Assessment of the UV/Cl2 advanced oxidation process for the degradation of the emerging contaminants amitriptyline hydrochloride, methyl salicylate and 2-phenoxyethanol in water systems

Construction of cubic CaTiO3 perovskite modified by highly-dispersed cobalt for efficient catalytic degradation of psychoactive pharmaceuticals

Sulfate radical mediated advanced oxidation processes (SR-AOPs) have emerged as a promising alternative for emerging contaminants degradation. However, high activity and great stability are commonly difficult to juggle, and the structure-activity correlations are still ambiguous. This study constructed the cubic CaTiO3 perovskite modified by highly-dispersed cobalt for peroxymonosulfate (PMS) activation to improve the specific lattice plane exposure and reduce the metal leaching simultaneously. 98% of amitriptyline (AMT) degradation was achieved within 60 min under the condition of 200 mg/L Co0.1-CTO and 100 mg/L PMS. The results indicated that surface Co2+/Co3+ redox couple and lattice oxygen were responsible for PMS activation, and the evolution of ·OH, SO4·- and 1O2 were revealed. According to density functional theory (DFT) calculations, the highly-dispersed Co on cubic surface effectively captured PMS and promoted electron transfer for the generation of ·OH and SO4·-, while more oxygen atoms exposed on Co0.1-CTO(200) surface facilitated the generation of 1O2. Briefly, this study provides a novel strategy of catalyst synthesis in PMS activation for water treatment.

Advanced oxidation mechanism of UV photolysis of electrochemically generated free bromine

In recent times, some researchers have successfully demonstrated the efficacy of UV photolysis of electrochemically generate free chlorine (UV/electro-chlorine) as for an advanced oxidation process. Since bromine as well as chlorine is an element belonging to halogen, it is expected that UV photolysis of electrochemically generated free bromine (UV/electro-bromine) also shows an advanced oxidation effect. To elucidate the feasibility of UV/electro-bromine system, its advanced oxidation mechanism was investigated using radical probes of 1,4-dioxane and nitrobenzene. In contrast to the UV/electro-chlorine system, the advanced oxidation effect of UV/electro-bromine system was inhibited under acidic conditions due to the accumulation of photochemically inert Br₂. The most abundant radical in UV/electro-bromine system was dibromine radical anion (Br₂˙^-) and the second-order reaction rate constant of Br₂˙^- with 1,4-dioxane was estimated to be 2.4 × 10⁵ M^-1 s^-1. As a result of the abundance and the reactivity of Br₂˙^-, it was the main contributor to 1,4-dioxane degradation. On the other hand, nitrobenzene was mainly decomposed by direct UV photolysis because Br₂˙^- does not react with nitrobenzene. The contribution of hydroxyl radical (HO˙) to 1,4-dioxane degradation was much lower than that of Br₂˙^- because its concentration was 4-5 order of magnitude lower than that of Br₂˙^-. However, the HO˙ concentration elevated with a decrease in the concentration of bromide ion (Br^-). Consequently, the reactivity of Br₂˙^- with pollutants and the Br^- concentration have critical impacts on the advanced oxidation performance of UV/electro-bromine system.

Ultrasound/chlorine sono-hybrid-advanced oxidation process: Impact of dissolved organic matter and mineral constituents

In this work, after exploring the first report on the synergism of combining ultrasound (US: 600 kHz) and chlorine toward the degradation of Allura Red AC (ARAC) textile dye, as a contaminant model, the impact of various mineral water constituents (Cl-, SO42-, NO3-, HCO3- and NO2-) and natural organic matter, i.e., humic acid (HA), on the performance of the US/chlorine sono-hybrid process was assessed for the first time. Additionally, the process effectiveness was evaluated in a real natural mineral water (NMW) of a known composition. Firstly, it was found that the combination of ultrasound and chlorine (0.25 mM) at pH 5.5 in cylindrical standing wave ultrasonic reactor (f = 600 kHz and Pe = 120 W, equivalent to PA ∼ 2.3 atm) enhanced in a drastic manner the degradation rate of ARAC; the removal rate being 320% much higher than the arithmetic sum of the two separated processes. The source of the synergistic effect was attributed to the effective implication of reactive chlorine species (RCS: Cl, ClO and Cl2-) in the degradation process. Radical probe technique using nitrobenzene (NB) as a specific quencher of the acoustically generated hydroxyl radical confirmed the dominant implication of RCS in the overall degradation rate of ARAC by US/chlorine system. Overall, the presence of humic acid and mineral anions decreased the efficiency of the sono-hybrid process; however, the inhibition degrees depend on the type and the concentration of the selected additives. The reaction of these additives with the generated RCS is presumably the reason for the finding results. The inhibiting effect of Cl-, SO42-, NO3- and NO2- was more pronounced in US/chlorine process as compared to US alone, whereas the inverse scenario was remarked for the effect of HA. These outcomes were associated to the difference in the reactivity of HA and mineral anions toward RCS and OH oxidizing species, in addition to the more selective character of RCS than hydroxyl radical. The displacement of the reaction zone with increasing the additive concentration may also be another influencing factor that favors competition reactions, which subsequently reduce the available reactive species in the reacting medium. The NMW exerted reductions of 43% and 10% in the process efficiency at pH 5.5 and 8, respectively, thereby confirming the RCS-quenching mechanism by the water matrix constituents. Hence, this work provided a precise understanding of the overall mechanism of chlorine activation by ultrasound to promote organic compounds degradation in water.

