Initial Sulfamethazine Concentration Research Articles

Ti3+ self-doped and nitrogen-annealed TiO2 nanocone arrays photoanode for efficient visible-LED-light-driven photoelectrocatalytic degradation of sulfamethazine

Developing efficient, durable and visible-light-driven photoanode with excellent environmental adaptability is of great significance for photoelectrocatalytic (PEC) degradation of organic pollutants. In this work, a novel Ti3+ self-doped and nitrogen-annealed TiO2 nanocone arrays (Ti3+-TiO2NCs(N2)) photoanode was prepared for efficiently photoelectrocatalytic degradation of sulfamethazine (SMT) under visible light emitting diode (LED) irradiation, which obtained 98.68% removal for initial SMT concentration of 10 mg/L within 60 min. The visible light harvesting and charge transfer of TiO2NCs were significantly improved after nitrogen annealing treatment. Additionally, the introduction of moderate Ti3+ sites further lowered charge transport resistance and introduced a new impurity energy level, which efficiently accelerated the transmission of photogenerated carriers and then generated more h+ and active species to degrade pollutants. After 15 recycling degradation experiments, Ti3+-TiO2NCs(N2) still obtained more than 97% SMT removal, demonstrating highly durable. Also, it exhibited promising application prospect for treatment of real wastewaters (secondary effluent, pharmaceutical wastewater and mariculture wastewater).

Efficient Bias-Free Degradation of Sulfamethazine by TiO2 Nanoneedle Arrays Photoanode and Co3O4 Photocathode System under LED-Light Irradiation

Solving high electrical-energy input for pollutants degradation is one of the core requirements for the practical application of photoelectrocatalytic (PEC) technology. Herein, we developed a self-driven dual-photoelectrode PEC system (TiO2 NNs-Co3O4) composed of a TiO2 nanoneedle arrays (TiO2 NNs) photoanode and Co3O4 photocathode for the first time. Under light-emitting-diode (LED) illumination, the bias-free TiO2 NNs-Co3O4 PEC system exhibited excellent PEC performance, with an internal bias as high as 0.19 V, achieving near complete degradation (99.62%) of sulfamethazine (SMT) with a pseudo-first-order rate constant of 0.042 min−1. The influences of solution pH, typical inorganic anions, natural organic matter, and initial SMT concentration on the PEC performance were investigated. Moreover, the main reactive oxygen species (h+, •OH, •O2−) in the dual-photoelectrode PEC system for SMT decomposition were elaborated. The practical application feasibility for efficient water purification of this unbiased PEC system was evaluated. It was proved that the TiO2 NNs photoanode provided a negative bias while the Co3O4 photocathode provided a positive bias for the photoanode, which made this system operate without external bias. This work elucidated the cooperative mechanism of photoelectrodes, providing guidance to develop a sustainable, efficient, and energy-saving PEC system for wastewater treatment.

Mechanism for biodegradation of sulfamethazine by Bacillus cereus H38

Degradation of sulfonamides (SAs) by microorganisms has become a focus of current research. Sulfamethazine (SMZ) is a type of SA widely used in the livestock and poultry industry. However, understanding the intermediate products, degradation pathways and mechanism of SMZ biodegradation is limited at present. In this study, a SMZ degrading bacterium Bacillus cereus H38, which can use SMZ as its only carbon source, was isolated from farmland soil. The bacterium was gram-positive with rod-shaped cells. The effects of initial SMZ concentration, pH, temperature and amount of inoculation on the biodegradation of SMZ were investigated by a single factor experiment. The results showed that the maximum degradation rate of SMZ was achieved in the environmental conditions at an initial SMZ concentration of 5 mg/L, pH of 7.0, temperature of 25 °C and inoculation amount of 5%. Under these optimum degradation conditions, strain H38 can completely degrade SMZ within 3 days. The effects of intracellular enzymes, extracellular enzymes and periplasmic enzymes on the SMZ degradation process were compared. It was found that intracellular enzymes contributed the most to the biodegradation of SMZ, and the degradation rate approached 70%. Three possible intermediates were identified by LC-MS/MS, and two degradation pathways were proposed. Whole genome sequencing results showed that the genome size of strain H38 was 5,477,631 bp, including 5599 coding sequences (CDSs), and the GC content was 35.21%. In addition, functional annotation of CDSs was performed to analyze the metabolic pathways of nitrogen and sulfur in strain H38 combining genomics and bioinformatics. This study proposes new insights into the mechanism for biodegradation of SAs and will inform future research.

