Electro-Fenton treatment of mature landfill leachate in a continuous flow reactor

Remediation of carcinogenic PAHs from landfill leachate by Electro-Fenton process - Optimization and modeling

PAHs is the group of emerging micro-pollutants present in most environmental matrices that has the tendency to bioaccumulate and cause carcinogenic effects to human health. The present research involved the quantification and treatment of leachate produced from secured landfill, to eliminate the PAHS. Electro-Fenton process, a class of advanced oxidation process, is adopted to degrade the PAHs using titanium electrodes as both anode and cathode. Artificial intelligence based statistical tool "Central Composite Design" a module of JMP -19 software was used to design the experiments and optimize the critical parameters involved in the research. It was observed that the value of P is significant (P < 0.05) for all the independent variables evidencing the significant correlation between experimental values and predicted values of the software. The value of R2 obtained was 0.96 and 0.97 for COD and PAHs respectively. The maximum removal efficiency of COD and PAH was found to be 84.24% and 90.78% respectively. The optimized conditions obtained from the central composite design were: pH = 5; Fe2+ = 0.1 g/L; H2O2 = 2 g/L; reaction time = 60 min; and electric intensity = 0.2 A. Additionally, optimized experimental conditions were used to study the removal efficiencies of individual 16 PAHs and are also reported. From the close proximity of experimental and predicted results of the software it can be proved that central composite design is efficient enough to be used as a statistical tool in design and analysis for treatment of landfill leachate.

Removal of ofloxacin using a porous carbon microfiltration membrane based on in-situ generated •OH

This study investigated the removal performance of ofloxacin (OFL) by a novel electro-Fenton enhanced microfiltration membrane. The membranes used in this study consisted of metal-organic framework derived porous carbon, carbon nanotubes and Fe2+, which were able to produce hydroxyl radicals (•OH) in-situ via reducing O2 to hydrogen peroxide. Herein, membrane filtration with bias not only concentrated the pollutants to the level that could be efficiently treated by electro-Fenton but also confined/retained the toxic intermediates within the membrane to ensure a prolonged contact time with the oxidants. After validated by experiments, the applied bias of -1.0 V, pH of 3 and electrolyte concentration of 0.1 M were the relatively optimum conditions for OFL degradation. Under these conditions, the average OFL removal rate could be reach 75% with merely 5% membrane flux loss after 4 cycles operation by filtrating 1 mg/L OFL. Via decarboxylation reaction, piperazinyl ring opening, dealkylation and ipso substitution reaction, etc., OFL could be gradually and efficiently degraded to intermediate products and even to CO2 by •OH. Moreover, the oxidation reaction was preferred to following first-order reaction kinetics. This research verified a possibility for antibiotic removal by electro-enhanced microfiltration membrane.

A Bipolar Membrane-Integrated Electrochlorination Process for Highly Efficient Ammonium Removal in Mature Landfill Leachate: The Importance of ClO• Generation

Electrochemical oxidation has been demonstrated to be a useful method for removing biorefractory organic pollutants in mature landfill leachate but suffers from low efficiency in eliminating ammonium because of its resistance to being oxidized by HO• or free chlorine (FC) at decreased pH. Here, we propose a new bipolar membrane-electrochlorination (BPM-EC) process to address this issue. We found that the BPM-EC system was significantly superior to both the undivided and divided reactors with monopolar membranes in terms of elevated rate of ammonium removal, attenuated generation of byproducts (e.g., nitrate and chloramines), increased Faradaic efficiency, and decreased energy consumption. Mechanistic studies revealed that the integration of BPM was helpful in creating alkaline environments in the vicinity of the anode, which facilitated production of surface-bound HO• and FC and eventually promoted in situ generation of ClO•, a crucial reactive species mainly responsible for accelerating ammonium oxidation and selective transformation to nitrogen. The efficacy of BPM-EC in treating landfill leachates with different ammonium concentrations was verified under batch and continuous-flow conditions. A kinetic model that incorporates the key parameters was developed, which can successfully predict the optimal number of BPM-EC reactors (e.g., 2 and 5 for leachates containing 589.4 ± 5.5 and 1258.1 ± 9.6 mg L-1 NH4+-N, respectively) necessary for complete removal of ammonium. These findings reveal that the BPM-EC process shows promise in treating ammonium-containing wastewater, with advantages that include effectiveness, adaptability, and flexibility.

