Membrane concentrated landfill leachate (MCLL) contains large amounts of recalcitrant organic matter that cause potential hazards to the environment. Knowledge on the compositional variation of MCLL during treatment is important for a better understanding on the degradation pathway of organic pollutants. In this work, the structural change of MCLL during Fenton oxidation process was examined using spectroscopic techniques. The removal rates of COD, TOC and UV254 reached 78.9 ± 1.3%, 70.2 ± 1.4% and 90.64 ± 1.6%, respectively, under the optimal condition (i.e., dosage of H2O2 = 9.0 mL/200 mL, H2O2/Fe(II) molar ratio = 3.0, pH = 3.0, time = 40 min). Spectral analyses suggested that aromatic/CC structure and CO bonds in MCLL can be successfully destroyed by Fenton oxidation, resulting in a decrease in molecular weight. One fulvic-like and one humic-like components were identified in MCLL, both of which can be removed by Fenton treatment. In addition, two-dimensional correlation spectroscopic analyses suggested the oxidative changes of MCLL structure in the order of fulvic-like component/unsaturated conjugated bond > aromatic structure > humic-like component. The results may provide a new insight to the understanding on the structure variation of MCLL during treatment, which is beneficial for the design of cost-effective treatment strategies.

Environmental pollution by heavy metals (HMs) has raised considerable attention due to their toxic impacts on plants, animals and human beings. Thus, the environmental cleanup of these toxic (HMs) is extremely urgent both from the environmental and biological point of view. To remediate HMs-polluted environment, several nanoparticles (NPs) such as metals and its oxides, carbon materials, zeolites, and bimetallic NPs have been documented. Among these, Fe-based NPs have emerged as an effective choice for remediating environmental contamination, due to infinite size, high reactivity, and adsorption properties. This review summarizes the utilization of various Fe-based NPs such as nano zero-valent iron (NZVI), modified-NZVI, supported-NZVI, doped-NZVI, and Fe oxides and hydroxides in remediating the HMs-polluted environment. It presents a comprehensive elaboration on the possible reaction mechanisms between the Fe-based NPs and heavy metals, including adsorption, oxidation/reduction, and precipitation. Subsequently, the environmental factors (e.g., pH, organic matter, and redox) affecting the reactivity of the Fe-based NPs with heavy metals are also highlighted in the current study. Research shows that Fe-based NPs can be toxic to living organisms. In this context, this review points out the environmental hazards associated with the application of Fe-based NPs and proposes future recommendations for the utilization of these NPs.

Disinfection means the killing of pathogenic organisms (e.g. bacteria and its spores, viruses, protozoa and their cysts, worms, and larvae) present in water to make it potable for other domestic works. The substances used in the disinfection of water are known as disinfectants. At municipal level, chlorine (Cl₂), chloramines (NH₂Cl, NHCl₂), chlorine dioxide (ClO₂), ozone (O₃) and ultraviolet (UV) radiations, are the most commonly used disinfectants. Chlorination, because of its removal efficiency and cost effectiveness, has been widely used as method of disinfection of water. But, disinfection process may add several kinds of disinfection by-products (DBPs) (∼600–700 in numbers) in the treated water such as Trihalomethanes (THM), Haloacetic acids (HAA) etc. which are detrimental to the human beings in terms of cytotoxicity, mutagenicity, teratogenicity and carcinogenicity. In water, THMs and HAAs were observed in the range from 0.138 to 458 μg/L and 0.16–136 μg/L, respectively. Thus, several regulations have been specified by world authorities like WHO, USEPA and Bureau of Indian Standard to protect human health. Some techniques have also been developed to remove the DBPs as well as their precursors from the water. The popular techniques of DBPs removals are adsorption, advance oxidation process, coagulation, membrane based filtration, combined approaches etc. The efficiency of adsorption technique was found up to 90% for DBP removal from the water.

Anaerobic ammonium oxidation (anammox), denitrifying anaerobic methane oxidation bacteria (DAMO) have received great attention for their excellent performance in nitrogen removal. However, not much study focused on the co-existence of anammox, DAMO, and denitrification in constructed wetlands, not to mention the advantage of their application in mitigating the necessary byproduct nitrous oxide (N₂O), methane (CH₄) from the biodegradation process. In this study, the result indicated the construction of integrated vertical constructed wetlands (IVCWs) contributed to the high-efficient stable simultaneous anammox, DAMO and denitrification (SADD) process for the nutrients removal, with denitrification being the least contributor to nitrogen reduction. Besides the succession of SADD process was largely the driver for the variation of N₂O, CH₄ emission. The structural equation method (SEM) further suggested that the three biological pathways of qnorB/bacteria, archaea/qnorB, and anammox/nirK accounted for the N₂O production, as were top-controlled by mcrA/DAMO in IVCWs. Besides the anammox-associated nitrifier denitrification was the main source for N₂O production. And that the trade-off effect between the CH₄ and N₂O production was exerted by the DAMO, while the influence was far from satisfactory under the methane constraints.

