Catalysis of MnO2-cellulose acetate composite films in DBD plasma system and sulfamethoxazole degradation by the synergistic effect

Mechanistic investigation of ciprofloxacin degradation using NiFe2O4/CA-cellulose acetate composite films in a novel dielectric barrier discharge plasma system

Conventional wastewater treatments often exhibit limited efficiency in removing antimicrobial residues, thus requiring innovative methods to tackle antimicrobial contamination in the environment. This study employed a dielectric barrier discharge (DBD) plasma reactor with NiFe2O4-cellulose acetate (CA) composite films for ciprofloxacin (CIP) degradation in water. The catalytic efficiency of NiFe2O4/CA films was tested across the degradation rate of CIP in synthesized wastewater, reaction kinetics, energy utilization, and reductions in total organic carbon (TOC) and chemical oxygen demand (COD), both with and without the films in the DBD system. Optimal degradation conditions of 10 mg/L CIP concentration, 195 V, 6.5 Hz, 9% catalyst loading, and 4.32 L/min flow rate achieved 89.63% CIP removal within 60 minutes, with alkaline pH further enhancing degradation. UV-Vis analysis confirmed that extending DBD treatment time improved degradation rates. Variations in solution conductivity, pH, and concentrations of H2O2 and O3 were tracked to verify the catalytic role of NiFe2O4/CA films. Moreover, radical scavengers such as tert-butanol (TBA), benzoquinone (BQ), and triethylenediamine (TEDA) were introduced to the system which identified that •OH, , and 1O2 were the key reactive oxygen species responsible for CIP degradation. Liquid chromatography-mass spectrometry (LC-MS) was used to determine the intermediate and by-products of the CIP degradation and four potential degradation pathways were proposed. Pathway III was considered the prominent route involving hydroxylation and piperazine ring cleavage, producing fewer toxic intermediates supported by density functional theory (DFT) calculations. Toxicity assessment showed most intermediates had reduced developmental toxicity and bioaccumulation potential compared to CIP. This highlights the environmental safety of the DBD plasma and NiFe2O4/CA system, as a promising, eco-friendly alternative to traditional methods, with reduced toxicity, minimal bioaccumulation, and potential for sustainable, large-scale application.

Degradation of sulfamethoxazole in a falling film dielectric barrier discharge system: Performance, mechanism and toxicity evaluation

The ubiquitous presence of sulfonamides (SAs) in wastewater poses serious risks to human health and ecosystem safety. This study evaluated the performance of a falling film dielectric barrier discharge (DBD) system on the removal of five SAs, namely sulfamethoxazole (SMX), sulfisoxazole (SIZ), sulfathiazole (STZ), sulfadiazine (SDZ) and sulfamerazine (SMR). Removal efficiencies >99 % were observed for all target SAs within 30 min of treatment, with pseudo-first order rate constants varying between 0.17 and 0.27 min-1. Superior removal efficiencies were achieved under acidic conditions compared to neutral and alkaline conditions. Using SMX as a model compound, mechanistic investigations revealed that the synergy of reactive oxygen species (ROS) and reactive nitrogen species (RNS) led to its efficient degradation, with peroxynitrites (ONOO-/ONOOH) and hydroxyl radical (OH) playing pivotal roles. SMX degradation pathways encompassing nitration/nitrosation, hydroxylation, deamination, CS and SN bond cleavage were proposed. The toxicity evaluation results demonstrated that the solution toxicity diminished following the plasma treatment under specific conditions. In particular, the solution treated with air or oxygen discharge enhanced the growth of wheat seedlings, suggesting the potential for reusing plasma-treated wastewater in agriculture. This study enhances our understanding of the underlying mechanisms involved in the plasma degradation of SAs and reveals the significant potential of plasma technology as a sustainable approach for treating wastewater.

Plasma treatment of sulfamethoxazole contaminated water: Intermediate products, toxicity assessment and potential agricultural reuse

The increasing global water demand has prompted the reuse of treated wastewater. However, the persistence of organic micropollutants in inefficiently treated effluents can have detrimental effects depending on the scope of the reclaimed water usage. One example is the presence of sulfamethoxazole, a widely used antibiotic whose interference with the folate synthesis pathway negatively affects plants and microorganisms. The goal of this study is to assess the suitability of a non-thermal plasma-ozonation technique for the removal of the organic pollutant and reduction of its herbicidal effect. Fast sulfamethoxazole degradation was achieved with apparent reaction rate constants in the range 0.21-0.49 min-1, depending on the initial concentration. The highest energy yield (64.5 g/kWh at 50 % removal) exceeds the values reported thus far in plasma degradation experiments. During treatment, 38 degradation intermediates were detected and identified, of which only 9 are still present after 60 min. The main reactive species that contribute to the degradation of sulfamethoxazole and its intermediate products were hydroxyl radicals and ozone, which led to the formation of several hydroxylated compounds, ring opening and fragmentation. The herbicidal effect of the target compound was eliminated with its removal, showing that the remanent intermediates do not retain phytotoxic properties.

Environment-friendly and efficient electrochemical degradation of sulfamethoxazole using reduced TiO2 nanotube arrays-based Ti membrane coated with Sb-SnO2

This study focused on the preparation, characterization, and sulfamethoxazole (SMX) removal performance of the SnO₂-coated reactive electrochemical membrane (REM). This REM was fabricated by loading SnO₂ on the reduced TiO₂ nanotube arrays (RTNA)-based Ti membrane (TM). Regarding the dopant for SnO₂, Sb was more effective in boosting the electrocatalytic activity than Bi, and the energy consumption for Sb-SnO₂-coated REM (TM/RTNA/ATO) was lower than Bi-SnO₂-coated REM (TM/RTNA/BTO). As for the internal layer, RTNA provided TM/RTNA/ATO with more electroactive surface areas and prolonged the service lifetime. Compared with batch mode, the SMX removal efficiency in flow-through mode was increased up to 8.4-fold. The SMX degradation performances were also affected by fluid velocity, current density, initial SMX concentration, and electrolyte concentration. The synergistic effects of ^•OH oxidation and direct electron transfer were responsible for the effective removal of SMX. TM/RTNA/ATO was proved to be stable and durable by multi-cycle and accelerated lifetime tests. Its extensive applicability was verified with high removal efficiencies of SMX in the surface water and wastewater effluent. These results demonstrate the promise of TM/RTNA/ATO for water treatment applications.