High Efficiency Anaerobic Diagestion Performance Of Rice Straw

China is the largest rice producer in the world,and the production of rice accounts for 31%of the world's total rice production.As the waste after harvesting rice,the production of rice straw(RS)can reach 6.04×109 tons per year.At present,the main treatment methods of RS are incineration and straw recycling.These treatments for RS not only cause serious pollution to our environment,but also waste biomass.Anaerobic digestion(AD)is a quite suitable way to handle RS,which not only realizes reasonable utilization of rice straw,but also produces methane(a kind of clean energy)to alleviate energy crisis and environmental pollution in China.Therefore,in this study,the anaerobic digestion conditions of RS were researched,and pretreatments and anaerobic co-digestion of pretreated RS and manures had been carried out to improve the methane production of RS.Firstly,the central composite design method(CCD)of response surface methodology(RSM)was used to explore the influence and the optimal conditions(initial pH,organic load and inoculation ratio)of anaerobic digestion of RS.The results showed that the factors of organic loading and inoculation ratio would influence the cumulative methane production of RS significantly,and an interaction was also found in these two factors.The optimal digestion conditions for RS were F/I ratio of 0.75,organic load of 20.6 g-VS/L and initial pH of 7.75,and the maximum cumulative methane production was 252.4 mL/g-VS,BD was 52.89%.Secondly,different pretreatments including KOH,NaOH,alkali hydrogen peroxide(AHP),HC1,H2SO4,steam explosion(SE)and microwave(MW)were carried out to improve the ability of anaerobic digestion of RS.The results showed that the alkali pretreatments had more significant effect on the methane production of RS than that of acid pretreatments and physical pretreatments,especially 3%NaOH,3%AHP.The cumulative methane production of these two pretreatments were 289.7 mL/g-VS and 285.8 mL/g-VS,respectively.Compared with the methane production of non-pretreated RS(151.8 mL/g-VS),the productions of these two pretreatments were increased to 90.77%and 88.25%,respectively.The biodegradation rates of these two pretreatments were 63.82%and 62.98%,respectively.However,there was no significant difference in these two pretreatments(p>0.05),and considered the cost problem and the environmental pollution problem,3%AHP was finally determined as the best pretreatment for RS to carry out the subsequent experiment.Finally,based on the results of pretreatments and RSM,the experiments were carried out the co-digestion of RS after 3%alkaline hydrogen peroxide pretreated and five different manures(racoon dog manure,chicken manure,pig manure,dairy manure and sheep manure).The results showed that sheep manure and dairy manure were not suitable for doing co-digestion with pretreated RS.But the racoon dog manure,pig manure,and chicken manure could improve the anaerobic co-digestion production with pretreated RS.The maximum synergistic effect index,maximum cumulative production and maximum biodegradation were all obtained by anaerobic co-digestion of chicken manure with pretreated RS,and value were 22.33%,384.69 mL/g-VS and 82.99%,respectively.In all words,the high-efficiency AD of RS was studied systematically and comprehensively in this research,which not only found an effective method to handle RS,but also provided a theoretical basis for the efficient utilization of RS in biogas project in the future.