| In China,with the rapid development of rural economy,the disposal of rural domestic waste has become an essential issue to be solved in the new countryside construction.Kitchen waste and paper waste are the main components of rural domestic waste,and they are also biomass energy with great potential.Anaerobic co-digestion is a sustainable technology which meets the requirements of“reduction,harmlessness,and resource”.Using anaerobic co-digestion to develop clean energy is an effective way to solve problems such as rural energy shortage and environmental pollution.In this study,the system used food waste?FW?and paper waste?PW?as the substrates.The mixing ratios,temperature and the organic loadings are the crucial factors to affect the anaerobic digestion process.Therefore,in hope to determine the optimal ratio under mesophilic?35??and thermophilic?55??conditions,this study used batch anaerobic co-digestion tests.On the basis of this,the co-digestion process of rural domestic waste was optimized from the two factors of temperature and organic loading,so as to determine the best operating conditions of the anaerobic co-digestion system.The results indicated that hydrolysis was the rate-limiting step for PW under mesophilic?35??conditions and had a low VFAs concentration.FW was easy to produce VFAs accumulation.Propionate and butyrate became the main component of accumulated VFAs.Co-digestion of FW and PW could improve the buffer capacity of the system,alleviate the accumulation of VFAs and accelerate the methanogenesis.The result showed that with FW proportion increasing,methane production rate increased first and then decreased.And,then when FW?PW=35?65,the system had the highest methane production rate.Under thermophilic?55??conditions,acetate,propionate and butyrate all showed different degrees of accumulation when the proportion of FW was100%and 80%.Moreover,acidogenesis and methanogenesis were found to be restricted due to the accumulation of VFAs.The other co-digestion systems could alleviate the inhibition caused by the product of hydrolysis and acetogenesis.The result showed that the system had the highest methane production rate when FW?PW=65?35.The optimization of co-digestion temperature conditions showed that the potential and rate of hydrolysis and acetogenesis had been increased significantly under thermophilic condition,and the high level of VFAs that occurred in the thermophilic condition.However,the ability of microorganisms to metabolize VFAs was lower than that of mesophilic,resulting accumulation of VFAs and lowering system stability.Moreover,the thermophilic had a low methanogenic activity and the longer methane production lag period,at the same time the methane production rate had not been improved.Therefore,the mesophilic condition was better than the thermophilic.Organic loading rate test had been designed under optimal mix ratio and temperature conditions.The results showed that when the organic loading rate was less than or equal to 13.44 g·VS·L-1,methane production rate decreased linearly with the increases of the organic loading.Acetate was the main component of VFAs.When the organic loading rate increased to 26.88 g·VS·L-1,propionate and butyrate became the main component of accumulated VFAs.Acidogenesis and methanogenesis of the systems were found to be restricted,but the system was self-recovery later.When the organic loading rate continued to increase to 53.76g·VS·L-1,the concentration of butyrate climbed to 12.2 gCOD/L and this system tend to fail.Therefore,VFAs accumulation was the main reason why the system was suppressed or even tended to fail.Organic loading rate of 13.44 g·VS·L-1 was the best operating condition for anaerobic co-digestion under mesophilic temperature.Under such a condition,the methane production rate may become the most prominent and the system could also be expected to be stable and efficient without acidification. |
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