Oxidising and disinfecting by hydrogen peroxide produced in a two-electrode cell

A redox-responsive macrocycle based on the crown ether C7Te for enhanced bacterial inhibition

Due to increasing bacterial resistance to disinfectants, there is an urgent need for new therapeutic agents and strategies to effectively inhibit bacteria. Accordingly, we have designed and synthesized a novel crown ether known as C7Te, and its oxidized form C7TeO. These compounds have demonstrated antibacterial effectiveness against Gram-negative E. coli (BL21). Notably, C7Te has the capability to enhance the inhibition of E. coli and the prevention of biofilm formation by H2O2 through a redox response. It can also effectively disrupt preformed E. coli biofilms by penetrating biofilm barriers effectively. Additionally, computer modeling of the bacterial cell membrane using nanodiscs composed of phospholipids and encircled amphipathic proteins with helical belts has revealed that C7Te can insert into and interact with phospholipids and proteins. This interaction results in the disruption of the bacterial cell membrane leading to bacterial cell death. The utilization of redox-responsive crown ethers to augment the antibacterial capabilities of H2O2-based disinfectants represents a novel approach to supramolecular bacterial inhibition.

Modified bio-electrocoagulation system to treat the municipal wastewater for irrigation purposes

A modified biological-integrated electrocoagulation method was explored to treat municipal wastewater (MWW) for irrigation purposes. To use treated wastewater for irrigation purposes a wide range of contaminants removal was focused on in this study (turbidity, hardness, conductivity, TDS, TSS, chloride, Ammonia nitrogen, BOD, COD, and total coliform). Raw municipal wastewater (RMWW) was treated in a modified Bio-Electrocoagulation (BEC) cell. The cell was operated in a continuous flow mode and consisted of an electrocoagulation stage using aluminum (Al) electrodes followed by a bioremediation stage using a fixed bio-filter (BF), the design of the cell was further modified by the addition of a sand filter (SF). The effect of several parameters such as applied voltage (22, 26, and 30 V), inlet flow rate (1, 3, and 5 Lh^-1), and initial pH (pH 3, 5, 7, 7.4, and 9) was investigated to determine the optimum operating conditions for selected responses. The most effective operating conditions for the BEC were investigated for the different irrigation water quality (WQ) indicators. It was observed that pH 7.4 and 26 V provide maximum removal efficiency of contaminants at the flow rate of 1 Lh^-1. A fixed film BF plays a positive role to improve the degradation of contaminants after the EC unit up to 4% of NH₃-N, 9.3% of BOD, and 7.8% of COD. In addition, using the SF improved the turbidity removal to 42.6%. The WQ specifications of the treated MWW using the BEC cell were compared with the standard specifications for restricted and unrestricted agricultural irrigation water. The overall operating cost of MWW treatment for irrigation purposes by using a modified bio-integrated electrocoagulation method was 0.76 $m^-3.

Microalgae removal technology for the cold source of nuclear power plant: A review

In the past three decades, nuclear energy has gained much attention as carbon-free electricity. Due to the supply of cooling water in nuclear power plant, large amount of waste heat will increase the water temperature, promote the microalgae and cyanobacteria propagation and increase the chance of red tide. Excess phytoplankton of cool source will result in abnormal operation of cooling system, even core overheating and nuclear leakage. Consequently, it is very important to remove microalgae and cyanobacteria from cold source of nuclear power plants. This review summarizes the formation mechanism and monitoring methods of red tide, compares the advantages and disadvantages of traditional microalgae removal technology including physical, chemical and biological methods. Furthermore, the improved electrochemical method and micro-nano bubble method are introduced in detail. Their combination is considered to be a low-cost, efficient and environmentally-friendly technology to prevent and control red tides for cold source of nuclear power plant.

Fast Generation of Hydroxyl Radicals by Rerouting the Electron Transfer Pathway via Constructed Chemical Channels during the Photo-Electro-Reduction of Oxygen

A strategy for the fast generation of hydroxyl radicals (HO·) via photo-electro-reduction of oxygen by rerouting the electron transfer pathway was proposed. The rate-determining step of HO· production is the formation of H₂O₂ and the simultaneous reduction of H₂O₂. Engineering of F-TiO₂ with single atom Pd bonded with four F and two O atoms favored the electrocatalytic 2-electron oxygen reduction to H₂O₂ with as high as 99% selectivity, while the additional channel bond HO-O···Pd-F-TiO₂ facilitates the photogenerated electron transfer from the conduction band to single atom Pd to reduce Pd···O-OH to HO·. The optimized HO· production rate is 9.18 μ mol L^-1 min^-1, which is 2.6-52.5 times higher than that in traditional advanced oxidation processes. In the application of wastewater treatment, this proposed photoelectrocatalytic oxygen reduction method, respectively, shows fast kinetics of 0.324 and 0.175 min^-1 for removing bisphenol A and acetaminophen. Around 93.2% total organic carbon and 99.3% acute toxicity removal were achieved. Additionally, the degradation efficiency was less affected by the water source and pH value because of the evitable usage of metallic active sites. This work represents a fundamental investigation on the generation rate of HO·, which would pave the way for the future development of photoelectrocatalytic technologies for water purification.

