Based on the application of sediment microbial fuel cell (SMFC) in the bioremediation of sediment, this study used the sediment microbial fuel cell technology as the leading reactor. Modification of anode carbon felts (CF) by synthesis of PANI/MnO₂ composited to improve the electrical performance of the sediment microbial fuel cell. This study investigated the degradation effects, degradation pathways of the specific contaminant enrofloxacin and microbial community structure in sediment microbial fuel cell systems. The results showed that the sediment microbial fuel cell system with modified anode carbon felt (PANI-MnO₂/CF) prepared by in-situ chemical polymerization had the best power production performance. The maximum output voltage was 602 mV and the maximum power density was 165.09 mW m⁻². The low concentrations of enrofloxacin (12.81 ng g⁻¹) were effectively degraded by the sediment microbial fuel cell system with a removal rate of 59.52%.

Synthetic azo dyes are extensively used in the textile industries, which are being released as textile effluent into the environment presence of azo dyes in the environment is great environmental concern therefore treatment of textile effluent is crucial for proper release of the effluent into the environment. Electrochemical oxidation (EO) is extensively used in the degradation of pollutants because of its high efficiency. In this study, photo-assisted electrooxidation (PEO) followed by biodegradation of the textile effluent was evaluated. The pretreatment of textile effluent was conducted by EO and PEO in a tubular flow cell with TiO₂–Ti/IrO₂–RuO₂ anode and titanium cathode under different current densities (10, 15, and 20 mA cm⁻²). The chemical oxygen demand level reduced from 3150 mg L⁻¹ to 1300 and 600 mg L⁻¹under EO and PEO, respectively. Furthermore, biodegradation of EO and PEO pretreated textile effluent shows reduction in chemical oxygen demand (COD) from 1300 mg L⁻¹ to 900 mg L⁻¹and 600 mg L⁻¹to 110 mg L⁻¹, respectively. The most abundant genera were identified as Acetobacter, Achromobacter, Acidaminococcus, Actinomyces, and Acetomicrobium from the textile effluent. This study suggests that an integrated approach of PEO and subsequent biodegradation might be an effective and eco-friendly method for the degradation of textile effluent.

In this work, a cylindrical flow-through electro-Fenton reactor containing graphite felt electrodes and an Fe(II) loaded resin was evaluated for the production of the Fenton reaction mixture and for the degradation of amoxicillin (AMX) and fecal coliforms containing aqueous solutions. First, the influence of several factors such as treatment time, current intensity, flow rate, and electrode position was investigated for the electrogeneration of H₂O₂ and the energetic consumption by means of a factorial design methodology using a 2⁴ factorial matrix. Electric current and treatment time were found to be the pivotal parameters influencing the H₂O₂ production with contributions of 40.2 and 26.9%, respectively. The flow rate had low influence on the responses; however, 500 mL min⁻¹ (with an average residence time of 1.09 min obtained in the residence time distribution analysis) allowed to obtain a better performance due to the high mass transport to and from the electrodes. As expected, polarization was also found to play an important role, since for the cathode-to-anode flow direction, lower H₂O₂ concentrations were observed when compared with the anode-to-cathode flow arrangement, indicating that part of the H₂O₂ produced in the cathode was destroyed at the anode. A fluorescence study of hydroxyl radical production, on the other hand, showed that higher yields were obtained using an anode-to-cathode flow direction (up to 3.88 µM), when compared with experiments carried out using a cathode-to-anode flow path (3.11 µM). The removal of a commercial formulation of the antibiotic AMX was evaluated in terms of total organic carbon, achieving up to 57.9% and 38.63% of pollutant mineralization using synthetic and real sanitary wastewater spiked, respectively. Finally, the efficiency of the process on the inactivation of fecal coliforms in sanitary wastewater samples was assessed, reducing 90% of the bacteria after 5 min of electrolysis.

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K₃[Fe(CN)₆]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200 mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8 h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6 h and K₃[Fe(CN)₆] or NaCl concentrations were 200 mM, the highest power densities were 6.00, 6.45, and 6.64 mW·m⁻², respectively. With increasing K₃[Fe(CN)₆] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8 mg/m³·h and 428.0 ± 28.5 → 157.0 ± 35.7 mg/m³·h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30 mg/m³·h). Cathode aeration (0 → 8 h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7 mg/m³·h for 6 h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1 mg/m³·h). Our results demonstrate that adding an electron acceptor (K₃[Fe(CN)₆]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.

