Antibiotic ciprofloxacin removal from aqueous solutions by electrochemically activated persulfate process: Optimization, degradation pathways, and toxicology assessment.

Ciprofloxacin (CIP) is a commonly used antibiotic in the fluoroquinolone group and is widely used in medical and veterinary medicine disciplines to treat bacterial infections. When CIP is discharged into the sewage system, it cannot be removed by a conventional wastewater treatment plant because of its recalcitrant characteristics. In this study, boron-doped diamond anode and persulfate were used to degrade CIP in an aquatic solution by creating an electrochemically activated persulfate (EAP) process. Iron was added to the system as a coactivator and the process was called EAP+Fe. The effects of independent variables, including pH, Fe2+, persulfate concentration, and electrolysis time on the system were optimized using the response surface methodology. The results showed that the EAP+Fe process removed 94% of CIP under the following optimum conditions: A pH of 3, persulfate/Fe2+ concentration of 0.4 mmol/L, initial CIP concentration 30 mg/L, and electrolysis time of 12.64 min. CIP removal efficiency was increased from 65.10% to 94.35% by adding Fe2+ as a transition metal. CIP degradation products, 7 pathways, and 78 intermediates of CIP were studied, and three of those intermediates (m/z 298, 498, and 505) were reported. The toxicological analysis based on toxicity estimation software results indicated that some degradation products of CIP were toxic to targeted animals, including fathead minnow, Daphnia magna, Tetrahymena pyriformis, and rats. The optimum operation costs were similar in EAP and EAP+Fe processes, approximately 0.54 €/m3.

Degradation of Ampicillin with antibiotic activity removal using persulfate and submersible UVC LED: Kinetics, mechanism, electrical energy and cost analysis.

Effective water treatment to remove antibiotics and its activity from contaminated water is urgently needed to prevent antibiotic-resistant bacteria (ARB) emergence. In this study, we investigated degradation of Ampicillin (AMP), an extensively used ß-lactam antibiotic, using submersible Ultraviolet C Light Emitting Diode (λmax = 276 nm) irradiation source, and Persulfate (UVC LED/PS system). Pseudo first order rate constant (kobs) for degradation of AMP (1 ppm) by UVC LED/PS system was determined to be 0.5133 min-1 (PS = 0.2 mM). kobs value at pH 2.5 (0.7259 min-1) was found to be higher than pH 6.5 (0.5133 min-1) and pH 12 (0.1745 min-1). kobs value for degradation of AMP in deionized water spiked with inorganic anions (Cl-=0.5369 min-1,SO42-=0.4545 min-1, NO3-=0.1526 min-1, HCO3-=0.0226 min-1), in real tap water (0.1182 min-1) and simulated ground water (0.0372 min-1) were presented. Radical scavenging experiment reveal involvement of sulfate radical anion and hydroxyl radical in UVC LED/PS system. EPR analysis confirms the generation of sulfate radical anion and hydroxyl radical. Importantly, 74% reduction of total organic carbon (TOC) occurred within 60 min of AMP treatment by UVC LED/PS system. Seven degradation by-products were identified by high resolution mass spectrometry, and degradation pathways were proposed. Antibacterial activity of AMP towards Bacillus subtilis and Staphylococcus aureus was completely removed after UVC LED/PS treatment. ECOSAR model predicted no very toxic degradation by-products generation by UVC LED/PS system. Electrical Energy per order (EEo) and cost of UVC LED/PS system were determined to be 0.9351 kW/m3/order and ₹ 7.91/m3 ($ 0.095/m3 or € 0.087/m3), respectively. Overall, this study highlights, UVC LED/PS system as energy efficient, low-cost, and its potential to emerge as sulfate radical anion based advanced oxidation process (AOP) to treat water with antibiotics.

Insights into the impacts of chloride ions on the oxidation of 2,4-dinitrotoluene using ferrous activated persulfate: Removal efficiency, reaction mechanism, transformation pathway, and toxicity assessment.

