Effect of electrogenerated hydroxyl radicals, active chlorine and organic matter on the electrochemical inactivation of Pseudomonas aeruginosa using BDD and dimensionally stable anodes

Advances on electrochemical disinfection research: Mechanisms, influencing factors and applications

Disinfection, a vital barrier against pathogenic microorganisms, is crucial in halting the spread of waterborne diseases. Electrochemical methods have been extensively researched and implemented for the inactivation of pathogenic microorganisms from water and wastewater, primarily owing to their simplicity, efficiency, and eco-friendliness. This review succinctly outlined the core mechanisms of electrochemical disinfection (ED) and systematically examined the factors influencing its efficacy, including anode materials, system conditions, and target species. Additionally, the practical application of ED in water and wastewater treatment was comprehensively reviewed. Case studies involving various scenarios such as drinking water, hospital wastewater, black water, rainwater, and ballast water provided concrete instances of the expansive utility of ED. Finally, coupling ED with other technologies and the resulting synergies were introduced as pivotal foundations for subsequent engineering advancements.

Synergistic mechanisms between chlorine-mediated electrochemical advanced oxidation and ultraviolet light for ammonia removal

The combination of chlorine-mediated electrochemical advanced oxidation (Cl-EAO) and ultraviolet (UV) radiation (UV-E/Cl) can efficiently remove ammonia from wastewater. However, the synergistic mechanisms between Cl-EAO and UV need to be explored in more detail. Thus, in this study, the ammonia oxidation performance of Cl-EAO and UV-E/Cl systems were compared, while the synergistic mechanisms were identified by the performance of UV/chlorine oxidation (UV-ClO) system and the results of electron paramagnetic resonance (EPR) analysis, free radical inhibition assays, and determination of steady-state concentration of free radicals. It was found that, compared with the Cl-EAO system, UV increased the ammonia removal rate by 42.85% and reduced the active chlorine concentration (56.64%) and nitrate yield (53.61%). In the Cl-EAO, and UV-E/Cl systems, Cl• were detected, and the free radical inhibition assays and determination of steady-state concentration of free radicals suggested that UV increased the concentration of Cl• by 51.47%, resulting in Cl• becoming the major contributor to ammonia oxidation in the UV-E/Cl system. Besides, UV also increase the concentrations of HO• and Cl2•-, which further promoted the organic matter removal in the real domestic wastewater. This study also discussed the ammonia oxidation performance of the UV-E/Cl system in real domestic wastewater, even with the presence of significant levels of organic and inorganic anions in the wastewater, UV increased the ammonia oxidation by 21.95%. The results of this study thus clarify the mechanisms and potential applications of UV-E/Cl technology.

Optimization of electrochemical regeneration of intercalated MXene for the adsorptive removal of ciprofloxacin: Prospective mechanism

2D-Ti3C2Tx MXene nanosheets intercalated with sodium ions (SI-Ti3C2Tx) were synthesized and utilized in simultaneous adsorption and electrochemical regeneration with ciprofloxacin (CPX). The primary focus of this study is to investigate the long-term stability of SI-Ti3C2Tx MXene and to propose the underlying regeneration mechanisms. The successful synthesis of Ti3AlC2, Ti3C2Tx MXene, and SI-Ti3C2Tx MXene was confirmed using X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. Electrochemical regeneration parameters such as charge passed, regeneration time, current density, and electrolyte composition were optimized with values of 787.5 C g-1, 7.5 min, 10 mA cm-2, and 2.5w/v% sodium chloride, respectively, enabling the complete regeneration of the SI-Ti3C2Tx MXene. In addition, the electrochemical regeneration significantly enhanced CPX removal from the SI-Ti3C2Tx MXene owing to partial amorphization, disorderliness, increased functional groups, delamination, and defect creation in the structure. Thus, the synthesized nano-adsorbent has proven helpful in practical water treatment with optimized electrochemical regeneration processes.

Bibliometric analysis of electrochemical disinfection: current status and development trend from 2002 to 2022

The removal of waterborne pathogens from water is critical in preventing the spread of waterborne diseases. Electrochemical methods have been extensively researched and implemented for disinfection, primarily owing to their simplicity, efficiency, and eco-friendliness. Thus, it is essential to conduct a review about the research progress and hotspots on this promising technique. In this paper, we provided a comprehensive bibliometric analysis to systematically study and analyze the current status, hotspots, and trends in electrochemical disinfection research from 2002 to 2022. This study analyzed literature related to electrochemical disinfection or electrochemical sterilization published in the Web of Science database from 2002 to 2022 using CiteSpace and Biblioshiny R language software packages. The analysis focused on the visualization and assessment of annual publication volume, discipline and journal distribution, collaborative networks, highly cited papers, and keywords to systematically understand the current status and trends of electrochemical disinfection. The results showed that between 2002 and 2022, 1171 publications related to electrochemical disinfection were published, with an exponential increase in the cumulative number of publications (y=17.518e0.2147x, R2= 0.9788). The publications covered 76 disciplines with many articles published in high-impact journals. However, the research power was characterized by a large number of scattered research efforts and insufficient cooperation, indicating the need for further innovative collaboration. The citation analysis and keyword analysis suggest that future development in this field may focus on optimizing electrode materials, investigating the disinfection performance of ·OH based systems, optimizing conditions for actual wastewater treatment, and reducing energy consumption to promote practical applications.

