Inactivation of E. coli and E. faecalis by solar photo-Fenton with EDDS complex at neutral pH in municipal wastewater effluents

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

Effect of microplastics on urban wastewater disinfection and impact on effluent reuse: Sunlight/H2O2 vs solar photo-Fenton at neutral pH

The interference of three types of microplastics (MPs) on the inactivation of Escherichia coli (E. coli) by advanced oxidation processes (AOPs) (namely, sunlight/H2O2 and solar photo-Fenton (SPF) with Ethylenediamine-N,N'-disuccinic acid (EDDS)), in real secondary treated urban wastewater was investigated for the first time. Inactivation by sunlight/H2O2 treatment decreased as MPs concentration and H2O2 dose were increased. Noteworthy, an opposite behaviour was observed for SPF process where inactivation increased as MPs concentration was increased. Biofilm formation and microbial attachment on surfaces of post-treated MPs were observed on polyethylene (PE) and polyvinyl chloride (PVC) MPs by field emission scanning electron microscopy. In presence of PE MPs, a complete inactivation of E. Coli was achieved by SPF with EDDS (Fe:EDDS = 1:2) after 90 min treatment unlike of sunlight/H2O2 treatment (∼4.0 log reduction, 40 mg/L H2O2 dose, 90 min treatment). The lower efficiency of sunlight/H2O2 process could be attributed to the blocking/scattering effect of MPs on sunlight, which finally reduced the intracellular photo Fenton effect. A reduced E. coli regrowth was observed in presence of MPs. SPF (Fe:EDDS = 1:1) with PE MPs was less effective in controlling bacterial regrowth (∼120 CFU/100 mL) than sunlight/H2O2 (∼10 CFU/100 mL) after 48 h of post-treatment. These results provide useful information about possible interference of MPs on urban wastewater disinfection by solar driven AOPs and possible implications for effluent reuse.

Urban wastewater disinfection by iron chelates mediated solar photo-Fenton: Effects on seven pathogens and antibiotic resistance transfer potential

The effects of solar photo-Fenton (SPF) process mediated by the iron chelate Fe3+ imminodisuccinic acid (Fe:IDS) on both the inactivation of seven relevant pathogens and the potential for antibiotic resistance transfer (degradation of antibiotic resistance genes (ARGs) and after treatment regrowth), in real secondary treated urban wastewater, were investigated for the first time. A comparison with results obtained by sunlight/H2O2 process and Fe3+ ethylenediaminedisuccinic acid (Fe:EDDS) SPF was also carried out. ARGs were quantified by polymerase chain reaction (PCR) in samples before and after (3 h) the treatment. The persistence of the selected pathogens and ARGs was also evaluated in regrowth tests (72 h) under environmentally mimicking conditions. Fe:IDS SPF resulted to be more effective (from 1.4 log removal for Staphylococcus spp. to 4.3 log removal for Escherichia coli) than Fe:EDDS SPF (from 0.8 log removal for Pseudomonas aeruginosa to 2.0 log removal for Total coliphages) and sunlight/H2O2 (from 1.2 log removal for Clostridium perfringens to 3.3 log removal for E. coli) processes for the seven pathogens investigated. Potential pathogens regrowth was also severely affected, as no substantial regrowth was observed, both in presence and absence of catalase. A similar trend was observed for ARGs removal too (until 0.001 fold change expression for qnrS after 3 h). However, a poor effect and a slight increase in fold change was observed after treatment especially for gyrA, mefA and intl1. Overall, the effect of the investigated processes on ARGs was found to be ARG dependent. Noteworthy, coliphages can regrow after sunlight/H2O2 treatment unlike SPF processes, increasing the risk of antibiotic resistance transfer by transduction mechanism. In conclusion, Fe:IDS SPF is an attractive solution for tertiary treatment of urban wastewater in small wastewater treatment plants as it can provide effective disinfection and a higher protection against antibiotic resistance transfer than the other investigated processes.