Persulfate/Fe2+-based advanced oxidation processes are widely used to treat water contaminated with 2,4-dinitrotoluene (DNT). However, the oxidation of DNT by persulfate/Fe2+ in the presence of the chloride ion (Cl⁻) has not been addressed, and the transformation pathways and toxicities of the intermediate products remain unclear. In this study, the effect of different Cl⁻ concentrations on the oxidation of DNT was investigated by persulfate/Fe2+. After the addition of 1.0 mM Cl⁻ and 6 h of oxidation, the removal efficiency of DNT increased by 68.5%. Scavenging experiments and an electron spin resonance analysis suggested that Cl⁻ caused hydroxyl radicals to increase in content in the persulfate/Fe2+ system, thus promoting the removal of DNT. Eight intermediate products of DNT were accurately detected using high-resolution mass spectrometry, and the transformation pathways of DNT were proposed, including hydroxylation/oxidation, elimination of the nitro group, and chlorination process. The acute and chronic toxicities of the intermediate products decreased during the oxidation process, but chlorinated by-products posed a higher toxicological risk. This result is vital for the practical application and environmental safety evaluation of persulfate/Fe2+-based advanced oxidation.

Electrochemical degradation of PFOA and its common alternatives: Assessment of key parameters, roles of active species, and transformation pathway.

This study investigates an electrochemical approach for the treatment of water polluted with per- and poly-fluoroalkyl substances (PFAS), looking at the impact of different variables, contributions from generated radicals, and degradability of different structures of PFAS. Results obtained from a central composite design (CCD) showed the importance of mass transfer, related to the stirring speed, and the amount of charge passed through the electrodes, related to the current density on decomposition rate of PFOA. The CCD informed optimized operating conditions which we then used to study the impact of solution conditions. Acidic condition, high temperature, and low initial concentration of PFOA accelerated the degradation kinetic, while DO had a negligible effect. The impact of electrolyte concentration depended on the initial concentration of PFOA. At low initial PFOA dosage (0.2 mg L-1), the rate constant increased considerably from 0.079 ± 0.001 to 0.259 ± 0.019 min-1 when sulfate increased from 0.1% to 10%, likely due to the production of SO4•-. However, at higher initial PFOA dosage (20 mg L-1), the rate constant decreased slightly from 0.019 ± 0.001 to 0.015 ± 0.000 min-1, possibly due to the occupation of active anode sites by excess amount of sulfate. SO4•- and •OH played important roles in decomposition and defluorination of PFOA, respectively. PFOA oxidation was initiated by one electron transfer to the anode or SO4•-, undergoing Kolbe decarboxylation where yielded perfluoroalkyl radical followed three reaction pathways with •OH, O2 and/or H2O. PFAS electrooxidation depended on the chemical structures where the decomposition rate constants (min-1) were in the order of 6:2 FTCA (0.031) > PFOA (0.019) > GenX (0.013) > PFBA (0.008). PFBA with a shorter chain length and GenX with -CF3 branching had slower decomposition than PFOA. While presence of C-H bonds makes 6:2 FTCA susceptible to the attack of •OH accelerating its decomposition kinetic. Conducting experiments in mixed solution of all studied PFAS and in natural water showed that the co-presence of PFAS and other water constituents (organic and inorganic matters) had adverse effects on PFAS decomposition efficiency.

Activated persulfate by iron-carbon micro electrolysis used for refractory organics degradation in wastewater: a review.

With the rapid economic development, the discharge of industrial wastewater and municipal wastewater containing many refractory organic pollutants is increasing, so there is an urgent need for processes that can treat refractory organics in wastewater. Iron-carbon micro electrolysis and advanced oxidation based on persulfate radicals (SO4-·) have received much attention in the field of organic wastewater treatment. Iron-carbon micro electrolysis activated persulfate (Fe-C/PS) treatment of wastewater is characterized by high oxidation efficiency and no secondary pollution. This paper reviews the mechanism and process of Fe-C/PS, degradation of organics in different wastewater, and the influencing factors. In addition, the degradation efficiency and optimal reaction conditions (oxidant concentration, catalyst concentration, iron-carbon material, and pH) of Fe-C/PS in the treatment of refractory organics in wastewater are summarized. Moreover, the important factors affecting the degradation of organics by Fe-C/PS are presented. Finally, we analyzed the challenges and the prospects for the future of Fe-C/PS in application, and concluded that the main future directions are to improve the degradation efficiency and cost by synthesizing stable and efficient catalysts, optimizing process parameters, and expanding the application scope.