Ferrate (VI) as efficient oxidant for elimination of sulfamethazine in aqueous wastes: Real matrix implications

The presence of antibiotics in aquatic environments has become a serious concern since they develop the antibiotic/multi-drug-resistant bacteria which further affect to living beings. The study intended to assess the freshly synthesized ferrate (VI) in the degradation of an important emerging micro-pollutant i.e., sulfamethazine (SMZ). Moreover, the real matrix implications are extensively conducted for implication of ferrate (VI) technology as safer and viable options. Batch reactor studies enabled the molar ratio of ferrate (VI) to sulfamethazine is 2:1 with overall rate constant 6,128 mM-2.min-1. Percentage elimination of sulfamethazine was observed Ca. 80% at initial sulfamethazine concentration 0.02 mM and ferrate (VI) dose 0.1 mM. Presence of several co-ions NaCl, Na2HPO4, NaNO3, oxalic acid and NaNO2 showed insignificant effect on elimination of sulfamethazine; whereas the efficiency of ferrate (VI) was lowered due to glycine and EDTA. Mineralization of sulfamethazine is significantly increased at lower pH value (pH 5.0). Further, the removal of sulfamethazine in the real water matrix showed that the elimination efficiency of sulfamethazine is almost unaffected as compared to the distilled water treatment. This implied that ferrate (VI) is a viable and greener option for treatment of emerging water pollutants to enhance the efficiency of existing wastewater treatment plants.

MOF-derived Cu0/C activation of molecular oxygen for efficient degradation of sulfamethazine

Zero-valent copper (ZVC) has shown potential as an oxygen activator for the degradation of organic pollutants from aqueous solution. Nevertheless, the high leaching of copper ions and the demand for acidic condition limited its application. In this study, a novel mesoporous carbon hybrid loaded zero-valent copper (Cu0/C) was successfully synthesized from Cu-based metal–organic framework (Cu3(BTC)2) through a pyrolysis method and applied to efficiently degrade sulfamethazine (SMT) at neutral pH under aeration condition. The performance of Cu0/C composite for the activation of molecular oxygen was evaluated based on the effect of different reaction parameters, such as, initial SMT concentration, initial pH, activator dosage and reaction temperature. The results showed a high efficiency for SMT removal over a broad pH range (3.0–7.0). Moreover, the Cu0/C composite exhibited excellent stability and reusability for SMT degradation, and a 96.7% SMT removal and a 68.8% total organic carbon (TOC) conversion were achieved at pH 5.8 after continuous three cycles. Combined with the determination results of reactive oxidizing species and physical-chemical characterization, cupryl species (Cu3+) rather than OH produced by the reaction of the in-situ generated H2O2 with Cu+ were the major reactive species. Additionally, the possible reaction mechanism of Cu0/C activated oxygen was tentatively proposed.

Mass-production of iron nanopowders by liquid-phase reductive precipitation in a rotating packed bed with blade packings

Iron nanopowders were mass-produced using liquid-phase reductive precipitation and a rotating packed bed (RPB) with blade packings. The effects of the concentration of the reactants, iron valence, iron source, rotational speed, and flow rates of the reactants on the characteristics of the iron nanopowders were studied. The highest mass-production rate was around 13 kg/day, which was obtained using an FeCl2 concentration of 0.2 mol/L, an NaBH4 concentration of 0.4 mol/L, a rotational speed of 1800 rpm, a flow rate of aqueous FeCl2 of 0.9 L/min, and a flow rate of aqueous NaBH4 of 0.9 L/min. The mean size of the iron nanopowders that were mass-produced using this process was 42 nm, as determined by TEM. Therefore, an RPB with blade packings can be effectively used in the commercial production of iron nanopowders. The degradation of sulfamethazine (SMT) by persulfate in water was used to evaluate the activity of the iron nanopowders in the activation of persulfate. At 25 °C, a degradation time of 30 min, an initial SMT concentration of 10 mg/L, an iron nanopowders dosage of 0.028 g/L, and an Na2S2O8 concentration of 0.24 g/L, the efficiency of degradation of SMT by the mass-produced iron nanopowders was 97%, which greatly exceeded the 9% that was achieved using commercial iron nanopowders that had been purchased from Alfa Aesar. The results herein indicate that the mass-produced iron nanopowders with persulfate is highly effective for degrading SMT in water.

