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Formation of halogenated disinfection by-products (DBPs) in sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted considerable concerns recently. Previous studies have focused on the formation of chlorinated and brominated DBPs. This research examined the transformation of I − in heat activated PS oxidation process. Phenol was employed as a model compound to mimic the reactivity of dissolved natural organic matter (NOM) toward halogenation. It was found that I − was transformed to free iodine which attacked phenol subsequently leading to iodinated DBPs such as iodoform and iodoacetic acids. Iodophenols were detected as the intermediates during the formation of the iodoform and triiodoacetic acid (TIAA). However, diiodoacetic acid (DIAA) was formed almost concomitantly with iodophenols. In addition, the yield of DIAA was significantly higher than that of TIAA, which is distinct from conventional halogenation process. Both the facts suggest that different pathway might be involved during DIAA formation in SR-AOPs. Temperature and persulfate dose were the key factors governing the transformation process. The iodinated by-products can be further degraded by excessive SO 4 − and transformed to iodate. This study elucidated the transformation pathway of I − in SR-AOPs, which should be taken into consideration when persulfate was applied in environmental matrices containing iodine. [ABSTRACT FROM AUTHOR]

In this study, the removal of bisphenol A (BPA) and phosphate in zero-valent iron activated persulfate (ZVI/PS) oxidation process was investigated. Activation of PS by ZVI mainly produces strong oxidizing sulfate radicals (SO 4 − ) which can efficiently degrade organic contaminants. ZVI is ultimately transformed to ferric iron (Fe 3+ ) which works as a coagulant to remove phosphate. It was demonstrated that BPA and phosphate could be simultaneously removed in this system. The oxidation of BPA in ZVI/PS process followed pseudo-first-order kinetics. The reaction rate increased with increased PS and ZVI dosage. Eight transformation products were identified using gas chromatography–mass spectrometry (GC–MS) technique. SO 4 − -induced oxidative transformation of BPA included electron transfer and hydrogen abstraction mechanisms. Carbonate exhibited no obvious influence on the removal both of phosphate and BPA. Natural organic matter (NOM) showed inhibitory effect on BPA degradation but had no appreciable negative effect on phosphate removal. Simultaneous removal of BPA and phosphate was also observed in wastewater treatment plant effluent with relatively high efficiency. The results of this work indicate that ZVI/PS process could serve as a novel treatment technique for removal of trance organic contaminants and phosphate simultaneously. [ABSTRACT FROM AUTHOR]

Sulfamethazine (SMZ) is widely used in livestock feeding and aquaculture as an antibiotic agent and growth promoter. Widespread occurrence of SMZ in surface water, groundwater, soil and sediment has been reported. In this study, degradation of SMZ by heat-activated persulfate (PS) oxidation was investigated in aqueous solution. Experimental results demonstrated that SMZ degradation followed pseudo-first-order reaction kinetics. The pseudo-first-order rate constant ( k obs ) was increased markedly with increasing concentration of PS and temperature. Radical scavenging tests revealed that the predominant oxidizing species was SO 4 − with HO playing a less important role. Aniline moiety in SMZ molecule was confirmed to be the reactive site for SO 4 − attack by comparison with substructural analogs. Nontarget natural water constituents affected SMZ removal significantly, e.g., Cl − and HCO 3 − improved the degradation while fulvic acid reduced it. Reaction products were enriched by solid phase extraction (SPE) and analyzed by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI–MS/MS). 6 products derived from sulfonamide S N bond cleavage, aniline moiety oxidation and Smiles-type rearrangement were identified, and transformation pathways of SMZ oxidation were proposed. Results reveal that heat-activated PS oxidation could be an efficient approach for remediation of water contaminated by SMZ and related sulfonamides. [ABSTRACT FROM AUTHOR]

Contamination of herbicides such as atrazine (ATZ) poses a significant threat to human health and aquatic ecosystem. In this study, we demonstrated that heat-activated persulfate could effectively degrade ATZ in water. Complete disappearance of 50 μM ATZ could be obtained after 2 h reaction in the presence of 1 mM persulfate under 60 °C. Increasing the initial persulfate concentration or temperature significantly enhanced the degradation efficiency. Natural organic matter (NOM) decreased the degradation rate, but complete removal of ATZ could still be obtained. The presence of chloride (Cl − ) and bicarbonate (HCO 3 − ) had little effects on ATZ degradation at lower concentration (e.g., 5 mM). However, inhibitory effects were observed when concentrations of Cl − and HCO 3 − increased (e.g., 100 mM). Radical scavenging test revealed that sulfate radical (SO 4 − ) was the predominant radical species at acidic to neutral pH, while hydroxyl radical (HO ) was predominant at basic pH. Eight intermediates and products were identified by applying solid phase extraction and liquid chromatography–tandem mass spectrometry (SPE-LC–MS/MS) techniques. Transformation pathways including dealkylation, alkyl chain oxidation, and dechlorination–hydroxylation were proposed, and the underlying mechanisms for each pathway were systematically analyzed. [ABSTRACT FROM AUTHOR]

