In-situ electrochemical generation of permanganate for the treatment of atrazine

Novel Synthesis Pathways for Highly Oxidative Iron Species: Generation, Stability, and Treatment Applications of Ferrate(IV/V/VI)

Difficulties arise related to the economy-of-scale and practicability in applying conventional water treatment technologies to small and remote systems. A promising oxidation technology better suited for these applications is that of electro-oxidation (EO), whereby contaminants are degraded via direct, advanced, and/or electrosynthesized oxidant-mediated reactions. One species of oxidants of particular interest includes ferrates (Fe(VI)/(V)/(IV)), where only recently has their circumneutral synthesis been demonstrated, using high oxygen overpotential (HOP) electrodes, namely boron-doped diamond (BDD). In this study, the generation of ferrates using various HOP electrodes (BDD, NAT/Ni-Sb-SnO2, and AT/Sb-SnO2) was investigated. Ferrate synthesis was pursued in a current density range of 5-15 mA cm-2 and initial Fe3+ concentrations of 10-15 mM. Faradaic efficiencies ranged from 11-23%, depending on operating conditions, with BDD and NAT significantly outperforming AT electrodes. Speciation tests revealed that NAT synthesizes both ferrate(IV/V) and ferrate(VI), while the BDD and AT electrodes synthesized only ferrate(IV/V) species. A number of organic scavenger probes were used to test the relative reactivity, including nitrobenzene, carbamazepine, and fluconazole, whereby ferrate(IV/V) was significantly more oxidative than ferrate(VI). Finally, the ferrate(VI) synthesis mechanism by NAT electrolysis was elucidated, where coproduction of ozone was found to be a key phenomenon for Fe3+ oxidation to ferrate(VI).

Simultaneous remediation of arsenic and organic chemicals contaminated soil and groundwater using chemical oxidation and precipitation/stabilization: a case study

After the departure of industrial facilities, reuse of the land in developed cities in China is problematic, due to the land contamination issues. The rapid remediation of sites with complex contamination is crucial and urgently needed. Herein, the case of on-site remediation of arsenic (As) in soil, as well as benzo(a)pyrene, total petroleum hydrocarbons, and As in groundwater was reported. For contaminated soil, the oxidant and deactivator (consisting of 20% sodium persulfate, 40% ferrous sulfate (FeSO4), and 40% portland cement) were applied to oxidize and immobilize As. As a result, the total amount and lixivium concentration of As were constrained under 20 mg/kg and 0.01 mg/L, respectively. Meanwhile, for contaminated groundwater, As and organic contaminants were treated by FeSO4/ozone and FeSO4/hydrogen peroxide with mass ratios of 1:5 and 1:8, respectively. The continuous monitoring of contaminants in 22 monitoring wells shown that all contaminants in groundwater were treated to meet the standards. In addition, the risk of secondary pollution and operation cost was effectively reduced by proper disposal and resourceful utilization. The findings indicated that the method of oxidation and precipitation/stabilization is technically, environmentally, and economically feasible for the remediation of contaminated sites with similar complex pollutants.

Functional Bimetal/Carbon Composites Co/Zr@AC for Pesticide Atrazine Removal from Water

Atrazine is a toxic and refractory herbicide that poses threats to human health and the ecological environment. In order to efficiently remove atrazine from water, a novel material, Co/Zr@AC, was developed. This novel material is prepared by loading two metal elements, cobalt and zirconium, onto activated carbon (AC) through solution impregnation and high-temperature calcination. The morphology and structure of the modified material were characterized, and its ability to remove atrazine was evaluated. The results showed that Co/Zr@AC had a large specific surface area and formed new adsorption functional groups when the mass fraction ratio of Co²⁺:Zr⁴⁺ in the impregnating solution was 1:2, the immersion time was 5.0 h, the calcination temperature was 500 °C, and the calcination time was 4.0 h. During the adsorption experiment on 10 mg/L atrazine, the maximum adsorption capacity of Co/Zr@AC was shown to be 112.75 mg/g and the maximum removal rate was shown to be 97.5% after 90 min of the reaction at a solution pH of 4.0, temperature of 25 °C, and Co/Zr@AC concentration of 60.0 mg/L. In the kinetic study, the adsorption followed the pseudo-second-order kinetic model (R² = 0.999). The fitting effects of Langmuir and Freundlich isotherms were excellent, indicating that the process of Co/Zr@AC adsorbing atrazine also conformed to two isotherm models, so the adsorption of atrazine by Co/Zr@AC had multiple effects including chemical adsorption, mono-molecular layer adsorption, and multi-molecular layer adsorption. After five experimental cycles, the atrazine removal rate was 93.9%, indicating that Co/Zr@AC is stable in water and is an excellent novel material that can be used repeatedly.

