Chlorate reduction by dithionite/UV advanced reduction process

Chlorate is one of the disinfection byproducts that are formed when chlorine/chlorine dioxide is used as a primary disinfectant. This study investigated the removal of chlorate by photochemical degradation using an advanced reduction process, which is a treatment method that combines a reducing agent with an activating method to generate reducing radicals. The effectiveness of combinations of reducing agents and three UV light sources having a peak output at 254, 365, and 312 nm were evaluated for chlorate removal. Dithionite irradiated by broad-band UVB lamp having the peak energy at 312 nm showed the highest chlorate removal. In pursuit of finding the optimum advanced reduction process conditions, the environmental process variables including pH, reducing agent dose, and light intensity were investigated. Dithionite/UV-B advanced reduction process was effective in weakly acidic conditions (pH < 5), and chlorate removal occurred in two steps. The first was an initial rapid decrease in chlorate concentration that occurred before initiating UV irradiation and was attributed to reaction with dithionite decomposition products. The second step was a slow decrease during UV irradiation that is caused by radicals produced by photolysis of the products of dithionite decomposition. The major product of chlorate destruction was chloride, with negligible amounts of chlorite produced.     

A novel continuous magnetic nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/perlite fixed bed reactor for catalytic wet peroxide oxidation of dyes: reactor structure

In the present work, a continuous catalytic wet peroxide oxidation fixed bed reactor was employed to treat a simulated wastewater sample with malachite green dye, as a contaminant. Natural perlite particle-supported nano-Fe₃O₄ catalyst was used as a fixed bed inside a reactor, and it was immobilized by a persistent magnetic field. The range of (perlite) particle sizes was from 100 to 1000 nm. The effects of various operating parameters, including temperature of the reactor, pH, initial hydrogen peroxide concentration and initial dye concentration, were investigated on the percentage removal of malachite green dye. Load of catalyst of 2 g and volumetric flow rate of 1 L/h were selected for all the tests. Maximum malachite green degradation was 99.5 ± 0.3%. This removal percentage was attained at temperature of 80 °C, pH = 6, initial dye concentration of 6 mg/L and initial hydrogen peroxide concentration of 100 mg/L. The process was isotherm, and the catalyst showed high catalytic activity in the steady-state condition. The loss of catalyst was less than 0.3%.     

Photocatalytic activity evaluation of TiO<Subscript>2</Subscript> nanoparticles based on COD analyses for water treatment applications: a standardization attempt

Evaluation of the photocatalytic activities of TiO₂ nanomaterials based on the chemical oxygen demand (COD) analyses under identical experimental conditions was not previously reported. In this work, COD has been selected as an adequate industrial water quality measure toward the establishment of a representative standard test method. The initial COD values of six organic pollutants representing dye, surfactants, phenols and alcohol were set at 30 ± 2 mg/L. Ten of different commercial and synthesized TiO₂ samples representing anatase, rutile and mixed phases were used and characterized. The data of photocatalytic processes were compared to that obtained using the commonly widespread Degussa-P25 TiO₂ (TD). The COD of all pollutants was completely removed by TD at UV exposure dose ≤9.36 mWh/cm². Consequently, the maximum irradiation dose was set at this value in all experiments. The percentages of COD removal as well as the values of the accumulated UV doses required for complete removal of pollutants were measured using the different TiO₂ samples. TiO₂ samples show different performance abilities toward the various pollutants compared to TD. Based on the obtained data, TiO₂ photocatalysts were divided into two categories according to the hydroxyl radical formation rates. Comparison with previous studies reveals that the photocatalytic efficiency evaluation depends on the method of measurement. COD is recommended to be used as an adequate technique of analysis that meets the purpose of water treatment applications.     

