatment with Different HRTs

The characteristics of organics transformation and sludge morphology of in an ABR(anaerobic baffled reactor) for sewage treatment with different HRTs were investigated based on reactor performance, particle size distribution, and scanning electron microscopy (SEM). Results showed that the COD removal rate was stably maintained above 90.0% when the HRT decreased from 15 h to 4 h. However, the first compartment of ABR contributed to 90%, 78.56%, 74.18%, and 58.91% of the total COD removal when the HRT was 10, 7.5, 5, and 4 h, respectively. When the HRT was reduced, the total amount of volatile fatty acids (VFAs) in the first compartment of ABR significantly increased, and the abundance of acetic acid, being the major constituent of VFAs, gradually increased from 51.36% to 58.77%; the concentrations of butyric acid and propionic acid were maintained and constituted a minority of the VFAs. The sludge morphology in ABR significantly changed in the wake of run time. On day 111, granulation of sludge was achieved. Additionally, the degree of sludge granulation showed a decreasing trend with the direction of water flow. SEM observations of granular sludge showed that the separation of biomass did occur in the ABR. Along the direction of water flow, filamentous bacteria, M. methane, monococci, and bacilli were the dominant microbes in each compartment of the ABR.