Membrane aerated biological reactors (MABRs) to enhance the biological treatment process at a WWTP
Giuseppe Campo, Alberto Cerutti, Mariachiara Zanetti, Barbara Ruffino
Abstract
The goal of climate neutrality, under the provision of the European Green Deal, will require great efforts to wastewater treatment plants (WWTPs) to reduce and optimize their energy consumption. The utilization of membrane aerated biological reactors (MABRs) to renovate existing WWTPs could be an opportunity in this sense. In this study, the control of the flow at the outlet of a pure, open-end MABR was used as a strategy to minimize the oxygen consumption and obtain high oxygen transfer efficiencies (OTEs). OTE values of more than 80% were observed, which are not so common in the literature and are comparable to those obtained with a close-end configuration. High efficiencies (85%) were found for the removal of both COD and total nitrogen from samples of real wastewater. A techno-economic analysis, comparing a conventional activate sludge (CAS) plant with a MABR, both with a treatment capacity of 25,000 equivalent inhabitants (e.i.), found that the MABR only needed approx. 1/5 of the energy required by the CAS. A MABR plant could become a profitable investment, under a fixed return time of 5 years, compared to a CAS with a CAPEX of 123.7 k€, if the overall cost of the cassettes was inferior to 237 k€. A sensitivity analysis imposing a variation of ±50% on the input parameters (cost of blower, diffusers, electric energy, and opportunity cost of capital) demonstrated that the cost of electric energy had the highest impact on the maximum allowable value of the MABR investment, which was affected by ± 26% with respect to the value calculated in the reference scenario. • Reduction and optimization of air flows is strategic for energy efficiency at WWTPs. • MABRs can increase the efficiency in oxygen utilization and save space at WWTPs. • Outlet flow control of a pure, open-end MABR was used to maximize oxygen transfer. • COD and N removal efficiencies were comparable to those obtainable with CAS plants. • Electric energy had the highest impact on the maximum allowable MABR investment.