Solar-driven Advanced Oxidation Processes Research Articles

Ozonation Vs sequential solar driven processes as simultaneous tertiary and quaternary treatments of urban wastewater: A life cycle assessment comparison

Solar driven advanced oxidation processes (S-AOPs) have been successfully investigated in the last years as tertiary and quaternary treatment of urban wastewater for simultaneous inactivation of microorganisms and removal of contaminants of emerging concern (CECs), respectively. However, the lack of data about the comparison with consolidated technologies, including also the evaluation of their impact on the environment, has contributed to humper their application at full scale so far. In this study, the environmental impact of a new S-AOP, namely sequential treatment (ST) with sunlight/H2O2 and solar photo-Fenton (SPF) at neutral pH (using Ethylenediamine-N, N′-disuccinic acid (EDDS) as chelating agent) operated at pilot scale in a raceway pond reactor, was compared to a pilot scale ozonation (O3) treatment unit in terms of simultaneous bacteria inactivation and CECs removal, through a Life Cycle Assessment (LCA). Different urban wastewater treatment plant (UWWTP) sizes and scenarios (namely effluent disposal and reuse) were evaluated. While the reuse scenario resulted in a higher impact compared to the disposal scenario in the construction/deconstruction phase, due to the more stringent limits that resulted in longer treatment time and a higher consumption of raw materials, the positive impact on water resources saving compared to disposal makes the reuse scenario a more sustainable solution. Despite O3 disinfection by-products were taken into account, ST resulted in a higher toxicity to human health (0.27·10−9 DALYs Vs 2.11 10−9 DALYs, respectively) due to the higher residual concentration of the target CECs. However, it is noteworthy that both values are significantly lower than the acceptable DALYs value (≤10−6). Chemicals, energy, groundwater consumption and residual CECs can affect resources 1125 and 1874 times more for O3 treatment than for the ST, for disposal and reuse scenarios, respectively. The total impact of O3 on the human health was 13 and 19 times higher compared to ST, for disposal and reuse scenarios, respectively, due to the higher energy and chemical consumption. According to the LCA results, ST resulted in a better overall environmental performance compared to O3 and it is a more sustainable and attractive solution in particular for small UWWTPs.

Photocatalytic application of a phosphonate-based metal-organic framework for the removal of bisphenol A under natural sunlight

Photocatalytic removal of bisphenol A, one of the most widely and emerging pollutants in the aquatic environment, was investigated by advanced oxidation process under natural sunlight. The removal process by a metal-organic framework, synthesized with phosphonic acid ligand, namely STA-12 (Fe) and hydrogen peroxide revealed excellent results. Therefore, the optimal conditions for the degradation of bisphenol A by the photo-Fenton mechanism were studied. The removal process follows the first-order kinetics with respect to the contaminant and a significant synergy was observed in the catalytic system of hydrogen peroxide/sunlight/STA-12 (Fe). The Optimal values for pH, irradiation time, catalyst amount and H2O2 dosage for oxidation of bisphenol A in 30 mg / l aqueous solution were determined to be 5, 90 minutes, 10 mg and 12 μl, respectively. Under these conditions, the best removal efficiency was 79.8%. Also, the mineralization value of organic pollutant was determined to equal 51% by measuring TOC. To determine the most important species that affected the photocatalytic reduction, trapping experiments were carried out, using various kinds of scavengers and the results showed that the hydroxyl radicals (•OH) are the main oxidizing agent in the photocatalytic system and superoxide radical and the holes in the photocatalyst surface are less involved in the process of contaminant degradation. Finally, a probable reaction mechanism has been investigated in detail. In addition, the catalyst has recyclability and stability in the photocatalytic reaction. This study is the first report for application of a phosphonate-based MOF for the removal of an emerging pollutant with a photo-Fenton mechanism and presents a new example of solar-driven advanced oxidation process for the treatment of aquatic sources and environmental protection.