Minerals as catalysts of heterogeneous Electro-Fenton and derived processes for wastewater treatment: a review

Advanced oxidation processes (AOPs) such as Fenton's reagent, which generates highly reactive oxygen species, are efficient in removing biorefractory organic pollutants from wastewater. However, Fenton's reagent has drawbacks such as the generation of iron sludge, high consumption of H₂O₂, and the need for pH control. To address these issues, Electro-Fenton (EF) and heterogeneous Electro-Fenton (HEF) have been developed. HEF, which uses solid catalysts, has gained increasing attention, and this review focuses on the use of mineral catalysts in HEF and derived processes. The reviewed studies highlight the advantages of using mineral catalysts, such as efficiency, stability, affordability, and environmental friendliness. However, obstacles to overcome include the agglomeration of unsupported nanoparticles and the complex preparation techniques and poor stability of some catalyst-containing cathodes. The review also discusses the optimal pH range and dosage of the heterogeneous catalysts and compares the performance of iron sulfides versus iron oxides. Although natural minerals appear to be the best choice for effluents at pH>4, no scale-up reports have been found. The need for further development in this field and the importance of considering the environmental impact of trace toxic metals or catalytic nanoparticles in the treated water on the receiving ecosystem is emphasized. Finally, the article acknowledges the high energy consumption of HEF processes at the lab scale and calls for their performance development to achieve environmentally friendly and cost-effective results using real wastewaters on a pilot scale.

Treatment of nanofiltration concentrate of landfill leachate using advanced oxidation processes incorporated with bioaugmentation

Advanced oxidation processes have been broadly applied in wastewater treatment, but few studies have focused on its degradative effect on refractory organic contaminants in membrane concentrates of landfill leachate. In this study, the treatment effects of advanced oxidation processes including electrocoagulation (EC), ozone (OZ), anodic oxidation (AO) and electro-Fenton (EF) incorporated with genetically engineered nitrifying bacteria Rhodococcus erythropolis expressing Nirs and AMO (rRho-NM) on nanofiltration concentrate (NFC) of old landfill leachate were investigated in a lab-scale experiment. The results showed that advanced oxidation processes degraded the refractory organic contaminants including coagulation-resistant substances (CRS), humic acid (HA), fulvic acid (FvA), macro molecular organics (MMOs) and benzene ring compounds (BRCs) and increased the biodegradability in NFC of old landfill leachate. Compared to activated sludge (AS), rRho-NM exhibited an excellent removal performance for total organic carbon (TOC), ammonia nitrogen (NH₄-N), total nitrogen (TN), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) for advanced oxidation processes-treated NFC of old landfill leachate. Advanced oxidation processes incorporated with bioaugmentation demonstrated an outstanding degradation performance for removing refractory organic contaminants, TOC, NH₄-N, TN, BOD, COD and heavy metal in NFC of old landfill leachate. In addition, OZ incorporated with rRho-NM (OZ-rRho-NM) showed the optimal removal efficacy in reduction of refractory organic contaminants, TOC, NH₄-N, TN, BOD and COD, the shortest hydraulic retention time (HRT) and the minimum energy consumption in NFC of landfill leachate. Furthermore, the cheapest treatment cost for NFC could be achieved by EC incorporated with rRho-NM (EC-rRho-NM). More impressively, rRho-NM remained stable in expressing Nirs and AMO genes, increased nitrification and denitrification rate, and improved MBR effluent quality in the treatment of NFC. In conclusion, this work provides new insights into the application of advanced oxidation processes incorporated with bioaugmentation using rRho-NM for the treatment of NFC of old landfill leachate.

Recent progress in treatment of dyes wastewater using microbial-electro-Fenton technology

Globally, textile dyeing and manufacturing are one of the largest industrial units releasing huge amount of wastewater (WW) with refractory compounds such as dyes and pigments. Currently, wastewater treatment has been viewed as an industrial opportunity for rejuvenating fresh water resources and it is highly required in water stressed countries. This comprehensive review highlights an overall concept and in-depth knowledge on integrated, cost-effective cross-disciplinary solutions for domestic and industrial (textile dyes) WW and for harnessing renewable energy. This basic concept entails parallel or sequential modes of treating two chemically different WW i.e., domestic and industrial in the same system. In this case, contemporary advancement in MFC/MEC (METs) based systems towards Microbial-Electro-Fenton Technology (MEFT) revealed a substantial emerging scope and opportunity. Principally the said technology is based upon previously established anaerobic digestion and electro-chemical (photo/UV/Fenton) processes in the disciplines of microbial biotechnology and electro-chemistry. It holds an added advantage to all previously establish technologies in terms of treatment and energy efficiency, minimal toxicity and sludge waste, and environmental sustainable. This review typically described different dyes and their ultimate fate in environment and recently developed hierarchy of MEFS. It revealed detail mechanisms and degradation rate of dyes typically in cathodic Fenton system under batch and continuous modes of different MEF reactors. Moreover, it described cost-effectiveness of the said technology in terms of energy budget (production and consumption), and the limitations related to reactor fabrication cost and design for future upgradation to large scale application.

