Sequential electrocoagulation-electrooxidation for virus mitigation in drinking water

Bibliometric analysis and systematic review of electrochemical methods for environmental remediation

Electrochemical methods are increasingly favored for remediating polluted environments due to their environmental compatibility and reagent-saving features. However, a comprehensive understanding of recent progress, mechanisms, and trends in these methods is currently lacking. Web of Science (WoS) databases were utilized for searching the primary data to understand the knowledge structure and research trends of publications on electrochemical methods and to unveil certain hotspots and future trends of electrochemical methods research. The original data were sampled from 9080 publications in those databases with the search deadline of June 1st, 2022. CiteSpace and VOSviewer software facilitated data visualization and analysis of document quantities, source journals, institutions, authors, and keywords. We discussed principles, influencing factors, and progress related to seven major electrochemical methods. Notably, publications on this subject have experienced significant growth since 2007. The most frequently-investigated areas in electrochemical methods included novel materials development, heavy metal remediation, organic pollutant degradation, and removal mechanism identification. "Advanced oxidation process" and "Nanocomposite" are currently trending topics. The major remediation mechanisms are adsorption, oxidation, and reduction. The efficiency of electrochemical systems is influenced by material properties, system configuration, electron transfer efficiency, and power density. Electro-Fenton exhibits significant advantages in achieving synergistic effects of anodic oxidation and electro-adsorption among the seven techniques. Future research should prioritize the improvement of electron transfer efficiency, the optimization of electrode materials, the exploration of emerging technology coupling, and the reduction in system operation and maintenance costs.

Stormwater runoff treatment through electrocoagulation: antibiotic resistant bacteria removal and its transmission risks

Recently, increasing attention has been paid to antibiotic resistant bacteria (ARB) in stormwater runoff. However, there were little data on ARB removal through electrocoagulation (EC) treatment. In this study, batch experiments were conducted to investigate key designs for ARB removal, role of SS, effects of water matrix, and potential risks after EC treatment under the pre-determined conditions. EC treatment with 5 mA/cm2 of current density and 4 cm of inter-electrode distance was optimal with the highest ARB removal (3.04 log reduction for 30 min). The presence of SS significantly improved ARB removal during EC treatment, where ARB removal increased with the increase of SS levels when SS less than 300 mg/L. Large ARB removal was found under particles with size lower than 150 μm with low contribution (less than 10%) of the settlement without EC treatment, implying that the enhancement of ARB adsorption onto small particles could be one of the reasonable approaches for ARB removal through EC treatment. ARB removal increased firstly and then decreased with the increase of pH, while had proportional relationship with conductivity. After the optimal condition, there were weak conjugation transfer but high transformation frequency (5.5 × 10-2 for blaTEM) for target antibiotic resistance genes (ARGs), indicating that there could be still a risk of antibiotic resistance transformation after EC treatment. These suggested that the combination of EC and other technologies (like electrochemical disinfection) should be potential ways to control antibiotic resistance transmission through stormwater runoff.

Iron complex regulated synergistic effect between the current and peroxymonosulfate enhanced ultrafast oxidation of perfluorooctanoic acid via free radical dominant electrochemical reaction

Iron complex regulated electrochemical reaction was triggered for revealing the reaction mechanism, degradation pathway, and applied potential of perfluorooctanoic acid (PFOA). The increased PMS concentrations, electrode spacing, and current density significantly enhanced PFOA elimination, with current density exhibiting a relatively strong interdependency to PFOA complete mineralization. The synergy between PMS and electrochemical reactions greatly accelerated PFOA decomposition by promoting the generation of key reaction sites, such as those for PMS activation and electrochemical processes, under various conditions. Furthermore, density functional theory calculations confirmed that the reciprocal transformation of Fe2+ and Fe3+ complexes was feasible under the electrochemical effect, further promoting the generation of active sites. The developed electrochemical oxidation with PMS reaction (EO/PMS) system can rapidly decompose and mineralize PFOA while maintaining strong tolerance to changing water matrices and organic and inorganic ions. Overall, it holds promise for use in treating and purifying wastewater containing PFOA.

