Technology And Application Of Rumen Microorganisms In Anaerobic Digestion Of Agriculture Solid Organic Waste

China is a large agricultural country.It is widely noted that a large number of solid organic wastes are produced in the process of agricultural activities,which cause serious environmental pollution.The typical agricultural solid organic wastes include lignocellulosic biomass and livestock manure.Compared with other treatment technologies,anaerobic digestion is suggested as a sustainable and environmentally friendly method for converting such a high organic content waste into the renewable energy.However,biological conversion of lignocellulose has been hampered by its relatively refractory structure,such as the crystallinity of cellulose and the association between cellulose and hemicellulose with lignin.Some common improvements have been used for improving the digestibility of lignocellulosic wastes.However,it is restricted by complicated operation and additional processing costs.In this case,an economic pretreatment method and an effective biological conversion microbial population for recycling these agricultural solid organic wastes should be explored.Based on the principle of high conversional efficiency for lignocellulosic wastes by ruminal microorganisms,this study focuses on the performance enhancment by 1)biogas liquid in pretreatment of lignocellulosic wastes and 2)rumen microorganisms in anaerobic digestion of maize straw with livestock manure.The main research achievements of this study have been obtained as follows:(1)An orthogonal array was performed for optimizing the effect of pretreatment of maize straw by biogas liquid from the residues of anaerobic digestion.It was found that the surface structure of maize straw was destroyed together with the ester and ether linkage between cinnamic acids and lignin/polysaccharides of cutin from the waxy cuticular layer cleaved.The crystallinity index clearly demonstrated that there were various degrees of decline in the crystallinity index for biogas liquid treated maize straw,from 80%of untreated straw to the lowest 36.2%of treated straw.The optimum conditions of pretreatment were 9 days,25 ?and 50%(v/w)dosage of biogas liquid.The ordering sequence of the influential factors for pretreatment was treated time>temperature>dosage of biogas liquid.Besides,the acetate limiting-step concentration and DMD improved 40%and 18%,respectively.Compared with conventional pretreatment method,the surface and interior structure of maize straw were destroyed more seriously.Saccharification and acidification were promoted in the process of anaerobic fermentation by rumen microorganisms.(2)Simulating the environment of rumen,a continuous lab-scale anaerobic digestion system was conducted for tentatively exploring the domesticating and cultivating process of rumen microorganisms in vitro.It was noted that the simulative digestion system for cultivating the rumen microorganisms was successfully started up within 30 days under the technological conditions of pH>6.5,39? and stirring rate at 120 rpm.The composition of buffer solution was simulated from ruminant saliva.Intermediate product,enzymatic activity and biogas yiled were affected by solid content and retention time.The biogas yield was obtained at 405 mL/(g· VS)at the retention time of 9 days and dry matter content of 1 g/(L·d)in this continuous anaerobic reactor.A methane content of 60%was found,together with the carbon dioxide and hydrogen content of 40%and 0%when the operation of the system was stable.(3)Both Box-Behnken design and response surface methodology(RSM)were conducted for parametric optimization,and later evaluated the performance enhancement in acidogenesis and biogas production.The optimal pretreatment time and mixing ratio(C/N ratio)were obtained at 3 days and 1:1(19.37:1),corresponding the crystallinity index decreased from 81.8%to 54.74.The rate of hydrolysis acidification in a co-fermentation system was faster than in a single substrate system.Subsequently,after a start-up time of 23 days,the continuous co?digestion reactor was successfully operated with the rumen microorganisms.Co-metabolism played a more important role in this process.The biogas yield was detected at 430 mL/(g·VS)at the retention time of 9 days and dry matter content of 1 g/(L·d)or 2 g/(L·d)in this continuous anaerobic reactor.The composition of biogas included methane,hydrogen and carbon dioxide with a content of 60%,0%and 40%.