Improved blackwater disinfection using potentiodynamic methods with oxidized boron-doped diamond electrodes

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.

Technologies for pollutant removal and resource recovery from blackwater: a review

Blackwater (BW), consisting of feces, urine, flushing water and toilet paper, makes up an important portion of domestic wastewater. The improper disposal of BW may lead to environmental pollution and disease transmission, threatening the sustainable development of the world. Rich in nutrients and organic matter, BW could be treated for resource recovery and reuse through various approaches. Aimed at providing guidance for the future development of BW treatment and resource recovery, this paper presented a literature review of BWs produced in different countries and types of toilets, including their physiochemical characteristics, and current treatment and resource recovery strategies. The degradation and utilization of carbon (C), nitrogen (N) and phosphorus (P) within BW are underlined. The performance of different systems was classified and summarized. Among all the treating systems, biological and ecological systems have been long and widely applied for BW treatment, showing their universality and operability in nutrients and energy recovery, but they are either slow or ineffective in removal of some refractory pollutants. Novel processes, especially advanced oxidation processes (AOPs), are becoming increasingly extensively studied in BW treatment because of their high efficiency, especially for the removal of micropollutants and pathogens. This review could serve as an instructive guidance for the design and optimization of BW treatment technologies, aiming to help in the fulfilment of sustainable human excreta management.

Inactivation behavior and intracellular changes in Escherichia coli during electro-oxidation process using Ti/Sb-SnO2/PbO2 anode: Elucidation of the disinfection mechanism

This study investigates the behavior and intracellular changes in Escherichia coli (model organism) during electro-oxidation with Ti/Sb-SnO₂/PbO₂ anode in a chlorine free electrochemical system. Preliminary studies were conducted to understand the effect of initial E. coli concentration and applied current density on disinfection. At an applied current density 30 mA cm^-2, 7 log reduction of E. coli was achieved in 75 min. The role of reactive oxygen species' (ROS) in E.coli disinfection was evaluated, which confirmed hydroxyl (•OH) radical as the predominant ROS in electro-oxidation. Observations were carried out at cell and molecular level to understand E.coli inactivation mechanism. Scanning electron microscopy images confirmed oxidative damage of the cell wall and irreversible cell death. Intracellular and extracellular protein quantification and genetic material release further confirmed cell component leakage due to cell wall rupture and degradation due to •OH radical interaction. Change in cell membrane potential suggests the colloidal nature of E. coli cells under applied current density. Plasmid deoxyribonucleic acid degradation study confirmed fragmentation and degradation of released genetic material. Overall, effective disinfection could be achieved by electro-oxidation, which ensures effective inactivation and prevents regrowth of E. coli. Disinfection of real wastewater was achieved in 12 min at an applied current density 30 mA cm^-2. Real wastewater study further confirmed that effective disinfection is possible with a low cost electrode material such as Ti/Sb-SnO₂/PbO₂. Energy consumed during disinfection was determined to be 4.978 kWh m^-3 for real wastewater disinfection at applied current density 30 mA cm^-2. Cost of operation was estimated and stability of the electrode was studied to evaluate the feasibility of large scale operation. Relatively low energy and less disinfection time makes this technology suitable for field scale applications.

Degradation performance of high-concentration coking wastewater by manganese oxide ore acidic oxidation

The degradation of coking wastewater using a manganese oxide ore acidic oxidation was investigated. This work was performed in three stages. Firstly, the advantageous degradation conditions were measured by the degradation tests, and under the optimal conditions percentage degradation was obtained of 91.6% chemical oxygen demand measured by potassium dichromate oxidation (COD_cr), 94.7% total nitrogen (TN), 98.3% phenols, 98.2% fatty acid, 89.5% tar, and 98.9% sulphide for the oxidized effluent, simultaneously cogenerating a Mn²⁺concentration of 46.2 g/L for Mn-electrolytic stock solution. Secondly, the transformation analysis of the special chemical group of coking wastewater contaminants illustrated that the employment of manganese oxide ore generated the degradation of low and high molecular weight organics, especially causing polymers to break down into oligomers. Thirdly, the electrochemical characteristics of the interface between wastewater and ore revealed that the contaminant degradation of coking wastewater greatly depended on the oxidation capacity of the surface oxide species, involving a simple answer to the MnO₂ oxidation for small-molecule organic materials and a strengthening response to the MnO·OH oxidation for high-weight molecule organic substances. The treatment of coking wastewater using the Mn-oxide ore acidic oxidation process is an effective and value-added method, which is particularly applicable to high-concentration coking wastewater.

