Electrochemical removal of nitrate from a Donnan dialysis waste stream

A systematic review of strategies to overcome barrier for nitrate separation systems from drinking water: Focusing on waste streams treatment processes

By 2030, the UN General Assembly issued the Sustainable Development Goal 6, which calls for the provision of safe drinking water. However, water resources are continuously decreasing in quantity and quality. NO3- is the most widespread pollutant worldwide, threatening both human health and ecosystems. NO3- separation systems (NSS) using IX and membrane-based techniques (MBT) are considered practical and efficient technologies, but the management of IX waste brine (IXWB) and concentrate streams for MBT (CSM), as well as the high salt requirements for IX regeneration, are challenging from both economic and environmental perspectives. It is essential to classify the different waste management strategies in order to examine the current state of research and identify the best option to address these issues. This review provides harmonized information on IXWB/CSM management strategies. This study is the first systematic review of all papers available in the Web of Science, Scopus, and PubMed databases published until February 2023. 75% of the studies focused on the use of biological denitrification (BD) and catalytic denitrification (CD). Although innovative technologies (bio-regeneration and direct CD) have advantages over indirect processes, they are not yet practical for large-scale plants because their reliability is unknown. Moreover, the generation of NH4+ is the major challenge for application large-scale of chemical reduction. An innovative work flow diagram, challenges, and future prospects are presented. The review shows that integrating modified NSS with IXWB/CSM treatment is a promising sustainable solution, as the combination could be economically and environmentally beneficial and remove barriers to NNS application.

Simultaneous removal of fluoride and nitrate from synthetic aqueous solution and groundwater by the electrochemical process using non-coated and coated anode electrodes: A human health risk study

Co-presence of fluoride (F^-) and nitrate (NO₃^-) in water causes numerous health complications. Thus, they should be eliminated by an appropriate method like the EC process. In this research, simultaneous removal of F^- and NO₃^- from synthetic aqueous solution and groundwater has been considered by the EC technique under operational parameters like anode materials (un-coated (Al and Fe) and synthesized coated (Ti/TiRuSnO₂ and Ti/PbO₂)), cathode materials (Cu, St, and Gr), current density (12, 24, and 36 mA/cm²), inter-electrode distance (0.5, 1, and 2 cm), pH (5.5, 7, and 8.5), NaCl concentrations (0.5, 1, and 1.5 g/L), electrolysis time (15, 30, 45, 60, 90, and 120 min), NO₃^- concentrations (75, 150, and 225 mg/L), and F^- concentrations (2, 4, 6, and 8 mg/L) for the first time in this research. The results proved that Al as non-coated anode and Cu as cathode electrodes were more effective in the co-removal of F^- and NO₃^-. The maximum removal efficiencies of 94.19 and 95% were observed at the current density of 36 mA/cm², 1 cm of inter-electrode distance, pH 7, 1 g/L of NaCl, and 90 min electrolysis time by Al-Cu electrode for F^- (2 mg/L) and NO₃^- (75 mg/L), respectively. The higher efficiency of Al-Cu electrodes was due to the simultaneous occurrence of electrocoagulation, electroreduction, and electrooxidation processes. Al-Cu electrode application considerably diminished f- and NO3- concentrations in the groundwater. Health risk assessment proved that HQ of F^- was significantly decreased after treatment by the Al-Cu electrode. Thus, the EC process using an appropriate and effective electrode is a promising technique for treating aqueous solutions containing F^- and NO₃^-.

Effective and selective electroreduction of aqueous nitrate catalyzed by copper particles on multi-walled carbon nanotubes

Drinking-water contamination with nitrate ions is inevitable and wide spreading, which demands feasible removal. Water de-nitration by potentiostatic electroreduction is described here. A novel electrocatalyst based on nano-copper particles, supported onto multi-walled carbon nanotubes (MWCNTs), and spray-deposited onto fluorine doped tin oxide-glass substrates, is described. The Cu/MWCNT/FTO electrode has been characterized by several methods and assessed as a working electrode in aqueous nitrate ion electroreduction, in comparison with MWCNT sprayed on FTO (MWCNT/FTO) with no copper. Comparison with earlier reported electrodes is also described. XRD patterns confirm the presence of nano-copper crystallites, in the electrode, with average size ⁓45 nm. Within 2 h of electrolysis, Cu/MWVNT/FTO exhibits more than 65% removal of nitrate at -1.80 V (vs. SCE). In longer time (7 h) the electrode completely converts the nitrate into N₂ (∼65%) and (NH₄⁺) ∼35% with no NO₂^- ions. The kinetics show 0.76 order with respect to nitrate, and a rate constant 4.53 × 10^-2 min^-1 higher than earlier counterparts. The new electrode functions under various conditions of temperature, pH, electrolyte type and concentration and inter-electrode spacing, only at ambient applied potential. Moreover, the electrode exhibits stability under nitrate electroreduction conditions, and can be recovered and reused for multiple times without efficiency loss. XRD and EDS results also confirm the electrode stability after multiple reuse. Compared to earlier systems, the Cu/MWCNT/FTO is environmentally stable, safe, non-costly with high nitrate removal efficiency and selectivity.

Preparation of Cu/GO/Ti electrode by electrodeposition and its enhanced electrochemical reduction for aqueous nitrate

A Cu/GO/Ti electrode was prepared by electrodeposition for removal of nitrate by means of the electrochemical reduction. The structure, morphology and characteristics of the electrode were characterized by scanning electron microscopy (SEM), Raman spectroscopy (RS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical workstation, and Cu/GO/Ti was used as the cathode to remove nitrate in water by electrochemical process. Characterization results indicated that GO was successfully deposited on the Ti plate and it was partially reduced to reduced graphene. Dendritic and granular Cu particles are agglomerated on the surface of GO layer by chemical interaction in the form of metallic Cu, Cu₂O and CuO, and the dendrite Cu layer increased the specific surface area of Cu layer. The addition of GO layer increases the electroreduction activity for nitrate. Furthermore, through comparison with Cu/Ti electrode, Cu/GO/Ti electrode improved the percentage of nitrate removal from 78.8% to 91.5%, and energy consumption decreased from 0.82 to 0.47 kW h/g NO₃^--N. The present results showed the promising application of GO-based electrodes with Cu in electrocatalytic nitrate removal.