Ti/RuO2-IrO2 anodic electrochemical oxidation composting leachate biochemical effluent: Response surface optimization and failure mechanism.

In this work, the electrolytic process conditions for the electrochemical oxidation (EO) of composting leachate biochemical effluent (CLBE) were optimized via the response surface methodology (RSM). Meanwhile, a comparative study had been done on the failure characteristics of Ti/RuO2-IrO2 anodes in a single electrolyte solution system (H2SO4 and NaCl) and real wastewater (CLBE) by accelerated life tests, respectively. The RSM optimization results showed that the COD, NH3-N and TN removal rates were 50.53%, 100% and 95.61% at 30 min, respectively, with a desirability value of 0.993. In parallel, the electrochemical and material characterizations were carried out on the electrodes before and after failure, by which the failure mechanism of Ti/RuO2-IrO2 anodes was clarified. On the whole, the true failure in the H2SO4 solution was attributed to coating dissolution and Ti substrate oxidation. In contrast, the electrode exhibited "apparent failure" due to the "bubble effect" in both NaCl and CLBE solutions, and the "effective roughness" formed compensated for the loss of activity caused by the absence of the coating. Besides, additional dissolution of the Ti substrate occurred in the CLBE solution due to the current edge effect and the presence of organic matter. This paper takes the actual wastewater as the research object and reveals its electrode failure mechanism, which provides a theoretical basis and reference for the subsequent optimization of the actual electrode service life.

Performance of alkali and Cu-modified ZSM-5 during catalytic ozonation of polyvinyl alcohol in aqueous solution.

A novel hierarchical Cu/ZSM-5 was prepared over alkaline treatment and incipient wet impregnation method for the catalytic ozonation of polyvinyl alcohol (PVA). Under the optimum preparation conditions, hierarchical Cu/ZSM-5 exhibited an excellent mineralization performance during the PVA degradation process, and the removal rate of TOC after 60 min of reaction was 47.86%, much higher than that of ozonation alone (5.40%). Its high catalytic activity could attribute to the large pore volume (0.27 cm3/g) and pore size (6.51 nm) which are beneficial for the distribution of loaded copper and adsorption performance for PVA. Compared to ·OH, 1O2 (2.66 times in 10 min) contributed more to the removal of PVA. The degradation of PVA was a combined process of direct ozone oxidation, catalytic ozonation and adsorption. With its high catalytic performance and stability, hierarchical Cu/ZSM-5 has a very broad application prospect in the process of catalytic ozonation of refractory pollutants.

Sodium hypochlorite and Cu-O-Mn/ columnar activated carbon catalytic oxidation for treatment of ultra-high concentration polyvinyl alcohol wastewater.

Complete degradation of high concentration polyvinyl alcohol (PVA) is challenging. In this article, a two-stage process of NaClO pre-oxidation and columnar activated carbon (loaded with metal active components) catalytic oxidation was used to treat high concentration PVA wastewater. The degree of polymerization of PVA is 2400 and the water concentration is 15 wt %. In the first stage, NaClO efficiently broken long chain to short, the viscosity of PVA solution decreased from 45,100 mPaS to 4.65 mPaS. And in the second stage, the short chain was further oxidized to small molecules under H2O2 with catalysts. The solution COD decreased from 206,240 mg/L to 38.38 mg/L. The composition of catalysts and the reaction conditions were optimized, the degradation mechanism was discussed. According to the experimental results, small pore size (8-10 mesh) activated carbon loaded copper and manganese catalyst (C1M1AC-S) was the best choice. The optimal conditions of C1M1AC-S were: molar ratio of copper to manganese was 2:1, the loading rate was 25 wt% and the dosage was 9.76 mg/100 ml. The whole process is mild (25 °C-40 °C) and reaction time is short (100 min). Moreover, free radical scavenging experiments shown that the catalytic oxidation stage follows the mechanism of hydroxyl radical reaction.