Mechanisms of base, mineral, and soil activation of persulfate for groundwater treatment

The purpose of this study was to examine mechanisms of base, mineral, and soil persulfate activation when used for ground water treatment by in situ chemical oxidation. Four base-activated persulfate systems (adjusting the pH to 12 and using molar ratios of 1:1, 2:1, or 3:1 base to persulfate) were studied using three reaction-specific probe compounds and two radical scavengers. Rapid degradation of oxidative probes occurred at pH 12, but minimal degradation of the reductive probe, carbon tetrachloride, was observed at pH 12. Degradation of all probe compounds occurred in molar ratios systems. The results of this research demonstrate that the reactivity of persulfate formulations increases with increasing base:persulfate ratios. The potential for 13 minerals to mediate the decomposition of persulfate and generate a reactive oxygen species was investigated. Reactions were conducted at 25?C using 2 g of minerals and 5 ml of 0.5 M sodium persulfate with the addition of oxidative, reductive, and nucleophilic probes. The decomposition of persulfate and the probes by minerals varied extensively. Most of the minerals mediated the decomposition of persulfate, but did not promote the generation of reactive oxygen species, although cobaltite, ilmenite, and pyrite did. The results demonstrate that most of the minerals evaluated do not activate persulfate. The decomposition of persulfate by 11 soils was investigated in order to observe the impact of these soils on pH and persulfate concentration. Reactions were conducted at 25?C using 10 g of soil and 20 mL of either 0.5 M or 0.1 M persulfate. Reactions were conducted using base:persulfate molar ratios of 1:1, 2:1, or 3:1 over 120 d. Decomposition of persulfate and pH varied greatly between soils, although not between 0.1 M and 0.5 M persulfate. A second set of experiments were conducted in which anisole was used a probe for the overall reactivity of the system. These experiments used 0.5 M persulfate in a 2:1 base:persulfate molar ratio and two soils. The results demonstrated a reduction in anisole destruction when the pH declined. This research demonstrated the importance of pH and soil properties in the use of persulfate treatments

Electrokinetic delivery of persulfate to remediate PCBs polluted soils: Effect of different activation methods

Persulfate-based in-situ chemical oxidation (ISCO) for the remediation of organic polluted soils has gained much interest in last decade. However, the transportation of persulfate in low-permeability soil is very low, which limits its efficiency in degrading soil pollutants. Additionally, the oxidation-reduction process of persulfate with organic contaminants takes place slowly, while, the reaction will be greatly accelerated by the production of more powerful radicals once it is activated. Electrokinetic remediation (EK) is a good way for transporting persulfate in low-permeability soil. In this study, different activation methods, using zero-valent iron, citric acid chelated Fe²⁺, iron electrode, alkaline pH and peroxide, were evaluated to enhance the activity of persulfate delivered by EK. All the activators and the persulfate were added in the anolyte. The results indicated that zero-valent iron, alkaline, and peroxide enhanced the transportation of persulfate at the first stage of EK test, and the longest delivery distance reached sections S4 or S5 (near the cathode) on the 6th day. The addition of activators accelerated decomposition of persulfate, which resulted in the decreasing soil pH. The mass of persulfate delivered into the soil declined with the continuous decomposition of persulfate by activation. The removal efficiency of PCBs in soil followed the order of alkaline activation > peroxide activation > citric acid chelated Fe²⁺ activation > zero-valent iron activation > without activation > iron electrode activation, and the values were 40.5%, 35.6%, 34.1%, 32.4%, 30.8% and 30.5%, respectively. The activation effect was highly dependent on the ratio of activator and persulfate

