Ammonium Removal\nfrom Domestic Wastewater Using Selective\nBattery Electrodes

Abstract

Conventional technologies\nfor ammonium removal from wastewaters\nare based on biological conversion to nitrogen gas, eliminating the\npossibility for ammonium recovery. A new electrochemical approach\nwas developed here to selectively remove ammonium using two copper\nhexacyanoferrate (CuHCF) battery electrodes separated by an anion\nexchange membrane, at low applied voltages (0.1 to 0.3 V). The CuHCF\nbattery electrodes removed NH₄⁺ from a synthetic\nwastewater with a selectivity >5 (i.e., percent removed of NH₄⁺/percent removed of Na⁺) when operated\nwith a 0.1 V applied voltage, despite the much higher initial Na⁺ concentration in the sample (20 mM) than NH₄⁺ (5 mM). In contrast, we observed only negligible selective\nremoval of NH₄⁺ over Na⁺ (<2)\nwhen using nonselective electrodes or ion-selective membranes (10\nmM Na⁺, 5 mM NH₄⁺, 0.1 V). The selectivity\nfurther increased to 9 when using equimolar concentrations of NH₄⁺ and Na⁺ (10 mM). With an actual domestic\nwastewater, the CuHCF electrodes removed 85% of NH₄⁺ (3.4 to 0.5 mM) with a selectivity >4 versus Na⁺ in the presence of other competing cations. These results demonstrate\nthat CuHCF electrodes can be used to selectively remove NH₄⁺ from various waters containing multiple ions.