Advancements in combined electrocoagulation processes for sustainable wastewater treatment: A comprehensive review of mechanisms, performance, and emerging applications

This review explores the potential and challenges of combining electrochemical, especially electrocoagulation (EC) process, with various - wastewater treatment methods such as membranes, chemical treatments, biological methods, and oxidation processes to enhance pollutant removal and reduce costs. It emphasizes the advantages of using electrochemical processes as a pretreatment step, including increased volume and improved quality of permeate water, mitigation of membrane fouling, and lower environmental impact. Pilot-scale studies are discussed to validate the effectiveness of combined EC processes, particularly for industrial wastewater. Factors such as electrode materials, coating materials, and the integration of a third process are discussed as potential avenues for improving the environmental sustainability and cost-effectiveness of the combined EC processes. This review also discusses factors for improvement and explores the EC process combined with Advanced Oxidation Processes (AOP). The conclusion highlights the need for combined EC processes, which include reducing electrode consumption, evaluating energy efficiency, and conducting pilot-scale investigations under continuous flow conditions. Furthermore, it emphasizes future research on electrode materials and technology commercialization. Overall, this review underscores the importance of combined EC processes in meeting the demand for clean water resources and emphasizes the need for further optimization and implementation in industrial applications.

Sequential photo electro oxidation and biodegradation of textile effluent: Elucidation of degradation mechanism and bacterial diversity

Textile effluent contains a highly toxic and refractory azo dyes. Eco-friendly method for efficient decolorization and degradation of textile effluent is essential. In the present study, treatment of textile effluent was carried through sequential electro oxidation (EO) and photo electro oxidation (PEO) using RuO₂-IrO₂ coated titanium electrode as an anode and cathode followed by biodegradation. The pre-treatment of textile effluent by photo electro oxidation for 14 h exhibited 92% of decolorization. Subsequent biodegradation of the pre-treated textile effluent enhanced the reduction of chemical oxygen demand to 90%. Metagenomics results exhibited that Flavobacterium, Dietzia, Curtobacterium, Mesorhizobium, Sphingobium, Streptococcus, Enterococcus, Prevotellaand Stenotrophomonas bacterial communities majorly involved in the biodegradation of textile effluent. Hence, integrating sequential photo electro oxidation and biodegradation proposed an efficient and eco-friendly approach for treating textile effluent.

Tertiary treatment of bio-treated landfill leachate by a two-step electrochemical process including electrooxidation and electrocoagulation: a bench-scale trial

A two-step electrochemical process including electrooxidation (EO) and electrocoagulation (EC) was proposed for the tertiary treatment of bio-treated landfill leachate (BTLL). The operating conditions of sole EO and EC technology were optimized via batch tests. Batch tests indicate that EO displayed superior removal efficiency towards color (89%) and UV₂₅₄ (64%) under optimal experimental conditions. EC with the electrode combinations Fe-Fe-Fe-Fe (four plates, anode-cathode-anode-cathode) performed better than the other electrode combinations (Fe-Al-Fe-Al, Al-Fe-Al-Fe, Al-Al-Al-Al) and showed excellent removal efficiency towards COD (60%) and color (85%). In continuous-flow tests of 13 h, compared to sequential EC-EO process, the sequential EO-EC process was more effective than the sequential EC-EO process in reducing organic matters (COD, TOC) and residual chlorine. The sequential EO-EC process could remove 50% COD, 55% TOC, 72% UV₂₅₄, and 96% color. The average concentration of residual chlorine in the final effluent of EO-EC process (147 mg/L) was significantly lower than that of EC-EO process (463 mg/L). UV-vis and GC-MS analyses indicate that the BTLL mainly contained humic acid and fulvic acid-like substances with unsaturated bonds. Conjugated unsaturated organics could be degraded into organic of small molecular weight after the sequential EO-EC process. EEM spectroscopic analysis revealed that soluble microbial byproducts became the predominant organics in the final effluent. This work verifies the synergism between EO and EC and provides some insights into the removal and degradation performance of organic substances in BTLL during the sequential EO-EC treatment.

Characterizing spatial dependence of boron, arsenic, and other trace elements for Permian groundwater in Northern Anhui plain coal mining area, China, using spatial autocorrelation index and geostatistics

Anthropogenic and geological factors play an essential role in the variability of groundwater quality, resulting in a weak spatial dependence of groundwater trace elements. Thus, it is an essential study to investigate the factors affecting groundwater quality and its spatial abundance of trace elements (including As, B, and other metalloids). In this study, samples are obtained from a Permian sandstone fracture aquifer in a coal mining area. A multivariate statistical analysis, hydrogeochemistry modeling, and spatial autocorrelation analysis were used to analyze the data. The results showed that Moran index was positive for all trace elements, which had good spatial autocorrelation. The Local indicators of spatial association (LISA) indicated that trace elements were clustered. The hydrogeochemical modeling results indicated that the precipitation and stability of iron-phase minerals, such as rhodochrosite and arsenic (As) absorption on the surface of iron-phase minerals in the aquifer, may limit concentrations in the southern region. The spatial autocorrelations of both As and Boron (B) were positive (high-high) in the western areas, indicating that As contamination occurred from both natural geological causes and human coal mining activities. In contrast, B contamination was mainly linked to the influence of human agricultural or industrial activities. Over 96% of the groundwater concentrations of As (10 μg/L) and B (300 μg/L) in the study area exceeded World Health Organization (WHO) limits. Overall, the results of this work could help decision-makers involved in regional water quality management visualize disperse zones where specific anthropogenic and geological processes may threaten groundwater quality.

