Electrochemical Oxidation/Disinfection of Urine Wastewaters with Different Anode Materials

Anodic oxidation by electrical power pulses for alachlor degradation

This article explores the benefits of electrochemical oxidation in pulsed mode, using potential, current, and power pulses. While potential and current pulse electrochemical technology has been previously studied for wastewater treatment, no study has included power pulses until now. The objective of this work is to highlight the advantages of power pulses by applying this pulse type to the electrochemical oxidation of a probe molecule, alachlor. For this aim, the influence of operating parameters and the comparison of the different pulse modes were investigated and compared to the results obtained with the electrochemical oxidation of alachlor in continuous mode. The study shows that the best results were obtained with the power pulse electrochemical oxidation with 100% alachlor degradation after 180 min and a mineralisation yield of 38.3% after 240 min. These results were better than those reported in the literature for treatments with continuous current input using platinum electrodes. This new technique could be an effective and efficient way to treat contaminated water and reduce the pressure on freshwater reserves.

MMO-induced batch and pilot-scale electro-oxidation treatment of municipal wastewater

The present research aimed to explore the durability of MMO electrodes through electro-oxidation (EO) in purifying secondary treated actual sewage wastewater using batch and pilot-scale setups. The main aim is to inactivate bacteria in sewage treatment plants before they are released into the environment, thus contaminating water and soil. Process parameters such as current density (j), NaCl dose (n), and treatment time (t) were optimized using response surface methodology in a lab-scale EO reactor under batch conditions. The results showed that optimization of current density at 5.90 mA/cm2 and NaCl concentration at 1.31 g/L led to 93.90% of bacterial inactivation (Q1) within 8 min of treatment and 0.48 kWh/m3 energy consumption (Q2). Biological analysis was conducted to validate bacterial cell destruction and count coliform bacteria in the EO-treated sewage wastewater. XRD, cyclic voltammetry studies, and FE-SEM/EDS analysis were done to confirm the MMO anode's durability and stability after 100 recycles. The study prioritized bacterial inactivation along with organic matter degradation. Besides that, a small pilot-scale study on the actual sewage wastewater with a volume of 10-50 L was done in batch mode under previously optimized conditions to analyze the efficacy of the MMO anodes in terms of bacterial inactivation.

Electrochemical degradation of acetaminophen in urine matrices: Unraveling complexity and implications for realistic treatment strategies

Urine has an intricate composition with high concentrations of organic compounds like urea, creatinine, and uric acid. Urine poses a formidable challenge for advanced effluent treatment processes following urine diversion strategies. Urine matrix complexity is heightened when dealing with pharmaceutical residues like acetaminophen (ACT) and metabolized pharmaceuticals. This work explores ACT degradation in synthetic, fresh real, and hydrolyzed real urines using electrochemical oxidation with a dimensional stable anode (DSA). Analyzing drug concentration (2.5 - 40 mg L-1) over 180 min at various current densities in fresh synthetic effluent revealed a noteworthy 75% removal at 48 mA cm-2. ACT degradation kinetics and that of the other organic components followed a pseudo-first-order reaction. Uric acid degradation competed with ACT degradation, whereas urea and creatinine possessed higher oxidation resistance. Fresh real urine presented the most challenging scenario for the electrochemical process. Whereas, hydrolyzed real urine achieved higher ACT removal than fresh synthetic urine. Carboxylic acids like acetic, tartaric, maleic, and oxalic were detected as main by-products. Inorganic ionic species nitrate, nitrite, and ammonium ions were released to the medium from N-containing organic compounds. These findings underscore the importance of considering urine composition complexities and provide significant advancements in strategies for efficiently addressing trace pharmaceutical contamination.