Inactivation of simulated aquaculture stream bacteria at low temperature using advanced UVA- and solar-based oxidation methods

In this work the effect of water temperature (6 ± 1 °C and 22 ± 1 °C) on inactivation of bacteria (104 –106 CFU mL−1; Pseudomonas spp., Aeromonas spp. and Enterobacter spp.) in simulated aquaculture streams (SAS) using UVA based advanced oxidation processes (AOP) (H2O2-assisted UVA; photocatalysis; H2O2-assisted photocatalysis) and solar driven AOPs (H2O2-assisted solar disinfection, SODIS) was studied. Efficiency at 22 °C in terms of inactivation rate was higher using H2O2-assisted photocatalysis (H2O2/UVA-TiO2/polysiloxane) > H2O2-assisted UVA disinfection (UVA/H2O2 – 10 mg L-1) > photocatalysis (UVA-TiO2/polysiloxane) > UVA disinfection. At low temperature (6 °C) the inactivation rate increased with SODIS/H2O2 > SODIS > H2O2-assisted UVA disinfection (UVA/H2O2 – 10 mg L-1) > H2O2-assisted photocatalysis (H2O2/UVA-TiO2/polysiloxane) > photocatalysis (UVA-TiO2/polysiloxane). The main results indicate that the inactivation rates increased when hydrogen peroxide (10 mg L-1) was used during H2O2-assisted UVA disinfection and photocatalysis. In addition, exposure of SAS to hydrogen peroxide for 24 h (in absence of light) at room temperature decreased the subsequent exposure UVA irradiation dose by almost four times.Drastic increase of inactivation rate was observed at low water temperature (6 ± 1 °C) when UVA- and solar-based AOPs were employed compared to 22 ± 1 °C. The treatment with SODIS proved to be more effective in Finland than in Spain. The effect of the low temperature (6 ± 1 °C) was proposed as a critical factor during UVA disinfection (UVA/H2O2 and photocatalysis) that can increase the disinfection rate constant (kmax) by 1.3–5.2 times, leading to a reduction of the treatment costs (€ m−3) by 1.3–3.3 times. The mechanism of observed enhanced disinfection at low water temperature (6 ± 1 °C) when natural solar light and UVA are employed as irradiation sources for UVA/H2O2 and photocatalytic bacteria inactivation was proposed. No regrowth was observed in case of H2O2-assisted AOPs.

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, t1/2 = 0.47 min for E. coli and k = 1.193 min−1, t1/2 = 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, t1/2 = 0.55 min for E. coli and k = 1.150 min−1, t1/2 = 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.

Oxidative degradation and mineralization of the endocrine disrupting chemical bisphenol-A by an eco-friendly system based on UV-solar/H2O2 with reduction of genotoxicity and cytotoxicity levels

A solar-driven advanced oxidation process at a lab scale was studied for the degradation and mineralization of the known endocrine disrupting chemical (EDC), bisphenol A (BPA). Preliminary tests were performed varying the irradiation source, BPA/H2O2 ratio, temperature, initial H2O2 concentration, initial solution pH, and initial BPA concentration, then, the operational conditions of the UV-solar/H2O2 were optimized by a response surface methodology (RSM), providing the following responses: UV-solar/H2O2 process at pH 3.0, [BPA]0 = 25 mg L−1, [H2O2] = 350 mg L−1, T = 50 °C, achieving BPA degradation of 77.4% and BPA mineralization of 38.2%, H2O2 consumption of 230 mg L−1. From the optimized condition, different pH ranges were tested (3.0; 5.0; 7.0; 9.0; and 11.0), where, at solution pH 5.0 the best removal rates were achieved (89.2% BPA degradation and 49.0% BPA mineralization). The BPA amount in solution was monitored by High Performance Liquid Chromatography (HPLC) and a study of the intermediate reaction by-products was performed by Gas Chromatography–Mass Spectrometry (GC–MS) analyses, highlighting the lower amount of by-products identified when the solution pH 5.0 was employed, rather than the solution pH 3.0. Genotoxicity tests with Zebrafish (Danio rerio) and cytotoxicity tests with Allium cepa were performed aiming to evaluate errors in the cells and nuclear abnormalities of the tested organisms induced by BPA raw samples, as well as by the BPA samples treated by the UV-solar/H2O2 process. Therefore, the bio-toxicity levels for an animal and a vegetal bio-indicator were reduced by applying a renewable source of energy as the irradiation source for the UV/H2O2 process, representing an efficient and eco-friendly alternative for BPA treatment in aqueous solutions.