Solar heterogeneous photo-Fenton for complete inactivation of Escherichia coli and Salmonella typhimurium in secondary-treated wastewater effluent

In this work, complete elimination of Escherichia coli and Salmonella typhimurium was achieved in 120 min using a heterogeneous photo-Fenton process under sunlight at pH 6.5 in distilled water. A face-centered composite central design 22 with one categoric factor and three replicates at the central point was used to evaluate the effect of iron (III) oxide concentration (0.8-3.4 mg L-1), H2O2 (2-10 mg L-1), and the type of iron oxide phase (maghemite and hematite) on the inactivation of both bacteria. The results showed that the amount of catalyst, H2O2 concentration and their interaction were significant factors (p < 0.05) in the elimination of the microorganisms. Thus, under the best conditions (3.4 mg L-1 of iron (III) oxide and 10 mg L-1 of H2O2) in the experimental ranges, complete inactivation of E. coli and S. typhimurium was achieved (6-log reduction) in 120 min using the photo-Fenton treatment with both iron-oxide phases. Furthermore, the photocatalytic elimination of both bacteria by the photo-Fenton process using hematite and maghemite in secondary-treated wastewater effluent was performed obtaining slower inactivation rates (1.2-5.9 times) than in distilled water due to the matrix effect of the effluent from a wastewater treatment plant. Nevertheless, the process continued to be effective in the effluent, achieving complete bacterial elimination in 150 min using the hematite phase. Additionally, the SEM images of the bacterial cells showed that the heterogeneous photo-Fenton treatment generated permanent and irreversible cell damage, resulting in complete cell death.

EDDS and polystyrene interactions: implications for soil health and management practices

Ethylenediamine-N,N'-disuccinic acid (EDDS) has been studied extensively for its potential use as an amendment in agriculture due to its numerous beneficial properties. The widespread usage of microplastics (MPs) poses a growing threat to plant growth. This study investigated the effects of Polystyrene MPs (PSMPs) and EDDS on soil pH, EC, organic matter (OM), available nutrients, and maize (Zea mays L.) growth in a calcareous soil. Results showed that both PS and EDDS had significant effects on soil pH, with higher concentrations leading to a decrease in pH. PSMPs negatively impacted soil health by increasing EC and decreasing OM, nitrogen (N), phosphorus (P), and potassium (K). EDDS had potential applications in soil remediation and phytoremediation by decreasing EC and increasing N, P, and K. The interaction between EDDS and PSMPs suggests that their effects on soil pH may be modulated by each other. The study highlights the potential negative impacts of high concentrations of PS on soil health and the potential benefits of using EDDS at lower concentrations in soil remediation and phytoremediation. However, further research is needed to understand the mechanisms and environmental impacts of EDDS and the combined effects of EDDS and PSMPs on soil properties and plant growth.

Application of Fe(III)–EDDS complexes and soybean peroxidase in photo-Fenton processes for organic pollutant removal: insights into possible synergistic effects

Photo-Fenton processes activated by biodegradable Fe(III)–EDDS complexes have attracted huge attention from the scientific community, but the operative mechanism of the photo-activation of H2O2 in the presence of Fe(III)–EDDS has not been fully clarified yet. The application of the Fe(III)–EDDS complex in Fenton and photo-Fenton (mainly under UV-B light) processes, using 4-chlorophenol (4-CP) as a model pollutant was explored to give insights into the operative mechanism. Furthermore, the potential synergistic contribution of soybean peroxidase (SBP) was investigated, since it has been reported that upon irradiation of Fe(III)–EDDS the production of H2O2 can occur. SBP did not boost the 4-CP degradation, suggesting that the possibly produced H2O2 reacts immediately with the Fe(II) ion with a quick kinetics that does not allow the diffusion of H2O2 into the bulk of the solution (i.e., outside the solvent cage of the complex). So, a concerted mechanism in which the photochemically produced H2O2 and Fe(II) react inside the hydration sphere of the Fe(III)–EDDS complex is proposed.

