Complete Total Organic Carbon Removal Research Articles

Photocatalytic Activity and Reusability of F, Sm3+ Co-Doped TiO2/MWCNTs Hybrid Heterostructure for Efficient Photocatalytic Degradation of Brilliant Black Bis-Azo Dye

A global freshwater pollution catastrophe is looming due to pollutants of emerging concern (PECs). Conventional water treatment methods are limited in removing PECs such as pharmaceuticals and dye house effluent from aquatic systems. This study provides an effective potential solution by developing an innovative wastewater treatment method based on solar-light-responsive semiconductor-based photocatalysts. A sol-gel synthesis technique was used to produce Fluorine-Sm3+ co-doped TiO2 (0.6% Sm3+) (FST3) photocatalysts. This was followed by loading multi-walled carbon nanotubes (MWCNTs) in the range of 0.25 to 1 wt% into the FST3 matrix. Solid state UV-visible spectroscopy measurements showed a bathochromic shift into the visible light region after the co-doping of TiO2, whereas XRD analysis confirmed the presence of predominantly anatase polymorphs of TiO2. The FT-IR and EDX results confirmed the presence of the F and Sm3+ dopants in the synthesised photocatalysts. XRD and TEM measurements confirmed that the crystallite sizes of all synthesised photocatalysts ranged from 12–19 nm. The resultant photocatalysts were evaluated for photocatalytic degradation of Brilliant Black BN bis-azo dye in aqueous solution under simulated solar irradiation. FST3 completely degraded the dye after 3 h, with a high apparent rate constant (Ka) value (2.73 × 10−2 min−1). The degree of mineralisation was evaluated using the total organic carbon (TOC) technique, which revealed high TOC removal (82%) after 3 h and complete TOC removal after 4 h. The incorporation of F improved the optical properties and the surface chemistry of TiO2, whereas Sm3+ improved the quantum efficiency and the optical properties. These synergistic effects led to significantly improved photocatalytic efficiency. Furthermore, incorporating MWCNTs into the F and Sm3+ co-doped TiO2 (0.6% Sm3+) improved the reaction kinetics of the FST3, effectively reducing the reaction time by over 30%. Recyclability studies showed that after 5 cycles of use, the FST3/C1 degradation efficiency dropped by 7.1%, whereas TiO2 degradation efficiency dropped by 33.4% after the same number of cycles. Overall, this work demonstrates a sustainable and efficient dye-removal technique.

Ozonation of Amoxicillin and Ciprofloxacin in Model Hospital Wastewater to Increase Biotreatability.

Amoxicillin (AMX) and Ciprofloxacin (CIP) are antibiotics commonly used in human medicine with high environmental toxicity and poor biodegradability. They have been found in various hospital effluents and groundwater, and their environmental impact is still not fully understood. In this work, we investigated the possibility of treating model wastewaters containing the antibiotics AMX and CIP using ozonation, with the addition of H2O2 under various conditions, including different pH values, H2O2, and ozone dosages. The quantification of and treatment efficacy for antibiotic removal were determined via solid phase extraction followed by chromatographic separation by liquid chromatography coupled with tandem triple quadrupole mass spectrometry (LC/MS/MS). This analytical system is quite efficient for the detection of all major antibiotic classes, even if they are present at very low concentrations. The efficiency of ozonation was determined by measuring the TOC (Total Organic Carbon) changes after ozonation of the model wastewater and by measuring the concentration of the two antibiotics. In a sequential activated sludge process of ozone-treated model wastewater, almost complete TOC removal and an overwhelming decrease in antibiotic concentrations (up to 99%) were observed. Ozonation resulted in complete removal of AMX and CIP in less than 30 and 120 min, respectively. The results of this work indicate that ozonation could be a suitable pretreatment method to reduce the toxicity of contaminants (AMX and CIP) and improve the biodegradability of hospital wastewater.

