| With the processing of China's urbanization and the continuous growth of the population,the amount of discharged sewage for treatment continue to increase.While the traditional wastewater treatment process has greatly improved the environmental contamination,it also faces many problems such as high energy consumption,large greenhouse gas emissions,as well as sludge production.Therefore,it is increasingly important to integrate the concept of "sustainable development" into wastewater treatment.Coupling membrane separation technology and anaerobic fermentation for wastewater treatment can effectively intercept slow-growing anaerobic microorganisms,and realize the totally separation of hydraulic retention time(HRT)and sludge retention time(SRT),and also reduce sludge production and energy consumption caused by aeration,as well as achieve the energy recovery by converting organic matter in sewage into methane,this idea brings about the research and application of anaerobic membrane bioreactor(AnMBR).However,the AnMBR still needs to overcome two difficulties:one is the high cost,high energy consumption and membrane fouling,and the other is the low efficiency of direct anaerobic digestion of municipal wastewater with low organic concentration.For this reason,based on the low cost and low energy consumption of dynamic membrane technology,this study proposes to use cheap coarse-pored mesh as the supporting material to make the dynamic membrane modules,and construct a two-stage dynamic membrane system for wastewater treatment and energy recovery with high-efficiency.The first stage is completing the enrichment and concentration of organic matter in municipal wastewater by direct dynamic membrane filtration(DMF);the second stage is achieving energy recovery by anaerobic digestion of wastewater concentrate using the anaerobic dynamic membrane bioreactor(AnDMBR).Combining the batch and continuous experiments,the treatment characteristics and stable operation of the two-stage dynamic membrane system(DMF-AnDMBR)were studied,the distribution of matters in the municipal wastewater and its concentrate was analyzed,and the organic matter and energy balance of the system were evaluated.The calculation of COD mass and energy balance in the DMF-AnDMBR has laid a theoretical and technical basis for the practical application of the process.The research work carried out in this paper and the main results obtained are as follows:(1)The particle size and organic matter components in the real sewage were analyzed,and the DMF process was successfully constructed to achieving sewage concentrate.The COD concentration of the real sewage in the experiment was around 440 mg/L,and the SS concentration was about 170 mg/L.The main components of COD are protein,lipids and polysaccharides.Organics in the sewage can be directly enriched by DMF,the wastewater concentrate with COD of 2125.89±273.71 mg/L can be obtained after a single cycle of operation for 24 h.In the concentrate,the proportion of settable SS and suspended SS are 63.4%and 33.8%,and protein and lipid accounted for 40%and 4%.The methane production potential of the concentrate reached 262.52±11.86 mL CH4/g COD,which provided favorable conditions for the recovery of bio-energy.(2)Two groups of anaerobic dynamic membrane bioreactors(SF-AnDMBR and PC-AnDMBR)were constructed based on the self-forming(SF)dynamic membrane and pre-coated(PC)dynamic membrane formation methods.The dynamic membrane formation process and wastewater treatment performance were investigated.The results showed that robust dynamic membranes could be formed by the two methods,with TMP increased slowly.However,the effluent turbidity of PC-AnDMBR was more stable(27.1±9.44 NTU),and the COD removal rate was higher(83.2%).The contribution of microbial degradation and dynamic membrane interception to organic matter removal was compared and analyzed.It was found that there was little difference between the two AnDMBRs.The contribution of biodegradation to the removal of organic matter was more than 65%,and the retention effect of pre-coated dynamic membrane on dissolved organic matter(DOM)was better than that of self-forming dynamic membrane.(3)The optimal operating conditions for the formation of DM in AnDMBR was determined.The influence of set flux and suction time of effluent pump on the dynamic membrane formation process,the nature of the DM and filtering performance was investigated.The condition as high flux(380 L/m2·h)under a short period of suction time(15 s)to pre-coated DM was put forward.Under this condition,robust DM can be quickly formed and good effluent quality can be achieved.Thus this condition was chosen as the optimal operating condition for DM precoating in subsequent experiments.(4)The effects of operating temperature(25? and 37?)and reactor configuration(CSTR and upflow)on the efficiency of AnDMBR in fermentation of concentrated wastewater were studied.Under different temperature and reactor configurations,slow TMP growth and efficient removal of COD and turbidity(>96%)can be achieved in AnDMBRs.Compared with the operating temperature as 25?,the anaerobic microbial activity is higher at 37?,which improves the methanation efficiency of the concentrated wastewater.At 37?,CSTR-AnDMBR enhanced mass transfer and the hydrolytic acidification under the help of mixing,reached a higher methane conversion rate(0.16 L CH4/g CODremoved).The diversity of bacteria and archaea also were improved,including dominant microorganisms such as Proteobacteria,Firmicutes,Chloroflexi,Bacteroidetes.In particular,Firmicutes,which are involved in the hydrolysis and acidification of organic matter,have higher relative abundance.Methanothrix,the acetic acid trophic bacteria,also have higher relative abundance.(5)Based on the analysis of effluent quality and COD mass as well as the energy balance,the process performance of DMF-AnDMBR was comprehensively evaluated.The first stage DMF process realized the enrichment and concentration of organic matter in wastewater,and the second stage AnDMBR finished anaerobic digestion.The effluent of the two-stage reactor is characterized by low concentration of organic matter,high concentration of nitrogen and phosphorus,and low concentration of SS,which can meet the requirements of agricultural irrigation reuse water.In the whole system,due to poor to intercept t of soluble organic matter,with the COD of effluent loss occupy about 33%,although the COD in wastewater can be converted into methane proportion is not high(24%),but through anaerobic fermentation,the produced energy converted into electrical energy can reach 1.29 kWh/m3,higher than that of the energy consumption of the system itself,achieving a substantial energy surplus. |
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