Graphical abstract

Nanomaterials photocatalytic activities for waste water treatment: a review

Water is necessary for the survival of life on Earth. A wide range of pollutants has contaminated water resources in the last few decades. The presence of contaminants incredibly different dyes in waste, potable, and surface water is hazardous to environmental and human health. Different types of dyes are the principal contaminants in water that need sudden attention because of their widespread domestic and industrial use. The toxic effects of these dyes and their ability to resist traditional water treatment procedures have inspired the researcher to develop an eco-friendly method that could effectively and efficiently degrade these toxic contaminants. Here, in this review, we explored the effective and economical methods of metal-based nanomaterials photocatalytic degradation for successfully removing dyes from wastewater. This study provides a tool for protecting the environment and human health. In addition, the insights into the transformation of solar energy for photocatalytic reduction of toxic metal ions and photocatalytic degradation of dyes contaminated wastewater will open a gate for water treatment research. The mechanism of photocatalytic degradation and the parameters that affect the photocatalytic activities of various photocatalysts have also been reported.

Simultaneous disinfection and microcontaminants elimination of urban wastewater secondary effluent by solar advanced oxidation sequential treatment at pilot scale

The effect of different times of Fe:Ethylenediamine-N, N'-disuccinic acid (EDDS) dosing and H₂O₂ as well as different Fe:EDDS concentrations in the sequential treatment sunlight/H₂O₂ followed by sunlight/H₂O_2/Fe:EDDS at circumneutral pH was investigated for the first time focusing both in contaminants of emerging concern (CECs) and bacteria removal in urban wastewater treatment plant effluents. Process efficiency was evaluated in terms of (i) degradation of five CECs (namely caffeine, carbamazepine, diclofenac, sulfamethoxazole and trimethoprim) at the initial concentration of 100 μgL^-1 each and (ii) bacteria inactivation (Escherichia coli (E. coli) and Salmonella spp). The effect of H₂O₂, Fe and EDDS concentration and Fe:EDDS dosing time was evaluated. 60% removal of the sum of total CECs and pathogens inactivation below the detection limit (DL) were observed by the sequential treatment with Fe:EDDS additions at 60 min and 45 min in simulated urban wastewater effluent. Sequential treatment was validated in actual urban wastewater effluent, being able to remove 60% of the target CECs and inactivate bacteria below the DL. Increasing EDDS concentration negatively affected Salmonella spp inactivation. Sequential treatment based on 120 min of sunlight/H₂O₂ (50 mg L^-1) and subsequent SPF with Fe:EDDS (0.1:0.1 mM) was chosen as best operation conditions for full scale treatment in urban wastewater treatment plants.

Disinfection of roof harvested rainwater inoculated with E. coli and Enterococcus and post-treatment bacterial regrowth: Conventional vs solar driven advanced oxidation processes

Solar driven advanced oxidation processes (AOPs) (an alternative solar photo Fenton like process (SPF), sunlight/H₂O₂ (SHP) and sunlight/chlorine (SCL)) and respective dark conditions, were compared for the first time to conventional (chlorination and UV-C radiation) disinfection processes, in the inactivation of E. coli and Entero strains inoculated in real roof-harvested rainwater (RHRW), to evaluate their possible safe use for crop irrigation. In this regard, bacterial regrowth was also evaluated 6, 12, 24 and 48 h after disinfection treatment. The SPF, using iminodisuccinic acid (IDS)-Cu complex as catalyst, was optimized (H₂O₂/IDS-Cu 55/1 best molar ratio) under mild conditions (spontaneous pH) and sunlight. The faster inactivation kinetics were observed for the SCL process (k = 1.473 min^-1, t_1/2 = 0.47 min for E. coli and k = 1.193 min^-1, t_1/2 = 0.57 min for Entero), while the most effective processes in controlling bacterial regrowth were SPF and SCL. Although UV-C radiation (0-1.3 × 10⁴ μW s cm^-2 dose range) was the second faster disinfection process (k = 1.242 min^-1, t_1/2 = 0.55 min for E. coli and k = 1.150 min^-1, t_1/2 = 0.60 min for Entero), it was the less effective process in controlling bacterial regrowth (>10 CFU 100 mL^-1 already after 6 h post-treatment incubation). According to the bacterial inactivation and regrowth tests carried out in this work, SPF and SCL are interesting options for RHRW disinfection, in case of effluent use for crop irrigation.

