Mathematical model for photocatalytic destruction of organic contaminants in air

Photocatalytic oxidation (PCO) was investigated in a bench-scale reactor for the abatement of two airborne organic contaminants: toluene and ethanol. A mathematical model that includes the impacts of light intensity, initial contaminant concentration, catalyst thickness, and relative humidity (RH) on the degradation of organic contaminants in a photocatalytic reactor was developed to describe this process. The commercially available catalyst Degussa-PtTiO2 was selected to compare with the MTU-PtTiO2-350 catalyst, which was synthesized by the sol-gel process, platinized, and calcined at 350 degrees C. For toluene removal using the MTU-PtTiO2-350 catalyst, the degradation rate increased with increases in light intensity from 0.2 to 2.2 mW/cm2 and in catalyst thickness from 0.00037 to 0.00361 cm. However, further increases in light intensity and catalyst thickness had only slight effect on the toluene degradation rate. Increasing the initial concentration from 6.29 to 127.9 microg/L and the RH from 10 to 85% resulted in decreases in the toluene degradation rate. For ethanol removal using the MTU-PtTiO2-350 catalyst, the degradation rate increased more rapidly with an increase in RH from 17 to 56%; the RH had little effect on the ethanol degradation rate while it further increased from 56% to 82%. We discuss applicability of the model to estimate the influence of process variables and to evaluate photocatalyst performance.     

Enhanced Fenton's destruction of non-aqueous phase perchloroethylene in soil systems

The Fenton's system is applied to the destruction of perchloroethylene (PCE) present as a dense non-aqueous phase liquid (DNAPL) in soil slurry systems; the initial concentration of PCE was 45 times higher than its aqueous solubility. Studies were conducted in two matrices: Ottawa sand and soil from Warsaw, IN. In Ottawa sand, a 60-62% decrease in PCE concentration was observed, and Cl(-) recovery was 47-58%, whereas in Warsaw soil, a 44-49% decrease in PCE concentration and a Cl(-) recovery of 40-42% were observed after the addition of 600 mM H(2)O(2) and 10 mM dissolved iron. Significantly enhanced destruction resulted during application of N-(2-hydroxyethyl) iminodiacetic acid (HEIDA) to Warsaw soil. For example, in the absence of HEIDA in Warsaw soil, 36% PCE loss and 33% Cl(-) release were observed at 600 mM H(2)O(2) and 5 mM Fe(III), while 74% PCE loss and 63% Cl(-) release were achieved at 600 mM H(2)O(2) and 5 mM Fe(III)-HEIDA. For both soils, the catalytic activities of Fe(II) and Fe(III) were nearly equivalent. These findings clearly demonstrate that system design can be optimized with regard to process variables in Fenton's treatment of DNAPL in soils.     

VOC destruction by water diluted hydrogen mild combustion

This study represents a preliminary numerical evaluation of the effect of steam dilution and hydrogen addition on the oxidation of formaldehyde and benzene, chosen as representative of the volatile organic compounds (VOC), in mild condition by evaluating the autoignition time and the steady state attainment. These parameters are important in the design of thermal VOC destruction plants since they influence the abatement efficiency and, therefore, the plant dimension. It has come out that, in comparison with the system diluted in nitrogen, steam induces lower autoignition times and, on the other hand, longer times for the attainment of the steady state. In contrast, for very high water content the autoignition time slightly increases. In particular results have shown that is possible to identify an optimum value of steam content that allows for the attainment of the steady state condition by the lowest residence time. Hydrogen addition to systems diluted in nitrogen promotes the oxidation reactions and anticipates the steady state condition. In steam diluted systems hydrogen delays the autoignition of the mixtures even though anticipates the attainment of the complete destruction of the VOC. The rate of production analysis has showed that the H(2)/O(2) reactions, that promote the ignition and the destruction of VOC, are sensibly modified by the presence of water and hydrogen.     

Catalytic destruction of dichloromethane using perovskite-type oxide catalysts

Dichloromethane (DCM, also known as methylene chloride [CH2Cl2]) is often present in industrial waste gas and is a valuable chemical product in the chemical industry. This study addresses the oxidation of airstreams that contain CH2Cl2 by catalytic oxidation in a tubular fixed-bed reactor over perovskite-type oxide catalysts. This work also considers how the concentration of influent CH2Cl2 (Co = 500-1000 ppm), the space velocity (GHSV = 5000-48,000 1/hr), the relative humidity (RH = 10-70%) and the concentration of oxygen (O2 = 5-21%) influence the operational stability and capacity for the removal of CH2Cl2. The surface area of lanthanum (La)-cobalt (Co) composite catalyst was the greatest of the five perovskite-type catalysts prepared in various composites of La, strontium, and Co metal oxides. Approximately 99.5% CH2Cl2 reduction was achieved by the catalytic oxidation over LaCoO3-based perovskite catalyst at 600 degrees C. Furthermore, the effect of the initial concentration and reaction temperature on the removal of CH2Cl2 in the gaseous phase was also monitored. This study also provides information that a higher humidity corresponds to a lower conversion. Carbon dioxide and hydrogen chloride were the two main products of the oxidation process at a relative humidity of 70%.     

