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Graphical abstract Highlights • Exfoliated graphitic carbon nitride (g-C 3 N 4) was synthesised and characterized. • The metal-free photocatalyst was studied under visible light. • Efficient removal of micropollutants from secondary urban wastewater was achieved. • g-C 3 N 4 was supported on glass rings to avoid its recovery from treated wastewater. Abstract Heterogeneous photocatalysis under visible light was employed for the degradation of organic micropollutants (MPs) found in the biologically treated effluents of an urban wastewater treatment plant (UWWTP). The irradiation source consisted in 4 light emitting diodes (LEDs) with a nominal power of 400–500 W m–2 at 417 nm. Metal-free exfoliated graphitic carbon nitride (gCN T), which was synthetized through a simple thermal treatment using dicyandiamide as precursor, was employed as photocatalyst. The gCN T material was characterized using different techniques: N 2 adsorption isotherms at 77 K, electron microscopy (scanning and transmission) and diffuse reflectance UV–Vis. The photocatalytic performance of the material was compared to the commercial TiO 2 -P25, confirming that gCN T led to a remarkable higher removal efficiency of the target MPs. Most of these MPs were removed in less than 10 min to levels below the limit of quantification (carbamazepine > isoproturon > clopidogrel > diclofenac > atenolol > bezafibrate > tramadol > venlafaxine > fluoxetine). Indirect photolysis, resulting from the secondary reactive oxidants generated during the irradiation of the aqueous matrix components, was found to partially contribute for the elimination of the occurring MPs. In addition, the gCN T photocatalyst was immobilized on glass rings for use under continuous mode operation, a minimum residence time of 25 min being required to attain significant removal efficiencies. Phytotoxicity experiments showed that heterogeneous photocatalysis did not enhance the toxicity of the wastewaters. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiO 2 was grown and crystallized on polysulfone, PTFE and PVDF membranes. • Diclofenac and 17α-ethinylestradiol were removed by adsorption and photocatalysis. • 17α-ethinylestradiol was preferentially adsorbed regardless of the membrane tested. • TiO 2 -polysulfone was the most active membrane for the removal of both pollutants. • TiO 2 -PVDF presented the highest stability in consecutive reaction cycles. TiO 2 in situ growth on three commercial membranes (polysulfone – PS, polyvinylidene fluoride – PVDF and polytetrafluoroethylene – PTFE) and its hydrothermal post-crystallization to transform TiO 2 into a photocatalytically-active phase, were investigated under mild synthesis conditions to preserve the textural properties of the supports. The membranes were successfully prepared and characterized by scanning electron microscopy, thermogravimetry analysis, N 2 physisorption, X-ray diffraction, and water contact angle measurements, among other techniques. Membrane supports with a more opened porosity and high hydrophilicity allowed to enhance the content and distribution of the anatase TiO 2 nanoparticles on the membrane surface. The efficiency and the permeate flux of the developed membranes were investigated to simultaneously remove diclofenac (DCF) and 17α-ethinylestradiol (EE2) from water by adsorption and UV–LED (light-emitting diode) photocatalysis under continuous recirculating mode. All TiO 2 membranes achieved removal efficiencies above 90% for both contaminants, EE2 being always preferentially adsorbed over DCF due to electrostatic repulsions between the DCF molecules and the surface of these membranes. The permeate flux of TiO 2 membranes was enhanced after UV-LED exposure as a consequence of the degradation of the contaminants adsorbed on the membrane surface during the dark phase. Moreover, the stability of TiO 2 nanoparticles on these membranes was studied by static tests under sonication and several consecutive reaction cycles. The TiO 2 membrane prepared with PVDF was the most stable, also presenting a high photocatalytic activity. [ABSTRACT FROM AUTHOR]

The threat of antibiotic resistance to the wellbeing of societies is well established. Urban wastewater treatment plants (UWTPs) are recognised sources for antibiotic resistance dissemination in the environment. Herein a novel cerium-doped zinc oxide (Ce-ZnO) photocatalyst is compared to ZnO and the benchmark TiO2-P25 in the immobilised form on a metallic support, to evaluate a photocatalytic process as a possible tertiary treatment in UWTPs. The catalysts were compared for the removal of two antibiotics, trimethoprim (TMP) and sulfamethoxazole (SMX), and for the inactivation of Escherichia coli (E. coli) strain DH5-Alpha in isotonic sodium chloride solution and of autochthonous bacteria in real secondary wastewater. In real wastewater, E. coli and other coliforms were monitored, as well as the respective fractions resistant to ofloxacin and azithromycin. In parallel, Pseudomonas aeruginosa and the respective sub-population resistant to ofloxacin or ciprofloxacin were also monitored. Photocatalysis with both ZnO and Ce-ZnO was faster than using TiO2-P25 at degrading the antibiotics, with Ce-ZnO the fastest against SMX but slower than undoped ZnO in the removal of TMP. Ce-ZnO catalyst reuse in the immobilised form produced somewhat slower kinetics maintained >50% of the initial activity, even after five cycles of use. Approximately 3 log10 inactivation of E. coli in isotonic sodium chloride water was recorded with reproducible results. In the removal of autochthonous bacteria in real wastewater, Ce-ZnO performed better (more than 2 log values higher) than TiO2-P25. In all cases, E. coli and other coliforms, including their resistant subpopulations, were inactivated at a higher rate than P. aeruginosa. With short reaction times no evidence for enrichment of resistance was observed, yet with extended reaction times low levels of bacterial loads were not further inactivated. Overall, Ce-ZnO is an easy and cheap photocatalyst to produce and immobilise and the one that showed higher activity than the industry standard TiO2-P25 against the tested antibiotics and bacteria, including antibiotic-resistant bacteria. [ABSTRACT FROM AUTHOR]