Persulfate (PS) is widely used as an oxidant for in situ chemical remediation of contaminated groundwater. In this study we demonstrated for the first time that PS could be activated by bicarbonate. Acetaminophen was used as the probe compound to examine the reactivity of PS/bicarbonate system. It was found that acetaminophen could be effectively transformed and the reaction rate appeared pseudo-first-order to the concentrations of both acetaminophen and PS. Radical scavenger tests indicated that neither free radicals (SO 4 - and HO ) nor superoxide (O 2 - ) was responsible for acetaminophen transformation. Generation of singlet oxygen ( 1 O 2 ) was verified using furfuryl alcohol (FFA) as a probe. Formation of 1 O 2 was further quantified in D 2 O fortified solution based on kinetic solvent isotopic effect (KSIE) but it was found that 1 O 2 contributed only 51.4% of the total FFA transformation. The other 48.6% was presumed to be ascribed to the reaction with peroxymonocarbonate (HCO 4 − ). However, the transformation of acetaminophen was mostly due to the reaction with HCO 4 − but not 1 O 2 . Instead of degradation, HCO 4 − oxidized acetaminophen via a one-electron abstraction mechanism resulting in the generation of acetaminophen radicals which coupled to each other to form dimers and trimers. HCO 4 − also hydrolyzed rapidly to form hydrogen peroxide (H 2 O 2 ) which led to the formation of 1 O 2 , during which O 2 - was a key intermediates. Because bicarbonate is ubiquitously presented in groundwater, the findings of this research provide important insights into the fundamental processes involved in PS oxidation in subsurface. [ABSTRACT FROM AUTHOR]

The widespread occurrence of sulfonamides (e.g., sulfamethoxazole) in natural environment has raised growing concerns due to their potential to induce antibiotic-resistant genes. In this study, the degradation of SMX and related sulfonamides by thermo activated persulfate (PS) oxidation was investigated. Experimental results demonstrated that SMX degradation followed pseudo-first-order reaction kinetics. The pseudo-first-order rate constant ( k obs ) was increased markedly with increasing temperature and pH. The presence of bicarbonate manifested promoting effect on SMX degradation while fulvic acid reduced it. Radical scavenging tests revealed that the predominant oxidizing species was SO 4 •− at neutral pH. Aniline moiety in SMX molecule was confirmed to be the primary reactive site for SO 4 •− attack by comparison with substructural analogues. Reaction products were enriched by solid phase extraction (SPE) and analyzed by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS). A total of 7 products derived from hydroxylation, sulfonamide S–N bond cleavage, aniline moiety oxidation and coupling reaction were identified, and transformation pathways of SMX oxidation were proposed. Degradation of sulfonamides was appreciably influenced by the heterocyclic ring present in the molecules. Results reveal that thermo activated PS oxidation could be an efficient approach for remediation of water contaminated by SMX and related sulfonamides. [ABSTRACT FROM AUTHOR]

Sulfate radicals ( S O 4 − · ) are applied to degrade various organic pollutants. Due to its high oxidative potential, S O 4 − · is presumed to be able to transform bromide to reactive bromine species that can react with natural organic matter subsequently to form brominated products including brominated disinfection by-products (Br-DBPs). This research was designed to investigate the transformation of bromide in thermo activated persulfate oxidation process in the presence of humic acid (HA). Significant formation of bromoform and bromoacetic acids was verified. Their formation was attributed to the reactions of HA and reactive bromine species including Br·, B r 2 − · HOBr − , and free bromine resulted from the oxidation of bromide by S O 4 − · . Yields of Br-DBPs increased monotonically at persulfate concentration of 1.0 mM and working temperature of 70 °C. However, the time-depended formation exhibited an increasing and the decreasing profile when persulfate was 5.0 mM, suggesting further degradation of organic bromine. HPLC/ICP-MS analysis demonstrated that the organic bromine was eventually transformed to bromate at this condition. Thus, a transformation scheme was proposed in which the bromine could be recycled multiple times between inorganic bromide and organic bromine before being finally transformed to bromate. This is the first study that reveals the comprehensive transformation map of bromine in S O 4 − · based reaction systems, which should be taken into consideration when such technologies are used to eliminate contamination in real practice. [ABSTRACT FROM AUTHOR]

In this study, the transformation of five amino acids (AAs), i.e., glycine (GLY), alanine (ALA), serine (SER), aspartic acid (ASP), and methionine (MET), in a heat activated peroxydisulfate (PDS) oxidation process was investigated. Experimental data showed that the nitrogen in the AA molecules was oxidized to NH 4 + and nitrate (NO 3 -) sequentially. However, in the presence of natural organic matter (NOM), nitrophenolic byproducts including 4-nitrophenol, 2,4-dinitrophenol, 5-nitrosalicylic acid, 3,5-dinitrosalicylic acid were formed. The nitrogen dioxide radical (NO 2 •) generated during the transformation of NH 4 + to NO 3 - was presumed to be the key nitrating agent. It reacted with phenolic moieties in NOM and was transformed to nitrophenolic byproducts. Among the selected AAs, SER showed the highest nitrophenolic byproducts formation potential. A total yield of 0.258 μM was observed at the condition of 0.1 mM SER, 5 mg/L (as TOC) NOM, 2 mM PDS, and pH 7.0. The formation from GLY and ALA was lowest, only 0.009 μM detected under the same conditions. The nitrophenolic byproducts formation potential of the AAs was positively related to their reactivity toward SO 4 •- and can be explained by the local nucleophilicity index (N k). These findings underline the potential risks in the application of SO 4 •- based oxidation technology. [Display omitted] • Nitrophenolic byproducts were formed during the degradation of AAs by heat/PDS. • NO 2 • formed during the transformation of NH 4 + to NO 3 - was the nitrating agent. • AA's reactivity to SO 4 •- dictates its nitrophenolic byproducts formation potential. • Transformation pathways of AAs in the heat/PDS process were proposed. [ABSTRACT FROM AUTHOR]