High-temperature gas-phase formation and destruction of polychlorinated dibenzofurans

The high-temperature gas-phase decomposition of a PCB isomer was studied using a tubular flow reactor. The formation and destruction of various PCDFs were investigated in atmospheres containing different concentrations of O₂.     

Evidence for destruction of PCBs by the OH radical in urban atmospheres

Evidence for reaction of polychlorinated biphenyl (PCB) congeners with the hydroxyl (OH) radical in the troposphere was observed in diurnal variations in ambient gas-phase PCB concentrations at three urban sampling sites located in the Chicago, IL; Baltimore, MD; and Jersey City, NJ urban/industrial areas. The magnitude of the depletion of individual PCB congeners decreased by about 10-20% for each additional chlorine substituent, reflecting slower reaction rates for higher MW congeners with the OH radical. Octa- and nonachlorobiphenyls, which are largely unreactive with the OH radical, were used as tracers to investigate the effects of dilution on diurnal variation. The environmental rate constants for disappearance of the PCBs range from about 1.0 day(-1) for trichlorobiphenyls to about 0.3 day(-1) for hexachlorobiphenyls. Assuming a OH radical concentration of 3 x 10(6) molecules cm (-3), the second-order rate constants for reaction of specific congeners with the OH radical are consistent with laboratory measurements. More importantly, the relative reactivity of PCB homologues agrees well with the relationship predicted by other researchers from laboratory measurements, suggesting that losses of PCBs during daytime tropospheric transport are due at least in part to reactions with the OH radical.     

Thermal destruction of wastes containing polychlorinated naphthalenes in an industrial waste incinerator

A series of verification tests were carried out in order to confirm that polychlorinated naphthalenes (PCNs) contained in synthetic rubber products (Neoprene FB products) and aerosol adhesives, which were accidentally imported into Japan, could be thermally destroyed using an industrial waste incinerator. In the verification tests, Neoprene FB products containing PCNs at a concentration of 2800 mg/kg were added to industrial wastes at a ratio of 600 mg Neoprene FB product/kg-waste, and then incinerated at an average temperature of 985 °C. Total PCN concentrations were 14 ng/m³N in stack gas, 5.7 ng/g in bottom ash, 0.98 ng/g in boiler dust, and 1.2 ng/g in fly ash. Destruction efficiency (DE) and destruction removal efficiency (DRE) of congener No. 38/40, which is considered an input marker congener, were 99.9974 and 99.9995 %, respectively. The following dioxin concentrations were found: 0.11 ng-TEQ/m³N for the stack gas, 0.096 ng-TEQ/g for the bottom ash, 0.010 ng-TEQ/g for the boiler dust, and 0.072 ng-TEQ/g for the fly ash. Since the PCN levels in the PCN destruction test were even at slightly lower concentrations than in the baseline test without PCN addition, the detected PCNs are to a large degree unintentionally produced PCNs and does not mainly stem from input material. Also, the dioxin levels did not change. From these results, we confirmed that PCNs contained in Neoprene FB products and aerosol adhesives could be destroyed to a high degree by high-temperature incineration. Therefore, all recalled Neoprene FB products and aerosol adhesives containing PCNs were successfully treated under the same conditions as the verification tests.     

Ultrasonic destruction of surfactants: application to industrial wastewaters.

This research focused on the use of sonication to destroy surfactants and surface tension properties in industrial wastewaters that affect traditional water treatment processes. We have investigated the sonochemical destruction of surfactants and a chelating agent to understand the release of metals from surfactants during sonication. In addition, the effects of physical properties of surfactants and the effect of ultrasonic frequency were investigated to gain an understanding of the factors affecting degradation. Sonochemical degradation of surfactants was observed to be more effective than nonsurfactant compounds. In addition, as the concentration is increased, the degradation rate constant does not decrease as significantly as with nonsurfactant compounds in the near-field acoustical processor reactor. The degradation of metal complexes is not as effective as in the absence of the metal. However, this is likely an artifact of the model complexing agent used. Surfactant metal complexes are expected to be faster, as they will accumulate at the hot bubble interface, significantly increasing ligand exchange kinetics and thus degradation of the complex.     