Additive-manufactured paper-PMMA hybrid microfluidic chip for simultaneous monitoring of creatinine and pH in artificial urine

Nowadays, kidney dysfunction is a common health issue due to the modernized lifestyle. Even though medications are commercially available to treat kidney diseases, early diagnosis is crucial and challenging. Clinically, measuring urine creatinine and pH has gained significant interest as a way to diagnose kidney diseases early. In the present work, we attempted to develop a low-cost, robust, accurate and naked-eye colorimetric method to determine both creatinine levels and pH variations in artificial urine samples using a simple 3D-printed hybrid microfluidic device. Creatinine was detected by the incorporation of the traditional Jaffe test onto the hybrid paper-PMMA microfluidic device and pH (4-8) was measured by a simple anthocyanin test. Notably, the tests were established without employing any sophisticated or costly instrument clusters. The developed 3D-printed microfluidic probe showed a limit of detection (LOD) of 0.04 mM for creatinine over a concentration range of 1-10 mM, with a regression coefficient (R2) of 0.995 in laboratory conditions. Interestingly, the experimental data obtained with artificial urine exhibited a wide linear range from 0.1 mM to 5 mM under different pH values ranging from 4 to 8 in the presence of matrices commonly found in urine samples other than proteins, indicating the potential use of this method in pre-clinical analysis. Since the wide linear range of urine creatinine in artificial urine samples falls well below the clinically relevant concentrations in humans (0.07-0.27 mM), the developed lab-on-chip device is further suitable for clinical evaluation with proper ethical clearance. This 3D-printed hybrid microfluidic colorimetry-based creatinine detection and pH indicator platform can be beneficial in the healthcare sector due to the on-site testing capability, cost-effectiveness, ease of use, robustness, and instrument-free approach.

Degradation of the antibiotic ciprofloxacin in urine by electrochemical oxidation with a DSA anode

Ciprofloxacin (CIP) is a commonly prescribed fluoroquinolone antibiotic that, even after uptake, remains unmetabolized to a significant extent-over 70%. Unmetabolized CIP is excreted through both urine and feces. This persistent compound manages to evade removal in municipal wastewater facilities, leading to its substantial accumulation in aquatic environments. This accumulation raises concerns about potential risks to the health of various living organisms. Herein, we present a study on the remediation of CIP in synthetic urine by electrochemical oxidation in an undivided cell with a DSA (Ti/IrO2) anode and a stainless-steel cathode. Physisorbed hydroxyl radical formed at the anode surface from water discharge and free chlorine generated from Cl- oxidation were the main oxidizing agents. The effect of pH and current density (j) on CIP degradation was examined, and its total removal was easily achieved at pH ≥ 7.0 and j ≥ 60 mA cm-2 due to the action of free chlorine. The CIP decay always followed a pseudo-first-order kinetics. The components of the synthetic urine were also oxidized. The main nitrogenated species released was NH3. A very small concentration of free chlorine was quantified at the end of the treatment, thus demonstrating the good performance of electrochemical oxidation and its effectiveness to destroy all the organic pollutants. The present study demonstrates the simultaneous oxidation of the organic components of urine during CIP degradation, thus showing a unique perspective for its electrochemical oxidation that enhances the environmental remediation strategies.

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

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

New diamond coatings for a safer electrolytic disinfection

In this work, a new coating of boron-doped diamond ultra-nanocrystalline (U-NBDD), tailored to prevent massive formation of perchlorates during disinfection, is evaluated as electrode for the reclaiming of treated secondary wastewater by the electrochemically assisted disinfection process. Results obtained are compared to those obtained by using a standard electrode (STD) that was evaluated as a standard in previous research showing outstanding performance for this application. First tests were carried out to evaluate the chlorine speciation obtained after the electrolysis of synthetic chloride solutions at two different ranges of current densities. Concentrations of hypochlorite obtained using the U-NBDD anode at 25 mA cm-2 were 1.5-fold higher, outperforming STD anode; however, at 300 mA cm-2, an overturn on the behavior of anodes occurs where the amount of hypochlorite produced on STD anode was 1.5-fold higher. Importantly, at low current density the formation of chlorates and perchlorates is null using U-NBDD. Then, the disinfection of the real effluent of the secondary clarifier of a municipal wastewater treatment facility is assessed, where inactivation of Escherichia coli is achieved at low charge applied per volume electrolyzed (0.08 A h L-1) at 25 mA cm-2 using the U-NBDD. These findings demonstrate the appropriateness of the strategy followed in this work to obtain safer electro-disinfection technologies for the reclaiming of treated wastewater.