Stormwater herbicides removal with a solar-driven advanced oxidation process: A feasibility investigation

The solar driven advanced oxidation process (AOP) has the potential to be developed as a passive stormwater post-treatment method. Despite its widespread studies in wastewater treatment, the applicability of the process for micropollutant removal in stormwater (which has very different chemical properties from wastewater) is still unknown. This paper investigated the feasibility of three different AOP processes for the degradation of two herbicides (diuron and atrazine) in pre-treated stormwater: (i) photoelectrochemical oxidation (PECO), (ii) electrochemical oxidation (ECO), and (iii) photocatalytic oxidation (PCO). The durability of different anode materials, the effects of catalyst loading, and solar photo- and thermal impacts under different applied voltages were studied. Boron-doped diamond (BDD) was found to be the most durable anode material compared to carbon fiber and titanium foil for long-term operation. Due to the very low electroconductivity of stormwater, a high voltage was required, causing severe oxidation of the carbon fiber material. PECO achieved the best degradation results compared to ECO and PCO, with over 90% degradation of both herbicides in 2 h under 5 V, following a first-order decay process (with a half-life value of 0.40 h for diuron and 0.58 h for atrazine). The voltage increase had a positive impact on the oxidation processes, with 5 V found to be the optimal applied voltage, while catalyst loading had a negligible effect. Interestingly, the solar thermal effect plays a dominant role in enhancing the performance of the PECO process, which indicates the potential of integrating a photovoltaic chamber with a PECO system to harness both the light and heat of solar energy for stormwater treatment.

Comparison between heterogeneous and homogeneous solar driven advanced oxidation processes for urban wastewater treatment: Pharmaceuticals removal and toxicity

The release of toxic contaminant of emerging concern from urban wastewater treatment plants (UWTPs) into the environment calls for more effective (tertiary) treatment methods. In this manuscript, homogeneous solar-driven advanced oxidation processes (AOPs), namely H2O2/sunlight, solar photo-Fenton (Fe+2/H2O2/sunlight) and solar photo-Fenton with ethylenediamine-N,N'-disuccinic acid (EDDS) complex (Fe+2/H2O2/EDDS/sunlight) were compared to a new heterogeneous process (supported nitrogen-doped TiO2 (N-TiO2)/sunlight), with the aim of contributing to fill the gap between lab scale tests and full scale applications as well as to provide a sustainable solution for tertiary treatment in small UWTPs. Process efficiency was evaluated in terms of effluent toxicity and degradation of a mixture of three pharmaceuticals (namely carbamazepine (CBZ), diclofenac and trimethoprim), at initial concentration of 200 µg/L each, in deionized water (DW) and real wastewater (WW). Fe2+/H2O2/EDDS/sunlight was found to be the most effective process (98% removal of CBZ from WW in 60 min, 5.6 kJ/L as cumulative solar energy per unit of volume). Conventional solar photo Fenton was drastically and negatively affected by water matrix, due to the spontaneous neutral pH and iron precipitation in real WW. Although N-TiO2/sunlight process was not so affected by water matrix, it was found to be less efficient (30% removal of CBZ in 180 min, 13.3 kJ/L) than Fe2+/H2O2/EDDS/sunlight process. Toxicity values were found to be lower in WW compared to DW matrix. Class weight scores for WW samples showed a toxicity reduction up to the no acute toxicity level for N-TiO2/sunlight and Fe2+/H2O2/EDDS/sunlight treatments, while H2O2/sunlight and Fe2+/H2O2/sunlight increased the final effluent toxicity up to slightly acute levels.