Metalaxyl is a broad-spectrum chiral fungicide that used for the protection of plants, however extensive use of metalaxyl resulted in serious environmental problems. Thus, a study on the detoxification mechanism in algae/cyanobacteria and their ability for phycoremediation is highly recommended. Here, we investigated the physiological and biochemical responses of two cyanobacterial species; Anabaena laxa and Nostoc muscorum to R-metalaxyl toxicity as well as their ability as phycoremediators. Two different levels of R-metalaxyl, at mild (10 mg/L) and high dose (25 mg/L), were applied for one-week. We found that A. laxa absorbed and accumulated more intracellular R-metalaxyl compared to N. muscorum. R-metalaxyl, which triggered a dose-based reduction in cell growth, photosynthetic pigment content, and photosynthetic key enzymes’ activities i.e., phosphoenolpyruvate carboxylase (PEPC) and ribulose‒1,5‒bisphosphate carboxylase/oxygenase (RuBisCo). These decreases were significantly less pronounced in A. laxa. On the other hand, R-metalaxyl significantly induced oxidative damage markers, e.g., H₂O₂ levels, lipid peroxidation (MDA), protein oxidation and NADPH oxidase activity. However, these increases were also lower in A. laxa compared to N. muscorum. To alleviate R-metalaxyl toxicity, A. laxa induced the polyphenols, flavonoids, tocopherols and glutathione (GSH) levels as well as peroxidase (POX), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-s-transferase (GST) enzyme activities. On the contrary, the significant induction of antioxidants in N. muscorum was restricted to ascorbate, catalase (CAT) and ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) enzyme activities. Although A. laxa accumulated more R-metalaxyl, it experienced less stress due to subsequent induction of antioxidants. Therefore, A. laxa may be a promising R-metalaxyl phycoremediator. Our results provided basic data for understanding the ecotoxicology of R-metalaxyl contamination in aquatic habitats and the toxicity indices among cyanobacteria.

NO₂ oxidation of soot exhausted from engines is more efficient than O₂ under low-temperature conditions, and is crucial for diesel particulate filter to control soot pollution. To explore the principle behind accelerating soot oxidation by NO₂, this paper uses density functional theory to reveal soot oxidation process by NO₂. This study contributes to understanding rules of soot oxidation by NO₂ and perfecting soot oxidation models to develop soot emission control technologies. Results show that NO₂ oxidation of pyrene radical involves three steps. Firstly, NO₂ attacks the C∗ atom to form –C (NO₂) with reaction energy of 306.3 kJ/mol, which decomposes to produce a –C (O) compound. Secondly, another NO₂ molecule climbs over an energy barrier of 8.8 kJ/mol, and changes into a –C (ONO₂) intermediate on –C (O). Finally, the N or O atom of NO₂ attacks –C (O) for a second time to help open aromatic ring for releasing CO or CO₂. Further decomposition of –C (NO₂) and –C (ONO₂) requires activation energies of 81.6 kJ/mol, 75.7 kJ/mol, and 53.5 kJ/mol, respectively, on preferential pathways. Calculations prove that attacks of O atom from NO₂ on C∗ help open the aromatic ring more efficiently than N atom.

Cylindrospermopsin (CYN) is an important cyanobacterial toxin posing a major threat to surface waters during cyanobacterial blooms. Hence, methods for cyanotoxin removal are required to confront seasonal or local incidences to sustain the safety of potable water reservoirs. Non-thermal plasmas provide the possibility for an environmentally benign treatment which can be adapted to specific concentrations and environmental conditions without the need of additional chemicals. We therefore investigated the potential of two different non-thermal plasma approaches for CYN degradation, operated either in a water mist, i.e. in air, or submerged in water. A degradation efficacy of 0.03 ± 0.00 g kWh⁻¹ L⁻¹ was found for a dielectric barrier discharge (DBD) operated in air, while a submerged pulsed corona-like discharge resulted in an efficacy of 0.24 ± 0.02 g kWh⁻¹ L⁻¹. CYN degradation followed a pseudo zeroth order or pseudo first order reaction kinetic, respectively. Treatment efficacy of the corona-like discharge submerged in water increased with pH values of the initial solution changing from 5.0 to 7.5. Notably, a pH-depending residual oxidative effect was observed for the submerged discharge, resulting in ongoing CYN degradation, even without further plasma treatment. In this case hydroxyl radicals were identified as the dominant oxidants of CYN at acidic pH values. In comparison, degradation by the DBD could be related primarily to the generation of ozone.

