Efficacious degradation of ethylene glycol by ultraviolet activated persulphate: reaction kinetics, transformation mechanisms, energy demand, and toxicity assessment.

Ethylene glycol or 1,2-ethanediol (EG) is a persistent and toxic substance in the environment and extensively applied in petrochemical, surfactants, antifreeze, asphalt emulsion paints, cosmetics, plastics, and polyester fiber industries. Degradation of EG by using ultraviolet (UV) activated hydrogen peroxide (H2O2) and persulfate (PS) or persulfate anion (S2O82-) based advanced oxidation processes (AOPs) were explored. The result obtained demonstrate that UV/PS (85.7 ± 2.5%) has exhibited improved degradation efficiency of EG as compared to UV/H2O2 (40.4 ± 3.2%) at optimal operating conditions of 24 mM of EG concentration, 5 mM of H2O2, 5 mM of PS, 1.02 mW cm-2 of UV fluence, and pH of 7.0. Impacts of operating factors, including initial EG concentration, oxidant dosage, reaction duration, and the impact of different water quality parameters, were also explored in this present investigation. The degradation of EG in Milli-Q® water followed pseudo - first order reaction kinetics in both methods having a rate constant of about 0.070 min-1 and 0.243 min-1 for UV/H2O2 and UV/PS, respectively, at optimum operating conditions. Additionally, an economic assessment was also conducted under optimal experimental conditions, and the electrical energy per order and total operational cost for treating per m3 of EG-laden wastewater was observed to be about 0.042 kWh m-3 order-1 and 0.221 $ m-3 order-1, respectively, for UV/PS, which was slightly lower than UV/H2O2 (0.146 kWh m-3 order-1; 0.233 $ m-3 order-1). The potential degradation mechanisms were proposed based on intermediate by-products detected by Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS). Moreover, real petrochemical effluent containing EG was also treated by UV/PS, demonstrating 74.7 ± 3.8% of EG and 40.7 ± 2.6% of total organic carbon removal at 5 mM of PS and 1.02 mW cm-2 of UV fluence. A toxicity tests on Escherichia coli (E. coli) and Vigna radiata (green gram) confirmed non-toxic nature of UV/PS treated water.

Remediation and immobilization of Cr(VI)-contaminated soil using stabilized nanoscale iron sulfide and ecological impact.

Soil contaminated with hexavalent chromium seriously threatens the environment and human health. The use of FeS, which has a high redox activity and excellent reduction capacity, limits its application in soil remediation due to its premature surface oxidation and massive aggregation. To prevent premature surface oxidation and agglomeration, cetyltrimethylammonium bromide-supported nano-ferrous sulfide (CTAB-nFeS) was chemically synthesized and used for immobilizing Cr(VI) in contaminated soil. In order to evaluate the role of CTAB stabilization of nFeS and interaction mechanisms were investigated by XPS, FTIR, XRD, and FESEM. Batch experiments showed a complete reduction of Cr(VI) within 3 h with only 235% excess of CTAB-nFeS at a soil pH of 8 compared to days as reported in the literature with alternative FeS forms. The reduction kinetic data could be satisfactorily fitted into the second-order rate model. The rate constant linearly depends on the soil-to-water ratio, but its logarithmic form is linear in the given pH range. The oxidation-reduction potential increases with decreasing initial pH, thus positively impacting the reduction process. XPS analysis revealed the reduction process as multi-steps (reduction, adsorption, and co-precipitation). Ecological studies showed improved plant growth and earthworm survival rate in the remediated soil. Medium-term stability experiments suggested a significant decrease in TCLP leachate concentration of Cr after CTAB-nFeS treatment and remained stable for 60 d. Overall results of our study suggested a sustainable, feasible, and effective strategy for in-situ remediation of Cr(VI)-contaminated soil using CTAB-nFeS at natural pH.

Zinc oxide nano-particles--sonochemical synthesis, characterization and application for photo-remediation of heavy metal.

Zinc oxide nanoparticles have been synthesized sonochemically from zinc acetate solution in aqueous methanol, ethanol and iso-propanol containing about 5 volume% of alcohol. Characterization with FESEM, XRD, AFM and BET surface area shows that the synthesized particles differ in shape and size. ZnO synthesized using isopropanol was observed to be the most crystalline one. The synthesized nanoparticles were used for the photocatalytic reduction of hexavalent chromium in aqueous medium under solar radiation. It was observed that the initial reduction rates varied with the difference in morphology of ZnO crystallites.

Removal of mercury(II) from aqueous solutions using the leaves of the Rambai tree (Baccaurea motleyana).

This study was undertaken to evaluate the biosorption potential of a natural, low-cost biosorbent, Rambai leaves (Baccaurea motleyana), to remove trace amounts of Hg(II) from aqueous solutions. It was found that the amount of Hg(II) biosorption by Rambai leaves increased with initial metal ion concentration, contact time, and solution pH but decreased as the amount of biosorbent increased. The maximum biosorption capacity was 121.95 mg/g for an initial concentration range of 5 to 120 ppb. Overall, kinetic studies showed that the Hg(II) biosorption process followed pseudo-second-order kinetics based on pseudo-first-order and intraparticle diffusion models. Isotherm data revealed that the biosorption process followed both Freundlich and Langmuir isotherms. The value of separation factor, R(L), from the Langmuir equation and rate of biosorption, n, from the Freundlich model also indicated favorable adsorption.

Metal ion removal from aqueous solution using physic seed hull.

