Chemical Oxidation Technology Research Articles

Novel catalytic self-cleaning membrane with peroxymonosulfate activation for dual-function wastewater purification: Performance and mechanism

The integration of in-situ chemical oxidation (ISCO) and membrane separation technology (MST) was appealing for one-step efficient removal of complex dye-contaminated oily wastewater. However, the construction of catalytic membranes remains an arduous challenge due to the critical restriction of unsatisfactory degradation and poor stability. In current work, manganese dioxide (MnO2)/carboxyl functionalized carbon nanotube (C-CNT) composites were prepared through a facile hydrothermal process. It was found that, the degradation rate of rhodamine B (Rh B, 100 ppm) in MnO2/C-CNT (0.2 g/L)/peroxymonosulfate (PMS, 0.5 g/L) system reached 2.071 min−1, which was 4.6 and 10.9 times higher than that of MnO2 and C-CNT (0.4541 and 0.1942 min−1), respectively. The vacuum-assisted filtration was utilized to construct MnO2/C-CNT@ polyvinylidene fluoride (PVDF) membrane, which exhibited excellent filtration catalytic activity and stability for dyes and natural small-molecular organics. Scavenger experiments and electron paramagnetic resonance (EPR) analysis verified the synergistic effect of radicals and nonradicals while 1O2 was the dominator for Rh B degradation. The MnO2/C-CNT@PVDF membrane also possessed high permeation flux (170.2 L/(m2·h)), separation efficiency (99.5%) and anti-oil properties for filtrating n-hexane/water emulsion. Moreover, the modified membrane could achieve the dual purification for one-step catalytic degradation of dyes and oil/water separation. Meanwhile, the flux recovery rate of the prepared membrane reached 91% after filtering the PMS solution for 10 min, indicating its brilliant self-cleaning performance. This study provided a novel insight into development of dual-function catalytic self-cleaning membranes for water treatment.

Treatment and recovery of iron from acid mine drainage: a pilot-scale study

The acid mine drainage (AMD) formed during copper mining and smelting has a low pH, high sulfate concentration, and large amounts of valuable metals such as Fe, Cu, and Mn. In order to achieve step-by-step recovery of these resources, it is necessary to first remove high concentrations of iron from the wastewater. In this study, chemical oxidation technology was applied to establish a 12 m3/d pilot-scale treatment process to precipitate high-concentration iron (510.3 ± 50 mg/L) under acidic conditions. The experimental results showed that the Fe2+ oxidation rate and TFe (total Fe) removal rate exceeded 99%, while the loss of Cu and Mn did not exceed 4%. The average Fe content of the recovered sludge was 26.85%, which signifies good recycling value. In addition, an economic analysis showed that this method was 14 cents cheaper per m3 than the traditional lime neutralization method for treating AMD, which would result in large annual savings for sludge treatment costs.

Corrigendum to “Conditioning of resuspension excess sludge with chemical oxidation technology: The respective performance of filtration and expression stage in compression dewatering” [Sep. Purif. Technol. 237 (2020) 116317

Corrigendum to “Conditioning of resuspension excess sludge with chemical oxidation technology: The respective performance of filtration and expression stage in compression dewatering” [Sep. Purif. Technol. 237 (2020) 116317

Catalyzed H2O2 decomposition over iron oxides and oxyhydroxides: Insights from oxygen production and organic degradation

