Comparison of temperature-phased, two phase, and single stage anaerobic co-digestion of municipal solid waste and primary wastewater solids

摘要

The objective of this research was to evaluate the application of the temperature-phased process for the co-digestion of the organic fraction of municipal solid waste (OFMSW) and primary wastewater solids (PS) and to compare the process performance with both two phase and single stage anaerobic digestion. The temperature-phased (TPAD) and two phase (2P) processes both consisted of a thermophilic reactor operated at 55°C followed by a mesophilic reactor operated at 35°C. The pH of the thermophilic stage of the 2P system was controlled at 5.6, while the thermophilic stage of the TPAD system was operated at a neutral pH range. The single stage system (SS) was a single reactor operated at 35°C;The experiment was conducted by incrementally increasing the OFMSW percentage in the feed from 0, 20, 40, 60 to 80 percent. The performance of both the TPAD and 2P systems were greater than the SS system when the feed contained 60 and 80 percent OFMSW, due to increasing hydrolysis limitations. The TPAD, 2P, and SS systems had maximum methane yields of 0.42, 0.34, and 0.37 L/g VS fed, respectively. Maintaining syntrophic relationships between acidogenic, acetogenic, and methanogenic bacteria in the first stage of the TPAD system led to superior system performance when feeding 0, 20, and 40 percent OFMSW as compared to the both 2P and SS systems. The superior performance was characterized from VS removal and methane production. When the OFMSW content of the feed was 60 and 80 percent, the difference between the performance of the TPAD and 2P systems was less evident;Hydrolysis rates were determined from particulate chemical oxygen demand (PCOD) in operating temperature-phased and two phase systems. Methanogenic first-order rates were determined using batch tests with inocula from operating TPAD and 2P systems. The first stage of the TPAD system had higher hydrolysis rates than the first stage of the 2P system at all conditions tested. The temperature phased system had specific hydrolysis rates ranging from 0.048 to 0.285 g PCOD/g VS.d. The two phase system had specific hydrolysis rates ranging from 0.063 to 0.190 g PCOD/g VS.d.