UASB/MBR Based Anaerobic Treatment Of Purified Terephthalic Acid Wastewater Focusing On Performance Optimization And Microbial Community

Purified terephthalic acid（PTA）,as an important chemical raw material,has been widely used in the production of polyethylene terephthalic bottle,polyester textile fiber,polyester film,pesticides,etc.PTA wastewater has become a tricky problem in the field of wastewater treatment because of its complex composition,high organic load and poor biodegradability.The development of stable,efficient and energy recyclable water treatment process is an important guarantee to realize the detoxification and energy conversion of industrial wastewater in the context of promoting carbon peak.In this study,PTA wastewater was treated with UASB and HF-An MBR as the core technologies.The objectives of this study were to optimize pollutant removal efficiency and methane convertion rate through parameter regulation and process coupling,hoping to provide theoretical guidance for the anaerobic biological treatment of real PTA wastewater.The main conclusions are as follows:（1）A lab-scale UASB reactor was operated to investigate the influence of HRT on pollutant removal efficiency,methane conversion rate,sludge characteristics and microbial community structure.The results indicated that when HRT=30 h(OLR 2.81±0.22 g-COD/L_reactor/d),the COD removal efficiency reached 65.3±4.4%,biogas and methane production rate were 0.34±0.03 L/L_reactor/d and 0.24±0.04 L/L_reactor/d,respectively,methane content maintained about 75.4±2.7%.In the later stages(OLR3.05-19.30 g-COD/L_reactor/d),the COD removal rate decreased with the decrease of HRT.Sludge particle size gradually decreased with the increase of influent flow caused by decreased HRT.The microorganisms on the surface of granular sludge were mainly cocci-shaped and rod-shaped.16S r RNA results showed that Proteobacteria and Bacteroidetes were critical microorganisms for degrading benzene pollutants in wastewater,accounting for 33.5%～47.7%and 8.3～16.5%,respectively.While Methanosaeta was the main methanogenic archaea,accounting for 61.4～81.6%of the total archaea.（2）To enhance the methane conversion rate in UASB,a lab-scale UASB-BES reactor was operated to investigate the influence of voltage intensity on pollutant removal and methane conversion efficiency.The results showed that UASB-BES promoted COD degradation and methane conversion rate.As the applied voltage increased from 0 V to 1.0 V,the pollutant removal efficiency and methane recovery rate of the system continueously increased.The COD removal rate increased from 52.0±3.2%（0 V）to 75.8±0.7%（1.0 V）,the methane production rate increased from 0.26±0.02 L/L_reactor/d to 0.55±0.01 L/L_reactor/d,and the methane content in biogas was about 78%.Micro current stimulation created favorable redox environment（-340～-390）,stimulated the secretion of extracellular polymers and ensured the stable progress of anaerobic digestion.BES improved the relative abundance of key microorganisms and electroactive bacteria（Proteobacteria,Chloroflex,Methanosaeta and Methnobacterium,etc.）in anaerobic digestion,and promoted the synergy between different microorganisms.Overall,UASB-BES system is a promising strategy for enhancing the methane conversion efficiency of PTA wastewater.（3）In view of the washout of granular sludge which leads to the reduction of COD removal efficiency in UASB reactor,anaerobic treatment of PTA Wastewater by HF-An MBR was carried out,and the effects of HRT on pollutant removal efficiency,methane conversion,membrane fouling and microbial community structure were investigated.HRT of 24 h(OLR 3.05±0.29 g-COD/L_reactor/d)proved to be the optimum,when the average COD removal rate was 65.8%,the biogas production rate was 0.33±0.02 L/L_reactor/d,and methane production rate was 0.22±0.01 L/L_reactor/d.Most of the sludge particles in HF-An MBR maintained in the range of 3.4～100μm,effectively avoiding the loss of granular sludge.Slight membrane fouling was observed,which was mainly caused by gel layer,accounting for 49.8%of total resistance.The CLSM analysis further showed that membrane pollution was mainly caused by microbial metabolites（such as protein and polysaccharide）.The results of 16S r RNA indicated that the dominant bacteria of HF-An MBR system were Proteobacteria and Acetothermia,and dominant archaea were Methanoseata and Methanolinea.（4）Although HF-An MBR can effectively avoid the loss of granular sludge,membrane pollution occured during the long-term operation,which affected the treatment efficiency.Therefore,the feasibility of anaerobic treatment of PTA wastewater by an integrated UASB-MBR was carried out on the basis of traditional UASB and MBR.The effects of HRT variation and the introduction of ethylene glycol（EG）on pollutant removal efficiency,membrane fouling and microbial community structure were discussed.The results showed that the p H and alkalinity were within the favorable range for microorganisms that UASB-MBR can be operated stably for a long time.In the first stage,with the continuous reduction of HRT(OLR 1.74～4.54 g-COD/L_reactor/d),the COD removal rate increased from 50.4±2.9%to 61.2±0.9%.When HRT was 18 h,methane production rate reached 0.70±0.01 L/L_reactor/d.In the second stage,with the increasing proportion of EG,the COD removal rate increased from 66.5±1.4%to 75.5±0.5%,the methane production rate was 1.05±0.07L/L_reactor/d,simultiniouly.In the stable operation stage,the proportion of CH₄ in biogas remained between 70%～80%.The introduction of EG reduced the toxicity of aromatic compounds,enhancing the adaptability and stability of microbial population and promoting methane conversion efficiency.This paper comprehensively investigated the optimal HRT of UASB/HF-An MBR from operation stability,methane conversion efficiency,sludge characteristics and microbial community changes,and verified the enhanced methanation efficiency of UASB-BES system.Meanwhile,based on the traditional UASB and MBR,a new UASB-MBR reactor was designed,offsetting the technical defects of traditional UASB and MBR and thus providing a new strategy for the energy conversion process of PTA wastewater.