Pulsed electric field application reduces carbapenem- and colistin-resistant microbiota and blaKPC spread in urban wastewater

Wastewater flows from metropolitan areas, especially those with healthcare inputs, can serve as transport reservoirs for the dissemination of clinically-relevant antimicrobial resistant bacteria (ARB) such as carbapenem- (CR) and colistin-resistant (CoR) strains. Pulsed electric field (PEF) is an emerging wastewater management tool for reducing bacterial loads without generating environmentally harmful byproducts, but it's ability to reduce ARB and their genetic determinants is not well reported. We collected 86, 10-L raw wastewater influent samples from a large metropolitan wastewater treatment plant in Columbus, Ohio and subjected them to low (34 kV cm^-1 for 67 μsec) and high (36 kV cm^-1 for 89 μsec) PEF treatment. We quantified the PEF effectiveness by measuring concentrations of total coliform bacteria, CR and CoR bacteria, and the epidemic carbapenemase gene, bla_KPC, before and after PEF treatment. Utilizing marginal linear regression models with generalized estimating equations, we observed that low and high PEF treatment resulted in a 1.94 (95% CI 2.06-1.81; P < 0.001) and 2.32 (95% CI 2.46-2.18; P < 0.001) log reduction of total coliform bacteria concentrations, respectively. Low and high PEF treatment produced similar log reductions between CR E. coli (2.01 (95% CI 2.15-1.86; P < 0.001); 2.14 (95% CI: 5.30-4.61; P < 0.001)) and CR Enterobacteriaceae concentrations (1.55 (95% CI 1.70-1.41; P < 0.001); 1.86 (95% CI 2.05-1.68; P < 0.001)), and resulted in a 1.15 log (95% CI 1.38-0.93, P < 0.001) and 1.28 log (95% CI 1.54-1.03, P < 0.001) reduction of absolute bla_KPC concentrations. Log CoR E. coli concentrations were reduced by 2.47 (95% CI 2.78-2.15; P < 0.001) and 2.52 (95% CI 2.91-2.15; P < 0.001) and CoR Enterobacteriaceae by 2.24 (95% CI 2.52-1.95; P < 0.001) and 2.50 (95% CI 2.89-2.11; P < 0.001) following low and high PEF application. PEF can be applied for wastewater management as an independent treatment method, particularly at critical control points, such as an on-site management of wastewater from hospitals or other healthcare facilities, or in series with other conventional methods to reduce total bacterial loads and concentrations of clinically-relevant ARB.

Electroosmotically generated disinfectant from urine as a by-product of electricity in microbial fuel cell for the inactivation of pathogenic species

This work presents a small scale and low cost ceramic based microbial fuel cell, utilising human urine into electricity, while producing clean catholyte into an initially empty cathode chamber through the process of electro-osmostic drag. It is the first time that the catholyte obtained as a by-product of electricity generation from urine was transparent in colour and reached pH>13 with high ionic conductivity values. The catholyte was collected and used ex situ as a killing agent for the inactivation of a pathogenic species such as Salmonella typhimurium, using a luminometer assay. Results showed that the catholyte solutions were efficacious in the inactivation of the pathogen organism even when diluted up to 1:10, resulting in more than 5 log-fold reduction in 4 min. Long-term impact of the catholyte on the pathogen killing was evaluated by plating Salmonella typhimurium on agar plates and showed that the catholyte possesses a long-term killing efficacy and continued to inhibit pathogen growth for 10 days.

Comparison of carbonized and graphitized carbon fiber electrodes under flow-through electrode system (FES) for high-efficiency bacterial inactivation

The disinfection performance of a flow-through electrode system (FES) was systematically evaluated using different carbonized (C1, C2, and C3) and corresponding graphitized (G1, G2, and G3) carbon fiber felt (CFF) electrodes. The physicochemical and electrochemical properties were characterized to identify the differences among CFFs. Graphitized CFFs (gCFFs) can achieve complete inactivation of Escherichia coli (>6 log) at the voltage of 3 V and flux of 120-3600 L/(m² h) for high conductivity and chemical stability, while carbonized CFFs (cCFFs) only achieved around 1 log removal with obvious carbon corrosion. For the gCFFs, G1 (>6 log removal) with higher conductivity, better graphite structure, and larger surface area (related to fiber diameter and density) presented better disinfection performance at the flow rate of 30 mL/min than G2 (∼3 log) and G3(∼1 log). Furthermore, no regrowth and reactivation of bacteria occurred during the storage under visible light illumination after FES treatment. Three parallel FESs with G1 were operated continuously for one week (24 h per day, 7 days) treating the solution with an E. coli concentration ranging from 10⁶ to 10⁷ CFU/mL at the applied voltage of 3 V and the flow rate of 20 mL/min. No live bacteria were detected in the effluent of any of these three FESs. In-situ sampling experiments demonstrated that the inactivation of bacteria on anode was the dominant mechanism for FES treatment, which can be attributed to the sequential adsorption, direct-oxidation and desorption process on anode, instead of indirect oxidation by generating chemical oxidants. In addition, hydroxide ion generated from cathode reaction enhanced anode adsorption and inactivation of bacteria by providing alkaline environment. Combining the analysis results of material properties and disinfection performance, the gCFF-based FES was suggested to be a low-cost, high-efficiency, and safe alternative for future water disinfection.