In Situ-Formed PdFe Nanoalloy and Carbon Defects in Cathode for Synergic Reduction–Oxidation of Chlorinated Pollutants in Electro-Fenton Process

Complete dechlorination and mineralization of chlorophenols via the reduction-oxidation-mediated electro-Fenton process with a composite bulk cathode is first proposed. The in situ formation of a PdFe nanoalloy and carbon defects as key active sites is mutually induced during the formation of a carbon aerogel-based electrode. Specifically, the PdFe nanoalloy promotes the generation of [H]ads as reduction sites and improves the electron transfer via an electrical circuit, while the carbon defects selectively favor the 2e- oxygen reduction pathway. Notably, this work implies a novel electrocatalytic model for the formation of ·OH via (2 + 1)e- oxygen reduction by a consecutive reaction with carbon defects and a PdFe nanoalloy. Complete total organic carbon removal and dechlorination of 3-chlorophenol were performed after 6 h. The kinetic rate constant for removing haloacetamides (HAMs) in drinking water was 0.21-0.41 h-1, and the degradation efficiency was self-enhanced after electrolysis for 2 h because of the increased concentration of [H+]. The specific energy consumption was ∼0.55 W·h·g-1 at 100% removal of some HAMs, corresponding to a power consumption of 0.6-1.1 kW·h for complete dehalogenation per ton of drinking water in waterworks. Moreover, the PdFe alloy/CA exhibited extreme mechanical and electrochemical stability with limited iron (∼0.07 ppm) and palladium (0.02 ppm) leaching during the actual application.

Electrooxidation of cardanol on mixed metal oxide (RuO2-TiO2 and IrO2-RuO2-TiO2) coated titanium anodes: insights into recalcitrant phenolic compounds

In Brazil, the cashew-nut industry has an important role in national economy, but the lack of suitable treatment of the residues generated by this activity represents a serious risk to the environment and biodiversity. Cardanol (CDN) is a highly toxic and recalcitrant phenolic compound, and it is the major component from this activity. This work evaluated, for first time, the performance of mixed metal oxide DSA®-type anodes (Ti/TiO2-RuO2 and Ti/TiO2-RuO2-IrO2) to develop a suitable electrochemical treatment for the cashew-nut industry residues, using CDN as model molecule. Results clearly showed that for both Ti/TiO2-RuO2 and Ti/TiO2-RuO2-IrO2 active anodes, an increase on the current densities (j) enhanced the percentage of total organic carbon (TOC) removal as a function of the electrolysis time (t). The complete TOC removal was efficiently achieved with Ti/TiO2-RuO2 (j≥40mAcm−2 and t≥5.0h) at 25°C, although Ti/TiO2-RuO2-IrO2 ternary anode has also showed suitable performance for this purpose (j=60mAcm−2 and t≥4.0h). UV-visible spectrophotometric data showed similarity between the CDN electrooxidation kinetics for both anodes, independently of the applied current density. Analyses performed by gas chromatography coupled to mass spectrometry confirmed the complete mineralization of CDN and its intermediates, mainly at higher densities. A positive effect in the degradation performances was achieved when an increase on the temperature was attained, at both anodes; despite the satisfactory results achieved at 25°C, favor an affordable cost.

Ultrasound-enhanced electrochemical mineralization of perfluorooctanoic acid in aqueous solutions: Assessed by response surface methodology

Aims: The sonoelectrochemical mineralization of the synthetic aqueous solution of the perfluorooctanoic acid (PFOA) on Ti/PbO 2 anode was investigated using the response surface methodology based on a central composite design (CCD). Materials and Methods: The CCD was performed using three different variables such as current density (CD) (mA/cm 2 ), pH, and supporting electrolyte (EL) concentration (mM). The total organic carbon (TOC) removal was determined as an indicator of PFOA mineralization. A Shimadzu TOC analyzer was used to measure the TOC of the samples. The Ti/PbO 2 electrode was prepared using the electrochemical deposition method. In order to enhance the electrochemical mineralization, ultrasonic (US) radiation was used. The US frequency was 20 kHz. Results: The optimum conditions for PFOA mineralization in synthetic solution were EL concentration of 94 mM, pH of 2, and CD of 83.64 mA/cm 2 , which resulted in complete TOC removal. The results indicated that the most effective factor for PFOA mineralization was CD. Besides, the TOC removal efficiency significantly increased with increasing CD. Conclusions: Under optimum conditions, the mineralization of PFOA was almost completed after 90 min of sonoelectrolysis. Therefore, sonoelectrolysis was found to be a more effective technique for mineralization of an environmentally persistent compound.