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

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

Effect of electrode parameters in the electro-production of reactive oxidizing species via boron-doped diamond under batch mode

Ozone and hydroxyl radicals (^• OH) are powerful reactive oxidizing species (ROS) that are commonly utilized in water disinfection. The electrochemical advanced oxidation process (EAOP) is often used to generate such oxidants, whereas optimizing its experimental setup and electrode parameters plays a crucial role in its performance. This research aims to find the optimal setup for ROS generation process from tap water via the boron-doped diamond. The effect of electrode's active area, type of electrode substrates (mesh or sheet), type of mesh substrate (rolled and unrolled), and number of anodes and cathodes are examined. The results showed that the use of two long-rolled BDD/Nb meshes as anode and one long-rolled mesh as a cathode gives the optimal performance of electrolysis process at 15 V potential and 3 min. These results will provide a start for developing a cost accepted, health-safe, household disinfection device that reduces susceptibility to human life-threatening waterborne diseases. PRACTITIONER POINTS: This research aims to find the optimal setup for ROS generation process from tap water via the boron-doped diamond. The effect of electrode's parameters on the electro-production of ROS is examined. The best performance is achieved using rolled mesh electrodes. Two long-rolled BDD/Nb meshes as anode electrodes and one long-rolled mesh cathode electrode give the optimal electrolysis process performance.

Electrochemical oxidation of landfill leachate using boron-doped diamond anodes: pollution degradation rate, energy efficiency and toxicity assessment

Electrochemical oxidation (EO), due to high efficiency and small carbon footprint, is regarded as an attractive option for on-site treatment of highly contaminated wastewater. This work shows the effectiveness of EO using three boron-doped diamond electrodes (BDDs) in sustainable management of landfill leachate (LL). The effect of the applied current density (25-100 mA cm^-2) and boron doping concentration (B/C ratio: 500 ppm, 10,000 ppm and 15,000 ppm) on the performance of EO was investigated. It was found that, of the electrodes used, the one most effective at COD, BOD₂₀ and ammonia removal (97.1%, 98.8% and 62%, respectively) was the electrode with the lowest boron doping. Then, to better elucidate the ecological role of LLs, before and after EO, cultivation of faecal bacteria and microscopic analysis of total (prokaryotic) cell number, together with ecotoxicity assay (Daphnia magna, Thamnocephalus platyurus and Artemia salina) were combined for the two better-performing electrodes. The EO process was very effective at bacterial cell inactivation using each of the two anodes, even within 2 h of contact time. In a complex matrix of LLs, this is probably a combined effect of electrogenerated oxidants (hydroxyl radicals, active chlorine and sulphate radicals), which may penetrate into the bacterial cells and/or react with cellular components. The toxicity of EO-treated LLs proved to be lower than that of raw ones. Since toxicity drops with increased boron doping, it is believed that appropriate electrolysis parameters can diminish the toxicity effect without compromising the nutrient-removal and disinfection capability, although salinity of LLs and related multistep-oxidation pathways needs to be further elucidated.

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.

Superior selectivity of high-frequency ultrasound toward chorine containing-pharmaceuticals elimination in urine: A comparative study with other oxidation processes through the elucidation of the degradation pathways