Research progress of electrochemical oxidation and self-action of electric field for medical wastewater treatment

A large number of pathogenic microorganisms exist in medical wastewater, which could invade the human body through the water and cause harm to human health. With the global pandemic coronavirus (COVID-19), public health safety become particularly important, and medical wastewater treatment is an important part of it. In particular, electrochemical disinfection technology has been widely studied in medical wastewater treatment due to its greenness, high efficiency, convenient operation, and other advantages. In this paper, the development status of electrochemical disinfection technology in the treatment of medical wastewater is reviewed, and an electrochemical three-stage disinfection system is proposed for the treatment of medical wastewater. Moreover, prospects for the electrochemical treatment of medical wastewater will be presented. It is hoped that this review could provide insight and guidance for the research and application of electrochemical disinfection technology to treat medical wastewater.GRAPHICAL ABSTRACT.

A review on disinfection methods for inactivation of waterborne viruses

Water contamination is a global health problem, and the need for safe water is ever-growing due to the public health implications of unsafe water. Contaminated water could contain pathogenic bacteria, protozoa, and viruses that are implicated in several debilitating human diseases. The prevalence and survival of waterborne viruses differ from bacteria and other waterborne microorganisms. In addition, viruses are responsible for more severe waterborne diseases such as gastroenteritis, myocarditis, and encephalitis among others, hence the need for dedicated attention to viral inactivation. Disinfection is vital to water treatment because it removes pathogens, including viruses. The commonly used methods and techniques of disinfection for viral inactivation in water comprise physical disinfection such as membrane filtration, ultraviolet (UV) irradiation, and conventional chemical processes such as chlorine, monochloramine, chlorine dioxide, and ozone among others. However, the production of disinfection by-products (DBPs) that accompanies chemical methods of disinfection is an issue of great concern due to the increase in the risks of harm to humans, for example, the development of cancer of the bladder and adverse reproductive outcomes. Therefore, this review examines the conventional disinfection approaches alongside emerging disinfection technologies, such as photocatalytic disinfection, cavitation, and electrochemical disinfection. Moreover, the merits, limitations, and log reduction values (LRVs) of the different disinfection methods discussed were compared concerning virus removal efficiency. Future research needs to merge single disinfection techniques into one to achieve improved viral disinfection, and the development of medicinal plant-based materials as disinfectants due to their antimicrobial and safety benefits to avoid toxicity is also highlighted.

Application of hybrid electrocoagulation and electrooxidation process for treatment of wastewater from the cotton textile industry

The hybrid electrocoagulation-electrooxidation (EC-EO) process was evaluated for its capability to remove color, total organic carbon (TOC), and chemical oxygen demand (COD). Aluminum (Al/Al) and iridium dioxide-coated onto titanium (IrO₂/Ti) electrodes were selected as anode/cathode for EC and EC-EO experiments, respectively. The box-Behnken statistical experimental design was used to optimize different operating conditions of the processes. The selected EC operating parameters are the concentrated dye concentration, applied current density, electrolysis time, and pH. The three chosen operating conditions for hybrid EC- EO processes are applied current density, pH, and electrolysis time. The results were evaluated based on the interaction effects of operating parameters of the treatment methods on the percentage of COD, TOC, and color removal. The EC process achieved 89% color and 76% COD removal rate at the optimum operating conditions. Likewise, the hybrid EC-EO process obtained 97% COD and color removal efficiency. FT-IR and ¹H and ¹³C NMR spectroscopy combined approach was employed to analyze the dye degradation extent. Both analysis results confirm the complete degradation of the organic contaminants into carbon dioxide and water. Thus, this study discloses that the treatment method using mesh IrO₂/Ti electrodes is a promising technology that could reach the discharge limit for industrial effluents. In addition, the optimum operating conditions are tested for real industrial wastewater effluents and show excellent performance in removing pollutants. Furthermore, the treatment method's mineralization study and economic analysis were performed and compared to other studies.

