A Novel Two-stage Bioreactor For Domestic Wastewater Treatment Pilot Study

In this paper, a novel technology using a two-stages bioreactor in order to achieve wastewater reclamation was developed. It was combined with a granular sequencing batch reactor (SBR) and a membrane bioreactor (MBR). During the first process, the organic matter could be removed effectively by the cultivated aerobic granules in the SBR. At the same time, little excess sludge was produced while the suspended solid (SS) washed out with the effluent became the nutrient of the protozoan and metazoa in the MBR. The second process could have the wastewater further treatment on the basis of the first process to improve the effluent quality, and realize the excess sludge reduction through the microfauna predation.The aerobic granules could be cultivated successfully in the SBR by changing the operating conditions, and the shorter settling time was the primary affecting factor. The zoogloea granules predominated in the lower settling velocity, then filamentous microorganisms granules could be formed with the increasing of the settling velocity. The organic loading rate (OLR) had some effects on the granular structure. With the increasing of OLR, higher settling velocity and denser granules could be shaped, but the removal efficiency of COD did not alter obviously. The removal of organic pollutants happened during the former period mainly. The removal efficiency of ammonia nitrogen was about 24%, while nitrate and nitrite were almost absent in the effluent. Simultaneous nitrification and denitrification might occur in the reactor.Adding PAC to the MBR could ameliorate the characteristics of sludge mixture and reduce the membrane fouling effectively. The effluent quality could also be advanced and reused after some other relevant treatment. Results showed that the combined technology could improve the membrane filtration performance evidently and increased the using period of membrane. The adsorption effect of PAC reduced the membrane fouling caused by EPS. The presence of PAC on the membrane surface minished the thickness of the concentration polarization and hydraulic boundary layer. The transferring velocity of the filtered matter was enhanced. At the same time, the PAC layer could also filter the microorganisms and colloids to cut down the amount landing on the membrane surface.The combined process could ensure the effluent quality without discharging sludge. The COD was reduced by 95% and the ammonium concentration in the effluent was under 1mg/L. There was no SS in the effluent, and the turbidity was less than 0.3NTU. At the same time, the membrane fouling could be alleviated and the cleaning and replacing period was prolonged.The two-stages bioreactor is not only the way of sludge reduction but also the effective measure to prevent the membrane fouling. It is a high efficiency and saving energy novel technology to realize the wastewater reclamation, which shows good economic and environmental benefit and broad market.