Innovative Treatment of Organic Contaminants in Reverse Osmosis Concentrate from Water Reuse: a Mini Review

Reverse osmosis concentrate (ROC) from wastewater reclamation in water reuse retains concentrated toxic bio-refractory organics, and developing technologies for their removal is essential. This paper reviews innovative treatment technologies for organic contaminants in the ROC, and treatment options for applications are proposed. To adequately manage ROC, volume reduction and quality improvement are important. Forward osmosis (FO) can reduce the ROC volume. Advanced oxidation processes (AOPs) result in degrading organic contaminants and producing biodegradable organics, but the reduction of energy consumption is required. Coagulation is an effective option as a pre-treatment of AOPs and can improve the biodegradability of ROC. Partial use of short-time AOPs can transform high molecular weight organics into relatively biodegradable organics. Among AOPs, a rotating advanced oxidation contactor (RAOC) can be an energy-saving technique for removing bio-refractory organics from ROC using solar light irradiation. Post-biological treatment can significantly save energy and efficiently eliminate biodegradable organics that are produced by AOPs. Microalgae cultivation is also an effective option for resource recovery from ROC. Considering the techniques, an integrated process comprising FO, pre-coagulation, short-time and/or solar-driven AOPs (e.g., RAOC), and post-biological treatment is proposed as an energy-saving and cost-effective technology for ROC treatment.

Sodium doping and 3D honeycomb nanoarchitecture: Key features of covalent triazine-based frameworks (CTF) organocatalyst for enhanced solar-driven advanced oxidation processes

Herein, we designed a novel sodium-doped covalent triazine-based framework with a 3D honeycomb nanoarchitecture (H-CTF-Na) as visible-light-responsive organocatalyst to efficiently drive advanced oxidation processes (AOPs). Experimental and theoretical findings reveal that Na doping narrows the band gap by elevating the band edges and the 3D hierarchical nanocellular morphology improves light harvesting and electron transfer. With these merits, H-CTF-Na showed a photoactivity enhancement of 4.9–6.0-fold for the degradation of carbamazepine (CBZ) compared to those of pristine CTFs and g-C3N4 through peroxymonosulfate (PMS) activation under visible-light irradiation. The quenching and EPR results indicate that a synergistic effect between photooxidation (h+) and PMS activation (•OH and SO4•−) derived from the vigorous capture of photogenerated e− by PMS is responsible for the marked efficacy of H-CTF-Na/vis/PMS system. Moreover, this system exhibited excellent versatility in degrading other organics (such as various phenols and dyes) and good reusability in terms of five high-efficiency recycled uses.

Solar-driven advanced oxidation process catalyzed by metal–organic frameworks for water depollution

Phosphonate-based MOF materials namely, STA-12(M) (M = Mn, Fe, Co, Ni), show photocatalytic activity for the degradation of methylene blue (MB) and methyl Orange (MO) from aqueous solution under natural sunlight irradiation. Thus, photo-Fenton oxidative discoloration of dyes have been surveyed by H2O2 catalyzed with the STA-12(M). The degradation of the dyes, appears to be faster with STA-12(Fe) than other synthesized MOFs. The reaction is first order with respect to MO and MB dyes and the synergistic index in the STA-12(Fe)/sunlight/H2O2system reached as high as 431%. Mineralization of dyes was discussed by spectroscopic and TOC measurement. Besides, the efficiency of STA-12(Fe) used in photo-Fenton process was attentively investigated through the characterization of reactive radicals, the stability and reusability of the photocatalyst, also the effect of operational parameters such as H2O2 dosage, solution pH and initial dye concentration. This work demonstrates the first example of facilitating photo-Fenton excitation of H2O2 via phosphonate based metal organic frameworks as photocatalysts and explained a new opportunity for sunlight-induced photocatalytic environmental remediation and protection.