Sunlight advanced oxidation processes vs ozonation for wastewater disinfection and safe reclamation

Solar processes (sunlight/H₂O_2, solar photo-Fenton with EDDS at neutral pH) were compared to a consolidated technology (ozonation) in the inactivation of target bacteria (E. coli, Salmonella spp. and Enterococcus spp.) under realistic conditions (real secondary treated urban wastewater (WW), pilot scale reactors, natural sunlight) to evaluate their possible industrial application. The highest bacteria inactivation rate (all the target pathogens were inactivated below the detection limit (DL) (100 CFU/100 mL) within 45 min treatment) was observed for ozonation (83 mgO₃/L h). Similar inactivation behavior for all bacteria was observed for sunlight/H₂O₂ (50 mg/L) and solar photo-Fenton (SPF) with EDDS (1:1 molar ratio, 0.1 mM of Fe and 50 mg/L of H₂O₂). Although the DL was not reached, faster inactivation kinetics (0.007, 0.013 and 0.002 1/min for E. coli, Salmonella spp. and Enterococcus spp., respectively) and lower bacterial concentration after a 180 min treatment were observed for sunlight/H₂O₂ process compared to SPF (0.005, 0.01 1/min and no inactivation, respectively), Enterococcus spp. being the higher resistance microorganism. The negative effect of carbonates on disinfection performance was also evaluated. Quantitative microbial risk assessment for the ingestion of lettuce irrigated with untreated and treated WW was estimated. Disinfection by ozonation and sunlight/H₂O₂ processes were found to drastically decrease the associated microbiological risk (the mean risk of illness decreased from 0.10 (untreated) to 1.35 × 10^-4 (treated) for E. coli and from 0.03 to 2.21 × 10^-6 for Salmonella).

Mixtures of chelating agents to enhance photo-Fenton process at natural pH: Influence of wastewater matrix on micropollutant removal and bacterial inactivation

Three organic fertilizers (EDTA (Ethylenedinitrilotetraacetic acid), EDDS (Ethylenediamine-N, N'-disuccinic acid) and DTPA (Diethylene triamine pentaacetic acid)) were tested as Fe-complexes in photo-Fenton process at natural pH for micropollutants (MPs) abatement and simultaneous E.coli inactivation. Less stable Fe-complexes show high iron precipitation, stopping MPs degradation. On the contrary, stable Fe-complexes imply low kinetic rates for MPs removal. To solve these inconveniences, three mixtures of organic fertilizers were also tested, trying to improve the kinetic rates of micropollutants oxidation and overcome iron precipitation. Three different pollutants (propranolol (PROP), acetamiprid (ACMP) and sulfamethoxazole (SMX)) were used as the target compounds. As the iron release is, in part, linked to the hardness of water, two water matrices from two different secondary wastewaters (Membrane Bioreactor (MBR) and Conventional Activated Sludge (CAS)) were tested. The best performance in micropollutant degradation and E.coli inactivation was achieved with the combination of EDDS + EDTA, accomplishing a good equilibrium between iron precipitation and rate of MPs removal. For instance, total removal of propranolol was achieved at 45 min in MBR, while it was only 85.7% in CAS, being an improvement of the process comparing with that obtained using single organic fertilizers. At the end of the treatment, 2.1 log-inactivation for E.coli was reached in CAS. The differences observed between both wastewaters were related to CAS' higher DOC, turbidity, and hardness. Finally, from the physicochemical characterization conducted, including Biochemical Oxygen Demand at 5 days and phytotoxicity, it is possible to highlight the suitability of these treated effluents for its reuse in irrigation, as long as in CAS matrix the final values of E. coli are within the legal limit.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Microcystis aeruginosa inactivation and microcystin-LR degradation by the photo-Fenton process at the initial near-neutral pH

