Abstract
Bioelectrochemical systems (BES) have the potential to deliver energy-neutral wastewater treatment. Pilot-scale tests have proven that they can operate at low temperatures with real wastewaters. However, volumetric treatment rates (VTRs) have been low, reducing the ability for this technology to compete with activated sludge (AS). This paper describes a pilot-scale microbial electrolysis cell (MEC) operated in continuous flow for 6 months. The reactor was fed return sludge liquor, the concentrated filtrate of anaerobic digestion sludge that has a high chemical oxygen demand (COD). The use of a wastewater with increased soluble organics, along with optimisation of the hydraulic retention time (HRT), resulted in the highest VTR achieved by a pilot-scale MEC treating real wastewater. Peak HRT was 0.5-days, resulting in an average VTR of 3.82 kgCOD/m3∙day and a 55% COD removal efficiency. Finally, using the data obtained, a direct analysis of the potential savings from the reduced loading on AS was then made. Theoretical calculation of the required tank size, with the estimated costs and savings, indicates that the use of an MEC as a return sludge liquor pre-treatment technique could result in an industrially viable system.
Highlights
Bioelectrochemical systems (BESs) are a wastewater treatment technology that use anaerobic and electrochemically active microorganisms (EAMs) within the wastewater to break down pollutants and recover energy
In order to calculate the length of the tank that would be needed to remove fully the organics to legal discharge standards, and to understand if the optimal hydraulic retention time (HRT) was still relevant with lower strength wastewaters, a further experiment was conducted where the return sludge liquor (RSL) was continually recirculated through the tank
There was no apparent trend between performance and positioning within the tank
Summary
Bioelectrochemical systems (BESs) are a wastewater treatment technology that use anaerobic and electrochemically active microorganisms (EAMs) within the wastewater to break down pollutants and recover energy. The combined liquid fraction from these dewatering steps returns to the top of the treatment works and passes back through the AS process in an internal loop This waste stream is one of the most energetically resource-laden sections of the wastewater treatment plant, and currently there is no economically attractive solution [23]. As BESs have shown increased performance when treating a substrate with a high COD content [30,31], this waste stream could be an ideal location for a pilot-scale BES, where it may be possible to get economically viable treatment rates. This is where wastewater flows around rectangular cassette style electrodes with two external anodes and an internal cathode (Figure 1) In these studies, the reactors were run using different HRTs and supplied different voltages.
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