Abstract Urban wastewater treatment plants (WWTPs) are among the main anthropogenic sources for the release of contaminants of emerging concern (CECs) into the environment, which can result in toxic and adverse effects on aquatic organisms and consequently on humans. Unfortunately, WWTPs are not designed to remove CECs and secondary (e.g., conventional activated sludge process, CAS) and tertiary (such as filtration and disinfection) treatments are not effective in the removal of most CECs entering WWTP. Accordingly, several advanced treatment methods have been investigated for the removal of CECs from wastewater, including consolidated (namely, activated carbon (AC) adsorption, ozonation and membranes) and new (such as advanced oxidation processes (AOPs)) processes/technologies. This review paper gathers the efforts of a group of international experts, members of the NEREUS COST Action ES1403 who for three years have been constructively discussing the state of the art and the best available technologies for the advanced treatment of urban wastewater. In particular, this work critically reviews the papers available in scientific literature on consolidated (ozonation, AC and membranes) and new advanced treatment methods (mainly AOPs) to analyse: (i) their efficiency in the removal of CECs from wastewater, (ii) advantages and drawbacks, (iii) possible obstacles to the application of AOPs, (iv) technological limitations and mid to long-term perspectives for the application of heterogeneous processes, and (v) a technical and economic comparison among the different processes/technologies. Graphical abstract Unlabelled Image Highlights • Adsorption, O 3 , NF and RO membranes filtration can effectively remove CECs. • (Solar driven) AOPs appear competitive for CECs removal from urban wastewater. • When applying O 3 or AOPs ecotoxicological studies should be performed. • Lack of comparative investigations between consolidated and new processes • Conclusive evaluation of the most suitable and cost effective solution/s not yet possible [ABSTRACT FROM AUTHOR]

Photocatalytic ozonation was employed for the first time in continuous mode with TiO 2 -coated glass Raschig rings and light emitting diodes (LEDs) to treat urban wastewater as well as surface water collected from the supply area of a drinking water treatment plant (DWTP). Different levels of contamination and types of contaminants were considered in this work, including chemical priority substances (PSs) and contaminants of emerging concern (CECs), as well as potential human opportunistic antibiotic resistant bacteria and their genes (ARB&ARG). Photocatalytic ozonation was more effective than single ozonation (or even than TiO 2 catalytic ozonation) in the degradation of typical reaction by-products (such as oxalic acid), and more effective than photocatalysis to remove the parent micropollutants determined in urban wastewater. In fact, only fluoxetine, clarithromycin, erythromycin and 17-alpha-ethinylestradiol (EE2) were detected after photocatalytic ozonation, by using solid-phase extraction (SPE) pre-concentration and LC-MS/MS analysis. In surface water, this treatment allowed the removal of all determined micropollutants to levels below the limit of detection (0.01–0.20 ng L −1 ). The efficiency of this process was then assessed based on the capacity to remove different groups of cultivable microorganisms and housekeeping (16S rRNA) and antibiotic resistance or related genes ( intI1, blaTEM , qnrS , sul1 ). Photocatalytic ozonation was observed to efficiently remove microorganisms and ARGs. Although after storage total heterotrophic and ARB (to ciprofloxacin, gentamicin, meropenem), fungi, and the genes 16S rRNA and intI1 , increased to values close to the pre-treatment levels, the ARGs ( blaTEM , qnrS and sul1 ) were reduced to levels below/close to the quantification limit even after 3-days storage of treated surface water or wastewater. Yeast estrogen screen (YES), thiazolyl blue tetrazolium reduction (MTT) and lactate dehydrogenase (LDH) assays were also performed before and after photocatalytic ozonation to evaluate the potential estrogenic activity, the cellular metabolic activity and the cell viability. Compounds with estrogenic effects and significant differences concerning cell viability were not observed in any case. A slight cytotoxicity was only detected for Caco-2 and hCMEC/D3 cell lines after treatment of the urban wastewater, but not for L929 fibroblasts. [ABSTRACT FROM AUTHOR]

Direct photolysis and TiO 2 -photocatalytic degradation of naproxen (NPX) in aqueous solution were studied using a UV lamp and solar irradiation. The degradation of NPX was found to be in accordance with pseudo-first order kinetics, the photocatalytic process being more efficient than photolysis. The NPX removal by photolysis (pH initial 6.5) was 83% after 3 h, with 11% of chemical oxygen demand (COD) reduction, whereas the TiO 2 -UV process led to higher removals of both NPX (98%) and COD (25%). The apparent pseudo-first-order rate constant ( k app ) for NPX degradation by photolysis ranged from 0.0050 min −1 at pH 3.5 to 0.0095 min −1 at pH 6.5, while it was estimated to be 0.0063 min −1 under acidic conditions in photocatalysis, increasing by 4-fold at pH 6.5. Ultra High Performance Liquid chromatography (UHPLC) coupled with a triple quadrupole detector and also a hybrid mass spectrometer which combines the linear ion trap triple quadrupole (LTQ) and OrbiTrap mass analyser, were used to identify NPX degradation products. The main intermediates detected were 1-(6-methoxynaphtalene-2-yl) ethylhydroperoxide, 2-ethyl-6-methoxynaphthalene, 1-(6-methoxynaphtalen-2-yl) ethanol, 1-(6-methoxynaphtalen-2-yl) ethanone and malic acid. Solar photocatalysis of NPX showed COD removals of 33% and 65% after 3 and 4 h of treatment, respectively, and some reduction of acute toxicity, evaluated by the exposure of Eisenia andrei to OECD soils spiked with NPX-treated solutions. [ABSTRACT FROM AUTHOR]