Study On The Characteristics Of Biochar-assisted Anaerobic Membrane Bioreactor Treating High-strength Swine Wastewater

China is the largest pork consumer in the world.The large farming volume means a large amount of Swine Wastewater（SW）generation.SW is considered as one of the factors threatening the environment due to higher organic loading rate（OLR）and residues of toxic substances（heavy metals,antibiotics.etc）,so it is important to treat SW through sustainable development technologies for green development of swine industry.Anaerobic Digestion（AD）is widely used in SW treatment because of its ability to treat high concentrations of organic wastewater while recovering bioenergy,however,conventional AD requires a large footprint and low treatment efficiency.Therefore,as an efficient AD technology,Anaerobic Membrane Bioreactor（An MBR）is used to replace traditional AD.Biochar added into AD has been widely studied for promoting energy recovery and better microbial activity under the stress of toxic substances.improved methane production through direct interspecies electron transfer（DIET）,in addition,it has a certain effect on alleviating membrane pollution.Therefore,an efficient energy recovery system（BC-An MBR）was established in this study.Compared with the traditional An MBR,the efficiency of system stability,methane production,effluent quality and membrane fouling under different OLR was explored.The microbial communities and potential methanogenic pathways under high OLR were analyzed to reveal the potential mechanisms of biochar regulation of An MBR performance.The main studies and findings are as follows.（1）The methanogenic phase of An MBR was the main obstacle during the start-up phase.The An MBR had almost no methane generation and the effluent COD gradually increased under the start-up condition of organic loading rate of 5.3 g CODL/d.The gas production gradually resumed after the OLR was reduced to half.The addition of biochar can shorten the start-up time by 44%.The analysis shows that biochar can promote the syntrophic oxidation of volatile fatty acids（VFA）to accelerate the start-up of An MBR.The biochar addition increased the CH₄ yield at all OLRs during the steady-state operation phase,and there was almost no accumulation of VFA during the steady-state operation in this study.It was found that the OLR limit of An MBR treated SW was 21.1 g COD/L/d,and biochar addition could increase the COD removal rate of An MBR from 90%to 95%at an OLR of 21.1 g COD/L/d,promote 6.0%-12.3%acid production rate,7.1%-10.5%acetic acid production rate and 5.9-9.6%methane production rate.Moreover,biochar can provide a shelter for microorganisms due to its own structure,thus enhancing the stability of An MBR under unfavorable environment and promoting the CH₄ yield under different OLRs by acting as an electron transfer conductor through redox functional groups to stimulate potential DIET action.（2）The membrane fouling was investigated at different hydraulic retention times（HRT）and the results showed that An MBR has difficulty in maintaining a stable trans-membrane pressure（TMP）growth rate at higher TS and high fluxes.In this study,the membrane fouling was mitigated to some extent by reducing the sludge retention time（SRT）to reduce the TS at HRT=3d.The sludge proliferation rate in this study increased from 1.5 g COD/g VS to 2.5 g COD/g VS after reducing the SRT,while biochar addition did not improve the sludge yield in An MBR.Filtration text showed that the cake layer（cake）resistance was the main filtration resistance accounting for 98%,biochar addition reduced the EPS content in the cake layer to some extent,in the meanwhile,the average particle size of sludge decreased from 259.8μm to 128.1μm in CT,while the smaller particle size and lower mechanical strength of biochar in this study had a certain negative effect on membrane fouling.（3）The relative abundance of Candidatus＿Cloacamonas in CT decreased from21.7%to 4.4%with the increase of OLR to 21.1 g COD/L/d,which may be the reason for the decrease of COD removal efficiency in CT at high OLR.The addition of biochar increased the relative abundance of acid-producing bacteria Petrimonas（Bacteroidetes）and VFA syntrophic oxidizing bacteria Syntrophomonas（Firmicutes）by 0.6-2.4 times.From the archaeal perspective,the relative abundance of the dominant archaebacterium Methanosaeta in CT ranged from 53.9%to 68.6%,indicating that acetoclastic methanogenesis was the main methanogenic pathway in CT,whereas biochar addition caused the relative abundance of Methanobrevibacter to increase greatly to 70.9%at an OLR of 21.1 g COD/L/d.Metabolic pathway analysis revealed that biochar not only strengthened hydrogenotrophic methanogenesis pathway,but also upregulated the genes encoding electron transfer carriers and riboflavin metabolism,suggesting the role of biochar facilitating direct interspecies electron transfer for syntrophic methanogenesis.The excellent energy yield performances under high OLR confirmed BC-An MBR as an advanced system for high-strength swine wastewater treatment.