The feasibility of removal of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺–N) from landfill leachate by an electrochemical assisted HClO/Fe²⁺ process is demonstrated for the first time. The performance of active chlorine generation at the anode was evaluated in Na₂SO₄/NaCl media, and a higher amount of active chlorine was produced at greater chloride concentration and higher current density. The probe experiments confirmed the coexistence of hydroxyl radical (•OH) and Fe(IV)-oxo complex (FeᴵⱽO²⁺) in the HClO/Fe²⁺ system. The influence of initial pH, Fe²⁺ concentration, and applied current density on COD and NH₄⁺–N abatement was elaborately investigated. The optimum pH was found to be 3.0, and the proper increase in Fe²⁺ dosage and current density resulted in higher COD removal due to the accelerated accumulation of •OH and FeᴵⱽO²⁺ in the bulk liquid phase, whereas, the NH₄⁺–N oxidation was significantly affected by the applied current density because of the effective active chlorine generation at higher current but was nearly independent of Fe²⁺ concentration. The reaction mechanism of electrochemical assisted HClO/Fe²⁺ treatment of landfill leachate was finally proposed. The powerful •OH and FeᴵⱽO²⁺, in concomitance with active chlorine and M(•OH), were responsible for COD abatement, and active chlorine played a key role in NH₄⁺–N oxidation. The proposed electrochemical assisted HClO/Fe²⁺ process is a promising alternative for the treatment of refractory landfill leachate.

TiO₂-based photocatalysts are a potential technology for removing indoor formaldehyde (CHOH) owing to their strong photooxidation ability. However, their photooxidation performance is generally weakened when suffering from the competitive adsorption of H₂O. In a method inspired by the oxygen evolution reaction (OER) to generate intermediates with hydroxyl radicals on the anode electrode catalysts, an electric field was employed in this research and applied to the photooxidation of CHOH to prevent the competitive adsorption of H₂O. Additionally, 0.5–5% Fe₂O₃ decorated TiO₂ was employed to improve the photoelectrocatalytic activity. The influence of an electric field on hydroxyl-radical production was investigated by both density functional theory (DFT) with direct-imposed dipole momentum and photoelectrocatalytic experimental tests. The surface characterization of the photocatalysts, including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR), was conducted. DFT results show that a positive electric field with a strength of 0.05 Å/V was more favorable to produce hydroxyl on Fe₂O₃/TiO₂(010) than was a negative electric field. Fe₂O₃ decoration can significantly boost hydroxyl formation, resulting from a decrease in the binding energy between the Fe of Fe₂O₃ and the oxygen and hydrogen atoms of H₂O. The dissociated hydrogen atom of the H₂O preferentially remained on the catalysts’ surface rather than being released into the gas flow. The experimental results demonstrated that applying 150 V could not directly enhance the photooxidation of CHOH by either TiO₂ or Fe₂O₃/TiO₂ but that it could relieve the H₂O inhibitory effect by more than 10% on the Fe₂O₃/TiO₂.

Carbamazepine (CBZ) is one of the most widely used antiepileptic drugs in Malaysia. It was detected frequently in wastewater. The electrochemical treatment process has been applied for the degradation of CBZ using graphite–PVC as an anode under these conditions: 0.5 g sodium chloride (NaCl)) as supporting electrolyte, 5 V and 0–60 min electrolysis time in 100 mL of solution. However, 10,11-dihydro10-hydroxy carbamazepine (HDX-CBZ) and 10,11-epoxycarbamazepine (EPX-CBZ) as the main by-product have been analysed and quantified using liquid chromatography–time of flight/mass spectrometry (LC-TOF/MS). Both by-products were analysed in positive ionization mode, and they were separated on a chromatographic C18 column (5 μm, 2 mm × 150 mm) at a flow rate of 0.3 mL/min. Solid-phase extraction (SPE) was applied as a pre-concentration step for the enhancement of the sensitivity and detectability for both HDX-CBZ and EPX-CBZ by-products. Methanol (MeOH) has been selected as the best elution solvent for both by-products compared to methyl tertiary butyl ether (MTBE) and acetone (AC). However, the recovery was 85% and 92% for HDX-CBZ and EPX-CBZ by-products, respectively. The limit of quantification (LOQ) was 0.588 and 0.109 µg/L for HDX-CBZ and EPX-CBZ by-products, respectively. After 20 min of electrolysis time, both by-products HDX-CBZ and EPX-CBZ appeared at maximum concentrations of 343 and 144 μg/L then they were decreased to 17.2 and 9.8 μg/L, respectively, after 40 min. At the end of electrochemical treatment, both by-products were completely eliminated after 60 min.

