Antibiotics mineralization by electrochemical and UV-based hybrid processes: evaluation of the synergistic effect

Phyto-mediated photocatalysis: a critical review of in-depth base to reactive radical generation for erythromycin degradation

Erythromycin (ERY), designated as a risk-prioritized macrolide antibiotic on the 2015 European Union watch list, is the third most commonly used antibiotic, most likely due to its ability to inhibit the protein. ERY has revealed record-high aquatic concentrations threatening the entire ecosystem and hence demands priority remedial measures. The inefficiency of various conventional ERY degradation methodologies opened up a gateway to advanced technologies. The conventional approach comprising of a chemically formulated, single photocatalyst has a major drawback of creating multiple environmental stresses. In this context, photocatalysis is grabbing tremendous attention as an efficient and cost-effective antibiotic treatment approach. Several studies have ascertained that ZnO, TiO₂, Fe₃O₄, and rGO nanoparticles possess remarkable pollution minimizing operational capabilities. Additionally, composites are found much more effective in antibiotic removal than single nanoparticles. In this review, an attempt has been made to provide a comprehensive baseline for efficient reactive radical production by a phyto-mediated composite kept under a certain source of irradiation. Considerable efforts have been directed towards the in-depth investigation of rGO-embedded, phyto-mediated ZnO/TiO₂/Fe₃O₄ photocatalyst fabrication for efficient ERY degradation, undergoing green photocatalysis. This detailed review provides photocatalytic nanocomposite individualities along with a hypothetical ERY degradation mechanism. It is assumed that derived information presented here will provoke innovative ideas for water purification incorporating green photocatalysis, initiating the construction of high-performance biogenic hierarchical nanocatalysts.

Pharmaceutical compounds used in the COVID-19 pandemic: A review of their presence in water and treatment techniques for their elimination

During the COVID-19 pandemic, high consumption of antivirals, antibiotics, antiparasitics, antiprotozoals, and glucocorticoids used in the treatment of this virus has been reported. Conventional treatment systems fail to efficiently remove these contaminants from water, becoming an emerging concern from the environmental field. Therefore, the objective of the present work is to address the current state of the literature on the presence and removal processes of these drugs from water bodies. It was found that the concentration of most of the drugs used in the treatment of COVID-19 increased during the pandemic in water bodies. Before the pandemic, Azithromycin concentrations in surface waters were reported to be in the order of 4.3 ng L^-1, and during the pandemic, they increased up to 935 ng L^-1. Laboratory scale studies conclude that adsorption and advanced oxidation processes (AOPs) can be effective in the removal of these drugs. Up to more than 80% removal of Azithromycin, Chloroquine, Ivermectin, and Dexamethasone in aqueous solutions have been reported using these processes. Pilot-scale tests achieved 100% removal of Azithromycin from hospital wastewater by adsorption with powdered activated carbon. At full scale, treatment plants supplemented with ozonation and artificial wetlands removed all Favipiravir and Azithromycin, respectively. It should be noted that hybrid technologies can improve removal rates, process kinetics, and treatment cost. Consequently, the development of new materials that can act synergistically in technically and economically sustainable treatments is required.

Degradation mechanism of tributyl phosphate by UV/H2O2 treatment and parameters optimization towards the design of a pilot reactor

While activated sludge treatment is currently the preferred process for the removal of tributyl phosphate (TBP) at the mg.L^-1 level, it is well known that this recalcitrant molecule is incompletely degraded, stimulating research into alternative approaches, such as advanced oxidation. The aim of this study was to characterize the degradation mechanism of TBP during ultraviolet/H₂O₂ treatment using ³¹P NMR, ionic chromatography and total organic carbon analysis. The effects of initial pH, amount of oxidant and pollutant concentration were also assessed using an experimental design approach. The results of this parametric study show that ultraviolet/H₂O₂ photo-oxidation efficiently degrades TBP at concentrations up to 600 mg.L^-1, with >90% phosphate release and up to 95% removal of total organic carbon within 1 h. The data also show that the main reaction intermediates are short carboxylic acids, resulting from the released alkyl groups, meaning that an interesting application of this process may be to rapidly pre-treat industrial effluent upstream of activated sludge reactors.

UV-irradiation and BDD-based photoelectrolysis for the treatment of halosulfuron-methyl herbicide

This paper reports the development of a novel photoelectrochemical (PEC) oxidation technique based on UV-C irradiation and boron-doped diamond (BDD) anode and its application for the effective removal of the commercial herbicide halosulfuron-methyl (HSM). The study evaluated the influence of the following key operating variables in the photoelectrochemical process: current density, pH, temperature, and initial HSM concentration. With regard to HSM degradation/mineralization, the application of high current densities was found to be more advantageous once it promoted a more rapid degradation and mineralization, with 96% of total organic carbon removal, though the process became more energy-demanding over time. The initial concentration of HSM did not modify the relative degradation rate, though the degradation process became more efficient as expected in a mass-transfer controlled process. The use of acidic pH (pH 3) was found to be more suitable than neutral conditions; this is probably because an anionic resonant form of HSM may be formed in neutral conditions. The temperature level was also found to affect the rate of HSM removal and the degradation efficiency. Finally, the substitution of Na₂SO₄ by NaCl promoted a more rapid and effective degradation; this is attributed to high production of powerful oxidants. However, only 70% mineralization was reached after 3 h of treatment; this is probably related to the formation of recalcitrant chlorinated sub-products.

Selecting and improving activated homogeneous catalytic processes for pollutant removal. Kinetics, mineralization and optimization

The degradation of a model pollutant, tartrazine, very used in food industry and usually present in WWTPs effluents and surface waters, was investigated by nine activated homogeneous catalytic processes, namely, Fe³⁺/H₂O₂, Fe²⁺/H₂O₂, UV/H₂O₂, UV/S₂O₈^2-, UV/Fe²⁺/H₂O₂, UV/Fe³⁺/H₂O₂, UV, VIS/Fe³⁺/H₂O₂, and VIS/Fe³⁺/H₂O₂/C₂O₄^2-. In order to compare the mineralization and oxidation ability of each process, the removal of dye, chemical oxygen demand (COD) and total organic carbon (TOC) were analyzed, as well as the overall kinetic rate constant. Also, the different oxidation path-ways (direct photolysis and/or oxidation by free radicals) were estimated for each system. After the comparison, the Fenton process, which had the highest mineralization values, was tested in luminous and dark phases using designed experiments, and the influences of all operating variables were studied by RSM.