Effectiveness of using nanoscale zero-valent iron and hydrogen peroxide in degrading sulfamethazine in water

This investigation elucidates the performance of using nanoscale zero-valent iron (nZVI) and hydrogen peroxide (H2O2) in the degradation of sulfamethazine in water. nZVI was mass-produced using the reductive precipitation method in a rotating packed bed with blade packings. The dependences of the degradation efficiency of sulfamethazine on pH, H2O2 concentration, nZVI dosage, and initial sulfamethazine concentration were assessed. The degradation efficiency of sulfamethazine at pH 3 substantially exceeded those at other pH 5, 7, 9, and 11. An optimal H2O2 concentration for degrading sulfamethazine (10 mg/L) at pH 3 and an nZVI dosage of 28 mg/L was 1 mmol/L. The degradation efficiency of sulfamethazine increased as the nZVI dosage was increased and the initial sulfamethazine concentration was decreased. The degradation efficiency of sulfamethazine (10 mg/L) within 5 min was 99% at pH 3 with an H2O2 concentration of 1 mmol/L and an nZVI dosage of 28 mg/L. However, the degradation efficiency of sulfamethazine (10 mg/L) using the nZVI/H2O2 process with commercial nZVI from Sigma-Aldrich was 4% at 5 min under the same conditions. Accordingly, the nZVI/H2O2 process with the mass-produced nZVI has considerable potential for the enhanced degradation of sulfamethazine in water.

Sulfamethazine degradation by heterogeneous photocatalysis with ZnO immobilized on a glass plate using the heat attachment method and its impact on the biodegradability

In this paper, the degradation of sulfamethazine (SMT) was performed using of photocatalytic process in the presence of ZnO catalyst immobilized on glass plate (on ZnO/glass plate) under UV light. The ZnO/glass plate was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra; the results of the characterization demonstrated that the properties of ZnO/glass plate were maintained unmodified. The adsorption and the photolysis tests revealed the absence of adsorption of SMT onto ZnO/glass plate and the absence of direct photolysis of SMT. The effect of the initial solution pH, the flow rate and the initial concentration of SMT on the photocatalytic process was studied and optimized by using central composite design (CCD). The model equation obtained led to a classification of these parameters based on their level of significance. The results suggested that the most influential factor was the initial concentration of SMT (x2), which had the strongest effect on the response (− 11.6) and the negative sign of the coefficient suggested that the degradation of SMT decreased for increasing initial SMT concentration. It was followed by the flow rate with positive effect on the yield of SMT degradation (+ 2.06). The model also demonstrated the absence of pH effect in the studied interval and that the strongest interaction was between the pH and the flow rate. The kinetic of degradation of the SMT can be described by a pseudo-first order kinetic model for 10 and 50 mg/L of SMT; while the kinetic of degradation was described by a pseudo-second-order kinetic model for the highest initial concentration, [SMT]0 = 100 mg/L. The optimal values of the solution pH, the flow rate and the initial concentration of SMT were 6, 0.56 L/min and 11 mg/L. Under these conditions the removal efficiency of SMT was 96% and the BOD5/COD ratio increased from 0 to 0.20 after 5 h of irradiation time.