Hydrogen peroxide generation from O2 electroreduction for environmental remediation: A state-of-the-art review

The electrochemical production of hydrogen peroxide (H2O2) by 2-electron oxygen reduction reaction (ORR) is an attractive alternative to the present complex anthraquinone process. The objective of this paper is to provide a state-of-the-arts review of the most important aspects of this process. First, recent advances in H2O2 production are reviewed and the advantages of H2O2 electrogeneration via 2-electron ORR are highlighted. Second, the selectivity of the ORR pathway towards H2O2 formation as well as the development process of H2O2 production are presented. The cathode characteristics are the decisive factors of H2O2 production. Thus the focus is shifted to the introduction of commonly used carbon cathodes and their modification methods, including the introduction of other active carbon materials, hetero-atoms doping (i.e., O, N, F, B, and P) and decoration with metal oxides. Cathode stability is evaluated due to its significance for long-term application. Effects of various operational parameters, such as electrode potential/current density, supporting electrolyte, electrolyte pH, temperature, dissolved oxygen, and current mode on H2O2 production are then discussed. Additionally, the environmental application of electrogenerated H2O2 on aqueous and gaseous contaminants removal, including dyes, pesticides, herbicides, phenolic compounds, drugs, VOCs, SO2, NO, and Hg0, are described. Finally, a brief conclusion about the recent progress achieved in H2O2 electrogeneration via 2-electron ORR and an outlook on future research challenges are proposed.

Designing and modeling of a novel electrolysis reactor using porous cathode to produce H2O2 as an oxidant

The entry of toxic organic pollutants and resistant to biodegradation has increased the concern about human health. The use of advanced oxidation (AO) processes to degrade these pollutants has been developing. One of the AO processes is based on the use of hydrogen peroxide in removing resistant organic pollutants.

This study aimed to develop a new reactor capable of producing H₂O₂ in the solution. Therefore, a porous electrode made of stainless steel with the capability of air injection in the electrode center was used. The 30 cm rod graphite electrodes were also used as an anode electrode in a 4000 ml reactor. The effects of variables, including current density (30–40 mA/cm²), time (10–30 min), and electrolyte concentration (12–17 mM/L) on the amount of H₂O₂ production were evaluated by Box behenken design under response surface methodology using Design expert software. The results of this study showed that H₂O₂ can be produced at the electrode surface of porous cathode under optimal conditions of 36 mA/cm² current density, 16 mM/l electrolyte concentration, in 23 min, and in the amount of 34 ppm. Using a porous cathode electrode causes the maximum contact among the solution, water, and air, and increases the production of H₂O₂.

The release of resistant organic compounds to the waste water is a serious problem to the environment. By the application of the Electro-oxidation (EO)reactor with the ability to produce H₂O₂, this issue is resolved. Furthermore, this technique is applied for non-selective degradation of the toxic organic compounds.

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The electro-oxidation process is a useful method for destruction of persistent organic matter from wastewater.

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Due to use of porous cathode in this method, contact between the electrode and the sewage is at its maximum level which increases the efficiency and speed of sewage treatment.

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This method can produce H₂O₂ as a high potential oxidant that can reduce persistent organic properties of sewage and make the wastewater suitable for biological treatment.

Electrochemical disinfection of bacterial contamination: Effectiveness and modeling study of E. coli inactivation by electro-Fenton, electro-peroxi-coagulation and electrocoagulation

The present work undertakes an examination and comparison of electro-Fenton (EF), electro-peroxi-coagulation (EPC) and electrocoagulation (EC) applied to the E. coli inactivation in batch reactor. Indeed, platinum (Pt (anode), EF), stainless steel (SS (cathode), EF, EPC) and ordinary steel (Fe (anode), EPC) and aluminum (Al, EC) were used respectively. The current intensity, nature of electrolytic support, bacterial density and hydrogen peroxide (H₂O₂) concentration are the most influenced study parameters. The obtained results showed that the high current intensities were significant for better inactivation and destruction of E. coli cells and caused a maximum of energy consumption. Both disinfection and energy consumption were improved by adding NaCl (or Na₂SO₄) in the three processes. Higher cellular density limited the electrochemical process and has negative effect in E. coli inactivation and the energy consumption. Only in the EPC case, the disinfection was considerably increased in function with H₂O₂ concentration. The modeling parameters of the inactivation kinetics of E. coli showed a good fitting of the established model (0.9560 < R² < 0.9979, 0.9267 < R² adjusted <0.997 and 0.0189 < RMSE <0.4821), faster kinetics of E. coli inactivation (significant values of K_max and Sl) in the case of high current intensity (0.2442<K_max<0.7440 and 10.50 < Sl < 24.69), the presence of chlorides or sulfates (0.6662<K_max<0.7818 and 11.67 < Sl < 18.59), and the sufficient H₂O₂ concentration (0.4712<K_max<0.9204 and 13.00 < Sl < 16.38). Moreover, the analysis of the results revealed that the EF is more effective in terms of the E. coli inactivation and the energy consumption comparatively to the other studied processes.

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

Electrochemical disinfection (ECD) has become an important blackwater disinfection technology. ECD is a promising solution for the 2 billion people without access to conventional sanitation practices and in areas deficient in basic utilities (e.g., sewers, electricity, waste treatment). Here, we report on the disinfection of blackwater using potential cycling compared to potentiostatic treatment methods in chloride-containing and chloride-free solutions of blackwater (i.e., untreated wastewater containing feces, urine, and flushwater from a toilet). Potentiodynamic treatment is demonstrated to improve disinfection energy efficiency of blackwater by 24% and 124% compared to static oxidation and reduction methods, respectively. The result is shown to be caused by electrochemical advanced oxidation processes (EAOP) and regeneration of sp²-surface-bonded carbon functional groups that serve the dual purpose of catalysts and adsorption sites of oxidant intermediates. Following 24 h electrolysis in blackwater, electrode fouling is shown to be minimized by the potential cycling method when compared to equivalent potentiostatic methods. The potential cycling current density is 40% higher than both the static oxidative and reductive methods. This work enhances the understanding of oxygen reduction catalysts using functionalized carbon materials and electrochemical disinfection anodes, both of which have the potential to bring a cost-effective, energy efficient, and practical solution to the problem of disinfecting blackwater.

