| With the development of urbanization in China,a large amount of sludge is directly affected by the large scale of sewage treatment.According to statistics from relevant departments,it is expected that by 2020,the total amount of sludge produced in China will exceed 60 million tons.Chinese traditional anaerobic digestion system is often aimed at achieving the sludge resource,stabilization,reduction and harmless utilization,but in actual operation,there are some issues such as insufficient biogas production,low biogas production rate,and gas production has not reached the design.To solve these problems,pretreatment facilities are often added before traditional anaerobic digestion.As a new clean anaerobic digestion pretreatment method,microaeration pretreatment can accelerate the hydrolysis rate of the enzyme in anaerobic digestion,improve the relative abundance of the microbial population and improve the solubility of COD in sludge.It can also improve the efficiency of anaerobic digestion to produce methane.At present,domestic and foreign experts and scholars have explored the operation effect of the micro-aeration pretreatment system,mostly focusing on verifying the feasibility of micro-aerobic pretreatment to improve the efficiency of anaerobic digestion and methane production.The screening of the best process conditions for pretreatment,and further research and summary are needed.Therefore,this article based on the municipal sludge as the research object,and uses micro-aerobic pretreatment technology for pretreatment to improve its anaerobic digestion treatment efficiency,by studying different pretreatment conditions on sludge properties,methane production and extracellular polymers to explore the optimal process conditions for micro-aeration pretreatment.The main research results are as follows:(1)The study on condition optimization of microaeration pretreatment to improve the performance of municipal sludge showed that microaeration pretreatment can promote the release of organic matter in municipal sludge and significantlyimprove the anaerobic digestion potential of the sludge.The solubility of organic matter concentration with the increase of the intensity of aeration and aeration time presents the rising trend,aeration intensity of 0.30 vvm,aeration time of 12 h were the best pretreatment conditions for the release of organic matter from municipal sludge.At this time,the SCOD,soluble protein,soluble carbohydrate value could reach the original clay respectively 4.20,2.60,and 7.04 times,COD dissolution rate increased from 1.21% to 3.84%.At the same time,the micro-aeration pretreatment could increase the p H of the entire system.The p H of the 0.30 vvm after 12 hours of operation was 6.89,which improves the release of organic matter and creates favorable conditions for the subsequent anaerobic digestion methanogenesis.High temperature(55 ?)micro-aeration pretreatment could also improve the hydrolysis and dissolution of macromolecular organic matter.(2)The experiment of the influence of micro-aeration pretreatment on the efficiency of municipal sludge's mid-temperature anaerobic digestion showed that under the condition of medium temperature,micro-aeration pretreatment can promote the anaerobic digestion of municipal sludge to produce methane.The cumulative methane production per unit VS showed an upward trend with the increase of aeration intensity and the extension of aeration time.The sludge pretreated by the above optimal conditions(aeration intensity 0.30 vvm,aeration time 12 h)showed good performance for its anaerobic digestion performance,the cumulative methane production per unit VS was 257.17 m L·g-1 VS,which is about 26.8% higher than that of the control group without pretreatment.(3)The experiment of the effect of micro-aeration pretreatment on municipal sludge high temperature anaerobic digestion efficiency showed that under high temperature conditions,micro aeration pretreatment can promote municipal sludge anaerobic digestion to produce methane.The cumulative methane production per unit VS showed an upward trend with the extension of the aeration time,in which the pretreated sludge(aeration intensity of 0.30 vvm,aeration time of 12h)showed goodanaerobic digestion performance,and its mixture The accumulative methane production per unit VS of the test sludge was 268.53 m L·g-1VS,which was about14.59% higher than that of the control group without pretreatment.(4)The effect of microaeration pretreatment on extracellular polymer of municipal sludge showed that microaeration pretreatment can not only promote the increase of EPS content of sludge,but also change the layered structure of sludge EPS.The total amount of EPS and the contents of various dissolved organic compounds showed an increasing trend with the increase of aeration intensity and the extension of aeration time.In the pretreatment process,the hydraulic shear force generated by aeration can cause EPS to gradually move from the TB-EPS attached to the cell to the relatively loose LB-EPS and S-EPS,and then release into the liquid phase.The proportion of S-EPS and LB-EPS in the total EPS increases,while the proportion of TB-EPS decreases.The effects of micro-aeration pretreatment on the remaining sludge active cells were mainly in two aspects: firstly,it could make the extracellular polymer peel,and moved from the TB-EPS attached to the cells to the loose S-EPS and LB-EPS,so as to improve the dissolution efficiency of soluble organic compounds and had an impact on the improvement of anaerobic digestion efficiency;The second was to crack the active microorganisms,so that organic substances from the cell dissolution,for the subsequent anaerobic digestion to provide a substrate. |
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