| Several studies have reported the feasibility and benefits of the leach-bed reactor configuration in two-phase anaerobic digestion of crop and livestock organic solid wastes (CLOSWs). However, only a few studies have addressed the modeling of this process. This study was to develop a refined mechanistic process model for hydrolysis/acidogenesis in anaerobic digestion of CLOSWs. This dissertation presents the model development and experimental results to validate the model. Cattle manure was used as a model CLOSW.; The proposed model is based on the following hypothesis: (1) cattle manure primarily contains a readily degradable fraction (hemicellulose) and a slowly degradable fraction (cellulose), each with different hydrolysis and biodegradation rates; (2) hydrolysis and acidogenesis are the only processes occurring in the leach-bed reactor. Based on the above premises, three hydrolytic reaction models---first-order reaction, second-order reaction, and surface-limiting reaction, were first evaluated. It was found that the surface-limiting hydrolytic reaction model fitted the laboratory data well. Four hydrolysis process parameters (K1h and K1sh for hemicellulose and K1c and K1sc for cellulose) and four biological process parameters (k h and Ksh for hemicellulose and kc and K sc for cellulose) for this model were established from batch experiments. From a sensitivity analysis on each of these eight modeling parameters, the hydrolysis process parameter for cellulose (K1c was found to be the rate-limiting parameter.; Based on these findings, a new model for a leach-bed reactor was developed. A second set of experiments was conducted to further validate this model and to improve the rate limiting parameter. In these experiments, 114-L (30 gal) leach-bed reactors were evaluated with and without leachate recirculation. The model for these reactors included the surface-limiting hydrolytic reaction, advective and diffusive transport of dissolved organics through the leach-bed, and acidogenesis.; From the second set of experiments, four hydrolysis process parameters and four biological process parameters were again established. The model was verified with another set of laboratory tests.; The prediction made by the models agreed well with the measured data under a wide range of test conditions. It is proposed that the two-component model for hydrolysis/acidogenesis can be applied in dry-digestion of other CLOSWs. |