This work considered the sonochemical degradation (using a bath-type reactor, at 375 kHz and 106.3 W L^-1, 250 mL of sample) of three representative halogenated pharmaceuticals (cloxacillin, diclofenac, and losartan) in urine matrices. The action route of the process was initially established. Then, the selectivity of the sonochemical system, to degrade the target pharmaceuticals in simulated fresh urine was compared with electrochemical oxidation (using a BDD anode, at 1.88 mA cm^-2), and UVC/H₂O₂ (at 60 W of light and 500 mol L^-1 of H₂O₂). Also, the treatment of cloxacillin in an actual urine sample by ultrasound and UVC/H₂O₂ was evaluated. More than 90% of the target compounds concentration, in the simulated matrix, was removed after 60 min of sonication. However, the sono-treatment of cloxacillin in the real sample was less efficient than in the synthetic urine. The ultrasonic process achieved 43% of degradation after 90 min of treatment in the actual matrix. In the sonochemical system, hydroxyl radicals in the interfacial zone were the main degrading agents. Meanwhile, in the electrochemical process, electrogenerated HOCl was responsible for the elimination of pharmaceuticals. In turn, in UVC/H₂O₂ both direct photolysis and hydroxyl radicals degraded the target pollutants. Interestingly, the degradation by ultrasound of the pharmaceuticals in synthetic fresh urine was very close to the observed in distilled water. Indeed, the sonodegradation had a higher selectivity than the other two processes. Despite the sono-treatment of cloxacillin was affected by the actual matrix components, this contrasts with the UVC/H₂O₂, which was completely inhibited in the real urine. The sonochemical process led to 100% of antimicrobial activity (AA) elimination after 75 min sonication in the synthetic urine, and ∼ 20% of AA was diminished after 90 min of treatment in the real matrix. The AA decreasing was linked to the transformations of the penicillin nucleus on cloxacillin, the region most prone to electrophilic attacks by radicals according to a density theory functional analysis. Finally, predictions of biological activity confirmed that the sono-treatment decreased the activity associated with cloxacillin, diclofenac, and losartan, highlighting the positive environmental impact of degradation of chlorinated pharmaceuticals in urine.

A review on disinfection technologies for controlling the antibiotic resistance spread

The occurrence of antibiotic-resistant bacteria (ARB) in water bodies poses a sanitary and environmental risk. These ARB and other mobile genetic elements can be easily spread from hospital facilities, the point in which, for sure, they are more concentrated. For this reason, novel clean and efficient technologies are being developed for allowing to remove these ARB and other mobile genetic elements before their uncontrolled spread. In this paper, a review on the recent knowledge about the state of the art of the main disinfection technologies to control the antibiotic resistance spread from natural water, wastewater, and hospital wastewater (including urine matrices) is reported. These technologies involve not only conventional processes, but also the recent advances on advanced oxidation processes (AOPs), including electrochemical advanced oxidation processes (EAOPs). This review summarizes the state of the art on the applicability of these technologies and also focuses on the description of the disinfection mechanisms by each technology, highlighting the promising impact of EAOPs on the remediation of this important environmental and health problem.

Irreversible inactivation of carbapenem-resistant Klebsiella pneumoniae and its genes in water by photo-electro-oxidation and photo-electro-Fenton - Processes action modes

Carbapenem-resistant Klebsiella pneumoniae is a critical priority pathogen according to the World Health Organization's classification. Effluents of municipal wastewater treatment plants (EWWTP) may be a route for K. pneumoniae dissemination. Herein, the inactivation of this microorganism in simulated EWWTP by the photo-electro-oxidation (PEO) and photo-electro-Fenton (PEF) processes was evaluated. Firstly, the disinfecting ability and action pathways of these processes were established. PEO achieved faster K. pneumoniae inactivation (6 log units in 75 min of treatment) than the PEF process (6 log units in 105 min of treatment). PEO completely inactivated K. pneumoniae due to the simultaneous action of UVA light, electrogenerated H₂O_2, and anodic oxidation pathways. The slower inactivation of K. pneumoniae when using PEF was related to interfering screen effects of iron oxides on light penetration and the diffusion of the bacteria to the anode. However, both PEO and PEF avoided the recovery and regrowth of treated bacteria (with no detectable increase in the bacteria concentration after 24 h of incubation). In addition to the bacteria evolution, the effect of treatment processes on the resistance gene was examined. Despite inactivation of K. pneumoniae by PEF was slower than by PEO, the former process induced a stronger degrading action on the gene, conferring the resistance to carbapenems (PEF had a Ct value of 24.92 cycles after 105 min of treatment, while PEO presented a Ct of 19.97 cycles after 75 min). The results of this research indicate that electrochemical processes such as PEO and PEF are highly effective at dealing with resistant K. pneumoniae in the EWWTP matrix.