Iron minerals, such as iron oxides and iron oxyhydroxides, are the main influential soil components in catalyzed hydrogen peroxide propagation (CHP). Due to their dual effects on H2O2 activation to produce reactive oxygen species (ROS) and invalid consumption to produce oxygen, the intrinsic reactivity of iron minerals toward H2O2 decomposition requires comprehensive investigations. Herein, six iron minerals (hematite, magnetite, maghemite, goethite, feroxyhyte, and ferrihydrite) for H2O2 decomposition were investigated by a combination of normalized kinetic rate constants of H2O2 decomposition (NkH2O2), O2 production (NkO2), benzoic acid degradation (NkBA), and hexachloroethane degradation (NkHCA) over the surface area of each mineral. The results indicate H2O2 decomposition over iron minerals is a surface-related heterogeneous process. Hematite and goethite are the most promising minerals for environmental cleanup in terms of ROS production, because their H2O2 utilization efficiency for benzoic acid (BA) degradation (0.138 and 0.024 mol BA/mol H2O2 for hematite and goethite, respectively) are highest among the six iron minerals. Magnetite and maghemite are highly active for both H2O2 decomposition and O2 production at neutral and basic pHs. The presence of organic compounds suppresses O2 production by more than 60%, which favors H2O2 utilization. Ferrihydrite and feroxyhyte are considered as the problematic mineral for CHP due to that the two minerals acquire a high O2 production and negligible ROS generation at all pHs. The results of this study provide new insights to increase the understandings of H2O2-iron mineral systems and guide the application of iron minerals in chemical oxidation technologies.

Effective degradation of VOCs from wood by Fe2+ chelate activated dual oxidant (H2O2-PS)

Wood is rich in extractives and volatile oils that emit unpleasant odors and some harmful volatile organic compounds (VOCs). Chemical oxidation technologies processes high efficiency on the destruction of aqueous organic components via oxidation by radicals, however, wood block treatment scenarios suffer from the low availability of radicals in aqueous conditions owing to the special structure of the wood blocks, limitations of mass transfer and the short life of free radicals. Herein, ethylenediaminetetraacetic acid (EDTA) is selected as a chelating agent to synthesize EDTA-Fe2+ chelate, thus introducing Fe2+ into the wood by vacuum impregnation. The Fe2+ is evenly distributed and immobilized in the wood to form a chemical oxidation system via in-situ activation of the dual oxidant (H2O2-PS), which truncates the contact distance between free radicals and extractives/volatile oils thus enhancing the removal efficiency. Various controlling factors, including EDTA/Fe2+ molar ratio, Fe2+dosage, PS/H2O2 molar ratio, and persulfate (PS) dosage are evaluated. The degradation products of VOCs by headspace solid-phase micro-extraction combined with gas chromatography-mass spectrometry (HS-SPME/GC-MS) indicate that the wood VOC removal rate is ∼80%. The Electron paramagnetic resonance (EPR) analysis further reveals that SO4−· and ·OH are the primary reactive species. The characterization of wood properties illustrates that the process has no destructive effect. The results of this work may provide a theoretical basis for feasibility of the practical application of the EDTA-Fe2+/H2O2-PS system.

Removal of Heavy Metal from Wastewater using Water Chestnut Shell as an Adsorbent

The contamination of water resources as a result of industrial activity is on the rise and is a global concern. The heavy metals found in wastewater are long lasting and non-biodegradable. Contamination with heavy metals over acceptable limits could result in major health problems. Chemical precipitation, chemical oxidation, ion exchange, membrane separation, reverse osmosis, electrodialysis, adsorption, and other technologies are used to lessen the influence of heavy metals on water bodies. Some procedures are extremely costly, energy-intensive, and frequently result in the production of harmful by-products. The use of adsorption as a cost-effective approach for removing heavy metals from industrial wastewater has been examined. The usage of Trapa bispinosa peels/shell as a low-cost adsorbent for wastewater treatment is discussed in this paper. Chemical activation was used to make activated carbons from Trapa bispinosa peels and shells. Activated carbons made from a combination of Trapa bispinosa peels/shells and Phosphoric acid with varying impregnation ratios. The results revealed that the activating temperature for the production of Trapa bispinosa-derived activated carbon is 500℃ (AC). CHNS, X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy were used to analyze the activated carbons.