Treatment of aquatic medium containing common and emerging contaminants using an aero-electrochemical process based on graphite cathode and three metal oxides alloy as anode: Central composite design and photo/sono-enhancement

An aero-electrochemical advanced oxidation process (aero-EAOP) equipped with graphite cathode and dimensionally stable anodes was utilized for the treatment of aquatic media containing common and emerging contaminants. Among various anode materials, the application of Ti/RuO₂/IrO₂/SnO₂ anode resulted in the highest effectiveness. Central composite experimental design (CCED) was used to attain the optimum operational parameters in terms of chlorine generation. Simultaneous decolorization and ammonium removal by the aero-EAOP process were investigated. Accordingly, the decolorization efficiency of 94%, along with the ammonium removal of 65.2%, was obtained within 30 min. Implementation of ultrasound and UV irradiation resulted in the complete decolorization within 25 and 20 min, respectively. In comparison, the influence of ultrasound and UV irradiation on the ammonium removal by the aero-EAOP reactor was not remarkable. Mineralization efficiency of 75.1% was obtained during the short reaction time of 30 min. With increasing hydraulic retention time (HRT) from 2 to 20 min, decolorization efficiency increased from 12.0 to 55.7% and ammonium removal efficiency increased from 16.6 to 37.8%, respectively. The complete degradation of amoxicillin (AMX) and tetracycline (TC) antibiotics were achieved within 25 and 30 min, respectively. The degradation efficiencies of ibuprofen (IBP), acetaminophen (APAP) and endocrine disrupting compound of bisphenol A (BPA) were obtained to be 58, 66 and 78% within 30 min, respectively. Photo-assisted aero-EAOP was more efficient than the aero-EAOP in degrading target emerging pollutants.

Combining yeast MBR, Fenton and nanofiltration for landfill leachate reclamation

This study investigated the best way to combine nanofiltration (NF) and Fenton with membrane bioreactor inoculated with Saccharomyces cerevisiae (MBRy) for the treatment of landfill leachate, aiming at compliance with legislation and water reuse. Firstly, the permeate from MBRy was treated by Fenton process followed by NF (MBRy - Fenton - NF). Another alternative evaluated was the polishment of MBRy permeate by NF and treatment of NF concentrate by Fenton process (MBRy - NF - Fenton_{(concentrate)}). COD removal in the Fenton step was optimized according to central composite design (CCD) and 85.5% removal was obtained at pH = 3, Fe²⁺:H₂O₂ molar ratio = 1:9.81 and C:H₂O₂ molar ratio = 1:1.14. Increased toxicity was observed with the Fenton application (EC₅₀ = 2.45%). The NF showed the best performance treating the MBRy permeate. High permeate flux (8.9 ± 1.6 L h^-1 m^-2) and ion rejection (82 ± 4.2%), and low membrane fouling was observed in this condition. Although both NF permeate presented potential for reuse, the final COD concentration was lower in the MBRy - Fenton effluent (88 mg L^-1). The Fenton application for the NF concentrate was able to remove 87.24% of COD. With a preliminary economic analysis, it was verified that the MBRy - NF - Fenton_{(concentrate)} combination is the most advantageous due to the lower chemical reagent and membrane area requirements. Thus, this route presents itself as an alternative for landfill leachate reclamation.

Enhanced mass transfer and service time of mesh Ti/Sb-SnO2 electrode for electro-catalytic oxidation of phenol

Titanium-based SnO₂ with Sb dopant (Ti/Sb-SnO₂) was of interest in the field of electro-catalytic oxidation due to its high organic oxidation rates. However, the relatively poor mass transfer performance and short service time limited its practical application. To overcome this problem, Ti/Sb-SnO₂ electrode was fabricated on mesh substrate and used as the anode for electrochemical oxidization of phenol. Compared to the anode prepared on planar Ti, the mesh anode with compact and uniform catalyst surface lowered electron transfer resistance and higher O_ads content (17.41%), which benefited the generation of hydroxyl radicals (·OH) (increment of 24.5%). In addition, this structure accelerated the fluid perturbation around electrode in microscopic scale as the COMSOL simulation result indicated; the electric potential on mesh anode varied regularly along the undulant terrain of electrode so that the mass transfer coefficient was enhanced by 1.67 times. These structure-dependent characteristics contributed to the superior electro-catalytic performance toward degradation of phenol. Experimental results showed that mesh anode had a higher TOC removal efficiency of 90.6% and mineralization current efficiency of 20.1% at current density of 10 mA cm^-2, which was 9.95% and 21.6% higher than the planar anode, and the service lifetime was 1.89 times longer than planar anode. This highly electro-catalytically active and stable Ti/Sb-SnO₂ mesh electrode showed a potential application prospect toward electro-catalytic degradation process.

