Anaerobic Methane Conversion And Membrane Fouling Mechanism Of Anaerobic Membrane Reactor Treating Sewage Sludge

Anaerobic membrane biological treatment technology has been widely concerned by researchers because it has both pollutant removal,energy recovery and less digestive residue.However,the low methane conversion efficiency and serious membrane pollution of anaerobic membrane bioreactor（An MBR）limit its practical application.In this paper,the following three experiments were conducted to investigate anaerobic digestion conversion and membrane fouling mechanism based on the addition of iron at different forms and An MBR system,including:（1）The effect of Blast furnace dust（BFD）on anaerobic methanation and kinetics of sludge was investigated to explore the feasibility of BFD as an economic,efficient and low-cost additive in enhancing methane conversion and thus achieve the purpose of"treating waste with waste";（2）The effect of sulphate-persulfate(Fe（II）/S₂O₈^2-)pretreatment on the long-term performance and sludge change characteristics of An MBR anaerobic digestion was evaluated by using persulfate pretreatment strategy.The dynamic behavior of microorganisms in sludge stimulated by trace Fe（II）/S₂O₈^2-and the mitigation mechanism of An MBR membrane fouling were investigated;（3）In the co-digestion of An MBR system,a mixture substrate with sludge and food waste（FW）were used to enhance sludge anaerobic methanation and explore the effect on the start-up of anaerobic membrane reactor,methane conversion efficiency and organic matter removal efficiency was explored.The main conclusions are as follows:1)The mechanism of BFD in sludge anaerobic methanation was discussed through batch experiments.BFD could promote the hydrolysis rate of sludge anaerobic methanation,and enhance the activity of methanogenic microorganisms.The fitting results of different model showed that Cone model had better adaptability.At the same time,the dehydration rate of digestive residue in 10 min was further improved with the addition of BFD.When BFD dosage was 1.5 g/g-VS,the moisture content of filter cake layer（10 min）was 19.5±0.5%,and its dehydration capacity was increased by 62.5%.Therefore,sludge showed excellent hydrolysis and dewatering performance after the addition of BFD.2)Anaerobic membrane biological treatment system was introduced,and Fe（II）was used to activate persulfate oxidation to enhance methane conversion.When Fe（II）/S₂O₈^2-dosage was 0.1/0.08 mmol/g-VS,the optimal biogas yield was 0.04L/L_reactor·d^-1,which was 25.0%higher than that without Fe（II）/S₂O₈^2-,and the proportion of methane also increased by 16.5%.When Fe（II）/S₂O₈^2-dosage was0.1/0.08 mmol/g-VS,the organic pollution resistance was reduced to 1.9×10¹¹ m^-1,and the third stage（0.2/0.16 mmol/g-VS）was further reduced to 1.8×10¹¹ m^-1.These results indicate that Fe（II）/S₂O₈^2-could effectively reduce the resistance of organic pollution in membrane fouling,and the iron-sulfur system could effectively control the organic pollution in membrane fouling.The results of EPS and SEM showed that trace Fe（II）/S₂O₈^2-was beneficial to the release of organic matter in sludge anaerobic fermentation,while excessive Fe（II）/S₂O₈^2-had certain damage to microorganisms3)Anaerobic co-digestion of SS-FW based on An MBR could significantly improve methane production performance,and the concentration of mixture also showed a great influence on AD system.When the sludge concentration was 40 g/L,the biogas yield reached 3.0±0.1 L/L_reactor·d^-1,which was 9.5 times of that when the sludge concentration was 10g/L,and the maximum methane yield could be achieved.The change of sludge concentration did not have a great influence on membrane flux,which remained at a relatively stable level of 10.7±0.2 LMH,and its TMP value≤5.1 kpa.The analysis of the membrane pollutants showed that EPS could make the pollutants gather and closely adhere to the membrane surface.When the sludge concentration was 40 g/L,the membrane pollutants were tightly bonded and orderly microbial clusters.The poor operational performance of AD system was caused by overloaded（>50 g/L）through decreasing the liquidity of solids and the mixing efficiency of internal gas circulation,and then resulting in the increase of membrane pollution.The microbial community analysis further showed that the microbial community structure in the An MBR system was optimized.The proliferation and enrichment of organic-degrading bacteria（such as Proteobacteria,Firmicutes,Smithella,etc.）and methanogenic bacteria（such as Methanosaeta,Methanobacterium,etc.）had promoted the good operation of An MBR system.