Mechanochemical destruction of mirex co-ground with iron and quartz in a planetary ball mill

Mechanochemical destruction (MCD) has been recognized as a promising non-combustion technology for the disposal of obsolete pesticides belonging to the persistent organic pollutants (POPs). Mirex, a termiticide ever used for many years in China, was ball milled in the presence of various reagent(s) in a planetary ball mill at room temperature to investigate the destruction efficiency. The ground samples were characterized and analyzed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, gas chromatography (GC), and ion chromatography (Martins, Bicego et al.). Under the same conditions of mill rotary rate and charge ratio, the mixture of iron powder and quartz sand (Fe/SiO₂) was found best in promoting the mirex destruction. Mirex was completed destroyed after 2 h grinding at a charge ratio of 36:1 (reagent/mirex, m/m) and a mill rotation speed of 550 rpm. No organic compound was detected by GC/μECD screening. The yield of water-soluble chlorine determined by ion chromatography (Martins, Bicego et al.) in the final residue accounted for 90.7% of chlorine in the original mirex, which indicated a nearly complete dechlorination. Signals of both graphite and amorphous carbon were found in the Raman spectra of the co-ground powder samples. With the main final degradation products of water soluble Cl and carbon, the mechanism of the mechanochemical destruction approach should be dechlorination followed by the carbonization.     

Impact of ozone mini-holes on the heterogeneous destruction of stratospheric ozone

A comprehensive study of ozone mini-holes over the mid-latitudes of both hemispheres is presented, based on model simulations with the coupled climate-chemistry model ECHAM4.L39(DLR)/CHEM representing atmospheric conditions in 1960, 1980, 1990 and 2015. Ozone mini-holes are synoptic-scale regions of strongly reduced total ozone, directly associated with tropospheric weather systems. Mini-holes are supposed to have chemical and dynamical impacts on ozone levels. Since ozone levels over northern mid-latitudes show a negative trend of approximately -4%/decade and since it exists a negative correlation between total column ozone and erythemally active solar UV-radiation reaching the surface it is important to understand and assess the processes leading to the observed ozone decline. The simulated mini-hole events are validated with a mini-hole climatology based on daily ozone measurements with the TOMS (total ozone mapping spectrometer) instrument on the satellite Nimbus-7 between 1979 and 1993. Furthermore, possible trends in the event frequency and intensity over the simulation period are assessed. In the northern hemisphere the number of mini-hole events in early winter decreases between 1960 and 1990 and increases towards 2015. In the southern hemisphere a positive trend in mini-hole event frequency is detected between 1960 and 2015 in spring associated with the increasing Antarctic Ozone Hole. Finally, the impact of mini-holes on the stratospheric heterogeneous ozone chemistry is investigated. For this purpose, a computer-based detection routine for mini-holes was developed for the use in ECHAM4.L39(DLR)/CHEM. This method prevents polar stratospheric cloud formation and therefore heterogeneous ozone depletion inside mini-holes. Heterogeneous processes inside mini-holes amount to one third of heterogeneous ozone destruction in general over northern mid- and high-latitudes during winter (January-April) in the simulation.     

Rapid reductive destruction of hazardous organic compounds by nanoscale Fe0

Fe0-mediated reductive destruction of hazardous organic compounds such as chlorinated organic compounds (COCs) and nitroaromatic compounds (NACs) in the aqueous phase is one of the latest innovative technologies. In this paper, rapid reductive degradation of COCs and NACs by synthesized nanoscale Fe0 in anaerobic batch systems was presented. The nanoscale Fe0, characterized by high specific surface area and high reactivity, rapidly transformed trichloroethylene (TCE), chloroform (CF), nitrobenzene (NB), nitrotoluene (NT), dinitrobenzene (DNB) and dinitrotoluene (DNT) under ambient conditions, which results in complete disappearance of the parent compounds from the aqueous phase within a few minutes. GC analysis reported that the main products of the dechlorination of TCE and CF were ethane and methane as well as that most of the nitro groups in NACs were reductively transformed to amine groups. These results suggest that the rapid reductive destruction by nanoscale Fe0 is potentially a viable in situ or aboveground treatment of groundwater contaminated with hazardous organic compounds including COCs and NACs.     

Synergistic effects of combination of photolysis and ozonation on destruction of chlorophenols in water.

