Upgrading of a mechanical biological treatment plant with a solid anaerobic digestion batch: a real case study.

The energetic and treatment efficiency analysis of an existing mechanical biological treatment (MBT) plant shows that more than 60% of the 25 kWh consumed per each tonne of non-differentiated waste (NDW) treated is due to the electric fans. About 7.5 kWh per tonne of NDW is used for supplying the process air for stabilizing the waste organic fraction (WOF). Exploitation of the solid anaerobic digestion batch (SADB) for processing the WOF before it enters the aerobic section of the MBT leads to the production of biogas and, when subsequently fed to a gas engine, electric power at a magnitude of about 150 kWh per tonne of WOF, resulting in an energy surplus of about 48 kWh per tonne of NDW treated by the MBT facility. The SADB can also reduce the organic load rate at which the aerobic section operates up to 40%, leading to further positive effects on the whole MBT process.