Water treatment and reclamation by implementing electrochemical systems with constructed wetlands

Seasonal or permanent water scarcity in off-grid communities can be alleviated by recycling water in decentralized wastewater treatment systems. Nature-based solutions, such as constructed wetlands (CWs), have become popular solutions for sanitation in remote locations. Although typical CWs can efficiently remove solids and organics to meet water reuse standards, polishing remains necessary for other parameters, such as pathogens, nutrients, and recalcitrant pollutants. Different CW designs and CWs coupled with electrochemical technologies have been proposed to improve treatment efficiency. Electrochemical systems (ECs) have been either implemented within the CW bed (ECin-CW) or as a stage in a sequential treatment (CW + EC). A large body of literature has focused on ECin-CW, and multiple scaled-up systems have recently been successfully implemented, primarily to remove recalcitrant organics. Conversely, only a few reports have explored the opportunity to polish CW effluents in a downstream electrochemical module for the electro-oxidation of micropollutants or electro-disinfection of pathogens to meet more stringent water reuse standards. This paper aims to critically review the opportunities, challenges, and future research directions of the different couplings of CW with EC as a decentralized technology for water treatment and recovery.

Preparation and characterization of PMT-TiO2-NTs@NiO-C/Sn-Sb composite electrodes by a two-step pulsed electrodeposition method for the degradation of crystalline violet

To overcome the limitations imposed by Sn-Sb electrodes, the titanium foam (PMT)-TiO₂-NTs@NiO-C/Sn-Sb composite electrodes with cubic crystal structure are synthesized by introducing NiO@C nanosheet arrays interlayer on the TiO₂-NTs/PMT matrix through hydrothermal and carbonization process. Then a two-step pulsed electrodeposition method is used to prepare the Sn-Sb coating. Benefiting from the advantages of stacked 2D layer-sheet structure, the obtained electrodes exhibit enhanced stability and conductivity. Synergy of inner and outer layers fabricated by different pulse times strongly influence the electrochemical catalytic properties of the PMT-TiO₂-NTs@NiO-C/Sn-Sb (Sn-Sb) electrode. Hence, the Sn-Sb (b0.5 h + w1 h) electrode is the optimal electrode to degrade the Crystalline Violet (CV). Next, the effect of the four experimental parameters (initial CV concentration, current density, pH value and supporting electrolyte concentration) on the degradation of CV by the electrode are investigated. The degradation of the CV is more sensitive to alkaline pH, and the rapid decolorization of CV when the pH is 10. Moreover, the possible electrocatalytic degradation pathway of CV is performed using HPLC-MS. Results from the tests show that the PMT-TiO₂-NTs/NiO@C/Sn-Sb (b0.5 h + w1 h) electrode is an interesting alternative material in industrial wastewater applications.

In situ generation of highly localized chlorine by laser-induced graphene electrodes during electrochemical disinfection

Laser-induced graphene (LIG) has gained popularity for electrochemical water disinfection due to its efficient antimicrobial activity when activated with low voltages. However, the antimicrobial mechanism of LIG electrodes is not yet fully understood. This study demonstrated an array of mechanisms working synergistically to inactivate bacteria during electrochemical treatment using LIG electrodes, including the generation of oxidants, changes in pH-specifically high alkalinity associated with the cathode, and electro-adsorption on the electrodes. All these mechanisms may contribute to the disinfection process when bacteria are close to the surface of the electrodes where inactivation was independent of the reactive chlorine species (RCS); however, RCS was likely responsible for the predominant cause of antibacterial effects in the bulk solution (i.e., ≥100 mL in our study). Furthermore, the concentration and diffusion kinetics of RCS in solution was voltage-dependent. At 6 V, RCS achieved a high concentration in water, while at 3 V, RCS was highly localized on the LIG surface but not measurable in water. Despite this, the LIG electrodes activated by 3 V achieved a 5.5-log reduction in Escherichia coli (E.coli) after 120-min electrolysis without detectable chlorine, chlorate, or perchlorate in the water, suggesting a promising system for efficient, energy-saving, and safe electro-disinfection.

Evaluation of pathogen disinfection efficiency of electrochemical advanced oxidation to become a sustainable technology for water reuse

Water treatment and reuse is gaining acceptance as a strategy to fight against water contamination and scarcity, but it usually requires complex treatments to ensure safety. Consequently, the electrochemical advanced processes have emerged as an effective alternative for water remediation. The main objective here is to perform a systematic study that quantifies the efficiency of a laboratory-scale electrochemical system to inactivate bacteria, bacterial spores, protozoa, bacteriophages and viruses in synthetic water, as well as in urban wastewater once treated in a wetland for reuse in irrigation. A Ti|RuO₂-based plate and Si|BDD thin-film were comparatively employed as the anode, which was combined with a stainless-steel cathode in an undivided cell operating at 12 V. Despite the low resulting current density (<15 mA/cm²), both anodes demonstrated the production of oxidants in wetland effluent water. The disinfection efficiency was high for the bacteriophage MS2 (T99 in less than 7.1 min) and bacteria (T99 in about 30 min as maximum), but limited for CBV5 and TuV, spores and amoebas (T99 in more than 300 min). MS2 presented a rapid exponential inactivation regardless of the anode and bacteria showed similar sigmoidal curves, whereas human viruses, spores and amoebas resulted in linear profiles. Due the different sensitivity of microorganisms, different models must be considered to predict their inactivation kinetics. On this basis, it can be concluded that evaluating the viral inactivation from inactivation profiles determined for bacteria or some bacteriophages may be misleading. Therefore, neither bacteria nor bacteriophages are suitable models for the disinfection of water containing enteric viruses. The electrochemical treatment added as a final disinfection step enhances the inactivation of microorganisms, which could contribute to safe water reuse for irrigation. Considering the calculated low energy consumption, decentralized water treatment units powered by photovoltaic modules might be a near reality.

