Abstract
AbstractThe potential benefits of applying microbial electrolysis cell (MEC) technology to wastewater treatment are clear and profound. Previous pilot studies have demonstrated a ‘proof of concept' with domestic waste at ambient temperatures, but have not yet treated waste to required discharge standards, and have not reached energy neutrality. In addition, these reactors have been many orders of magnitude smaller than would be needed for full scale wastewater treatment plants. Scale‐up affects many of the parameters that underpin performance; understanding its impact will be vital to further progress. Modifying a previously tested cassette‐style design, we reduced the internal resistance, and increased the module size by a factor of 16, constructing an MEC with six 1 m2 anodes. This created an anodic surface area to volume ratio of 34 m2 m−3. The system was operated at a hydraulic retention time of 5 hours on settled domestic wastewater for 217 days, producing more current than a scaled‐down reactor, which was run in parallel. The large MEC produced 0.8 L of 93% pure H2 d−1 at ambient winter temperatures (11.4 ± 2.5 °C). Chemical oxygen demand (COD) removal averaged 63.5% with an average effluent quality of 124.7 mgCOD L−1, achieving the European Urban Wastewater Treatment Directive (1991) consent.
Highlights
Conventional wastewater treatment is a series of unit processes that provide different levels of treatment: preliminary, primary, and secondary
We describe the scale-up of an microbial electrolysis cell (MEC) treating authentic domestic wastewater, without significant detrimental impact on performance
MEC technology has advanced from the litre to the m3 scale, accompanied by a 16-fold increase in electrode size and a reduction in hydraulic retention time (HRT) to 5 h
Summary
Conventional wastewater treatment is a series of unit processes that provide different levels of treatment: preliminary, primary, and secondary. Secondary treatment, which aims to remove biodegradable organic matter, suspended solids and nutrients, often uses aerated processes (such as activated sludge) to achieve a high effluent quality [1]. Aerating wastewater accounts for 50% of the energy use in wastewater treatment [2]. ~ Paper presented at the 3rd Meeting of the International Society for Microbial Electrochemistry and Technology (EU-ISMET 2016); held 26–28 September 2016 in Rome, Italy; organized by www.is-met.org. Microbial electrolysis cells (MECs) have been promoted as an emerging technology that could change the energy balance of wastewater treatment [5, 6]. In an MEC, electrochemically active bacteria form a biofilm on an electrode, consuming the organic material in the wastewater, donating electrons to the anode and liberating protons in the process. The electrons travel in a circuit producing an electrical current, which can be used to produce electricity, or (with the protons released and an added potential) products at the cathode, such as hydrogen gas [7]
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