Research On A Combined System Of Membrane Bioreactor And Worm Reactor For Sludge Reduction And Membrane Fouling Mitigation

Membrane bioreactor (MBR) is combined the active sludge process and membrane separation together. It has many merits, such as, low sludge production, high quality effluent and small footprint, while membrane fouling has become a key factor, which limits its development and wide spread. Mico-fauna’s predation can achieve sludge reduction, as well as, sludge characteristic transform or change, though mico-fauna’s predation or digestion on active sludge floc and microbes. In this study, a combined system of MBR and worm reactor was established, and1) the efficiency of wastewater treatment,2) the performance of sludge reduction,3)and the mechanism of membrane fouling mitigation of the combined system were analyzed.Firstly, the study of Tubificidae-reactor showed delightful performances in optimum operation condition. The amount of average sludge reduction and efficiency were481±84mgMLVSS·L-1·d-1and30%, respectively. The characteristics of sludge between Tubificidae-reactor and none-Tubificidae-reactor had change a lot. Contracted with the none-Tubificidae-reactor, the MLVSS/MLSS of sludge, in Tubificidae-reactor, decreased from0.835to0.778, and the sludge volume index (SVI) of sludge flocks changed significantly, from234mL/g to151mL/g, which means the salting ability of sludge had been greatly improved. Nutrient release during predation was controlled effectively, due to the simultaneous nitrification and denitrification in the Tubificidae-reactor. It showed that NH4+-N and COD release could be reduced by63.0%and72.5%, respectively.A new process that combined a membrane bioreactor (S-MBR) and a novel worm reactor was also proposed in this study. The removal efficiencies of chemical oxygen demand (COD) and NH4+-N of the combined system reached to93.6±3.2%and96.4±4.5%, respectively. The COD and total nitrogen (TN) discharge rate in the combined system were only14.4%and57.1%, which much less than that of the conventional MBR, indicating an excellent performance of wastewater treatment. Compared with the conventional MBR, the combined system got a high percentage of sludge reduction of81.8%, and the SVI and specific resistance filtration (SRF) of the combined system decreased33%and35%, respectively. The combined system enhanced the salting ability and dewater capability of the sludge remarkably. The combination of MBR and worm reactor had an alleviation of membrane fouling on both sludge cake fouling and membrane pores clogging. The trans-membrane pressure (TMP) of the combined system reduced91.2%, when contrasted with the conventional MBR. Finally, the mechanism of the fouling mitigation of the combined system was analyzed. The clogging tendency of both soluble and collide organic pollutant on membrane pores, in the combined system, had been reduced. The extracellular polymeric substances (EPS) of the combined system can be cut down and modified. Compared with the conventional MBR, the EPS was15%lower, and the proportion of protein to polysaccharides in EPS decreased27%, in the combine system, which reduced the sludge’s hydrophobicity, and delayed the fouling of sludge cake. The combined system had restrained the filamentous bacteria, and the value of EFLI/FAI (the ratio between the extended filamentous lengths and the floc area) was47.5%lower, relatively to conventional MBR. The value of Ro (roundness), FF (form factor) and AR (Aspect Ratio) of combined system were all closed to1, demonstrating the homogenization and spheroidization of sludge floc. These changes hindered the tendency of sludge’s accumulation on the membrane’s surface, and controlled the formation of sludge cake. The study illustrated the membrane fouling mitigation of the combined system was relative to the cut down of key membrane fouling pollutants, suppression of filamentous, and the homogenization and spheroidization of sludge floc.As analyzed before, the combined system can obtain high efficiency of wastewater treatment and excellent sludge reduction, and achieve effective mitigation of membrane fouling, in the same time. It has a significant meaning for our country’s control of wastewater and sludge.