Evaluation of ammonium removal from sludge return liquor using a pilot‐scale microbial electrolysis cell

Abstract BACKGROUND Microbial electrochemical technologies (METs) enable separation of ammonium from nutrient‐rich waste streams, such as sludge return liquors, using bioanodes that consume organic matter to generate electrical current. Quantification of ammonia recovery performance in pilot scale METs treating real wastes under industrially relevant conditions is scarce. This study evaluates ammonium removal rates and transport mechanisms in a cassette‐style pilot microbial electrolysis cell (MEC) treating real sludge return liquor for the first time at a wastewater treatment facility at ambient temperatures (3–18 °C). RESULTS Preliminary screening of the return liquor determined it contained enough electrons within readily biodegradable organic matter to support bio‐electrochemical ammonium recovery. Recovery potentials were 8.8 and 5.9 based on soluble COD and total VFA content, respectively. Current densities of 0.15 to 0.20 A m −2 were achieved which allowed the catholyte to accumulate total ammonia nitrogen (TAN) from 238 to 1521 mg L −1 in around 15 days. The highest TAN removal rate was 1.7 g m −2 d −1 and migration contributed most to ammonium transport despite the cells generating low current densities. CONCLUSION A combination of low substrate mixing due to large spacing between cells and high internal resistance (6.5 Ω m 2 ) were the primary factors that limited ammonia recovery. These results provide a baseline and insights for future scale‐up research to build upon for MET‐based ammonia recovery from return liquors. Reducing internal resistances by at least two orders of magnitude is required to significantly improve TAN removal rates, this can be achieved by improving current collector systems and reactor configuration in scaled‐METs. © 2025 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).