Electrochemical disinfection may increase the spread of antibiotic resistance genes by promoting conjugal plasmid transfer

Current in the milliampere range can be used for electrochemical inactivation of bacteria. Yet, bacteria-including antibiotic resistant bacteria (ARB) may be subjected to sublethal conditions due to imperfect mixing or energy savings measures during electrochemical disinfection. It is not known whether such sublethal current intensities have the potential to stimulate plasmid transfer from ARB. In this study, conjugal transfer of plasmid pKJK5 was investigated between Pseudomonas putida strains under conditions reflecting electrochemical disinfection. Although the abundance of culturable and membrane-intact donor and recipient cells decreased with applied current (0-60 mA), both transconjugant density and transconjugant frequency increased. Both active chlorine and superoxide radicals were generated electrolytically, and ROS generation was induced. In addition, we detected significant over expression of a core oxidative stress defense gene (ahpCF) with current. Expression of selected conjugation related genes (traE, traI, trbJ, and trbL) also significantly correlated with current intensity. ROS accumulation, SOS response and subsequent derepression of conjugation are therefore the plausible consequence of sublethal current exposure. These findings suggest that sublethal intensities of current can enhance conjugal plasmid transfer, and that it is essential that conditions of electrochemical disinfection (applied voltage, current density, time and mixing) are carefully controlled to avoid conjugal ARG transmission.

Electrocatalytic oxidation of antidiabetic drug metformin adsorbed on intercalated MXene

Two-dimensional (2D) Ti₃C₂T_x transition metal carbide (MXene) nanosheets intercalated with sodium ions (SI-Ti₃C₂T_x MXene) were used in the adsorption and electrochemical regeneration process for removal of the antidiabetic drug metformin (MF) as a model emerging pollutant. After MF adsorption, SI-Ti₃C₂T_x MXene oxidized the MF on its surface through its electrocatalytic activity at very low current density and cell potential. For complete oxidation the optimum parameters were 0.525 C g^-1, 0.005 mA cm^-2, and pH 6 in absence of NaCl or 26.25 C g^-1 and 0.5 mA cm^-2 in the presence of 2.5 w/v% NaCl. The overall regeneration of SI-Ti₃C₂T_x is governed by a combined mechanism, i.e., desorption followed by degradation. The degradation mechanism, such as direct electron transfer or indirect oxidation, depends on the applied operating conditions. Thus, the investigation suggests that these 2D sheets are good nanoadsorbents as well as good electrocatalysts and proves their usefulness in practical water-treatment applications.

The role of bromides upon electrochemical mineralization of bisphenol A with boron-doped diamond anode

Anodic oxidation with boron-doped diamond (BDD) has been regarded as outstanding option for wastewater treatment. However, in the presence of halide, the extreme promise of the technology may be hampered by the formation of toxic halogenated by-products. While the behaviors of chloride are relatively understood, little is currently known about the role of bromide and its effect on the generation of brominated transformation by-products (BTPs). Herein, we reported for the first time the bromide-mediated electrochemical mineralization of bisphenol A with BDD anodes. Firstly, we employed statistical methodology to determine the impacts of the main operating variables on the mineralization performance, and the novel and peculiar roles of bromides during the electrolytic oxidations were identified. Next, LC/MS analysis was used to identify the reaction intermediates, and plenty of BTPs (including oligomers of complex structures) were thus detected. Detailed transformation mechanisms responsible for the BTPs were also proposed. Lastly, we used ECOSAR program to determine the ecological toxicity of all detected by-products, and the structure-toxicity relation involved was discussed. Overall, the above results are of particular interest to understand BTPs formation mechanism in electrochemical oxidation processes, which as well provide guidelines to minimize potential risks of BDD technology for phenolic wastewater treatment.

Upgrading the peroxi-coagulation treatment of complex water matrices using a magnetically assembled mZVI/DSA anode: Insights into the importance of ClO radical

The electrochemical technologies for water treatment have flourished over the last decades. However, it is still challenging to treat the actual complex water effluents by a single electrochemical process, often requiring coupling of technologies. In this study, an upgraded peroxi-coagulation (PC) process with a magnetically assembled mZVI/DSA anode has been devised for the first time. COD, NH₃-N and total phosphorous were simultaneously and effectively removed from livestock wastewater. The advantages, influence of key parameters and evolution of electrogenerated species were systematically investigated to fully understand this novel PC process. The fluorescent substances in livestock wastewater could also be almost removed under optimal conditions (300 mA, 0.2 g ZVI particles and pH 6.8). The interaction between OH and active chlorine yielded ClO with a high steady-state concentration of 6.85 × 10^-13 M, which did not cause COD removal but accelerated the oxidation of NH₃-N. The Mulliken population suggested that OH and NH₃-N had similar electron-donor behavior, whereas ClO acted as an electron-withdrawing species. Besides, although the energy barrier for the reaction between OH and NH₃-N (17.0 kcal/mol) was lower than that with ClO (18.8 kcal/mol), considering the tunneling in the H abstraction reaction, the Skodje-Truhlar method adopted for calculations evidenced a 17-fold faster NH₃-N oxidation rate with ClO. In summary, this work describes an advantageous single electrochemical process for the effective treatment of a complex water matrix.

Rethinking electrochemical oxidation of bisphenol A in chloride medium: Formation of toxic chlorinated oligomers

Using boron-doped diamond (BDD) anodes to degrade bisphenol A (BPA) had been an active area of research interest within the past 20 years. A major concern about the process lie in the formation of toxic chlorinated aromatic by-products when chloride electrolytes were present in the reaction system. In this contribution, we highlighted the formation of complex poly-chlorinated oligomer by-products in electrochemical oxidation processes, which had often been overlooked in previous studies. Moreover, the distribution and complexity of the chlorinated oligomers were found to be strongly linked to the adopted initial chloride concentration. Formation of simple chlorinated by-products was ascribed to the electrophilic substitution reactions mediated by active chlorine species, while the oligomer by-products (including chlorinated dimers, trimers and tetramers) were generated through the coupling reactions between various chlorinated phenoxy radicals. The possible mechanisms describing the formation of these by-products were also proposed. The obtained results shed light on the possible risk of BDD technology in the treatment of phenolic wastewater containing chloride electrolytes.

