Study On Dry Anaerobic Fermentation Of Agriculture Organic Solid Waste By Rumen Microorganisms

Recently, the yield of agricultural organic solid waste including straw and livestock breeding waste is about billions of tons per year in China. Improper handling and disposal of the gigantic amount of agricultural organic solid wastes could cause serious pollution to ecological environment. As an emerging technology, dry anaerobic fermentation has a broad application prospects, because of its advantages of low water requirement, small volume, low capital cost, low running energy consumption. Meanwhile, residues of fermentation could be directly used as organic fertilizer or soil conditioner by simply subsequent treatment, and almost no biogas liquid is produced. However, poor mass transfer effect and accumulation of intermediate metabolites in traditional dry anaerobic fermentation system caused by high total solids content, easily lead to low efficiency of fermentation and poorer straw degradation effect.Aiming at problems including low efficiency and long start-up of dry anaerobic fermentation system, rumen microorganisms after acclimation and culture in vitro, of high hydrolysis and methane producing efficiencies was inoculated. Orthogonal experimental design was used to investigating impacts of major factors (Total Solid, C/N ratio, and Inoculation Rate) on dry anaerobic fermentation system. The optimal system parameters was achieved based on the experimental results. Moreover, fertilizer characteristics of digestate were evaluated and analyzed. The research results are as follows:(1) Using ammoniated straw as fermentation substrate, after acclimation and culture in vitro, the CMC enzyme activity of rumen microorganisms stabilized at 8-12 U/mL, the FPA enzyme activity stabilized at 4-5 U/mL, and the methane content was about 50%. The rumen microorganisms presented excellent enzyme activity and methanogenic performance, resulting in quick hydrolysis of straw and transformation of intermediate metabolites like volatile fatty acids.(2) Using ammoniated straw and chicken manure as fermentation substrate, dry anaerobic fermentation obtained a better biogas production efficiency and dry matter degradation rate when the total solids was 20%, C/N was 30, inoculation rate was 20%. Under these conditions, the biogas yield was 263.5 mL/g TS, the methane content was up to 54.21% and the dry matter degradation rate was 53.2%.(3) By increasing rumen microorganisms inoculation rate, conversion efficiency of volatile fatty acids and methane production were increased, while the accumulation of volatile fatty acids was avoided, thus shortening start-up of the fermentation system.(4) Digestate of dry anaerobic fermentation contained abundant organic matter and nutrient elements which are indispensable to plants growth such as nitrogen, phosphorus, potassium. The organic matter was above 75% and total nutrient content was up to 6.7%. Moreover, digestate had suitable electrical conductivity and pH was about 8.0, while higher moisture content than the organic fertilizer standards, which could be decreased by subsequent composting before used as fertilizer.