Degradation of pharmaceuticals from wastewater in a 20-L continuous flow bio-electro-Fenton (BEF) system

The bio-electro-Fenton (BEF) technology has proven to be an effective and energy-saving method for treating wastewaters containing a single pharmaceutical in the lab-scale. However, the continuous degradation of pharmaceuticals in a scaled-up BEF has never been reported. In this study, a 20-L dual-chamber BEF reactor was designed and tested for treating six model pharmaceuticals. The effect of key operational factors including applied voltage, cathode Fe²⁺ dosage, initial pharmaceuticals concentration and hydraulic retention time (HRT), were assessed. By implementing 0.1 V voltage, 0.3 mM Fe²⁺ and HRT of 26 h, the six selected pharmaceuticals (500 μg L^-1 for each) were removed completely. Moreover, transformation products during clofibric acid degradation, such as 4-chlororesorcinol, were detected and the relevant transformation pathway was proposed. Additionally, it successfully removed these pharmaceuticals in the real wastewater matrix. This paper contributes to scaling-up the BEF process for continuous and effective treating pharmaceuticals-contaminated wastewater.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Pre-magnetized Fe0 as heterogeneous electro-Fenton catalyst for the degradation of p-nitrophenol at neutral pH

Pre-magnetized Fe⁰ (Pre-Fe⁰) was for the first time applied as heterogeneous catalyst to enhance the oxidation efficiency of electro-Fenton (EF) for the degradation of p-nitrophenol (PNP). The parameters including current, initial pH and pre-Fe⁰ dosage of Pre-Fe⁰/EF process were optimized and compared with other two processes (conventional Fe⁰/EF and electro-oxidation) to confirm its advantage. The rate constants of PNP removal were 1.40-3.82 folds of those by Fe⁰/EF process under various experimental conditions. The application of pre-Fe⁰ as catalyst could extend the working pH range from 3.0 to neutral conditions for PNP removal and reduce the Fe⁰ dosage from 2 to 0.5 mM corresponding to Fe⁰/EF, avoiding the second pollution of iron sludge. The superiority of Pre-Fe⁰/EF process was also verified to improve the degradation and mineralization of other phenols and antibiotics. Furthermore, a possible pathway of PNP degradation was revealed by the identification of intermediates and organic acids, and the possible mechanism of pre-Fe⁰ efficiently enhanced the EF efficiency was proposed. This work demonstrated that such a novel heterogeneous EF process using pre-Fe⁰ catalyst was clean and promising for the degradation of refractory organic pollutants.

Characterization and treatment of landfill leachates by electro-Fenton process: A case study in Algeria

The feasibility of the electro-Fenton (EF) process to improve the biodegradability of Algerian leachates was examined, in order to prepare this kind of flux for conventional biological treatment. This work also included, for the first time in Algeria, the control and monitorization of a landfill-the "Hamici" landfill. Several physicochemical parameters were determined allowing its classification into an intermediate degradation phase, namely considering their alkaline pH (8.7), high ammonium concentration (3,120 mg/L), low content in heavy metals, and biodegradability (BOD₅ /COD = 0.22). The effects of important parameters such as current intensity, treatment time, and temperature on COD removal have been studied and optimized by using response surface analysis of a central composite design, where 91.1% of COD was removed with a treatment time of 285 min, a current intensity of 3 A, and a temperature of 20°C. A biodegradability test, which was performed on a solution electrolyzed with 120 min, 2 A, and 20°C, allowed to improve the leachates biodegradability from 0.2 to 0.42, with a removal rate of COD and TOC of 53.35% and 34.5%, respectively. However, the current efficiency declined from 137% to 76.6% when the current intensity was rise from 0.5 to 2 A. These results showed the relevance of EF process applied on raw intermediate leachates and its possible benefit in the Algiers leachates treatment processes. Thus, it was concluded that biological treatment can be combined with EF process for optimal mineralization of leachates with clear advantages in this studied location. PRACTITIONER POINTS: Characterization and treatment of leachates by electro-Fenton (EF) process were carried out. The leachates are intermediate type and therefore biologically recalcitrant. The operating parameter for EF process were modeled and optimized by the central composite design. Current intensity of 2 A reduces COD and TOC of 53.35% and 34.5%, respectively. The ratio BOD₅ /COD increased from 0.2 to 0.42 after 120 min of electrolysis time.