Optimization and mechanism insights into the sulfamethazine degradation by bimetallic ZVI/Cu nanoparticles coupled with H2O2

Zero-valent iron has been recognized as a promising catalyst for the degradation of micropollutants via Fenton-like reactions, however, the enhancement of its performance is insufficiently studied. In this feature, we investigate the activity of bimetallic copper/zero-valent iron nanoparticles (ZVI/Cu) as a heterogeneous catalyst for the degradation of sulfamethazine (SMZ), and intensively elucidate the reaction mechanism. The characterization of the catalyst by XRD, TEM, and EDS confirmed the growth of Cu° on the surface of the ZVI particles. Response surface methodology (RSM) coupled with a central composite design (CCD) optimized operating parameters such as pH, catalyst loading, H2O2 dose, and initial SMZ concentration. Under the optimum conditions (pH = 3.0, H2O2 concentration =2.0 g/L, ZVI/Cu loading =0.8 g/L), SMZ fell below the detection limit (0.036 mg/L) after 30 min of the reaction. The degradation mechanism revealed that hydroxyl radicals were the dominant oxidant species. However, the accumulated iron oxides on the shell of ZVI contributed to SMZ removal by adsorption. We propose a potential pathway for SMZ degradation based on the detected transformation products. This includes an early cleavage of the mediated sulfonamide group, which suggests an efficacious degradation into tentatively single-ring transformation compounds.

A novel photocatalytic reactor for the extended reuse of W–TiO2 in the degradation of sulfamethazine

In this study, a photocatalytic reactor with a novel engineering design has been used for the extended degradation of sulfamethazine (SMZ). The reactor employed four consecutive stainless-steel plates immobilized by tungsten-dope TiO2 (W–TiO2) using polysiloxane. The characterization of W–TiO2 by X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray (EDX) denoted successful doping of tungsten in the lattice of anatase crystals of TiO2 suggesting a high photocatalytic activity under UV and visible light. A Box-Behnken experimental design was employed for the optimization of the operating parameters such as solution pH, flow rate, and the initial SMZ concentration. The residual SMZ concentration was below the detection limit after 30 min of the photocatalytic reaction under the optimum operating conditions. A highly remarkable degradation of SMZ was observed in five consecutive cycles, which reveals an extended stable photocatalytic activity offered by the reactor design. The transformation products were identified by tandem mass spectrometry, and they were employed to propose the degradation pathway. These results highlight the importance of using the photocatalysts in retained forms and open additional avenues for the practical application of photocatalysis in wastewater treatment.

Performance of a large reactor in degrading sulfamethazine in water using UV and persulfate

This study evaluates the performance of a large reactor in the degradation of sulfamethazine (SMT) in water using UV and persulfate (PS), as well as the effects of UV wavelength, PS concentration, initial SMT concentration, and addition of anions on this process. The degradation efficiency and rate of SMT using the UV-254 nm/PS process were higher than those using the UV-365 nm/PS process. The degradation efficiency of SMT using the UV-254 nm/PS process increased with PS concentration. However, PS at high concentration inhibited the SMT degradation rate using the UV-254 nm/PS process. Reducing the initial SMT concentration increased the degradation efficiency and rate of SMT under UV-254 nm. The SMT degradation using the UV-254 nm/PS process in a large reactor followed pseudo-first-order kinetics. Radical scavenging tests revealed that SO4− dominated in the SMT degradation using the UV-254 nm/PS process in a large reactor. Adding anions decreased the degradation efficiency and rate of SMT using the UV-254 nm/PS process in the order NO3− > SO42− > Cl−. In the UV-254 nm/PS process, SMT (5 mg/L) was completely degraded in 2 min at a PS concentration of 10 mM without the addition of anions. Therefore, a large reactor with high PS concentrations is very effective in degrading SMT in water using the UV-254 nm/PS process.

Error Analysis of Adsorption Isotherm Models for Sulfamethazine onto Multi Walled Carbon Nanotubes

In the present study, Multi walled carbon nanotubes (MWCNTs) was used for the adsorption of Sulfamethazine (SMZ) antibiotics. The adsorbent was characterized by scanning electron microscopy, surface area (BET) and transmission electron microscopy. Batch experiments were carried out by varying the parameters like contact time, adsorbent dosage and initial Sulfamethazine concentration at fixed pH and temperature. The equilibrium data were tested with Langmuir, Freundlich, Tempkin, Dubinin–Radushkevich (D–R), Redlich-Peterson (R-P), Sips, Toth and Khan isotherm models at five Error Analysis EABS, X2, ARE, RMSE and SD and it was found that the Langmuir and Toth isotherms best fitted the adsorption of SMZ with highest value of R2 and lowest overall experimental error. Also according to the results, a maximum removal efficiency of 99.1% was obtained at pH of 7 and the contact time of 60 min; initial SMZ concentration 20 mg/L and adsorbent dose 0.8 g/L.