Experimental and modeling evidence of hydroxyl radical production in iron electrocoagulation as a new mechanism for contaminant transformation in bicarbonate electrolyte

Iron electrocoagulation is designed for sustainable high-efficiency and high-flexibility water purification applications. Recent advances reported that hydroxyl radicals (•OH)-based oxidative transformation of organic contaminants can occur in iron electrocoagulation. However, there is still a lack of mechanistic understanding the production of •OH in bicarbonate electrolyte, which presents a critical knowledge gap in the optimization of iron electrocoagulation technology towards practical application. Combined with contaminant degradation, radical quenching experiments, and spectroscopic techniques, we found that •OH was produced at rate of 16.1 μM∙h ^- 1 during 30-mA iron electrocoagulation in bicarbonate electrolyte through activation of O₂ by Fe(II) under pH-neutral conditions. High yield of •OH occurred at pH 8.5, likely due to high adsorbed Fe(II) that can activate O₂ to enhance •OH production. Mössbauer and X-ray photoelectron spectroscopy measurements substantiated that Fe(II)-adsorbed lepidocrocite was the dominant solid Fe(II) species at pH 8.5. A process-based kinetic modeling was developed to describe the dynamic of •OH production, Fe(II) oxidation, and contaminant degradation processes in iron electrocoagulation. Findings of this study extend the functionality of electrocoagulation from phase separation to •OH-based advanced oxidation process, which provides a new perspective for the development of electrocoagulation-based next generation sustainable water purification technology.

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.

Removal of tetracycline from livestock wastewater by positive single pulse current electrocoagulation: Mechanism, toxicity assessment and cost evaluation

The widespread use of veterinary antibiotics has led to the significant problem of contamination of livestock wastewater with significant amount of antibiotics. Electrocoagulation (EC) has become a prominent research topic because of the technique's ability to remove antibiotics from livestock wastewater. However, an urgent solution is needed to reduce the high operating costs associated with the process. Therefore, in this study, we developed a positive single pulse current (PSPC)-EC system to remove tetracycline (TC) from synthetic and actual livestock wastewater. Influential factors were investigated, and the optimal PSPC-EC operating parameters were identified as follows: duty ratio = 60%, pH = 4, electrode spacing = 1 cm, current intensity = 0.2 A, and conductivity = 2 mS cm^-1. The mechanism of PSPC-EC was characterised using techniques including scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TC decomposition pathway was proposed based on the generation of its intermediate products. A toxicity estimation software tool (TEST) model was used to evaluate the toxicity of TC and its main degradation products, and most of its intermediates were found to be less toxic than TC. The contribution ratios of floc adsorption and electrochemical oxidation for removing TC were 74.17% and 21.48%, respectively. The highest TC removal rate reached 95% with an operating cost of 0.011 USD/m³. Finally, under the optimum conditions identified, actual livestock wastewater was treated by PSPC-EC. Compared with conventional EC and coagulation treatment techniques that consume electricity and produce pollution, the results indicate that the PSPC-EC technique with changing current operation mode is a more cost-effective and attractive option for removing TC from livestock wastewater.

Comparative effectiveness of membrane technologies and disinfection methods for virus elimination in water: A review

The pandemic of the 2019 novel coronavirus disease (COVID-19) has brought viruses into the public horizon. Since viruses can pose a threat to human health in a low concentration range, seeking efficient virus removal methods has been the research hotspots in the past few years. Herein, a total of 1060 research papers were collected from the Web of Science database to identify technological trends as well as the research status. Based on the analysis results, this review elaborates on the state-of-the-art of membrane filtration and disinfection technologies for the treatment of virus-containing wastewater and drinking water. The results evince that membrane and disinfection methods achieve a broad range of virus removal efficiency (0.5-7 log reduction values (LRVs) and 0.09-8 LRVs, respectively) that is attributable to the various interactions between membranes or disinfectants and viruses having different susceptibility in viral capsid protein and nucleic acid. Moreover, this review discusses the related challenges and potential of membrane and disinfection technologies for customized virus removal in order to prevent the dissemination of the waterborne diseases.

Exploring key reaction sites and deep degradation mechanism of perfluorooctane sulfonate via peroxymonosulfate activation under electrocoagulation process

Perfluorooctane sulfonate (PFOS), normally present in groundwater and surface water, is an emerging environmental contaminants, but is extremely difficult to be degraded due to high energy of the C-F bond. Here, an electrocoagulation (EC) technique coupled with peroxymonosulfate (PMS) activation was used to deeply degrade PFOS. Results showed that approximately 100% PFOS was removed from the solution in the monopolar serial (MS) mode within 60 min and achieved a high kinetic rate of 0.074 min^-1, which was significantly higher than those of reported studies (Table S3). Energy consumption (2.06 kWh/kg) in the MS mode was significantly lower than that of Al (52.30 kWh/kg) and Zn (213.50 kWh/kg) electrodes, which further confirmed the potential application prospects of EC technique. The quenching experiments, electron spin response (ESR) analysis, and DFT calculations can verify that ·OH was the main radical from the reaction of Fe²⁺-OH reaction site with PMS. In addition, results from fluorine balance and TOC removal also indicated the complete mineralization and degradation of PFOS in the EC process. Quantum chemical calculations can confirm the PFOS degradation mechanism and key active sites for direct electron transfer and radical attack. After five cycle operations of PFOS degradation, the EC process was still effective in degrading PFOS with a removal efficiency above 98%. Thus, this work provided a novel alternative for the high-effective treatment of PFOS from contaminated environmental water bodies.