Modifying graphite felt cathode by HNO3 or KOH to improve the degradation efficiency of electro-Fenton for landfill leachate

Based on graphite felt (GF), the cathode of an electro-Fenton (EF) system was modified by HNO₃ and KOH respectively to improve the degradation efficiency for actual landfill leachate. The results of Fourier transform infrared spectroscopy (FTIR) spectra, Boehm titration experiments, contact angle, scanning electron microscopy (SEM) and adsorption experiments illustrated that the surface of the modified GFs had more oxygen-containing functional (OG) groups, and possessed better hydrophilicity and larger specific surface area. In 180 min H₂O₂ electrogeneration experiments, the cumulative amount of H₂O₂ produced by unmodified GF (GF-0), HNO₃ modified GF (GF-1) and KOH modified GF (GF-2) was 526 mg/L, 891 mg/L and 823 mg/L respectively. In 180 min EF reaction, the removal rate of chemical oxygen demand (COD) in GF-0, GF-1 and GF-2 EF systems was 31.88%, 60.65% and 52.08% respectively; the removal rate of NH₄ ⁺-N in GF-0, GF-1 and GF-2 EF systems was 43.37%, 98.10% and 94.81% respectively. In addition, both the performance of GF-1 and GF-2 for Fe²⁺ regeneration was greatly enhanced, and GF-1 was superior to GF-2. The degradation efficiency for landfill leachate was enhanced obviously by employing the modified EF system, suggesting that the two modified cathodes have great potential in practical production.

Application of electro-Fenton process for treatment of composting plant leachate: kinetics, operational parameters and modeling

BACKGROUND

Composting plant leachate is considered as one of the highly polluted wastewaters which is necessary to be treated by simple, economic, fast and environmentally compatible methods. In this study, treatment of fresh composting plant leachate by electro-Fenton (EF) process was investigated.

METHODS

The effect of various input variables like pH (2-7), DC currents (1.5-3 A), H₂O₂ concentrations (theoretical ratio H₂O₂/COD: 0.1-0.6), TDS changes (4-6%), feeding mode, and BOD/COD ratio at the optimal point were studied. The settling characteristics of the waste sludge produced by the treatment (sludge volumes after 30-min sedimentation: V₃₀) were also determined. Artificial neural network (ANN) approach was used for modeling the experimental data.

RESULTS

Based on the results, the best removal rate of COD was obtained at pH: 3, 3 A constant DC current value, 0.6 theoretical ratio H₂O₂/COD and the feeding mode at four step injection. BOD/COD ratio at the optimal point was 0.535 and the maximum COD removal was achieved at TDS = 4%. In the optimal conditions, 85% of COD was removed and BOD/COD ratio was increased from 0.270 to 0.535. The data follow the second-order kinetic (R² > 0.9) and neural network modeling also provided the accurate prediction for testing data.

CONCLUSION

Results showed that EF process can be used efficiently for treatment of composting plant leachate using the proper operating conditions.

Zn0-CNTs-Fe3O4 catalytic in situ generation of H2O2 for heterogeneous Fenton degradation of 4-chlorophenol

A novel Zn⁰-CNTs-Fe₃O₄ composite was synthesized by the chemical co-precipitation combined with high sintering process at nitrogen atmosphere. The as-prepared composite was characterized by SEM, EDS, XRD, XPS, VSM and N₂ adsorption/desorption experiments. A novel heterogeneous Fenton-like system, composed of Zn⁰-CNTs-Fe₃O₄ composite and dissolved oxygen (O₂) in solution, which can in situ generate H₂O₂ and OH, was used for the degradation of 4-chlorophenol (4-CP). The influences of various operational parameters, including the initial pH, dosage of Zn⁰-CNTs-Fe₃O₄ and initial concentration of 4-CP on the removal of 4-CP were investigated. The removal efficiencies of 4-CP and total organic carbon (TOC) were 99% and 57%, respectively, at the initial pH of 1.5, Zn⁰-CNTs-Fe₃O₄ dosage of 2 g/L, 4-CP initial concentration of 50 mg/L and oxygen flow rate of 400 mL/min. Based on the results of the radical scavenger effect study, the hydroxyl radical was considered as the main reactive oxidants in Zn⁰-CNTs-Fe₃O₄/O₂ system and a possible degradation pathway of 4-CP was proposed.