Of all cyanobacteria, Microcystis aeruginosa is the most commonly found species in bloom episodes all over the world. This species is known to produce cyanopeptides with hepatotoxic effects, namely microcystins (MCs). In this regard, Advanced Oxidation Processes (AOPs) have been widely studied for cyanotoxin degradation, but very few studies focused on cyanobacteria inactivation combined with toxin removal. To our knowledge, this is the first report of the photo-Fenton process application focusing on M. aeruginosa inactivation and microcystin-LR (MC-LR) degradation. This research work aimed to evaluate the photo-Fenton process under three different conditions with regard to Fe2+/H2O2 ratios (0.6/10, 5/50, and 20/100 mg L-1) at the initial near-neutral pH. Process efficiency was measured by immediate cell density reduction, growth inhibition, effect on MC-LR concentrations, and scanning electron microscopy (SEM) to analyze any alterations in cell morphology. Growth inhibition test (GIT) results pointed to cell inactivation under all conditions tested, and MC-LR concentrations were reduced below WHO's maximum limit at medium and higher concentrations of reagents. The possible mechanisms of cell inactivation by oxidative species are discussed.

Simultaneous removal of antibiotic resistant bacteria, antibiotic resistance genes, and micropollutants by a modified photo-Fenton process

Although photo-driven advanced oxidation processes (AOPs) have been developed to treat wastewater, few studies have investigated the feasibility of AOPs to simultaneously remove antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and micropollutants (MPs). This study employed a modified photo-Fenton process using ethylenediamine-N,N'-disuccinic acid (EDDS) to chelate iron(III), thus maintaining the reaction pH in a neutral range. Simultaneous removal of ARB and associated extracellular (e-ARGs) and intracellular ARGs (i-ARGs), was assessed by bacterial cell culture, qPCR and atomic force microscopy. The removal of five MPs was also evaluated by liquid chromatography coupled with mass spectrometry. A low dose comprising 0.1 mM Fe(III), 0.2 mM EDDS, and 0.3 mM hydrogen peroxide (H₂O₂) was found to be effective for decreasing ARB by 6-log within 30 min, and e-ARGs by 6-log within 10 min. No ARB regrowth occurred after 48-h, suggesting that the proposed process is an effective disinfectant against ARB. Moreover, five recalcitrant MPs (carbamazepine, diclofenac, sulfamethoxazole, mecoprop and benzotriazole at an initial concentration of 10 μg/L each) were >99% removed after 30 min treatment in ultrapure water. The modified photo-Fenton process was also validated using synthetic wastewater and real secondary wastewater effluent as matrices, and results suggest the dosage should be doubled to ensure equivalent removal performance. Collectively, this study demonstrated that the modified process is an optimistic 'one-stop' solution to simultaneously mitigate both chemical and biological hazards.

Simultaneous removal of contaminants of emerging concern and pathogens from urban wastewater by homogeneous solar driven advanced oxidation processes

Simultaneous removal of contaminants of emerging concern and bacteria inactivation in simulated municipal wastewater effluent (SMWW) through solar advanced oxidation processes, namely sunlight/H₂O₂ and solar photo-Fenton with Ethylenediamine-N,N'-disuccinic acid (EDDS) at neutral pH was investigated. Process efficiency was evaluated in terms of (i) degradation of five contaminants of emerging concern (CECs, namely caffeine, carbamazepine, diclofenac, sulfamethoxazole and trimethoprim) at the initial concentration of 100 μgL^-1 each and (ii) bacteria inactivation (E. coli, S. enteritidis and E. faecalis), at the initial concentration of 10³ CFU mL^-1 each. Solar photo-Fenton process was first investigated at lab scale in a solar simulator to evaluate the effect of iron concentration (0.1 mM and 0.05 mM) and Fe:EDDS ratio (1:2 and 1:1). Subsequently, sunlight/H₂O₂ and solar photo-Fenton with EDDS (molar ratio 1:1, Fe(III) 0.1 mM) at neutral pH were singularly and sequentially investigated at pilot scale in a raceway pond reactor. Sunlight/H₂O₂ (50 mg L^-1) tests resulted in total bacteria inactivation in 60 min (0.69 kJ L^-1) but low CECs removal efficiency. On the opposite, solar photo-Fenton was effective in the removal of the total CECs (87% removal after 20 min and 0.14 kJ L^-1) but not in E. faecalis inactivation (the initial concentration did not change even after 180 min). However, when the two processes were operated sequentially, a complete bacteria inactivation was observed in 15 min (0.17 kJ L^-1), 20 min (0.23 kJ L^-1) and 60 min (0.70 kJ L^-1) of treatment for E. coli, S. enteritidis and E. faecalis, respectively and 80% removal of total CECs was achieved after 10 min of Fe:EDDS addition. Sequential combination of sunlight/H₂O₂ and solar photo-Fenton would be an effective solution for simultaneous CECs removal and bacteria inactivation in the same photo-reactor.