Electrocoagulation technology for water purification: An update review on reactor design and some newly concerned pollutants removal

Water shortage and quality deterioration are plaguing people all over the world. Providing sustainable and affordable treatment solutions to these problems is a need of the hour. Electrocoagulation (EC) technology is a burgeoning alternative for effective water treatment, which offers the virtues such as compact equipment, easy operation, and low sludge production. Compared to other water purification technologies, EC shows excellent removal efficacy for a wide range of contaminants in water and has great potential for addressing limitations of conventional water purification technologies. This review summarizes the latest development of principle, characteristics, and reactor design of EC. The design of key parameters including reactor shape, power supply type, current density, as well as electrode configuration is further elaborated. In particular, typical water treatment systems powered by renewable energy (solar photovoltaic and wind turbine systems) are proposed. Further, this review provides an overview on expanded application of EC in the removal of some newly concerned pollutants in recent years, including arsenite, perfluorinated compounds, pharmaceuticals, oil, bacteria, and viruses. The removal efficiency and mechanisms of these pollutants are also discussed. Finally, future research trend and focus are further recommended. This review can bridge the large knowledge gap for the EC application that is beneficial for environmental researchers and engineers.

The impact of coronavirus SARS-CoV-2 (COVID-19) in water: potential risks

This review summarizes research data on SARS-CoV-2 in water environments. A literature survey was conducted using the electronic databases Science Direct, Scopus, and Springer. This complete research included and discussed relevant studies that involve the (1) introduction, (2) definition and features of coronavirus, (2.1) structure and classification, (3) effects on public health, (4) transmission, (5) detection methods, (6) impact of COVID-19 on the water sector (drinking water, cycle water, surface water, wastewater), (6.5) wastewater treatment, and (7) future trends. The results show contamination of clean water sources, and community drinking water is vulnerable. Additionally, there is evidence that sputum, feces, and urine contain SARS-CoV-2, which can maintain its viability in sewage and the urban-rural water cycle to move towards seawater or freshwater; thus, the risk associated with contracting COVID-19 from contact with untreated water or inadequately treated wastewater is high. Moreover, viral loads have been detected in surface water, although the risk is lower for countries that efficiently treat their wastewater. Further investigation is immediately required to determine the persistence and mobility of SARS-CoV-2 in polluted water and sewage as well as the possible potential of disease transmission via drinking water. Conventional wastewater treatment systems have been shown to be effective in removing the virus, which plays an important role in pandemic control. Monitoring of this virus in water is extremely important as it can provide information on the prevalence and distribution of the COVID-19 pandemic in different communities as well as possible infection dynamics to prevent future outbreaks.

Impacts of COVID-19 pandemic on the wastewater pathway into surface water: A review

With global number of cases 106 million and death toll surpassing 2.3 million as of mid-February 2021, the COVID-19 pandemic is certainly one of the major threats that humankind have faced in modern history. As the scientific community navigates through the overwhelming avalanche of information on the multiple health impacts caused by the pandemic, new reports start to emerge on significant ancillary effects associated with the treatment of the virus. Besides the evident health impacts, other emerging impacts related to the COVID-19 pandemic, such as water-related impacts, merits in-depth investigation. This includes strategies for the identification of these impacts and technologies to mitigate them, and to prevent further impacts not only in water ecosystems, but also in relation to human health. This paper has critically reviewed currently available knowledge on the most significant potential impacts of the COVID-19 pandemic on the wastewater pathway into surface water, as well as technologies that may serve to counteract the major threats posed, key perspectives and challenges. Additionally, current knowledge gaps and potential directions for further research and development are identified. While the COVID-19 pandemic is an ongoing and rapidly evolving situation, compiling current knowledge of potential links between wastewater and surface water pathways as related to environmental impacts and relevant associated technologies, as presented in this review, is a critical step to guide future research in this area.

Efficacy of electrochemical membrane bioreactor for virus removal from wastewater: Performance and mechanisms

Wastewater treatment facilities play pivotal roles in preventing the transmission of water-borne viruses and protecting human health. In this study, a new electrochemical membrane bioreactor (EMBR) was proposed to achieve a long-lasting and efficient removal of virus from wastewater. Results showed that applying a low electric field (2.0 V) in EMBR system could achieve ~100% removal efficiency at both batch tests and continuous flow experiments. In contrast, the control MBR, without the exertion of electric field, exhibited a very low removal efficiency (19.8% on average). Moreover, the fouling in EMBR was significantly mitigated, which enabled its operation duration almost 3 times longer than that of the control. Further explorations suggested that the reactive oxidants generated on electrodes in the EMBR system were mainly responsible for MS2 removal. This study demonstrated the potential of utilizing the EMBR process to achieve an enhanced virus disinfection efficiency during the wastewater treatment process.

