The effects of voltage intensity on the nutrient removal performance and microbial community in the iron electrolysis-integrated aerobic granular sludge (AGS) system were investigated over a period of 15 weeks. Results revealed that the application outcomes of iron electrolysis for AGS systems relied on voltage intensity. When a constant voltage of 1.5 V was applied, the sludge granulation was most obviously accelerated with a specific growth rate of the sludge diameter of 0.078 day⁻¹, and the removal efficiencies of total nitrogen (TN) and total phosphorus (TP) increased by 14.1% and 20.2%, respectively, compared to the control reactor (without the iron electrolysis-integration). Moreover, the AGS developed at different voltages included different microbial communities, whose shifts were driven by the Fe content and the average diameter of AGS. Both heterotrophic nitrifiers and mixotrophic denitrifiers were significantly enriched in the AGS developed at 1.5 V, which effectively enhanced TN removal. Together with the response of the functional genes involved in Fe, N, and P metabolism, the electrolytic iron-driven nutrient degradation pathway was further elaborated. Overall, this study clarified the optimum voltage condition when iron electrolysis was integrated into the AGS system, and revealed the enhancement mechanism of this coupling technology on nutrient removal during the treatment of low-strength municipal wastewater.

The hydrothermal preparation of o-dianisidine and triazine interlinked porous organic polymer and its successive derivatisation via metal infusion (Ni, Cu) under hydrothermal and calcination conditions (700 °C) to yield pristine (ANIPOP-700) and Ni/Cu decorated porous carbon are described here (Ni-ANIPOP-700 and Cu-ANIPOP-700). To confirm their chemical and morphological properties, the as-prepared materials were methodically analyzed using solid state ¹³C and ¹⁵N NMR, X-ray diffraction, Raman spectroscopy, field emission scanning and high resolution transmission electron microscopic techniques, and x-ray photoelectron spectroscopy. Furthermore, the electrocatalytic activities of these electrocatalysts were thoroughly investigated under standard oxygen evolution (OER) and hydrogen evolution reaction (HER) conditions. The results show that all of the materials demonstrated significant activity in water splitting as well as displayed excellent stability (22 h) in both acidic (HER) and basic conditions (OER). Among the electrocatalysts reported in this study, Ni-ANIPOP-700 exhibited a lower overpotential η₁₀ of 300 mV in basic medium (OER) and 150 mV in acidic medium (HER), as well as a lower Tafel slope of 69 mV/dec (OER) and 181 mV/dec (HER), indicating 30% lower energy requirement for overall water splitting. Gas chromatography was used to examine the electrolyzed products.

Via the thermal sintering, a nanocrystalline IrO₂ coating was formed on the Ti substrate to successfully prepare a Ti/IrO₂ electrode. Based on the electrochemical analysis, the prepared Ti/IrO₂ electrode was found to have powerful oxidation effect on the organics in the TNT red water, where the nitro compound was oxidized through an irreversible electrochemical process at 0.6 V vs. SCE. According to the analysis of the nitro compound content, the UV–vis spectra, and the FTIR spectra of 2,4,6-trinitrotoluene (TNT) red water with electrolytic periods, the degradation mechanism of the dinitrotoluene sulfonate (DNTS) was developed. And the intermediates were characterized by UPLC-HRMS. The DNTS mainly occurred one electron transfer reaction on the Ti/IrO₂ electrode. At the early stage of the electrolysis, the polymerization of DNTS was mainly dominated. The generated polymer did not form a polymer film on the electrode surface, but instead it promoted a further reduction. After electrolyzing for 30 h, all NO₂ function group in the TNT red water was degraded completely.

Polycyclic aromatic hydrocarbons (PAH) have been listed by the United States Environmental Protection Agency (US EPA) and by the European Community as priority environmental pollutants. The removal of PAHs from soils, sediments and waste water has attracted attention of scientists and engineers for several decades. Electrochemical oxidation of PAH compounds in water, is receiving increasing attention, due to its convenience and simplicity. In this study we performed electrochemical oxidation of 16 EPA PAHs mixture in 10% NaCl aqueous solution in potentiostatic conditions, at voltage 1 V. Decrease of concentration of some individual PAHs, up to 70% referred to their starting concentration, after 60 min of electrolysis, was confirmed by UPLC/PDA analysis. In further work investigation was extrapolated to in situ removal of PAHs from concrete, as the medium where, to our knowledge, such way of PAH removal has not been investigated before.High concentrations of PAH contamination occurred in the concrete structure of the residential buildings in Belgrade in 2014. Application of DC voltage of 50 V between nickel and stainless steel electrodes packed in the concrete wall, moisturized with the 10% NaCl solution, led to considerable removal of the pollutants by oxidation process throughout the concrete.

