Sulfamethoxazole Degradation Rate Research Articles

Persulfate activation by modified red mud for the oxidation of antibiotic sulfamethoxazole in water

Different pre-conditioning treatments were evaluated in order to stabilize red mud, a waste product from bauxite processing, for obtaining heterogeneous catalysts (named as B1–B3) that can be employed as suitable activators of sodium persulfate (SPS) for the degradation of sulfamethoxazole (SMX), a model antibiotic, in water. The presence of Fe3O4 in the composition of the catalysts was found to be a key factor for a suitable activation of SPS, according to the XPS measurements. The oxidation of SMX was successfully fitted to a pseudo-first-order kinetic model (r2 > 0.96), obtaining a 68% removal after 180 min when 0.8 mg/L of SMX was oxidized with 2 g/L of SPS and 2 g/L of catalyst B3. The presence of organic and/or inorganic constituents in the water matrix significantly hindered the degradation rate of SMX, the apparent kinetic constants being from 2 to 3 times lower than that determined in ultrapure water test. The use of ultrasound irradiation coupled to the addition of B3 catalyst improved importantly the SMX oxidation in real aqueous matrices, thus attaining values of removal which almost triplicated the ones obtained in absence of ultrasounds.

Iron precursor salt effect on the generation of [rad]OH radicals and sulfamethoxazole degradation through a heterogeneous Fenton process using Carbon-Fe catalysts

The influence of the iron precursor salt on the preparation of Carbon-Fe catalysts was evaluated based on the generation of OH radicals in a heterogeneous Fenton process applied to the degradation of sulfamethoxazole (SMX). Carbon catalysts were obtained with 9% Fe by weight using three iron salts: iron acetate (C-AC-AFe), iron sulfate (C-AC-SFe) and iron nitrate (C-AC-NFe). Characterization of catalysts was evaluated by N2 physisorption, X-ray diffraction, scanning electron microscopy and spectroscopic techniques (FTIR, EDX, XPS); these properties were related to the OH generation kinetics and to SMX degradation rate. The iron precursor salt favors the anchoring of the metal in different oxidation state on the catalyst in a proportion of: Fe2+ / Fe3+ = 4.1 for C-AC-AFe, 1.5 for C-AC-SFe and 1.7 for C-AC-NFe, which is related to the OH generated: 53.8 μM g−1, 37.9 μM g−1 and 42.4 μM g−1, respectively. The OH generation kinetics were described by a pseudo-first-order model with rate constants of 0.0252 and 0.0299 min−1 for C-AC-AFe and C-AC-SFe respectively, which coincide with the kinetic constants for the degradation of SMX (0.0262 and 0.0297 min−1), therefore, the oxidation process is carried out by OH. In the case of C-AC-NFe, Fe was fixed within the texture of the carbon and the OH generation was the lowest (0.0005 min−1), explaining the reaction is limited by diffusion. For SMX, the degradation percentage achieved for 20 mg L−1 was: 98.2 % in 120 min for C-AC-AFe, 98.1 % in 180 min for C-AC-SFe and 92.8 % in 210 min for C-AC-NFe.

Enhanced Degradation of Sulfamethoxazole (SMX) in Toilet Wastewater by Photo-Fenton Reactive Membrane Filtration.

Pharmaceutical residuals are increasingly detected in natural waters, which made great threat to the health of the public. This study evaluated the utility of the photo-Fenton ceramic membrane filtration toward the removal and degradation of sulfamethoxazole (SMX) as a model recalcitrant micropollutant. The photo-Fenton catalyst Goethite (α-FeOOH) was coated on planar ceramic membranes as we reported previously. The removal of SMX in both simulated and real toilet wastewater were assessed by filtering the feed solutions with/without H2O2 and UV irradiation. The SMX degradation rate reached 87% and 92% respectively in the presence of UV/H2O2 for the original toilet wastewater (0.8 ± 0.05 ppb) and toilet wastewater with a spiked SMX concentration of 100 ppb. The mineralization and degradation by-products were both assessed under different degradation conditions to achieve deeper insight into the degradation mechanisms during this photo-Fenton reactive membrane filtration. Results showed that a negligible removal rate (e.g., 3%) of SMX was obtained when only filtering the feed solution through uncoated or catalyst-coated membranes. However, the removal rates of SMX were significantly increased to 67% (no H2O2) and 90% (with H2O2) under UV irradiation, respectively, confirming that photo-Fenton reactions played the key role in the degradation/mineralization process. The highest apparent quantum yield (AQY) reached up to approximately 27% when the H2O2 was 10 mmol·L−1 and UV254 intensity was 100 μW·cm−2. This study lays the groundwork for reactive membrane filtration to tackle the issues from micropollution.