Comparison of Fenton,ultraviolet–Fenton and ultrasonic–Fenton processes on organics and colour removal from pre-treated natural gas produced water

Produced water (PW) from natural gas field, characterized with high organic contents, has brought high environmental concerns world widely. Fenton and enhanced Fenton technologies were considered as the potential methods to degrade the organic contaminates in the PW, but with very limited data or reference. Here, we examined the optimum conditions of Fenton on organics and colour removal from natural gas PW after coagulation pre-treatment. Simultaneously, the optimal Fenton process integrated with ultraviolet (UV) and ultrasonic (US) irradiation were applied to enhance pollutants removal efficiencies. The optimal Fenton conditions were found at 60 min with molar ratios of 6:1 and 25:1 for H₂O₂/COD and H₂O₂/Fe²⁺, respectively and the initial pH of 3. Among these the three treatment processes, chemical oxygen demand (COD), total organic carbon, 5-day biological oxygen demand (BOD₅), and colour removal efficiencies were highest during UV–Fenton (82, 73, 68, and 95%,) followed by US–Fenton (79, 70, 66, and 95%) and Fenton treatment (70, 58, 51, and 92%), respectively. High biodegradability (BOD₅/COD) was also observed after UV–Fenton process (0.76) than the others (both 0.73). The current study showed a satisfactory carbon and colour removal efficiencies from PW using different Fenton processes; however, there still is a need for final polishing such as biological treatment or low cost constructed wetland before discharge. This study can be a good reference for engineering application PW treatment.     

Biodegradation of phenol from a synthetic aqueous system using acclimatized activated sludge

Phenol is one of the aromatic hydrocarbons. Phenol and its derivatives are highly toxic. These pollutants can be observed in the effluents of many industries. This research investigates the removal of phenol by the use of activated sludge in a batch system. The effects of influencing factors on biodegradation efficiency have been evaluated. The main factors considered in this study were the volume of acclimatized activated sludge inoculation, pH, temperature, and initial concentration of phenol. The inoculation volumes of 1, 3, and 5 mL of acclimatized activated sludge were taken into account. Different pH values of 3, 5, 7, 9, and 11 were examined. The experiments were conducted for temperatures of 25, 30, 35, and 40 °C and initial phenol concentrations of 400, 800, 1,000, and 1,500 ppm. The results show that the acclimatized activated sludge has a high capacity for the removal of phenol. From a 100-mL aqueous solution was removed 1,500 ppm of phenol after 80 h. Furthermore, maximum phenol removal was observed for an inoculation volume of 5 mL for three different phenol concentrations of 100, 400, and 800 ppm. The best pH was 7 for the biodegradation process, and the optimum temperature was 30 °C. It was further found that an increase in the phenol concentration increased its removal time. Moreover, the activated sludge could effectively remove about 99.9 % of phenol from a synthetic aqueous solution in a batch system.     

Removal of Cr(VI) and phenol coupled with the reduction of sulfate by sulfate-reducing bacteria sludge

Biological treatment of industrial wastewater containing heavy metal and organic pollutant has attracted extensive attention. In this study, Cr(VI) reduction coupled with phenol degradation was investigated by the sulfate-reducing bacteria (SRB) sludge with addition of zero-valent iron (ZVI). The results showed that the SRB wet sludge (SWS) had a good bioactivity in the reduction of Cr(VI) only when the initial concentration of Cr(VI) was below 60 mg L^?1. The addition of ZVI significantly enhanced the bioactivity and reusability of SWS, and the reduction percentage of Cr(VI) achieved 98% after SWS was successively used for seven cycles. SWS coupled with ZVI showed a high activity in phenol degradation, with more than 94% phenol being degraded in each cycle. However, in the simultaneous removal of Cr(VI) and phenol, phenol degradation was inhibited due to the toxicity of Cr(VI) to phenol degrading microbes in SWS. On the other hand, reduction of sulfate and Cr(VI) was not affected by the presence of phenol, with more than 95% of sulfate and Cr(VI) being removed at the end of the 5th cycle. This study enriches our understanding on the applications of the SRB sludge in the removal of organic and inorganic contaminants in wastewater.     