In this study, an electrokinetic technique for remediation of Pb²⁺, Zn²⁺ and Cu²⁺ contaminated soil was explored using sodium alginate (SA) and chitosan (CTS) as promising biodegradable complexing agents. The highest Cu²⁺ (95.69%) and Zn²⁺ (95.05%) removal rates were obtained at a 2 wt% SA dosage, which demonstrated that SA significantly improved the Cu²⁺ and Zn²⁺ removal efficiency during electrokinetic process. The abundant functional groups of SA allowed metal ions desorption from soil via ion-exchange, complexation, and electrolysis. Pb²⁺ ions were difficult to remove from soil by SA due to the higher gelation affinity with Pb²⁺ than Cu²⁺ and Zn²⁺, despite the Pb²⁺ exchangeable fraction partially transforming to the reducible and oxidizable fractions. CTS could complex metal ions and migrate into the catholyte under the electric field to form crosslinked CTS gelations. Consequently, this study proved the suitability of biodegradable complexing agents for treating soil contaminated with heavy metals using electrokinetic remediation.

In this work, the electrochemical degradation of antibiotic ceftazidime has been studied using a novel rare earth metal Ce and carbon nanotubes codoped PbO₂ electrode. A competitively high oxygen evolution potential (2.4 V) and enhanced catalytic surface area were obtained, evidence by LSV and CV electrochemical characterization. The G/CNT-Ce/PbO₂–Ce electrode possessed a more compact structure and a smaller grain size than the other PbO₂ and Ce–PbO₂ electrodes, exhibiting a prolonged service lifetime, evidence by accelerated lifespan test and recycling degradation experiment. As electrolysis time reached 120 min, the removal efficiency of ceftazidime and TOC arrived at 100.0% and 54.2% respectively in 0.05 M Na₂SO₄ solution containing 50 mg⋅L⁻¹ ceftazidime. The effect of applied current density, pH value, initial ceftazidime concentration and chloride contents on the degradation performance were systematically evaluated. The results demonstrated that electrochemical oxidation of ceftazidime over the G/CNT-Ce/PbO₂–Ce electrode was highly effective, and the mineralization rate was greatly improved, compared with pristine PbO₂ electrode. Considering the toxicity was increased after 30 min electrolysis, the intermediates were quantitatively investigated through HPLC-MS, GC-MS and IC technology. According to the identified products, a reaction mechanism has been proposed and pyridine and aminothiazole were detected with concentration from approximately 1 to 3 mg⋅L⁻¹, which were regarded as toxic byproducts during electrooxidation. Further electrocatalyzing by ring cleavage reaction and complete mineralization to CO₂, NO₃⁻ and NH₄⁺ was proposed, which demonstrated the G/CNT-Ce/PbO₂–Ce electrode exhibited high efficiency for ceftazidime removal in mild conditions.

The humic-like substances were the main organic components in most wastewater (e.g. domestic sewage, toilet wastewater and landfill leachate). Two types of actual humic-like substances (fulvic acid (FA) and biologically treated landfill leachate (BTLL)) were selected to describe the changes in the properties of humic-like substances (complexation ability, aromaticity and mobility) during electrochemical oxidation. Meanwhile, the acute cytotoxicity of FA and BTLL was also tested by acute toxicological test of luminescent bacteria. The results showed that the consumption of coordinating groups such as phenolic groups and hydrogen bonds reduced the complexation ability of FA and BTLL. The functional groups were degraded with the removal order of quinone group, phenolic group and aromatic group, and finally realized the molecular saturation and aromaticity decrease for humic-like substances. The mobility of FA and BTLL was decreased because of the enhancement of hydrophobicity during electrolysis process. Furthermore, the available chlorine produced during electrochemical oxidation was the main acute cytotoxicity substance, therefore, it is necessary to remove it before discharge in order to reduce ecological risks. This study provides a basis for understanding and evaluating the electrochemical degradation process of humic-like substances in detail.

