Heat recovery during treatment of highly concentrated wastewater: economic evaluation and influencing factors.

This paper assesses the economics of heat recovery from biological wastewater treatment plants (WWTPs) treating concentrated wastewater, as higher concentrations result in higher heat generation in the treatment basin. A heat balance model has been applied to calculate the amount of recoverable heat from the system and the effect of the heat extraction capacity on the economics of a heat pump installation, evaluated using the internal rate of return. A sensitivity analysis has been performed to evaluate the effect of several parameters on the economics of heat recovery in this type of WWTP: the electricity price, the price of the fuel substituted by heating savings, the investment costs, the coefficient of performance (COP) and the amount of heat extracted from the system. It was calculated that the heat pump capacity has to be high enough to recover a significant amount of heat, but low enough to improve the economics of the system. The economic performance of the system is very dependent on the energy prices of both electrical power to run the heat pump and the fuel (heat) cost substituted by the heat pump.