Efficacy And Comparative Study Of Anaerobic Digestion Process Of Municipal Sludge At Different Temperatures

With the strengthening of sewage treatment in China,the sewage treatment plant has effectively alleviated the problem of sewage.Therefore,the reduction,stabilization,harmlessness and resource utilization of sludge are particularly important.There are currently several technologies to choose from,such as combustion,pyrolysis,gasification and anaerobic digestion.Anaerobic digestion is a proven technology that has been proven to reduce excess sludge and produce methane-rich biogas.In the traditional anaerobic digestion process,it is affected by low organic matter concentration,long hydraulic retention time,and accumulation of residual organic matter.Anaerobic digestion is a technical unit that is particularly important for sludge treatment.In this study,Cambi160?thermal hydrolysis pretreatment(THP)technology was used to conduct mesophilic anaerobic digestion(MAD)and thermophilic anaerobic digestion(TAD)experiments under different Sludge Retention Time(SRT):(1)Under the condition of anaerobic digestion,the organic matter process based on thermal hydrolysis pretreatment of sludge and the anaerobic digestion process of sludge were optimized,and the mechanism of pretreatment affecting the hydrolysis of sludge organic matter and strengthening anaerobic digestion was explored.(2)Comparison of THP-MAD,THP-TAD,two different combinations of anaerobic digestion processes on sludge organic matter reduction and methanogenic potential.According to the influence of potential,the process parameters of mesophilic anaerobic digestion and thermophilic anaerobic digestion treatment of enhanced sludge thermal hydrolysis under different SRT were optimized.Finally,the optimized process conditions were as follows:(1)the mesophilic anaerobic digestion SRT was the best for methane production at15 days,which was 384.19±37.4 CH4 m~3/kg VS added.The removal rate of volatile organic matter(Volatile Solid,VS for short)was up to 43.1%~54.3%.Among them,in the process of shortening SRT to thermal anaerobic digestion of sludge after thermal hydrolysis,the changes of protease and acetate kinase in the hydrolysis acidification stage are significant,which is fully prepared for subsequent methanogenesis,and protease and acetate kinase affect sludge.The key enzyme activities of hydrolytic acidification and dissolved organic matter were significantly changed in the mesophilic anaerobic digestion.The initial activity of the coenzyme F420 in the methanogenic stage was different,but the utilization rate was not much different(±0.1);(2)thermophilic anaerobic digestion when the SRT is 20 days,the best methanogenesis is 372.33±43.62 CH4 m~3/kg VS added.The removal rate of VS after digestion is up to 45.2%~52.8%.The gas production by thermophilic anaerobic digestion decreases the methane production with SRT keep decreasing.This is due to the reduction of the content of the key enzyme coenzyme F420,which does not provide sufficient enzymatic digestion of acetic acid,so that the dynamic equilibrium of acetic acid is continuously decomposed into carbon dioxide and hydrogen.(3)The comparison of MAD and TAD found that the MAD methanogenesis was better because the hydrolysis of the sludge in the MAD system was more thorough,and the protease and acetate kinase activities were strong during the hydrolysis process.In addition,the abundance of Methanoculleus and Methanolinea microorganisms in the MAD system.They are carbon dioxide reduction-type and acetic acid-type methanogens,and the multi-method methanation stage makes the mid-temperature production period the best.The most direct cause of low gas production is that the organic loading rate of TAD system has not reached the maximum.Within a certain SRT experiment range,the TAD gas production has not decreased significantly,that is,the TAD still has the potential for methanogenesis.