Anaerobic Co-digestion Of Anaerobic Membrane Reactor(AnMBR) Enhanced By Digested Residue-derived Biochar

Anaerobic membrane bioreactor（AnMBR）,as a widely used organic solid waste treatment process,can simultaneously realize energy recovery and waste sludge reduction by degrading organic matter for biogas production.Therefore,it exhbits great advantages and prospects in terms of technology and economy.At present,AnMBR is faced with several severe challenges in practical application,including low anaerobic digestion performance,difficult digestion residue,and membrane pollution,etc.Biochar is a kind of material duo to simple preparation and economic feasibility.It has great potential in improving anaerobic digestion performance and alleviating membrane pollution.Based on the AnMBR co-digestion technology,the critical membrane fouling parameters were determined by changing the instantaneous membrane flux,initial TS value and hydraulic retention time（HRT）,etc.Then,the digestion residue of anaerobic co-digestion was pyrolyzed for biochar preparation.The physicochemical and electrochemical properties of the pyrolyzed biochar at different temperatures were characterized.Furthermore,Batch experiments were designed to slecte the optimal dosage of anaerobic co-digestion residue biochar（CB）.The underlying mechanism of CB on direct interspecific electron transfer（DIET）in anaerobic digestion was also analyzed.Finally,the optimized CB was added to the AnMBR co-digestion system under the operating conditions of critical membrane pollution,and the effects of CB addition on the gas production performance,membrane pollution,effluent water quality,and microbial community of AnMBR co-digestion were investigated.Overall,the main conclusions are as follows:（1）AnMBR combined with anaerobic digestion process was constructed,and sewage sludge（SS）-food waste（FW）were used as co-digestion substrate.The operation parameters of AnMBR critical membrane fouling were determined by changing the instantaneous membrane flux of AnMBR,initial TS value,and HRT.Results showed that the increasing instantaneous membrane flux had little effect on the performance of AnMBR,when the initial TS value was 20 g/L and HRT was 20 d.Further reduction of HRT at high instantaneous membrane flux would deteriorate the performance of AnMBR.（2）Biochar was fabricated by pyrolysis with co-digesting residues at different temperatures.The physicochemical and electrochemical properties of CB were investigated at different temperatures.Then,the optimized CB was added to the co-digesting systems with SS and FW as substrate to explore the influence of CB on the anaerobic co-digesting performance.Results showed that CB（CB-800）pyrolyzed at800℃exhibited the largest specific surface area.the more stable structure,the larger electron exchange capacity,and the smaller internal resistance.In addition,the dosage of CB was 0.12g/g-TS,and exhibited the best co-digestion performance.Microbial community structure analyisis showed that the abundance of Chloroflexi increased,but Proteobacteria decreased after CB addition.This result suggested that it was also possible to promote DIET by enriching archaea Methanosaeta and Methanolinea,thus improving the efficiency of anaerobic digestion.（3）Based on the AnMBR co-digestion SS-FW system,operating under the parameters of critical membrane pollution,the CB with the optimal pyrolysis temperature was firstly added to the AnMBR co-digestion system with the optimal dosage to improve the co-digestion performance,and alleviate membrane pollution.Compared with the stage without CB,the production of CH₄ increased to 153.46±15.47 m L/（L reactor）/d after CB was added under the condition of HRT of 10 days,increasing by 9.91%.Secondly,the addition of CB could prolong the time to reach threshold value of membrane pressure,and reduce the membrane pollution caused by cake layer and organic dirt.In addition,the addition of CB greatly improved the effluent quality,the effluent chroma decreased from 379±7.07 to 184±7.48 NTU with the removal rate of 51.45%.Moreover,CB also greatly reduced the concentrations of PN,PS,NH₄⁺-N,fulic acids and humic acids in the effluent.Meanwhile,microbial community structure analysis elucidated that the addition of CB could increase the abundance of Chloroflexi,which enhanced the hydrolysis efficiency of PN and PS in the anaerobic co-digestion process,and accelerated the process of DIET by enriching the relative abundance of Methanosaeta.