Research On The Relations Between Basic Characteristics Of Agricultural Biomass And Anaerobic Digestion For Biogas And Organic Acid Production

The annual yields of agricultural wastes are considerable,but the characteristics of agro-waste make the low lignocellulose degradation rate,ammonia inhibition and digestate with over-high solid content become bottleneck problems of anaerobic digestion(AD)from agro-waste.To establish the correlation between the basic characteristics of feedstocks and their according AD performance is the scientific basis for the resolution of problems mentioned above and the rational utilization of agro-waste.Aiming at the problem that the characteristic data of agro-feedstocks is not uniform,the 10 typical agricultural wastes were studied,and 20 kinds of physical and chemical properties were analyzed comprehensively to complete the first database for agro-biomass characteristics in China.At the same time,aiming at the problem of high cost of property analysis,the principal component analysis(PCA)method was used to summarize the main characteristics of different types of feedstocks.As the AD performance evaluation methods are not unified,AD performance was evaluated for 14 kinds of agro-waste feedstocks by going through the biochemical methane potential(BMP)test,reaction kinetics analysis and continuous system test.It was found that the AD performance index,including biogas and acid producing potential,biodegradability,retention time,gas production rate,utilization rate of nutrient elements and toxic substances accumulation degree was related to the type and content of chemicals groups in feedstocks.Among them,lignin removal could improve the AD performance from a number of aspects;high nitrogen and solid content cause deterioration of biogas producing in continuous AD system,but effectively stimulated acid production potentials.Aiming at the problem of lignocellulose resulting in poor AD performance,the alkaline hydrogen peroxide(AHP)pretreatment was applied to improve physical and chemical properties of the lignocellulose feedstocks.By breaking down the ester and ether bond in lignin,pretreatment could recovery about 90% glucan and 80% xylan,while remove 30%-50% lignin,thus to improve the AD performance of biogas production.Due to the loss of organic matter,the methane potential and biodegradability enhancement brought by AHP pretreatment could only obversed in certain kinds of agro-waste.Aiming at the problems of acidification in continuous AD brought by high nitrogen and high solid content in feedstocks,co-digestion of un-dilutied chicken manure and maize silage was conducted on CSTR,in order to study the co-inhibition from ammonia and low heat and mass transfer effciency on the AD performance of biogas and acid production.Results showed that methanogenesis from high nitrogen and high solid content agro-wastes was feasible when the digestate concentration less than 18%,total ammonia concentration less than 7000 mg/L;while the acid producing potential was considerable(>60000 mg organic acid/L)when digestate concentration more than 20% and total ammonia concentration more than 9000 mg/L.In view of trace elements lackage in certain agro-waste,as well as low trace elements availability caused by heat and mass transfer inhibition in continuous AD system,trace elements addition was applied in CSTR system,to discuss the control effect of trace elements on AD with multiple inhibitions.Results showed that Ni,Se and Co concentrations lower than 0.30 and 0.10 and 0.10 mg/L caused propionic acid accumulation;with limited trace elements effectiveness caused by multiple inhibitions,trace elements addition could enhance biogas production performance to some degree.In sum,the relationships between agro-waste characteristics and their according AD performance were preliminarily clarified,which provides scientific basis and guidence for the prediction of bio-energy production in large-scale plant from agro-waste biomass.