Photo Augmented Copper-based Fenton Disinfection under Visible LED Light and Natural Sunlight Irradiation

Copper-based Fenton disinfection system (Cu(II)/H₂O₂) is an emerging advanced oxidation process (AOP). Previous works have used reducing agents and organic ligands to improve the disinfection efficiency of Cu(II)/H₂O₂ system. Here, we report visible light/Cu(II)/H₂O₂ system showed enhanced disinfection compared to Cu(II)/H₂O₂ system, without the need of reducing chemical agent or organic ligand. Energy-efficient LED array was used as a visible light source in the visible light/Cu(II)/H₂O₂ system. Under the optimized condition, pseudo-first-order inactivation rate constant (k_obs) of E. coli by visible light/Cu(II)/H₂O₂ (0.613 ± 0.005 min^-1) was about ~8 times greater than Cu(II)/H₂O₂ (0.08 ± 0.011 min^-1). Scanning electron microscopy and Baclight Live/Dead assay proved enhanced cell membrane damage by visible light/Cu (II)/H₂O₂ in comparison with Cu(II)/H₂O₂. Based on the bovine serum albumin (BSA) degradation and OH˙ radical measurement by visible light/Cu(II)/H₂O₂, a ligand to metal charge transfer (LMCT) mechanism by Cu(II)-bacterial complex is proposed for enhanced disinfection. Electrical energy efficiency (E _E,1) for a log reduction of E. coli and the total treatment cost of visible light/Cu(II)/H₂O₂ was determined to be 32.64 KWh/m³ and 350 ₹/m³ (3.9 €/m³ or 4.74 $/m³), respectively, indicating its cost-effectiveness. Disinfection efficiency by sunlight/Cu(II)/H₂O₂ system (solar irradiance; 746 ± 138 W/m²) was almost comparable to LED-based visible light/Cu(II)/H₂O₂ system, with total treatment cost estimated to be 80 ₹/m³ (0.9 €/m³ or 1.1 $/m³).

Are iron chelates suitable to perform photo-Fenton at neutral pH for secondary effluent treatment?

There have been concerns about which iron chelate is most suitable for application in the photo-Fenton process as well as the fate of these chelates after application. In this study, five chelating agents, i.e. citric acid (CA), oxalic acid (OA), ethylenediamine disuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), representing the most used iron chelates were assessed for suitability of application in homogeneous photo-Fenton-like process at pH of 7. The efficiency of the iron chelates were assessed in the disinfection of secondary effluent. The results for the disinfection and bacteria regrowth followed the order EDTA>OA>NTA>CA>OA. All the iron chelates were observed to have increased the COD of the effluent with EDDS having the highest COD contribution. The ability of the chelates to remove aromaticity was measured by the UV₂₅₄ measurement. The efficiency of the chelates to remove aromaticity decreased in the order CA>EDDS>NTA>CA>OA. To determine the fate of the chelates, toxicity tests were conducted on the chelates before and after irradiation and the results revealed a decrease in toxicity after photoirradiation, implying the chelates were degraded and the products/intermediates produced were of less toxicity as compared to the parent compounds.

Iron oxide-mediated photo-Fenton catalysis in the inactivation of enteric bacteria present in wastewater effluents at neutral pH

The pressure on natural water resources associated with increasing water scarcity highlights the value of using reclaimed water through the development of efficient and environmentally friendly treatment technologies. In this work, the use of magnetic nanoparticles in photo-Fenton catalysis for water disinfection was considered to inactivate natural enteric bacteria present in municipal wastewater effluents under white light and neutral pH. The most recommended ranges were evaluated in key variables such as the loading and composition of nanoparticles (NPs), hydrogen peroxide (H₂O₂) concentration, the light source (UV and visible) and treatment time were evaluated in wastewater disinfection expressed in terms of total coliforms and Escherichia coli colony forming units (CFU). The magnetic separation of NPs allowed the disinfection process to be carried out in different cycles, facilitating the recovery of the nanocatalyst and avoiding its discharge with the treated effluent.