Solar treatment (H2O2, TiO2-P25 and GO-TiO2 photocatalysis, photo-Fenton) of organic micropollutants, human pathogen indicators, antibiotic resistant bacteria and related genes in urban wastewater

Solar-driven advanced oxidation processes were studied in a pilot-scale photoreactor, as tertiary treatments of effluents from an urban wastewater treatment plant. Solar-H2O2, heterogeneous photocatalysis (with and/or without the addition of H2O2 and employing three different photocatalysts) and the photo-Fenton process were investigated. Chemical (sulfamethoxazole, carbamazepine, and diclofenac) and biological contaminants (faecal contamination indicators, their antibiotic resistant counterparts, 16S rRNA and antibiotic resistance genes), as well as the whole bacterial community, were characterized.Heterogeneous photocatalysis using TiO2-P25 and assisted with H2O2 (P25/H2O2) was the most efficient process on the degradation of the chemical organic micropollutants, attaining levels below the limits of quantification in less than 4 h of treatment (corresponding to QUV < 40 kJ L−1). This performance was followed by the same process without H2O2, using TiO2-P25 or a composite material based on graphene oxide and TiO2.Regarding the biological indicators, total faecal coliforms and enterococci and their antibiotic resistant (tetracycline and ciprofloxacin) counterparts were reduced to values close, or beneath, the detection limit (1 CFU 100 mL−1) for all treatments employing H2O2, even upon storage of the treated wastewater for 3-days. Moreover, P25/H2O2 and solar-H2O2 were the most efficient processes in the reduction of the abundance (gene copy number per volume of wastewater) of the analysed genes. However, this reduction was transient for 16S rRNA, intI1 and sul1 genes, since after 3-days storage of the treated wastewater their abundance increased to values close to pre-treatment levels. Similar behaviour was observed for the genes qnrS (using TiO2-P25), blaCTX-M and blaTEM (using TiO2-P25 and TiO2-P25/H2O2). Interestingly, higher proportions of sequence reads affiliated to the phylum Proteobacteria (Beta- and Gammaproteobacteria) were found after 3-days storage of treated wastewater than before its treatment. Members of the genera Pseudomonas, Rheinheimera and Methylotenera were among those with overgrowth.

Solar-driven advanced oxidation processes for full mineralisation of azo dyes in wastewater

Environmental contextFull mineralisation of synthetic azo dyes in industrial wastewater is a tough job for traditional wastewater treatment technologies. There is an urgent need for the development of both sustainable and environmentally friendly technology capable of fully mineralising these azo compounds. We show that solar-driven advanced oxidation processes are capable of completely mineralising azo compounds with high utilisation of solar energy. AbstractMineralisation of synthetic azo dyes in industrial wastewater is an energy-intensive process in treatment technology. The Solar Thermal Electrochemical Process for advanced oxidation processes (STEP-AOPs) utilises solar energy and electricity for the activation and electrooxidation of organic pollutants to harmless, small and non-toxic molecules with no other energy consumption. Based on molecular structure and chemistry, the STEP-AOPs for the treatment of azo dyes in wastewater, as exemplified with a typical azo dye, methyl orange, is reported for the first time. Thermodynamic calculations of the temperature-dependent potentials of methyl orange demonstrate that Gibbs free energy decreased by 161kJmol–1 and the potential decreased by 0.019V with an increase of temperature from 20 to 80°C, which indicates that the drop in both energy and potential specifically fits the STEP-AOPs technique. Experimental results showed that the STEP-AOPs achieved a total organic carbon (TOC) removal of 95.6% for methyl orange. The TOC removal rate improved by 39.8% and the unit TOC electricity consumption decreased by 53.8% at 80°C compared with conventional methods (20°C). The mineralisation mechanism for methyl orange was a gradual shortening of the molecular chain through cleavage of the azo bond, breakdown of the benzene ring and formation of inorganic small molecules susceptible to be oxidised to non-toxic small molecules, and carbon dioxide via STEP-AOPs. The evidence shows that the STEP-AOPs is capable of mineralising azo compounds completely.

