Abstract
Greywater normally represents the largest fraction of wastewater generated in buildings and may be suitable for non-potable reuse after on-site treatment. Conventional technologies for greywater treatment include sequencing batch reactors, membrane filtration, and membrane biological reactors. Even though these can be very effective, they are highly energy consuming and may negatively impact the energy balance of the building where they are installed. Microbial fuel cells (MFCs) have emerged as a sustainable technology for contaminant removal and energy production from a variety of substrates. In this study, the application of MFCs for greywater treatment is reported, with a particular focus on the analysis of energy losses, in view of non-potable reuse. MFCs were fed with different types of greywater, characterized by either high or low conductivity, because greywater’s conductivity may greatly differ based on its origin; in either case, organic matter (chemical oxygen demand; COD) removal was higher than 85% and not influenced by the influent conductivity, coupled with a maximum power production of 0.46 mW L−1 and 0.38 mW L−1. Electrolyte overpotentials were dramatically higher in the case of low conductivity greywater (20% vs. 10%, compared to high conductivity influent); these overpotentials are related to the conductivity of the influent, showing that low conductivity hindered energy generation, but not COD removal. Polarization and power curves showed higher internal resistance in the case of low conductivity, confirming the overpotentials’ analysis. Results showed the feasibility of the use of MFCs in greywater treatment, with potential to reduce the energy demand connected to its reuse compared to conventional technologies; coupling with a disinfection stage would be necessary to fully comply with most non-potable reuse regulations.
Highlights
Water scarcity and resource recovery issues have led to the formulation of innovative water paradigms, with particular focus on decentralized on-site treatment [1], source separation [2], and fit-for-purpose reuse [3]
When fed with low conductivity GW, Microbial fuel cells (MFCs) achieved maximum voltage generation after a long lag time in each batch, as shown in Figure 3A; this trend was confirmed in all tests with low conductivity GW
Current and power density trends during the experimentation are available in the Supplementary Materials (Figures S1 and Compared to the tests with high conductivity GW (Figure 3B), in the case of low conductivity GW, a much slower voltage increase, as well as lower observed peak voltage, are noticeable
Summary
Water scarcity and resource recovery issues have led to the formulation of innovative water paradigms, with particular focus on decentralized on-site treatment [1], source separation [2], and fit-for-purpose reuse [3]. Membrane filtration and its coupling with biological treatment, MBR, are common due to their simplicity, compactness, and solid-free effluents [3,13] This makes them suitable for onsite application in single buildings or groups thereof, even in dense conurbations. Some of the cited technologies are highly energy demanding: values of 0.16–0.24, 0.5–0.7, 0.1–0.3, and 0.11–0.22 kWh m−3 were measured for biological aerated filter, MBR, sequential batch reactor and conventional activated sludge, respectively, operated at pilot scale for urban non-potable reuse of greywater [19]. Matos et al [20] reported energy consumption up to 1.89 kWh m−3 for MBR treatment of greywater in decentralized in-building applications This aspect may negatively impact the local energy and emissions balance of the installation site [21]. An application of a double-chamber MFC for GW treatment for possible reuse purposes, focusing on organic matter removal, energy production, and internal energy losses, is presented, and analyzed
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