The Removal of Binary Mixture of Dyes by Heterogeneous Fenton Oxidation: Kinetics, Product Identification and Toxicity Assessment.

The removal of mixture of two azo dyes, Acid blue 29 and Ponceau xylidine, was studied by heterogeneous Fenton and Fenton-type processes using hydrogen peroxide and sodium persulphate as oxidants in the presence of and nano and micro- particles as catalysts. The synthesised nano- particles were characterised using analytical techniques viz. FT-IR, TEM, EDX, powder XRD and VSM. We have examined the effects of particle size on the COD removal efficiency and the reusability of the catalyst after optimising pH, and concentrations of catalyst and oxidant. Combination of nano-  and hydrogen peroxide possessed higher COD removal efficiency, which was accelerated in acidic pH and inhibited at pH > 6. Total consumption of hydrogen peroxide confirmed the efficiency of the optimised parameters. The mechanism of the formation of intermediate ions and products are proposed. COD removal and consumption of hydrogen peroxide follow pseudo-first-order kinetics. The toxicity of the solutions was assessed using Aliivibrio fischeri light loss and Escherichia coli growth inhibition assays. Both the assays showed different toxicity levels for the same solution.

Final Amended Safety Assessment of Sodium Sulfate as Used in Cosmetics.

The Expert Panel for Cosmetic Ingredient Safety (Panel) reopened the safety assessment of Sodium Sulfate, a cosmetic ingredient that is an inorganic salt reported to function in cosmetics as a viscosity increasing agent-aqueous. The Panel reviewed the relevant new data for the ingredient, including frequency of use and concentration of use, and considered data from the previous Panel assessment. The Panel concluded that Sodium Sulfate is safe in cosmetics in the present practices of use and concentrations described in this safety assessment when formulated to be nonirritating.

Are all ulvans equal? A comparative assessment of the chemical and gelling properties of ulvan from blade and filamentous Ulva.

Green seaweeds of the genus Ulva are rich in the bioactive sulfated polysaccharide ulvan. Herein we characterise ulvan from Ulva species collected from the Bay of Plenty, Aotearoa New Zealand. Using standardised procedures, we quantified, characterised, and compared ulvans from blade (U. australis, U. rigida, U. sp. B, and Ulva sp.) and filamentous (U. flexuosa, U. compressa, U. prolifera, and U. ralfsii) Ulva species. There were distinct differences in composition and structure of ulvans between morphologies. Ulvan isolated from blade species had higher yields (14.0-19.3 %) and iduronic acid content (IdoA = 7-18 mol%), and lower molecular weight (Mw = 190-254 kDa) and storage moduli (G' = 0.1-6.6 Pa) than filamentous species (yield = 7.2-14.6 %; IdoA = 4-7 mol%; Mw = 260-406 kDa; G' = 22.7-74.2 Pa). These results highlight the variability of the physicochemical properties of ulvan from different Ulva sources, and identifies a morphology-based division within the genus Ulva.

Fast and Low-Cost Surface-Enhanced Raman Scattering (SERS) Method for On-Site Detection of Flumetsulam in Wheat.

The pesticide residues in agri-foods are threatening people's health. This study aims to establish a fast and low-cost surface-enhanced Raman scattering (SERS) method for the on-site detection of flumetsulam in wheat. The two-step modified concentrated gold nanoparticles (AuNPs) acted as the SERS substrate with the aid of NaCl and MgSO4. NaCl is served as the activator to modify AuNPs, while MgSO4 is served as the aggregating agent to form high-density hot spots. The activation and aggregation are two essential collaborative procedures to generate remarkable SERS enhancement and achieve the trace-level detection of flumetsulam. This method exhibits good enhancement effect with an enhancement factor of 106 and wide linear range (5-1000 µg/L). With simple pretreatment, the flumetsulam residue in real wheat samples can be successfully detected with the limit of detection (LOD) down to 0.01 µg/g, which is below the maximum residue limit of flumetsulam in wheat (0.05 µg/g) set in China. The recovery of flumetsulam residue in wheat ranges from 88.3% to 95.6%. These results demonstrate that the proposed SERS method is a powerful technique for the detection of flumetsulam in wheat, which implies the great application potential in the rapid detection of other pesticide residues in various agri-foods.