Evaluation of applying an alkaline green tea/ferrous iron system to lindane remediation impacts to soil and plant growth-promoting microbial community

Application of in situ chemical oxidation or reduction (ISCO/ISCR) technologies for contaminated soil remediation and its subsequent impact on soil is gaining increased attention. Reductive reactivity, generated from green tea (GT) extract mixed with ferrous (Fe2+) ions under alkaline conditions (the alkaline GT/Fe2+ system), has been considered as a promising ISCR process; however, its impact on soil has never been studied. In this study, the impact of applying the alkaline GT/Fe2+ system on soil was evaluated by analyzing the variations of the soil microbial community, diversity, and richness using next-generation 16S rRNA amplicon sequencing while mimicking the lindane-contaminated soil remediation procedure. Lindane was reductively degraded by the alkaline GT/Fe2+ system with reaction rate constants of 0.014 to 0.057 μM/h depending on the lindane dosage. Environmental change to the alkaline condition significantly decreased the microbial diversity and richness, but the recovery of the influence was observed subsequently. Bacteria that mainly belong within the phylum Firmicutes, including Salipaludibacillus, Anaerobacillus, Bacillaceae, and Paenibacillaceae, were greatly enhanced due to the alkaline condition. Besides, the dominance of heterotrophic, iron-metabolic, lindane-catabolic, and facultative bacteria was observed in the other corresponding conditions. From the results of principal component analysis (PCA), although dominant microbes all shifted significantly at every lindane-existing condition, the set of optimal lindane treatment with the alkaline GT/Fe2+ system had a minimized effect on the plant growth-promoting bacteria (PGPB). Nitrogen-cycling-related PGPB is sensitive to all factors of the alkaline GT/Fe2+ system. However, the other types, including plant-growth-inducer producing, phosphate solubilizing, and siderophore producing PGPB, has less impact under the optimal treatment. Our results demonstrate that the alkaline GT/Fe2+ system is an effective and soil-ecosystem-friendly ISCR remediation technology for lindane contamination.

Incorporation of ozone-driven processes in a treatment line for a leachate from a hazardous industrial waste landfill: Impact on the bio-refractory character and dissolved organic matter distribution

The current work aimed to evaluate the feasibility of including ozone (O3)-based advanced oxidation processes (AOPs), as an intermediate step, in a multistage treatment system for non-biodegradable sulphur-rich leachate from a hazardous industrial solid waste landfill (HISWL), combining chemical and biological oxidation technologies. O3-based AOPs covered perozonation (O3/H2O2), photo-assisted ozonation (O3/UVC), and photo-assisted perozonation (O3/H2O2/UVC). All O3-driven processes were applied to HISWL leachate directly after sulphur compounds removal via catalytic oxidation and chemical precipitation. Moreover, ozonation was also tested after a sequential coagulation step using ferric or aluminium salts (O3/Fe2+ or O3/Al3+), and O3/H2O2/UVC system was likewise tried after Fe-mediated coagulation targeting photo-Fenton-assisted ozonation (O3/PF). The best-performing treatment train encompassed: (i) catalytic oxidation with H2O2 (stoichiometric amount) under free pH, to convert sulphite and sulphide ions into oxidised sulphur species, including sulphate; (ii) chemical precipitation of sulphate as barite mineral without pH correction; (iii) O3/H2O2 process for ca. 2.1-h (natural pH; room temperature; 3.5 kg O3 and 1.1 kg H2O2 per m3 leachate), to degrade refractory organic matter and improve biodegradability; and (iv) biological oxidation to remove the remaining bioavailable organics fraction. This four-stage approach allowed shifting from a highly recalcitrant wastewater to an effluent in full agreement with the regulation for industrial wastewater discharge into the municipal sewer network. Furthermore, the effectiveness of the O3/H2O2 process over the dissolved organic matter transformation was corroborated by fluorescence excitation-emission matrix and size exclusion chromatography analysis.