The potential of physic seed hull (PSH), Jantropha curcas L. as an adsorbent for the removal of Cd(2+) and Zn(2+) metal ions from aqueous solution has been investigated. It has been found that the amount of adsorption for both Cd(2+) and Zn(2+) increased with the increase in initial metal ions concentration, contact time, temperature, adsorbent dosage and the solution pH (in acidic range), but decreased with the increase in the particle size of the adsorbent. The adsorption process for both metal ions on PSH consists of three stages-a rapid initial adsorption followed by a period of slower uptake of metal ions and virtually no uptake at the final stage. The kinetics of metal ions adsorption on PSH followed a pseudo-second-order model. The adsorption equilibrium data were fitted in the three adsorption isotherms-Freundlich, Langmuir and Dubinin-Radushkevich isotherms. The data best fit in the Langmuir isotherm indication monolayer chemisorption of the metal ions. The adsorption capacity of PSH for both Zn(2+) and Cd(2+) was found to be comparable with other available adsorbents. About 36-47% of the adsorbed metal could be leached out of the loaded PSH using 0.1M HCl as the eluting medium.

Reduction of hexavalent chromium in aqueous medium with zerovalent iron.

Hexavalent chromium, emanating primarily from the tannery and electroplating industries, can be reduced to the less toxic trivalent variety by several methods, including reduction with metallic iron. In the present work, electrolytic-grade iron dust was used to reduce chromium(VI) in the form of potassium dichromate. Loading of iron dust was varied from 0.5 to 1.0 g in 50 mL of solution; the pH of the medium was varied from 1.5 to 3.5; and the initial concentration of the dichromate solution was varied from 50 to 125 mg/L. Under the specified experimental conditions, maximum removal of the hexavalent chromium achieved was approximately 90% of its original value. The time-concentration data followed a pseudo-first-order kinetic model. The conversion and rate of reduction increased with an increase in iron loading and acidity of the medium, whereas an increase in the initial concentration of chromium(VI) caused a decrease in the reduction.

Bicarbonate-enhanced transformation of phenol upon irradiation of hematite, nitrate, and nitrite.

Bicarbonate enhances the transformation of phenol upon irradiation of hematite, and phenol nitration upon irradiation of both nitrate and nitrite. Hematite under irradiation is able to oxidise the carbonate ion to the CO3-. radical, which in turn oxidises phenol to the phenoxyl radical faster compared to the direct photo-oxidation of phenol by hematite. The formation of CO3-. from hematite and carbonate under irradiation is supported by the detection of 3,3'-dityrosine from tyrosine, added as a probe for CO3-.. It is shown that Fe(III) might be an important photochemical source of CO3-. in Fe-rich waters, e.g. waters that contain more than 1 mg L(-1) Fe. The enhancement by bicarbonate of phenol nitration upon nitrate irradiation is probably accounted for by an increased photogeneration rate of nitrogen dioxide. The process could lead to enhanced phenol photonitration by nitrate in waters rich of inorganic carbon (>10 mM bicarbonate). Bicarbonate also increases the transformation and nitration rates of phenol upon nitrite photolysis. The effect is due to the combination of basification that enhances phenol nitrosation and nitration, and of peculiar bicarbonate chemistry. It is shown that bicarbonate-enhanced phenol nitration upon nitrite photolysis could be a significant photonitration pathway, leading to the generation of toxic nitrated compounds in natural waters in which the scavenging of hydroxyl radicals by nitrite is competitive with that of Dissolved Organic Matter (DOM).

Application of biodegradable natural polymers for flocculated sedimentation of clay slurry.

Tamarind seed kernel powder (TSKP) is a cheap starchy biodegradable material that has not been tested before for its flocculating properties. Sedimentation of clay slurry has been studied using this material. We have also done experiments with chemical grade starch and its blends with TSKP and compared their performance with that of potash alum for sedimentation of the clay slurry. The sedimentation phenomenon showed constant and falling rate zones. Sedimentation velocity, mass flux and concentration have been calculated at different time intervals for all the flocculants. Among the three types of natural flocculants, starch showed the highest rate constant in the constant rate zone and TSKP offers faster sedimentation in the falling rate zone. Thus TSKP, starch and their blends are potentially attractive environmentally benign flocculants. A qualitative explanation of the flocculating property of TSKP has been given.

On the adsorption and diffusion of Methylene Blue in glass fibers.

The adsorption and diffusion phenomena of Methylene Blue dye on glass fiber have been explored. Both isotherm and kinetics have been studied. Effect of process parameters such as pH, adsorbent loading, and initial dye concentration was investigated. Temperature had a little effect on adsorption. A diffusion model was developed to estimate the diffusivity of the dye in glass fiber. The diffusivity was found to be varying exponentially with the dye concentration.

Photocatalytic degradation of model textile dyes in wastewater using ZnO as semiconductor catalyst.

Semiconductor photocatalysis often leads to partial or complete mineralization of organic pollutants. Upon irradiation with UV/visible light, semiconductors catalyze redox reactions in presence of air/O2 and water. Here, the potential of a common semiconductor, ZnO, has been explored as an effective catalyst for the photodegradation of two model dyes: Methylene Blue and Eosin Y. A 16 W lamp was the source of UV-radiation in a batch reactor. The effects of process parameters like, catalyst loading, initial dye concentration, airflow rate, UV-radiation intensity, and pH on the extent of photo degradation have been investigated. Substantial reduction of COD, besides removal of colour, was also achieved. A rate equation for the degradation based on Langmuir-Hinshelwood model has been proposed.