Investigation of photocatalytic ozonation treatment of water over WO3 under visible light irradiation

The aim of this study is to develop a highly efficient and environmentally friendly water treatment technique. Water treatment by photocatalytic ozonation over bare WO3 under visible light irradiation (O3/vis/WO3) system was performed under different experimental conditions using a phenol aqueous solution as model wastewater. The effects of parameters such as the initial phenol concentration, water temperature, and initial solution pH on the total organic carbon (TOC) removal efficiency in the O3/vis/WO3 system were investigated. The results suggest that the TOC removal process consists of three stages, and the combined effect of photocatalysis and ozonation, which is important for complete TOC removal, became dominant in the third stage. Furthermore, the TOC removal efficiency increased with increasing water temperature in the O3/vis/WO3 system.

Microbial Conversion of Olive Oil Mill Wastewaters into Lipids Suitable for Biodiesel Production

Lipomyces starkey were able to survive and proliferate in the presence of olive oil mill wastewaters (OMW), a medium difficult to process by biological treatments, due to the antimicrobial activities of their phenolic components. The microorganisms were grown in the presence of undiluted OMW, without external organic supplements, producing a significant reduction of both the total organic carbon (TOC) and the total phenols content. The OMW treated by L. starkey showed a significant increase of the germination index. The preliminary dilution of OMW enhanced the reduction of polluting components of OMW, leading to a complete TOC removal, as well as to lower levels of residual phenols. The activities of extracellular lipases and esterases significantly increased in the course of the OMW fermentation. A significant increase in lipid yield was observed in L. starkey in the course of the OMW treatment, particularly enhanced when the feedstock was preliminarily diluted. The fatty acid distribution showed a prevalence of oleic acid, demonstrating the potential of L. starkeyi as a source of lipids to be used as a feedstock for the synthesis of II generation biodiesel.

On the kinetics and mechanisms of photolytic/TiO2-photocatalytic degradation of substituted pyridines in aqueous solutions

Pyridine and pyridine derivatives are extensively used for the production of pesticides, medicinal drugs, industrial solvents, dyes, rubber chemicals etc. They are encountered in their wastewaters and due to their hazardous effects on ecosystems and human health, their removal is imperative. However, the methods for their treatment need to be improved or replaced by more effective alternatives. With this in mind and following our previous work on photolytic treatment of 2-halogenated pyridines (2-HalPys), the combined photolytic/photocatalytic (TiO2 P-25) at 254nm degradation and mineralisation of 2-chloropyridine (2-CPY), 2-fluoropyridine (2-FPY) and 2-hydroxypyridine (2-HPY), a major photolytic product of all 2-HalPys but 2-FPY are studied in a range of conditions. In order to probe into the mechanisms and factors affecting their degradation, the effects of pH, radical scavenger tert-butanol and inorganic ions, were examined. The former had a substantial impact on 2-CPY photocatalytic removal rate, which, however, remained practically unaffected by the latter. 2-CPY photocatalytic removal was faster at near neutral pH. 2-HPY degradation was faster in the presence of TiO2, low pH and in the presence of F− or SO42− anions. On the contrary, Cl− anions or the presence of tert-butanol had a pronouncedly detrimental effect on 2-HPY degradation rate. Main reaction by-products accompanying the purely photocatalytic destruction of 2-CPY and 2-FPY were identified. Complete total organic carbon removal was achieved in all cases.

2-Hydroxypyridine photolytic degradation by 254 nm UV irradiation at different conditions

The degradation and mineralisation of (400 mL, 3.15 mM) aqueous solutions of 2-hydroxypyridine (2-HPY), a primary intermediate formed during the photolytic degradation of 2-chloropyridine (2-CPY), 2-bromopyridine (2-BPY) and 2-iodopyridine (2-IPY), was studied at 50 °C, under 254 nm UV irradiation in a range of conditions. The rate of 2-HPY disappearance was found to heavily depend on agitation, dissolved oxygen, pH and hydroxyl radical scavenger presence. pH has a pronounced effect on the phototreatment of 2-HPY, i.e. 2-HPY removal is faster at lower pH, but except for their influence on the solution pH, Cl − or F − do not appear to affect 2-HPY rate of removal or mineralisation. 2-HPY removal rate increases with dissolved oxygen, thus indicating a prominent 2-HPY photooxidation pathway. Helium purging of the solution before and during the measurement reduced 2-HPY removal rate, thus supporting the existence of a photooxidation pathway. Pure photolytic 2-HPY removal, i.e. when photooxidation is limited, fits pseudo-first order kinetics, and a kinetic model was developed for 2-HPY formation and removal during 2-CPY, 2-BPY and 2-IPY photolytic degradation under laminar flow. The addition of radical scavenger ( tert-butanol) had a detrimental effect on the photolytic degradation of 2-HPY. Complete total organic carbon removal was achieved.