Inactivation of Escherichia coli and Enterococci in urban wastewater by sunlight/PAA and sunlight/H2O2 processes

Two solar driven Advanced Oxidation Processes (AOPs), namely sunlight/H2O2 and sunlight/peracetic acid (PAA), were investigated for the inactivation of two bacterial families (Escherichia coli and Enterococci) in real urban wastewater. Preliminary lab scale experiments were performed by using a solar simulator in order to evaluate the proper initial dose of H2O2 and PAA, respectively. According to the results achieved, 50 and 100mgL−1 of H2O2 and 4 and 8mgL−1 of PAA were chosen for the subsequent pilot scale experiments in a Compound Parabolic Collector (CPC) based reactor. The sunlight/PAA process resulted in a higher inactivation rate (3.52 log units of E. coli and 4.50 log units of Enterococci with an initial dose of 8mg PAA L−1) compared to sunlight/H2O2 process (3.13 log units of E. coli and 2.45 log units of Enterococci with an initial dose of 100mg H2O2 L−1) after 120min of solar irradiation (7.42kJL−1 cumulative energy per unit of volume). It is noteworthy that significantly lower initial doses of PAA allowed to achieve a higher inactivation rate compared to H2O2, which makes sunlight/PAA an attractive option for wastewater disinfection in small communities.

Inactivation and regrowth of multidrug resistant bacteria in urban wastewater after disinfection by solar-driven and chlorination processes

Solar disinfection and solar-driven advanced oxidation processes (AOPs) (namely H2O2/sunlight, TiO2/sunlight, H2O2/TiO2/sunlight, solar photo-Fenton) were evaluated in the inactivation of indigenous antibiotic-resistant bacteria (ARB) in real urban wastewater. A multidrug resistant (MDR) Escherichia coli strain isolated from the effluent of the biological process of an urban wastewater treatment plant was the target ARB. The higher inactivation rates (residual density under detection limit, 2CFUmL−1) were achieved with H2O2/TiO2/sunlight (cumulative energy per unit of volume (QUV) in the range 3–5kJL−1, depending on H2O2/TiO2 ratio) and H2O2/sunlight (QUV of 8kJL−1) processes. All investigated processes did not affect antibiotic resistance of survived colonies. Moreover, H2O2/sunlight was compared with conventional chlorination process to evaluate bacterial regrowth potential and particularly the proportion of indigenous MDR E. coli with respect to total indigenous E. coli population. Chlorination (1.0mg Cl2L−1) was more effective than H2O2/sunlight (50mg H2O2L−1) to achieve total inactivation of MDR E. coli (15min Vs 90min) but less effective in controlling their regrowth (24h Vs 48h). Interestingly, the percentage of MDR E. coli in H2O2/sunlight treated samples decreased as incubation time increased; the opposite was observed for chlorinated samples.

Urban wastewater disinfection for agricultural reuse: effect of solar driven AOPs in the inactivation of a multidrug resistant E. coli strain

The occurrence of antibiotics in urban wastewater treatment plants (UWTPs) may result in the development of antibiotic resistance and subsequently in the release of multidrug resistant bacteria (MDR) and genes into the effluent. Conventional disinfection processes are only partially effective in controlling ARB spread, so advanced oxidation processes (AOPs) have been investigated as alternative option in this work. In particular, the aim of this work was to comparatively assess the efficiency of solar disinfection and solar driven AOPs (namely H2O2/sunlight, TiO2/sunlight, H2O2/TiO2/sunlight, natural photo-Fenton) for the inactivation of a multidrug (namely ampicillin, ciprofloxacin and tetracycline) resistant E. coli strain isolated from the effluent of the biological process of an UWTP. Different concentrations of H2O2 (0.588–1.470–2.205mM), TiO2 (50–100mgL−1), H2O2/TiO2 (0.147mM/50mgL−1, 0.588mM/100mgL−1) and Fe2+/H2O2 (0.090/0.294, 0.179/0.588, 0.358/1.176mM) were evaluated at pilot-scale (in compound parabolic collector reactor) in real biologically treated wastewater. All investigated processes resulted in a complete inactivation (5-log decrease) of bacteria until detection limit, but the best disinfection efficiency in terms of treatment time (20min to reach the detection limit) and required energy (0.98kJL−1) was observed for photo-Fenton at pH 4 (Fe2+/H2O2:0.090/0.294mM). Antimicrobial susceptibility was tested by Kirby-Bauer disk diffusion method. Ampicillin and ciprofloxacin (to which the selected strain is resistant), cefuroxime and nitrofurantoin were chosen as tested antibiotics. None of the investigated processes affected antibiotic resistance of survived colonies.