Electrocoagulation-electrooxidation for mitigating trace organic compounds in model drinking water sources

In-situ water treatment can be accomplished using electrochemical treatments such as electrocoagulation (EC), which generates coagulants, and electrooxidation (EO), which generates oxidants (e.g., free chlorine and reactive oxygen species) via electrolysis using boron-doped diamond electrodes. In sequential EC-EO, EC can remove oxidant scavengers present in dissolved organic carbon (DOC), thereby improving the efficacy of downstream oxidation via EO. This study evaluated sequential EC-EO (and each process independently for comparison) for mitigating the trace organic compounds (TOrCs) acyclovir (ACY), trimethoprim (TMP), and benzyldimethyldecylammonium chloride (BAC-C10) in model groundwaters and surface waters. EO-only removed greater than 70% of ACY and TMP but negligible BAC-C10 in model groundwaters. In model surface waters, EO-only removed ∼55-75% BAC-C10, but had less removal for ACY and TMP (∼20-55%), primarily due to DOC interference. Sequential-EC-EO was investigated to better gauge the potential process improvement due to the addition of EC ahead of EO. EC removed 74 ± 7% DOC from model surface water and improved downstream EO treatment relative to EO-only by a factor of 3.4 for ACY, 1.7 for TMP, and 1.4 for BAC-C10. When treating model groundwater, EC-EO resulted in no improvement compared to EO-only for ACY and TMP. BAC-C10 removal was attributed to the particle separation step between EC and EO rather than electrochemical inputs. EO-only treatment was more energy efficient for model groundwater compared to model surface waters based on electrical energy per order (E_EO) values. Sequential EC-EO further improved the energy efficiency for treating model river water.

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.

Low voltage iron electrocoagulation as a tertiary treatment of municipal wastewater: removal of enteric pathogen indicators and antibiotic-resistant bacteria

In this paper we analyse the feasibility of low voltage iron electrocoagulation as a means of municipal secondary effluent treatment with a focus on removal of microbial indicators, Antibiotic Resistant Bacteria (ARB) and nutrients. A laboratory scale batch unit equipped with iron electrodes was used on synthetic and real secondary effluent from a municipal wastewater treatment plant. Synthetic secondary effluent was separately assayed with spiked Escherichia coli WR1 and with bacteriophage ΦX174, while real effluent samples were screened before and after treatment for E. coli, Extended Spectrum Betalactamase-producing E. coli, Enterococci, Vancomycin Resistant Enterococci, Clostridium perfringens spores and somatic coliphages. Charge dosage (CD) and charge dosage rate (CDR) were used as the main process control parameters. Experiments with synthetic secondary effluent showed >4log₁₀ and >5log₁₀ removal for phage ΦX174 and for E. coli WR1, respectively. In real effluents, bacterial indicator removal exceeded 3.5log₁₀, ARB were removed below detection limit (≥2.5log₁₀), virus removal reached 2.3log₁₀ and C. perfringens spore removal exceeded 2.5log₁₀. Experiments in both real and synthetic wastewater showed that bacterial removal increased with increasing CD and decreasing CDR. Virus removal increased with increasing CD but was irresponsive to CDR. C. perfringens spore removal increased with increasing CD yet reached a removal plateau, being also irresponsive to CDR. Phosphate removal exceeded 99%, while total nitrogen and chemical oxygen demand removal were below 15% and 58%, respectively. Operational cost estimates were made for power and iron plate consumption, and were found to be in the range of 0.01 to 0.24€/m³ for the different assayed configurations. In conclusion, low voltage Fe-EC is a promising technology for pathogen reduction of secondary municipal effluents, with log₁₀ removals comparable to those achieved by conventional disinfection methods such as chlorination, UV or ozonation.

