Advanced technologies for the determination of quantitative structure-activity relationships and degradation efficiency of micropollutants and their removal in water - A review

Enhanced micropollutant degradation over catalyst-free synergistic activation of periodate and persulfate under solar light

Micropollutants are ubiquitous in water sources, posing threats to both human health and ecosystems. Conventional water and wastewater treatment processes are inefficient in micropollutant removal. In this study, the energy-effective and environmentally friendly solar light-driven periodate (PI) and peroxydisulfate (PDS) synergistic activation process (PI/PDS/solar light) is developed for efficient micropollutant decontamination. The PI/PDS/solar light process (0.5 mM PI and 0.25 mM PDS) achieves 100% degradation of 2 ppm CBZ in 15 min with a CBZ degradation rate constant of 0.31 min-1, which is 6.6 and 13.2 times that of PI/solar light (0.046 min-1, 0.5 mM PI) and PDS/solar light (0.023 min-1, 0.5 mM PDS). Mechanistic studies reveal that the enhanced solar light utilization and charge transfer between PI and PDS lead to the synergistic activation of the dual oxidants in the PI/PDS/solar light process, thus promoting micropollutant degradation. Additionally, the scavenging tests demonstrate that •OH and SO4•- are the dominant radicals for CBZ degradation. Furthermore, the PI/PDS/solar light process exhibits excellent applicability in different types of water sources, where several water components (pH, natural organic matter, and anions) pose insignificant impacts on CBZ degradation. Nonetheless, the developed process still has a disadvantage in that the degradation intermediates of PPCPs may bring potential toxicity. The study offers valuable mechanistic insights into the novel synergistic PI and PDS coactivation process under solar light and highlights the practicability of the developed technique as an efficient strategy for micropollutant decontamination.

The Impact of Organic Micropollutants on the Biochemical Composition and Stress Markers in Wolffia arrhiza

For many years, there has been a growing pollution of the aquatic environment with personal care products and industrial chemicals, the main source of which is municipal and industrial wastewater. This raises the need to assess the impact of these pollutants on ecosystems, including plants living in the aquatic environment. It is important to develop methods for their removal from wastewater, among which using plants for phytoremediation is a promising solution. This study aimed to evaluate the response of the aquatic plant Wolffia arrhiza (Lemnaceae) to low concentrations of bisphenol A (BPA), N,N-diethyl-m-toluamide (DEET), triclosan (TRC), benzophenone (BPH), endosulfan alpha (α-END), and endosulfan beta (β-END). The plant growth, the content of cellular components, and oxidative stress markers were assessed in response to plant contact with single compounds at concentrations of 0.1 mg/L and 1 mg/L, and their mixture at a total concentration of 1 mg/L. All of the pollutants used in the study inhibited the W. arrhiza growth and stimulated the degradation of proteins but enhanced the level of saccharides. TRC, BPH, α-END, and β-END had a negative impact on the content of photosynthetic pigments. Increased concentrations of the oxidative stress markers MDA and H2O2 were registered in the plants exposed to BPA, TRC, and β-END. The mixture of pollutants had higher toxic effects than individual substances.

"Catch-and-feed": Janus catalytic flow-through membrane enables highly efficient removal of micropollutants in water

Micropollutants, due to their low concentrations, exceptional chemical stability, and profound toxicity, present a significant challenge in water treatment. While electrocatalysis and photocatalysis have shown promise as potential water purification techniques, their inherent limitations in mass transfer often result in elevated energy requirements and suboptimal efficiency. In this study, a Janus catalytic flow-through membrane (JCFM) was utilized to successfully remove two notorious micropollutants dichlorvos (DDVP) and azoxystrobin (AZX) from water based on the "catch-and-feed" strategy. This membrane adopts a ``sandwich'' configuration, comprising platinum-modified reduced titanium (Pt@rTO) as the electrocatalytic layer, porous titanium (Ti) as the current collector, and rTO as the photocatalytic layer. The JCFM exhibited remarkable performance, maintaining an •OH energy conversion efficiency of up to 20.12 nM and displaying catalytic activity (kJCFM = 6.97 × 10-4 s-1) in degrading AZX far superior to that of photocatalysis (kPC = 9.51 × 10-5 s-1) or electrocatalysis (kEC = 9.89 × 10-5 s-1) alone. It is evidenced that the Pt@rTO layer efficiently generates reactive oxygen species (ROS), which, along with the micropollutants, flow through the JCFM ("feed"), which strengthens mass transfer and facilitates efficient reactions within the confined space ("catch"). The ROSs then seep through the rTO layer, where they are reactivated by UV light radiation. The mechanism and the alternative reaction pathway of DDVP and AZX has also been proposed. In sequential testing, the JCFM achieved continuous and energy-efficient removal of micropollutants, exceeding 97.5 % over 200 h. The scale-up application of this technology has proven effective in the treatment of secondary biochemical effluent from municipal sewage, coking wastewater, and landfill leachate, achieving the concurrent degradation of various micropollutants.