Assessment of solar photo-Fenton, photocatalysis, and H2O2 for removal of phytopathogen fungi spores in synthetic and real effluents of urban wastewater

Abstract Scarcity of fresh water is a major environmental problem, and properly treated wastewater could be an alternative renewable water resource, especially for agriculture as the final point-of-use. But before wastewater can be reused, it must be treated to meet chemical and biological quality standards, which depend on the final use and legislation. Advanced Oxidation Processes (AOPs) have been demonstrated to be very efficient in decreasing the pathogen load in contaminated water. This study presents the experimental evaluation of several solar-driven AOPs, i.e., photo-Fenton (Fe2+, Fe3+) at low reagent concentration, heterogeneous photocatalysis (TiO2), and solar photoassisted H2O2 treatment for removal of the spores of Fusarium sp., a worldwide phytopathogen. The experimental work was done in a pilot solar photoreactor with Compound Parabolic Collector (CPC). Disinfection of Fusarium solani spores by all treatments was excellent in distilled water, in simulated municipal wastewater effluent (SMWWE), and in real municipal wastewater effluents (RMWWE). Degradation of dissolved organic carbon (DOC) was also evaluated. The inactivation rates varied depending on the water matrix, and disinfection was fastest in distilled water followed by SMWWE, and RMWWE. The best F. solani inactivation rate was with photo-Fenton treatment (10/20 mg/L of Fe2+/H2O2) at pH 3, followed by H2O2/Solar (10 mg/L) and finally TiO2/Solar was the slowest. These results underline the importance of solar AOPs and the CPC reactor technology as a good option for waterborne pathogen removal.

Utilizing solar energy for the purification of olive mill wastewater using a pilot-scale photocatalytic reactor after coagulation-flocculation

This study investigated the application of a solar-driven advanced oxidation process (solar Fenton) combined with previous coagulation/flocculation, for the treatment of olive mill wastewater (OMW) at a pilot scale. Pre-treatment by coagulation/flocculation using FeSO4·7H2O (6.67 g L−1) as the coagulant, and an anionic polyelectrolyte (FLOCAN 23, 0.287 g L−1) as the flocculant, was performed to remove the solid content of the OMW. The solar Fenton experiments were carried out in a compound parabolic collector pilot plant, in the presence of varying doses of H2O2 and Fe2+. The optimization of the oxidation process, using reagents at low concentrations ([Fe2+] = 0.08 g L−1; [H2O2] = 1 g L−1), led to a high COD removal (87%), while the polyphenolic fraction, which is responsible for the biorecalcitrant and/or toxic properties of OMW, was eliminated. A kinetic study using a modified pseudo first-order kinetic model was performed in order to determine the reaction rate constants. This work evidences also the potential use of the solar Fenton process at the inherent pH of the OMW, yielding only a slightly lower COD removal (81%) compared to that obtained under acidic conditions. Moreover, the results demonstrated the capacity of the applied advanced process to reduce the initial OMW toxicity against the examined plant species (Sorghum saccharatum, Lepidium sativum, Sinapis alba), and the water flea Daphnia magna. The OMW treated samples displayed a varying toxicity profile for each type of organism and plant examined in this study, a fact that can potentially be attributed to the varying oxidation products formed during the process applied. Finally, the overall cost of solar Fenton oxidation for the treatment of 50 m3 of OMW per day was estimated to be 2.11 € m−3.

Application of biological oxidation and solar driven advanced oxidation processes to remediation of winery wastewater