Recent advances on inactivation of waterborne pathogenic microorganisms by (photo) electrochemical oxidation processes: Design and application strategies

Compared with other conventional water disinfection processes, (photo) electrochemical oxidation (P/ECO) processes have the characteristics of environmental friendliness, convenient installation and operation, easy control and high efficiency of inactivating waterborne pathogenic microorganisms (PMs), so that more and more research work has been focused on this topic, but there is still a huge gap between the research and practical application. Here, the research network of inactivating PMs by P/ECO processes has been comprehensively summarized, and the electrode/reactor/process design strategies based on strengthening direct and indirect oxidation, enhancing mass transfer efficiency and electron transfer efficiency, and improving the effective dose of electrogenerated oxidants are discussed. Furthermore, the factors affecting the inactivation of PMs and the issues regarding to stability and lifetime of the electrode are discussed respectively. Finally, the important research priorities and possible research challenges of P/ECO processes are put forward to make significant progress of this technology.

Decontamination of real urban sewage-comparison between Fenton and electrochemical oxidation

Advanced oxidation processes have been used for wastewater treatment due to their capacity to reduce the organic loading and for their fast reactions. In this paper, we explore the viability of isolated and sequential use of electrochemical oxidation and Fenton processes into treatment of real raw urban sewage. The electrochemical process was carried out using DSA®-Cl₂ electrodes and factorial planning in order to investigate the influence of pH, current density, and electrolyte. Fenton reaction was also used and H₂O₂ and Fe²⁺ concentration effects were investigated. The efficiency was estimated by chemical oxygen demand (COD) removal and in the optimized conditions the effluent was characterized by turbidity, suspended/dissolved/total solids, ammonia, chloride ions, free chlorine, nitrite, and potassium analysis and bioassays with Artemia ssp. and Lactuca sativa. The study demonstrated that the use of electrochemical technique followed by Fenton allowed an improvement in the degradation of organic matter and reduction of turbidity and solid content, reaching reductions of 86.8, 96.4, 99.4, 56.1, and 66.7% for COD, turbidity, SS, DS, and TS, respectively. The associated treatment also contributed to the reduction of energy consumption by 74.9%, from the 23.9 kWh m^-3 observed during the electrochemical treatment isolated to the 6 kWh m^-3 during the associated process. All the treatments presented toxicity reduction, with the electrochemical process achieving the best results.

Electrochemical flow-through disinfection reduces antibiotic resistance genes and horizontal transfer risk across bacterial species

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs), as emerging pollutants, are released into environment, increasing the risk of horizontal gene transfer (HGT). However, a limited number of studies quantified the effects of ARB disinfection on the HGT risk. This study investigated the inactivation of E. coli 10667 (sul) and the release and removal of ARGs using an electrochemical flow-through reactor (EFTR). Furthermore, the transfer frequencies and potential mechanisms of HGT after disinfection were explored using non-resistant E. coli GMCC 13373 as the recipient and E. coli DH5α carrying plasmid RP4 as the donor. A threshold of current density (0.25 mA/cm²) was observed to destroy cells and release intracellular ARGs (iARGs) to increase extracellular ARGs (eARGs) concentration. The further increase in the current density to 1 mA/cm² resulted in the decline of eARGs concentration due to the higher degradation rate of eARGs than the release rate of iARGs. The performance of ARGs degradation and HGT frequency by EFTR were compared with those of conventional disinfection processes, including chlorination and ultraviolet radiation (UV). A higher ARGs degradation (83.46%) was observed by EFTR compared with that under chlorination (10.23%) and UV (27.07%). Accordingly, EFTR reduced the HGT frequency (0.69) of released ARGs into the recipient (Forward transfer), and the value was lower than that by chlorination (2.69) and UV (1.73). Meanwhile, the surviving injured E. coli 10667 (sul) with increased cell permeability was transferred by plasmid RP4 from the donor (Reverse transfer) with a higher frequency of 0.33 by EFTR compared with that under chlorination (0.26) and UV (0.16). In addition, the sul3 gene was the least resistant to EFTR than sul1 and sul2 gene. These findings provide important insights into the mechanism of HGT between the injured E. coli 10667 (sul) and environmental bacteria. EFTR is a promising disinfection technology for preventing the spread of antibiotic resistance.

Impact of electrolyte solution on electrochemical oxidation treatment of Escherichia coli K-12 by boron-doped diamond electrodes

We studied the disinfection efficacy of boron-doped electrodes on Escherichia coli-contaminated water-based solutions in three different electrolytes, physiological solution (NaCl), phosphate buffer (PB), and phosphate buffer saline (PBS). The effect of the electrochemical oxidation treatment on the bacteria viability was studied by drop and spread plate cultivation methods, and supported by optical density measurements. We have found that bacterial suspensions in NaCl and PBS underwent a total inactivation of all viable bacteria within 10 min of the electrochemical treatment. By contrast, experiments performed in the PB showed a relatively minor decrease of viability by two orders of magnitude after two hours of the treatment, which is almost comparable with the untreated control. The enhanced bacterial inactivation was assigned to reactive chlorine species (RCS), capable of penetrating the bacterial cytoplasmic membrane and killing bacteria from within.