Electrochemical wet absorption composite system has an excellent potential to remove Hg⁰ from flue gas. In this study, ruthenium iridium titanium platinum quaternary composite electrode is used as an anode and titanium electrode is used as the cathode, and KI/I₂ absorption solution is introduced into the electrocatalysis system as an electrolyte to form KI/I₂ electrochemical catalytic oxidation system. The removal rate of Hg⁰ in flue gas can be increased to 92.3%. The effects of electrolytic voltage, current, Pt content, I₂ concentration, and the ratio of KI/I₂ on the removal of Hg⁰ were discussed. The possible free radicals in the electrochemical cathode, anode, and solution were characterized and tested by XRD, SEM, UV-Vis (detection of H₂O₂, ·OH, O₃), and FTIR (detection of IO₃⁻). Combined with experimental data and theoretical derivation, the mechanism of Hg⁰ removal from flue gas by electrochemical catalytic oxidation alloy formation wet absorption combined process was studied. The results show that the combined process, which is a promising technology can not only improve the removal efficiency of Hg⁰, but also realize the resource recovery of Hg⁰ and I₂, and provide a feasibility study for the subsequent regeneration of KI/I₂ absorption solution.

The efficient and harmless treatment of cyanide tailings is necessary for gold extraction processes. The present study reports the effects of ClO⁻ generation in a slurry electrolysis system containing NaCl on the removal rate of cyanide and heavy metal ions in cyanide tailings. The chemical dissolution of metallic minerals and the reaction mechanisms were investigated by Fourier-transform infrared (FT-IR) and X-ray diffraction (XRD) analyses. The obtained results evidenced the key role of ClO⁻ in the removal of cyanide and heavy metal ions through the slurry electrolysis system with NaCl addition. Furthermore, ClO⁻ formation increased with the NaCl concentration, resulting in a higher removal rate of cyanide and heavy metal ions and enhanced metallic mineral dissolution. The cyanide tailings showed the best harmless effect with a NaCl concentration of 15 g/L. With this condition, the removal rates of CNT, CN⁻, Cu, Zn and Fe were 96.15%, 98.34%, 98.62%, 99.32% and 79.31%, respectively; furthermore, Cu and Fe precipitated at the cathode. The relative hematite content decreased by 3.12%. Under the effect of an electric field, the cyanide and metal cyanide complexes in the cyanide tailings oxidised and decomposed to release metal cations by the strongly oxidising ClO⁻ generated at the anode. The metal cations and hematite were reduced at the cathode, while the metal oxide mineral hematite in the electrolyte underwent chemical dissolution. In the toxic degradation of cyanide tailings, the comprehensive recovery of metals and destruction of metallic minerals in tailings will provide favourable conditions for subsequent comprehensive utilisation.

In this work, the use of natural organic wastes (orange and lemon peels) as sources of citric acid was evaluated along with the application of the photoelectro-Fenton (PEF) system under non-modified pH as a novel alternative to degrade a complex mixture of pharmaceuticals: sulfamethoxazole (SMX—7.90 × 10–⁵ mol/L) and trimethoprim (TMP—6.89 × 10–⁵ mol/L). The system was equipped with a carbon felt air diffusion cathode (GDE) and a Ti/IrO₂ anode doped with SnO₂ (DSA). A 3.6 × 10–⁵ mol/L solution of commercial citric acid was used as a reference. The pharmaceuticals’ evolution in the mixture was followed by high-performance liquid chromatography (HPLC). The addition of natural products showed an efficient simultaneous degradation of the antibiotics (100% of SMX and TMP at 45 min and 90 min, respectively) similar to the performance produced by adding the commercial citric acid to the PEF system. Moreover, the addition of natural products allowed for an increment of biodegradability (100% removal of TOC by a modified Zahn Wellens test) and a decrease in ecotoxicity (0% in the bioassay with D. Magna) of the treated solutions. The antibacterial activity was eliminated after only 45 min of treatment, suggesting that the degradation by-products do not represent a significant risk to human health or the environment in general. Results suggest that, because of the efficient formation of Fe-citrate complexes, the PEF could be enhanced by the addition of natural organic wastes as a sustainable alternative ecological system for water contaminated pharmaceuticals. Additionally, the potential of reusing natural organic wastes has been exposed, contributing to an improved low-cost PEF by decreasing the environmental contamination produced by this type of waste.