Transient and quasi-steady-state dissolution of biotite at 22-25°C in high pH, sodium, nitrate, and aluminate solutions

Biotite dissolution under conditions of high pH and high aluminum, sodium, and nitrate concentrations analogous to those found in tank wastes at the Hanford Site was investigated using continuously stirred flow-through reactors at 22 to 25 °C. Experiments were designed to simulate tank leaks into the Hanford vadose zone where Fe(II) from biotite is the dominant reducing agent available to immobilize certain contaminants. Both non-steady-state and steady-state dissolution kinetics were quantified; interest in non-steady-state kinetics derives from the inherently transitory nature of tank leaks. Biotite was conditioned in pH 8 solutions to simulate the alkaline environment of the Hanford sediment, and then reacted in pH 10-14 solutions, some including 0.055 M Al(NO₃)₃ and/or 2 M or 6 M NaNO₃. Initial dissolution transients (intervals of rapid release rates that decay to slower steady-state rates) showed fast preferential release of K followed by near-stoichiometric release of Si, Al, and Mg, and slower release of Fe. Each increase in pH resulted in a second transient with the greatest amounts of Si, Al, and K released at pH 14, followed by pHs 13, 12, 11, and 10. Fe release also was highest at pH 14, but unchanging at pHs 10-13 within experimental error. Transient releases at high pH are attributed to dissolution of amphoteric secondary phases such as ferrihydrite that are inferred from saturation calculations and solid analyses to form during the conditioning interval. Transient release of Si was inhibited by the presence of 0.055 M Al(NO₃)₃; the effects of Al(NO₃)₃ and NaNO₃ on the release rates of Al, Fe, Mg, and K were variable and generally outweighed by the effect of pH. Quasi-steady-state release rates were slowest at pH 11-12 (10^−12.2 mol biotite m⁻² s⁻¹ for Si) and increased in either direction in pH away from this minimum (to 10^−11.5 at pHs 8 and 14 for Si). Fe release rates at high pH were sufficient to account for observed Cr(VI) reduction at Hanford. The net release rates of the major framework cations, from which the biotite dissolution rate is inferred, may reflect the precipitation of secondary phases or the alteration of biotite to vermiculite. The most extensive solid-phase alterations were observed in Na-enriched solutions.     

Evolution of the chemistry of Fe bearing waters during CO2 degassing

The rates of Fe(II) oxidation and precipitation from groundwater are highly pH dependent. Elevated levels of dissolved CO₂ can depress pH and cause difficulty in removing dissolved Fe and associated metals during treatment of ferruginous water. This paper demonstrates interdependent changes in pH, dissolved inorganic C species, and Fe(II) oxidation rates that occur as a result of the removal (degassing) of CO₂ during aeration of waters discharged from abandoned coal mines. The results of field monitoring of aeration cascades at a treatment facility as well as batchwise aeration experiments conducted using net alkaline and net acidic waters in the UK are combined with geochemical modelling to demonstrate the spatial and temporal evolution of the discharge water chemistry. The aeration cascades removed approximately 67% of the dissolved CO₂ initially present but varying the design did not affect the concentration of Fe(II) leaving the treatment ponds. Continued removal of the residual CO₂ by mechanical aeration increased pH by as much as 2 units and resulted in large increases in the rates of Fe(II) oxidation and precipitation. Effective exsolution of CO₂ led to a reduction in the required lime dose for removal of remaining Fe(II), a very important factor with regard to increasing the sustainability of treatment practices. An important ancillary finding for passive treatment is that varying the design of the cascades had little impact on the rate of CO₂ removal at the flow rates measured.     

Comparison of methods for the removal of organic carbon and extraction of chromium, iron and manganese from an estuarine sediment standard and sediment from the Calcasieu River estuary, Louisiana, U.S.A.