Electrochemically Activated Persulfate for Ciprofloxacin Degradation

Electrochemically activated persulfate (EAP) is a potential point source treatment for wastewater effluents containing high pharmaceutical content. This dissertation explores the fundamental mechanisms of EAP to better understand this technology for practical application. Ciprofloxacin, a fluoroquinolone antibiotic, was chosen as the model compound to assess parameters of EAP. Ciprofloxacin was selected for its high environmental risk factor and prevalence in hospital wastewater, a potential application for EAP. During the evaluation of EAP as a point source treatment, degradation kinetics and pathways of ciprofloxacin were elucidated.In the first stage of this study, persulfate activation by solid iron with and without applied current was characterized and applied to the degradation of ciprofloxacin. It was found that persulfate activation increased with iron surface area and increased to a plateau with increasing current. Ciprofloxacin degraded via first-order kinetics; however, applied current did not affect ciprofloxacin removal.In the second part of this study, electrochemical persulfate activation without iron, using boron-doped diamond (BDD) anodes and graphite or platinum cathodes, was examined. Sulfate radical formation at a BDD anode and persulfate activation at a graphite cathode were elucidated using different electrolytes and electrochemical set-ups. In this system, ciprofloxacin degraded via first order-kinetics, with persulfate electrolyte enhancing ciprofloxacin removal over sulfate or nitrate.In the final phase of this study, parameters such as reactor configuration, electrode surface area, persulfate concentrations and the presence of a complex matrix were examined to determine their impact on contaminant removal. Due to mass transfer limitations and relative cathode sizes, a flow-through reactor was least benefited by persulfate addition while a rotating-disk electrode reactor showed enhanced ciprofloxacin removal with persulfate electrolyte. Ciprofloxacin removal from synthetic hospital effluent using electrochemically activated persulfate was found to be less than that in pure electrolyte but still followed a first-order mechanism. Considerable total organic carbon removal of ciprofloxacin and other organic components of the effluent was achieved. Similar degradation was achieved with persulfate and sulfate electrolyte in the effluent. Chlorate, chlorite and perchlorate were formed in significant amounts during the electrochemical process, with formation independent of the presence of persulfate

OXIDATIVE DEGRADATION OF 2-CHLOROPHENOL BY PERSULFATE

The degradation of 2-chlorophenol (2-CP) by persulfate was investigated. The kinetics of persulfate oxidation of 2-chlorophenol in aqueous solutions at various pH, oxidant concentration, temperature, Fe2+ and Cu2+ ions content was studied. Maximum of 2-CP degradation occurred at pH 8. The oxidation rate of 2-CP increased with increasing the persulfate molar excess. The degradation process was significantly influenced by temperature – the higher temperature results in a faster degradation of 2-CP. The activation of persulfate by ferrous and copper ions was also studied. Results showed that persulfate is activated more effectively by iron(II) than copper(II) ions. A comparison of different persulfate activation methods revealed that heat-activation was the most effective. Under optimal conditions, in the presence of ferrous ions at 50 °C, complete degradation of 2-chlorophenol was achieved after about 30 minutes

Oxidative Degradation of Tetracycline by Magnetite and Persulfate: Performance, Water Matrix Effect, and Reaction Mechanism.

This study presents a strategy to remove tetracycline by using magnetite-activated persulfate. Magnetite (Fe3O4) was synthesized at high purity levels-as established via X-ray diffractometry, transmission electron microscopy, and N2 sorption analyses-and tetracycline was degraded within 60 min in the presence of both magnetite and persulfate (K2S2O8), while the use of either substance yielded limited degradation efficiency. The effects of magnetite and persulfate dosage, the initial concentration of tetracycline, and the initial pH on the oxidative degradation of tetracycline were interrogated. The results demonstrate that the efficiency of tetracycline removal increased in line with magnetite and persulfate dosage. However, the reaction rate increased only when increasing the magnetite dosage, not the persulfate dosage. This finding indicates that magnetite serves as a catalyst in converting persulfate species into sulfate radicals. Acidic conditions were favorable for tetracycline degradation. Moreover, the effects of using a water matrix were investigated by using wastewater treatment plant effluent. Comparably lower removal efficiencies were obtained in the effluent than in ultrapure water, most likely due to competitive reactions among the organic and inorganic species in the effluent. Increased concentrations of persulfate also enhanced removal efficiency in the effluent. The tetracycline degradation pathway through the magnetite/persulfate system was identified by using a liquid chromatograph-tandem mass spectrometer. Overall, this study demonstrates that heterogeneous Fenton reactions when using a mixture of magnetite and persulfate have a high potential to control micropollutants in wastewater

Effort to improve coupled in situ chemical oxidation with bioremediation: a review of optimization strategies