Enhanced photocatalytic degradation of sulfamethazine by Bi-doped TiO2 nano-composites supported by powdered activated carbon under visible light irradiation

The antibiotic sulfamethazine (SMT) has emerged as a water pollutant that is recalcitrant to conventional water treatment process. A number of technologies based on hydroxyl radical or sulfate radical induced SMT degradation have been described, but photo-induced degradation is not widely examined. Herein, photocatalysts of Bi-doped TiO2 nano-composites supported by powdered activated carbon (PAC) were prepared, with variable molar ratios of Bi/Ti (0.06:1(6%), 0.08:1(8%), 0.1:1(10%) and 0.12:1(12%)) by a sol-hydrothermal method. The ratio of 10% (Bi-Ti/PAC (10%)) was most efficient to degrade SMT. Experimental variables during photocatalytic degradation were optimized for solution pH, catalyst dosage, initial SMT concentration, and coexisted anions. Under optimal conditions of 1.0 g/L catalyst, 20 mg/L initial SMT concentration, pH 6.0 and visible light irradiation at 400–780 nm, the degradation rate reached 81.18% in 300 min. Compared to Bi-Ti(10%) nano-composite without PAC, pure TiO2 or commercially available P25, Bi-Ti/PAC(10%) was superior for SMT degradation with a degradation kinetic rate of 0.00531 min−1. The properties of the prepared photocatalysts were characterized by X-ray powder diffraction, scanning electron microscope, X-ray photo-electron spectroscopy, Brunauer-Emmett-Teller and ultraviolet-visible diffuse reflection spectroscopy. This revealed that Bi-Ti/PAC (10%) had a smaller crystal size, larger specific surface area, larger pore size, stronger visible light absorption ability and lower band gap energy than pure TiO2. Ten intermediates of SMT were identified and a possible degradation pathway was proposed.

Feasibility of using UV/H2O2 process to degrade sulfamethazine in aqueous solutions in a large photoreactor

This investigation evaluates the performance of a large photoreactor in degrading sulfamethazine (SMT) in aqueous solutions by the UV/H2O2 process. The effects of UV wavelength, initial H2O2 concentration, initial SMT concentration, and added anions on the efficiency of degradation of SMT were studied. The degradation of SMT proceeded more rapidly in the UV-254 nm/H2O2 process than in the UV-365 nm/H2O2 process. A higher initial H2O2 concentration was associated with more efficient degradation of SMT. However, an excessive initial H2O2 concentration limited the degradation of SMT. The efficiency of degradation of SMT increased with decreasing initial SMT concentration. The degradation of SMT by the UV/H2O2 process in a large photoreactor exhibited pseudo-first-order kinetics. Moreover, SO42− and NO3− did not retard the degradation of SMT but Cl− slightly inhibited the degradation of SMT. SMT was completely degraded in 10 min by the UV-254 nm/H2O2 process at an initial SMT concentration of 5 mg/L and an initial H2O2 concentration of 10 mM in the absence of anions. These results clearly reveal the potential of the UV/H2O2 process in a large photoreactor in the effective degradation of SMT in aqueous solutions.

Synergistic degradation of antibiotic sulfamethazine by novel pre-magnetized Fe0/PS process enhanced by ultrasound

Sulfamethazine (SMT) is widely used in human and veterinary medicine as growth promoters and antibacterial drugs and it can pose potential threats to human and ecosystem health. In this study, removal of SMT by ultrasound pre-magnetized Fe0/PS process was investigated for the first time. Degradation rate for removing SMT increased 3.3 folds and the synergy factor increased from 1.2 to 2.7 compared with US/Fe0/PS process. Affecting factors such as pH (3–10), Fe0 dosage (0–0.8 mM) and initial SMT concentration (0–10 mg L−1) were studied. Stronger signals of DMPO–OH and DMPO–SO4 adduct also illustrated more and faster SO4− and OH radicals produced in the system. FeOOH was detected through the mossbauer spectrum which could both enhance the catalysis of H2O2 and activation of PS. The intermediates of the SMT degradation were investigated, and a degradation pathway was proposed. Higher correlation factor (△k and △S) in US/pre-magn-Fe0/PS system illustrated the good synergistic effect between US input power and magnetic field. Moreover, the process could efficiently remove SMT in municipal wastewater and keep pH neutral. So, US/pre-magn-Fe0/PS process is a energy saving and promising approach to remove antibiotics in real wastewater.