Effect of the structure of stacked electro-Fenton reactor on treating nanofiltration concentrate of landfill leachate

The membrane concentrate from landfill leachate has great potential risks of the environmental pollution. The aim of this study was to investigate the structure effect of stacked electro-Fenton (EF) reactor on the nanofiltration (NF) concentrate treatment from landfill leachate. The stacked EF reactor was constructed with a carbon-PTFE gas diffusion cathode and an IrO₂-Ta₂O₅ anode with different electrode spacings (i.e., 2, 5, 10, and 40 mm) and electrode pairs (i.e., 1, 3, 6, and 9). Results showed that smaller electrode spacing and more electrode pairs in the stacked EF reactor improved the COD removal in the NF concentrate treatment. The specific energy consumption decreased with smaller electrode spacing but increased with more electrode pairs. Under the current density of 15 mA cm^-2, Fe²⁺ dosage of 560 mg L^-1, the stacked EF reactor with 9 electrode pairs and the electrode spacing of 2 mm removed 71 ± 6% of the total COD in the NF concentrate within 6 h and the specific energy consumption was 207 ± 20 kWh∙kg COD^-1. The COD removal was kept stable in the stacked EF reactor within 3 cycles of operation. Three-dimensional fluorescence spectroscopic and gas chromatographic mass spectrometric analysis showed that humic acids and aromatic proteins were efficiently degraded in the EF process and large amount of aromatic hydrocarbons was detected in the treated NF concentrate. Our stacked EF reactor could be used to treat leachate concentrates with effectively degradation of the refractory organic pollutants.

Zn-Fe-CNTs catalytic in situ generation of H2O2 for Fenton-like degradation of sulfamethoxazole

A novel Fenton-like catalyst (Zn-Fe-CNTs) capable of converting O₂ to H₂O₂ and further to OH was prepared through infiltration fusion method followed by chemical replacement in argon atmosphere. The catalyst was characterized by SEM, EDS, TEM, XRD and XPS. The reaction between Zn-Fe-CNTs and O₂ in aqueous solution could generate H₂O₂ in situ, which was further transferred to OH. The Fenton-like degradation of sulfamethoxazole (SMX) using Zn-Fe-CNTs as catalyst was evaluated. The results indicated that Zn-Fe-CNTs had a coral porous structure with a BET area of 51.67m²/g, exhibiting excellent adsorption capacity for SMX, which enhanced its degradation. The particles of Zn⁰ and Fe⁰/Fe₂O₃ were observed on the surface of Zn-Fe-CNTs. The mixture of Zn⁰ and CNTs could reduce O₂ into H₂O₂ by micro-electrolysis and Fe⁰/Fe₂O₃ could catalyze in-situ generation of H₂O₂ to produce OH through Fenton-like process. When initial pH=1.5, T=25°C, O₂ flow rate=400mL/min, Zn-Fe-CNTs=0.6g/L, SMX=25mg/L and reaction time=10min, the removal efficiency of SMX and TOC was 100% and 51.3%, respectively. The intermediates were detected and the possible pathway of SMX degradation and the mechanism of Zn-Fe-CNTs/O₂ process were tentatively proposed.

Electro-Fenton oxidation of reverse osmosis concentrate from sanitary landfill leachate: Evaluation of operational parameters

The electro-Fenton oxidation of a concentrate from reverse osmosis of a sanitary landfill leachate, with an initial chemical oxygen demand (COD) of 42 g L^-1, was carried out using a carbon-felt cathode and a boron doped diamond anode. The influence of the applied current intensity, initial pH and dissolved iron initial concentration on the electro-Fenton process was assessed. For the experimental conditions used, results showed that the initial pH is the parameter that more strongly influences the current efficiency of the electro-Fenton process, being this influence more pronounced on the oxidation rate than on the mineralization rate of the organic matter. The increase in iron initial concentration was found to be detrimental, since the natural amount of iron present in the effluent, 73 mg L^-1 of total iron and 61 mg L^-1 of dissolved iron, was sufficient to ensure the electro-Fenton process at the applied intensities - 0.2-1.4 A. For the more favourable conditions studied, initial pH of 3 and natural iron concentration, it was found an increase in the organic load and nitrogen removals with the applied current intensity. For the highest current intensity applied, a COD removal of 16.7 g L^-1 was achieved after 8-h experiments.