Assessment of photo-Fenton and biological treatment coupling for Diuron and Linuron removal from water

The coupling of photo-Fenton (chemical) and biological treatments has been used for the removal of Diuron and Linuron herbicides from water. The chemical reaction was employed as a pre-treatment step for the conversion of the toxic and non-biodegradable herbicides into biodegradable intermediates that were subsequently removed by means of a biological sequencing batch reactor (SBR). Multivariate experimental design was used to select four photo-Fenton reagent dose combinations for the coupling experiments. Concentrations of hydrogen peroxide between 10 and 250 mg L −1, and iron (II) concentrations between 2 and 20 mg L −1 have been tested. 15.9 mg L −1 of Fe(II) and 202 mg L −1 of H 2O 2 were needed to convert initial toxic and non-biodegradable herbicides into suitable intermediates for a subsequent biological treatment. Detrimental effects due to the excess of reactants were detected. Chemical oxygen demand (COD), average oxidation state (AOS), total organic carbon (TOC) and hydrogen peroxide concentration are the parameters used to trace the experiments course. Also, toxicity (EC 50 15) and biodegradability (BOD 5/COD) tests were carried out at the end of each chemical oxidation. Complete disappearance of the herbicides from water was observed after the chemical treatment, while 3,4-dichloroaniline and 3,4-dichlorophenyl isocyanate were identified as the main by-products of the degradation process. Complete TOC removal was achieved after biological treatment in a SBR using a hydraulic retention time (HRT) of 2 days.

Enhancing Fenton oxidation of TNT and RDX through pretreatment with zero-valent iron

The effect of reductive treatment with elemental iron on the rate and extent of TOC removal by Fenton oxidation was studied for the explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using a completely stirred tank reactor (CSTR). The results support the hypothesis that TNT and RDX are reduced with elemental iron to products that are oxidized more rapidly and completely by Fenton's reagent. Iron pretreatment enhanced the extent of total organic carbon (TOC) removal by approximately 20% and 60% for TNT and RDX, respectively. Complete TOC removal was achieved for TNT and RDX solutions with iron pretreatment under optimal conditions. On the other hand, without iron pretreatment, complete TOC removal of TNT and RDX solutions was not achieved even with much higher H 2O 2 and Fe 2+ concentrations. Nitrogen was recovered as NH 4 + and NO 3 − when Fe(0)-treated TNT and RDX solutions were subjected to Fenton oxidation. The bench-scale iron treatment-Fenton oxidation integrated system showed more than 95% TOC removal for TNT and RDX solutions under optimal conditions. These results suggest that the reduction products of TNT and RDX are more rapidly and completely degraded by Fenton oxidation and that a sequential iron treatment-Fenton oxidation process may be a viable technology for pink water treatment.

Peroxi‐coagulation of Aniline in Acidic Medium Using an Oxygen Diffusion Cathode

A novel electrochemical method for wastewater treatment, called peroxi‐coagulation, is presented in this paper. Degradation of aniline in acidic solution of pH ∼ 3 has been studied using this method. Electrolyses were performed in an undivided cell with an Fe anode and a carbon‐polytetrafluoroethylene ‐fed cathode which continuously electrogenerates . The anode dissolves yielding and . This last ion gives a precipitate of hydrated Fe(III) oxide. Aniline and its intermediates are oxidized mainly by reaction with OH•, which is produced from Fenton's reaction between electrogenerated and . Competitive coagulation of oxidation products with the hydrated Fe(III) oxide precipitate also occurs. These processes allow a fast and almost complete total organic carbon removal for aniline solutions in short‐time electrolyses. The method has higher decontamination power than other electrochemical treatments tested, such as electrocoagulation with a graphite cathode, and electro‐Fenton and photoelectro‐Fenton with a Pt anode. Benzoquinone, nitrobenzene, , and were detected in electrolyzed solutions. Precipitates contain coagulated organics with a major proportion of nitrogen‐containing compounds. A pathway for aniline peroxi‐coagulation involving these species is proposed.