Z-scheme heterojunction g-C3N4@PDA/BiOBr with biomimetic polydopamine as electron transfer mediators for enhanced visible-light driven degradation of sulfamethoxazole

Visible-light photocatalysis boosted by Z-scheme photocatalysts has been deemed as an economic and effective way in eliminating emerging antibiotics pollution. A Z-scheme heterojunction photocatalyst g-C3N4@PDA/BiOBr (CNPB) was hereby facilely constructed through polydopamine (PDA) modification of g-C3N4 followed by deposition of BiOBr component via a solvothermal reaction. The structure, morphology, optical and photoelectrochemical properties etc. of CNPB were characterized and explored. The photocatalytic activity of CNPB was assessed on the degradation of sulfamethoxazole (SMX). CNPB manifested remarkably improved photocatalytic performance than the as-prepared g-C3N4, BiOBr and g-C3N4/BiOBr heterojunction in the degradation of SMX under visible light irradiation. SMX could be nearly completely degraded in 60 mins by CNPB, while the degradation rate of SMX under g-C3N4, BiOBr, g-C3N4/BiOBr heterojunction, and the “g-C3N4@PDA + BiOBr” mixture were 30%, 42%, 71%, and 47%, respectively. The highly enhanced photocatalytic efficiency of CNPB was attributed to the synergistic effect of improved light harvesting and accelerated transport and separation of photo-generated carriers in the Z-scheme structure with PDA as efficient electron transfer mediators. A Z-scheme charge transfer mechanism was confirmed by experiments on radical scavenging and electron spin resonance (ESR) signals trapping, which demonstrated that the h+ and O2− were the major reactive species in oxidizing SMX. The degradation mechanism, main intermediates and reaction pathways were further explored. Besides, CNPB exhibited good stability and reusability in multiple uses. The construction of Z-scheme photocatalyst using biomimetic polydopamine as electron transfer mediators may provide an insight into designing new and efficient photocatalysts for environmental applications.

Nitrogen, sulfur and oxygen co-doped carbon-armored Co/Co9S8 rods (Co/Co9S8@N-S-O-C) as efficient activator of peroxymonosulfate for sulfamethoxazole degradation

In this study, nitrogen, sulfur and oxygen co-doped carbon armored cobalt sulfide (Co/Co9S8@N-S-O-C) composite was synthesized, characterized and used to activate peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). SMX (0.04 mM) can be completely degraded within 20 min in the presence of 0.8 mM PMS and 0.1 g/L Co/Co9S8@N-S-O-C composite. The first-order kinetics constant of SMX degradation was 0.307 min-1, and the mineralization of SMX was 30.1 %. The Quenching experiments of the free radicals and the identification of degradation products demonstrated that sulfate radicals played a dominant role in SMX degradation. The degradation rate of SMX increased with temperature, and activation energy was calculated to be 48.6 kJ/mol. The degradation rate of SMX increased firstly then decreased with increase of pH. Chloridion and humic acid decreased the degradation rate of SMX no matter what their initial concentration was. The effect of carbonate on SMX degradation depended on its initial concentration. Co/Co9S8@N-S-O-C composite showed good stability, the removal efficiency of SMX was 98.4 % in the fifth experiment. Based on the characterization results of the catalyst before and after use, it was concluded that cobalt, sulfur, pyridnic N and graphitic N were responsible for PMS activation.