The multiple role of inorganic and organic additives in the degradation of reactive green 12 by UV/chlorine advanced oxidation process

The impact of various mineral anions, diverse organic substrates and different environmental matrices on the removal of C.I. reactive green 12 (RG12), a refractory textile dye, by UV/chlorine emerging advanced oxidation process (AOP) was performed. The co-exposure of RG12 (20 mg L^-1) to UV and chlorine (0.5 mM) at pH 5 produced a strong synergism on the degradation rate. Radical probe technique showed that ^●OH and Cl₂^●- were the main source of the synergistic effect. Bromide, bicarbonate and chloride at small dosage, i.e. 1 mM, enhanced the rate of RG12 degradation, but higher concentrations of these anions quenched the degradation process. Sulphate anions did not alter the degradation rate of the dye, but nitrite quenched it at ∼ 90%. The inhibiting effect of nitrate appeared only at advanced reaction time (>1 min).On the other hand, natural organic matter (NOM) reduced effectively the degradation rate. Besides, SDS surfactant at only 1 µM accelerated the degradation efficiency by ∼12%. However, Tween 80 has shown an insignificant effect, whereas reductions of 10% and 30% were recorded by Triton X100 and Tween 20, respectively. The RG12-degradation rate was not affected in the mineral water, but it was drastically improved in seawater. Conversely, a huge drop in the RG12-degradation efficiency was obtained in the wastewater effluent. UV/chlorine process is highly viable for degrading pollutant in matrices free of NOM. However, the process losses its potential application in matrices riche of NOM.

Current Approaches to and Future Perspectives on Methomyl Degradation in Contaminated Soil/Water Environments

Methomyl is a broad-spectrum oxime carbamate commonly used to control arthropods, nematodes, flies, and crop pests. However, extensive use of this pesticide in agricultural practices has led to environmental toxicity and human health issues. Oxidation, incineration, adsorption, and microbial degradation methods have been developed to remove insecticidal residues from soil/water environments. Compared with physicochemical methods, biodegradation is considered to be a cost-effective and ecofriendly approach to the removal of pesticide residues. Therefore, micro-organisms have become a key component of the degradation and detoxification of methomyl through catabolic pathways and genetic determinants. Several species of methomyl-degrading bacteria have been isolated and characterized, including Paracoccus, Pseudomonas, Aminobacter, Flavobacterium, Alcaligenes, Bacillus, Serratia, Novosphingobium, and Trametes. The degradation pathways of methomyl and the fate of several metabolites have been investigated. Further in-depth studies based on molecular biology and genetics are needed to elaborate their role in the evolution of novel catabolic pathways and the microbial degradation of methomyl. In this review, we highlight the mechanism of microbial degradation of methomyl along with metabolic pathways and genes/enzymes of different genera.

Paraquat Degradation From Contaminated Environments: Current Achievements and Perspectives

Paraquat herbicide has served over five decades to control annual and perennial weeds. Despite agricultural benefits, its toxicity to terrestrial and aquatic environments raises serious concerns. Paraquat cannot rapidly degrade in the environment and is adsorbed in clay lattices that require urgent environmental remediation. Advanced oxidation processes (AOPs) and bioaugmentation techniques have been developed for this purpose. Among various techniques, bioremediation is a cost-effective and eco-friendly approach for pesticide-polluted soils. Though several paraquat-degrading microorganisms have been isolated and characterized, studies about degradation pathways, related functional enzymes and genes are indispensable. This review encircles paraquat removal from contaminated environments through adsorption, photocatalyst degradation, AOPs and microbial degradation. To provide in-depth knowledge, the potential role of paraquat degrading microorganisms in contaminated environments is described as well.