Modeling assisted evaluation of direct electricity generation from waste heat of wastewater via a thermoelectric generator

Abstract The thermal energy represents a significant portion of energy potential in municipal wastewater and may be recovered as electricity by a thermoelectric generator (TEG). Converting heat to all-purpose electricity by TEG has been demonstrated with large heat gradients, but its application in waste heat recovery from wastewater has not been well evaluated. Herein, a bench-scale Bi 2 Te 3 -based waste heat recovery system was employed to generate electricity from a low temperature gradient through a combination of experiments and mathematical modeling. With an external resistance of 7.8 Ω and a water (hot side) flow rate of 75 mL min −1 , a maximum normalized energy recovery of 4.5 × 10 −4  kWh m −3 was achieved under a 2.8 °C temperature gradient (Δ T ). Model simulation indicated a boost in both power output and energy conversion efficiency from 0.76 mW and 0.13% at Δ T = 2 . 8  °C to 61.83 mW and 1.15% at Δ T = 25  °C. Based on the data of two-year water/air temperature obtained from the Christiansburg Wastewater Treatment Plant, an estimated energy generation of 1094 to 70,986 kWh could be expected annually with a saving of $163 to $6076. Those results have revealed a potential for TEG-centered direct electricity generation from low-grade heat towards enhanced resource recovery from wastewater and encouraged further exploration of this approach.