Mechanistic insights into a novel nitrilotriacetic acid-Fe0 and CaO2 process for efficient anaerobic digestion sludge dewatering at near-neutral pH

Traditional Fenton or Fenton-like oxidation has been widely studied for waste activated sludge dewaterability. However, the narrow pH range (2.0-4.0) and the instabilities of Fe²⁺ and H₂O₂ have hindered its commercial application. Owing to the high alkalinity of anaerobic digestion (AD) sludge, traditional Fenton or Fenton-like oxidation is economically unfeasible for its dewatering. In this study, we successfully demonstrated a novel and feasible method that used nitrilotriacetic acid (NTA)-Fe⁰ combined with CaO₂ (NTA-Fe⁰/CaO₂) at near-neutral pH (∼6.0) (a slight pH adjustment) in which capillary suction time ratio (CST₀/CST) and centrifuged weight reduction (CWR) improved by 6 folds and 42.98 ± 0.37%, respectively, under the optimal conditions. The presence of NTA accelerated the Fe⁰ corrosion, Fe²⁺ stability and turnover between Fe²⁺ and Fe³⁺. As such, Fe⁰ could effectively catalyze CaO₂ to produce hydroxyl radicals (•OH) under near-neutral conditions. Accordingly, various molecular weight hydrophilic compounds in different extracellular polymeric substances fractions were significantly reduced after treatment. The hydrophilic functional groups especially protein molecules were largely reduced. Consequently, the viscosity of sludge and particle size effectively decreased, while the release of bound water, surface charge, flocculation, and flowability of sludge were improved. The cost-benefit analysis further demonstrated the NTA-Fe⁰/CaO₂ treatment has high reusability and stability and is also more economical over the FeCl₃/CaO and Fenton's reagent/CaO treatments. In summary, the NTA-Fe⁰/CaO₂ process is a cost-effective and practically feasible technology for improving AD sludge dewaterability.

Efficient inactivation of antibiotic resistant bacteria and antibiotic resistance genes by photo-Fenton process under visible LED light and neutral pH

Antibiotic resistance has been recognized as a major threat to public health worldwide. Inactivation of antibiotic resistant bacteria (ARB) and degradation of antibiotic resistance genes (ARGs) are critical to prevent the spread of antibiotic resistance in the environment. Conventional disinfection processes are effective to inactivate water-borne pathogens, yet they are unable to completely eliminate the antibiotic resistance risk. This study explored the potential of the photo-Fenton process to inactivate ARB, and to degrade both extracellular and intracellular ARGs (e-ARGs and i-ARGs, respectively). Using Escherichia coli DH5α with two plasmid-encoded ARGs (tetA and bla_TEM-1) as a model ARB, a 6.17 log ARB removal was achieved within 30 min of applying photo-Fenton under visible LED and neutral pH conditions. In addition, no ARB regrowth occurred after 48-h, demonstrating that this process is very effective to induce permanent disinfection on ARB. The photo-Fenton process was validated under various water matrices, including ultrapure water (UPW), simulated wastewater (SWW) and phosphate buffer (PBS). The higher inactivation efficiency was observed in SWW as compared to other matrices. The photo-Fenton process also caused a 6.75 to 8.56-log reduction in eARGs based on quantitative real-time PCR of both short- and long amplicons. Atomic force microscopy (AFM) further confirmed that the extracellular DNA was sheared into short DNA fragments, thus eliminating the risk of the transmission of antibiotic resistance. As compared with e-ARGs, a higher dosage of Fenton reagent was required to damage i-ARGs. In addition, the tetA gene was more easily degraded than the bla_TEM-1 gene. Collectively, our results demonstrate the photo-Fenton process is a promising technology for disinfecting water to prevent the spread of antibiotic resistance.