Assessment of schwertmannite, jarosite and goethite as adsorbents for efficient adsorption of phenanthrene in water and the regeneration of spent adsorbents by heterogeneous fenton-like reaction.

Schwertmannite, jarosite or goethite are commonly used to remove metals and/or metalloids from contaminated water via adsorption processes, but it is still unclear whether they can be used as adsorbents to remove hydrophobic organic pollutants (HOCs), such as polycyclic aromatic hydrocarbons (PAHs), from groundwater or wastewater. Here, the feasibility of using these iron (oxyhydr) oxide minerals as adsorbents for phenanthrene (a model PAH) adsorption and regenerating the spent adsorbents via heterogeneous Fenton-like reaction was investigated. Results showed that they exhibited rapid adsorption rates and considerable adsorption capacities for phenanthrene. The maximum Langmuir capacities (Qmax) for phenanthrene adsorption at 28 °C were in an ascending order of goethite (567 µg·g-1) < schwertmannite (727 µg·g-1) < jarosite (2088 µg·g-1). The adsorption process was a spontaneous and exothermic process along with the decrease of randomness at the solid/liquid interfaces, which was influenced by temperature, adsorbent dosage, and the coexistence of inorganic anions. Both schwertmannite and jarosite were superior to goethite in light of their easy separation from the bulk solution after the adsorption processes. A multi-cycle experiment demonstrated that the regeneration efficiency of schwertmannite (97.9-99.7%) was much higher than that of jarosite (80.1-87.2%), and the mineral structure, morphology and functional groups of schwertmannite were not changed during the successive adsorption-regeneration processes. Therefore, among the investigated three iron (oxyhydr) oxide minerals, schwertmannite was an attractive and regenerable adsorbent for the removal of phenanthrene from water owing to its high adsorption capacity, good separation ability, and excellent reusability.

Assessment of antiherpetic activity of nonsulfated and sulfated polysaccharides from Azadirachta indica.

Azadirachta indica leaf is used by Indian population for the healing of various diseases including viral infection. Herein, we analyzed the antiherpetic (HSV-1) activity of two polysaccharides (P1 and P2) isolated from the leaf of A. indica and their chemically sulfated derivatives (P1S and P2S). The molecular weights of P1S and P2S are 41 and 11 kDa, respectively. Sulfate groups are located at positions C3 of the Araf and C6 of both Galp and Glcp residues of the most active polysaccharide (P1S). These compounds were not cytotoxic in HEp-2 cells, up to 1000 µg/mL. Both P1S and P2S exhibited antiviral activity when used simultaneously to HSV-1, with 50% inhibitory concentration/selectivity index, respectively, of 31.1 µg/mL/>51.4 and 80.5 µg/mL/>19.8. P1S showed better inhibitory effect (91.8%) compared to P1 (50%), P2 (71.1%) and P2S (70%) at 200 µg/mL. Synthesis of viral protein showed a dose-dependent response and the nucleic acid synthesis was inhibited up to 25 µg/mL, by P1 and P1S and up to 50 µg/mL, by P2 and P2S. The antiviral effect is probably due to the interference of polysaccharides at the early stages of HSV-1 replication, including adsorption. Further studies are under way to get insight into the mechanism of action of the substances.

Chemically sulfated polysaccharides from natural sources: Assessment of extraction-sulfation efficiencies, structural features and antiviral activities.

The provisioning of compound libraries with a high degree of diversity and attractive pharmacological properties is a limiting step in drug development. This study reports the production of highly bioactive sulfated polysaccharides, originally present in a nonsulfated, dormant state in natural sources, and demonstrates their antiviral activity (human cytomegalovirus EC50 values of 2.34-7.77 µg/mL) at a low degree of cytotoxicity. Furthermore, data strongly suggested the inhibition of virus entry as the main mode of antiviral action. Remarkably, the utilized oleum-DMF reagent was able to generate a range of sulfated polysaccharides from various natural sources, possessing varying saccharide compositions, degrees of sulfation (0.4-1.7) and molecular masses (38-94,000 g/mol). Typically, in a matter of minutes, this reagent not only solubilized polysaccharides but also chemically converted their hydroxyl functionality into sulfates. The most active sulfated polysaccharide (EC50 of 2.62 µg/mL) proved to be a 94,000 g/mol branched glucan with sulfates at C-6/C-3,6/C-2,3,6 positions. In conclusion, the important determinants of such compounds' antiviral activity are: (i) degree of sulfation, (ii) molecular mass and (iii) structural features. Thus, our approach offers a huge prospect for the improvement of natural source-derived libraries based on biologically active polysaccharides with diversified chemical profiles.

