Study On The Characteristics Of Domestic Sewage Treatment And Bioenergy Recovery In Two-stage Dynamic Membrane Process

In recent years,domestic sewage is regarded as a valuable resource and energy carrier,rather than waste,which makes the sewage treatment mode shifting from pollution control to resource and energy recovery.In this study,a new dynamic membrane filtration method（DMF）is used to concentrate the organic matter in domestic sewage to obtain the concentrated solution rich in organic matter,and the concentrated solution is treated with the anaerobic dynamic membrane bioreactor（AnDMBR）process to achieve the purpose of producing the biological energy.This paper mainly studied the selection of dynamic membrane（DM）supporting materials,the pre-concentration process and performance of DMF wastewater,evaluated the methane-producing potential of organic concentrate,and investigated the treatment effect and methane-producing efficiency of AnDMBR for concentrated organic concentrate.The main research results are as follows:（1）The optimization of DMF process and the concentration performance analysis of domestic sewage were carried out.DMF process optimization experiment results show that a DM membrane module with a three-layer structure supported by 25μm stainless steel mesh can rapidly form a DM layer within 1h with the assistance of suspended particles rich in raw sewage.DMF process can run stably at high flux of 30-54 L/m²h under the condition that the transmembrane pressure is less than 40kPa.In the continuous operation of DMF,the average influent COD was 305mg/L,the effluent COD average was 7008 mg/L,and the removal efficiency of other pollutants（such as nitrogen and phosphorus）was different.The results show that the interception effect of DM layer on different pollutants is different.The physical method of air backwashing with film surface scrubbing can effectively regenerate the DM layer and maintain long-term stable operation,but with the increase of filtration cycle,the growth rate of TMP increases somewhat.This may be due to the accumulation of irreversible contaminants between stainless steel wire screens.The COD balance analysis is that 37%of the influent COD is lost with the effluent from the DM layer,indicating that the effect of the DM layer on the dissolved organic matter is poor and the COD loss of about 12%,which may be caused by the incomplete cleaning of the organic matters on the biodegradation or stainless steel wire net.But still 51%of the cod is enriched in the organic concentrate in a recyclable form,which provides a matrix for subsequent anaerobic fermentation production of methane.The biochemical methane-producing potential（BMP）of DMF concentrate is 0.20 L CH₄/g COD,which is equivalent to the gas production of municipal wastewater anaerobic digestion,indicating that the combination of DMF process and anaerobic digestion to realize synchronous sewage treatment and energy conversion is feasible.（2）AnDMBR is used to treat the concentrated wastewater produced by the DMF process.The changes of sludge particle size,extracellular polymer（EPS）and dissolved organic matter（DOM）were analyzed by instrumental analysis.The experiment of treating concentrated wastewater with AnDMBR is divided into two stages.The first stage is the start-up stage（that is,the acclimatization period）,the influent COD is about 1000 mg/L for 30 days,the effluent turbidity of the start-up stage is always below 40NTU,and the COD removal rate is 89.3%-91.1%.The second stage is stable operation stage,the influent COD is about 2000 mg/L,for 30 days,the turbidity of effluent is always less than 20 NTU,and the lowest removal rate of 9.5 NTU.The removal rate of the COD was 96.7%-97.3%.However,it has no removal effect on ammonia nitrogen and phosphate.During the operation of the reactor,the anaerobic sludge did not change much compared with the inoculated sludge.The average particle size of the inoculated sludge was 48.6μm,and the average particle size of the sludge after stable operation for one month was 52.2μm.For the potential membrane contaminants such as EPS,it was found that the total amount and components（protein and polysaccharide）increased with time,which was accompanied by the aggravation of membrane fouling.The DOM of influent,supernatant and effluent was analyzed by three-dimensional fluorescence spectroscopy（EEM）,the results showed that tryptophan and aromatic proteins were easily degraded by microorganisms,and the dynamic membrane also had a certain interception effect on them.Humic acid organic compounds and fulvic acid organic compounds had poor degradation,and their contents remained basically unchanged along the treatment process.In addition,due to the slow growth of methanogenic microorganisms,long domestication time and the complexity of wastewater concentrate matrix,the actual methane production rate of AnDMBR process is low,which requires further research and improvement.