Urine, which is an important waste biomass resource, is the main source of nitrogen in sewage and contains large quantities of emerging contaminants (ECs). In this study, we propose a new method to efficiently remove urine, simultaneously eliminate ECs, and control the generation of toxic chlorate during urine treatment using a photoelectrocatalytic-chlorine (PEC-Cl) system. A type-II heterojunction of WO₃/BiVO₄ was used as a photoanode to generate chlorine radicals (Cl•) by decreasing the oxidation potential of WO₃ valence band for the highly selective conversion of urine to N₂ and the simultaneous degradation of ECs in an efficient manner. The method presented surprising results. It was observed that the amount of toxic chlorate was significantly inhibited by circumventing the over-oxidation of Cl⁻ by holes or hydroxyl radicals (•OH). Moreover, the removal of urea nitrogen reached 97% within 90 min, while the degradation rate of trimethoprim in urine was above 98.6% within 60 min, which was eight times more than that in the PEC system (12.1%). Compared to the bare WO₃ photoanode, the toxic chlorate and nitrate generated by the WO₃/BiVO₄ heterojunction photoanode decreased by 61% and 44%, respectively. Thus, this study provides a safe, efficient, and environmentally-friendly approach for the disposal of urine.

Considering the increasing use of Lithium (Li) and the necessity to fulfil this demand, labile Li occurrence in the environment will be enhanced. Thus, additional research is needed regarding the presence of this element in marine environment and its potential toxic impacts towards inhabiting wildlife. The aim of the present study was to evaluate Li toxicity based on the exposure of Mytilus galloprovincialis to this metal, assessing the biochemical changes related with mussels’ metabolism, oxidative stress and neurotoxicity. For this, organisms were exposed to different Li concentrations (100, 250, 750 μg/L) for 28 days. The results obtained clearly demonstrated that Li lead to mussels’ metabolism depression. The present study also revealed that, especially at the highest concentrations, antioxidant and biotransformation enzymes were not activated, leading to the occurrence of lipid peroxidation and loss of redox homeostasis, with increased content in oxidized glutathione in comparison to the reduced form. Furthermore, after 28 days, higher Li exposure concentrations induced neurotoxic effects in mussels, with a decrease in acetylcholinesterase enzyme activity. The responses observed were closely related with Li concentrations in mussels’ tissues, which were more pronounced at higher exposure concentrations. Such results highlight the potential toxic effects of Li to marine species, which may even be higher under predicted climate changes and/or in the presence of other pollutants.

Recently, sulfate radical-based advanced oxidation processes (SR-AOPs) have been studied extensively for the removal of pollutants, however, few researches focused on the activation of bisulfite by nanoscale zerovalent iron (nZVI), especially, surface reaction mechanism and sulfate radical-mediated degradation pathway have not been elucidated in detail. In this study, influencing factors, the kinetics, transformation pathway and mechanism of triphenyl phosphate (TPHP) degradation in the nZVI/bisulfite system were systematically discussed. Compared with Fe²⁺, nZVI was found to be a more efficient and long-lasting activator of bisulfite via gradual generation of iron ions. The optimal degradation efficiency of TPHP (98.2%) and pseudo-first-order kinetics rate constant (kₒbₛ = 0.2784 min⁻¹) were obtained by using 0.5 mM nZVI and 2.0 mM bisulfite at the initial pH 3.0. Both Cl⁻ and NO₃⁻ inhibited the degradation of TPHP and the inhibitory effect of Cl⁻ was stronger than that of NO₃⁻ due to the higher reaction rate of Cl⁻ with •SO₄⁻. Furthermore, SEM, XRD and XPS characterization revealed that a thin passivation layer (Fe₂O₃, Fe₃O₄, FeOOH) deposited on the surface of fresh nZVI and a few iron corrosion products generated and assembled on the surface of reacted nZVI. Radical quenching tests identified that •SO₄⁻ was the dominant reactive oxidative species (ROS) for TPHP removal. Based on HRMS analysis, six degradation products were determined and a sulfate radical-mediated degradation pathway was proposed. In a word, this study revealed that the nZVI/bisulfite system had a great potential for the TPHP elimination in waterbody.