Novel Advanced Oxidation Processes for Wastewater Treatment

Ammonia (NH₃) plays a significant role in the manufacture of fertilizers, nitrogen-containing chemical production, and hydrogen storage. The electrochemical nitrogen reduction reaction (e-NRR) is an attractive prospect for achieving clean and sustainable NH₃ production, under mild conditions driven by renewable energy. The sluggish cleavage of N≡N bonds and poor selectivity of e-NRR are the primary challenges for e-NRR, over the competitive hydrogen evolution reaction (HER). The rational design of e-NRR electrocatalysts is of vital significance and should be based on a thorough understanding of the structure–activity relationship and mechanism. Among the various explored e-NRR catalysts, metal-based electrocatalysts have drawn increasing attention due to their remarkable performances. This review highlighted the recent progress and developments in metal-based electrocatalysts for e-NRR. Different kinds of metal-based electrocatalysts used in NH₃ synthesis (including noble-metal-based catalysts, non-noble-metal-based catalysts, and metal compound catalysts) were introduced. The theoretical screening and the experimental practice of rational metal-based electrocatalyst design with different strategies were systematically summarized. Additionally, the structure–function relationship to improve the NH₃ yield was evaluated. Finally, current challenges and perspectives of this burgeoning area were provided. The objective of this review is to provide a comprehensive understanding of metal-based e-NRR electrocatalysts with a focus on enhancing their efficiency in the future. Full article

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

Herein, we loaded cobalt-based zeolite imidazolate frameworks, ZIF-67 (Co), onto commercial filter paper to prepare catalytic filter paper (ZFP) for the in situ degradation of bisphenol A (BPA) in water by activating peroxymonosulfate. The results showed that ZIF-67 (Co) was densely and uniformly distributed on the surface of the filter paper. The prepared ZFP could effectively degrade BPA in situ through a gravity-driven filtration process. Specifically, when the flow rate of the BPA solution passing through ZFP was lower than 10 mL/min, 0.02 mM of BPA could be completely degraded by ZFP. Furthermore, ZFP showed promising water matrix adaptability, which could provide promising BPA degradation efficiency in a wide pH range or in the existence of multiple anions. The scavenging tests demonstrated that both sulfate radical and hydroxyl radical were generated for BPA degradation, in which hydroxyl radical was the dominant active species. The ZFP also exhibited promising long-time use stability with a high mineralization rate. This study provides a novel method to prepare high-efficient catalyst paper for the in situ organic pollutant removal in water media via a prompt filtration process. 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

Zero-valent iron/peroxymonosulfate (Fe⁰/PMS) has been considered as a promising approach for wastewater treatment. Anions and cations are widely present in wastewater and have significant effects on the performance of the Fe⁰/PMS system for wastewater treatment. Thus, in the present study, tartrazine was selected as the target model; SO₄²⁻, NO₃⁻, HCO₃⁻, and Cl⁻ were selected as representative anions and Ca²⁺, Cu²⁺, Mg²⁺, and Mn²⁺ were chosen as representative cations. The effect of these anions and cations on tartrazine removal and major radicals in the Fe⁰/PMS were systematically investigated. The presence of a certain concentration of SO₄²⁻ and Cl⁻ had positive, NO₃⁻ had negative, and HCO₃⁻ had negligible effects on tartrazine removal in the Fe⁰/PMS system. SO₄²⁻ and HCO₃⁻ had a small effect on the contribution proportion of reduction, SO₄^•− and ^•OH; a certain concentration of Cl⁻ could enhance the contribution proportion of ^•OH; and NO₃⁻ would decrease the contribution proportion of SO₄^•− and ^•OH. A certain concentration of each of Ca²⁺, Cu²⁺, Mg²⁺, and Mn²⁺ could enhance the tartrazine removal in the Fe⁰/PMS system. Ca²⁺, Cu²⁺, and Mg²⁺ had no effect of the contribution of reduction, SO₄^•− and ^•OH, while a certain concentration of Mn²⁺ could enhance the contribution proportion of SO₄^•−. These results can provide some references for the Fe⁰/PMS system to treat actual wastewater containing anions and cations. 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