Abstract
Biological municipal wastewater treatments lead to high sludge generation and long retention times, and the possibilities for recovery of the energy content of the input waste stream are very limited due to the low operating temperature. As an alternative, we propose a sequence of exclusively physicochemical, non-biological stages that avoid sludge production, while producing high-grade energy outflows favoring recovery, all in shorter times. Ultrafiltration and evaporation units provide a front-end concentration block, while a supercritical water oxidation reactor serves as the main treatment unit. A new approach for energy recovery from the effluent of the reactor is proposed, based on its injection in a gas turbine, which presents advantages over simpler direct utilization methods from operational and efficiency points of view. A process layout and a numerical simulation to assess this proposal have been developed. Results show that the model process, characterized with proven operating parameters, found a range of feasible solutions to the treatment problem with similar energy costs, at a fast speed, without sludge production, while co-generating the municipality’s average electricity consumption.
Highlights
IntroductionThe municipal wastewater treatment plants (WWTP) in prevailing use are composed of a set of physicochemical and biological processes that have been evolved over a long period of time, with the Conventional Activated Sludge (CAS) process at its core [1,2,3]
Detailed modeling of SCWO reactors requires a major effort [34], so we have considered a lumped parameter model, restricted to experimental results suited to our purposes, based on experiments carried out at the SCWO facility installed at the University of Valladolid [14,25]
The numerical model was used in three different ways; firstly, to find operating conditions that produce specific values of power exported to the grid (0, 1000, 2000, 3000 and 4073 kW) for a constant process configuration, i.e., a set of process design parameters of interest: CUF = 40 gO2 COD/L, WSCF = 9.80%W/W, WINJ = 20% and CW/Feed mass flowrates ratio (CFR) = 0.385 kg Cooling Water (CW)/kg
Summary
The municipal wastewater treatment plants (WWTP) in prevailing use are composed of a set of physicochemical and biological processes that have been evolved over a long period of time, with the Conventional Activated Sludge (CAS) process at its core [1,2,3]. These technologies allow degrading organic matter in sewage, working at nearly ambient pressure and temperature. A more appropriate route would be to concentrate pollutants as much as possible by using physicochemical methods and oxidize both the biodegradable and non-biodegradable compounds as fully as possible, since this would use their chemical energy to produce higher grade energy content effluents, facilitating energy recovery from this source
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