APLICAÇÕES AMBIENTAIS DE PERSULFATO: REMEDIAÇÃO DE ÁGUAS SUBTERRÂNEAS E SOLOS CONTAMINADOS

ENVIRONMENTAL APPLICATIONS OF PERSULFATE: REMEDIATION OF CONTAMINATED GROUNDWATER AND SOILS. Environmental remediation represents a major technological challenge due to the complexity of the environmental matrices and the high treatment cost. In recent years, in situ chemical oxidation technologies (ISCO) have shown a good cost/benefit ratio, which as favored their use in the degradation of several relevant environmental pollutants. In this context, persulfate-mediated processes are of relevant importance once persulfate can be activated in situ, promoting the formation of highly oxidative radical species. Persulfate-based treatments have been frequently reported in environmental remediation studies because they guarantee the effective degradation of pollutants without producing significant changes in the remediated matrix. Given these statements, this study aims to discuss the main ways of activating persulfate and the relevant applications in the remediation of groundwater and soils contaminated with resistant organic pollutants.

Rapid removal of organic pollutants by a novel persulfate/brochantite system: Mechanism and implication

Using natural minerals as persulfate activators can develop effective and economical in situ chemical oxidation technology for environmental remediation. Yet, few natural minerals can provide a high activation efficiency. Here, we demonstrate that brochantite (Cu4SO4(OH)6), a natural mineral, can be used as a persulfate activator for the rapid degradation of tetracycline hydrochloride (TC-H). Approximately 70% of TC-H was removed in Cu4SO4(OH)6/PDS within 5 min, which much higher than that of Cu3P (61.99%), CuO (29.75%), CNT (25.83%), Fe2O3, (14.48%) and MnO2 (9.76%). Experiments and theoretical calculations suggested that surface copper acts as active sites induce the production of free radicals. The synergistic effect of Cu/S promotes the cycle between Cu+/Cu2+. Sulfate radicals and hydroxyl radicals are the main reactive oxygen species that are responsible for the rapid removal of TC-H. The findings of this work show a novel persulfate/brochantite system and provide useful information for the environmental remediation.

Performance of UV/acetylacetone process for saline dye wastewater treatment: Kinetics and mechanism

Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has stimulated the quest for novel “halotolerant” chemical oxidation technology. Acetylacetone (AA) has proven to be a potent photo-activator in the degradation of dyes, but the applicability of UV/AA for saline wastewater treatment needs to be verified. In this study, degradation of crystal violet (CV) was investigated in the UV/AA system in the presence of various concentrations of exogenic Cl- or Br-. The results reveal that degradation, mineralization and even accumulation of adsorbable organic halides (AOX) were not significantly affected by the addition of Cl- or Br-. Rates of CV degradation were enhanced by elevating either AA dosage or solution acidity. An apparent kinetic rate equation was developed as r = -d[CV]/dt = k[CV]a[AA]b = (7.34 × 10-4 mM1-(a+b) min-1) × [CV]a=0.16 [AA]b=0.97. In terms of results of radical quenching experiments, direct electron/energy transfer is considered as the major reaction mechanism, while either singlet oxygen or triplet state (3(AA)*) might be involved. Based on identification of degradation byproducts, a possible degradation pathway of CV in the UV/AA system is proposed.

Enhancing remediation of PAH-contaminated soil through coupling electrical resistance heating using Na2S2O8