Microwave-enhanced catalytic wet peroxide oxidation of quinoline: the influence of pH and H2O2dosage and identification of reactive oxygen species

This article presents a study about the initial pH and H₂O₂dosage influence on TOC abatement by MW-CWPO with Cu/Ni-catalyst and reactive oxygen identification based on quinoline mineralization inhibition using the specific radical scavengers.

Electrochemical treatment of concentrate from reverse osmosis of sanitary landfill leachate

Conventional sanitary landfill leachate treatment has recently been complemented and, in some cases, completely replaced by reverse osmosis technology. Despite the good quality of treated water, the efficiency of the process is low and a large volume of reverse osmosis concentrate has to be either discharged or further treated. In this study, the use of anodic oxidation combined with electro-Fenton processes to treat the concentrate obtained in the reverse osmosis of sanitary landfill leachate was evaluated. The anodic oxidation pretreatment was performed in a pilot plant using an electrochemical cell with boron-doped diamond electrodes. In the electro-Fenton experiments, a boron-doped diamond anode and carbon-felt cathode were used, and the influence of the initial pH and iron concentration were studied. For the experimental conditions, the electro-Fenton assays performed at an initial pH of 3 had higher organic load removal levels, whereas the best nitrogen removal was attained when the electrochemical process was performed at the natural pH of 8.8. The increase in the iron concentration had an adverse impact on treatment under natural pH conditions, but it enhanced the nitrogen removal in the electro-Fenton assays performed at an initial pH of 3. The combined anodic oxidation and electro-Fenton process is useful for treating the reverse osmosis concentrate because it is effective at removing the organic load and nitrogen-containing species. Additionally, this process potentiates the increase in the biodegradability index of the treated effluent.

Integration of US/Fe(2+) and photo-Fenton in sequencing for degradation of landfill leachate

The landfill leachate treated by sonication in presence of Fe(2+) (US/Fe(2+)) and then by photo-Fenton achieved the highest total organic carbon (TOC) removal efficiency among the screened processes. The lower initial pH, dosage of Fe(2+) and initial concentration of leachate were helpful in raising TOC removal efficiency of leachate by US/Fe(2+). The optimal conditions for the US-photo-Fenton process were as follows: initial pH at 3.0, [H2O2]/[TOC0] at 2, [H2O2]/[Fe(2+)] at 5 and initial concentration of landfill leachate at 600 mg/L. The removal efficiency of TOC, chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5) were 68.3, 79.6 and 58.2%, while the BOD5/COD rose from 0.20 to 0.43 at optimum condition. Based on gas chromatography-mass spectrometry (GC-MS) results, 36 of a total of 56 pollutants were completely degraded by US-photo-Fenton treatment.

Removal of refractory contaminants in municipal landfill leachate by hydrogen, oxygen and palladium: a novel approach of hydroxyl radical production

Municipal solid waste (MSW) leachate contains various refractory pollutants that pose potential threats to both surface water and groundwater. This paper established a novel catalytic oxidation process for leachate treatment, in which OH is generated in situ by pumping both H2 and O2 in the presence of Pd catalyst and Fe(2+). Volatile fatty acids in the leachate were removed almost completely by aeration and/or mechanical mixing. In this approach, a maximum COD removal of 56.7% can be achieved after 4h when 200mg/L Fe(2+) and 1250mg/L Pd/Al2O3 (pH 3.0) are used as catalysts. After oxidation, the BOD/COD ratio in the proposed process increased from 0.03 to 0.25, indicating that the biodegradability of the leachate was improved. By comparing the efficiency on COD removal and economical aspect of the proposed Pd-based in-situ process with traditional Fenton, electro-Fenton and UV-Fenton for leachate treatments, the proposed Pd-based in-situ process has potential economic advantages over other advanced oxidation processes while the COD removal efficiency was maintained.

Design of a highly efficient and wide pH electro-Fenton oxidation system with molecular oxygen activated by ferrous-tetrapolyphosphate complex