Boosting exciton dissociation and molecular oxygen activation by in-plane grafting nitrogen-doped carbon nanosheets to graphitic carbon nitride for enhanced photocatalytic performance

The metal-free graphitic carbon nitride (g-C3N4) polymer is a promising photocatalyst for energy production and environmental protection. However, attempts to intrinsically improve its low activity in photooxidation are rarely effective for the poor molecular oxygen (O2) activation. Here we report a synthesis of directionally nitrogen-doped in-plane metal-free heterostructure, through coplanar grafting nitrogen-doped carbon nanosheets (NDCN) to g-C3N4. The in-plane grafted NDCN not only promoted exciton dissociation and charge transfer but also enhanced activating O2 to reactive oxygen species, including superoxide radicals (O2−) and H2O2. The optimal C3N4-NDCN coplanar heterojunction (C3N4-NDCN-3) photocatalytically degraded 96.3% of sulfamethoxazole (SMX) under visible light irradiation at a low light intensity of 14.5 mW cm−2 in 4 h, whose SMX degradation rate was 37.7-fold higher than that of pure g-C3N4. Furthermore, C3N4-NDCN-3 exhibited 95.3% removal of SMX under sunlight irradiation (59.8 mW cm−2) in 1 h, higher than the 58.0% of pristine g-C3N4. First-principles calculations and material characterizations demonstrated that the coplanar NDCN served as electron sink and catalytic center for hot-electron involved O2 activation. The improved charge carrier separation and O2 activation promoted generation of photoexcited hole and superoxide for photocatalytic degradation of SMX. The design strategy in this work inspires a new approach for high-performance polymer photocatalysts in solar energy storage and environmental remediation.

Effect of Complexation of Humic Acid with Iron Minerals on Microbial Degradation of Sulfamethoxazole

Microbial Shewanella oneidensis MR-1 can degrade sulfamethoxazole (SMX) and act as a microorganism with strong electron donating properties, which can accelerate the degradation of SMX when it cooperates with electronic shuttle and disproportionated iron. By adding different TOC concentrations, different molecular weight humic acids, and magnetite and hematite suspensions, the optimal system growth conditions, ie, the temperature of 30°C, pH = 7, the TOC concentration, The effect of humic acid with different molecular weights and the addition and synergistic addition of different iron minerals on the degradation of SMX by Shewanella oneidensis MR-1. The study found that humic acid stock solution, small molecule humic acid, iron mineral and both of them will accelerate the degradation of SMX by microbial MR-1. The concentration of small molecule humic acid will degrade SMX by Shewanella oneidensis MR-1. The effect of the humic acid is greater than that of the original solution. The addition of magnetite and hematite suspension to the reactor alone promotes the degradation of SMX by Shewanella oneidensis MR-1, and the addition of humic acid will improve the degradation rate of SMX.

Singlet oxygen-dominated peroxydisulfate activation by sludge-derived biochar for sulfamethoxazole degradation through a nonradical oxidation pathway: Performance and mechanism

In this study, sludge-derived biochar (SDBC) was prepared and applied in peroxydisulfate (PDS) activation for sulfamethoxazole (SMX) degradation. Compared to the slight adsorption (16.5%) by SDBC alone and low direct oxidation (10.1%) by PDS alone, the SMX degradation rate was drastically increased to 94.6% in the combined SDBC/PDS system, suggesting that SDBC can successfully and efficiently activate PDS. The observed rate constant of the combined SDBC/PDS system was 48.3 times those of both PDS alone and SDBC alone processes. Material characterization and comparative experiments showed nitrogen doping and iron loading into the carbon layer might be the important active sites of the graphene-like SDBC material in PDS activation for SMX degradation. More importantly, singlet oxygen (1O2), instead of traditional sulfate radicals or hydroxyl radicals, was the predominant reactive species of the SDBC/PDS system, which involved a new nonradical oxidation method for PDS activation by SDBC. The SMX degradation pathways by the nonradical 1O2 oxidation were first studied by combining density functional theory (DFT) calculations with experimental results. Different from the well-known pathways of SMX through the cleavage of the sulfanilamide bond by the attack of radicals, the 1O2 was likely to attack the aniline ring of SMX to initiate and accelerate the decomposition process. Finally, the energy cost analysis of the SDBC/PDS system further demonstrated the possible and economic application of the SDBC/PDS technique for SMX degradation. Thus, this study proposed a novel and economic method for PDS activation through a new nonradical oxidation pathway predominated by 1O2, which also promoted the safe and efficient transformation of antibiotics or other contaminants by PDS activation processes.