Anodic Oxidation of Industrial Winery Wastewater Using Different Anodes

Winery wastewater represents the largest waste stream in the wine industry. This deals with the mineralization of the organic matter present in winery wastewater using anodic oxidation and two types of anodes—namely, a boron-doped diamond electrode (BDD) and two mixed metal oxides (MMO), one with the nominal composition Ti/Ru0.3Ti0.7O2 and the other with Ti/Ir0.45Ta0.55O2. To conduct the study, the variability of different quality parameters for winery wastewater from the Chilean industry was measured during eight months. A composite sample was treated using anodic oxidation without the addition of supporting electrolyte, and the experiments were conducted at the natural pH of the industrial wastewater. The results show that this effluent has a high content of organic matter (up to 3025 ± 19 mg/L of total organic carbon (TOC)), which depends on the time of the year and the level of wine production. With MMO electrodes, TOC decreased by 2.52% on average after 540 min, which may be attributed to the presence of intermediate species that could not be mineralized. However, when using a BDD electrode, 85% mineralization was achieved due to the higher generation of hydroxyl radicals. The electrolyzed sample contained oxamic, acetic, and propionic acid as well as different ions such as sulfate, chloride, nitrate, and phosphate. These ions can contribute to the formation of different species such as active species of chlorine, persulfate, and perphosphate, which can improve the oxidative power of the system.

Effect of Yellow Wine Lees Supplementation on Milk Antioxidant Capacity and Hematological Parameters in Lactating Cows under Heat Stress

Simple Summary

The yellow wine lees (YWL), a byproduct of the yellow wine brewing industry which contain high levels of crude protein and anti-oxidative substrates can be a suitable ingredient in dairy rations. Total mixed rations (TMR) containing unfermented/fermented YWL were greater in total phenolic and flavonoid concentrations. Feeding lactating cows under heat stress with TMR containing unfermented or fermented YWL mix can reduce their inflammation response and oxidative stress, as well as improve fatty acid quality and oxidative stability of their milk.

Abstract

Fifteen multiparous lactating Chinese Holstein dairy cows were used in a replicated 3 × 3 Latin Square Design to evaluate the effect of total mixed rations (TMR) containing unfermented and fermented yellow wine lees (YWL) on the oxidative status of heat-stressed lactating cows and the oxidative stability of the milk and milk fatty acids they produced. Cows were fed with three isonitrogenous and isocaloric diets as follows: (1) TMR containing 18% soybean meal, (2) TMR containing 11% unfermented YWL (UM), and (3) TMR containing 11% fermented YWL (FM). The rectal temperature (at 1300 h) and respiratory rate were higher in control cows than in cows fed UM or FM. Both types of YWL were greater in total phenolic and flavonoid contents, reducing power, and radical scavenging abilities than soybean meal. Cows fed UM or FM had higher blood neutrophil, white blood cell, and lymphocyte counts, as well as lower plasma malondialdehyde level, higher plasma superoxide dismutase, glutathione peroxidase, and 2,2-diphenyl-1-picryl-hydrazyl-hydrate levels, and higher total antioxidant capacity in the plasma than those fed control diet. The proportion of milk unsaturated fatty acids was higher and that of saturated fatty acids was lower in UM- and FM-fed animals than in the control animals. Milk from UM- and FM-fed cows had lower malondialdehyde content but higher 2,2-diphenyl-1-picryl-hydrazyl-hydrate content than the control cows. In conclusion, feeding TMR containing UM and FM to cows reduced both the oxidative stress in heat-stressed cows and improved the oxidative capacity of their milk.

Advanced hybrid electro-oxidation & O3 technology for water reuse in the fruit and vegetable process industry

Alternative sanitising agents are required in the fruit and vegetable processing industry, capable of effectively disinfecting both the product and the washing water to increase its reuse, while not producing harmful by-products like chlorine-based agents. In the present work, electro-oxidation (EO) and ozone are proposed for vegetable process water reuse, being optimised for their individual and combined application. The application of hybrid electro-oxidation and ozone achieved 7 log reduction after 15 min of treatment in batch using boron-doped diamond (BDD) as anode material, showing important synergistic effects when compared with the individual treatments. When the process was applied in continuous mode, up to 6 log reduction of total bacteria was achieved using EO alone with Ru as the anode and stainless steel as the cathode, under 11 mA/cm² of current density, a cell retention time of 12 s and no addition of chemical reagents (electrolyte). Under these conditions, the absence of microorganisms in water was maintained for more than 24 h, no harmful by-products (chlorate, bromate) were detected and no damage to lettuce seeds were observed when evaluating water reuse potential.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Electrochemical Disinfection in Water and Wastewater Treatment: Identifying Impacts of Water Quality and Operating Conditions on Performance

Electrochemical disinfection-a method in which chemical oxidants are generated in situ via redox reactions on the surface of an electrode-has attracted increased attention in recent years as an alternative to traditional chemical dosing disinfection methods. Because electrochemical disinfection does not entail the transport and storage of hazardous materials and can be scaled across centralized and distributed treatment contexts, it shows promise for use both in resource limited settings and as a supplement for aging centralized systems. In this Critical Review, we explore the significance of treatment context, oxidant selection, and operating practice on electrochemical disinfection system performance. We analyze the impacts of water composition on oxidant demand and required disinfectant dose across drinking water, centralized wastewater, and distributed wastewater treatment contexts for both free chlorine- and hydroxyl-radical-based systems. Drivers of energy consumption during oxidant generation are identified, and the energetic performance of experimentally reported electrochemical disinfection systems are evaluated against optimal modeled performance. We also highlight promising applications and operational strategies for electrochemical disinfection and propose reporting standards for future work.

