Degradation of carbamazepine by high-voltage direct current gas-liquid plasma with the addition of H2O2 and Fe2

Degradation and transformation of carbamazepine in aqueous medium under non-thermal plasma oxidation process

Carbamazepine (CBZ) is a pharmaceutical compound detected in various water resources. With a view to removing this contaminant, the applicability of non-thermal plasma (NTP) oxidation process has been widely tested in recent years. This study utilized NTP from a dielectric barrier discharge reactor in the treatment of CBZ. NTP on the surface of a water sample containing 25 mg.L-1 of CBZ resulted in a removal efficiency of over 90% with an energy yield of 0.19 g. (kWh)-1. On the other hand, a rapid reduction in pH and an increase of conductivity and nitrate/nitrite ions concentration were observed during the degradation. The applied voltage amplitude significantly affected the removal efficiency and the energy yield as the degradation efficiency was 55%, 70%, and 72% respectively with an applied voltage of 8, 10, and 12 kV. The water matrices containing inorganic anions such as chloride and carbonate ions reduced the removal efficiency by scavenging the reactive species. Accordingly, a reduction in the removal efficiency was observed in tap water. The high-resolution mass spectrometry (HRMS) results revealed that both reactive oxygen and nitrogen species take part in the reaction process which yields many intermediate products including aromatic nitro-products. This study concluded that NTP can effectively degrade CBZ in both pure and tap water, but special attention must be paid to changes in the water quality parameters (pH, conductivity, and nitrate/nitrite ions) and the fate of nitro products.

Mechanistic investigation of the electricity and gallic acid synergistically accelerated Fe(III)/Fe(II) cycle for the degradation of carbamazepine

This study investigated the application of a natural plant polyphenol, gallic acid (GA) to form complex with iron to promote the redox cycle of Fe(III)/Fe(II) under neutral initial pH conditions in the electrochemical (EC) system for activation of peroxymonosulfate (PMS) to efficiently degrade carbamazepine (CBZ). Results demonstrated that the synergistic effects of GA and EC significantly improved the removal efficiency, and the EC/GA/Fe(III)/PMS system effectively removed 100% of CBZ within a wide initial pH range of 3.0-7.0. The optimum stoichiometric ratio of GA to Fe(III) was found as 2:1. Investigations including quenching experiment, chemical probe analysis, and electron paramagnetic resonance (EPR) analysis were conducted to identify the primary reaction radicals as •OH, SO4•-, along with the 1O2 and Fe(IV). In the EC/GA/Fe(III)/PMS system, the synergistic effect of GA and electrochemistry led to a remarkable enhancement in the generation of •OH. Furthermore, the complexation reduction mechanism of GA and Fe(III) was proposed based on experimental and instrumental analyses, which demonstrated that the semi-quinone products of GA were the main substances promoting the Fe(III)/Fe(II) cycle. Mass spectrometry results showed that CBZ generated 27 byproducts during degradation, with formic acid as the main product of GA. The degradation efficiency of the EC/GA/Fe(III)/PMS system remained stable and excellent, exhibiting remarkable performance in the presence of various inorganic anions, including Cl- and NO3-, as well as naturally occurring organic compounds such as fulvic acid (FA). Overall results indicated that the EC/GA/Fe(III)/PMS system can be applied to effectively treat practical wastewater treatment without requirement of pH adjustment.

Simultaneous removal of antibiotic-resistant Escherichia coli and its resistance genes by dielectric barrier discharge plasma

As emerging contaminants, antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have been widely detected in various aqueous environments. For antibiotic resistance to be inhibited in the environment, it is essential to control ARB and ARGs. In this study, dielectric barrier discharge (DBD) plasma was used to inactivate antibiotic resistant Escherichia coli (AR E. coli) and remove ARGs simultaneously. Within 15 s of plasma treatment, 108 CFU/mL of AR E. coli were inactivated by 97.9%. The rupture of the bacterial cell membrane and the increase of intracellular ROS are the main reasons for the rapid inactivation of bacteria. Intracellular ARGs (i-qnrB, i-blaCTX-M, i-sul2) and integron gene (i-int1) decreased by 2.01, 1.84, 2.40, and 2.73 log after 15 min of plasma treatment, respectively. In the first 5 min of discharge, extracellular ARGs (e-qnrB, e-blaCTX-M, e-sul2) and integron gene (e-int1) decreased by 1.99, 2.22, 2.66, and 2.80 log, respectively. The results of the ESR and quenching experiments demonstrated that ·OH and 1O2 played important roles in the removal of ARGs. This study shows that DBD plasma is an effective technique to control ARB and ARGs in waters.

Butachlor (BTR) degradation by dielectric barrier discharge plasma in soil: Affecting factors, degradation route, and toxicity assessment

Over the past few decades, the frequent and excessive usage of pesticides has had detrimental effects on the soil and other habitats. In terms of removing organic contaminants from soil, non-thermal plasma has become one of the most competitive advanced oxidation methods. The study used dielectric barrier discharge (DBD) plasma to repair soil contaminated by butachlor (BTR). BTR degradation was investigated in actual soil under various experimental parameters. According to the results, DBD plasma treatment at 34.8 W destroyed 96.10% of BTR within 50 min, and this degradation was consistent with the model of first order kinetics. Boosting the discharge power, lowering the initial BTR concentration, using appropriate soil moisture content and air flow rate, and using oxygen as the working gas for discharge are all beneficial to the degradation of BTR. The changes in soil dissolved organic matter (DOM) before and after plasma treatment were assessed using a total organic carbon (TOC) analyzer. A Fourier transform infrared (FTIR) spectroscopy and an Ultra Performance Liquid Chromatography Tandem Mass Spectrometry (UPLC-MS) were employed to investigate the degradation of BTR. A wheat growth test showed that the best growth was achieved at 20 min of plasma soil remediation, but too long treatment would lower soil pH and thus affect wheat growth.