Bioaugmentation of membrane bioreactor with Achromobacter denitrificans strain PR1 for enhanced sulfamethoxazole removal in wastewater

Achromobacter denitrificans strain PR1, previously found to harbour specific degradation pathways with high sulfamethoxazole (SMX) degradation rates, was bioaugmented into laboratory-scale membrane bioreactors (MBRs) operated under aerobic conditions to treat SMX-containing real domestic wastewater. Different hydraulic retention times (HRTs), which is related to reaction time and loading rates, were considered and found to affect the SMX removal efficiency. The availability of primary substrates was important in both bioaugmented and non-bioaugmented activated sludge (AS) for cometabolism of SMX. High HRT (24 h) resulted in low food to microorganism ratio (F/M) and low SMX removal, due to substrate limitation. Decrease in HRT from 24 h to 12 h, 6 h and finally 4 h led to gradual increases in primary substrates availability, e.g. organic compounds and ammonia, resulted in increased SMX removal efficiency and degradation rate, and is more favorable for high-rate wastewater treatment processes. After inoculation into the MBRs, the bioaugmentation strain was sustained in the reactor for a maximum of 31 days even though a significant decrease in abundance was observed. The bioaugmented MBRs showed enhanced SMX removal, especially under SMX shock loads compared to the control MBRs. The results of this study indicate that re-inoculation is required regularly after a period of time to maintain the removal efficiency of the target compound.

Electron shuttles enhance the degradation of sulfamethoxazole coupled with Fe(III) reduction by Shewanella oneidensis MR-1

The ability of anthraquinone-2,6-disulfonate (AQDS) and riboflavin to enhance the sulfamethoxazole (SMX) degradation coupled with the Fe(III) reduction by Shewanella oneidensis MR-1 was investigated. The results indicated that the SMX degradation rate was 38.5% with an initial SMX concentration at 0.04 mM. For the overall performance of AQDS and riboflavin mediated SMX degradation and iron reduction, the SMX degradation rate was gradually increased with the enhancement of iron reduction. Riboflavin had a stronger enhancement on SMX degradation and iron reduction than AQDS, but the enhancement was not positively correlated with electron shuttles concentration. A quantitative characterization of the electron transfer capacity (ETC) of the electron shuttles showed that the ETC was higher for riboflavin than AQDS. The S. oneidensis MR-1 16S rRNA gene copies results indicated that electron shuttles had a positive effect on the microbial activity of S. oneidensis MR-1. The LCMS result indicated that the products of the SMX biodegradation were 3-amino-5-methylisoxazole and 4-aminobenzenesulfonic acid, which suggested that the SMX biodegradation was caused by SN bond cleavage. This study indicates that the biochemical mechanisms play a vital role in SMX transformation and Fe(II) generation in this system.

Degradation of emerging contaminants diclofenac, sulfamethoxazole, trimethoprim and carbamazepine by bentonite and vermiculite at a pilot solar compound parabolic collector

This study was aimed at evaluating bentonite (BEN) and vermiculite (VER) clays as photoactive materials for photodegrading a low-concentration (100 μg L−1) mixture of four emerging contaminants (ECs): trimethoprim (TMP), sulfamethoxazole (SMX), carbamazepine (CBZ) and diclofenac (DCF), using a solar advanced oxidation process. The experiments were performed in a stirred magnetic batch reactor (SMBR) and a solar pilot plant compound parabolic collector (CPC). The effect of mass, type of catalyst clay and H2O2 dose were evaluated, and the photodegradation of ECs was followed by Ultra Performance Liquid Chromatography (UPLC) and Dissolved Organic Carbon content (DOC). The results showed that the optimal dose of clays for EC degradation in both SMBR and CPC reactors was 0.2 g L−1. The photodegradation of ECs at optimal conditions by BEN and VER in the CPC decreased in the following order: DCF > TMP > SMX > CBZ and DCF > SMX > TMP > CBZ, respectively. The photodegradation rate constants for VER were 2, 32 and 1.1 times higher than those for BEN when SMX, CBZ and DCF were photodegraded with the optimal dose of clay, correspondingly. The percentage removal of DCF and SMX in experiments using BEN or VER was similar to TiO2. The TMP, SMX, CBZ and DCF degradation rate constants increased 9.05, 18.9, 2.08 and 23 times by adding [H2O2] = 200 mg L−1 and VER. The percentage removal of DOC was 16, 40 and 48% when VER and 50, 100 or 200 mg L−1 of hydrogen peroxide were added into the system, respectively. Similar results were obtained by adding BEN.