A Conceptual Framework for Incorporation of Composting in Closed-Loop Urban Controlled Environment Agriculture

Controlled environment agriculture (CEA), specifically advanced greenhouses, plant factories, and vertical farms, has a significant role to play in the urban agri-food landscape through provision of fresh and nutritious food for urban populations. With the push towards improving sustainability of these systems, a circular or closed-loop approach for managing resources is desirable. These crop production systems generate biowaste in the form of crop and growing substrate residues, the disposal of which not only impacts the immediate environment, but also represents a loss of valuable resources. Closing the resource loop through composting of crop residues and urban biowaste is presented. Composting allows for the recovery of carbon dioxide and plant nutrients that can be reused as inputs for crop production, while also providing a mechanism for managing and valorizing biowastes. A conceptual framework for integrating carbon dioxide and nutrient recovery through composting in a CEA system is described along with potential environmental benefits over conventional inputs. Challenges involved in the recovery and reuse of each component, as well as possible solutions, are discussed. Supplementary technologies such as biofiltration, bioponics, ozonation, and electrochemical oxidation are presented as means to overcome some operational challenges. Gaps in research are identified and future research directions are proposed.

Electrodisinfection of bacteria-laden in surface water using modified Ti electrode by antimony-and nickel-doped tin oxide composite

Providing clean and safe drinking water by point of use (POU) disinfection methods has become a critical issue, especially in crises and epidemics. In this study, antimony-and nickel-doped tin oxide electrode (Ni-Sb-SnO₂) was employed as an electrode for electro-catalytic disinfection of surface water. The synthetized electrodes were characterized using scanning electron microscope, linear sweep voltammetry and X-Ray diffraction techniques. The results revealed that the highest electrochemical disinfection efficiency was achieved by the Ni-Sb-SnO₂ electrode under weak acidic conditions and its performance decreased with increasing pH towards alkaline environment. Based on the results, total coliform (TC) and fecal coliform (FC) were completely removed at current density of 0.67 mA cm^-2. Moreover, the electrochemical disinfection of microorganisms showed that the process efficiency was directly proportional to increasing time and at 0.6 C cm^-2 of charge passed, 3-log removal of the both indicators occurred after 15 min. The highest removal efficiency of TC and FC was also achieved at 8 mmol of NaCl concentration at <10 min of detention time. The results of this study depicted that the Ti/Ni-Sb-SnO₂ electrode provides higher disinfection efficiency for the removal of TC and FC compared with Ti and SS/PbO₂ electrodes. Moreover, the proposed system was able to completely eliminate heterotrophic, Streptococcus faecalis and Pseudomonas aerogenes indicators under optimal conditions. Therefore, it can be concluded that the proposed electrochemical system can be efficiency applied as a POU disinfection system for disinfection of water contaminated with microbial indicators, especially for crises and epidemics.

Degradation of hydroxychloroquine by electrochemical advanced oxidation processes

In this work, the degradation of hydroxychloroquine (HCQ) drug in aqueous solution by electrochemical advanced oxidation processes including electrochemical oxidation (EO) using boron doped diamond (BDD) and its combination with UV irradiation (photo-assisted electrochemical oxidation, PEO) and sonication (sono-assisted electrochemical oxidation, SEO) was investigated. EO using BDD anode achieved the complete depletion of HCQ from aqueous solutions in regardless of HCQ concentration, current density, and initial pH value. The decay of HCQ was more rapid than total organic carbon (TOC) indicating that the degradation of HCQ by EO using BDD anode involves successive steps leading to the formation of organic intermediates that end to mineralize. Furthermore, the results demonstrated the release chloride (Cl-) ions at the first stages of HCQ degradation. In addition, the organic nitrogen was converted mainly into NO3 - and NH4 + and small amounts of volatile nitrogen species (NH3 and NOx). Chromatography analysis confirmed the formation of 7-chloro-4-quinolinamine (CQLA), oxamic and oxalic acids as intermediates of HCQ degradation by EO using BDD anode. The combination of EO with UV irradiation or sonication enhances the kinetics and the efficacy of HCQ oxidation. PEO requires the lowest energy consumption (EC) of 63 kWh/m3 showing its cost-effectiveness. PEO has the potential to be an excellent alternative method for the treatment of wastewaters contaminated with HCQ drug and its derivatives.

Removal of antipyrine through two-dimensional and three-dimensional electrolysis: comparison, modification, and improvement

In this work, removal of antipyrine was studied through two-dimensional (2D) and three-dimensional (3D) electrolysis. 2D electrolysis was firstly studied with the Ti/SnO₂-Ta₂O₅-IrO₂ anode as working electrode. Operating parameters affecting antipyrine removal, such as current density, electrode distance, and initial concentration of antipyrine, were investigated and optimized. As the limited antipyrine removal efficiency of 48.0% was not satisfying, 3D electrolysis with γ-Al₂O₃ as particle electrodes was introduced in the purpose of improving the antipyrine removal. An obviously enhanced removal efficiency of 78.3% was obtained, which seemingly validated the effect of particle electrodes in improving antipyrine removal. Hence, an effort to further enhance the antipyrine removal efficiency was made through improving the electrochemical characteristics of γ-Al₂O₃ as particle electrodes. Modified Sn-Sb-Bi/γ-Al₂O₃ particles were thus prepared through impregnation method. And a desirable antipyrine removal efficiency of 94.4% and energy consumption of 0.18 kWh/g antipyrine were achieved in the 3D electrolysis with Sn-Sb-Bi/γ-Al₂O₃ as particle electrodes. Furthermore, possible mechanism and pathway of antipyrine degradation in 3D electrolysis were explored through detection of ·OH using terephthalic acid fluorescent probe method and detection of antipyrine degradation intermediates using LC-MS.

Testing the use of cells equipped with solid polymer electrolytes for electro-disinfection

This work focuses on disinfection of water using electrolysis with boron doped diamond (BDD) coatings and faces this challenge by comparing the performance of two different cells manufactured by CONDIAS GmbH (Izehoe, Germany): CONDIACELL® ECWP and CabECO cells. They are both equipped with diamond electrodes, but the mechanical design is completely different, varying not only by geometry but also by the flow conditions. ECWP is a flow-through cell with perforated electrodes while the CabECO cell is a zero-gap cell with a proton exchange membrane as a solid polymer electrolyte (SPE) separating the anode and cathode. At 0.02 Ah dm^-3 both cells attain around 3-5 logs pathogen removal, but design and sizing parameters give an advantage to the CabECO: it can minimize the production of chlorates and perchlorates when operating in a single-pass mode, which becomes a really remarkable point. In this paper, we report tests in which we demonstrate this outstanding performance and we also explain the differences observed in the two cells operating with the same water.

