| The resource utilization of municipal sewage is one of the important measures to solve the shortage of water resources in China.Reverse osmosis(RO)technology is a common technical method for providing fresh water in the process of municipal wastewater treatment.Since RO concentrate contains highly concentrated contaminants,its discharge without proper treatment will damage the bio-ecological environment.With the advantages of high utilization rate of oxygen,simultaneous nitrification and denitrification,etc.,membrane-aerated biofilm reactor(MABR)has wide application prospects in the field of municipal wastewater utilization,especially in the advanced treatment of RO concentrates.In this study,MABR was employed to nitrogen removal of municipal RO concentrate for the first time.The RO concentrate has the characteristics of high total nitrogen concentration,low carbon-nitrogen ratio and high salinity.Effects of operational conditions,including the aeration pressure,the C/N ratio and the hydraulic retention time,on the nitrogen removal performance were evaluated systematically.The nitrogen removal mechanism was evaluated by monitoring the effluent concentrations of nitrogen-contents in the intermittent mode.Furthermore,the microbial tolerance of MABR under elevating salinity were identified.Finally,the stability of MABR for nitrogen removal was investigated during the long-term run.Results indicated that the operating parameters of MABR system needed to be controlled within a proper range to achieve the optimal efficiency of nitrification and denitrification.The optimal TN removal efficiency of 79.2%was achieved under the aeration pressure of 0.02 MPa,hydraulic retention time of 24 h,and the C/N ratio of5.8,respectively.The TN treatment load of unit membrane area was 0.73 g/m~2d.The inhibitory effect of salinity on denitrifying bacteria and nitrite oxidizing bacteria was significant.The increase of influent salinity would lead to the decrease of TN removal rate.The TN removal efficiency remained more than 70%with NaCl addition amount below 20 g/L.The nitrogen removal efficiency of MABR kept stable during a long-term run,indicating its potential of long-term application.In addition,the microbial community structure and diversity of the biofilm were studied by 16s rDNA high throughput sequencing.The effect of salinity increase on the succession of microbial community was investigated.The result showed that both microbial richness and diversity of the biofilm were reduced by high salinity.In addition,a variety of denitrification modes existed in the MABR system.This work preliminarily demonstrated the feasibility of MABR for the nitrogen removal of municipal RO concentrate with low C/N ratio,which laid a good foundation for the development of corresponding MABR technology. |
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