Visible light plays a significant role during bacterial inactivation by the photo-fenton process, even at sub-critical light intensities

The aim of this research is to clarify the contribution of sunlight wavelengths, irradiance and Fe²⁺/H₂O₂ during bacterial disinfection by the photo-Fenton process in clear surface waters. We considered different solar spectrum distributions (visible, UVA-Visible), sub-critical irradiances (0-400 W/m²), focusing on the action modes of E. coli inactivation by the constituents involved in the composite process, at low μM reactants concentration (Fe²⁺/H₂O₂) in in ultrapure (MQ) water. We report that solar disinfection improved with Fenton reagents (photo-Fenton process) is a reality from very low light irradiance values (200 W/m²), and made possible even without the presence of UVA radiation, even when using low quantities of the Fenton reagents (0.5 mg/L Fe²⁺, 5 mg/L H₂O₂). Under light exposure, H₂O₂ was found to augment the intracellular Fenton process and Fe²⁺ to initiate further, distinct oxidative actions. Finally, validation was performed in Lake Geneva water over a wider irradiance range, where the photo-Fenton process was found to be reagent-dependent in low irradiance, shifting to light-driven in the higher values.

Hybrid Material Based on an Amorphous-Carbon Matrix and ZnO/Zn for the Solar Photocatalytic Degradation of Basic Blue 41

Innovative composites based on an amorphous-carbon matrix containing a second phase ZnO oxide and/or highly dispersed Zn metallic were synthesized via a modified Pechini route, in which a partial pyrolysis method was reached. Studies of adsorption in the dark and the photocatalytic activity for the cationic azo-dye, basic blue 41, and degradation were carried out. X-ray diffraction patterns for the carbon matrix and its composite with Zn show characteristics of the amorphous carbon. The infrared in the mid region of the composite prepared with ZnO and Zn exhibit vibrational bands related to bonds zinc oxide. The surface pH of the material is the main factor responsible for the adsorption of the azo-dye, but the contribution of mesopores favored the diffusion of molecules from the bulk of solution to the pore framework. Esters-like functional groups on the surface of carbons hinder the adsorption of the azo-dye. When Zn is embedded within amorphous carbon the photocatalytic activity of the composites showed up to 2.4 higher than neat ZnO. The enhancement in the photocatalytic activity and stability of C/ZnO/Zn and C/Zn composites is discussed in terms of a protector effect by the carbon layers inserted in composites. Carbon layers are responsible to inhibit the lixiviation of ZnO particles along irradiation.

Efficient bacteria inactivation by ligand-induced continuous generation of hydroxyl radicals in Fenton-like reaction

Fenton/Fenton-like reaction is often used as an efficient method to generate hydroxyl radicals (HO) for bacteria inactivation in aqueous solution. However, inactivation efficiency of bacteria in aqueous solution using Fenton/Fenton-like reactions needs to further improve as a result of transient generation of HO. In this paper, we found that the formation of Tris-Co(II) complexes could decrease the redox potential of Co(III)/Co(II), facilitating the transformation of Tris-Co(III) complexes into Tris-Co(II) complexes. Therefore, HO could be generated continuously in the presence of H₂O₂. Especially, Tris-Co(II) complexes are apt to combine with Escherichia Coli cells by electrostatic interactions, inducing a higher utilization ratio of the generated HO. Therefore, the proposed Tris-Co(II) complex-H₂O₂ system could be employed as a high-efficiency sterilizing reagent for inactivation of E. Coli. This work provides a promising strategy for bacterial inactivation via an economic and eco-friendly manner.

Solar Concentration for Wastewaters Remediation: A Review of Materials and Technologies

As the effectiveness of conventional wastewater treatment processes is increasingly challenged by the growth of industrial activities, a demand for low-cost and low-impact treatments is emerging. A possible solution is represented by systems coupling solar concentration technology with advanced oxidation processes (AOP). In this paper, a review of solar concentration technologies for wastewater remediation is presented, with a focus on photocatalyst materials used in this specific research context. Recent results, though mostly on model systems, open promising perspectives for the use of concentrated sunlight as the energy source powering AOPs. We identify (i) the development of photocatalyst materials capable of efficiently working with sunlight, and (ii) the transition to real wastewater investigation as the most critical issues to be addressed by research in the field.