The mechanism of aquatic photodegradation of organophosphorus sensitized by humic acid-Fe3+ complexes

Chlorination of L-tyrosine and metal complex: degradation kinetics and disinfection by-products generation

The presence of metal ions in drinking water treatment and distribution systems may affect the disinfection process of organic matter, which had aroused people's concern. L-tyrosine can complex with metal ions through carboxyl, carbonyl, and amino groups and affect its chemical reactions. In this paper, the complexation of L-tyrosine with common metal ions was studied and the influence of complexation on chlorination with different experimental factors was investigated. It was inferred that L-tyrosine complexed with metal ions by single dentate ligand or double dentate chelation in a ratio of 2:1. The degradation of L-tyrosine-metal complex followed the pseudo-first-order reaction kinetic. TCM, DCAA, and TCAA were the main species DBPs in the chlorination of L-tyrosine. Compared with L-tyrosine, the reaction rate constants of complex increased by 5.6%, the formation of trihalomethane production decreased by 21.5% and the formation of haloacetic acids production increased by 26.9% at the state of metal complexation. The effect of metal complexation on chlorination was more obvious than that of metal coexistence. For different metal complexation, the order of inhibition on trihalomethane production was Ca2+> Fe3+> Mn2+ and the order of promotion on haloacetic acids production was Mn2+> Fe3+> Ca2+. Moreover, it was found that alkaline conditions were favorable for the formation of DBPs due to the hydroxyl radical. The combination of ultraviolet and chlorine disinfection promoted L-Tyrosine degradation and DBPs generation, and the promotion efficiency follow the order: UV/Cl2> UV-Cl2> Cl2.

Abiotic transformation of kresoxim-methyl in aquatic environments: Structure elucidation of transformation products by LC-HRMS and toxicity assessment

In this study, abiotic transformation of an important strobilurin fungicide, kresoxim-methyl, was investigated under controlled laboratory conditions for the first time by studying its kinetics of hydrolysis and photolysis, degradation pathways and toxicity of possibly formed transformation products (TPs). The results indicated that kresoxim-methyl showed a fast degradation in pH9 solutions with DT₅₀ of 0.5 d but relatively stable under neutral or acidic environments in the dark. It was prone to photochemical reactions under simulated sunlight, and the photolysis behavior was easily affected by different natural substances such as humic acid (HA), Fe³⁺and NO₃^-which are ubiquitous in natural water, showing the complexity of degradation mechanisms and pathways of this chemical compound. The potential multiple photo-transformation pathways via photoisomerization, hydrolyzation of methyl ester, hydroxylation, cleavage of oxime ether and cleavage of benzyl ether were observed. 18 TPs generated from these transformations were structurally elucidated based on an integrated workflow combining suspect and nontarget screening by high resolution mass spectrum (HRMS), and two of them were confirmed with reference standards. Most of TPs, as far as we know, have never been described before. The in-silico toxicity assessment showed that some of TPs were still toxic or very toxic to aquatic organisms, although they exhibit lower aquatic toxicity compared to the parent compound. Therefore, the potential hazards of the TPs of kresoxim-methyl merits further evaluation.

Heterogeneous photocatalytic oxidation for the removal of organophosphorus pollutants from aqueous solutions: A review

Organophosphorus pollutants (OPs), which are compounds containing carbon‑phosphorus bonds or phosphate derivatives containing organic groups, have received much attention from researchers because of their persistence in the aqueous environment for long periods of time and the threat they pose to human health. Heterogeneous photocatalysis has been widely applied to the removal of OPs from aqueous solutions due to its better removal effect and environmental friendliness. In this review, the removal of OPs from aqueous matrices by heterogeneous photocatalysis was presented. Herein, the application and the heterogeneous photocatalysis mechanism of OPs were described in detail, and the effects of catalyst types on degradation effect are discussed categorically. In particular, the heterojunction type photocatalyst has the most excellent effect. After that, the photocatalytic degradation pathways of several OPs were summarized, focusing on the organophosphorus pesticides and organophosphorus flame retardants, such as methyl parathion, dichlorvos, dimethoate and chlorpyrifos. The toxicity changes during degradation were evaluated, indicating that the photocatalytic process could effectively reduce the toxicity of OPs. Additionally, the effects of common water matrices on heterogeneous photocatalytic degradation of OPs were also presented. Finally, the challenges and perspectives of heterogeneous photocatalysis removal of OPs are summarized and presented.

Roles of humic substances redox activity on environmental remediation

Humic substances (HS) as representative natural organic matters and the most common organic compounds existing in the environment, has been applied to the treatment and remediation of environmental pollution. This review systematically introduces and summarizes the redox activity of HS for the remediation of environmental pollutants. For inorganic pollutants (such as silver, chromium, mercury, and arsenic), the redox reaction of HS can reduce their toxicity and mobilization, thereby reducing the harm of these pollutants to the environment. The concentration and chemical composition of HS, environmental pH, ionic strength, and competing components affect the degree and rate of redox reactions between inorganic pollutants and HS significantly. With regards to organic pollutants, HS has photocatalytic activity and produces a large number of reactive oxygen species (ROS) under the light which reacts with organic pollutants to accelerate the degradation of organic pollutants. Under the affection of HS, the redox of Fe(III) and Fe(II) can enhance the efficiency of Fenton-like reaction to degrade organic pollutants. Finally, the research direction of HS redox remediation of environmental pollution is prospected.