How does intensification influence the operational and environmental performance of photo-Fenton processes at acidic and circumneutral pH.

This study evaluates the technical, economical, and environmental impact of sodium persulfate (Na2S2O8) as an enhancing agent in a photo-Fenton process within a solar-pond type reactor (SPR). Photo-Fenton (PF) and photo-Fenton intensified with the addition of persulfate (PFPS) processes decolorize 97% the azo dye direct blue 71 (DB71) and allow producing a highly biodegradable effluent. Intensification with persulfate allowed reducing treatment time in 33% (from 120 to 80 min) and the consumption of chemical auxiliaries needed for pH adjustment. Energy, reagents, and chemical auxiliaries are still and environmental hotspot for PF and PFPS; however, it is worth mentioning that their environmental footprint is lower than that observed for compound parabolic concentrator (CPC)-type reactors. A life-cycle assessment (LCA) confirms that H2O2, NaOH, and energy consumption are the variables with the highest impact from an environmental standpoint. The use of persulfate reduced the relative impact in 1.2 to 12% in 12 of the 18 environmental categories studied using the ReCiPe method. The PFPS process emits 1.23 kg CO2 (CO2-Eqv/m3 treated water). On the other hand, the PF process emits 1.28 kg CO2 (CO2-Eqv/m3 treated water). Process intensification, chemometric techniques, and the use of SPRs minimize the impact of some barriers (reagent and energy consumption, technical complexity of reactors, pressure drops, dirt on the reflecting surfaces, fragility of reactor materials), limiting the application of advanced oxidation systems at an industrial level, and decrease treatment cost as well as potential environmental impacts associated with energy and reagents consumption. Treatment costs for PF processes (US$0.78/m3) and PFPS processes (US$0.63/m3) were 20 times lower than those reported for photo-Fenton processes in CPC-type reactors.

Optimization of strong-base anion exchange O&M costs for hexavalent chromium treatment.

Hexavalent chromium [Cr(VI)] in drinking water is pending regulation in California and is being considered for regulation in other locations. While strong-base anion exchange (SBA-IX) can efficiently remove Cr(VI) to low-levels that may be required to comply with future MCLs, operational and maintenance (O&M) costs can be considerable if the spent brine is disposed of as hazardous waste. Through bench- and pilot-scale experiments and full-scale demonstrations, this study examined the ability of emerging and established brine treatment and reuse techniques as well as recently developed resins to decrease O&M costs. When profiling anion elution during regeneration with nanofiltration treated and untreated spent brine, it appeared that at least 1 and 3 reuse cycles were feasible, respectively. Stannous- and ferrous-based reductants were more efficient than sulfur-based reductants when treating spent brine. Bed volumes to 8 µg/L chromium breakthrough with 7 resins varied by as much as a factor of 2 and correlated (R2 = 0.84) with resin total exchange capacities. Spent brine reuse, segmented regeneration (an optimized brine reuse method), ferrous reduction, and nanofiltration of spent brine were estimated to decrease O&M costs by 30, 70, 63, and 61%, respectively. Selection of high performing resins was the most simple way to decrease O&M costs (up to 70% savings). The sum of nitrate and sulfate raw water equivalent concentrations was found to be the principal water quality parameter that influenced the performance of 4 resins in 7 different groundwaters because nitrate and sulfate concentrations were orders of magnitude greater than chromium concentrations. Resins with higher chromium capacities eluted more co-contaminants including arsenic, selenium, uranium, and vanadium because they likely had higher co-contaminant capacities. Co-contaminant elution was found to be complex because associations can form between regenerant and co-eluting anions. Sodium chloride was the most efficient regenerant, though other regenerants provided benefits such as enhanced uranium elution most likely by complexing with uranium to inhibit its precipitation. Nitrate peaking was found to be limited even when reusing untreated and nanofiltration treated spent brine.