Soil polycyclic aromatic hydrocarbons (PAHs) contamination caused by factory relocations is a serious environmental issue across the world. Electrical resistance heating (ERH) and chemical oxidation are two promising in-situ methods for treating volatile and semi-volatile organic pollutants in contaminated soil. Coupling of ERH and chemical oxidation technologies to improve the remediation efficiency for PAH-contaminated soil was estimated in this study. PAH removal ratio in contaminated soils using ERH treatment were significantly negatively correlated with the boiling point of the pollutants (P = 0.002), and 21.63% (DBA high boiling point) to 71.53% (Nap low boiling point) of PAHs in the contaminated soil were removed in 120 min. With oxidant Na2S2O8 coupling, the removal ratio were increased as more oxidant was added. For one Phe, 35.90% was removed by ERH treatment and increased to 52.90% and 79.42% when 0.05 or 2.5 mmol/g oxidant was added, respectively. PAHs with higher boiling points had more obvious removal ratio, such as Bap, which increased from 23.50% to 85.47% when coupling ERH with Na2S2O8, and Phe which increased from 35.90% to 79.42%. Relationships between boiling points and PAH removal ratio changed with coupled oxidants, indicating a change of mechanism from volatilization to coupling effects of volatilization and oxidation with the introduction of Na2S2O8. A dynamic experiment showed that Na2S2O8 can accelerate 45.50% of the treatment process. The results of this research demonstrated a novel, cost-effective coupling approach for remediating soil contaminated by organic pollutants.

Formation of chloronitrophenols upon sulfate radical-based oxidation of 2-chlorophenol in the presence of nitrite

Sulfate radical (SO4−)-based advanced oxidation processes (SR-AOPs) are promising in-situ chemical oxidation technologies widely applied for soil/groundwater remediation. The presence of non-target water constituents may interfere the abatement of contaminants by SR-AOPs as well as result in the formation of unintended byproducts. Herein, we reported the formation of toxic chloronitrophenols during thermally activated persulfate oxidation of 2-chlorophenol (2CP) in the presence of nitrite (NO2−). 2-Chloro-4-nitrophenol (2C4NP) and 2-chloro-6-nitrophenol (2C6NP) were identified as nitrated byproducts of 2CP with total yield up to 90%. The formation of nitrated byproducts is a result of coupling reaction between 2CP phenoxyl radical (ClPhO) and nitrogen dioxide radical (NO2). As a critical step, the formation of ClPhO was supported by density functional theory (DFT) computation. Both 2C4NP and 2C6NP could convert to 2-chloro-4,6-dinitrophenol (2C46DNP) upon further treatment via a denitration-renitration process. The formation rate of 2C4NP and 2C6NP was closely dependent on the concentration of NO2−, solution pH, and natural water constituents. ECOSAR calculation suggests that chloronitrophenols are generally more hydrophobic and ecotoxic than 2CP. Our result therefore reveals the potential risks in the abatement of chlorophenols by SR-AOP, particularly when high level of NO2− is present in water matrix.

Conditioning of resuspension excess sludge with chemical oxidation technology: The respective performance of filtration and expression stage in compression dewatering

Excess sludge has a high yield, rich in organic matter and high water content. The combinational method from chemical oxidation treatment and secondary mechanical dehydration is a powerful approach to further reduce the moisture content of the sludge. This work mainly studies the physicochemical properties of resuspension excess sludge (RES) with the treatment of chemical oxidation, the samples are processed by the compression filter device in a laboratory scale, and the three-stage Terzaghi-Voigt model was used to characterize the expression stage dewatering of samples. The experimental results indicate that: i) The improvement of the dewaterability of resuspension excess sludge is due to moderate chemical oxidation, which is related to the mode of migration and mineralization of organic substances in the stratified structure of the extracellular polymer substance (EPS). ii) When the protein in supernatant + slime is more mineralized than moved in, the dewaterability of the sample is improved. iii) The change of moisture removal for ternary consolidation was very consistent with the change of SRF in the filtration stage (ρ = 0.95, p < 0.01). Based on the results, we discuss how chemical oxidation affects the dewatering performance of filtration and expression stages in the solid-liquid separation. This means that the surface characteristics of the sludge particle and the liquid properties play critical roles in solid-liquid separation mechanism.