How to avoid the formation of hazardous chlorates and perchlorates during electro-disinfection with diamond anodes?

This work focuses on disinfection of water using electrolysis with diamond coatings avoiding or minimizing the formation of hazardous chlorates and perchlorates using a special type of commercial cells designed by CONDIAS (Itzehoe, Germany) in two different sizes: the CabECO and the MIKROZON cells. In these cells, the electrolyte that separates the anode and cathode is a proton exchange membrane. This helps to minimize the production of perchlorate and this behavior is enhanced in the smallest cell for which the very low contact times between the electrodes and the water allows to avoid the production of perchlorates when operating in a single-pass mode, which becomes a really remarkable point. In this paper, we report tests in which we demonstrate this outstanding performance and we also explain the differences observed in the two cells operating with the same water.

A continuous electroreduction cell composed of palladium nanocatalyst immobilized on discarded cigarette filters as an active bed for Cr(VI) removal from groundwater

In this research, a unique continuous electrochemical cell was designed and applied for the disinfection of groundwater and simultaneous Cr(VI) reduction and Cr(III) precipitation. Discarded cigarette filters (DCFs) were utilized as an efficient bed for palladium nanoparticles (PdNPs) immobilization located between porous anode and cathode made of graphite felt. The characterization of the bed was performed using FE-SEM, EDS, BET, and FT-IR analysis. The results confirmed the distribution of palladium nanoparticles on the surface of DCFs. The proposed design for electrochemical cell obviated the need to divide the anolyte and catholyte because the anode was located at the outlet of the cell, thereby avoiding the reaction between hydrogen radicals produced on the surface of PdNPs and oxygen and chlorine produced in the anode. The hydrogen gas produced in the cathode was converted to hydrogen radicals, acting as the most prominent species for the reduction. Hydroxide ions produced in the cathode increased the pH of the solution between electrodes, resulting in the precipitation of Cr (III) with an efficiency of 96%. Furthermore, free chlorine at the concentration of 1 mg L^-1 was generated through chloride ion oxidation in the anode, which can be effective for disinfection. The effect of initial Cr (VI) concentration (C₀), flow rate (Q), and current (I) was investigated, and the maximum removal efficiency (99.7%) was observed at the flow rate of 5 mL min^-1 and current of 0.05 A, respectively. No interference ensued from the various coexisting ions in groundwater. The findings of this study suggested that the proposed electrochemical cell is capable of in-situ total chromium removal and free chlorine production in groundwater simultaneously.

Electrolytic Oxidation as a Sustainable Method to Transform Urine into Nutrients

In this work, the transformation of urine into nutrients using electrolytic oxidation in a single-compartment electrochemical cell in galvanostatic mode was investigated. The electrolytic oxidation was performed using thin film anode materials: boron-doped diamond (BDD) and dimensionally stable anodes (DSA). The transformation of urine into nutrients was confirmed by the release of nitrate (NO3−) and ammonium (NH4+) ions during electrolytic treatment of synthetic urine aqueous solutions. The removal of chemical oxygen demand (COD) and total organic carbon (TOC) during electrolytic treatment confirmed the conversion of organic pollutants into biocompatible substances. Higher amounts of NO3− and NH4+ were released by electrolytic oxidation using BDD compared to DSA anodes. The removal of COD and TOC was faster using BDD anodes at different current densities. Active chlorine and chloramines were formed during electrolytic treatment, which is advantageous to deactivate any pathogenic microorganisms. Larger quantities of active chlorine and chloramines were measured with DSA anodes. The control of chlorine by-products to concentrations lower than the regulations require can be possible by lowering the current density to values smaller than 20 mA/cm2. Electrolytic oxidation using BDD or DSA thin film anodes seems to be a sustainable method capable of transforming urine into nutrients, removing organic pollution, and deactivating pathogens.

Role of Near-Electrode Solution Chemistry on Bacteria Attachment and Poration at Low Applied Potentials

This research investigated mechanisms for biofouling control at boron-doped diamond (BDD) electrode surfaces polarized at low applied potentials (e.g., -0.2 to 1.0 V vs Ag/AgCl), using Pseudomonas aeruginosa as a model organism. Results indicated that electrostatic interactions between bacteria and ionic electrode functional groups facilitated bacteria attachment at the open-circuit potential (OCP). However, under polarization, the applied potential governed these electrostatic interactions and electrochemical reactions resulted in surface bubble formation and near-surface pH modulation that decreased surface attachment under anodic conditions. The poration of the attached bacteria occurred at OCP conditions and increased with the applied potential. Scanning electrochemical microscopy (SECM) provided near-surface pH and oxidant formation measurements under anodic and cathodic polarizations. The near-surface pH was 3.1 at 1.0 V vs Ag/AgCl and 8.0 at -0.2 V vs Ag/AgCl and was possibly a contributor to bacteria poration. Interpretation of SECM data using a reactive transport model allowed for a better understanding of the near-electrode chemistry. Under cathodic conditions, the primary oxidant formed was H₂O₂, and under anodic conditions, a combination of H₂O₂, Cl^•, HO₂^•, Cl₂^•-, and Cl₂ formations likely contributed to bacteria poration at potentials as low as 0.5 V vs Ag/AgCl.