Assessment of socioeconomic inequality based on virus-contaminated water usage in developing countries: A review

Water is an essential resource required for various human activities such as drinking, cooking, and other recreational activities. While developed nations have made significant improvement in providing adequate quality water and sanitation devoid of virus contaminations to a significant percentage of the residences, many of the developing countries are still lacking in these regards, leading to many death cases among the vulnerable due to ingestion of virus-contaminated water and other waterborne pathogens. However, the recent global pandemic of COVID-19 seems to have changed the paradigm by reawakening the importance of water quality and sanitation, and focusing more attention on the pervasive effect of the use of virus-contaminated water as it can be a potential driver for the spread of the virus and other waterborne diseases, especially in developing nations that are characterized by low socioeconomic development. Therefore, this review assessed the socioeconomic inequalities related to the usage of virus-contaminated water and other waterborne pathogens in developing countries. The socioeconomic factors attributed to the various waterborne diseases due to the use of virus-contaminated water in many developing countries are poverty, the standard of living, access to health care facilities, age, gender, and level of education. Some mitigation strategies to address the viral contamination of water sources are therefore proposed, while future scope and recommendations on tackling the essential issues related to socioeconomic inequality in developing nations are highlighted.

Assessment of socioeconomic inequality based on virus-contaminated water usage in developing countries: A review

Water is an essential resource required for various human activities such as drinking, cooking, and other recreational activities. While developed nations have made significant improvement in providing adequate quality water and sanitation devoid of virus contaminations to a significant percentage of the residences, many of the developing countries are still lacking in these regards, leading to many death cases among the vulnerable due to ingestion of virus-contaminated water and other waterborne pathogens. However, the recent global pandemic of COVID-19 seems to have changed the paradigm by reawakening the importance of water quality and sanitation, and focusing more attention on the pervasive effect of the use of virus-contaminated water as it can be a potential driver for the spread of the virus and other waterborne diseases, especially in developing nations that are characterized by low socioeconomic development. Therefore, this review assessed the socioeconomic inequalities related to the usage of virus-contaminated water and other waterborne pathogens in developing countries. The socioeconomic factors attributed to the various waterborne diseases due to the use of virus-contaminated water in many developing countries are poverty, the standard of living, access to health care facilities, age, gender, and level of education. Some mitigation strategies to address the viral contamination of water sources are therefore proposed, while future scope and recommendations on tackling the essential issues related to socioeconomic inequality in developing nations are highlighted.

Disinfection and antimicrobial processes

This is a review of some of the literature published in 2019 related to disinfection and antimicrobial processes. This review includes the following main sections: drinking water disinfection, wastewater disinfection, and antimicrobial resistance. PRACTITIONER POINTS: Emerging technologies to disinfect viruses in drinking water treatment plants are growing. Developing processes to adequately treat bypass wastewater exceeding the plant's capacity is crucial. Antimicrobial resistance poses a major challenge leading to being classified as emerging pollutants.

Effective treatment of spacer tube reverse osmosis membrane concentrated leachate from an incineration power plant using coagulation coupled with electrochemical treatment processes

Membrane concentrated leachate is an important secondary pollutant in incineration plants and needs to be treated properly in order to achieve the "zero discharge" standard for pollutants from incineration plants. In this study, coagulation followed by the electro-oxidation (EO), and electro-coagulation (EC) methods were studied. Each of these processes was used to treat the spacer tube reverse osmosis membrane concentrated leachate from an incineration plant. A single factor experiment was used to determine the optimal conditions for each individual process. In addition, a two-stage electrochemical treatment was investigated after combining the optimized EO and EC processes. The results showed that the two-stage electrochemical treatment process can achieve much higher removal efficiencies than when only EO or EC are applied. The optimal conditions for the two-stage electrochemical treatment process were 180 min of the optimized EO process as the 1st stage treatment process, followed by 60 min of the optimized EC process as the 2nd stage treatment process. After the optimized coagulation-EO-EC process, the total organic carbon (TOC), UV₂₅₄, ammonia nitrogen (NH₃-N), total nitrogen (TN), color (CN), turbidity (TUB), and solution conductivity (SC) removal efficiencies were 96.19%, 98.98%, 96.54%, 88.21%, 99.72%, 98.24%, and 54.67%, respectively. This study can provide a theoretical basis for the treatment of concentrated leachate from MSW incineration plants.

In-situ determination of current density distribution and fluid modeling of an electrocoagulation process and its effects on natural organic matter removal for drinking water treatment

Electrocoagulation is a burgeoning technology now being considered for niche water treatment applications. Although much research has been conducted to determine the efficacy of electrocoagulation to remove various contaminants, the more fundamental electrochemical aspects of the technology are often overlooked. This research provides insight into the fundamental relationship of water flow, electrochemical metal dissolution and current density distribution through computational fluid dynamic (CFD) models, mathematical models and in-situ current density distribution identification experiments. Theoretically, it was determined that current distributed along the electrode was inversely proportional to the water flowrate. The turbulent flow through the EC reactor was simulated with varying inter-electrode gaps and flowrates, while the average velocity segments across the electrode surface was calculated, corresponding to the same segments used to experimentally determine the current distribution. Through the CFD models and current distribution determining technique, it was observed that current density was distributed unevenly and followed the trend predicted by theory. Areas of lower current density were generally accompanied by higher velocity flow. More uniform current was yielded with larger inter-electrode gaps, due to the greater flow uniformity. While operating with a 1 mm gap, the current and water velocity varied across the electrode by Δ27.6 mA/cm² and Δ0.220 m/s, and was minimized to Δ3.6 mA/cm² and Δ0.062 m/s at a 10 mm gap. Although current uniformity was increased, the overall current density decreased significantly due to the greater ohmic resistance associated with the larger gap. The removal of natural organic matter was reduced as much as 79% when the inter-electrode gap was reduced from 10 to 1 mm.