In this study, a novel electro-Fenton (EF) system was developed with iron wire, activated carbon fiber, and sodium tetrapolyphosphate (Na6TPP) as the anode, cathode, and electrolyte, respectively. This Na6TPP-EF system could efficiently degrade atrazine in a wide pH range of 4.0-10.2. The utilization of Na6TPP instead of Na2SO4 as the electrolyte enhanced the atrazine degradation rate by 130 times at an initial pH of 8.0. This dramatic enhancement was attributed to the formation of ferrous-tetrapolyphosphate (Fe(II)-TPP) complex from the electrochemical corrosion (ECC) and chemical corrosion (CC) of iron electrode in the presence of Na6TPP. The Fe(II)-TPP complex could provide an additional molecular oxygen activation pathway to produce more H2O2 and (•)OH via a series single-electron transfer processes, producing the Fe(III)-TPP complex. The cycle of Fe(II)/Fe(III) was easily realized through the electrochemical reduction (ECR) process on the cathode. More interestingly, we found that the presence of Na6TPP could prevent the iron electrode from excessive corrosion via phosphorization in the later stage of the Na6TPP-EF process, avoiding the generation of iron sludge. Gas chromatograph-mass spectrometry, liquid chromatography-mass spectrometry, and ion chromatography were used to investigate the degradation intermediates to propose a possible atrazine oxidation pathway in the Na6TPP-EF system. These interesting findings provide some new insight on the development of a low-cost and highly efficient EF system for wastewater treatment in a wide pH range.

Electrochemical advanced oxidation and biological processes for wastewater treatment: a review of the combined approaches

As pollution becomes one of the biggest environmental challenges of the twenty-first century, pollution of water threatens the very existence of humanity, making immediate action a priority. The most persistent and hazardous pollutants come from industrial and agricultural activities; therefore, effective treatment of this wastewater prior to discharge into the natural environment is the solution. Advanced oxidation processes (AOPs) have caused increased interest due to their ability to degrade hazardous substances in contrast to other methods, which mainly only transfer pollution from wastewater to sludge, a membrane filter, or an adsorbent. Among a great variety of different AOPs, a group of electrochemical advanced oxidation processes (EAOPs), including electro-Fenton, is emerging as an environmental-friendly and effective treatment process for the destruction of persistent hazardous contaminants. The only concern that slows down a large-scale implementation is energy consumption and related investment and operational costs. A combination of EAOPs with biological treatment is an interesting solution. In such a synergetic way, removal efficiency is maximized, while minimizing operational costs. The goal of this review is to present cutting-edge research for treatment of three common and problematic pollutants and effluents: dyes and textile wastewater, olive processing wastewater, and pharmaceuticals and hospital wastewater. Each of these types is regarded in terms of recent scientific research on individual electrochemical, individual biological and a combined synergetic treatment.

Factorial design analysis for COD removal from landfill leachate by photoassisted Fered-Fenton process

The Fered-Fenton process has been shown to be an effective method for leachate treatment, but it still faces problems of inadequate regeneration of ferrous ion. However, the use of the photoassisted Fered-Fenton process could overcome this difficulty and improve the efficiency of chemical oxygen demand (COD) removal since photoassisted Fered-Fenton process induces the production of hydroxyl radicals from the regeneration of ferrous ions and the reaction of hydrogen peroxide with UV light. As there are so many operating parameters in photoassisted Fered-Fenton process, it is necessary to develop a mathematical model in order to produce the most economical process. In the present study, a factorial design was carried out to evaluate leachate treatment by photoassisted Fered-Fenton process. The influence of the following variables: H₂O₂ concentration, Fe(2+) concentration, current density, and initial pH in the photoassisted Fered-Fenton process was investigated by measuring COD removal efficiencies after 60-min reaction. The relationship between COD removal and the most significant independent variables was established by means of an experimental design. The H₂O₂ concentration, Fe(2+) concentration, initial pH, and the interaction effect between current density and initial pH were all significant factors. The factorial design models were derived based on the COD removal efficiency results and the models fit the data well.

Effect of organic matter strength on anammox for modified greenhouse turtle breeding wastewater treatment

Anaerobic ammonium-N removal from modified greenhouse turtle breeding wastewater with different chemical oxygen demand (COD) strengths (194.0-577.8 mg L(-1)) at relatively fixed C/N ratios (≈ 2) was investigated using a lab-scale up-flow anaerobic sludge blanket (UASB) anammox reactor. During the entire experiment, the total nitrogen (TN) removal efficiency was about 85% or higher, while the average COD removal efficiency was around 56.5 ± 7.9%. Based on the nitrogen and carbon balance, the nitrogen removal contribution was 79.6 ± 4.2% for anammox, 12.7 ± 3.0% for denitrification+denitritation and 7.7 ± 4.9% for other mechanisms. Denaturing gradient gel electrophoresis (DGGE) analyses revealed that Planctomycete, Proteobacteria and Chloroflexi bacteria were coexisted in the reactor. Anammox was always dominant when the reactor was fed with different COD concentrations, which indicated the stability of the anammox process with the coexistence of the denitrification process in treating greenhouse turtle breeding wastewater.