U.S. National Bureau of Standards (NBS) estuarine sediment 1646 from the Chesapeake Bay, Maryland, and surface sediment collected at two sites in the Calcasieu River estuary, Louisiana, were used to evaluate the dilute hydrochloric acid extraction of Cr, Fe and Mn from air-dried and freeze-dried samples that had been treated by one of three methods to remove organic carbon. The three methods for the oxidation and removal of organic carbon were: (1) 30% hydrogen peroxide; (2) 30% hydrogen peroxide plus 0.25 mM pyrophosphate; and (3) plasma oxidation (low-temperature ashing). There was no statistically significant difference at the 95% confidence level between air- and freeze-dried samples with respect to the percent of organic carbon removed by the three methods. Generally, there was no statistically significant difference at the 95% confidence level between air- and freeze-dried samples with respect to the concentration of Cr, Fe and Mn that was extracted, regardless of the extraction technique that was used. Hydrogen peroxide plus pyrophosphate removed the most organic carbon from sediment collected at the site in the Calcasieu River that was upstream from industrial outfalls. Plasma oxidation removed the most organic carbon from the sediment collected at a site in the Calcasieu River close to industrial outfalls and from the NBS estuarine sediment sample. Plasma oxidation merits further study as a treatment for removal of organic carbon. Operational parameters can be chosen to limit the plasma oxidation of pyrite which, unlike other Fe species, will not be dissolved by dilute hydrochloric acid. Preservation of pyrite allows the positive identification of Fe present as pyrite in sediments.     

Efficacy of ultraviolet radiation and hydrogen peroxide oxidation to eliminate large number of pharmaceutical compounds in mixed solution

Ultraviolet photolysis and ultraviolet and hydrogen peroxide oxidation of fourteen commonly used pharmaceutical compounds and two personal care products in mixed solution using low pressure ultraviolet lamp was investigated in laboratory batch experiments. Removal of the compounds followed the first-order reaction kinetic. Three distinct impacts of hydrogen peroxide on ultraviolet and hydrogen peroxide oxidation of the compounds (positive, negative and no significant effect) were observed. Removal behavior of the several tested compounds in mixed solution varied significantly than their respective behavior in absence of coexisting compounds. Clofibric acid, diclofenac, fenoprofen, isopropylantipyrine, ketoprofen, phenytoin and triclosan were removed very efficiently (> 96 %) by ultraviolet photolysis alone. Residual hydrogen peroxide during ultraviolet and hydrogen peroxide oxidation was quantitated for the first time. Hydrogen peroxide addition to ultraviolet photolysis was not worthy for majority of the tested compounds as their removal did not increase significantly and very big fractions (> 85 %) of the added hydrogen peroxide (0.29 ～ 1.47 mM) remained unused presumably due to small fluence of the lamp, very small molar absorption for hydrogen peroxide at 254 nm (27.06 /M.cm) and acidic pH of reaction solution (< 5.7). Further exploration on ultraviolet and hydrogen peroxide oxidation with higher fluence lamp and alkaline solution pH will clarify usefulness of the method to treat pharmaceutical contaminated waters.     

Photocatalytic performance of TiO<Subscript>2</Subscript> and WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanoparticles coated on urban green infrastructure materials in removing nitrogen oxide

This study investigated the performance of UV light active TiO₂ and UV–visible light active WO₃/TiO₂ nanoparticles as air purifying materials that can be potentially applied to urban green infrastructures such as rain gardens and pervious pavements. Using a laboratory-scale continuous gas flow photoreactor, the removal efficiency of gaseous nitrogen oxide (NO _x ) by two different photocatalytic nanoparticles coated on natural zeolites and pervious concrete blocks was evaluated. The results showed that the TiO₂- and WO₃/TiO₂-coated zeolites are excellent photoactive materials providing enhanced air purification function (~95% removal efficiency of NO _x ) under UV and UV–visible light irradiation, respectively. In contrast, both of the TiO₂- and WO₃/TiO₂-coated pervious concrete blocks showed a measurable NO _x removal (~60%) only under UV irradiation, whereas the visible light activity of the WO₃/TiO₂-coated concrete block was significantly reduced (~20%) mainly due to the decrease in the photocatalytic reaction sites for visible light. This study revealed the potential utility of photocatalytic nanoparticles in improving urban air quality, in the form of the surface component of various urban infrastructures.     