Mechanisms of mass transfer enhancement by phase-transfer catalysis for permanganate oxidizing dense non-aqueous phase liquid (DNAPL) TCE

Phase transfer catalysts (PTCs) have been shown to be effective in lowering the limitation of mass transfer between aqueous oxidant MnO4− and NAPLs in in-situ chemical oxidation (ISCO) technologies for remediation of NAPLs. This work researched the effects of pentyltriphenylphosphonium bromide (PTPP, used as the representative PTC) for the enhancement of TCE oxidation, the extent of different treatment effects contributions and generalizability of phase transfer. Experimental results revealed that MnO4− exchanged with Br− in PTPP by ion exchange mechanism and then transferred to NAPL phase due to biphasic nature of PTPP-MnO4-. PTPP enhanced TCE dissolution in aqueous phase but had no significant effect on TCE solubilization. Enhanced TCE dissolution gradually weakened after 2.0 h and disappeared after 5.5 h, while the percentage of MnO4− in phase transfer was 14.8% at 7.5 h, which indicated that dissolution acceleration was only effective at initial stage of reaction (0–2.5 h). Therefore, persistent phase transfer process played the leading role in TCE remediation enhancement. Moreover, for different NAPL phase, more effective phase transfer could be achieved in NAPLs with higher solubility and weaker hydrophobicity. The best-fit polynomial relationship (R2 = 0.992) existed between the percentage amount of MnO4− transferred and the solubility of NAPL.

Hydroxyl radical and non-hydroxyl radical pathways for trichloroethylene and perchloroethylene degradation in catalyzed H2O2 propagation systems

Catalyzed H2O2 propagations (CHP) is characterized by the most robust reactivity of any of the in situ chemical oxidation (ISCO) technologies because it generates the strong oxidant hydroxyl radical along with nucleophiles + reductants, such as superoxide radical. The most common groundwater contaminants, trichloroethylene (TCE) and perchloroethylene (PCE), were used as model contaminants in evaluating the effect of hydrogen peroxide (H2O2) dosage on contaminant destruction kinetics. Both TCE and PCE degradation rates increased with H2O2 dosages up to 0.1 M, and then decreased with higher H2O2 dosages. Parallel reactions conducted with the addition of the hydroxyl radical scavenger 2-propanol and the hydroxyl radical-specific probe nitrobenzene confirmed that hydroxyl radical is primarily responsible for TCE and PCE degradation; however, 5–20% of their degradation was attributed to a non-hydroxyl radical mechanism. Reactions conducted with the superoxide probe tetranitromethane showed that superoxide generation rates increased with increasing H2O2 doses. These results were confirmed by electron spin resonance spectroscopy. Therefore, the non-hydroxyl radical pathway for TCE and PCE degradation at H2O2 ≥0.5 M was likely via nucleophilic attack by superoxide. The results of this research demonstrate that contaminants present in the aqueous phase that are reactive with hydroxyl radical require only low doses of H2O2 (≤0.1 M), but subsurface systems contaminated with species not reactive with hydroxyl radical (e.g., carbon tetrachloride) require H2O2 concentrations ≥0.5 M.

Geoenvironmental characteristics of bisphenol A contaminated soil after persulfate treatment with different activation/enhancement methods.

Persulfate (PSF) is a strong oxidant that has been used extensively in the In-Situ Chemical Oxidation (ISCO) technology. The geoenvironmental impact of PSF treatment is barely investigated. This situation should be carefully considered as it may affect the reutilization of contaminated soil as engineering materials. This paper studied the removal of bisphenol A (BPA) by PSF with Nano Zero-Valent Iron (nZVI) and percarbonate (SPC) activated/enhanced and their subsequent impacts on the engineering properties of soil. The physicochemical and geotechnical properties of soils before and after treatment were evaluated using batch experiments. The results indicate that the introduced pristine PSF can be activated by some naturally occurring matters and subsequently lead to the mineralization of BPA. Both non-activated PSF and activated/enhanced PSF treatment led to the soil improvement in the undrained shear strength at different degrees. The primary mechanism of soil improvement is ascribed to the heterogeneous sulfate and/or carbonate precipitation. Meanwhile, Ca2+ in the pore fluid played a significant role in the enhancement of the soil strength. A conclusion was drawn that the treatment of both non-activated PSF, nZVI- and SPC-activated PSF treatment can achieve removal of BPA and soil improvement in the short-term simultaneously. This study can improve the PSF-involved remediation of brownfields and dredged sediments for a sustainable and low-carbon society.

