Energy recovery capacity evaluation within innovative biological wastewater treatment process

Experimental study we present is a full-scale energy recovery system able to extract, by means of a water sourced heat pump, the leftover thermal bioenergy available in a Sequencing Batch Biofilter Granular Reactor (SBBGR) within the wastewater treatment process. Heat pump compressor engine was powered by a 5.1 kW Photovoltaic plant, thermal energy being recovered is accumulated by two phase change materials tanks (PCM) for heat and cold latent energy storage whose capacity is 0.3 and 0.5 m3 respectively, thermal energy excess was dissipated through evaporator and condenser devices. Thermal energy extracted from SBBGR ranged from 0 to 14.5 kWh as function of environmental temperature and temperature set point of SBBGR. It was largely affected by environmental temperature during radiation and no deterioration of SBBGR performances were recorded during energy extraction even at lowest temperature set point (i.e. 15 °C). Results obtained demonstrated that SBBGR technology, thanks to its particular process scheme, allows wastewater heat extraction within the treatment process operation, making it actually the only wastewater treatment system able to exchange energy at low temperature (15 °C) without prejudice to treatment performances and, at the same time, to operate a thermal regulation of the treatment reactors, integrating the optimization of thermo-dependent biological processes with energy recovery systems.