Microbial electrolysis cells (MECs) provide a promising option to capture the energy from high-strength organic waste streams, including landfill leachate and animal wastewater, which are characterized by high total ammonia nitrogen (TAN) concentrations (i.e., 1–5 g N L–1). MECs rely on the unique ability of anode-respiring bacteria (ARB) to respire electrons from the organic matter into a solid electrode, i.e., the anode surface. The literature does not yield a consensus about the toxicity of TAN or free-ammonia nitrogen (FAN) for ARB. Here, we evaluated inhibition of ARB over a range of relevant TAN and FAN concentrations in the anode of continuous MECs fed acetate (15 mM) in a 100-mM phosphate buffer to maintain a pH of ~ 7.35 and with a hydraulic retention time of 18 h. Anode respiration was sustained over an influent TAN range of 0.1 and 2.2 g N L–1 (corresponding to 2 – 40 mg FAN L–1), with higher current density at higher TAN concentration: 7.1±0.8 A m–2 at 2.2 g TAN L–1 (~ 40 mg FAN L–1) compared to 5.2±0.8 A m–2 for 0.1 g TAN L–1 (~ 2 mg FAN–N L–1). However, a further increase in influent TAN concentration (i.e., 3 and 4.4 g L–1, giving FAN of 53 to 78 mg L–1) nearly stopped anode respiration, but the severe inhibition was reversed when the MECs were shifted to a feed of 0.1 mg TAN L-1. Anode respiration also was sustained over the pH range of 7.0 – 8.1 at fixed input TAN concentration of 2.2 g N L–1, which varied FAN from 18 to 200 mg L–1), and the highest current density occurred at the highest pH. Our results show that ARB are resistant to relatively high FAN concentrations, up to at least 200 mg L–1, but sensitive to TAN concentrations &gt; 2.2g L–1. The relatively high threshold for FAN toxicity by ARB may be a tool for managing microbial communities to favor ARB and high electron recovery in MECs fed with fermentable substrates, as long as TAN is not too high.

Response of anode-respiring bacteria to high ammonia concentration in a microbial electrolysis cell (MEC)

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.