Performance Of The Combined EGSB-MBR Reactor Treating Molasses Fermentation Wastewater

The purpose of this study was to investigate the performance of the combined anaerobic expanded granular sludge bed (EGSB) and membrane bioreactors (MBR) treating molasses fermentation wastewater.First to all, sucrose as carbon source was used as raw water for EGSB reactor starting up to investigate the effect of sulfate loading rate (SLR) on the treatment of EGSB under different influent SO42- concentration and hydraulic retention time (HRT).The methane gas production, the percent electron flow of different operation stages and the sludge morphology were analyzed too. Then the study on the real fermentation wastewater by EGSB-MBR was developed under different influent pH and MBR operation modes. The pollutants removal efficiency, the effluent GC-MS analysis and the sludge characteristics were analyzed under different operation conditions. PCR-DGGE was used as microbial community analysis technology to compare the microorganism composition under different conditions.The results showed that the removal efficiencies of COD and SO42- for the simulated fermentation wastewater were 92% and 82% respectively, while removal efficiencies for the real molasses fermentation wastewater were 75% and 60% under mesophilic condition (35±1℃) and HRT at 24 h. With the increase of SLR, COD and SO42- removal efficiencies reduced, but the percent electron flow of. sulfate reducing bacteria (SRB) increased by 1.9 times. The removal efficiencies of COD and SO42-dropped to 77.6% and 70% respectively and the reactor acidification occurred when the SLR was 1.3 kgSO42-(m3-d). During the running process of the system, the largest percent electron flow which sulfate reducing bacteria was achieved at 21.1% and the corresponding lowest COD/SO42-value was about 3.0.This is the most competitive time in the system, but the methanogens still remain high competitive. The MPB and SRB of the real fermentation wastewater electron flow percentage were 71.8% and 17.5% respectively.The results showed that EGSB was effective in removing the organic pollutants of the real fermentation wastewater at the pH 6.0. The effluent COD concentration was around 565 mg/L and it contained 27.2% VFAs, acetic acid accounted for about 15.1%, while COD removal rate reached 75%. The simultaneous nitrification-denitrification (SND) was realized under dissolved oxygen (DO) 1-2 mg/L. The best performance for TN removal was achieved under the aeration 3 h-stirring 1 h operating conditions, while the removal efficiencies of NH4+-N and TN were 85.13% and 58.57% respectively. Finally the COD remove efficiency of the combined treatment process was about 85%.With the change of operating conditions, great change has taken place in microbial community. Some sulfate reducing bacteria (SRB) was found in the EGSB reactor due to the higher concentration of SO42-Some denitrification bacteria, such as Thauera sp. bacterium, were found in the MBR under aeration-stirring operating conditions.