Sequential electrocoagulation-electrooxidation for virus mitigation in drinking water

Electrochemical water treatment is a promising alternative for small-scale and remote water systems that lack operational capacity or convenient access to reagents for chemical coagulation and disinfection. In this study, the mitigation of viruses was investigated using electrocoagulation as a pretreatment prior to electrooxidation treatment using boron-doped diamond electrodes. This research is the first to investigate a sequential electrocoagulation-electrooxidation treatment system for virus removal. Bench-scale, batch reactors were used to evaluate mitigation of viruses in variable water quality via: a) electrooxidation, and b) a sequential electrocoagulation-electrooxidation treatment train. Electrooxidation of two bacteriophages, MS2 and ΦX174, was inhibited by natural organic matter and turbidity, indicating the probable need for pretreatment. However, the electrocoagulation-electrooxidation treatment train was beneficial only in the model surface waters employed. In model groundwaters, electrocoagulation alone was as good or better than the combined electrocoagulation-electrooxidation treatment train. Reduction of human echovirus was significantly lower than one or both bacteriophages in all model waters, though bacteriophage ΦX174 was a more representative surrogate than MS2 in the presence of natural organic matter and turbidity. Compared to conventional treatment by ferric salt coagulant and free chlorine disinfection, the electrocoagulation-electrooxidation system was less effective in model surface waters but more effective in model groundwaters. Sequential electrocoagulation-electrooxidation was beneficial for some applications, though practical considerations may currently outweigh the benefits.

Carbon Fiber-Based Flow-Through Electrode System (FES) for Water Disinfection via Direct Oxidation Mechanism with a Sequential Reduction-Oxidation Process

Flow-through configuration for electrochemical disinfection is considered as a promising approach to minimize the formation of toxic byproducts and energy consumption via the enhanced convective mass transport as compared with conventional flow-by one. Under this hydrodynamic condition, it is essential to ascertain the effect of sequential electro-redox processes with the cathode/anode then anode/cathode arrangements on disinfection performance. Here, carbon fiber felt (CFF) was utilized to construct two flow-through electrode systems (FESs) with sequential reduction-oxidation (cathode-anode) or oxidation-reduction (anode-cathode) processes to systematically compare their disinfection performance toward a model Escherichia coli ( E. coli) pathogen. In-situ sampling and live/dead backlight staining experiments revealed that E. coli inactivation mainly occurred on anode via an adsorption-inactivation-desorption process. In reduction-oxidation system, after the cathode-pretreatment, bulk solution pH increased significantly, leading to the negative charge of E. coli cells. Hence, E. coli cells were adsorbed and inactivated easily on the subsequent anode, finally resulting in its much better disinfection performance and energy efficiency than the oxidation-reduction system. Application of 3.0 V resulted in ∼6.5 log E. coli removal at 1500 L m^-2 h^-1 (50 mL min^-1), suggesting that portable devices can be designed from CFF-based FES with potential application for point-of-use water disinfection.

Conductive diamond: synthesis, properties, and electrochemical applications

This review summarizes systematically the growth, properties, and electrochemical applications of conductive diamond.

Can CabECO® technology be used for the disinfection of highly faecal-polluted surface water?

In this work, the disinfection of highly faecal-polluted surface water was studied using a new electrochemical cell (CabECO^® cell, manufactured by CONDIAS) specifically designed to produce ozone in water with very low conductivity. The disinfection tests were carried out in a discontinuous mode to evaluate the influence of the electrode current charge passed. The effect of the current density was also studied in order to optimize the disinfection conditions and to simultaneously prevent the formation of undesirable by-products (chlorates and perchlorates) during the electrolysis. The results demonstrate that this technology is robust and efficient, and it can suitably disinfect water. During electrolysis, the chloride contained in the water was oxidized to hypochlorite, and this compound was combined with ammonia to form chloramines. Both hypochlorite and chloramines (formed by the well-known break point reaction) promoted persistent disinfection and seemed to be mainly responsible for the disinfection attained during the electrochemical process. Chlorate and perchlorate could also be produced, although the low concentrations of chloride in the tested water made them irrelevant. The removal of the total organic carbon under the applied operating conditions was not very efficient (although it reached 50% in 2 h) and the production of trihalomethanes was very low, below 100 ppb for all tests.

Inactivation of microbiota from urban wastewater by single and sequential electrocoagulation and electro-Fenton treatments

This work aims at comparing the ability of two kinds of electrochemical technologies, namely electrocoagulation (EC) and electro-Fenton (EF), to disinfect primary and secondary effluents from municipal wastewater treatment plants. Heterotrophic bacteria, Escherichia coli, enterococci, Clostridium perfringens spores, somatic coliphages and eukaryotes (amoebae, flagellates, ciliates and metazoa) were tested as indicator microorganisms. EC with an Fe/Fe cell at 200 A m^-2 and natural pH allowed >5 log unit removal of E. coli and final concentration below 1 bacteria mL^-1 of coliphages and eukaryotes from both effluents in ca. 60 min, whereas heterotrophic bacteria, enterococci and spores were more resistant. A larger removal was obtained for the primary effluent, probably because the flocs remove higher amount of total organic carbon (TOC), entrapping more easily the microbiota. EF with a boron-doped diamond (BDD) anode and an air-diffusion cathode that produces H₂O₂ on site was first performed at pH 3.0, with large or even total inactivation of microorganisms within 30 min. A more effective microorganism removal was attained as compared to EC thanks to ^•OH formed from Fenton's reaction. A quicker disinfection was observed for the secondary effluent owing to its lower TOC content, allowing the attack of greater quantities of electrogenerated oxidants on microorganisms. Wastewater disinfection by EF was also feasible at natural pH (∼7), showing similar abatement of active microorganisms as a result of the synergistic action of generated oxidants like active chlorine and coagulation with iron hydroxides. A sequential EC/EF treatment (30 min each) was more effective for a combined decontamination and disinfection of urban wastewater.