Mercury (Hg) emissions from point sources to air may disperse over long distance depending on Hg speciation in the plume. A significant fraction of Hg, particularly in its divalent forms, deposits locally and causes pollution to surrounding biomes. The objective of this study was to investigate (1) the historic Hg deposition to the immediate vicinity of an industrial complex that had intentional use of Hg (i.e., chlor-alkali and polyvinyl chloride production) for 5 decades until 2011, and (2) the Hg⁰ re-emission from soil to air soon after the closure of the facility. The spatial distribution of near-ground Hg⁰ vapor in air, soil Hg concentration and stable isotope ratio, air-soil Hg⁰ flux and Hg⁰ concentration in soil pore-gas were measured. It was found that the surrounding soils are severely contaminated with Hg due to the Hg release of the industrial complex, displaying soil Hg content up to 4.8 μg g⁻¹. A spatial trend of Hg mass dependent isotope fractionation signature (δ²⁰²Hg = −2.11‰ to 0.72‰) with respect to the distance from the closed facility was identified, representing a mixing between regional background and industrial Hg sources. Hg release from the industrial operation enhanced surface soil Hg content within a 6.5-km radius from the facility. Inside the facility, residual Hg wastes (i.e., electrolysis sludge and consumed HgCl₂ catalyst) represent a strong localized emission source of atmospheric Hg⁰. Near-ground atmospheric Hg⁰ concentration and soil Hg⁰ efflux progressively elevated toward the facility with an increase by 2–3 orders of magnitude compared to the values observed in the off-site background. These results suggest that the natural soil surfaces surrounding the closed industrial facility act as a large nonpoint source emitting legacy deposited Hg as much as the release from naturally enriched mines.

In this study, we firstly used alginate to enhance an electrokinetic technology to remediate soil contaminated with divalent heavy metals (Pb²⁺, Cu²⁺, Zn²⁺). The mechanisms of alginate-associated migration of metal ions in electric field were confirmed. Alginate resulted in a high electrical current during electrokinetic process, and soil conductivity also increased after remediation. Obvious changes in both electroosmotic flow and soil pH were observed. Moreover, these factors were affected by increasing alginate dosage. The highest Cu (95.82%) and Zn (97.33%) removal efficiencies were obtained by introducing 1 wt% alginate. Alginate can desorb Cu²⁺ and Zn²⁺ ions from soil by forming unstable gels, which could be dissociated through electrolysis. However, Pb²⁺ ions did not easily migrate out of the contaminated soil. The density functional theory (DFT) calculations show Pb²⁺ ions could form a more stable coordination sphere in metal complexes than Cu²⁺ and Zn²⁺ ions. The metal removal efficiency was decreased by increasing alginate dosage at a high level. More alginate could provide more carboxyl ligands for divalent metal ions to stabilize gels, which were difficult to dissociate by electrolysis. In summary, the results indicate it is potential for introducing alginate into an electrokinetic system to remediate Cu- and Zn- contaminated soil.

Carbamazepine (CBZ) decay by electro-Fenton (EF) oxidation using a novel FeS₂/carbon felt (CF) cathode, instead of a soluble iron salt, was studied with the aim to accelerate the reaction between H₂O₂ and ferrous ions, which helps to produce more hydroxyl radicals (•OH) and eliminate iron sludge. First, fabricated FeS₂ and its derived cathode were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Anodes were then screened, with DSA (Ti/IrO₂–RuO₂) showing the best performance under EF oxidation regarding CBZ degradation and electrochemical characterization. Several operating parameters of this EF process, such as FeS₂ loading, current density, gap between electrodes (GBE), initial [CBZ], and electrolyte type, were also investigated. Accordingly, a nonconsecutive empirical kinetic model was established to predict changes in CBZ concentration under the given operational parameters. The contribution of different oxidation types to the EF process was calculated using kinetic analysis and quenching experiments to verify the role of the FeS₂-modified cathode. The reaction contributions of anodic oxidation (AO), H₂O₂ electrolysis (EP), and EF oxidation to CBZ removal were 12.81%, 7.41%, and 79.77%, respectively. The •OH exposure of EP and EF oxidation was calculated, confirming that •OH exposure was approximately 22.45-fold higher using FeS₂-modified CF. Finally, the 19 intermediates formed by CBZ degradation were identified by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. Accordingly, four CBZ degradation pathways were proposed. ECOSAR software was used to assess the ecotoxicity of intermediates toward fish, daphnia, and green algae, showing that this novel EF oxidation process showed good toxicity reduction performance. A prolonged EF retention time was proposed to be necessary to obtain clean and safe water, even if the targeted compound was removed at an earlier time.