Ammonium Removal from Domestic Wastewater Using Selective Battery Electrodes

Abstract

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

Faradaic Electrodes Open a New Era for Capacitive Deionization

“…In addition to the aforementioned novel ion-selective Na + /Cl − capture electrode materials [47,57,58] and various cell designs, [43,46,49] some recent promising developments of Faradaic electrodes have been achieved, such as research on the influences of operational parameters on CDI performance metrics, [41,43,59] and some typical scientific and practical application. [40,[60][61][62][63] However, it appears that Faradaic electrodes used in CDI cells are still not mature enough to meet the requirement for practical implementation and commercialization, which can be attributed to major challenges such as not fully understanding the ion capture mechanisms and behaviors of materials, matching issues between the Na + capture cathode and Cl − capture anode, and the need to establish standardized test conditions, etc.…”

“…As for the specific removal of a particular cations among other cations in solution such as Na + , K + , Mg 2+ , Ca 2+ , NH 4 + , etc., sodium manganese oxides, [39,62] NASICON-type phosphates, [301] and metal hexacyanometalates [40,51,61] have been investigated. NMO and NTP both show affinity for Na + over K + and some divalent ions (Ca 2+ and Mg 2+ ).…”

“…+ over Na + when tested with equimolar concentrations (10 × 10 −3 m). [61] When tested with real domestic wastewater, the CuHCF electrodes removed 85% of NH 4…”

Membrane and Electrochemical Processes for Water Desalination: A Short Perspective and the Role of Nanotechnology

“…These membranes facilitate the conversion of ammonium into ammonia or enhance the mass transfer of the target compound. The use of electrochemical cells such as CDI, ED, and BDI can efficiently produce nutrients or rare element-enriched streams from wastewater or seawater [ 85 , 86 , 105 , 106 , 107 , 108 , 109 , 110 ], primarily because most of the nutrients in wastewater are present in ionic forms, and the electrochemical process separate (or intercalate) the charged ions using electrostatic (or Faradaic) reactions. For instance, a three-staged BDI system successfully produced an ammonium-enriched stream from 5 mM to 32 mM using synthetic wastewater [ 85 ].…”

Interpretation of the Role of Composition on the Inclusion Efficiency of Monovalent Cations into Cobalt Hexacyanoferrate

“…In addition, as the concentration of Cs in environmental water is comparatively negligible, the absolute selectivity of PBAs for this ion may not hinder their application for NH 4 uptake. As expected, in recent years, the separation or decontamination related studies of PBAs have expanded to other environmental causes such as the adsorption of dissolved or gaseous ammonia . NH 4 removal and recovery is usually faced with selectivity problems because the application area often contains chemical fertilizer or biomass matrices, making selectivity an extremely important factor when choosing the adsorbent .…”