Degradation of organic micropollutant by vacuum ultraviolet process: a kinetics study

A bibliometric analysis of green technologies applied to water and wastewater treatment

Freshwater scarcity, a problem that has arisen particularly as a result of the progressive environmental damage caused by human consumption patterns, is strongly associated with a loss of living quality and a drop in global socioeconomic development. Wastewater treatment is one of the measures being taken to mitigate the current situation. However, the majority of existing treatments employ chemicals that have harmful environmental consequences and low effectiveness and are prohibitively expensive in most countries. Therefore, to increase water supplies, more advanced and cost-effective water treatment technologies are required to be developed for desalination and water reuse purposes. Green technologies have been highlighted as a long-term strategy for conserving natural resources, reducing negative environmental repercussions, and boosting social and economic growth. Thus, a bibliometric technique was applied in this study to identifying prominent green technologies utilised in water and wastewater treatment by analysing scientific publications considering authors, keywords, and countries. To do this, the VOSviewer software and Bibliometrix R Package software were employed. The results of this study revealed that constructed wetlands and photocatalysis are two technologies that have been considered as green technologies applicable to the improvement of water and wastewater treatment processes in most scientific articles.

The overlooked role of UV185 induced high-energy excited states in the dephosphorization of organophosphorus pesticide by VUV/persulfate

Vacuum ultraviolet (VUV) based advanced oxidation processes (AOPs) recently attracted widespread interests. However, the role of UV₁₈₅ in VUV is only considered to be generating a series of active species, while the effect of photoexcitation has long been overlooked. In this work, the role of UV₁₈₅ induced high-energy excited state for the dephosphorization of organophosphorus pesticides was studied using malathion as a model. Results showed malathion degradation was highly related to radical yield, while its dephosphorization was not. It was UV₁₈₅ rather than UV₂₅₄ or radical yield that was responsible for malathion dephosphorization by VUV/persulfate. DFT calculation results demonstrated that the polarity of P-S bond was further increased during UV₁₈₅ excitation, favoring dephosphorization while UV₂₅₄ did not. The conclusion was further supported by degradation path identification. Moreover, despite the fact that anions (Cl^-, SO₄^2- and NO₃^-) considerably affected radical yield, only Cl^- and NO₃^- with high molar extinction coefficient at 185 nm significantly affected dephosphorization. This study shed light on the crucial role of excited states in VUV based AOPs and provided a new idea for the development of mineralization technology of organophosphorus pesticides.

Removal of pesticide residues from fresh vegetables by the coupled free chlorine/ultrasound process

Pesticide residue in vegetables has been considered as a serious food safety problem across the whole world. This study investigates a novel advanced oxidation process (AOP), namely the coupled free chlorine/ultrasound (FC/US) process for the removal of three typical pesticides from lettuce. The removal efficiencies of dimethoate (DMT), trichlorfon (TCF) and carbofuran (CBF) from lettuce reached 86.7%, 79.8% and 71.3%, respectively by the FC/US process. There existed a synergistic effect in the coupled FC/US process for pesticide removal and the synergistic factors reached 22.3%, 19.0% and 36.4% for DMT, TCF and CBF, respectively. Based on the analysis of mass balance of pesticides, the synergistic effect was probably attributed to the efficient oxidation of pesticides both in vegetables and in water by the generated free radicals and FC. The surface area and surface structure of vegetables strongly affected the removal of pesticides by FC/US. The removal efficiency of DMT increased from 80.9% to 88.1% as solution pH increased from 5.0 to 8.0, and then decreased to 84.1% when solution pH further increased to 9.0. When the ultrasonic frequency changed from 20 to 40 kHz, a remarkable improvement in pesticide removal by FC/US was observed. As the FC concentration increased from 0 to 15 mg L^-l, the removal efficiencies of pesticides increased firstly, and then became stagnant when the FC concentration further increased to 25 mg L^-l. The pesticide degradation pathways based on the identified intermediates were proposed. The total chlorophyll content was reduced by less than 5% after the FC/US process, indicating a negligible damage to the quality of vegetables. It suggests that the FC/US process is a promising AOP for pesticides removal from vegetables.