Hybrid reactor based on hydrodynamic cavitation, ozonation, and persulfate oxidation for oxalic acid decomposition during rare-earth extraction processes

A cost-effective method for treating oxalic acid (OA) during rare-earth extraction was developed using hydrodynamic cavitation (HC), ozone (O3), and persulfate (PS) (HC@PS@O3 process). The results showed that the optimal inlet pressure during HC was 5.10 kg cm−2 with an orifice plate diameter of 2 mm. Moreover, HC was shown to activate PS, providing an alternative activation method to base or heat as an ultrasound activation method for chemical oxidation. O3 was also shown to activate PS. For OA oxidation using the HC@PS@O3 process, the optimum pH was 3 and the reaction rate increased with increasing temperature. Further, the activation energy was 36.69 kJ mol−1. The mechanisms unveiled in this study will allow optimization of the HC@PS@O3 process as a chemical oxidation technology. The kinetic investigation and economic evaluation of the HC@PS@O3 process can be used as the basis for real wastewater treatment processes in the future.

Sulfate radical-induced incorporation of NO2 group into chlorophenols

Sulfate radical ( $${\text{SO}}_{4}^{ \cdot - }$$ )-based advanced oxidation processes (SR-AOPs) are promising in situ chemical oxidation technologies that received increasing interest recently. The application of SR-AOPs for decontamination may, however, generate unexpected toxic by-products. This contribution reports that $${\text{SO}}_{4}^{ \cdot - }$$ can incorporate nitrite (NO2−) nitrogen into chlorophenols, resulting in the formation of chloronitrophenols which pose greater environmental concerns. Nitrogen dioxide radical ( $${\text{NO}}_{2}^{ \cdot }$$ ) and phenoxy radical are important precursors responsible for the formation of chloronitrophenols. High concentrations of NO2− inhibited the transformation of chlorophenol but promoted the formation of chloronitrophenol. This study underscores a need for caution in the application of SR-AOPs in the presence of NO2−, because chloronitrophenols can be more genotoxic and mutagenic than chlorophenols.

Decolorization of Reactive Red 239 Via Heat Activated Persulfate

Effluents of cotton dyeing process of textile industry is considered as extremely polluted due to presence of unfixed azo dyes and auxiliary chemicals. The complex aromatic structure and non-biodegradability nature of azo dyes involved new and efficient treatment technologies to eliminate intense color from textile wastewater. In recent years, in-situ chemical oxidation technology (ISCO) using persulfate (S2O82-) as an oxidant has appeared to be a promising method for removal of azo dyes. S2O82- can be activated by UV, heat or transition metals to generate sulfate radical (SO4-). In this study, decolorization of Reactive Red 239 (RR239) azo dye via heat activated S2O82- was explored. Experiments were conducted in a cylindrical batch reactor equipped with a water jacket. Effect of parameters such as temperature, pH and S2O82- concentration on decolorization of RR239 was investigated. The results show that decolorization efficiency was enhanced with increasing temperature from 45 to 55°C but further increase in temperature did not enhance decolorization. The pseudo first order rate constant values fit well Arrhenius equation, yielding an activation energy of 108.75 kJ mol-1 for decolorization of RR239. The highest decolorization efficiency was obtained at pH=3 under the tested pH range. As S2O82- concentration increased decolorization efficiency increased. 89.67% and 39.05% decolorization and aromatic degradation efficiencies were observed within 120 minutes of reaction time, respectively. These results show that heat activated S2O82- method was a feasible method for decolorization of RR239.