The inhibition of Microcystis aeruginos by electrochemical oxidation using boron-doped diamond electrode

Electrooxidation is used to study the inhibition behavior of Microcystis aeruginosa, a dominant algae species during water blooms mainly caused by non-point source pollution. The inhibitory effect of current density, A/V ratio, initial algae concentration, and algae growth phase on the growth of algae by electrochemical oxidation was investigated, respectively. Further, the effect of electrolysis on the photosynthesis of algae cells and the degradation of Microcystin-LR (MC-LR) in solution were also studied. The results showed that the inhibitory effect increased with the increase of current density and A/V ratio. The damage of cell structure and the leakage of intracellular substances were observed when the current density was 17 mA/cm². The intracellular chlorophyll a decreased significantly during the culture period. Only when the A/V ratio was 9.75 m^-1, the algal growth could be completely inhibited. The inhibitory effect of algae was decreased with the increase of initial algal concentration, and the inhibitory effect of algae in the log growth phase was better than that in the stationary phase. The degradation efficiency of total MC-LR was 91.7% at 90 min. Some other substances could be degraded simultaneously along with the degradation of MC-LR in electrochemical oxidation.

Rates of H2O2 Electrogeneration by Reduction of Anodic O2 at RVC Foam Cathodes in Batch and Flow-through Cells

The Electro-Fenton process for in-situ H₂O₂ electrogeneration is impacted by low O₂ utilization efficiency (<0.1%) and the need of acid for pH adjustment. An electrochemical flow-through cell can develop localized acidic conditions, coupled with simultaneous formation and utilization of O₂ to enhance H₂O₂ formation. Multiple electrode configurations using reticulated vitreous carbon (RVC) foam and Ti/mixed metal oxides (MMO) are proposed to identify the optimum conditions for H₂O₂ formation in batch and flow-through cells. A pH of 2.75±0.25 is developed locally in the flow-through cell that supports effective O₂ reduction. Up to 9.66 mg/L H₂O₂ is generated in a 180 mL batch cell under 100 mA, at pH 2, and mixing at 350 rpm. In flow-through conditions, both flow rate and current significantly influence H₂O₂ production. A current of 120 mA produced 2.27 mg/L H₂O₂ under a flow rate of 3 mL/min in a 3-electrode cell with one RVC foam cathode at 60 min. The low current of 60 mA does not enable effective H₂O₂ production, while the high current of 250 mA produced less H₂O₂ due to parasitic reactions competing with O₂ reduction. Higher flow rates decrease the retention time, but also increase the O₂ mass transfer. Furthermore, 3-electrode flow-through cell with two RVC foam cathodes was not effective for H₂O₂ production due to the limited O₂ supply for the secondary cathode. Finally, a coupled process that uses both O₂ and H₂ from water electrolysis is proposed to improve the H₂O₂ yield further.

Green electrochemical modification of RVC foam electrode and improved H2O2 electrogeneration by applying pulsed current for pollutant removal

The performance of cathode on H₂O₂ electrogeneration is a critical factor that limits the practical application of electro-Fenton (EF) process. Herein, we report a simple but effective electrochemical modification of reticulated vitreous carbon foam (RVC foam) electrode for enhanced H₂O₂ electrogeneration. Cyclic voltammetry, chronoamperometry, and X-ray photoelectron spectrum were used to characterize the modified electrode. Oxygen-containing groups (72.5-184.0 μmol/g) were introduced to RVC foam surface, thus resulting in a 59.8-258.2% higher H₂O₂ yield. The modified electrodes showed much higher electrocatalytic activity toward O₂ reduction and good stability. Moreover, aimed at weakening the extent of electroreduction of H₂O₂ in porous RVC foam, the strategy of pulsed current was proposed. H₂O₂ concentration was 582.3 and 114.0% higher than the unmodified and modified electrodes, respectively. To test the feasibility of modification, as well as pulsed current, EF process was operated for removal of Reactive Blue 19 (RB19). The fluorescence intensity of hydroxybenzoic acid in EF with modified electrode is 3.2 times higher than EF with unmodified electrode, illustrating more hydroxyl radicals were generated. The removal efficiency of RB 19 in EF with unmodified electrode, modified electrode, and unmodified electrode assisted by pulsed current was 53.9, 68.9, and 81.1%, respectively, demonstrating that the green modification approach, as well as pulsed current, is applicable in EF system for pollutant removal. Graphical abstract ᅟ.

Electrochemical disinfection of bacteria-laden water using antimony-doped tin-tungsten-oxide electrodes

Electrochemical disinfection has been shown to be an efficient method with a shortrequired contact time for treatment of drinking water supplies, industrial raw water supplies, liquid foodstuffs, and wastewater effluents. In the present work, the electrochemical disinfection of saline water contaminated with bacteria was investigated in chloride-containing solutions using Sb-doped Sn_80%-W_20%-oxide anodes. The influence of current density, bacterial load, initial chloride concentration, solution pH, and the type of bacteria (E. coli D21, E. coli O157:H7, and E. faecalis) on disinfection efficacy was systematically examined. The impact of natural organic matter and a radical scavenger on the disinfection process was also examined. The electrochemical system was highly effective in bacterial inactivation for a 0.1 M NaCl solution contaminated with ∼10⁷ CFU/mL bacteria by applying a current density ≥1 mA/cm² through the cell.100% inactivation of E. coli D21 was achieved with a contact time of less than 60 s and power consumption of 48 Wh/m³, by applying a current density of 6 mA/cm² in a 0.1 M NaCl solution contaminated with ∼10⁷ CFU/mL. Reactive chlorine species as well as reactive oxygen species (e.g. hydroxyl radicals) generated in situ during the electrochemical process were determined to be responsible for inactivation of bacteria.

