Nanoscale Fe/Ag particles activated persulfate: optimization using response surface methodology.

This work studied the bimetallic nanoparticles Fe-Ag (nZVI-Ag) activated persulfate (PS) in aqueous solution using response surface methodology. The Box-Behnken design (BBD) was employed to optimize three parameters (nZVI-Ag dose, reaction temperature, and PS concentration) using 4-chlorophenol (4-CP) as the target pollutant. The synthesis of nZVI-Ag particles was carried out through a reduction of FeCl2 with NaBH4 followed by reductive deposition of Ag. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area. The BBD was considered a satisfactory model to optimize the process. Confirmatory tests were carried out using predicted and experimental values under the optimal conditions (50 mg L-1 nZVI-Ag, 21 mM PS at 57 °C) and the complete removal of 4-CP achieved experimentally was successfully predicted by the model, whereas the mineralization degree predicted (90%) was slightly overestimated against the measured data (83%).

The photocatalytic reduction of NO3- to N2 with ilmenite (FeTiO3): Effects of groundwater matrix.

This work analyzes the role of natural groundwater, as well as the effect of HCO3-, Ca2+, Mg2+, K+, SO42- and Cl- concentrations, upon the photocatalytic nitrate reduction using ilmenite as catalyst and oxalic acid as hole scavenger. The nitrate removal and the selectivity towards N2 are significantly limited compared to previous experiments using ultrapure water matrix. Calcium (Ca2+), bicarbonate (HCO3-) as well as pH are claimed as the major controlling factors related to the process yield. Thus, Ca2+ promotes the formation of insoluble oxalate microcrystals, reducing the amount of hole scavenger available. The presence of HCO3- leads to a steeply increase in the pH value, favoring the adsorption onto the ilmenite surface of ions OH-instead of NO3-, NO2- and C2O42. The aforementioned issues are overcome by working with C2O42-/NO3- ratio well above the stoichiometric one, that also maintains the pH value in an acid range. A completed depletion of the starting NO3-, the no detection of either NO2- or NH4+ in the aqueous phase, and a selectivity towards N2 above 95% were achieved using two times the stoichiometric dose.

Diclofenac photodegradation with the Perovskites BaFeyTi1-yO3 as catalysts.

Perovskite oxides BaFeyTi1-yO3, with y = 0, 0.6, 0.8 and 1, were prepared by ceramic (CM) and complex polymerization methods (CPM) and utilized in UV-LED (365 nm) photocatalytic degradation assays of 25 mg L-1 diclofenac (DIC) model solutions. BaTiO3-CM was also used in the photocatalytic degradation test of a real mineral water for human consumption spiked with 2 mg L-1 DIC. The XRD patterns of the synthesized perovskites showed cubic structure for those prepared by CPM, with distortions of the cubic lattice to hexagonal or tetragonal when prepared by CM, except for BaTiO3. All the perovskites showed good catalytic activity, higher than photolysis, except BaFeO3-CM that presented similar results. BaTiO3-CM and CPM and BaFeO3-CPM were also utilized in UV-LED photocatalytic DIC degradation assays with peroxydisulfate addition. BaFeO3-CPM and BaTiO3-CPM showed better ability to persulfate activation, but the highest mineralization degree was obtained with BaTiO3-CM. This last perovskite was also able to perform DIC degradation in a real matrix. The studied oxides show potentiality for photocatalytic degradation of organic compounds, with or without persulfate addition. A degradation mechanism is proposed.

Coupled heat-activated persulfate - Electrolysis for the abatement of organic matter and total nitrogen from landfill leachate.

This work analyzes the viability of a coupled heat-activated persulfate (PS) and electro-oxidation treatment toabatetheorganic matter and nitrogen from ahigh polluted landfill leachate (5500 mg L-1 TOC; 5849 mg L-1 TN, pH: 8.4). These characteristics makes PS as a suitable oxidant to deal with the recalcitrant organic matter. Under the optimal conditions (70 °C and 60% of the stoichiometric amount of PS), around 60% of the initial organic load was mineralized. On the contrary, the nitrogen removal was below 20%. A subsequent electrolytic stage using Ti/IrO2-TaO2 anode at 175 mA cm-2 and 0.42 M NaCl during 60 min, led to overall organic matter and nitrogen removal above 85% and 90%, respectively, with energy requirement of 38 kWh per kg of nitrogen removed. In this sense, the combined process achieves a significant reduction in terms of energy consumption, up to one fifth in relation to sole electrolysis. These results confirm the feasibility of this combined process to treat landfill leachate.

Landfill leachate treatment by sequential combination of activated persulfate and Fenton oxidation.

This work assesses the feasibility of sequential persulfate and Fenton oxidation for the decolorization and mineralization of landfill leachate (5600 mg L-1 TOC; pH0: 8.6) in a continuous batch-recirculation system. Firstly, it was analyzed the role of the operational conditions upon the persulfate activation evaluating the effects of electrolysis, ilmenite (FeTiO3) as a source of Fe(II) and UV-LED (at 365 nm). The studied variables include current density (j) (50-200 mA cm-2), persulfate dose (46.8-234 mM) and mineral concentration (500-1500 mg L-1). The increase in j enhanced the hypochlorite generation and PS conversion to SO4- and, consequently, decolorization efficiency increasing the penetration of light through the solution and the photoreduction of Fe(III) to Fe(II) in the FeTiO3 surface. The combined electrolysis/FeTiO3/UV-LED showed synergetic effect compared to the individual processes, achieving mineralization around 53% under the optimum operating conditions (1 g L-1 of FeTiO3, using 234 mM of PS at 200 mA cm-2 under UV-LED radiation). The subsequent Fenton oxidation once the pH decreased up to around 3, led to overall mineralization above 90% after 480 min, confirming the suitability of this combined treatment to deal with recalcitrant and highly colored effluents.

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.

Electrochemical oxidation of landfill leachate in a flow reactor: optimization using response surface methodology.

Response surface methodology based on Box-Behnken (BBD) design was successfully applied to the optimization in the operating conditions of the electrochemical oxidation of sanitary landfill leachate aimed for making this method feasible for scale up. Landfill leachate was treated in continuous batch-recirculation system, where a dimensional stable anode (DSA(©)) coated with Ti/TiO2 and RuO2 film oxide were used. The effects of three variables, current density (milliampere per square centimeter), time of treatment (minutes), and supporting electrolyte dosage (moles per liter) upon the total organic carbon removal were evaluated. Optimized conditions were obtained for the highest desirability at 244.11 mA/cm(2), 41.78 min, and 0.07 mol/L of NaCl and 242.84 mA/cm(2), 37.07 min, and 0.07 mol/L of Na2SO4. Under the optimal conditions, 54.99% of chemical oxygen demand (COD) and 71.07 ammonia nitrogen (NH3-N) removal was achieved with NaCl and 45.50 of COD and 62.13 NH3-N with Na2SO4. A new kinetic model predicted obtained from the relation between BBD and the kinetic model was suggested.