Effects Of Salinity On The Performance And Microbial Community Structure Of Biofilm Reactor

In this study,a hybrid waterfall biofilm reactor-moving bed biofilm reactor(WFBR-MBBR)system was designed for the biological treatment of saline wastewater.First of all,the stability of long-term opration and the shift of mocribial community of the hybrid WFBR-MBBR were studied.Then the independent WFBR system and the hybrid WFBR-MBBR system were used to treat saline wastewater,respectively,which aimed at investigating the effects of salinity on the performance,biofilm morphylogy and microbial community structure.Conclusions were drawn as following:The hybrid WFBR-MBBR system could operate stably for a long term,and the removal efficiency of COD and NH₄⁺-N were 90%and 99%at stable period,respectively.The monitoring result within the cycle confirmed that WFBR had good function of adding dissolved oxygen.Proteobacteria and Cyanobacteria were the dominant microorganisms when the MBBR oprated independently,and Proteobacteria was the predominant microorganisms in long-term opration of hybrid WFBR-MBBR system.Besides,the richness and diversity of microbial community in MBBR decreased as WFBR installing.As the salinity increased from 0%to 0.6%,the average removal efficicency of COD in WFBR with an operation period of 24 h decreased slightly at stable phase,while the removal efficiency of NH₄⁺-N maintained above 99%.And removal efficiency of TN increased during the start-up phase and maintained stable above 80%at all saline stage.WFBR still showed good function of adding dissolved oxygen under saline condition.A large number of unknown particles appeared on the biofilm of WFBR at the salinity of 0.4%-0.6%.Proteobacteria and Bacteroidetes always occupied the most dominant position in WFBR in the range of 0%-0.6%salinity.Moreover,the increase of salinity had a certain positive effect on the improvement of microbial community diversity and richness in WFBR,and the diversity and richness reached the maximum at the salinity 0.3%and 0.5%,respectively.The opearion performance of the hybrid WFBR-MBBR system with an opration period of 12 h was better than that of the independent WFBR system.As the salinity increased from0%to 0.6%,the average removal efficiency of COD slightly decreased in stable phase,but the removal efficiency of NH₄⁺-N was stable above 99%all the time.And the hybrid system had a good TN removal performance,and the removal efficiency of TN fluctuated between85%and 90%at the salinity of 0.5%and 0.6%.The hybrid WFBR-MBBR showed good function of adding dissolved oxygen as well.Biofilms in WFBR and MBBR were observed some unknown particles at the salinity of 0.3%and 0.2%,respectively.However,the unknown particles on the biofilm of WFBR disappeared at the salinity of 0.6%.As the salinity increasing,the relative abundance of salt-tolerant microorganisms in the hybrid system increased,and the similiarity of microbial community between biofilm in WFBR and biofilm in MBBR decreased.And the community diversity and richness in hybrid system could be increased by increasing salinity in the range of 0%-0.6%,but the community diversity and richness of MBBR decreased if the salinity exceeded a certain range.