Ammonium recovery by microbial electrolysis cells (MEC) with different anodes and operating conditions

The feasibility of ammonium recovery from a synthetic influent simulating a real agro-industrial wastewater was investigated, using two double-chamber microbial electrolysis cells (MEC). Carbon felt and granular graphite (d> 2mm) were used as anodes in MEC-1 and MEC-2, respectively. Anodic chambers were fed continuously with a synthetic medium containing NH4-N (0.6-2.5 g/L) and acetate (2 g/L); cathodic chambers contained a solution of NaCl (0.1 M), and were connected to a recovery system consisting of stripping and adsorption columns. Influent NH4-N concentration was increased from 0.6 to 2.5 g/L (results not shown). At the target NH4-N concentration, influent flow-rate was progressively increased in order to evaluate the effects of different nitrogen loads (0.75, 1 and 1.25 gNH4-N/d) on MECs behavior. The NH4-N removal efficiency decreased in MEC-1 (from 48±5% to 41±5%) and -2 (from 33±5% to 15±3%) as the applied NH4-N load was increased. As for MEC-1, the slight decrease in NH4-N removal efficiency was counter-balanced by the higher amount of NH4-N treated per day, resulting in the increase in NH4-N recovery rate, up to 70±3 gNH4-N/d·m2; differently from MEC-1, the strong decrease in NH4-N removal efficiency observed in MEC-2 was accompanied by a slight decrease in NH4-N recovery rate. MEC-1 was able to successfully withstand increasing NH4-N loads, and showed better performance in terms of NH4-N removal efficiency and recovery rate, compared with MEC-2. Such results are promising, and need to be confirmed with real wastewater.