Treatment of groundwater contaminated with high levels of explosives using advanced oxidation processes

Current and former military installations around the world have numerous sites with groundwater contaminated with explosive compounds polluted from military related activities. The test influent used in this study was a groundwater collected from an US Army facility that was contaminated with high levels of military derived explosives. The sample had a total explosive concentration in excess of 75 mg/l. Bench-scale evaluations were performed to determine the effectiveness of the candidate advanced oxidation processes for treatment of the groundwater in terms of removing the pollutants to method sub-detection limits with these results formulating the basis for comparison along with generating data that can be used toward increasing the understanding of treatment mechanisms associated with the various processes. Results indicate that the ozonated systems generally resulted in the removal of the explosives to the targeted levels with 1,3,5-trinitrobenzene removal lagging in terms of removal due to its simultaneous formation and degradation. The oxidation system that was irradiated using the medium-pressure UV lamp and dosed with hydrogen peroxide and ozone achieved the best performance with complete removal of all targeted pollutants within 10 min of treatment.     

Simultaneous phytoremediation of chromium and phenol by L<Emphasis Type="Italic">emna minuta</Emphasis> Kunth: a promising biotechnological tool

The aim of this work was to evaluate the usefulness of Lemna minuta Kunth for the simultaneous removal of Cr(VI) and phenol. The impact of these contaminants on plant growth and some biochemical processes have also been discussed for a better understanding and utilization of this species in the field of phytoremediation. The optimal growth conditions and plant tolerance to Cr(VI) and/or phenol as well as removal were determined. Plants exposed to Cr(VI) and phenol were able to efficiently grow and remove both contaminants at high concentrations (up to 2.5 and 250 mg/L, respectively) after 21 days, indicating that they were resistant to mixed contamination. There were no significant differences between chlorophyll, carotene and malondialdehyde content of treated plants with respect to the controls, which would be due to an efficient antioxidant response. L. minuta showed a higher biomass than control without contaminant when was exposed to low concentrations of Cr(VI), suggesting an hormesis effect. The main removal process involved in chromium phytoremediation would be sorption or accumulation in the biomass. Moreover, our results suggest that phenol could be used as a donor of carbon and energy by these plants. These findings demonstrated that Lemna minuta Kunth might be suitable for treatment of different solutions contaminated with Cr(VI) and phenol, showing a high potential to be used in the treatment of effluents containing mixed contamination.     

Photocatalytic ozonation of 2, 4-dichlorophenoxyacetic acid in water with a new TiO2 fiber

More effective techniques are required to mineralize the increasing number of recalcitrant organic contaminants at low concentrations in the water environment using advanced oxidation process. Though relatively new, photocatalytic ozonation (O₃/UV/TiO₂) is considered superior to ozonation (O₃) and photocatalysis (UV/TiO₂), due to synergistic effects and use of immobilized TiO₂ photocatalysts is a milestone in advance oxidation process. This article aimed to elucidate 2, 4-dichlorophenoxyacetic acid (2, 4-D) mineralization characteristics in low aqueous solutions by O₃/UV/TiO₂ using the world’s first high-strength TiO₂ fiber catalyst in laboratory experiments. 2, 4-D degradation and TOC removal in O₃, UV/TiO₂ and O₃/UV/TiO₂ followed pseudo-first order reaction kinetic. The removal rates for 2, 4-D and TOC in O₃/UV/TiO₂ were respectively about 1.5 and 2.4-fold larger than the summation of the corresponding values in O₃ and UV/TiO₂. The O₃/UV/TiO₂ process was characterized by short-lived few aromatic intermediates, faster degradations of aliphatic intermediates and dechlorination as a major step in 2, 4-D mineralization. The significantly enhanced 2, 4-D mineralization in the process was attributed to increased ozone decomposition and reduced electron-hole recombination on TiO₂ surface resulting to a large number of OH generation. The O₃/UV/TiO₂ process with the TiO₂ fiber catalyst was very promising with respect to the major challenges being faced in AOP involving TiO₂, namely separation of powder catalyst in suspension and reduced efficiency of immobilized catalysts (e.g. TiO₂ film/fiber).     

