Anaerobic phased solids digester (APS-digester) system for biogasification of agricultural and food wastes

A newly developed anaerobic digestion system, Anaerobic Phased Solids Digester (APS-Digester) system, has been built and evaluated in this research. The APS-Digester system that consists of at least one hydrolysis reactor and one methanogenic reactor was tested for anaerobic digestion of rice straw and food waste at 35°C. Other anaerobic digestion systems that include Batch and Sequential Batch Anaerobic Composting (SEBAC) systems were compared with the APS-Digester system. A computer simulation was performed to study the daily biogas production as affected by the number of the hydrolysis reactors of the APS-Digester system. A computer-aided engineering design model was developed to design the APS-Digester system and study the heat losses and net energy balance of the system by using Microsoft Excel.;The effects of different pretreatment methods that include physical (mechanical), thermal and chemical (ammonia) treatment on anaerobic digestion of rice straw were investigated. A combination of grinding (10-mm length), heating (110°C), and ammonia treatment (2%) resulted in the highest biogas yield, 0.47 L/g VS fed, which was 17.5% higher than the biogas yield of untreated whole straw. The APS-Digester system demonstrated advantages in a handling higher organic loading over the Batch system and producing a higher methane yield over the SEBAC system. Computer simulation showed that one methanogenic reactor coupled with four hydrolysis reactors resulted in relatively constant daily biogas production with less than 7% variation.;Anaerobic digestion of food waste showed that the maximum methane production (0.29 L CH4/g VS fed) could be achieved when the pH in the hydrolysis reactor was controlled at 5.5 and the organic loading rate (OLR) and hydraulic retention time (HRT) of the methanogenic reactor were controlled at 11.7 g TS fed/L/day and 14 days, respectively.;Application of the computer model was demonstrated with a case study for anaerobic digestion of rice straw to design large-scale APS-Digester system, calculate net energy production and heat losses from the system.