Individual and simultaneous degradation of the antibiotics sulfamethoxazole and trimethoprim in aqueous solutions by Fenton, Fenton-like and photo-Fenton processes using solar and UV radiations

The aim of this study was to compare the effectiveness of advanced oxidation processes (AOPs) based on Fenton and Fenton-like reagents with Solar and UV radiation (UV, UV/H2O2, Solar, Solar/H2O2, UV/H2O2/Fe2+, UV/H2O2/Fe3+, Solar/H2O2/Fe2+ and Solar/H2O2/Fe3+) for the single and simultaneous degradation of the antibiotics sulfamethoxazole (SMX) and trimethoprim (TMP) in aqueous solution. For direct photolysis processes, the degradation rate of SMX was highly enhanced, whereas that of TMP was slightly reduced, when the solution pH was increased from 3 to 12. The different photolytic behavior of SMX and TMP was investigated by DFT calculations, estimating in both cases the relative energies of the ground singlet state, the first excited singlet state, and the first triplet state. SMX triplet state is about 7.5 Kcal mol−1 above the TMP triplet state, which could justify the higher photodegradation obtained for SMX. The removal percentages of both antibiotics in the photo-Fenton and photo-Fenton-like systems were much greater than those in the conventional Fenton processes. Additionally, in both photo-Fenton processes, the degradation rates of SMX and TMP were faster by applying UV radiation than solar radiation. Complete mineralization of SMX was achieved in UV/H2O2 process; however, the Solar/H2O2/Fe3+ system yielded a maximum extent of mineralization of 42% for TMP. SMX and TMP photodegradation by-products were identified in UV, UV/H2O2, Solar, and Solar/H2O2/Fe3+ systems. The removal percentages and rates of degradation of SMX and TMP were influenced by the water matrix. It was shown that the Solar/H2O2/Fe3+ system yielded the highest removal percentage of TMP in surface water and of SMX in ground water. A high degree of SMX and TMP mineralization was obtained with both UV/H2O2 and Solar/H2O2/Fe3+systems, but the by-products were 50% less toxic with the latter system. The removal percentage and reaction rate for the single antibiotic degradation were reduced when both antibiotics were degraded simultaneously, attributable to the competition of SMX and TMP for the hydroxyl radicals generated when both pollutants are present.

Activation of persulfate by magnetite: Implications for the degradation of low concentration sulfamethoxazole

Abstract Sulfamethoxazole (SMX) was widely detected in the effluent of sewage treatment plants and water environment. In this study, SMX with low concentration was effectively degraded by magnetite-activated persulfate (PS) system. The process mainly involved the sulphate radical (SO4 −) and hydroxyl radicals (HO ), formed from PS activated by Fe(II) and Fe(III) in Fe3O4. The second-order reaction rate constants for the reaction between SMX and HO /SO4 − were estimated. The SMX degradation rate decreased as the solution pH increased from pH 3.5–10.5 and the pH dependency of SMX degradation rate was closely related to the speciation of Fe2+. HO , SO4 − and O2 − were involved during PS activation. The effects of chloride were investigated. SMX degradation efficiency was significantly decreased due to the trapping of SO4 − by Cl− at pH 4.0, while it had no effect by Cl− at pH 10.5 due to the formation of HO . The potential recyclability of Fe3O4 was measured and it could be reused at least 4 times. The findings may have promising implications in the application of Fe3O4 on a new technology for the treatment of micro-contaminated waters and soils, especially the application of natural magnetite.

Enhanced degradation of antibiotic sulfamethoxazole by electrochemical activation of PDS using carbon anodes