Tailoring Microbial Electrochemical Cells for Production of Hydrogen Peroxide at High Concentrations and Efficiencies

A microbial peroxide producing cell (MPPC) for H₂ O₂ production at the cathode was systematically optimized with minimal energy input. First, the stability of H₂ O₂ was evaluated using different catholytes, membranes, and catalyst materials. On the basis of these results, a flat-plate MPPC fed continuously using 200 mm NaCl catholyte at a 4 h hydraulic retention time was designed and operated, producing H₂ O₂ for 18 days. H₂ O₂ concentration of 3.1 g L^-1 H₂ O₂ with 1.1 Wh g^-1 H₂ O₂ power input was achieved in the MPPC. The high H₂ O₂ concentration was a result of the optimum materials selected. The small energy input was largely the result of the 0.5 cm distance between the anode and cathode, which reduced ionic transport losses. However, >50 % of operational overpotentials were due to the 4.5-5 pH unit difference between the anode and cathode chambers. The results demonstrate that a MPPC can continuously produce H₂ O₂ at high concentration by selecting compatible materials and appropriate operating conditions.

The ability of electrochemical oxidation with a BDD anode to inactivate Gram-negative and Gram-positive bacteria in low conductivity sulfate medium

The disinfection of 100 mL of synthetic water containing 7 mM Na2SO4 with 10(6) CFU mL(-1) of either Gram-negative or Gram-positive bacteria has been studied by electrochemical oxidation. The electrolytic cell was a stirred tank reactor equipped with a boron-doped diamond (BDD) anode and a stainless steel cathode and the trials were performed at acidic and neutral pH, at 33.3 mA cm(-2) and 25 °C. Reactive oxygen species, pre-eminently hydroxyl radicals, were efficiently produced in both media from water oxidation at the BDD anode and the bacteria concentration was reduced by ≥ 5 log units after 60 min of electrolysis, thus constituting a good chlorine-free disinfection treatment. All the inactivation kinetics were described by a logistic model, with no significant statistical differences between acidic and neutral suspensions. The electrochemical disinfection with BDD was very effective for Gram-negative bacilli like Escherichia coli and Pseudomonas aeruginosa and Gram-positive ones like Bacillus atrophaeus, whereas the Gram-positive cocci Staphylococcus aureus and Enterococcus hirae were more resistant. Thus, the latter organisms are a better choice than E. coli as process indicators. Scanning electron microscopy highlighted a transition from initial cells with standard morphology supported on clean filters to inactivated cells with a highly altered morphology lying on dirty filters with plenty of cellular debris. Larger damage was observed for Gram-negative cells compared to Gram-positive ones. The inactivation effect could then be related to the chemical composition of the outer layers of the cell structure along with the modification of the transmembrane potentials upon current passage.

Can electrocoagulation process be an appropriate technology for phosphorus removal from municipal wastewater?

This paper evaluated a novel pilot scale electrocoagulation (EC) system for improving total phosphorus (TP) removal from municipal wastewater. This EC system was operated in continuous and batch operating mode under differing conditions (e.g. flow rate, initial concentration, electrolysis time, conductivity, voltage) to evaluate correlative phosphorus and electrical energy consumption. The results demonstrated that the EC system could effectively remove phosphorus to meet current stringent discharge standards of less than 0.2mg/L within 2 to 5min. This target was achieved in all ranges of initial TP concentrations studied. It was also found that an increase in conductivity of solution, voltages, or electrolysis time, correlated with improved TP removal efficiency and reduced specific energy consumption. Based on these results, some key economic considerations, such as operating costs, cost-effectiveness, product manufacturing feasibility, facility design and retrofitting, and program implementation are also discussed. This EC process can conclusively be highly efficient in a relatively simple, easily managed, and cost-effective for wastewater treatment system.

Electrochemical degradation of trichloroethylene in aqueous solution by bipolar graphite electrodes

In this study, we tested the use of the bipolar electrodes to enhance electrochemical degradation of trichloroethylene (TCE) in an undivided, flow-through electrochemical reactor. The bipolar electrode forms when an electrically conductive material polarizes between feeder electrodes that are connected to a direct current source and, therefore, creates an additional anode/cathode pair in the system. We hypothesize that bipolar electrodes will generate additional oxidation/reduction zones to enhance TCE degradation. The graphite cathode followed by graphite anode sequence were operated without a bipolar electrode as well as with one and two bipolar graphite electrodes. The system without bipolar electrodes degraded 29% of TCE while the system with one and two bipolar electrodes degraded 38% and 66% of TCE, respectively. It was found that the removal mechanism for TCE in bipolar mode includes hydrodechlorination at the feeder cathode, and oxidation through reaction with peroxide. The results show that the bipolar electrodes presence enhance TCE removal efficiency and rate and imply that they can be used to improve electrochemical treatment of contaminated groundwater.