Humic Substances as Microalgal Biostimulants—Implications for Microalgal Biotechnology

Humic substances (HS) act as biostimulants for terrestrial photosynthetic organisms. Their effects on plants are related to specific HS features: pH and redox buffering activities, (pseudo)emulsifying and surfactant characteristics, capacity to bind metallic ions and to encapsulate labile hydrophobic molecules, ability to adsorb to the wall structures of cells. The specific properties of HS result from the complexity of their supramolecular structure. This structure is more dynamic in aqueous solutions/suspensions than in soil, which enhances the specific characteristics of HS. Therefore, HS effects on microalgae are more pronounced than on terrestrial plants. The reported HS effects on microalgae include increased ionic nutrient availability, improved protection against abiotic stress, including against various chemical pollutants and ionic species of potentially toxic elements, higher accumulation of value-added ingredients, and enhanced bio-flocculation. These HS effects are similar to those on terrestrial plants and could be considered microalgal biostimulant effects. Such biostimulant effects are underutilized in current microalgal biotechnology. This review presents knowledge related to interactions between microalgae and humic substances and analyzes the potential of HS to enhance the productivity and profitability of microalgal biotechnology.

Optimum parameters for humic acid removal and power production by Al-air fuel cell electrocoagulation in synthetic wastewater

Although humic acid (HA) is a complex natural organic matter, it can potentially harm the environment and human health. In this study, aluminum-air fuel cell electrocoagulation (AAFCEC) was used to remove HAs from water while generating electricity. Initial pH, electrolyte concentration, HA concentration electrode distance and external resistance were investigated to determine the power generation and removal efficiency. The results showed that the better performance of power generation has been acquired in the alkaline solution and larger electrolyte concentration and short electrode distance. Further, Al-Ferron complexation timed spectrophotometry was used to determine the Al speciation distribution in the solution under different parameters. The power density of the cell reached 313.47 mW/cm² for the following conditions: 1 g/L NaCl concentration, 3 cm electrode distance, 20 Ω external resistor, and pH 9. After about an hour of electrolysis, the optimum removal rate of HA was above 99%. The results demonstrated that the AAFCEC is an efficient and eco-friendly water treatment process, and it could be further developed and disseminated in the rural areas and households.

Microcrystalline Cellulose-Blended Polyethersulfone Membranes for Enhanced Water Permeability and Humic Acid Removal

A novel polyethersulfone (PES)/microcrystalline cellulose (MCC) composite membrane for humic acid (HA) removal in water was fabricated using the phase inversion method by blending hydrophilic MCC with intrinsically hydrophobic PES in a lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) co-solvent system. A rheological study indicated that the MCC-containing casting solutions exhibited a significant increase in viscosity, which directly influenced the composite membrane's pore structure. Compared to the pristine PES membrane, the composite membranes have a larger surface pore size, elongated finger-like structure, and presence of sponge-like pores. The water contact angle and pure water flux of the composite membranes indicated an increase in hydrophilicity of the modified membranes. However, the permeability of the composite membranes started to decrease at 3 wt.% MCC and beyond. The natural organic matter removal experiments were performed using humic acid (HA) as the surface water pollutant. The hydrophobic HA rejection was significantly increased by the enhanced hydrophilic PES/MCC composite membrane via the hydrophobic-hydrophilic interaction and pore size exclusion. This study provides insight into the utilization of a low-cost and environmentally friendly additive to improve the hydrophilicity of PES membranes for efficient removal of HA in water.

Ultra-high synergetic intensity for humic acid removal by coupling bubble discharge with activated carbon

Humic acid (HA) removal research focuses on the global water treatment industry. In this work, efficient HA degradation with an ultra-high synergetic intensity is achieved by combined bubble discharge with activated carbon (AC). Adding AC to the discharge greatly improves HA removal efficiency and degradation speed; the synergetic intensity reaches 651.52% in the combined system, and the adsorption residual on AC is 4.52%. After 90 min of treatment, the HA removal efficiency reaches 98.90%, 31.29%, and 7.61% in the plasma-AC combined, solo bubble discharge, and solo AC adsorption systems, respectively. During the plasma process, the number of pore structures and active sites and the amount of oxygen-containing functional groups on the AC surface increase, resulting in a higher adsorption capacity to reactive species (H₂O₂ and O₃) and HA and promoting interactions on the AC surface. For HA mineralization, the presence of AC greatly promotes the destruction of aromatic structures and chromophoric HA functional groups.

Arsenate phytotoxicity regulation by humic acid and related metabolic mechanisms

The use of irrigation water containing arsenic (As) had led to large areas of As-contaminated farmland, and as a result, plants and food have become severely poisoned. Humic acid (HA) can be complexed with metals, which in turn affects the metals' behavior. Herein, we explored the accumulation of arsenate in lettuce treated with different concentrations of arsenate and studied the effects of HA on the accumulation and toxicity of arsenate. The addition of HA did not cause significant changes in the arsenate content in lettuce but had a significant effect on the activity of antioxidant enzymes, which improved the antioxidant capability of the lettuce plants. Furthermore, HA promoted the accumulation of nutrients, such as magnesium (Mg), calcium (Ca), molybdenum (Mo) and manganese (Mn), in the leaves. Arsenate disrupted metabolic pathways, such as amino acid metabolism, carbohydrate metabolism, and aminoacyl-tRNA biosynthesis. The addition of HA increased the contents of amino acids and sugars, thereby improving lettuce growth. The present study explored the effects of HA on As accumulation and related physiological changes (antioxidant enzyme activities, absorption of nutrients and metabolic mechanisms) and provided insights into the regulation of As contamination by HA, which is relatively inexpensive.