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

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.

Energy efficient portable air cathode electrochlorinator for point-of-use disinfection of toilet wastewater

Active chlorine is the most widely used disinfectant for water disinfection as well as surface sterilization. Here, we report an air cathode electrochlorinator for point-of-use disinfection of toilet wastewater. The air cathode dominated by a four-electron pathway to reduce O₂ to OH^- was more suitable for chlorine synthesis than through a two-electron pathway to H₂O₂, which could reduce chlorine back to chloride ions. The minimum driving potential of the air cathode electrochlorinator was as low as 0.94 V, which made it possible to be directly powered by a piece of commercial mini photovoltaic solar panel without electronic converter. Under the cell voltage of 2 V, the Faraday current efficiency was 82.0 % and the electrical energy required to produce 1 kg active chlorine was estimated to be only 1.75 kWh. The normalized energy consumption to disinfect simulated toilet wastewater with a pathogen concentration of 10⁷ CFU/mL was estimated to be 7.2 W h/m³. Moreover, the material cost for fabrication of the electrochlorinator was estimated to be less than $ 0.62. These features guarantee the air cathode electrochlorinator of high potential for point-of-use disinfection of toilet wastewater.

Novel Semiconductor Cu(C3H3N3S3)3/ZnTiO3/TiO2 for the Photoinactivation of E. coli and S. aureus under Solar Light

The use of semiconductors for bacterial photoinactivation is a promising approach that has attracted great interest in wastewater remediation. The photoinactivator Cu-TTC/ZTO/TO was synthesized by the solvothermal method from the coordination complex Cu(C₃H₃N₃S₃)₃ (Cu-TTC) and the hybrid semiconductor ZnTiO₃/TiO₂ (ZTO/TO). In this study, the effect of photocatalyst composition/concentration as well as radiation intensity on the photoinactivation of the gram-negative bacteria Escherichia coli and the gram-positive bacteria Staphylococcus aureus in aqueous solutions was investigated. The results revealed that 25 mg/mL of photoinactivator, in a Cu-TTC:ZTO/TO molar ratio of 1:2 (w/w%) presents a higher rate of bacterial photoinactivation under simulated solar light (λ = 300-800 nm) in comparison to the individual components. The evidence of this study suggests that the presence of the Cu(C₃H₃N₃S₃)₃ coordination complex in the ZnTiO₃/TiO₂ hybrid semiconductor would contribute to the generation of reactive oxygen species (ROS) that are essential to initiate the bacterial photoinactivation process. Finally, the results obtained allow us to predict that the Cu-TTC/ZTO/TO photocatalyst could be used for effective bacterial inactivation of E. coli and S. aureus in aqueous systems under simulated solar light.

Novel electro-oxidation unit for electro-disinfection of E. coli and some waterborne pathogens during wastewater treatment: batch and continuous experiments

The prime objective of the current investigation is to evaluate a promising alternative method for disinfection wastewater using a novel electro-oxidation unit. The study focused on determining the best-operating conditions from a techno-economic point of view to be applied to continuous flow simulating actual disinfection modules. The treatment unit consisted of a Plexiglas container with a 3 L volume containing nine cylindrical shape electrodes (6 graphite as anode and 3 stainless steel as a cathode) connected to a variable DC power supply. Determination of the best operating parameters was investigated in batch mode on synthetic wastewater by studying the effect of contact time, current density (CD), total dissolved solids concentration (TDS), and bacterial density. Moreover, the continuous mode experiment was considered on real wastewater from an agricultural drain and the secondary wastewater treatment plant effluent before chlorination. The batch mode results revealed that the best applicable operational conditions that achieved the complete removal of E. coli were at a contact time of less than 5 min, TDS of 2000 mg/L, and CD of 4 mA/cm². Application of these conditions on the continuous mode experiment indicated the complete removal of all bacterial indicators after 5 min in the drainage wastewater and after 3 min in the secondary treated wastewater. Physico-chemical characterization also suggested that no chlorine by-products displaying the hydroxide ion formed due to water electrolysis is the main reason for prohibiting the growth of pathogenic microbes. The electrical consumption was calculated in the continuous mode and found to be 0.5 kWh/m³ with an operational cost of about 0.06 $/m³, including the cost of adding chemicals to increase the TDS. The results proved that this novel electro-oxidation unit is a robust and affordable disinfection method for complete bacterial removal from wastewater and is more environmentally benign than other conventional disinfection methods.

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.

Interpretation of high perchlorate generated during electrochemical disinfection in presence of chloride at BDD anodes

Perchlorate is a disinfection by-product (DBP) of serious health concern. Herein, the long sought mechanism of high perchlorate production during electrochemical disinfection at boron-doped diamond (BDD) anode in the presence of chloride was elucidated. The generated perchlorate at BDD during electrochemical disinfection (in 10 mM NaCl) in 60 min reached 0.125 mM, which was 830 times higher than the EPA standard. In contrast, perchlorate at PbO₂ and SnO₂ anodes was below the detection limit. Further experiments employing NaClO₃ revealed that the conversion ratio from ClO₃^- to ClO₄^- in 10 h at BDD (98%) was considerably higher than PbO₂ (13%) and SnO₂ (12%). Such significant difference among anodes was fully interpreted with a two-step mechanism. The first step is essential to produce ·ClO₃ by oxidizing ClO₃^- at electrodes. Otherwise, the conversion to perchlorate would be impossible even with excessive ·OH, which was verified with the photocatalysis process. The second step is the perchlorate generation with radical reaction between ·ClO₃ and ·OH, where the primary role of ·OH was substantiated by scavenging test. Interestingly, the capability of perchlorate production was correlated with free ·OH instead of the total amount of ·OH. Despite the similar abilities of electron transfer between anodes and ClO₃^-, much higher free ·OH exists at BDD anode than at PbO₂ and SnO₂ anodes through chronoamperometry experiments and work function characterization, which reasonably provides interpretation of high perchlorate production at BDD anode.