Norfloxacin affects inorganic nitrogen compound transformation in tailwater containing Corbicula fluminea

The Asian clam, Corbicula fluminea, commonly used in engineered wetlands receiving tailwater, affects nitrogen compound transformation in water. This study investigates how a commonly observed antibiotic in tailwater, norfloxacin, impact nitrogen compound transformation in tailwater containing C. fluminea. The clam was exposed to artificial tailwater with norfloxacin (0, 0.2, 20, and 2000 μg/L) for 15 days. Water properties, C. fluminea ecotoxicity responses, microorganism composition and nitrification- or denitrification-related enzyme activities were measured. Results revealed norfloxacin-induced increases and reductions in tailwater NH4+ and NO2- concentrations, respectively, along with antioxidant system inhibition, organ histopathological damage and disruption of water filtering and digestion system. Microorganism composition, especially biodiversity indices, varied with medium (clam organs and exposure water) and norfloxacin concentrations. Norfloxacin reduced NO2- content by lowering the ratio between microbial nitrifying enzyme (decreased hydroxylamine oxidoreductase and nitrite oxidoreductase activity) and denitrifying enzyme (increased nitrate reductase and nitrite reductase activity) in tailwater. Elevated NH4+ content resulted from upregulated ammonification and inhibited nitrification of microorganisms in tailwater, as well as increased ammonia emission from C. fluminea due to organ damage and metabolic disruption of the digestion system. Overall, this study offers insights into using benthic organisms to treat tailwater with antibiotic residues, especially regarding nitrogen treatment.

Facile construction of efficient WO3/V2O5 coupled g-C3N4 ternary composite photocatalyst for environmental emergent aqueous pollutant degradation: Stability, degradation reaction pathway and effect of pH evaluation

Currently, one of the primary challenges that human society must overcome is the task of decreasing the amount of energy used and the adverse effects that it has on the environment. The daily increase in liquid waste (comprising organic pollutants) is a direct result of the creation and expansion of new companies, causing significant environmental disruption. Water contamination is attributed to several industries such as textile, chemical, poultry, dairy, and pharmaceutical. In this study, we present the successful degradation of methylene blue dye using g-C3N4 (GCN) mixed with WO3 and V2O5 composites (GCN/WO3/V2O5 ternary composite) as a photocatalyst, prepared by a simple mechanochemistry method. The GCN/WO3/V2O5 ternary composite revealed a notable enhancement in photocatalytic performance, achieving around 97% degradation of aqueous methylene blue (MB). This performance surpasses that of the individual photocatalysts, namely pure GCN, GCN/WO3, and GCN/V2O5 composites. Furthermore, the GCN/WO3/V2O5 ternary composite exhibited exceptional stability even after undergoing five consecutive cycles. The exceptional photocatalytic activity of the GCN/WO3/V2O5 ternary composite can be ascribed to the synergistic effect of metal-free GCN and metal oxides, resulting in the alteration of the band gap and suppression of charge recombination in the ternary photocatalyst. This study offers a better platform for understanding the characteristics of materials and their photocatalytic performance under visible light conditions.

Recent advances and future trends in metal oxide photocatalysts for removal of pharmaceutical pollutants from wastewater: a comprehensive review

The rapid and widespread increase in pharmaceutical micropollutants (PMPs) poses a significant and immediate threat to ecosystems and human health globally. With the demand for clean water becoming increasingly critical, particularly amid escalating global water scarcity challenges, there is an urgent need for innovative approaches. Among the potential solutions, metal oxide photocatalysts such as titanium dioxide-based (TiB) and zinc oxide-based (ZnB) have garnered attention due to their cost-effectiveness, efficient photodegradation capabilities, and inherent stability. This comprehensive review explores recent advancements in the application of TiB and ZnB for the removal of PMPs from wastewater. It examines the multifaceted impacts of PMPs on environmental and public health, evaluates various techniques for their removal, and assesses design strategies aimed at maximizing the photocatalytic efficiency of TiB and ZnB. The mechanisms responsible for the photocatalytic degradation of pharmaceutical micropollutants using TiB and ZnB photocatalysts are comprehensively detailed. Finally, the review outlines the prospects and challenges associated with the use of TiB and ZnB photocatalysts for the removal of PMPs from wastewater. It emphasizes their potential to effectively mitigate PMP contaminants and make substantial contributions to sustainable water management practices in the face of escalating environmental and public health concerns.