Purpose - In order to provide highly effective yet relatively inexpensive strategies for the remediation of recalcitrant organic contaminants, research has focused on in situ treatment technologies. Recent investigation has shown that coupling two common treatments-in situ chemical oxidation (ISCO) and in situ bioremediation-is not only feasible but in many cases provides more efficient and extensive cleanup of contaminated subsurfaces. However, the combination of aggressive chemical oxidants with delicate microbial activity requires a thorough understanding of the impact of each step on soil geochemistry, biota, and contaminant dynamics. In an attempt to optimize coupled chemical and biological remediation, investigations have focused on elucidating parameters that are necessary to successful treatment. In the case of ISCO, the impacts of chemical oxidant type and quantity on bacterial populations and contaminant biodegradability have been considered. Similarly, biostimulation, that is, the adjustment of redox conditions and amendment with electron donors, acceptors, and nutrients, and bioaugmentation have been used to expedite the regeneration of biodegradation following oxidation. The purpose of this review is to integrate recent results on coupled ISCO and bioremediation with the goal of identifying parameters necessary to an optimized biphasic treatment and areas that require additional focus. Conclusions and recommendations - Although a biphasic treatment consisting of ISCO and bioremediation is a feasible in situ remediation technology, a thorough understanding of the impact of chemical oxidation on subsequent microbial activity is required. Such an understanding is essential as coupled chemical and biological remediation technologies are further optimize

Fe2+/Persulfate / Clinoptilolite, catalytic oxidative treatment, as a cost effective process for Isocyanate and Meta Toluene Diamine Petrochemical unit wastewater

Background: Petrochemical wastewater from isocyanate units contains aromatic and hazardous compounds such as Diaminotoluenes, Mononitrotoluene, Dinitro-toluene, Nitro-phenol, Nitro-cresol. Persulfate and ferrous sulfate can produce sulfate radicals with strong standard oxidation potential. Clinoptilolite, a natural adsorbent; plus sulfate radicals can result in catalytic oxidation of these chemicals. The objective of this study is to evaluate the catalytic oxidation efficiency Fe2+/Persulfate/ Clinoptilolite and cost effectiveness of this process for treatment of petrochemical wastewater containing aromatics.Materials and methods: The effect of study variables including persulfate and ferrous sulfate concentrations, zeolite dosages, pH and oxidation time were investigated. The type and amount of aromatic compounds as well as COD and TSS removal efficiencies were determined. All procedures in study were conducted ethicallyResults: The COD and TSS removal efficiencies using catalytic oxidative treatment processes by Fe,Persulfate, Clinoptilolite were 96% and 95%, respectively. The corresponding COD and TSS removal efficiencies using Fe and Persulfate, without zeolite were 85% and 80%, respectively.Conclusion: The catalytic processes utilizing Fe2+/Persulfate/ Clinoptilolite demonstrates an excellent COD and TSS removal efficiency. Due to its natural nature, low cost compared to chemical oxidants, as well as improvements in the efficiency of advanced oxidation processes, Zeolite can be considered as anefficient and cost-effective alternative to upgrade the catalytic oxidative treatment

Homogeneous and Heterogeneous Photocatalytic Water Oxidation by Persulfate

Photocatalytic water oxidation by persulfate (Na2S2O8) with [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine) as a photocatalyst provides a standard protocol to study the catalytic reactivity of water oxidation catalysts. The yield of evolved oxygen per persulfate is regarded as a good index for the catalytic reactivity because the oxidation of bpy of [Ru(bpy)3]2+ and organic ligands of catalysts competes with the catalytic water oxidation. A variety of metal complexes act as catalysts in the photocatalytic water oxidation by persulfate with [Ru(bpy)3]2+ as a photocatalyst. Herein, the catalytic mechanisms are discussed for homogeneous water oxidation catalysis. Some metal complexes are converted to metal oxide or hydroxide nanoparticles during the photocatalytic water oxidation by persulfate, acting as precursors for the actual catalysts. The catalytic reactivity of various metal oxides is compared based on the yield of evolved oxygen and turnover frequency. A heteropolynuclear cyanide complex is the best catalyst reported so far for the photocatalytic water oxidation by persulfate and [Ru(bpy)3]2+, affording 100 % yield of O2 per persulfate.Waterworld: Homogeneous and heterogeneous catalysis and mechanisms of photocatalytic oxidation of water by persulfate with [Ru(bpy)]32+ are compared and discussed including the conversion from homogeneous precatalysts to heterogeneous catalysts.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137224/1/asia201501329.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137224/2/asia201501329_am.pd