Effectiveness Of Upflow AnDMBR Treating Domestic Sewage Enhanced By Granular Activated Carbon Addition

Anaerobic dynamic membrane bioreactor(An DMBR)is a novel wastewater treatment process that combines anaerobic digestion with dynamic membrane(DM)technology.An DMBR has the advantages of low cost,high flux and simple membrane cleaning.However,in the long-term operation process,the adsorption/deposition of anaerobic sludge on the membrane module leads to the increase of anaerobic dynamic membrane thickness,the decrease of pore size,the increase of filtration resistance,and the problem of membrane pollution still exists.Meanwhile,the stability of process performance needs to be improved urgently.Based on the technical idea of adding granular activated carbon(GAC)to improve the efficiency of the reactor,this paper constructed the process of adding C-An DMBR,C-AnMBR(anaerobic membrane bioreactor)and C-UASB(traditional anaerobic reactor)without GAC,and the process of adding G-An DMBR and G-UASB with GAC to treat the actual domestic sewage.The filtration properties of C-An DMBR and C-AnMBR were compared,and the technological properties of C-An DMBR and C-UASB were compared.The technological properties of G-An DMBR and the strengthening mechanism of GAC were mainly investigated.Meanwhile,the effects of GAC on anaerobic treatment of sewage were investigated through batch experiments.The main research achievements are as follows:(1)The effect of GAC dosage on anaerobic methanogenic performance of domestic sewage was studied by batch biochemical methanogenic potential(BMP)experiment,and the long-term methanogenic performance of G-An DMBR and C-An DMBR was compared based on process experiment.The results showed that,compared with the quartz sand control group,the cumulative methane production and maximum methane production rate of the GAC group were higher,and the lag time was not significantly different.When the mass concentration of GAC was 25 g/L,the anaerobic methanogenesis performance was the best.In addition,in the process experiment,the biogas yield,methane yield and gaseous methane production rate of G-An DMBR were increased by 67.1%,44.3% and 34.0%,respectively,compared with C-An DMBR,because GAC not only changed the microbial community structure and induced direct interspecific electron transfer(DIET),but also improved the sludge activity.The COD balance analysis showed that the conversion rate of COD into gaseous methane was the highest in G-An DMBR,and the energy balance showed that G-An DMBR improved the methane production and thus the energy and heat energy converted from methane.(2)The removal of pollutants and membrane filtration performance of UASB,CAn DMBR and G-An DMBR were compared and analyzed through process tests.The results show that the removal rates of COD by C-UASB,C-An DMBR and G-An DMBR were 79.2%,82.1% and 86.7%,respectively.The comparison between C-UASB and CAn DMBR shows that COD could be effectively captured by dynamic membrane.The comparison between C-An DMBR and G-An DMBR showed that GAC with adsorption property can effectively improve the removal of organic pollutants.After the operation of C-An DMBR and G-An DMBR for 20 days and 3 days respectively,the effluent turbidity could be reduced to below 25.0 NTU,which also indicated that the addition of GAC improved the initial effluent quality of An DMBR.The internal p H of G-An DMBR was more stable than that of C-An DMBR,indicating that GAC was helpful to maintain stable environmental conditions.In addition,the methanogenic activity(SMA)of G-An DMBR with VFAs as substrate was 1.1 to 2.1 times that of C-An DMBR,indicating that GAC enhanced SMA with VFAs as substrate.The TMP growth rate of G-An DMBR(0.045 k Pa/d)was lower than that of C-An DMBR(0.057 k Pa /d),indicating that the addition of GAC could alleviate membrane contamination and prolong operation time.The extracellular polymer(EPS)content of G-An DMBR sludge cake layer was lower than that of CAn DMBR,which suggested that GAC adsorbed EPS and improved the structural stability of sludge.After the operation of G-An DMBR,the membrane components were cleaned physically and chemically,and the flux of nylon mesh could be recovered by hydraulic cleaning.(3)Metagenomics was used to analyze the effects of GAC supplementation on microbial community structure,abundance of direct interspecific electron transfer(DIET)related genes,and key enzymes in methane metabolic pathways.The bacterial community analysis showed that the relative abundance of Bacteroidetes and Chloroflexi in the sludge and GAC-biofilm decreased after GAC was added,while the relative abundance of Bacteroidetes and Chloroflexi increased.Analysis of archaea community showed that GAC increased the relative abundance of Methanobacterium and Candidatus＿Methanofastidiosum.According to DIET related gene abundance analysis,GAC increased the gene abundance of type IV pili assemblin.GAC DIET through the following two aspects:(1)GAC itself acts as a conductor of electron transport;(2)Change microbial abundance electron transfer through conductive pili.GAC stimulated the gene expression of key enzymes in the methane metabolic pathway to improve the catalytic rate and thus enhanced the methanogenesis effect.