Experimental-design-guided approach for the removal of atrazine by sono-electrochemical-UV-chlorine techniques

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH₂Cl- and ClO₂-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.

Nano-sphere RuO2 embedded in MOF-derived carbon arrays as a dual-matrix anode for cost-effective electrochemical wastewater treatment

The electrodes' activity, surface area and cost hinder the deployment of electrochemical wastewater treatment. Using an economical microfiber-based carbon felt (CF) substrate, we design RuO₂ nanospheres confined by Co_xO cooperated carbon nanoarrays (RuO₂-Co_xO@TCF) to augment noble metal utilization and thus reduce the catalyst cost. RuO₂-Co_xO@TCF anode with vertical diffusion channels exhibits rapid generation ability of oxidizing species particularity in the presence of Cl^- ions, which play a crucial role in azo bond cleavage and benzene ring chlorination of methyl orange. As a result, the catalyst shows 99.5 % color removal and ∼ 70 % mineralization efficiency at a concentration of 60 ppm. In synthetic dyeing wastewater, RuO₂-Co_xO@TCF delivers a stable total organic carbon (TOC) removal throughout ten cycling tests. Moreover, the electricity consumption of RuO₂-Co_xO@TCF is far below the reference anode, showing great promise for dye degradation and remediation of industrial wastewater.

An ultrasound/O3 and UV/O3 process for atrazine manufacturing wastewater treatment: a multiple scale experimental study

An ultraviolet (UV) and ultrasound (US) enhanced ozonation method were developed to investigate their efficiency on the removal of atrazine and chemical oxygen demand (COD) in authentic atrazine manufacturing wastewater. The bench-scale tests suggested a positive effect of UV and US on the degradation of atrazine within a limited energy range. The pilot-scale flow-through system was further tested by using response surface methodology. The results showed that O₃ and its interaction with UV promoted the degradation of both COD and atrazine while its interaction with US inhibited the removal of COD but promoted the removal of atrazine. The optimal removal rate of atrazine (96.9%) was achieved in the condition of 6.86 W/L UV, 1.96 g/L·h O₃ and 294 W/L US. Chloride ions hindered the atrazine degradation, but the generated free chlorine radicals were still able to react with atrazine. In terms of energy-effectiveness, the configuration of 14.7 W/L UV and 1.96 g/L·h O₃ is the best option, which have the electrical energy per order of 181.6 kWh/m³ for atrazine and 0.13 kWh/g COD. These method and findings could be helpful in the development of energy-efficient advanced oxidation processes in treating wastewater with high salinity and COD loadings.

Application of central composite design to reveal resin deterioration during the removal of hexavalent chromium from wastewater

As a strong oxidant, aqueous Cr(VI) possibly oxidizes the polymer resin and weakens resin adsorption property during Cr(VI) removal from solutions by ion exchange. In the present study, to minimize the resin oxidation, central composite design approach based on response surface methodology was employed with different variables (Cr(VI) concentration of 100-1000 mg L^-1, temperature of 293-333 K, pH of 1-7, and reaction time of 0-120 min) using a strong anionic resin (D202). The pH and reaction time had the most significant effect on resin oxidation, followed by Cr(VI) concentration. The temperature had a comparatively less significant effect on resin oxidation. The minimal Cr(VI) reduction efficiency (0.4%) was achieved with a Cr(VI) concentration of 251.5 mg L^-1, temperature of 323.1 K, pH of 6.2 and reaction time of 52.5 min. Based upon a long-term operation and Fourier transform infrared rays analyses, the oxidation pathway of D202 resin was proposed. The rupture of the C-N bond led to the disappearance of the nitrogen-containing functional groups, which resulted in a significant decrease of resin exchange capacity.

The use of nanovermiculite catalyst in the study of removal of the organic load and degradation of atrazine via ozone process in RPB reactor

The main objective of this study is the degradation of a synthetic solution of atrazine by a modified vermiculite catalyzed ozonation, in a rotating packed bed (RPB) reactor. A 0.5 L RPB reactor was used to perform the experiments, using a Central Composite Design (CCD) response surface to construct the quadratic model based on the factors: pH, catalyst concentration and reactor rotation frequency. The response variable was the removal of the organic load measured in terms of Chemical Oxygen Demand (COD). After the complete quadratic model was constructed through the response surface, the COD degradation process had an optimal removal of 41% under the following conditions: pH 8.0, rotation of 1150 rpm and catalyst concentration 0.66 g L^-1.