Biodegradation of hexazinone by two isolated bacterial strains (WFX-1 and WFX-2)

Bacterial chemotaxis of herbicide atrazine provides an insight into the degradation mechanism through intermediates hydroxyatrazine, N-N-isopropylammelide, and cyanuric acid compounds

In recent times, the herbicide atrazine (ATZ) has been commonly used before and after the cultivation of crop plants to manage grassy weeds. Despite its effect, the toxic residues of ATZ affect soil fertility and crop yield. Hence, the current study is focused on providing insight into the degradation mechanism of the herbicide atrazine through bacterial chemotaxis involving intermediates responsive to degradation. A bacterium was isolated from ATZ-contaminated soil and identified as Pseudomonas stutzeri based on its morphology, biochemical and molecular characterization. Upon ultra-performance liquid chromatography analysis, the free cells of isolated bacterium strain was found to utilize 174 μg/L of ATZ after 3-days of incubation on a mineral salt medium containing 200 μg/L of ATZ as a sole carbon source. It was observed that immobilized based degradation of ATZ yielded 198 μg/L and 190 μg/L by the cells entrapped with silica beads and sponge, respectively. Furthermore, the liquid chromatography-mass spectroscopy revealed that the secretion of three significant metabolites, namely, cyanuric acid, hydroxyatrazine and N- N-Isopropylammelide is responsive to the biodegradation of ATZ by the bacterium. Collectively, this research demonstrated that bacterium strains are the most potent agent for removing toxic pollutants from the environment, thereby enhancing crop yield and soil fertility with long-term environmental benefits.

Application of lead oxide electrodes in wastewater treatment: A review

Electrochemical oxidation (EO) based on hydroxyl radicals (·OH) generated on lead dioxide has become a typical advanced oxidation process (AOP). Titanium-based lead dioxide electrodes (PbO₂/Ti) play an increasingly important role in EO. To further improve the efficiency, the structure and properties of the lead dioxide active surface layer can be modified by doping transition metals, rare earth metals, nonmetals, etc. Here, we compare the common preparation methods of lead dioxide. The EO performance of lead dioxide in wastewater containing dyes, pesticides, drugs, landfill leachate, coal, petrochemicals, etc., is discussed along with their suitable operating conditions. Finally, the factors influencing the contaminant removal kinetics on lead dioxide are systematically analysed.

Electrochemical degradation of insecticide hexazinone with Bi-doped PbO2 electrode: Influencing factors, intermediates and degradation mechanism

Electrochemical degradation of hexazinone in aqueous solution using Bi-doped PbO₂ electrodes as anodes was investigated. The main influencing parameters on the electrocatalytic degradation of hexazinone were analyzed as function of initial hexazinone concentration, current density, initial pH value and Na₂SO₄ concentration. The experiment results showed that the electrochemical oxidization reaction of hexazinone fitted pseudo-first-order kinetics model. 99.9% of hexazinone can be decontaminated using Bi-doped PbO₂ electrode as anode for 120 min. Comparing with pure PbO₂ electrode, the Bi-doped PbO₂ electrodes possess higher hexazinone and COD removal ratio, higher ICE and lower energy consumption in the electrocatalytic degradation process. The results revealed that electrochemical oxidation using Bi-doped PbO₂ anodes was an efficient method for the elimination of hexazinone in aqueous solution. The electrocatalytic oxidization mechanism of hexazinone with Bi-doped PbO₂ anode was discussed, then the possible degradation pathway of hexazinone with two parallel sub-routes was elucidated according to 15 intermediates identified using HPLC-MS.

Isolation and identification of hexazinone-degrading bacterium from sugarcane-cultivated soil in Kenya

The s-triazine herbicide hexazinone [3-cyclohexyl-6-dimethylamino-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], is widely used in agriculture for weed control. Laboratory biodegradation experiments for hexazinone in liquid cultures were carried out using sugarcane-cultivated soils in Kenya. Liquid culture experiments with hexazinone as the only carbon source led to the isolation of a bacterial strain capable of its degradation. Through morphological, biochemical and molecular characterization by 16S rRNA, the isolate was identified as Enterobacter cloacae. The isolate degraded hexazinone up to 27.3% of the initially applied concentration of 40 μg mL(-1) after 37 days of incubation in a liquid culture medium. The study reports the degradation of hexazinone and characterization of the isolated bacterial strain.