Wastewater reclamation and reuse in China: Opportunities and challenges

The growing water stress both in terms of water scarcity and quality deterioration promotes the development of reclaimed water as a new water resource use. This paper reviewed wastewater reuse practices in China, and the opportunities and challenges of expanding reclaimed water use were analyzed. Rapid urbanization with the increasing of water demand and wastewater discharge provides an opportunity for wastewater reuse. The vast amount of wastewater discharge and low reclaimed water production mean that wastewater reuse still has a great potential in China. Many environmental and economic benefits and successful reclamation technologies also provide opportunities for wastewater reuse. In addition, the overall strategy in China is also encouraging for wastewater reuse. In the beginning stage of wastewater reclamation and reuse, there are many significant challenges to expand wastewater reuse in China including slow pace in adopting urban wastewater reuse programs, the establishment of integrated water resources management framework and guidelines for wastewater reuse programs, incoherent water quality requirements, the limited commercial development of reclaimed water and the strengthening of public awareness and cooperation among stakeholders.

Semiquantitative Performance and Mechanism Evaluation of Carbon Nanomaterials as Cathode Coatings for Microbial Fouling Reduction

In this study, we examine bacterial attachment and survival on a titanium (Ti) cathode coated with various carbon nanomaterials (CNM): pristine carbon nanotubes (CNT), oxidized carbon nanotubes (O-CNT), oxidized-annealed carbon nanotubes (OA-CNT), carbon black (CB), and reduced graphene oxide (rGO). The carbon nanomaterials were dispersed in an isopropyl alcohol-Nafion solution and were then used to dip-coat a Ti substrate. Pseudomonas fluorescens was selected as the representative bacterium for environmental biofouling. Experiments in the absence of an electric potential indicate that increased nanoscale surface roughness and decreased hydrophobicity of the CNM coating decreased bacterial adhesion. The loss of bacterial viability on the noncharged CNM coatings ranged from 22% for CB to 67% for OA-CNT and was dependent on the CNM dimensions and surface chemistry. For electrochemical experiments, the total density and percentage of inactivation of the adherent bacteria were analyzed semiquantitatively as functions of electrode potential, current density, and hydrogen peroxide generation. Electrode potential and hydrogen peroxide generation were the dominant factors with regard to short-term (3-h) bacterial attachment and inactivation, respectively. Extended-time electrochemical experiments (12 h) indicated that in all cases, the density of total deposited bacteria increased almost linearly with time and that the rate of bacterial adhesion was decreased 8- to 10-fold when an electric potential was applied. In summary, this study provides a fundamental rationale for the selection of CNM as cathode coatings and electric potential to reduce microbial fouling.

Degradation of tyrosol by a novel electro-Fenton process using pyrite as heterogeneous source of iron catalyst

Tyrosol (TY) is one of the most abundant phenolic components of olive oil mill wastewaters. Here, the degradation of synthetic aqueous solutions of 0.30 mM TY was studied by a novel heterogeneous electro-Fenton (EF) process, so-called EF-pyrite, in which pyrite powder was the source of Fe(2+) catalyst instead of a soluble iron salt used in classical EF. Experiments were performed with a cell equipped with a boron-doped diamond anode and a carbon-felt cathode, where TY and its products were destroyed by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between Fe(2+) and H2O2 generated at the cathode. Addition of 1.0 g L(-1) pyrite provided an easily adjustable pH to 3.0 and an appropriate 0.20 mM Fe(2+) to optimize the EF-pyrite treatment. The effect of current on mineralization rate, mineralization current efficiency and specific energy consumption was examined under comparable EF and EF-pyrite conditions. The performance of EF-pyrite was 8.6% superior at 50 mA due to self-regulation of soluble Fe(2+) by pyrite. The TY decay in this process followed a pseudo-first-order kinetics. The absolute rate constant for TY hydroxylation was 3.57 × 10(9) M(-1) s(-1), as determined by the competition kinetics method. Aromatic products like 3,4-dihydroxyphenylethanol, 4-hydroxyphenylacetic acid, 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid and catechol, as well as o-benzoquinone, were identified by GC-MS and reversed-phase HPLC. Short-chain aliphatic carboxylic acids like maleic, glycolic, acetic, oxalic and formic were quantified by ion-exclusion HPLC. Oxalic acid was the major and most persistent product found. Based on detected intermediates, a plausible mineralization pathway for TY by EF-pyrite was proposed.

Reduction of pollutants and disinfection of industrial wastewater by an integrated system of copper electrocoagulation and electrochemically generated hydrogen peroxide

The objective of this study was to evaluate the effect of copper electrocoagulation and hydrogen peroxide on COD, color, turbidity, and bacterial activity in a mixed industry wastewater. The integrated system of copper electrocoagulation and hydrogen peroxide is effective at reducing the organic and bacterial content of industrial wastewater. The copper electrocoagulation alone reduces COD by 56% in 30 min at pH 2.8, but the combined system reduces COD by 78%, biochemical oxygen demand (BOD5) by 81%, and color by 97% under the same conditions. Colloidal particles are flocculated effectively, as shown by the reduction of zeta potential and the 84% reduction in turbidity and 99% reduction in total solids. Additionally, the total coliforms, fecal coliforms, and bacteria are all reduced by 99%. The integrated system is effective and practical for the reduction of both organic and bacterial content in industrial wastewater.