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.

Electrode passivation, faradaic efficiency, and performance enhancement strategies in electrocoagulation-a review

Treating water and wastewater is energy-intensive, and traditional methods that require large amounts of chemicals are often still used. Electrocoagulation (EC), an electrochemical treatment technology, has been proposed as a more economically and environmentally sustainable alternative. In EC, sacrificial metal electrodes are used to produce coagulant in-situ, which offers many benefits over conventional chemical coagulation. However, material precipitation on the electrodes during long term operation induces a passivating effect that decreases treatment performance and increases power requirements. Overcoming this problem is considered to be the greatest challenge facing the development of EC. In this critical review, the studies that have examined the nature of electrode passivation, and its effect on treatment performance are considered. A fundamental approach is used to examine the association between passivation and faradaic efficiency, a surrogate for EC performance. In addition, the strategies that have been proposed to remove or avoid passivation are reviewed, including aggressive ion addition, AC current operation, polarity reversal, ultrasonication, and mechanical cleaning of the electrodes. It is concluded that the success of implementing each method is dependent on critical operating parameters, and careful consideration should be taken when designing an EC system based on the phenomena discussed in this article. In conclusion, this review provides insight into passivation mechanisms, delivers guidelines for sustaining high treatment performance, and offers an outlook for the future development of EC.

Pharmaceuticals in source separated sanitation systems: Fecal sludge and blackwater treatment

This study investigated, for the first time, the occurrence and fate of 29 multiple-class pharmaceuticals (PhACs) in two source separated sanitation systems based on: (i) batch experiments for the anaerobic digestion (AD) of fecal sludge under mesophilic (37 °C) and thermophilic (52 °C) conditions, and (ii) a full-scale blackwater treatment plant using wet composting and sanitation with urea addition. Results revealed high concentrations of PhACs in raw fecal sludge and blackwater samples, with concentrations up to hundreds of μg L^-1 and μg kg^-1 dry weight (dw) in liquid and solid fractions, respectively. For mesophilic and thermophilic treatments in the batch experiments, average PhACs removal rates of 31% and 45%, respectively, were observed. The average removal efficiency was slightly better for the full-scale blackwater treatment, with 49% average removal, and few compounds, such as atenolol, valsartan and hydrochlorothiazide, showed almost complete degradation. In the AD treatments, no significant differences were observed between mesophilic and thermophilic conditions. For the full-scale blackwater treatment, the aerobic wet composting step proved to be the most efficient in PhACs reduction, while urea addition had an almost negligible effect for most PhACs, except for citalopram, venlafaxine, oxazepam, valsartan and atorvastatin, for which minor reductions (on average 25%) were observed. Even though both treatment systems reduced initial PhACs loads considerably, significant PhAC concentrations remained in the treated effluents, indicating that fecal sludge and blackwater fertilizations could be a relevant vector for dissemination of PhACs into agricultural fields and thus the environment.

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.

Elimination of bacterial contaminations by treatment of water with boron-doped diamond electrodes

Boron-doped diamond electrodes can be used to generate reactive oxygen species directly at the electrode's surface. This property was used in this study for in-situ electrochemical oxidation to eliminate different bacteria, i.e. Escherichia coli, Pseudomonas fluorescens and Pseudomonas aeruginosa, as well as Bacillus subtilis spores from water samples. Application of low voltages in the rage from 4 to 10 V and short incubation times in the range of minutes allowed a complete disinfection of water contaminated with enterobacteria and freshwater microbes including nosocomial pathogens as well as a significant reduction of spores. A pilot reactor was constructed, which allowed to decrease microbial contamination of sewage plant effluent drastically. Boron-doped diamond electrodes allow efficient reduction of bacterial contaminations in water samples.