| According to the 13th Five-Year Plan of our country,the local use as rural energy and organic fertilizer is the main direction to solve the problem of disposal and utilization of manure in large-scale livestock and poultry farms.In the process of anaerobic fermentation and biogas fertilizer treatment of agricultural waste,understanding the changes of carbon and nitrogen has important reference value for improving the nutrient content of biogas fertilizer.In this study,pig manure,chicken manure,and straw were mixed to perform mesophilic anaerobic fermentation for 30 days with 4%,8%,15%and 20%TS by a small controlled constant temperature fermenting device,to determine the optimal gas production stage.Then the 15-day and the 30-day biogas residue were rapidly separated from the 20%TS treatment,and the moisture contents were both adjusted to65%and 70%,and a temperature-controlled device was designed to aerobic compost for 15 days.The changes of carbon and nitrogen content were studied in the biogas residue from anaerobic stage to aerobic stage.The biogas slurry of 8%TS treatment group was rapidly separated and stored for 30 days in four ways:closed and settled(CS),closed and agitated(CA),opened and settled(OS),opened and agitated(OA).The changes of carbon and nitrogen content were studied in biogas slurry from anaerobic stage to storage stage.The results are as follows:1.A small controlled constant temperature fermenting device was designed,and four different TS concentrations of the materials:4%?8%?15%and 20%was used for the medium temperature anaerobic fermentation for 30 days.The daily gas productions of 4 treatments all reached their peak before day 8,which were 1201?1940?2602 and 4099 ml/kg,respectively.The daily gas productions of 4 treatments was less than a half of the peak at about 15 days,and the accumulative gas productions reached more than 70%productions of the whole cycle,The volumetric gas production rate is 1.91 m~3/(m~3·d),which is 41%higher than that at 30 d.2.In the anaerobic fermentation stage,the carbon and nitrogen content decreased continuously in the biogas residue,and the carbon and nitrogen content increased first and then decreased in the biogas slurry,and reached the maximum value at 13~18days.In the wet fermentation group,20.1%~28.1%of the carbon entered the biogas in the form of CH?and CO?,13.2%~15.8%entered the biogas slurry,66.3%~71.4%remained in the biogas residue;60.6%~64.8%of the nitrogen entered the biogas,and the rest remained.In the dry fermentation group,15.2%~19.3%of the carbon entered the biogas,while the rest remained in the residue,and the nitrogen elements were almost left in the biogas residue.3.Among the four composting groups 15dBR+65%MC?15dBR+70%MC?30dBR+65%MC?and 30dBR+70%MC,the pH value of the 15dBR+65%MC group was between 7.5 and 8.5,the electrical conductivity and E4/E6 value were the lowest,and the germination index was more than 90,which all meet the requirements of maturity of organic fertilizer.4.In the composting stage of biogas residue,the content of carbon decreased with the composting time,after 15 days,the decrease rates of carbon in the four treatment groups were 20.0%?17.8%?19.5%and 20.7%,respectively,and the carbon content of the organic manure was the highest.The nitrogen content generally decreased first and then increased.After 15 days,for the treatments of 30 d BR+65%MC and 30 d BR+70%MC,the nitrogen content decreased by 0.5%~1.2%than the initial content,while the content of nitrogen of the treatments of 15dBR+65%MC and15 d BR+70%MC was more than the initial content by 3.9%~1.7%.The content of carbon and nitrogen was 21.7%and 10.2%higher in the 15dBR+65%MC group than that in 30 d group.5.The biogas slurry was stored at room temperature for 30 days under 4 treatment conditions:closed and settled(CS),closed and agitated(CA),opened and settled(OS),and opened and agitated(OA).During storage of biogas slurry,pH values by closed storage were between 8.2 and 8.5,while pH values by open storage increased from8.3 to 9.0.In storage stage of biogas slurry,TC concentrations first decreased and then increased slowly,with an overall decrease of between 2.9%and 12.0%.The order of decrease of TC concentrations from the lowest to the highest degree was:OS<OA<CS<CA.TN concentrations first increased and then decreased during storage,with an overall decrease of between 4.2%and 56.2%.The order of decrease of TN concentrations was:CS<CA<OS<OA.In conclusion,the first 15 days of anaerobic fermentation was the optimal gas production stage,and the organic fertilizer obtained had higher carbon and nitrogen content by aerobic composting of 15-day biogas residue.The cycle of combined production of gas and fertilizer can be shortened by at least 15 days,which can reduce energy loss and save time.At the same time,using closed-settled storage and shortening storage time can reduce the loss of carbon and nitrogen in biogas slurry storage stage,and achieve the effect of improving nutrient of biogas slurry. |
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