IRRADIATOR SYSTEM FOR MANGANESE SULFATE BATH EFFICIENCY MEASUREMENTS USING A PLUTONIUM-BERYLLIUM NEUTRON SOURCE.

This study describes the use of a neutron irradiator system based on a plutonium-beryllium neutron source for MnSO4 solution activation for use to determine the MSB system efficiency. Computational simulations using Monte Carlo code were performed to establish the main characteristics of the irradiator system. Among the simulated geometries and volumes, semi-cylindrical shape with 84.5 cm3 of MnSO4 solution yielded the best option to be built. Activity measurements were performed with a high-pure germanium detector to validate the new irradiation system. Results showed an average efficiency and uncertainty of the experimental standard deviation of the mean: 5.742 × 10-4 ± 0.036 × 10-4 (coverage factor k = 1), for MSB system. Efficiency value obtained shows good correlation to other published methods (i.e. a relative difference of 0.07%). This alternative metrological method demonstrated the utility of neutron sources for the irradiation of solutions in metrology laboratories providing a cost-efficient alternative to nuclear reactors or particle accelerators.

Assessment of the effects of sulfated polysaccharides extracted from the red seaweed Irish moss Chondrus crispus on the immune-stimulant activity in mussels Mytilus spp.

Seaweeds contain a number of health enhancing and antimicrobial bioactive compounds including sulfated polysaccharides (SP). In the present study, SP extracted from a European red seaweed Irish moss Chondrus crispus was chemically analyzed, SP content extracted and the immune-response effect on wild Irish mussels Mytilus spp. investigated for the first time. A high percent yield of SP was extracted from C. crispus and the immune-stimulant activity of SP was assessed in a laboratory trial with mussels exposed to three different treatments of low (10 µg mL-1), medium (20 µg mL-1) and high (50 µg mL-1) SP dose concentrations and a control mussel group with no exposure to SP. An initial mussel sample was processed prior to the trial commencing and mussels were subsequently sampled on Days 1, 2, 3, 4, 7, and 10 post SP exposure. Both cell, humoral and immune related gene responses including haemocyte cell viability, haemocyte counts, lysozyme activity and expression of immune related genes (defensin, mytimycin and lysozyme mRNA) were assessed. No mussel mortalities were observed in either the treated or non-treated groups. Mussels exposed with SP showed an increase in haemocyte cell viability and the total number of haemocytes compared to control mussels. Lysozyme activity was also higher in treated mussels. Additionally, up-regulated expression of defensin, mytimycin and lysozyme mRNA was observed in SP treated mussels shortly after exposure (on Days 1, 2, and 3) to SP. These results indicate that a high quality yield of SP can be readily extracted from C. crispus and more importantly based on the animal model used in this study, SP extracted from C. crispus can rapidly induce health enhancing activities in Mytilus spp. at a cellular, humoral and molecular level and with a prolonged effect up to ten days post treatment.

Electro activation of persulfate using iron sheet as low-cost electrode: the role of the operating conditions.

This work assesses the role of the operational conditions upon the electro-activation of persulfate (PS) using sacrificed iron electrode as a continuous low-cost Fe2+ source. An aqueous phenol solution (100 mg L-1) was selected as model effluent. The studied variables include current density (1-10 mA cm-2), persulfate concentration (0.7-2.85 g L-1), temperature (30-90°C) and the solution conductivity (2.7-20.7 mS cm-1) using Na2SO4 and NaCl as supporting electrolyte. A mineralization degree of around 80% with Na2SO4 and 92% in presence of NaCl was achieved at 30°C using 2.15 g L-1 PS at the lowest current density tested (1 mA cm-2). Besides PS concentration, temperature was the main variable affecting the process. In the range of 30-70°C, it showed a positive effect, achieving TOC conversion above 95% (using Na2SO4 under the previous conditions) along with a significant increase in iron sludge, which adversely affects the economy of the process. A lumped and simplified kinetic model based on persulfate consumption and TOC mineralization is suggested. The activation energy obtained for the TOC decay was 29 kJ mol-1. An estimated operating cost of US$ 3.00 per m3 was obtained, demonstrating the economic feasibility of this process.