Real-Time Monitoring of the Atrazine Degradation by Liquid Chromatography and High-Resolution Mass Spectrometry: Effect of Fenton Process and Ultrasound Treatment

High resolution mass spectrometry (HRMS) was coupled with ultra-high-performance liquid chromatography (uHPLC) to monitor atrazine (ATZ) degradation process of Fenton/ultrasound (US) treatment in real time. Samples were automatically taken through a peristaltic pump, and then analysed by HPLC-HRMS. The injection in the mass spectrometer was performed every 4 min for 2 h. ATZ and its degradation metabolites were sampled and identified. Online Fenton experiments in different equivalents of Fenton reagents, online US experiments with/without Fe²⁺ and offline Fenton experiments were conducted. Higher equivalents of Fenton reagents promoted the degradation rate of ATZ and the generation of the late-products such as Ammeline (AM). Besides, adding Fe²⁺ accelerated ATZ degradation in US treatment. In offline Fenton, the degradation rate of ATZ was higher than that of online Fenton, suggesting the offline samples were still reacting in the vial. The online analysis precisely controls the effect of reagents over time through automatic sampling and rapid detection, which greatly improves the measurement accuracy. The experimental set up proposed here both prevents the degradation of potentially unstable metabolites and provides a good way to track each metabolite.

Degradation of Residual Herbicide Atrazine in Agri-Food and Washing Water

Atrazine, an herbicide used to control grassy and broadleaf weed, has become an essential part of agricultural crop protection tools. It is widely sprayed on corn, sorghum and sugar cane, with the attendant problems of its residues in agri-food and washing water. If ingested into humans, this residual atrazine can cause reproductive harm, developmental toxicity and carcinogenicity. It is therefore important to find clean and economical degradation processes for atrazine. In recent years, many physical, chemical and biological methods have been proposed to remove atrazine from the aquatic environment. This review introduces the research works of atrazine degradation in aqueous solutions by method classification. These methods are then compared by their advantages, disadvantages, and different degradation pathways of atrazine. Moreover, the existing toxicological experimental data for atrazine and its metabolites are summarized. Finally, the review concludes with directions for future research and major challenges to be addressed.

Degradation of the typical herbicide atrazine by UV/persulfate: kinetics and mechanisms

Atrazine (ATZ), a widely used herbicide, had received a significant amount of attention due to its widespread detection in aquatic environments as well as its potential risks to human health. UV/persulfate (PS) process is an emerging technology for degrading organic pollutants in water. Thus, the degradation of ATZ by a UV/PS process was investigated in this study. The results showed that the removal rate of ATZ was 98.4% with a PS dosage of 2 mg/L and an initial ATZ concentration of 0.1 mg/L. In addition, a relatively high degradation efficiency was obtained under pH = 7. However, the addition of humic acid (HA) reduced the removal rate of ATZ. Hydroxyl radicals (•OH) and sulfate radicals (•SO₄^-) respectively contributed to 21.7% and 29% of the ATZ degradation. The ATZ degradation pathway was proposed, and the main reactions of ATZ in this UV/PS process included dechlorination, demethylation, and deethylation. Moreover, the toxicity of ATZ and its degradation products was assessed using the Toxicity Estimation Software Tool (TEST), and the results showed that the toxicity of the ATZ solution was reduced after the UV/PS process. These results indicate that UV/PS shows good promise as a remediation technique for the treatment of persistent herbicides such as ATZ in contaminated water.