Metal Organic Framework with Coordinatively Unsaturated Sites as Efficient Fenton-like Catalyst for Enhanced Degradation of Sulfamethazine.

A novel Fenton-like catalyst, metal organic framework MIL-100(Fe) with FeII/FeIII mixed-valence coordinatively unsaturated iron center (CUS-MIL-100(Fe)), was synthesized, characterized, and used for the degradation of sulfamethazine (SMT). The catalytic performance of CUS-MIL-100(Fe) was investigated on the basis of various parameters, including initial pH, H2O2 concentration, catalyst dosage, and initial SMT concentration. The results showed that CUS-MIL-100(Fe) could effectively degrade SMT, with almost 100% removal efficiency within 180 min (52.4% mineralization efficiency), under the reaction conditions of pH 4.0, 20 mg L-1 SMT, 6 mM H2O2, and 0.5 g L-1 catalyst. Moreover, CUS-MIL-100(Fe) displayed a higher catalytic activity than that of MIL-100(Fe) for SMT degradation. Combined with the physical-chemical characterization, the enhanced catalytic activity can be ascribed to the incorporation of FeII and FeIII CUSs (coordinatively unsaturated metal sites), the large specific surface area, as well as the formation of mesopores. Furthermore, CUS-MIL-100(Fe) exhibited a good stability and reusability. The possible catalytic mechanism of CUS-MIL-100(Fe) was tentatively proposed.

The combination of photocatalysis process (UV/TiO2(P25) and UV/ZnO) with activated sludge culture for the degradation of sulfamethazine

ABSTRACTThe major factors affecting the removal efficiency of sulfamethazine (SMT) by photocatalysis process in the presence of TiO2 P25 or ZnO, namely the pH, the amount of catalyst and the initial SMT concentration were examined. The obtained results showed the absence of adsorption of SMT on the catalysts and the absence of degradation of SMT by direct photolysis under UV light in the absence of catalyst. The variation of the pH solution in the range 4–9 did not cause any significant degradation of SMT. The optimal amounts of each catalyst were, respectively, 0.5 and 0.25 g/L for TiO2 P25 and ZnO. Increasing the initial SMT concentration impacted negatively the removal efficiency, which decreased from 31% to 13% and from 100% to 27% in the presence of TiO2 P25 and ZnO in the presence of 10 mg/L and 50 of SMT after 30-min reaction time, respectively. The obtained results showed better efficiency of ZnO than TiO2 P25 regarding both removal efficiency and chemical oxygen demand (COD) abatement. However, removal efficiency and COD abatement were not complete, even after 7 h of photocatalysis, about 92% and 41%, respectively. The biodegradability was examined after photocatalysis performed in the following conditions: [SMT]0 = 50 mg/L, pH = 6, T = 25°C, ω = 360 rpm and 0.5 g/L of TiO2 P25 or 0.25 g/L of ZnO. In these conditions, the removal efficiencies were, respectively, 26% and 41% in the presence of TiO2 P25 and 55 and 92% in the presence of ZnO after 4 and 7 h of pretreatment times, respectively. The BOD5/COD ratio increased substantially and, respectively, from 0 to 0.25 and from 0 to 0.16 in the presence of TiO2 P25 and ZnO after 7 h of irradiation. Even if the limit of biodegradability (0.4) was not achieved, a subsequent biological treatment was considered in the presence of TiO2 P25, leading to 58% COD abatement after a 28-day culture.