Biological oxidation and solar driven advanced oxidation processes (AOPs) applied as a single stages were tested at a pilot plant equipped with an immobilized biological reactor (IBR) and a photocatalytic system with compound parabolic collectors (CPCs) for the remediation of a winery wastewater (DOCaverage=882mgL−1; pH 4.1). Due to the variable nature of winery wastewater composition and quantity, the application of AOPs as a single or as preliminary stage can be an effective alternative to only conventional biological treatment. Regarding the AOPs systems tested (TiO2/H2O2/UV and Fe2+/H2O2/UV), the solar photo-Fenton reaction (optimized at pH 2.8 and 55mg Fe2+L−1) showed the highest efficiency, being necessary an UV dose of 100kJUVL−1 and 338mM H2O2 (15mg H2O2mg C−1) to achieve a COD value lower than 150mg O2L−1, which is agreement with the discharge limits into receiving waters imposed by the Portuguese Legislation (Decree-law n° 236/98). To achieve the same COD target value using only the IBR system or the combination of solar-photo-Fenton (22kJUVL−1; 80mM H2O2 consumed) and biological systems, approximately 10 and 6 days (time necessary for the biological oxidation) are required. The efficiency of the AOPs in the treatment of simulated and real winery wastewaters was also compared.

Treatment of a pesticide-containing wastewater using combined biological and solar-driven AOPs at pilot scale

The present work focuses on treatment of a pesticide-containing wastewater resulting from phytopharmaceutical plastic containers washing, combining a preliminary biological pre-treatment step, using an immobilized biomass reactor (IBR), with further advanced oxidation processes (AOPs). Heterogeneous (TiO2/UV and TiO2/H2O2/UV, both with and without acidification) and homogeneous (UV, H2O2/UV, Fe2+/H2O2/UV and Fe2+/H2O2) systems were tested using a solar pilot plant with compound parabolic collectors (CPCs). The wastewater exhibited a moderate organic load (COD=1662–1960mgO2L−1; DOC=513–696mgCL−1), high biodegradability (BOD5=1350–1600mgO2L−1) and nineteen pesticides were quantified in the range of 0.02–45mgL−1, representing 14–19% of total DOC. Due to its high biodegradability, a biological treatment was performed prior to AOPs, leading to a COD, DOC and BOD5 reduction of 46–54%, 41–56% and 88–90% respectively, resulting in a recalcitrant wastewater with a residual pesticide content corresponding to 24–34% of DOC. The photo-Fenton reaction, performed with an initial iron concentration of 140mg Fe2+L−1, leading to an average dissolved iron concentration of 14mgL−1 after FePO4 precipitation, proved to be the most efficient process, showing an initial reaction rate 8.4, 8.7 and 5.1 times higher than for H2O2/UV, TiO2/H2O2/UV-without and with acidification systems, respectively. The reaction required 167mM of H2O2 and 21kJUVL−1 to achieve 86% mineralization and only 8kJUVL−1 to eliminate eighteen of the nineteen pesticides initially quantified to levels below the respective quantification limit. Despite the Fenton reaction revealed a slower mineralization profile, it can be quite efficient for significant pesticide abatement compared to the other AOPs employed.

Treatment of textile wastewaters by solar-driven advanced oxidation processes

Abstract Heterogeneous (TiO2/UV, TiO2/H2O2/UV) and homogenous (H2O2/UV, Fe2+/H2O2/UV) solar advanced oxidation processes (AOPs) are proposed for the treatment of recalcitrant textile wastewater at pilot-plant scale with compound parabolic collectors (CPCs). The textile wastewater presents a lilac colour, with a maximum absorbance peak at 516 nm, high pH (pH = 11), moderate organic content (DOC = 382 mg C L−1, COD = 1020 mg O2 L−1) and high conductivity (13.6 mS cm−1), associated with a high concentration of chloride (4.7 g Cl− L−1). The DOC abatement is similar for the H2O2/UV and TiO2/UV processes, corresponding only to 30% and 36% mineralization after 190 kJUV L−1. The addition of H2O2 to TiO2/UV system increased the initial degradation rate more than seven times, leading to 90% mineralization after exposure to 100 kJUV L−1. All the processes using H2O2 contributed to an effective decolourisation, but the most efficient process for decolourisation and mineralization was the solar-photo-Fenton with an optimum catalyst concentration of 100 mg Fe2+ L−1, leading to 98% decolourisation and 89% mineralization after 7.2 and 49.1 kJUV L−1, respectively. According to the Zahn–Wellens test, the energy dose necessary to achieve a biodegradable effluent after the solar-photo-Fenton process with 100 mg Fe2+ L−1 is 12 kJUV L−1.