Semicontinuous Temperature-Phased Anaerobic Digestion (TPAD) of Organic Fraction of Municipal Solid Waste (OFMSW). Comparison with single-stage processes

Abstract

The optimization of anaerobic digestion of organic wastes is a challenge to maximize energy production through biogas production process. In this study, semicontinuous TPAD (Temperature Phased Anaerobic Digestion) process has been used for the treatment of the Organic Fraction of Municipal Solid Waste (OFMSW) coming from a mechanical–biological-treatment (MBT) plant. TPAD combines the advantages of operating in different temperature ranges getting better efficiencies of organic matter removal and higher methane productivities than single-stage anaerobic digestion. In this study, the configuration used in the overall process was a thermophilic reactor (55–57 C) for the first phase followed by a mesophilic one (35–37 C) for the second phase. Two TPAD conditions have been tested in this paper: 4:10 and 3:6. The first digit means the SRT used in the first thermophilic phase while the second digit is related to the SRT used in the second mesophilic phase. Moreover, the performance of TPAD processes was compared with those from single-stage digesters operating at similar SRT (i.e., mesophilic and thermophilic reactors operating at 15 days SRT and thermophilic reactor operating at 10 days). The results showed that achievement reached in TPAD 4:10 was better than the corresponding one in TPAD 3:6, obtaining higher productivity of methane (35–45%) and removal of organic matter (6–19%). Moreover, the results indicate that TPAD processes reach higher efficiencies for organic matter removal (16%, 10% and 30% for DOC, CODsoluble and VS, respectively) and higher methane yields (26–60%) than single-stage systems operating at similar SRT.