Kinetics of H2-O2-H2O redox equilibria and formation of metastable H2O2 under low temperature hydrothermal conditions

Hydrothermal experiments were conducted to evaluate the kinetics of H_2(aq) oxidation in the homogeneous H₂-O₂-H₂O system at conditions reflecting subsurface/near-seafloor hydrothermal environments (55-250 °C and 242-497 bar). The kinetics of the water-forming reaction that controls the fundamental equilibrium between dissolved H_2(aq) and O_2(aq), are expected to impose significant constraints on the redox gradients that develop when mixing occurs between oxygenated seawater and high-temperature anoxic vent fluid at near-seafloor conditions. Experimental data indicate that, indeed, the kinetics of H_2(aq)-O_2(aq) equilibrium become slower with decreasing temperature, allowing excess H_2(aq) to remain in solution. Sluggish reaction rates of H_2(aq) oxidation suggest that active microbial populations in near-seafloor and subsurface environments could potentially utilize both H_2(aq) and O_2(aq), even at temperatures lower than 40 °C due to H_2(aq) persistence in the seawater/vent fluid mixtures. For these H₂-O₂ disequilibrium conditions, redox gradients along the seawater/hydrothermal fluid mixing interface are not sharp and microbially-mediated H_2(aq) oxidation coupled with a lack of other electron acceptors (e.g. nitrate) could provide an important energy source available at low-temperature diffuse flow vent sites.More importantly, when H_2(aq)-O_2(aq) disequilibrium conditions apply, formation of metastable hydrogen peroxide is observed. The yield of H₂O_2(aq) synthesis appears to be enhanced under conditions of elevated H_2(aq)/O_2(aq) molar ratios that correspond to abundant H_2(aq) concentrations. Formation of metastable H₂O₂ is expected to affect the distribution of dissolved organic carbon (DOC) owing to the existence of an additional strong oxidizing agent. Oxidation of magnetite and/or Fe⁺⁺ by hydrogen peroxide could also induce formation of metastable hydroxyl radicals (•OH) through Fenton-type reactions, further broadening the implications of hydrogen peroxide in hydrothermal environments.     

Control of disinfection by products formation potential by enhanced coagulation

Jar-test experiments were conducted to study enhanced coagulation effectiveness in removal of disinfection by products (DBPs) from Zayandehrud River at Isfahan Province-the center part of Iran-in 2004. In this study, the removal of suspended and colloidal particles and natural organic matter (NOM) at various coagulant doses and coagulation pHs was assessed through raw and treated water measurements of turbidity, UV₂₅₄ absorbance, TOC, and dissolved organic carbon (DOC). The trihalomethane formation potential (THMFP) was also determined by a mathematical relationship with TOC. Results indicated that NOM removal was a function of coagulant type, coagulant dose, and pH of coagulation. In general, TOC, DOC, and UV₂₅₄ absorbance removal enhanced with increasing coagulant dose. However, further increases in coagulant dosage had little effect on disinfection by-products precursors removal. Ferric chloride was consistently more effective than alum in removing NOM. Coagulation pH was appeared to be a determining factor for maximum NOM removal and the removal of DBPs precursors by enhanced coagulation was significantly enhanced at pH 5.5 in comparison with initial pH of water. Furthermore, it is specified that preadjustment of pH with sulfuric acid reduced the coagulant dosage and thus, production of sludge. The reduction in THMFP was consistent with the trends observed for DBPs precursors removal data (i.e. UV₂₅₄ and TOC data).     

Effect of Fenton process on treatment of simulated textile wastewater: optimization using response surface methodology

A large portion of water is consumed during various textile operations thereby discharging wastewaters with pollutants of huge environmental concern. The treatment of such wastewaters has promising impact in the field of environmental engineering. In this work, Fenton oxidation treatment was engaged to treat simulated textile wastewater. Box–Behnken design and response surface methodology were employed to optimize the efficiency of Fenton process. Iron dose, peroxide dose and pH were considered as input variables while the responses were taken as chemical oxygen demand and color removal. A total of 17 experiments were conducted and analyzed using second-order quadratic model. The quadratic models generated for chemical oxygen demand and color removal efficiencies were validated using analysis of variances, and it was found that the experimental data fitted the second-order model quite effectively. Analysis of variances demonstrated high values of coefficient of determination (R ²) for chemical oxygen demand and color removal efficiencies with values of 0.9904 and 0.9963 showing high conformation of predicted values to the experimental ones. Perturbation plots suggested that the iron dosage produced the maximum effect on both chemical oxygen demand and color removal efficiencies. The optimum parameters were determined as Fe²⁺ dose—550 mg/L, H₂O₂ dose—5538 mg/L, pH—3.3 with corresponding chemical oxygen demand and color removal efficiencies of 73.86 and 81.35%. Fenton process was found efficient in treatment of simulated textile wastewater, and optimization using response surface methodology was found satisfactory as well as relevant. From the present study, it can also be concluded that if this method is used as pretreatment integrated with biological treatment, it can lead to eco-friendly solution for treatment of textile wastewaters.     