Reclamation of used urban waters for irrigation purposes--a review of treatment technologies

The worldwide fresh water scarcity is increasing the demand for non-conventional water resources. Despite the technology being available for application of treated wastewater in irrigation, the use of effluent in agriculture is not being properly managed in the majority of cases. Industrial countries, where financial resources are available but restricted, face difficulties in some cases related to the lack of a complete definition of irrigation water quality standards, as well as to the lack of monitoring components that determine if the effluent is suitable for such use. The present paper presents a critical review on urban reclamation technologies for irrigation. The technologies are presented by the four most important parameters for irrigation water quality: salinity, pathogens, nutrients and heavy metals. An overview is given of the current, on-going evaluation of different reclamation technologies for irrigation.

The performance of Electro-Fenton oxidation in the removal of coliform bacteria from landfill leachate

Leachate pollution is one of the main problems in landfilling. Researchers have yet to find an effective solution to this problem. The technology that can be used may differ based on the type of leachate produced. Coliform bacteria were recently reported as one of the most problematic pollutants in semi-aerobic (stabilized) leachate. In the present study, the performance of the Electro-Fenton process in removing coliform from leachate was investigated. The study focused on two types of leachate: Palau Borung landfill leachate with low Coliform content (200 MPN/100 m/L) and Ampang Jajar landfill leachate with high coliform content (>24 × 10(4)MPN/100 m/L). Optimal conditions for the Electro-Fenton treatment process were applied on both types of leachate. Then, the coliform was examined before and after treatment using the Most Probable Number (MPN) technique. Accordingly, 100% removal of coliform was obtained at low initial coliform content, whereas 99.9% removal was obtained at high initial coliform content. The study revealed that Electro-Fenton is an efficient process in removing high concentrations of pathogenic microorganisms from stabilized leachate.

Stress-induced Hsp70 gene expression and inactivation of Cryptosporidium parvum oocysts by chlorine-based oxidants

Our research on the mechanisms of action of chlorine-based oxidants on Cryptosporidium parvum oocysts in water revealed a dual-phase effect: (i) response to oxidative stress, which was demonstrated by induced expression of the Hsp70 heat shock gene, and (ii) oocyst inactivation as a result of long-term exposure to oxidants. The relative biocidal effects of sodium hypochlorite (bleach) and electrolytically generated mixed oxidant solution (MOS) on C. parvum oocysts were compared at identical free chlorine concentrations. Oocyst inactivation was determined by quantitative reverse transcription-PCR (qRT-PCR) amplification of the heat-induced Hsp70 mRNA and compared with tissue culture infectivity. According to both assays, within the range between 25 and 250 mg/liter free chlorine and with 4 h contact time, MOS exhibits a higher efficacy in oocyst inactivation than hypochlorite. Other RNA-based viability assays, aimed at monitoring the levels of beta-tubulin mRNA and 18S rRNA, showed relatively slow decay rates of these molecules following disinfection by chlorine-based oxidants, rendering these molecular diagnostic viability markers inappropriate for disinfection efficacy assessment.

Procédés d’oxydation avancée dans le traitement des eaux et des effluents industriels: Application à la dégradation des polluants réfractaires

Cette synthèse traite des procédés d’oxydation avancée (POA) pour le traitement des eaux et des effluents industriels. Ces procédés mettent pour la plupart en combinaison deux ou trois réactifs (oxydants) afin de produire des radicaux hydroxyles. Les radicaux libres sont des espèces hautement actives capables de réagir rapidement et de manière non sélective sur la plupart des composés organiques, réputés difficilement oxydables par voie biologique ou par des traitements chimiques conventionnels. Les POA peuvent être subdivisés en quatre groupes : les procédés d’oxydation chimique en phase homogène (H2O2/Fe2+ et H2O2/O3), les procédés photocatalytiques en phase homogène et/ou hétérogène (H2O2/UV, O3/UV et Fe2+/H2O2/UV; TiO2/UV), les procédés d’oxydation sonochimique et les procédés d’oxydation électrochimique. Le couplage H2O2/Fe2+ représente le système d’oxydation avancée le plus connu et le moins complexe, lequel est souvent employé dans le traitement des effluents industriels. Cependant, dans le domaine de la potabilisation des eaux, le système le plus utilisé et le plus éprouvé est le couplage H2O2/O3 couramment employé pour l’élimination des composés phytosanitaires (pesticides). Les procédés d’oxydation électrochimiques, photocatalytiques et sonochimiques sont des technologies qui nécessitent en général moins de réactif et sont faciles d’automatisation par comparaison aux autres POA. Ces procédés sont présentement en pleine expansion dans le domaine des technologies environnementales, ceci afin d’améliorer les systèmes existants de traitement des eaux usées municipales et industrielles, ou à remplacer les technologies conventionnelles peu efficaces pour l’enlèvement de contaminants organiques réfractaires, inorganiques et microbiens. De nombreuses études réalisées à l’échelle laboratoire ont clairement prouvé l’efficacité des POA pour le traitement de divers effluents. Cependant, le développement de ces procédés dans les filières de traitement des eaux reste encore limité en raison des coûts d’investissement et des coûts opératoires associés. Des solutions et stratégies sont proposées dans ce document, telles que le développement de procédés hybrides et leur couplage avec des traitements biologiques conventionnels, et ce, afin de pallier certaines contraintes spécifiques des POA et faciliter ainsi leur insertion dans les filières de traitement des eaux et des effluents industriels. Ce document a pour objectif de faire une synthèse des différents POA, d’en expliquer leur principe de fonctionnement, de déterminer les différents paramètres les gouvernant, ainsi que leurs applications dans le traitement des eaux et des effluents.

