| Wastewater is rich in biomass energy,and the effective recovery of biomass can be of great significance in mitigating the energy crisis.Anaerobic membrane bioreactor?AnMBR?is a new type of wastewater treatment technology combining anaerobic biological treatment technology and membrane technology.It has the advantages of low sludge yield,low operating cost and high treatment efficiency,but the effluent of AnMBR contains dissolved methane.The direct discharge of effluent including dissolved methane will not only aggravate the greenhouse effect,but also represent the loss of available energy,which limits the development of the technology.The anaerobic forward osmosis membrane bioreactor?AnOMBR?is formed by replacing the ultrafiltration?UF?or nanofiltration?NF?membrane with a FO membrane in the AnMBR system,maintaining AnMBR extractable biomass capacity and some other advantages,to solve the problem of dissolved methane in AnMBR effluent in situ.In this paper,the energy recovery performance of the reactor was investigated by considering the parameters of the gas composition and methane production of the AnOMBR system.In addition,the permeability of the dissolved gas in the feed side to draw side was investigated.This paper mainly carried out the following two experimental studies.?1?Two kind of cellulose triacetate?CTA?membranes and membrane orientations?the active layer facing the feed solution and the active layer facing the draw solution?for system energy recovery and dissolved gas transfer performance were studied.The experimental results shown thatthe pH increased from 6.80 to 7.30 and the COD removal efficiency exceeded 93%under different conditions of membrane materials and membrane orientations.The decline rate of water flux and growth rate of conductivity were 0.39 LMH/d and 0.28 ms/?cm·d?in PRO mode,and 0.34 LMH/d and 0.23 ms/?cm·d?in FO mode.The CTA-NW membrane and CTA-ES membrane substantially retain the dissolved CH4,allow a small amount of dissolved CO2 to pass through,allow the passage of H2.There is no significant difference in the concentration of the dissolved gas in the feed side under different membrane materials and membrane orientations.The concentration of dissolved CH4 and CO2 in the feed side showed the same change trend during the experimental period.?2?Different operating temperatures?25? and 35??and different influent COD concentrations?3000 mg/L,6000 mg/L and 9000 mg/L?on system energy recovery and mass transfer performance of dissolved gases were studied.The experimental results shown that at35?,the water flux,salinity accumulation,gas percentage and methane production of AnOMBR system increased,VFA content decreased compared with 25?.Except for the slight fluctuation of COD removal efficiency in the early stage,there is no significant difference in AnOMBR system operating parameters between different influent COD concentrations,which indicates that the AnOMBR system can maintain good processing performance under high impact load.There is no significant difference in the concentration of the dissolved gas on the feed side.The gas permeation mechanism is used to explain the difference of the permeation rate of methane,carbon dioxide and hydrogen in the CTA membrane under different temperatures and influent COD concentrations.The ratio of permeability coefficient?=PCO2/PCH4 is 30.8,?=PH2/PCH4 is 60,so H2 can pass through FO membrane,CO2 can be slightly pass through the FO membrane,CH4 can hardly pass through the FO membrane.This solves the problem of dissolved methane in the effluent of the anaerobic reactor in situ,achieve energy recovery and avoid the intensification of the greenhouse effect.This also avoids the acidification phenomenon caused by the hydrogen accumulation in the reactor,which is beneficial to the anaerobic digestion.In the high salinity environment,the AnOMBR system has a maximum methane yield of 0.256 CH4/g·COD at 35?with an influent COD concentration of 6000mg/L,which shown good energy recovery. |
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