Enhanced Energy Recovery Efficiency And Membrane Fouling Mechanism Of AnMBR Treating Swine Wastewater

Recycling energy resources by anaerobic digestion is an important treatment way of pig wastewater,but the composition of pig wastewater is complex and there are many inhibitory factors.Seeking efficient anaerobic treatment technology has become a research hotspot.Anaerobic membrane bioreactor（An MBR）is a new type of high-efficiency anaerobic digestion technology with good interception performance.Therefore,taking the pig wastewater from a farm in Xi’an as the research object,this paper investigated the effects of temperature and organic load on the anaerobic fermentation and material conversion of pig wastewater through batch experiments,compared the pollutant removal effect,methanogenic efficiency and energy recovery efficiency of An MBR and traditional anaerobic reactor（UASB）in the treatment of pig wastewater,and preliminarily explored the strategies of An MBR to realize efficient methane recovery and membrane pollution control,The main research results are as follows:（1）Through a series of batch biochemical methanogenic potential（BMP）experiments,the anaerobic fermentation characteristics of organic matter in pig wastewater under different temperatures and organic loads were studied.The results show that under the condition of constant temperature and low organic load（F/M=0.1-4.0 g-COD/g MLVSS）,the cumulative methane production and maximum methane production rate increase with the increase of organic load.At 25℃and 35℃,the anaerobic fermentation time was 90 and 35 days respectively,and the cumulative methane production at 35℃was much higher than that at 25℃.When the temperature is raised to 55℃,the cumulative methane production does not increase significantly,and the methane production rate at 35℃(0.26-0.28L/g-COD_added)is much higher than that at 55℃(0.2-0.23L/g-COD_added),indicating that 35℃is more suitable for anaerobic digestion and methane production of swine wastewater.（2）Carry out batch BMP experiments with high organic load（F/M=5-12g COD/g MLVSS）to explore the influencing factors of anaerobic methanogenesis of swine wastewater.The results show that the cumulative methane production under medium temperature is significantly higher than that under high temperature,especially under high F/M（11-12 g COD/g MLVSS）.Under the conditions of high temperature（55℃）and high F/M,the methane production efficiency is seriously inhibited.The analysis shows that with the increase of organic load,the accumulation of ammonia nitrogen and organic acids（VFAs）is more and more serious,in which the accumulation of VFAs is mainly acetic acid,which further defines the impact of temperature and high organic load on the methane performance of pig waste aquatic products.（3）A pilot scale An MBR and a traditional anaerobic reactor（UASB）were constructed to compare the pollutant removal efficiency,methane generation characteristics and microbial community structure of the two in the treatment of pig wastewater.The results show that the COD removal efficiency of An MBR is maintained at 80-90%,while that of UASB is only 40-60%.Due to the stronger methanogenic activity of microorganisms,the methane yield of An MBR（the maximum is about 0.27 L/g-COD）is higher than that of UASB.An MBR is enriched with functional bacteria that can remove refractory organics and methanogens of acetic acid and hydrogen nutrition.The ways of organic degradation and methanogenesis are more diversified,which strengthens the effect of bioenergy recovery.In addition,the energy recovery efficiency of An MBR is higher than that of UASB system,which better realizes the net capacity of operation process（4.18 k Wh/m³）.（4）The behavior and mechanism of membrane fouling were explored by investigating the change of transmembrane pressure difference（TMP）,the effect of membrane physicochemical cleaning and the identification of membrane fouling functional bacteria.The results show that with the shortening of HRT,the increase rate of TMP is accelerated,the thickness of mud cake layer is increased,and the TMP after hydraulic backwashing is gradually increased,which is slightly higher than that in the early stage,indicating the accumulation of pollutants on the membrane surface.The membrane resistance after physical cleaning is about 0.25 k Pa/L/（m²h）.After sodium hypochlorite and citric acid cleaning,the membrane filtration resistance decreases significantly.The microbial community analysis of mud cake layer showed that the relative abundance of Firmicutes increased from 80.2%to 86.3%.Excessive enrichment of Firmicutes may cause a large increase of extracellular polymer（EPS）,thus accelerating membrane pollution.