Involvement of reactive oxygen species in the electrochemical inhibition of barnacle (Amphibalanus amphitrite) settlement

The role of reactive oxygen species (ROS) in electrochemical biofouling inhibition was investigated using a series of abiotic tests and settlement experiments with larvae of the barnacle Amphibalanus amphitrite, a cosmopolitan fouler. Larval settlement, a measure of biofouling potential, was reduced from 43% +/- 14% to 5% +/- 6% upon the application of pulsed electric signals. The application of ROS scavengers such as glutathione and catalase counteracted the inhibitory effects of the electric signals, allowing settlement, and thus indicating that ROS are antifouling agents. Based on the experimental evidence, the proposed mechanism for ROS-based fouling prevention with interdigitated electrodes involved the electrochemical generation of hydrogen peroxide by oxygen reduction, and its likely reduction to hydroxyl radicals. Either hydroxyl radicals or products of hydroxyl radical reactions appeared to be the main deterrents of larval settlement.

Mineralization of salicylic acid in acidic aqueous medium by electrochemical advanced oxidation processes using platinum and boron-doped diamond as anode and cathodically generated hydrogen peroxide

Solutions containing 164 mg L(-1) salicylic acid of pH 3.0 have been degraded by electrochemical advanced oxidation processes such as anodic oxidation, anodic oxidation with electrogenerated H(2)O(2), electro-Fenton, photoelectro-Fenton and solar photoelectro-Fenton at constant current density. Their oxidation power has been comparatively studied in a one-compartment cell with a Pt or boron-doped diamond (BDD) anode and a graphite or O(2)-diffusion cathode. In the three latter procedures, 0.5mM Fe(2+) is added to the solution to form hydroxyl radical (()OH) from Fenton's reaction between Fe(2+) and H(2)O(2) generated at the O(2)-diffusion cathode. Total mineralization is attained for all methods with BDD and for photoelectro-Fenton and solar photoelectro-Fenton with Pt. The poor decontamination achieved in anodic oxidation and electro-Fenton with Pt is explained by the slow removal of most pollutants by ()OH formed from water oxidation at the Pt anode in comparison to their quick destruction with ()OH produced at BDD. ()OH generated from Fenton's reaction oxidizes rapidly all aromatic pollutants, but it cannot destroy final Fe(III)-oxalate complexes. Solar photoelectro-Fenton treatments always yield quicker degradation rate due to the very fast photodecarboxylation of these complexes by UVA irradiation supplied by solar light. The effect of current density on the degradation rate, efficiency and energy cost of all methods is examined. The salicylic acid decay always follows a pseudo-first-order kinetics. 2,3-Dihydroxybenzoic, 2,5-dihydroxybenzoic, 2,6-dihydroxybenzoic, alpha-ketoglutaric, glycolic, glyoxylic, maleic, fumaric, malic, tartronic and oxalic acids are detected as oxidation products. A general reaction sequence for salicylic acid mineralization considering all these intermediates is proposed.

Efficiency of the UV/H2O2 process for the disinfection of humic surface waters

The efficiency of the UV/H2O2 process for the disinfection of total coliforms and the prevention of bacterial regrowth in humic surface waters were investigated. Inactivation of total coliforms was determined in water samples containing various concentrations ranging from 0-10 mg/L dissolved organic carbon (DOC) of fulvic acid, which were exposed to various doses (68-681 mWs/cm2) of UV radiation in the presence of 0.125 mg/L and 3.000 mg/L of hydrogen peroxide. Disinfection efficiencies of the UV radiation and the UV/H2O2 processes were compared. The results of bacterial inactivation experiments showed that the performances of the UV and the UV/H2O2 (0.125) were comparable whereas the UV/H2O2 (3.000) process showed significant improvement in performance, especially, in highly humic waters. Inactivation coefficient appeared to be almost doubled by the addition of 3.000 mg/L hydrogen peroxide during the treatment of highly humic waters. In contradiction to significant regrowth which occurred in the single UV radiation treatment, residual bacteria following the UV/H2O2 (0.125) and the UV/H2O2 (3.000) treatments were completely inactivated during dark incubation indicating the elimination of possible bacterial regrowth.

Inactivation of Escherichia coli in the electrochemical disinfection process using a Pt anode

Recently, the electrochemical disinfection has gained a great interest as one of the alternatives to conventional chlorination due to its high effectiveness and environmental compatibility. Despite the extensive reports on electro-chlorination disinfection, few researches were reported on the systems without generating chlorine. This study mainly focused on the potential disinfecting ability of electro-generated oxidants other than chlorine with using an inert medium (chloride-free phosphate buffer solution), which was intended to exclude the formation of chlorine during the electrolysis, as the Escherichia coli as an indicator bacterium was disinfected by applying the current to a platinum anode. The electrochemical inactivation of E. coli without chlorine production was demonstrated to occur in two distinct stages. The first stage inactivation takes place rapidly at the beginning of electrolysis, which appears to be achieved by the electrosorption of negatively charged E. coli cells to the anode surface, followed by a direct electron transfer reaction. As the electrolysis continues further, the inactivation becomes slower but steady, in contrast to the first stage of inactivation. This was attributed to the action of reactive oxidants generated from water discharge, such as hydroxyl radical. Overall, this study suggests that the electrochemical disinfection could be successfully performed even without producing chlorine, recommending the potential application for disinfecting water that does not allow including any chloride ions (such as the production of ultra-pure sterilized water for semiconductor washing).