Degradation of perfluorinated compounds by sulfate radicals - New mechanistic aspects and economical considerations.

Perfluorinated organic compounds (PFC) are an important group of pollutants, which are difficult to be degraded in conventional water treatment. Even hydroxyl radical based processes are not capable to degrade these compounds. Sulfate radicals can oxidize a group of PFC, i.e., perfluorinated carboxylic (PFCAs) acids. However, information in literature on kinetics and reaction mechanism is largely based on model simulations which are prone to errors. The present study provides mechanistic insights based on product formation, material balances, competition kinetics experiments and quantum chemical calculations. Furthermore, energy requirements for sulfate radical based degradation of PFCA is evaluated in the present study. PFCAs can be partly mineralized in chain reactions initiated by sulfate radicals (SO4─). The perfluorinated acetic acid (TFA), propionic acid, and butanoic acid are largely degraded in a primary reaction with sulfate radicals. In case of PFCA with a chain length of > 4 carbons low yields of PFCA products were observed. Regarding reaction kinetics sulfate radicals react very slow with PFCAs (≈ 104 M-1 s-1). Thus, the energy demand required for generation of SO4─ by photolysis of S2O82─ (UV/S2O82-) is very high. A 90% degradation of a PFCA by UV/S2O82- was estimated to be 55 kW h m-3 in pure water.

Oxidative degradation of tetramethylammonium hydroxide (TMAH) by UV/persulfate and associated acute toxicity assessment.

Tetramethylammonium hydroxide (TMAH) is widely used in high-tech industries as a developing agent. Ultraviolet (UV) light-activated persulfate (PS, S2O82-) can be used to generate strongly oxidative sulfate radicals, and it also exhibits the potential to treat TMAH-containing wastewater. This study initially investigated the effect of S2O82- concentration and UV strength on the UV/S2O82- process for the degradation of TMAH in a batch reactor. The results suggested that 15 watts (W) of UV-activated S2O82- at concentrations of 10 or 50 mM resulted in pseudo-first-order TMAH degradation rate constants of 3.1-4.2 × 10-2 min-1, which was adopted for determining the hydraulic retention time (HRT) in a continuous stirred tank reactor (CSTR). The operating conditions (15 W UV/10 mM S2O82-) with a HRT of 129 min resulted in stable residual concentrations of S2O82- and TMAH at approximately 2.6 mM and 20 mg L-1 in effluent, respectively. Several TMAH degradation intermediates including trimethylamine, dimethylamine, and methylamine were also detected. The effluent was adjusted to a neutral pH and evaluated for its biological acute toxicity using Cyprinus carpio as a bioassay organism. The "bio-acute toxicity unit" (TUa) was determined to be 1.41, which indicated that the effluent was acceptable for being discharged into an aquatic ecosystem.

Sulfate radical oxidation of aromatic contaminants: a detailed assessment of density functional theory and high-level quantum chemical methods.

Advanced oxidation processes that utilize highly oxidative radicals are widely used in water reuse treatment. In recent years, the application of sulfate radical (SO4˙-) as a promising oxidant for water treatment has gained increasing attention. To understand the efficiency of SO4˙- in the degradation of organic contaminants in wastewater effluent, it is important to be able to predict the reaction kinetics of various SO4˙--driven oxidation reactions. In this study, we utilize density functional theory (DFT) and high-level wavefunction-based methods (including computationally-intensive coupled cluster methods), to explore the activation energies of SO4˙--driven oxidation reactions on a series of benzene-derived contaminants. These high-level calculations encompass a wide set of reactions including 110 forward/reverse reactions and 5 different computational methods in total. Based on the high-level coupled-cluster quantum calculations, we find that the popular M06-2X DFT functional is significantly more accurate for OH- additions than for SO4˙- reactions. Most importantly, we highlight some of the limitations and deficiencies of other computational methods, and we recommend the use of high-level quantum calculations to spot-check environmental chemistry reactions that may lie outside the training set of the M06-2X functional, particularly for water oxidation reactions that involve SO4˙- and other inorganic species.