In this study, electrochemical activation of peroxydisulfate (PDS) using carbon anodes including multi-walled carbon nannotube (MWCNT), graphite (GR), black carbon (BC) and granular activated carbon (GAC) for degradation of antibiotic sulfamethoxazole (SMX) was investigated for the first time. The degradation of SMX by electrochemical activation of PDS using carbon anodes showed dual kinetics: an induction stage followed by a quick decay stage. In the latter stage, the degradation rate of SMX by electrochemical activation of PDS using MWCNT, GR, BC and GAC anodes increased about 15–35 times of that by electrolysis alone and 30–130 times of that by carbon/PDS (without applying current). The results of degradation of radical probes (atrazine (ATZ) and nitrobenzene (NB)) and radical scavenging effect manifest that nonradical oxidation, hydroxyl radical (HO) and sulfate radical (SO4−) jointly contributed to the degradation of SMX in electrochemical activation of PDS. The formation of transition state structure of PDS (activated PDS, PDS∗) between PDS molecule and carbon anodes by applying current was proposed to be responsible for nonradical oxidation, and its further decomposition resulted in the generation of HO and SO4−. Increasing PDS concentration (0.1–5 mM) or current density (10–200 A m−2) considerably promoted the degradation of SMX. Additionally, electrochemical activation of PDS using carbon anodes exhibited good resistance to water matrices.

Anaerobic degradation of sulfamethoxazole by mixed cultures from swine and sewage sludge

ABSTRACTThe objective of this study was to evaluate the anaerobic degradation of sulfamethoxazole (SMX) and the associated bacterial community changes in swine and sewage sludges. The degradation rate of SMX was higher in swine sludge than in sewage sludge. The addition of lactate, citrate, and sucrose had significant effects on SMX degradation, and sucrose addition yielded a higher SMX degradation rate than the other additives. At concentrations of 0.1–10 g/l sucrose, the SMX degradation rates increased in the sludge. The bacterial genera from swine sludge with sucrose exhibited the highest SMX degrading efficiency. Seventeen bacterial genera were found to be the major bacterial community members involved in SMX degradation in the sludge.

Impact of biogenic substrates on sulfamethoxazole biodegradation kinetics by Achromobacter denitrificans strain PR1.

Pure cultures have been found to degrade pharmaceutical compounds. However, these cultures are rarely characterized kinetically at environmentally relevant concentrations. This study investigated the kinetics of sulfamethoxazole (SMX) degradation by Achromobacter denitrificans strain PR1 at a wide range of concentrations, from ng/L to mg/L, to assess the feasibility of using it for bioaugmentation purposes. Complete removal of SMX occurred for all concentrations tested, i.e., 150mg/L, 500µg/L, 20µg/L, and 600ng/L. The reaction rate coefficients (kbio) for the strain at the ng/L SMX range were: 63.4±8.6, 570.1±15.1 and 414.9±124.2 L/g[Formula: see text]·day), for tests fed without a supplemental carbon source, with acetate, and with succinate, respectively. These results were significantly higher than the value reported for non-augmented activated sludge (0.41 L/(g[Formula: see text]·day) with hundreds of ng/L of SMX. The simultaneous consumption of an additional carbon source and SMX suggested that the energetic efficiency of the cells, boosted by the presence of biogenic substrates, was important in increasing the SMX degradation rate. The accumulation of 3-amino-5-methylisoxazole was observed as the only metabolite, which was found to be non-toxic. SMX inhibited the Vibrio fischeri luminescence after 5min of contact, with EC50 values of about 53mg/L. However, this study suggested that the strain PR1 still can degrade SMX up to 150mg/L. The results of this work demonstrated that SMX degradation kinetics by A. denitrificans PR1 compares favorably with activated sludge and the strain is a potentially interesting organism for bioaugmentation for SMX removal from polluted waters.

A comprehensive performance evaluation of heterogeneous Bi2Fe4O9/peroxymonosulfate system for sulfamethoxazole degradation.

In this study, a Bi2Fe4O9 catalyst with nanoplate morphology was fabricated using a facile hydrothermal method. It was used as a catalyst to activate peroxymonosulfate (PMS) for aqueous sulfamethoxazole (SMX) removal. A comprehensive performance evaluation of the Bi2Fe4O9/PMS system was conducted by investigating the effects of pH, PMS dosage, catalyst loading, SMX concentration, temperature, and halides (Cl- and Br-) on the degradation of SMX. The Bi2Fe4O9/PMS system demonstrated a remarkable catalytic activity with >95% SMX removal within 30min (conditions: pH 3.8, [Bi2Fe4O9]=0.1gL-1, [SMX]:[PMS] mol ratio =1:20). It was found that both Cl- and Br- can lead to the formation of PMS-induced reactive halide species (i.e. HClO, HBrO, and Br2) which can also react with SMX forming halogenated SMX byproducts. Based on the detected degradation byproducts, the major SMX degradation pathway in the Bi2Fe4O9/PMS system is proposed. The SMX degradation by Bi2Fe4O9/PMS system in the wastewater secondary effluent (SE) was also investigated. The results showed that SMX degradation rate in the SE was relatively slower than in the deionized water due to (i) reactive radical scavenging by water matrix species found in SE (e.g.: dissolved organic matters (DOCs), etc.), and (ii) partial deactivation of the catalyst by DOCs. Nevertheless, the selectivity of the SO4•- towards SMX degradation was evidenced from the rapid SMX degradation despite the high background DOCs in the SE. At least four times the dosage of PMS is required for SMX degradation in the SE to achieve a similar SMX removal efficiency to that of the deionized water matrix.

