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This study investigated an innovative and low-cost hybrid system that couples constructed wetland (CW) and solar photo-Fenton (SPF) to enhance the elimination of 17 different micropollutants (MPs) from urban wastewater. The CW unit explored two aquatic plants (Phragmites australis and Cyperus haspan) and two operational modes (with and without recirculation), resulting in four different microcosms. Photo-Fenton experiments were carried out in a bench solar simulator at natural pH using the commercial fertilizer DTPA as iron catalysts. The results showed that the constructed wetlands with recirculation obtained better MPs eliminations than microcosms without recirculation, with no significant difference between the two plants. The average removal of total MPs and different cycles was 67% and 41% in the unit planted with C. haspan, with recirculation and no recirculation, respectively. Additionally, the removal performance of total suspended solids (TSS) and dissolved organic carbon (DOC) from water was also high, reaching about 80% and 50% for TSS and DOC, respectively in the recirculation unit with no increase in nitrites content. The CWs performance resulted in a rise yields of overall MPs abatement in photo-Fenton process, from an average removal of 73% for the single process up to almost complete removal (95%) for the hybrid system. CW with recirculation combined with SPF would let to achieve the corresponding limits according the final use/fate of the effluent in a more economical, sustainable and green way.

In this paper, reaction kinetics, degradation mechanisms and associated toxicity have been assessed in detail concerning the abatement of neonicotinoid insecticide clothianidin (CLO) by ozone-based oxidation in water. The second-order rate constants for the reaction of CLO with molecular ozone (O3) and hydroxyl radical ([rad]OH) were determined by the direct and competition kinetics (with UV/H2O2 system as the radical source) methods, respectively, and estimated to be 103 M−1 s−1 and 3.7·109 M−1 s−1. This suggested a (potential) higher contribution of the indirect mechanism rather than the direct degradative pathway in the CLO ozonation process. Additionally, CLO oxidation was studied through an O3 and O3/H2O2 system for three complex real water matrices with distinct characteristics. DOC content was found to be the main parameter responsible for making difficult the achievement of high CLO degradations, whereas carbonate alkalinity did not exert a great impact on the process efficiency. Results indicated that typical ozone doses (up to 1 mg O3/mg DOC) were not enough for the complete removal of this micropollutant, ranging only from 50 to 80%. The study concerning the transformation products (TPs), performed by means of high-resolution mass spectrometry, allowed to suggest potential degradation routes based on the five major CLO-TPs identified. It was inferred that [rad]OH was involved in the formation of all TPs, whereas O3 was only involved in the formation of two of them. A preliminary toxicity assessment concerning CLO and its TPs during ozonation was conducted at three different trophic levels via the ECOSAR software. Results showed that none of the compounds was classified as very toxic for aquatic organisms, and all TPs exhibited minor toxicity than the parent compound. Changes in molecular structure, such as chlorothiazole ring breakdown, could be the main reason for this considerable decrease in toxicity. Overall, the present study demonstrates that ozonat

Nowadays, reaction mechanisms of photo-Fenton process with chelated iron are not yet clearly defined. In this study, five organic fertilizers were used as iron complexes to investigate the role of sunlight and oxygen in photo-Fenton at near neutral pH. UV absorbance and stability constant of each selected iron chelate is different, and this work demonstrates that these parameters affect the reaction mechanisms in SMX degradation. Irradiation experiments without H2O2 revealed that only EDDS-Fe and DTPA-Fe achieved SMX degradation, but different iron release. These results, together with soluble oxygen free experiments, allowed the proposal of complementary reaction mechanisms to those of the classical photo-Fenton. The proposed mechanisms start through the potential photoexcitation of the iron complex, followed by subsequent oxygen-mediated hydroxyl radical generation reactions that are different for EDDS-Fe and DTPA-Fe. Moreover, irradiation experiments using EDTA-Fe and HEDTA-Fe had negligible SMX degradation despite iron release was observed, evidencing the differences between iron chelates.