(4)Based on the results of lab-scale experiments,several pilot-scale tests were conducted for anaerobic digestion of agriculture solid organic wastes by rumen cultures.First,a pilot-scale pretreatment test was performed.The crystallinity index after pretreatment was about 50%?60%and DMD obtained from batch tests was 73.25%indicating a good performance on pilot-scale pretreatment by biogas liquid.The stability of anaerobic digestion system was affected by temperature and pH.There are almost no promotion for a single substrate digestion system after adding the urea.An anaerobic digestion reactor inoculated with rumen microorganisms was successfully operated at about 30 days.The biogas yield was detected at 395 L/(kg·DM)(1550 L/d)at a dry matter content of 3%(w/w)in an anaerobic reactor with the maize straw as a sole substrate.Similarly,the biogas yield was observed at 420L/(kg·DM)(5100?5300 L/d)at a dry matter content of 10%(w/w)in an anaerobic reactor with the maize straw and livestock manure as the co-substrate.The anaerobic reaction was not inhibited when the concentration of NH4+-N increased up to 3000 mg/L.The organic fertilizer produced from an aerobic composting system with a forced draft step by step control system reached to the national standard of"organic fertilizer"(NY525-2012)at a C/N ratio of 20:1.(5)The succession and collaborative mechanism of rumen microorganisms in vitro were discussed by Miseq high-throughput sequencing preliminarily.It was investigated that the structure of microbial communities had been changed from rumen to anaerobic digestion reactor.For all the microbial population,rumen bacteria was hard to adapt the environment in vitro,whereas the new microbial ecosystem reserved a high efficiency for degradation of lignocellulosic wastes.The core bacterial for degrading the fiber in original rumen microorganisms was reserved.Compared with rumen bacteria,rumen fungus could adapt the new system easily,which had a better ability to degrade cellulosic biomass.In the anaerobic digestion system with maize straw as a sole substrate,the function of advantage bacterium groups included the bacteria for hydrolyzing the cellulose,converting the pyruvic acid with sugars and the fungus for hydrolyzing the cellulose,hemicellulose with fructose.The methane was synthesized by hydrogenotrophic methanogens.The H2 used in methanogenesis was estimated from the syntrophic acetogen and acetoclastic bacteria.The dominant bacterial community of hydrolysis and acidification in co-digestion system was different from the sole substrate system.A synthetic route of methane was from hydrogenotrophic methanogens and acetotrophic methanogens.Generally speaking,there were three main factors inducing the succession of rumen microorganisms:1)environmental change causing an unacclimatization of microbes,2)inductive effect by substrates such as an increasing content of easily degradable substrates or ammonia nitrogen pressure.3)the metabolic pathways changed by an extensive enrichment of methanogens resulting in both a reduction of partial hydrogen pressure and a large number of syntrophic microorganisms.(6)Based on the achievement of pilot-scale tests,a demonstration project was conducted for comprehensively treating and recycling the agriculture organic solid wastes.IMFZ(Intergrated Methanation,Ferterlization and Zero emission technology)was conducted during this process.Taking a one hundred thousand pig farm with a livestock inventory for example,"Regional centre for the treatment and utilization of agriculture solid organic wastes" was designed.The total investment of this project was about 65 million yuan.48,600 tons pig manure,104,400 tons wastewater and 24,500 mu straw were converted into 3,960,000 Nm3 methane,10,800 tons organic fertilizer and 162,000 tons liquid commercial fertilizer,equivalent to a 13,700 tons reduction in carbon-dioxide emissions.The direct economic benefit was about 23.22 million yuan.Excluding the operating expenses and depreciation,the annual profit was about 9.66 million yuan.The investment return period was about 7 years.Acquisition cost is the major factor during the collection of raw materials.The shipping and delivery cost was lower but the transportation cost was higher when the project scale was larger.Finally,an integrated methanation,fertilization and zero emission technology with key equipments were established after a long-term lab-scale,pilot-scale and industrial scale tests.