Effect Of Granular Activated Carbon Addition On Dynamic Membrane Properties And Wastewater Treatment Performance In An AnDMBR

Anaerobic dynamic membrane bioreactor（AnDMBR）is an organic combination of anaerobic digestion and dynamic membrane technology,which has the advantages of easy control of membrane fouling,low cost and easy recovery of membrane filtration performance.However,there are still some problems,such as the low retention of pollutants at the beginning of the operation,the dynamic process of membrane formation and the contamination of the membranes,which still need to be regulated.Based on the successful experience of adding granular conductive materials to improve the process performance of anaerobic reactors,and in order to improve the process efficiency of the AnDMBR,the GAC-AnDMBR composite process to treat real domestic wastewater was constructed.The effects of GAC dosage（3,6,10,20 g/L）on methanogenesis performance,filtration performance and pollutant removal performance of intermittent biogas cycle mode AnDMBR process were investigated.The main research components and results of the thesis are as follows:（1）In order to investigate the effect of GAC dosage（3-20 g/L）on the removal performance and methanogenic performance of the GAC-AnDMBR process,batch and process experiments were carried out.The results of anaerobic methanogenesis batch experiments preliminarily confirmed the enhancement effect of GAC on methanogenesis.The results show that,compared to the control reactor without GAC addition,the COD removal rate of AnDMBR was increased by 5.7%-12.1%with the addition of 3-20 g/L GAC.The removal of other organic compounds was also improved,and there was a significant positive correlation between the removal rate of pollutants and the amount of GAC added.GAC enhances the retention of dynamic membranes.The adsorption and bioenrichment of GAC promotes the growth of microorganisms and the formation of bioactive carbon.The total methane production of the GAC-AnDMBR was 0.18-0.22LCH₄/g COD at each operation stage,which increased by 8.3%-23.7%compared with no GAC.The best methane production was achieved at a GAC dosage of 6 g/L.（2）The effect of GAC dosage on the filtration performance of the GAC-AnDMBR process was investigated.The dosage of GAC shortened the formation time of the dynamic membrane and reduced the effluent turbidity.The turbidity removal rate increased by 3.1%-12.3%with increasing GAC dosage.The average TMP growth rate（d TMP/dt）was 0.41,0.17,0.15,0.14 and 0.13 k Pa/d in the five stages,respectively.The TMP growth rate of GAC-AnDMBR was much less than that of the AnDMBR without GAC.GAC improves the structure of dynamic membranes,increases the compression resistance of dynamic membranes and delays membrane contamination.At the same time,GAC can prevent excessive accumulation of contaminants and control the thickness of dynamic membranes by flushing the membrane surface under hydraulic action.（3）It was studied that the effects of GAC dosage on the physical and chemical properties,microbial community structure and methanogenic metabolic pathways of anaerobic sludge and dynamic membrane.The average particle size of the sludge increased from 134.4μm to 238.5μm as the GAC dosing increased.The GAC continuously adsorbs small particles and extracellular polymers（EPS）,thus the amount of EPS in the anaerobic sludge and dynamic membrane gradually decreases.The addition of GAC increased the relative abundance of Proteobacteria,Chloroflexi and Firmicutes,as well as the relative abundance of methanotrophic bacteria.The GAC enhances the CO₂methanation,acetate methanation,and methylamine methanation pathways.The addition of GAC created a more suitable environment for hydrogenotrophic methanogens and methanotrophic methanogens and their symbiotic bacteria,enabling a shift from acetate methanogenesis pathway to the coexistence of multiple methanogenesis pathways.（4）The COD balance and energy balance in the GAC-AnDMBR process were analysed.It was found that anaerobic treatment of 1 m³ of municipal wastewater could generate 0.33-0.50 k Wh of electrical and thermal energy,and net energy production（0.17-0.34 k Wh/m³）could be achieved after removing the operational energy consumption of peristaltic pumps,aeration pumps and agitators.The contribution of dissolved methane to the COD balance is in the range of 23.9-25.1%,which is a relatively large proportion.If all the dissolved methane in the effluent is recovered,the net capacity can be increased to 0.50-0.67 k Wh/m³.Therefore,in view of the practical application of the AnDMBR process,it is important to pay attention to the efficient recovery or removal of dissolved methane.