| Maize is an important grain crop in China,and the number of straw produced by corn is up to 2.8 tons per year.With the increasingly prominent problem of environmental pollution in rural areas and the serious energy shortage,more and more people pay attention to biogas engineering.The corn straw is the main raw material in the biogas fermentation engineering because of its high ratio of straw to grain and coarse fiber content.In this paper,the composition of corn straw in different periods was analyzed,and the biogas production potential was studied to determine the best fermentation period.At the same time,the corn straw was treated by different methods to explore the effect of the optimum pretreatment conditions on biogas production of corn straw.1.The nutritional components and the corresponding gas production potential of corn stalk at different positions in different periods were studied.The results showed that the content of dry matter and neutral detergent fiber in foliage decreased gradually with the harvest time,while the content of crude protein and acid detergent fiber increased gradually.The content of dry matter,crude protein and acid detergent fiber in stalk decreased with the extension of time,and the content of neutral detergent fiber increased with the increase of harvest time.The best cumulative gas production rate of foliage was 11671 ml,and the maximum gas production rate was 2359ml/d in harvest time.The maximum cumulative gas production was 14711 ml,the time was 10 d after harvest,and the maximum gas production rate was 2354ml/d,which was 20 days later of the harvest time.2.With straw as raw material in the process of anaerobic fermentation,pretreatment of straw is an indispensable method to improve biogas production capacity.In the present study,corn straw was used as raw material.The current work was to explore a suitable ammonia pre-concentration and the influence of ammonia treatment on biogas production,straw structure,chemical oxygen demand(COD)removal rate and initial p H value of fermentation broth,which by using ammonium bicarbonate solution with mass fraction of 4%,6%,8%,10% and 12% to pretreat corn stalk powder,respectively.The results indicated that the biogas production of unit mass total solids(TS)with the ammonium bicarbonate solution mass fraction of 8% exhibited the best,which reached the value of 222.6 ml/g.And in this condition,the total gas production was 14690 ml,which was also the best and increased by 30.6% compared with non-pretreatment group.The Modified Gompertz equation could be fitted well with the experimental results and it showed that when ammonia concentration was 8%,the gas production and gas production rate could both obtain the best results.With the increase of the pretreatment concentration,the degree of surface structure was changed from smooth to rough.Gradually,when the treatment concentration increased by 12%,the surface structural damage of straw reached to the maximum extent.Appropriate pretreatment concentration could promote the COD removal rate of fermentation broth.When the pretreatment concentration was 8%,the fermentation broth removal rate of COD was 36%,which was the largest.Pretreatment with proper concentration can stabilize the p H value of anaerobic fermentation broth,and with the increase of ammonium bicarbonate mass fraction,the fluctuation of fermentation broth was smaller except for the 12% pretreatment group.3.The method of pretreatment of corn stalk by ultrasound combined with ammonium bicarbonate was used to evaluate the yield of reducing sugar.The effect of ultrasonic treatment time,treatment temperature and material liquid ratio on the yield of reducing sugar was studied,and optimized of ultrasonic parameters in ultrasonic processing by Response Surface Methodology.The results showed that in the single factor test,when the ratio of material to liquid was 15,reducing sugar yield maximum is 3.29mg/g.When the optimum processing temperature was 50,the reducing sugar yield was 4.15mg/g.When treatment time was 20 mins,the maximum reducing sugar yield was 2.34mg/g.The order of influence on reducing sugar yield was as follows: treatment time,treatment temperature and liquid material ratio.Treatment time and liquid to material ratio,treatment time and treatment temperature have significant interaction effect,and the effect of treatment time was greater than the ratio of liquid to material and the pretreatment temperature.The interaction of liquid to material ratio was not significant.The optimum conditions of the response surface were as follows: the ratio of liquid to material was 21.27:1,the temperature was 42.23 5.36mg/g and the treatment time was 48 min.Under this condition,the expected yield of reducing sugar is 5.36mg/g.After modification,the ratio of liquid to material was 21:1,the temperature was 42 48 min,and the yield of reducing sugar was 5.32mg/g.The experimental results were in good agreement with the simulation results.4.The current work was to explore the biogas production potential of corn straw in different harvest periods by using the whole plant corn of dough stage(a),waxy maize straw(b),and full ripe stage of corn straw(c),respectively.The changes of composition and gas production characteristics of corn straw before and after ensiling were studied in mesophilic anaerobic fermentation.The experimental results showed that the crude protein content of sample a was 11.56 and 14 times more than b and c,and the water soluble carbohydrates was 8.6 and 12.28 times more than b and c respectively.The cumulative gas production of unit TS of sample a before and after silage was 270.33ml/g and 271.2ml/g,which increased by 52.1% and 52% compared with sample b,and increased by 64.5% and 68.9% compared with that of sample c respectively.Daily biogas production of sample a before and after silage was 720 ml and 740 ml respectively,which was 40% higher or more than other samples.At about 20 th day of the reaction,the methane accumulation rate of sample a,b and c was stable at 170ml/g,155ml/g and 142ml/g respectively.Modified Gompertz equation fits well with the actual cumulative methane content of the experimental.The results showed that the cumulative methane content of sample a with silage was the highest,and the sample c before silage was the lowest.The p H value of fermentation broth decreased to the lowest in the 5th day,and that of sample a with no silage was 6.2,which was the lowest.Five days later of the fermentation,the p H value of feed liquid in each group was around 7.5.The maximum p H fluctuation ranged from 6.2 to 7.7 for sample a with no silage,and the minimum p H fluctuation ranged from 6.8 to 8.8 for sample a with silage. |
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