| Environmental pollution and resource waste is the result of agricultural waste can't be reasonable use.Anaerobic digestion technology can change organic matter into biogas,it is an important way to use agricultural waste.However,there is much content of lignin in agricultural waste,and the cellulose hemicellulose is covered by lignin.Thus,there are some problems,such as slow start,low efficiency of biogas,incomplete in fermentation,long cycle of fermentation and so on,if straws are fermented straightway.Dairy manure,rice straw and wheat straw are used as raw material of anaerobic digestion.Ultrasonic,composting,sodium hydroxide,ammonia,hydrochloric acid and acetic acid are used to pretreat raw material of anaerobic digestion.The rice straw or wheat straw is mixed with dairy manure by 1:1,then the mixtures are used to ferment in laboratory by batch test.This study probe efficient and economical pretreatment of raw material in anaerobic digestion,optimize different pretreatment methods,analyze the effect of pretreatments on initial fermentation environment and fermentation process environment,discuss the relationship between biogas production on initial fermentation environment and fermentation process environment,uncover the reason why pretreatments can improve biogas production,then calculate comprehensive benefits in anaerobic digestion of the best pretreatment conditions of different pretreatment ways.The main results of this study are showed as follow:(1)The suitable ultrasonic,composting,sodium hydroxide,ammonia,hydrochloric acid and acetic acid pretreatment ways can significantly enhance the total biogas production in anaerobic digestion(P<0.01).When optimize the different pretreatment ways,the result shows that: The total biogas productions in treatment groups of rice straw pretreated 20 minutes with dairy manure pretreated 40 minutes and wheat straw pretreated 20 minutes with dairy manure pretreated 30 minutes are the highest pretreated in ultrasonic pretreatment,they are 13679 mL and 13100 m L.The total biogas productions in treatment groups of rice straw and dairy manure pretreated 6 days under 35? and wheat straw and dairy manure pretreated 6 days under 35? are the highest in composting pretreatment,they are 16005 m L and 16515 mL.The total biogas productions in treatment groups of rice straw pretreated 4 days under 3% sodium hydroxide with dairy manure and wheat straw pretreated 4 days under 3% sodium hydroxide with dairy manure are the highest in sodium hydroxide pretreatment,they are 14365 m L and 13830 m L mL.The total biogas productions in treatment groups of rice straw pretreated 4 days under 8% ammonia with dairy manure and wheat straw pretreated 2 days under 8% ammonia with dairy manure are the highest in ammonia pretreatment,they are 16940 mL and 19925 mL.The total biogas productions in treatment groups of rice straw pretreated 4 days under 2% hydrochloric acid with dairy manure and wheat straw pretreated 2 days under 3% hydrochloric acid with dairy manure are the highest in hydrochloric acid pretreatment,they are 13225 m L and 20225 mL.The total biogas productions in treatment groups of rice straw pretreated 6 days under 4% acetic acid with dairy manure and wheat straw pretreated 4 days under 4% acetic acid with dairy manure are the highest in acetic acid pretreatment,they are 11605 m L and 11880 m L.(2)The cellulose activity,reducing sugar content,VFA content and pH in initial fermentation environment in co-anaerobic digestion of rice straw and dairy manure are affected by pretreatments.The highest cellulose activity,reducing sugar content,VFA content and p H are 4.22 IU /mL,11.29 mg /mL,746 mg /mL and 7.6 in ultrasonic pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 1.55 IU /mL,9.25 mg /m L,576 mg /m L and 7.9 in composting pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 5.47 IU /mL,30.03 mg /m L,511 mg /m L and 8.7 in sodium hydroxide pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 6.11 IU /mL,40.35 mg /m L,1092 mg /m L and 9.2 in ammonia pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 8.26 IU /mL,82.89 mg /m L,1194 mg /mL and 7.0 in hydrochloric acid pretreatment.The highest cellulose activity,reducing sugar content,VFA content and p H are 5.83 IU /m L,32.91 mg /m L,2623 mg /mL and 7.2 in acetic acid pretreatment.The cellulose activity,reducing sugar content,VFA content and pH in initial fermentation environment in co-anaerobic digestion of wheat straw and dairy manure are affected by pretreatments.The highest cellulose activity,reducing sugar content,VFA content and pH are 2.05 IU /mL,12.97 mg /m L,683 mg /m L and 7.7 in ultrasonic pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 1.42 IU /m L,8.88 mg /mL,315 mg /mL and 7.7 in composting pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 3.08 IU /m L,18.41 mg /mL,653 mg /mL and 8.3 in sodium hydroxide pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 5.98 IU /m L,54.30 mg /mL,1317 mg /mL and 9.2 in ammonia pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 8.82 IU /m L,36.87 mg /m L,873 mg /mL and 7.8 in hydrochloric acid pretreatment.The highest cellulose activity,reducing sugar content,VFA content and pH are 9.38 IU /m L,89.59 mg /m L,2753 mg /mL and 6.7 in acetic acid pretreatment.(3)Path analysis indicated that there are direct effect and indirect effect of cellulose activity,reducing sugar content,VFA content and pH in initial fermentation environment on total biogas production.Different pretreatment ways have different relationship between cellulose activity,reducing sugar content,VFA content,pH and total biogas production.In co-anaerobic digestion of rice straw and dairy manure,the residual path coefficient of path analysis of ultrasonic,composting,sodium hydroxide,ammonia,hydrochloric acid and acetic acid pretreatment are 0.766,0.827,0.596,0.762,0.468 and 0.379.In co-anaerobic digestion of wheat straw and dairy manure,the residual path coefficient of path analysis of ultrasonic,composting,sodium hydroxide,ammonia,hydrochloric acid and acetic acid pretreatment are 0.745,0.720,0.449,0.844,0.513 and 0.826.(5)Anaerobic digestion can produce economic benefits of energy,and all of the economic benefits of energy are higher than that of un-pretreated treatment.In co-anaerobic digestion of rice straw and dairy manure,the net income of rice straw and dairy manure are pretreated 6 days under 35? by composting,it is 296.07 yuan / year.In co-anaerobic digestion of wheat straw and dairy manure,the net income of wheat straw and dairy manure are pretreated 6 days under 35? by composting,it is 302.12 yuan / year.The acetic acid pretreatment is not suitable for the actual production but the ultrasonic,composting,sodium hydroxide,ammonia and hydrochloric acid pretreatment ways,thus ultrasonic,composting,sodium hydroxide,ammonia and hydrochloric acid pretreatment are suitable for the actual production.The ecological benefits of rice straw pretreated 4 days under 8% ammonia with dairy manure and wheat straw pretreated 2 days under 8% ammonia with dairy manure are the highest,thry are higher 159.00% and 181.53% than their un-pretreated treatments.(6)Pretreatment improve total biogas production by changing the relationship among daily biogas production,cellulose activity,reducing sugar content,VFA content and pH.Factor analysis indicated that the major effect factors of daily biogas production are different in different fermentation process,the major effect factors of daily biogas production of different treatments are different in same fermentation process.Pretreatment improve the highest daily biogas production and enhance it appear time.The stability of daliy biogas production,cellulose activity,reducing sugar content,VFA content and pH in fermentation process are affected by pretreatment.The stability of pH is lowered and VFA content is rose.The stability of factors in fermentation process are changed,which in interaction makes the stability of fermentation system,then promote the anaerobic digestion and improve total biogas production. |
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