| China is a traditional agricultural country,crop straw production is huge,rich in species.According to statistics,the annual output of crop straw in China is about 8.4×108 T,however,because of the long history of simple and crude disposal,it will not only lead to the waste of resources,but also an important cause of ecological and environmental problems such as haze,forest fire.Nowadays,widespread research shows that anaerobic fermentation technology is an efficient means to realize the resource disposal of crop stalks,and by this method,the biomass that is difficult to be directly used in crops can be converted into ethanol,hydrogen,methane and other clean energy.This method can not only relieve the pressure of lack of fossil energy resources,but also reduce the environmental risk caused by improper handling of straw.However,the existence of waxy layer on the straw surface and the tight cross-linking between cellulose and lignin in the straw will reduce the gas production efficiency of anaerobic fermentation,so it is necessary to pretreat the straw before anaerobic fermentation.In this study,the enzymatic ratio,amount,solid-liquid ratio and hydrolysis time of cellulose and xylanase were determined by single factor experiment of alkali-enzyme combination hydrolysis of straw.The molecular weight distribution of lyophilized hydrolysates of rice straw and wheat straw was analyzed by gel chromatography.The alkali pretreated rice straw,wheat straw and rice straw hydrolysate,wheat straw hydrolysate and the chrome leather scraps collagen liquid mixed anaerobic fermentation,explore the effects of different C/N ratio and different pretreatment degree on anaerobic fermentation gas production characteristics.Analyze the changes of fermentation system pH,concentration of VFAs,SCOD concentration,and ammonia nitrogen concentration during anaerobic fermentation.The microbial diversity of the post-fermentation fermentation system was analyzed by 16rRNA high-throughput sequencing.The main conclusions are as follows:(1)The optimal hydrolysis conditions of cellulose-xylanase in single factor experiment were as follows:enzyme ratio of 3:2,enzyme amount of 300 U:200 U,solid-liquid ratio of 1:20,hydrolysis duration of 72 h.The highest concentration of reducing sugar in the hydrolysate of rice straw was 17.19 mg/L,and the highest yield of reducing sugar was 84.04%.The highest concentration of reducing sugar in the hydrolysate of wheat straw was 12.55 mg/L,and the highest yield of reducing sugar was 69.00%.(2)The molecular weight distribution of rice straw and wheat straw hydrolysates was analyzed by gel chromatography.The number average molecular weight of rice straw hydrolysates was 1214 and the weight average molecular weight was 1372.The number average molecular weight and weight average molecular weight of wheat straw hydrolysate were 1223 and 1356 respectively.(3)When the C/N ratio was 25:1,the maximum values of daily gas production,total gas production and cumulative methane production of 4.5 g(denoted by TC)rice straw and wheat straw as carbon source were 159.0 mL and 190.0 mL,2002.1 mL and 1944.0 mL,1221.3 mL and 1277.2 mL,and methane content was 61.0%and 65.7%,respectively.The maximum daily gas production,total gas production and cumulative methane production of 4.5 g(denoted by TC)rice straw and wheat straw hydrolysate were 200.0 mL and 187.8 mL,2841.9 mL and 2814.1 mL,1960.9 mL and 1933.3 mL,respectively,and methane content was 69.0%and 68.7%,respectively.(4)When the C/N ratio was 25:1,the SCOD removal rates of rice straw and wheat straw as carbon sources were 75.1%and 58.6%,respectively,and the ammonia accumulation concentrations were 3108.0 mg/L and 2532.9 mg/L,respectively.Using rice straw and wheat straw hydrolysate as carbon source,the SCOD removal rates were 59.2%and 74.7%,respectively,and the accumulation concentrations of ammonia nitrogen were 2034.0 mg/L and 1828.6 mg/L,respectively.(5)The microbial diversity analysis of the four different fermentation systems with C/N of 25:1 showed that the microbial composition of the four different fermentation systems had little difference,and the species abundance difference was not significant.Anaerolinea was the dominant strain of the four different fermentation systems with carbon sources. |
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