Iodine-enhanced ultrasound degradation of sulfamethazine in water

This study investigated sulfamethazine (SMT) ultrasound degradation, enhanced by iodine radicals, generated by potassium iodide (KI) and hydrogen peroxide (H2O2) in situ. The results showed that the ultrasound/H2O2/KI (US/H2O2/KI) combination treatment achieved an 85.10 ± 0.45% SMT removal (%) in 60 min under the following conditions: pH = 3.2, ultrasound power of 195 W, initial SMT concentration of 0.04 mmol·L−1, H2O2 concentration of 120 mmol·L−1, and KI concentration of 2.4 mmol·L−1. UV-Vis spectrophotometric monitoring of molecular iodine (I2) and triiodide (I3−) revealed a correlation between the SMT degradation and the iodine change in the solution. Quenching experiments using methanol, t-butanol and thiamazole as radical scavengers indicated that iodine radicals, such as I and I2−, were more important than hydroxyl radicals (HO) for SMT degradation. SMT degradation under the US/H2O2/KI treatment followed pseudo-first order reaction kinetics. The activation energy (Ea) of SMT degradation was 7.75 ± 0.61 kJ·mol−1, which suggested the reaction was controlled by the diffusion step. Moreover, TOC removal was monitored, and the obtained results revealed that it was not as effective as SMT degradation under the US/H2O2/KI system.

Feasibility of using nanoscale zero-valent iron and persulfate to degrade sulfamethazine in aqueous solutions

Abstract This study investigates the effectiveness of the nanoscale zero-valent iron and persulfate (nZVI/PS) process in degrading sulfamethazine (SMT) in aqueous solutions. nZVI was formed using a rotating packed bed with blade packings. The dominant generated free radical in the nZVI/PS process for degrading SMT was SO4 −. nZVI can gradually release Fe2+, which subsequently activates PS to form SO4 −, increasing the efficiency of degradation of SMT by this process. The effects of the PS/nZVI molar ratio, initial SMT concentration, and species of inorganic anions on the efficiency of degradation of SMT were also studied. A PS/nZVI molar ratio of 1/0.5 in the nZVI/PS process was chosen to reduce the required nZVI dosage at PS concentrations of 0.5, 1, and 2 mmol/L. The efficiency of degradation of SMT declined as the initial SMT concentration was increased. Inorganic anions (SO42−, HCO3−, NO3−, and Cl− ions) at high concentrations inhibited the degradation of SMT and their suppressive effects followed the order SO42− > HCO3− > NO3− > Cl−. The efficiency of degradation of SMT using the formed nZVI significantly exceeded that using commercial nZVI that was purchased from Centron Biochemistry Technology. At an nZVI dosage of 56 mg/L, a PS concentration of 2 mmol/L, and an initial SMT concentration of 10 mg/L, the efficiency of degradation of SMT was 93% after 5 min in the absence of inorganic anions. Therefore, the nZVI/PS process is highly effective in degrading SMT in aqueous solutions.

Combination of the Electro/Fe3+/peroxydisulfate (PDS) process with activated sludge culture for the degradation of sulfamethazine

In this paper, the major factors affecting the degradation and the mineralization of sulfamethazine by Electro/Fe3+/peroxydisulfate (PDS) process (e.g. current density, PDS concentration, Fe3+ ions concentration and initial sulfamethazine (SMT) concentration) were evaluated. The relevance of this process as a pretreatment prior to activated sludge culture was also examined. Regarding the impact on SMT degradation and mineralization, the obtained results showed that they were significantly enhanced by increasing the current density and the PDS concentrations in the ranges 1–40mAcm−2 and from 1 to 10mM respectively; while they were negatively impacted by an increase of the initial SMT concentration and the Fe3+ concentration, from 0.18 to 0.36mM and from 1 to 4mM respectively. The optimal operating conditions were therefore 40mAcm−2 current density, 10mM PDS concentrations, 1mM Fe3+, and 0.18mM SMT. Indeed, under these conditions the degradation of SMT and its mineralization yield were 100% and 83% within 20min and 180min respectively. To ensure a significant residual organic content for activated sludge culture after Electro/Fe3+/PDS pre-treatment, the biodegradability test and the biological treatment were performed on a solution electrolyzed at 40mAcm−2, 10mM PDS concentrations, 1mM Fe3+, and 0.36mM SMT. Under these conditions the BOD5/COD ratio increased from 0.07 to 0.41 within 6h of electrolysis time. The subsequent biological treatment increased the mineralization yield to 86% after 30days, confirming the relevance of the proposed combined process.