Optimization And Microbial Analysis Of CSTR Fermentation System In Scale Farms

Disposal of agricultural waste has always been a problem.The current agricultural waste is mainly fibrous waste and livestock manure,among these two types of waste,straw and pig manure are typical representatives by volume.The treatment of agricultural waste by anaerobic fermentation technology can not only reduce the treatment cost,but also generate clean energy such as methane,thereby realizing the renewable use of agricultural waste.However,the current pretreatment method has the disadvantages of high cost and large energy loss,Moreover,the traditional CSTR reactor has low mass transfer efficiency,and the biogas residue and the biogas slurry are likely to cause secondary pollution after fermentation.This study uses lye to pretreat straw,through cellulose,COD,methanogenesis and other indicators,Combined with the material balance analysis in the pretreatment and fermentation process,the optimal conditions for straw pretreatment were determined.In view of some shortcomings of current CSTR reactors,an inner sleeve baffle is added to the CSTR reactor for improvement,After 180 days of start-up and stable operation,microbial analysis of bacteria and archaea in the reactor was carried out by high-throughput technology.Research indicates:(1)When the temperature was 35?,the straw was soaked in 1.2%NaOH solution for 2 days,a large amount of COD was decomposed,In the later stage of anaerobic fermentation gas production with pig manure,the time of gasproduction by pretreatment for 2 days was significantly earlier than that of the component with long pretreatment time,and the total amount of methanogenesis was the largest.According to the material balance analysis,the loss of straw was the smallest after 2-day pretreatment.In the anaerobic fermentation stage,the straw fermentation rate after 2-day pretreatment was the fastest,gas production.The rate was the highest.(2)The start-up of the new CSTR reactor was about 80 d.In the start-up phase,starch was used instead of straw.Compared with the straw which was difficult to be decomposed,the starch can make the new CSTR reactor reach a steady state.Finally,the inside of the reactor was basically stable,and the generated acid substances and the consumed COD substances were basically flat,resulting in a stable COD concentration,realizing a stable state inside the reactor,and the methanogenic rate reached about 68%,which continued until the reactor start-up was over.At this time,the activity of methanogens in the interior of the reactor reached a peak and the startup was successful.(3)In the early stage,the mixture of straw and starch was used as a substrate to enter the reactor,and then only a single straw was added as a substrate,and a mixture of pig manure and straw was added after the stable operation.The concentrations of volatile acid in the pre-run reactor all decreased,and as the cellulase activity in the reactor began to increase,the acid production and gas production efficiency also increased rapidly,The final reactor treated 80 g of straw and 20 g of pig manure per day,OLR reached 1.25g/L·d-1,the average gas production rate of the reactor was 375.72mL/g,the methanogenic rate was224.45mL/g,and the methane content reached 60 %,the substrate utilization rate was about 59.7%,and the carbon recovery rate was 50.1%.(4)The microbial function of different areas in the reactor was analyzed by high-throughput test.The main function of the A area was the hydrolysis ofstraw cellulose and the acid production of polysaccharide materials,The remaining cellulose flow into the B area along the water,and the B area contains a large amount of cellulolytic bacteria to further decompose the cellulose,and a part of the available substances produced by the decomposition was directly acidified,The other part entered the C area to decompose acid.From the perspective of archaea,the A area was inhibited by excessive acetic acid,mainly by hydrogen and carbon dioxide.After the acetic acid flow into the B area,the concentration changes,so the main methanogenic method in the B area is acetic acid fermentation,subsequent to the C area,the re-enriched hydrogen and carbon dioxide,and the appropriate concentration of acetic acid and other substances made the C area methane generation method diversified,and various methane generation pathways worked together.