Simultaneous solid-liquid separation and wastewater disinfection using an electrochemical dynamic membrane filtration system

An electrochemical dynamic membrane filtration (EDMF) system for simultaneous solid-liquid separation (also protecting electrodes against fouling) and sewage disinfection was developed. At a low voltage of 2.5 V, efficient disinfection performance was achieved in the EDMF, with ~100% log removal efficiency (no detectable bacteria in the effluent). Results also demonstrated that the EDMF system, operated at membrane flux of 100 L/(m² h), could maintain long-lasting bacterial disinfection efficiency of real wastewater (~100% log removal) in continuous flow tests. Transmembrane pressure (TMP) increased from 0.8 kPa to 22 kPa within 80 d (one operation cycle), and cleaning of EDMF could effectively restore TMP and biocidal behaviors for subsequent filtration cycles. In contrast, without dynamic membrane, the disinfection efficiency was decreased from initial ~100% log removal (with no detectable live bacteria) to ~44.4% log removal within 7 d. Reactive oxygen species (ROS)-mediated oxidation was responsible for bacteria disinfection in the EDMF, and HO• and H₂O₂ generated in this system played a dominant role, causing damage to cell membranes and K⁺ leakage from cytosol. Moreover, catalase and superoxide dismutase for intracellular ROS attenuation were inhibited, resulting in the increase of intracellular oxidative stress and thus high-efficient disinfection. These results highlight the potential of EDMF system to be used for wastewater treatment and disinfection.

Electrocoagulation as a Pretreatment for Electroxidation of E. coli

Insufficient funding and operator training, logistics of chemical transport, and variable source water quality can pose challenges for small drinking water treatment systems. Portable, robust electrochemical processes may offer a strategy to address these challenges. In this study, electrocoagulation (EC) and electrooxidation (EO) were investigated using two model surface waters and two model groundwaters to determine the efficacy of sequential EC-EO for mitigating Escherichia coli. EO alone (1.67 mA/cm2, 1 min) provided 0.03 to 3.9 logs mitigation in the four model waters. EC alone (10 mA/cm2, 5 min) achieved ≥1 log E. coli mitigation in all model waters. Sequential EC-EO did not achieve greater mitigation than EC alone. To enhance removal of natural organic matter, the initial pH was decreased. Lower initial pH (pH 5–6) improved E. coli mitigation during both stages of EC-EO. EC-EO also had slightly greater E. coli mitigation than EC alone at lower pH. However, EO alone provided more energy efficient E. coli mitigation than either EC or EC-EO.

Mechanisms of virus mitigation and suitability of bacteriophages as surrogates in drinking water treatment by iron electrocoagulation

Emerging water treatment technologies using ferrous and zero-valent iron show promising virus mitigation by both inactivation and adsorption. In this study, iron electrocoagulation was investigated for virus mitigation in drinking water via bench-scale batch experiments. Relative contributions of physical removal and inactivation, as determined by recovery via pH 9.5 beef broth elution, were investigated for three mammalian viruses (adenovirus, echovirus, and feline calicivirus) and four bacteriophage surrogates (fr, MS2, P22, and ΦX174). Though no one bacteriophage exactly represented mitigation of the mammalian viruses in all water matrices, bacteriophage ΦX174 was the only surrogate that showed overall removal comparable to that of the mammalian viruses. Bacteriophages fr, MS2, and P22 were all more susceptible to inactivation than the three mammalian viruses, raising concerns about the suitability of these common surrogates as indicators of virus mitigation. To determine why some bacteriophages were particularly susceptible to inactivation, mechanisms of bacteriophage mitigation due to electrocoagulation were investigated. Physical removal was primarily due to inclusion in flocs, while inactivation was primarily due to ferrous iron oxidation. Greater electrostatic attraction, virus aggregation, and capsid durability were proposed as reasons for virus susceptibility to ferrous-based inactivation. Results suggest that overall treatment claims based on bacteriophage mitigation for any iron-based technology should be critically considered due to higher susceptibility of bacteriophages to inactivation via ferrous oxidation.