Comparative study on the photodegradation of Indigo Caramine dye using commercial TiO<Subscript>2</Subscript> and natural rutile

The photocatalytic degradation of Indigo Caramine dye using commercial TiO₂ and fine grained natural rutile has been carried out. The commercial TiO₂ and natural rutile were characterized using powder X- ray diffraction (XRD) and Fourier transformed infra red spectroscopy (FTIR). The study on the photodegradation of Indigo Caramine dye using commercial TiO₂ and natural rutile were investigated both under Solar and UV irradiation. The degradation of Indigo Caramine dye was checked by the following parameters like Chemical Oxygen Demand (COD), %T, irradiation time and duration. In both cases using commercial TiO₂ and natural rutile, the COD of the dye solution was reduced from 288 mg/L to less than 20 mg/L, and similarly the %T was increased from 76% to 97% and the percentage decomposition upto 97% within the irradiation duration of 3.5 hrs. The preliminary results obtained on the photodegradation of Indigo Caramine dye are highly encouraging and further work is being carried out for the use of the natural rutile or anatase sources for the other organic decomposition and treatment of industrial effluents.     

锰钾矿光催化降解苯酚及其影响因素研究

利用回流法合成隧道结构的锰钾矿,并研究其光化学降解苯酚的效果及影响因素。分别采用X射线衍射、原子吸收光谱、扫描电镜、透射电镜和BET氮气吸附法对锰钾矿的晶体结构(包括晶型、晶胞参数和结晶度)、化学组成、微观形貌和比表面积进行了表征。研究表明,非光照时锰钾矿对苯酚的降解效果较差,光照能显著促进锰钾矿对苯酚的降解;光照条件下,p H值减小能显著促进锰钾矿对苯酚的降解;锰钾矿用量增加至1.00 g/L时能显著促进锰钾矿降解苯酚,但继续增加矿物用量却显著降低苯酚降解率;非光照条件下,p H值减小和矿物用量增加不能显著促进锰钾矿降解苯酚。     

Contamination of groundwater by arsenic and other constituents in an industrial complex

This study examined the natural and anthropogenic pollution of groundwater at a national groundwater monitoring station (NGMS) in a dyeing industry complex, Korea. The arsenic contamination of a shallow well at the NGMS was noticed, starting from 22 months after the well installation. Possibilities of several mechanisms for As pollution of the groundwater were examined. The arsenical pyrite oxidation as a source mechanism in the shallow aquifer may be disregarded because of deficiency of pyrite in the shallow sediments, concomitant with depleted dissolved oxygen and very low levels of redox potentials of the As-polluted groundwater. The effect of wastewater from the general industrial area through a covered sewer stream was also considered as a possible source. Even though occurrence patterns of phenol and volatile organic hydrocarbons were very similar to those of the polluted shallow groundwater, As was not detected in the wastewater. One of the most plausible sources of the arsenic pollution was believed to be the reductive dissolution of Fe hydroxide. The As-polluted shallow groundwater had also very high levels of pH, HCO₃, COD and very low levels of DO and NO₃, which support the possibility of As pollution by the reductive dissolution. Consequently, the shallow groundwater in and around the NGMS has been polluted with various contaminants including As, phenol, chlorinated solvents, and petroleum hydrocarbons through multiple sources of contamination, such as natural reductive dissolution, dyeing wastewater, industrial wastewater, and municipal sewage.