Kinetics of the Organic Compounds and Ammonium Nitrogen Electrochemical Oxidation in Landfill Leachates at Boron-Doped Diamond Anodes

Electrochemical oxidation (EO) of organic compounds and ammonium in the complex matrix of landfill leachates (LLs) was investigated using three different boron-doped diamond electrodes produced on silicon substrate (BDD/Si)(levels of boron doping [B]/[C] = 500, 10,000, and 15,000 ppm—0.5 k; 10 k, and 15 k, respectively) during 8-h tests. The LLs were collected from an old landfill in the Pomerania region (Northern Poland) and were characterized by a high concentration of N-NH₄⁺ (2069 ± 103 mg·L⁻¹), chemical oxygen demand (COD) (3608 ± 123 mg·L⁻¹), high salinity (2690 ± 70 mg Cl⁻·L⁻¹, 1353 ± 70 mg SO₄²⁻·L⁻¹), and poor biodegradability. The experiments revealed that electrochemical oxidation of LLs using BDD 0.5 k and current density (j) = 100 mA·cm⁻² was the most effective amongst those tested (C_8h/C₀: COD = 0.09 ± 0.14 mg·L⁻¹, N-NH₄⁺ = 0.39 ± 0.05 mg·L⁻¹). COD removal fits the model of pseudo-first-order reactions and N-NH₄⁺ removal in most cases follows second-order kinetics. The double increase in biodegradability index—to 0.22 ± 0.05 (BDD 0.5 k, j = 50 mA·cm⁻²) shows the potential application of EO prior biological treatment. Despite EO still being an energy consuming process, optimum conditions (COD removal > 70%) might be achieved after 4 h of treatment with an energy consumption of 200 kW·m⁻³ (BDD 0.5 k, j = 100 mA·cm⁻²).

Effects of process factors on the performance of electrochemical disinfection for wastewater in a continuous-flow cell reactor

Although electrochemical disinfection has been shown to be an effective approach to inactivate bacteria in saline water, the effects of process parameters and reactor design for its application in low-salinity water have not been well understood. In this study, factorial experiments were performed to investigate the direct and confounded effects of applied current (5-20 mA), contact time (2.5-20 min), anode surface area (185-370 cm²), and chloride concentration (50-400 mg L^-1) on the disinfection efficiency in fresh water and the secondary effluent of municipal wastewater. An electrochemical disinfection reactor cell with an internal volume of 75 cm³ was designed and fabricated. Residence time distribution analysis showed that the internal mixing of the reactor is similar to that of a dispersed plug-flow reactor. All studied process parameters showed significant effect on the kill efficiency, with the applied current and contact time having the most dominant effect. Although the effect of chloride concentration, which is responsible for electrochemical production of free chlorine in water, is statistically significant, it is not as prominent as those reported for high salinity water. A synergistic effect between chloride concentration and anode surface area was identified, leading to high kill efficiency (99.9%, 3 log kill) at low current density (0.0135 mA cm^-2). Response surface modeling results suggested that a scaled-up disinfection reactor can be designed using large anode surface area with long contact time for high chloride water (400 mg L^-1) or high current density with short contact time for low chloride water (50 mg L^-1). The power requirement of a portable system treating 37.85 m³ day^-1 (10,000 gpd) of municipal wastewater was estimated to be 1.9 to 8.3 kW to achieve a 3 log kill, depending on the reactor design.

Degradation of hydroxychloroquine by electrochemical advanced oxidation processes

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

Cytotoxic aquatic pollutants and their removal by nanocomposite-based sorbents

Water is an extremely essential compound for human life and, hence, accessing drinking water is very important all over the world. Nowadays, due to the urbanization and industrialization, several noxious pollutants are discharged into water. Water pollution by various cytotoxic contaminants, e.g. heavy metal ions, drugs, pesticides, dyes, residues a drastic public health issue for human beings; hence, this topic has been receiving much attention for the specific approaches and technologies to remove hazardous contaminants from water and wastewater. In the current review, the cytotoxicity of different sorts of aquatic pollutants for mammalian is presented. In addition, we will overview the recent advances in various nanocomposite-based adsorbents and different approaches of pollutants removal from water/wastewater with several examples to provide a backdrop for future research.

