High Solid Concentration Of Anaerobic Fermentation Characteristics Of Pig

Organic agricultural wastes can be converted into clean energy, e.g., biogas, through anaerobic digestion, and its final products can be made full use resulting in less environmental pollutions. However, the currently widely used wet digestion technology requires large amount of dilution water and produces wastewater with high concentrations of pollutants, which cause disadvantageous effects if being not properly applied or treated.High solid digestion of swine manure at mesophilic (35±1℃) and thermophilic (55±1℃) temperatures was investigated in this thesis. The effects on digestion process of inoculum cultivation and dosage, digestion tempratures, TS content and other factors were studied to determine the optimum digestion condition. The following indices were mainly selected as assessment parameters, including biogas yields, methane contents, effective digestion time (Tcff) and effective biogas production rates (μeff), and total solids (TS), volatile solids (VS), total chemical oxygen demand (TCOD) removal rates. In addition, the kinetic model and rate coefficients in anaerobic digestion among these conditions were analysed to make the mechanism of this complicated process more understood.The results indicated that increasing inoculum dosage and inoculum cultivation could shorten effective digestion time and improved biogas production rates. The optimum condition of this study could be summarized as follows:mesophilic digestion, TS=15%and with matured digestion residue as inoculum (20%inoculation rate). Under this condition, the final biogas and methane yields were 357.4ml/g-VS and 266.2ml-CH4/g-VS in 60 days, respectively. And TS, VS and TCOD removal rates were 36.1%,48.5%and 48.0%, respectively. Itsμcff could reach 10.76ml/g-VS/d with cumulative biogas yield being 81.3%of final biogas yield within Teff of 27 days.Free ammonia concentration was observed to significantly affect digestion process of swine manure under high solid condtion. Due to ammonia inhibition, thermophilic digestion of swine manure achieved about 70%biogas yield obtained under mesophilic conditions at TS of 15%. Based on experimental and simulation results, the initial inhibition concentration of free ammonia was about 1,100 mg-N/L, which possibly occurred when TS concentration greater than 15.6%and 7.4%at mesophilic and thermophilic conditions. The results showed that biogas yield, biogas production rate, methane content and TS, VS and TCOD removal rates decreased and Tcff increased with the increase of TS concentration. Under mesophilic conditions, the highest biogas yield calculated based on initial VS and digester volume were 393.4ml/g-VS and 33.1L/L respectively within 37 days of digestion, which were obtained when TS=5%and TS=20%, respectively. The biogas yields were about 80%of the above maximum values at TS of 15%.A two-stage first-order kinetic model was applied in this study, which well fit the experimental data obtained in the high solid digestion process of swine manure’The obtained kinetic parameters further verified the above experimental results in this study.