Redesigning a commercial kitchen grease trap for wastewater heat recovery: experimental and numerical investigation

Wastewater contains residual heat that can be exploited through technological innovation and is another source of renewable energy that can be used to heat water in buildings. This study focused on the development of novel wastewater heat recovery (WWHR) technology through a redesign of a commercial kitchen grease trap (GT). The GT acts as a heat reservoir where the primary function is to remove fats, oils and grease (FOG) from the wastewater before it is discharged into the sewer system. To exploit this heat resource, heat exchanger (HX) panels were integrated into the walls and baffle of a stainless-steel GT in order to optimally transfer heat from the hot wastewater to a clean cold-water supply. Experiments and numerical simulations were conducted to assess the thermal power available with varying wastewater and HX flow rates and temperatures. The thermal power available ranged from 1.81-4.54 kW with a heat transfer effectiveness of 54.1–89.7%. This would result in an annual energy recovery rate of 6.61–16.46 MWh/a, with a whole life carbon reduction of up to 83.9 tonnes of CO 2 e. The study also found that for every kg of FOG introduced, a deterioration of 0.3% in effectiveness was observed. Economically, the novel GT with integrated WWHR had payback periods ranging from 1-6 years depending on the fuel type and wastewater resources available. This redesigned GT-WWHR system has led to a reduction in energy use, costs and emissions and is a viable form of green technology for the hospitality industry