Electro-Oxidation of Humic Acids Using Platinum Electrodes: An Experimental Approach and Kinetic Modelling

Humic acids (HA) are a potential hazard to aquatic ecosystems and human health. Because biological treatment of contaminated water does not satisfactorily remove these pollutants, novel approaches are under evaluation. This work explores electrochemical oxidation of HA in aqueous solution in a lab-scale apparatus using platinum-coated titanium electrodes. We evaluated the effects of HA concentration, current density, chloride concentration and ionic strength on the rate of HA oxidation. The initial reaction rate method was used for determining the rate law of HA degradation. The results showed that the reaction rate was first-order relative to HA concentration, chloride concentration and current density. An appreciable effect of ionic strength was also observed, most likely due to the polyanionic character of HA. We propose a kinetic model that satisfactorily fits the experimental data.

Comprehensive treatment of urban wastewaters using electrochemical advanced oxidation process

This study mainly focuses on the efficiency of anodic oxidation process (Ti/Sb-SnO₂/PbO₂ as anode and stainless steel as the cathode) in treating two different streams of urban wastewater, one from the influent of sequence batch reactor (WW1) and other from the effluent of constructed wetland (WW2). The effect of different operational parameters such as current density, hydraulic retention time, exposed electrode surface area, phosphorous, ammonia-nitrogen, nitrates, and coliform bacteria was studied. For an optimized current density of 30 mA/cm² and an electrode surface area of 30 cm², almost complete removal of COD and ammonia-nitrogen were achieved with both wastewaters (WW1 & WW2), while in case of phosphorous, 50% and 98% removal efficiencies were observed. Electrode deposition was analyzed using SEM-EDS and XRD, which confirms the presence of calcium and magnesium phosphates on the surface on the anode, which attributes to the phosphate removal. Electrochemical disinfection studies showed that complete inactivation of bacteria takes place within 30 min for WW1 and 60 min for WW2, and the cell morphological changes were studied using SEM analysis. Degradation of different micropollutants present in the wastewaters was evaluated with the aid of GC-MS. ICP - MS analysis confirmed that there was no leaching of lead from the anode surface, and the lead which is already present in the wastewater gets reduced to a permissible level, which further increases the treatment efficiency. Hence cleaner and comprehensive treatment of real urban wastewaters through anodic oxidation process was successfully demonstrated in this work.

Performance and mechanism of methylene blue degradation by an electrochemical process

An exciting electrochemical oxidation (EO) process has been developed. Compared with electro-Fenton (EF) and electro-coagulation (EC) processes, this process had more advantages in the degradation of methylene blue. It is observed that methylene blue can be quickly degraded by EO, in which an iron rod is used as an anode, graphite is used as a cathode, and fly ash-red mud particles are used as particle electrodes. Compared to EC and EF processes that are affected by specific pH values, EO has excellent performance in the pH range of 3.0-11.0. In addition, the electric energy consumption (EEC) of EF, EC and EO is 81.51, 36.55 and 21.35 kW h m-3 respectively, suggesting EO is more economical. The free radical scavenging mechanism of i-PrOH is studied, and the contribution of EC, EF and fly ash-red mud particle electrodes in EO is inferred. Particle electrodes before and after use are characterized by SEM, EDS and BET to illustrate the role of particle electrodes in the EO system. Analysis of flocs and solutions by FTIR and GC-MS proves that EO can effectively degrade methylene blue, and the degradation route of methylene blue is speculated. The particle electrode dissolution experiment shows that the prepared fly ash-red mud particle electrode is considered to be suitable and safe for wastewater treatment. Finally, in actual surface water experiments, the EO process still has great potential.

Electrolytic Oxidation as a Sustainable Method to Transform Urine into Nutrients

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