Reducing the Energy and Environmental Impact of Commercial Kitchen Water Use: Assessment of Wastewater Heat Recovery in a Grease Interceptor and Its Impact on Fat, Oil, and Grease Removal Capabilities

Abstract

Significant amounts of energy are consumed in the heating of water in the hospitality and food services sectors. The majority of this energy is still present in the subsequent wastewater, which is sent to the sewer system, representing a significant waste of energy resources. The present research focuses on the recovery of waste heat from commercial kitchen wastewater to fulfill the dual objectives of reducing energy consumption and CO2 emissions, while simultaneously improving fat, oil, and grease (FOG) removal efficiency in grease interceptors or grease traps (GT). A GT was retrofitted with a novel heat exchanger design (termed a hybrid GT) to enable wastewater heat recovery and enhance FOG removal capabilities. Hot wastewater containing FOG was assessed in a full-scale experimental GT. The governing parameters of temperature, mass flow rate, and FOG content were monitored. Results indicated that the hybrid GT improves FOG removal performance by lowering the temperature of GT hot wastewater by 25%. The hybrid GT reduced primary energy consumption through heat recovery at a maximum rate of 0.9 kJ/s, and reduced the corresponding cost of conventional fossil fuel use for water heating. It also reduced the carbon footprint by 920 kg CO2e per kWh of energy saving. Heat recovery could bring down the cost of food preparation and increase profitability. The hybrid GT also improved FOG retention through lowering wastewater temperatures and encouraging faster solidification of FOG in the GT. Faster solidification of FOG retained greater amounts of FOG in the first chamber of the GT. FOG passing to the second chamber of the GT was reduced enhancing the systems utility. The present research highlights significant potential for further improvements in the process of heat recovery from GTs in commercial kitchens, as well as significant potential for energy, cost, and environmental benefits arising from the adoption of this technology.