Combined electrocoagulation and electrochemical oxidation treatment for groundwater denitrification. (1st May 2021)

• Record Type: Journal Article
• Authors: Benekos, Andreas K.; Tsigara, Maria; Zacharakis, Stergios; Triantaphyllidou, Irene-Eva; Tekerlekopoulou, Athanasia G.; Katsaounis, Alexandros; Vayenas, Dimitris V.
• Is Part Of: Journal of environmental management. Volume 285(2021)
• Publication Date: 2021-05-01
• Subjects: Denitrification -- Ammonium removal -- Nitrite removal -- Electrochemical oxidation -- Cathode effect -- Real nitrate-polluted groundwater; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2021.112068
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Electrocoagulation (EC) with an aluminum electrode arrangement as anode-cathode was applied to denitrify groundwater and electrooxidation (EO) was examined as a post-treatment step to remove the produced by-products. Initially, EC experiments were performed under batch operating mode using artificially-polluted tap water to investigate the effects of initial pH (5.5, 7.5, 8.5), initial NO3 − -N concentration (25, 35, 45, 55 mg L −1 ) and applied current density (10, 20 mA cm −2 ) on process efficiency. The effect of initial solution pH on ammonium cation concentration was also investigated as their generation (as a by-product) is the main drawback preventing wide-scale application of these treatment processes. Experimental results revealed high nitrate removal percentages (up to 96.3%) for initial pH 7.5 and all initial concentrations and current densities, while the final ammonium concentrations ranged between 5.3 and 9.2 mg NH4 + -N L −1 (for initial NO3 − -N of 25 mg L −1 ). Therefore, EO was examined to oxidize the ammonium cations to nitrogen gas on iridium oxide coated titanium electrodes (IrO2 /Ti) anode surface. The effects of cathode material (aluminum, stainless steel), total current density and anode surface area (3.3–30 mA cm −2 and 12–36 cm 2, respectively) were investigated, and lead to NH4 + -N percentage removals of between 25% (10 mA cm −2, 12 cm 2 ) and 100% (30 mA cm −2, 24 cm 2 ) for an initial NH4 + -N concentration of 10 mg L −1 . The optimum EC (20 mA cm −2, natural initial pH 7.5–7.8) and EO parameters (30 mA cm −2, 24 cm 2 surface area anode, Al cathode) were combined into a hybrid system to treat two real nitrate-polluted groundwaters with initial NO3 − -N concentrations of 25 and 75 mg L −1 . Results revealed that the proposed hybrid treatment system can be used to efficiently remove nitrate from groundwaters. Highlights: Two real nitrate-polluted ground water was successfully treated using EC and EO. Al electrodes were applied to reduce amount of nitrates to ammonium. Al/cathode and Ti/IrO2 /anode electrodes were applied to oxidize NH4 + to N2 . High nitrate (71.2%–96.71%) and complete NH4 + removal were achieved.