Externalanaerobic Ceramic Membrane Bioreactor Treating Domestic Sewage

In recent decades,the anaerobic membrane bioreactor has been greatly developed.It not only has the advantages of anaerobic treatment,but also can ensure the sludge concentration of the system through the prevention of the membrane module,achieve the separation of SRT and HRT,and improve the quality of effluent.But the membrane cleaning and replacement costs caused by membrane fouling are the main factors limiting the application of this technology.Therefore,it is necessary to improve the anaerobic membrane bioreactor in terms of the membrane material and operation mode to slow down the membrane fouling rate.Compared to organic membrane materials used most in wastewater treatment,ceramic membranes have the advantages of acid and alkali corrosion resistance,high temperature resistance,and pollution resistance.Therefore,its use in the treatment of domestic sewage may reduce the membrane fouling to a certain extent.Based on this,the paper coupled a ceramic membrane with an anaerobic reactor to establish an external Anaerobic Ceramic Membrane Bioreactor(An CMBR),which was applied to the treatment of actual domestic wastewater,explored operating efficiency and membrane fouling characteristics under different HRT,and the effects of different backwash frequency and time on membrane fouling were further studied.The results showed that the anaerobic reactor UASB was successfully started after60'days operation at a temperature of 30 ? and the influent was synthetic domestic sewage.On the 109 th day,the ceramic membrane module was coupled with the UASB to start the An CMBR system.After only 3 days,the COD removal rate exceeded 95%and the startup was successful.During stable period,the average effluent COD of the membrane was 28.83mg/L,the total COD removal rate of the system was 93.38%.The concentration of VFAs in membrane effluent was always less than 20mg/L,no acidification occurred in the reactor.The daily average yield of methane was 0.054m3/kg CODremoved.When the HRT was 12 h,the cycle of ceramic membrane fouling was14 d,and EPS was the main substance that causing membrane fouling.In addition,the protein concentrations in both EPS and SMP were higher than those of polysaccharides,therefore,the protein contributed the most to An CMBR membrane fouling.When the influent water was the actual domestic sewage,as HRT was shortenedfrom 18 h to 12 h and finally to 8h,the organic removal rate of the system was reduced from 84.76% to 82.21% and 73.27%.It was considered that the 8h was the best HRT for the treatment of actual domestic wastewater because the COD of the membrane effluent can still be maintained at about 50mg/L.Under this three HRT conditions,no significant accumulation of volatile acids occurred in the system.The p H of the UASB effluent and membrane effluent were all between 7.0 and 8.0,system was stable.The membrane fouling cycle of the An CMBR reactor was significantly affected by HRT.With the decrease of HRT,the cycle of membrane fouling was also shortened.The membrane fouling cycle was the shortest at HRT of 8h,only 6d.The concentration of EPS in mixed liquor was much higher than that of SMP,and the concentration of polysaccharide was slightly higher than protein.The SMP concentration of the cake layer was significantly higher than EPS,especially SMPc,and the polysaccharide concentration of SMP in cake layer was significantly higher than the protein.The concentration of SMP and EPS,polysaccharide and protein in mixed liquor increased with the decrease of HRT.When the frequency of backwash was 1 time per day and 2 times per day,the time for TMP reaching 25 k Pa was about 7 days,and when the frequency of backwash was 3times per day,TMP reached about 25 k Pa after about 11 days.When the backwash frequency was 3 times per day,the growth rates of TMP at the backwash time of 1min,2min,and 3min were 0.14 k Pa/h,0.13 k Pa/h,and 0.11 k Pa/h,respectively.TMP with a3 min backwash time had a relatively slow growth rate,however,the proportion of water used for daily backwash was relatively larger.Based on the changes in TMP and the processing efficiency of the membrane module,it was considered that the backwash frequency of 3 times per day and the backwash time of 2min were suitable ways to slow the membrane fouling rate.