Novel Advanced Oxidation Processes for Wastewater Treatment

Ecologically fragile areas in China account for more than half of its land area. Performing early warning assessments and trend analyses of resource and environment carrying capacity in ecologically fragile areas can lay a scientific foundation for ecological conservation in the areas. Based on the connotation of resource and environment carrying capacity, an early warning index system of resource and environment carrying capacity in Altay prefecture was constructed from the three aspects natural resource carrying capacity, eco-environment carrying capacity, and economic and social support capacity. The grey relational projection method model was used to analyze the current alarm situation of the resource and environment carrying capacity in Altay prefecture from 2011 to 2020, and then the back propagation (BP) neural network and a mathematical statistics software were used to predict the evolution of the alarm situation of the resource and environment carrying capacity in Altay prefecture from 2021 to 2025. The results demonstrated that (1) the natural resource carrying capacity subsystem was the main system of the development of the resource and environment carrying capacity in Altay prefecture, and its impact on the resource and environment carrying capacity in Altay prefecture was greater than the eco-environment carrying capacity and economic and social support capacity; (2) the resource and environmental carrying capacity of Altay prefecture showed a slight upward trend from 2011 to 2020, although the range was constrained and the level of warning remained “moderate warning”. A spatial pattern of “weak in the middle, strong in the two poles” was exhibited by the warning scenario about the carrying capacity of each county and city. Except for the warning of Habahe County and Qinghe County, where the warning was slightly worse than that in 2020, the warning of resource and environment carrying capacity in Altay prefecture and other counties and cities would show a trend of fluctuation and decline from 2021 to 2025. However, the degree of alarm did not change substantially and remained at the level of “moderate warning”; (3) the main factors restricting the mitigation of the warning of resource and environment carrying capacity in Altay prefecture included a low soil fertility index, a small total reservoir capacity, low per capita mineral resource reserves, a low water resource development and utilization rate, a low comprehensive utilization rate of industrial solid waste, and a low land output rate. Full article

Antibiotic resistance has been a serious health threat of widespread concern, as antibiotics are difficult to degrade effectively in the environment. In this study, sulfamethoxazole (SMZ), a common antibiotic in an aqueous solution, was irradiated by low-energy X-ray to investigate the effect of the absorption dose, initial concentration, initial pH, irradiation energy and other conditions on the degradation of SMZ, as well as the kinetic mechanism of SMZ degradation. The results showed that low-energy X-ray irradiation could effectively degrade SMZ in an aqueous solution at different initial concentrations and acid-base degrees, and the degradation effect of irradiation in the range of 60–80 keV is independent of the energy of X-rays. The degradation rate of the SMZ solution, with an initial concentration of 10.70 mg/L, was 94.6% at an absorbed dose of 890 Gray, with a pH of 3.5. Similar to other works on the degradation of antibiotics by ionizing irradiation, the degradation of SMZ solutions conformed to a pseudo-first-order kinetic mechanism. Full article

Spent caustic wastewater produced in a soda plant has a high concentration of ammonia nitrogen (NH₄⁺-N). As excessive NH₄⁺-N discharging into water bodies would cause eutrophication as well as destruction to the ecology balance, developing an efficient technology for NH₄⁺-N removal from the spent caustic wastewater is imperative in the current society. In this study, an electrochemical process with graphene electrodes was designed for the NH₄⁺-N removal in the spent caustic wastewater. The removal efficiency of the NH₄⁺-N during the electrochemical process could reach 98.7% at 4 A in a short treatment time (within 120 s) with an acceptable energy consumption (6.1 kWh/m³-order). NO₃⁻ and NO₂⁻ were not detected during the electrochemical process. An insignificant amount of NH₂Cl, NHCl₂, and NCl₃ produced in the treatment suggested that little of the NH₄⁺-N reacted with chlorine, that is, chlorination played a negligible role in the NH₄⁺-N removal. By electron equilibrium and nitrogen conversion analysis, we think that NH₄⁺-N was primarily converted to NH₂(ads) on the surface of a graphene electrode by one-electron transfer during the direct oxidation of the electrochemical process. Due to the high calcium ion (Ca²⁺) in the spent caustic wastewater, the electrode scale significantly increased to 1.4 g after treatment of 240 s at 4 A. By X-ray diffraction (XRD) analysis, the composition of the electrode scale is portlandite Ca(OH)₂. Although the electrode scale was obvious during the electrochemical treatment, it could be alleviated by alternating the electrode polarity. As a result, the life and efficiency of the graphene electrode for NH₄⁺-N removal could remain stable for a long time. These results suggest that the electrochemical process with a graphene electrode may provide a competitive technology for NH₄⁺-N removal in spent caustic wastewater treatment. Full article

In recent years, advanced oxidation process (AOPs) based on sulfate radical (SO₄^●−) and singlet oxygen (¹O₂) has attracted a lot of attention because of its characteristics of rapid reaction, efficient treatment, safety and stability, and easy operation. SO₄^●− and ¹O₂ mainly comes from the activation reaction of peroxymonosulfate (PMS) or persulfate (PS), which represent the oxidation reactions involving radicals and non-radicals, respectively. The degradation effects of target pollutants will be different due to the type of oxidant, reaction system, activation methods, operating conditions, and other factors. In this paper, according to the characteristics of PMS and PS, the activation methods and mechanisms in these oxidation processes, respectively dominated by SO₄^●− and ¹O₂, are systematically introduced. The research progress of PMS and PS activation for the degradation of organic pollutants in recent years is reviewed, and the existing problems and future research directions are pointed out. It is expected to provide ideas for further research and practical application of advanced oxidation processes dominated by SO₄^●− and ¹O₂. Full article