Constructed wetlands for the removal of organic micropollutants from wastewater: Current status, progress, and challenges

In this work, the practical utility of constructed wetlands (CWs) is described as a promising treatment option for micropollutants (MPs) in wastewater with the aid of their eco-friendly, low-energy, economically feasible, and ecologically sustainable nature. This paper offers a comprehensive review on CW technology with respect to the key strategies for MP removal such as phytoremediation, substrate adsorption, and microbial degradation. It explores the important factors controlling the performance of CWs (e.g., in terms of configurations, substrates, plant-microbe interactions, temperature, pH, oxygen levels, hydraulic loading rate, and retention time) along with the discussions on the pivotal role of microbial populations in CWs and plant-microbe cooperative remediation dynamics, particularly in relation to diverse organic MP patterns in CWs. As such, this review aims to provide valuable insights into the key strategies for optimizing MP treatment and for enhancing the efficacy of CW systems. In addition, the process-based models of constructed wetlands along with the numerical simulations based on the artificial neural network (ANN) method are also described in association with the data exploratory techniques. This work is thus expected to help open up new possibilities for the application of plant-microbe cooperative remediation approaches against diverse patterns of organic MPs present in CWs.

One-pot synthesis of g-C3N4/N-doped CeO2 nanocomposites and their potential visible light-driven photocatalytic degradation of methylene blue dye

In the pursuit of efficient photocatalytic materials for environmental applications, a new series of g-C3N4/N-doped CeO2 nanocomposites (g-C3N4/N-CeO2 NCs) was synthesized using a straightforward dispersion method. These nanocomposites were systematically characterized to understand their structural, optical, and chemical properties. The photocatalytic performance of g-C3N4/N-CeO2 NCs was evaluated by investigating their ability to degrade methylene blue (MB) dye, a model organic pollutant. The results demonstrate that the integration of g-C3N4 with N-doped CeO2 NCs reduces the optical energy gap compared to pristine N-doped CeO2, leading to enhanced photocatalytic efficiency. It is benefited from the existence of g-C3N4/N-CeO2 NCs not only in promoting the charge separation and inhibits the fast charge recombination but also in improving photocatalytic oxidation performance. Hence, this study highlights the potential of g-C3N4/N-CeO2 NCs as promising candidates for various photocatalytic applications, contributing to the advancement of sustainable environmental remediation technologies.

Mitigation of caffeine micropollutants in wastewater through Ag-doped ZnO photocatalyst: mechanism and environmental impacts

Micropollutants, such as caffeine (M-CF), pose a significant threat to ecosystems and human health through water and food sources. The utilization of metal oxide-based photocatalysts has proven to be an effective treatment method for the removal of organic pollutants. This study explores the efficacy of Ag-doped ZnO (Ag/ZnO) for removing M-CF from wastewater. The characterization of Ag/ZnO underscores the crucial role of band gap energy in the photocatalytic degradation process. This parameter influences the separation of electrons and holes (e-/h+) and the generation of reactive radicals. Under solar light, Ag/ZnO demonstrated markedly superior photocatalytic activity, achieving an impressive degradation efficiency of approximately 93.4%, in stark contrast to the 53.2% occurred by ZnO. Moreover, Ag/ZnO exhibited a remarkable degradation efficiency of M-CF in wastewater, reaching 83.5%. A key advantage of Ag/ZnO lies in its potential for recovery and reuse in subsequent treatments, contributing to a reduction in operational costs for industrial wastewater treatment. Impressively, even after five cycles, Ag/ZnO maintained a noteworthy photodegradation rate of M-CF at 78.6%. These results strongly suggest that Ag/ZnO presents a promising solution for the removal of micropollutants in wastewater, with potential scalability for industrial and large-scale applications.