Ultrasonic-assisted ozone oxidation process for sulfamethoxazole removal: impact factors and degradation process

In this study, sulfamethoxazole (SMX) degradation was investigated using an ultrasonic-assisted ozone oxidation process (UAOOP). The influencing factors of ozone concentration, pH, initial SMX concentration, ultrasound power density, and radical scavenger were studied. It was proved that ultrasound application enhanced ozonation function for SMX degradation. Color change of the water during the oxidation process was found to be corresponding to SMX concentration decay in wastewater. The results indicated that SMX degradation followed a pseudo-first-order kinetic model under experimental operating conditions. SMX degradation rate increased with ozone concentration, pH, and ultrasound power density, and was inversely proportional to the initial SMX concentration. Although the direct and indirect oxidation of ozone simultaneously existed in the UAOOP system, the direct oxidation was the predominant way. Meanwhile, the biological toxicity of the solution was weakened and biological oxygen demand/chemical oxygen demand ratio increased from 0 to 0.54. It was indicated that the UAOOP system was efficient to treat SMX wastewater and promote biodegradability for further biological treatment.

Heat-activated persulfate oxidation of sulfamethoxazole in water

Heat-activated persulfate to produce highly reactive sulfate radicals (SO4⋅-) to oxidize sulfamethoxazole (SMX) in water was studied. The SMX degradation rate was significantly influenced by the reaction temperature, persulfate dose, initial pH, and co-existing anions. Higher temperature achieved higher degradation rate. The calculated activation energy for hot persulfate oxidation of SMX was approximately 130.93 kJ/mol. The degradation rate constant was proportional to the persulfate dose. An alkaline condition favored the SMX degradation. Effects of anions on the SMX degradation were species-dependent. Cl−, SO42-, and NO3- inhibited the SMX degradation, to different degrees. In contrast, HCO3- accelerated the treatment. The SMX decomposition was associated with hydroxylation, sulfonamide bond breakage, and oxidation of the amine groups. Toxicity tests revealed production of more toxic products. Therefore, appropriate post-treatments need to be considered to address the undesirable byproducts.

Assessment of bimetallic and trimetallic iron-based systems for persulfate activation: Application to sulfamethoxazole degradation

Abstract This work investigated the potential of different iron-based systems to activate persulfate (PS) into sulfate radicals (SRs) through catalytic electron transfer. SRs were then used to degrade sulfamethoxazole (SMX) in water. PS activators like Fe2+, Fe0, AgFe and CoFe (bimetallics), AgCoFe and CoAgFe (trimetallics) were tested on SMX solution (39.5 μM) spiked with PS (1.0 mM). Results on SMX degradation showed better kinetics and efficiency in case of non-plated iron particles used compared to bimetallic and trimetallic systems as well as Fe2+ at early stage of the reaction. Direct and sequential addition of Fe2+ resulted in better reaction stoichiometric efficiency (RSE) however did not yield full SMX degradation in contrast to metallic particles. Bimetallic and trimetallic systems showed higher RSE than Fe0 initially due to less PS consumption while maintaining acceptable SMX degradation rate. Smooth corrosion was responsible of progressive release of iron corrosion products for SRs production. However, in case of improved corrosion, generated SRs were quenched by an excess of iron-based activators which negatively affected the RSE. SMX mineralization was greatly improved in oxic solution rather than in anoxic medium. This work demonstrated the potential of iron-based systems to sustain PS longer in oxic solutions without the production of heavy sludge or formation of transformation products that can burden the treatment process.