| Household biogas plays an important role in rural environmental protection,energy supply and other fields in China because of its strong advantages of“One biogas belt three materials,fertilizer,fuel,feed,three to promote five industries,farming,forestry,animal husbandry,side-line production and fishery”.Hence,it is usually used as the important gripper of a new rural construction,a beautiful rural construction,and a strategy for rejuvenating villages.With the development of the economy and society,the loosening of livestock and poultry of one family has gradually been replaced by large-scale farming,leading to major changes in the raw materials of rural household biogas digesters,mainly livestock and poultry excrement,which had to be replaced with other raw materials.As a supplement,crops with a large amount of crops and a wide range of crops in rural areas are incorporated into the biogas digesters.Therefore,the mixed fermentation technology of livestock manure and crop straw has to be put on the scientific research agenda.On the other hand,due to the apparent seasonality of straw production with agricultural activities,this also leads to a large change in the supply of raw materials for rural household biogas fermentation.Therefore,on the basis of mixed fermentation of livestock manure and crop straw,seeking simple and practical resistance to raw material impact technology,so as to ensure the efficient and stable gas production of biogas fermentation,which is the entry point for this study.In the study,using pig manure and corn stalk as raw materials,in moderate temperature condition,batch fermentation test,semi-continuous fermentation test and pilot test were used to optimize the technical parameters of efficient and stable gas production from mixed fermentation,and the microbial community structure of mixed fermentation was explored.Next,appropriate exogenous additives were used to study the recovery of the impact load of the fermentation raw material was researched,and suitable condition for the pilot fermentation was obtained.The research results obtained in this paper are as follows:In the semicontinuous fermentation experiment,uniform test design methods were used to optimize the operation control conditions(total solid concentration,feeding ratio,stirring frequency.The results showed that,the effect of aerogenesis improved as the TS concentration and feed ratio increased;the COD removal rate increased as the TS and stirring frequency decreased.Under the experimental conditions,the best fermentation conditions for aerogenesis were TS of 7%,feeding ratio of 5%,stirring frequency of 2 times per day;the condition for the highest COD removal rate was TS of 5%,feeding ratio of 10%,stirring frequency of 1 time per day.Reasonable refueling and stirring control were conducive to the improvement of biogas production.The former volume loading rate was increased from 0.242L·L-1·d-1 to 0.526 L·L-1·d-1;the latter volume loading rate was increased from 0.325 L·L-1·d-1to 0.614 L·L-1·d-1.Stable and efficient microflora had formed in both fermentation conditions.The dominant bacteria and archaea community accounted for more than 80%of the microbial population.The dominant bacteria under the two conditions were mainly Firmicutes and Bacteroidetes.The best conditions for aerogenesis were 39.17%and 46.87%,respectively,and the condition is 59.16%and 26.89%in the conditions with the highest COD removalrate;thepredominantarchaeaintheformerconditionwas Methanocorpusculum?45.81%?and Methanosarcina?35.03%?.The predominant archaea in the latter condition was Methanosarcina?65.88%?and Methanobacterium?18.01%?.Because of the presence of more functional microflora in the latter condition,it was conducive to the decomposition and utilization of organics and the improvement of aerogenesis.Given comprehensive consideration of aerogenesis,COD removal efficiency,and microflora structure,the condition of the highest COD removal rate was selected to be proper for anaerobic fermentation.Next,selecting the condition with the highest COD removal rate?5%TS,10%feeding ratio,stirring frequency of 1 time per day?for batch and semi-continuous fermentation tests,the aerogenesis effect in the reactor was obtained through the batch fermentation test of of adding activated carbon with different concentrations and NTA.The results showed that,Proper addition of activated carbon could effectively increase the biogas production.In the entire fermentation process,the VS removal efficiency was?90.6±3.5?%under the activated carbon condition of 10.0g·L-1,and the VS gas production rate and VS methane production rate were 426.1±13.7 and 233.0±7.7 mLg-1 respectively;the methane concentration reached a maximum of?71.8±2.7?%.Biogas production improved with the NTA concentration decreasing,and excessively high concentration of NTA would inhibit the methane production.The VS gas production rate with NTA of 2.0?mol·L-1 NTA was 374.0±14.6 mL·g-1 and the VS methane production rate was 195.3±3.3 mL·g-1,and the maximum methane concentration was?66.7±2.6?%.Through a further semi-continuous test,the activated carbon improved the gas production during fermentation with average volume loading rate of 1.2 L·L-1·d-1 greater than NTA(1.1 L·L-1·d-1),and the concentration of methane had been kept above 60%.And the COD removal rate was 70.6%,which was higher than NTA?67.9%?,and activated carbon had a certain buffering effect on the fermentation system.Thus,activated carbon of 10.0 g·L-1 was selected as the proper exogenous additive.Finally,inspecting the effect of the pilot plant operation under the suitable condition,in the process of continuous operation,the process of changing the effect of anaerobic fermentation to recover gas production when raw materials are insufficient can be studied by reducing the raw material TS and adding activated carbon.It is divided into five periods:fermentation start-up period,stable operation period?TS5%?,low TS load disturbance period?TS3%?,re-stabilization period?TS3%+activated carbon?,and recovery period?TS5%+activated carbon?.The results showed that,the fermentation process of the entire pilot scale test lasted for about 65 days,and the cumulative gas production was 38.102 L·L-11 with average volume loading rate of 0.586 L·L-1·d-1 and peak of 0.855 L·L-1·d-1,and the maximum concentration of methane was about 68.8%.Adding activated carbon had a significant acceleration effect on gas production rate and methane content.The gas production rate was increased by approximately 0.1 L·L-1·d-1,with concentration of methane increasing by5%10%.Proper refueling and addition of activated carbon can reduce the increase of ammonia nitrogen in the fermentation broth,which reached about 650mg·L-11 at the end of the fermentation,and no ammonia inhibition occurred(much less than the gas production inhibition threshold of 1700 mg·L-1).The main component of volatile aliphatic acid was acetic acid,which verifing the existence of acetogenic methanogens in the inoculum formed under the suitable condition,and activated carbon could promote the utilization effect of microorganism on acetic acid,thereby increasing the biogas production.In the case of sufficient raw material and normal biogas fermentation,the pH was basically around 7.4;and the VFA/TA was between 0.2 and 0.3,which was basically not affected by the input and output of raw materials and the addition of activated carbon.Obvious acidification did not occur all along during the fermentation process,and pH and VFA/TA indicated that the fermentation system was always in stable operation.The method of the suitable fermentation condition and adding activated carbon is worthy of promotion in the biogas digester in rural households. |
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