Synergistic effects including TOC elimination, ozone consumption and microtoxicity reduction for combination of photolysis and ozonation compared to those of direct photolysis and ozonation alone on destruction of chlorophenols including 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol were studied. It was found that the synergistic effects of combination of photolysis and ozonation increased obviously with increasing initial pH of solution to basic pH levels. Results showed that the synergistic effects of photolytic ozonation under the conditions imposed was notable with mineralization rate enlarging more than 100%, oxidation index (OI) decreasing 50%, and microtoxicity being reduced by 30%, indicating that the potentialities of photolytic ozonation compared to direct photolysis and ozonation alone was remarkable for treatment of industrial wastewater containing chlorophenols.     

Dechlorination/hydrogenation and destruction reactions of PCDDs in OCDD-added fly ash heated under vacuum

Octachlorodibenzo-p-dioxin (OCDD)-added, pretreated fly ash was heated under vacuum at sample temperatures ranging from T(s)=450 to 650 K. The fly ash and liquid nitrogen-cooled trap samples were analyzed for DD/DF through OCDD/DF. The total amounts of DD through OCDD decrease with increasing T(s), which indicates that dechlorination/hydrogenation (DCH) reactions are not the only reaction channels. Reduction of toxic equivalent (TEQ) for PCDDs by more than 99% was achieved in the fly ash by the vacuum heat treatment at T(s)=650 K for 4 h. The total amount of PCDDs and DD detected in the liquid nitrogen-cooled trap relative to that of added OCDD was about 17%, i.e., PCDDs and DD which were adsorbed to the fly ash surfaces can evaporate into the gaseous phase. The difference between the evaporation behavior of PCDDs in the present and the previous studies is discussed in the light of their states of existence.     

Performance of Gd-doped Ti-based Sb-SnO2 anodes for electrochemical destruction of phenol

The performance of electrodes for the electro-catalytic decomposition of a model pollutant (phenol) was enhanced using Gd-doped Ti/SnO(2)-Sb electrodes prepared by a thermal deposition method. Phenol degradation followed first-order rate kinetics, with the maximum rate achieved using a 2% Gd doping level (molar ratio based on Gd:Sn) for tests conducted over a doping range of 1-10%. The first-order rate constant with 2% Gd was 0.044 min(-1), versus 0.026 min(-1) obtained with the control (plain Ti/SnO(2)-Sb). TOC removal and UV scans revealed that different intermediates were produced for different Gd contents, and that destruction efficiencies of these intermediates also varied with Gd doping levels of 1-5%. Electrodes were characterized by scanning electron microscopy, X-ray diffraction, electron dispersive spectrometry, and X-ray photon-electron spectroscopy. It is suggested that the state of specific active sites on the electrode surface and the oxygen transfer activity at the electrode/electrolyte interface affect the performance of anodes with different compositions.     

The destruction of ground water threatening pesticides using high intensity UV light

Abstract

A high‐intensity short‐wavelength UV light system was studied for its ability to degrade the pesticides carbofuran, fenamiphos sulfoxide (nemacur sulfoxide), and propazine in aqueous solutions. Half‐lives, rate constants, and breakdown products were determined for all chemicals. The presence of hydrogen peroxide, an oxidant and potential source of hydroxyl radicals, had no effect on the rate of breakdown of any of the chemicals investigated. Short‐wavelength UV light appears to be solely responsible for the observed pesticide breakdown. The breakdown of all three pesticides followed first order kinetics. Carbofuran, nemacur sulfoxide, and propazine had half lives of 3.9, 1.1, and 3.9 minutes, respectively. Breakdown product analysis was performed using capillary gas chromatography/mass spectrometry.     

Effects of temperature on bacterial transport and destruction in bioretention media: field and laboratory evaluations

Microbial activities are significantly influenced by temperature. This study investigated the effects of temperature on the capture and destruction of bacteria from urban stormwater runoff in bioretention media using 2-year field evaluations coupled with controlled laboratory column studies. Field data from two bioretention cells show that the concentration of indicator bacteria (fecal coliforms and Escherichia coli) was reduced during most storm events, and that the probability of meeting specific water quality criteria in the discharge was increased. Indicator bacteria concentration in the input flow typically increased with higher daily temperature. Although bacterial removal efficiency was independent of temperature in the field and laboratory, column tests showed that bacterial decay coefficients in conventional bioretention media (CBM) increase exponentially with elevated temperature. Increases in levels of protozoa and heterotrophic bacteria associated with increasing temperature appear to contribute to faster die-off of trapped E. coli in CBM via predation and competition.     

International trade causes large net economic losses in tropical countries via the destruction of ecosystem services

Despite the large implications of the use of tropical land for exports (“land absorption”) on ecosystem services (ES) and global biodiversity conservation, the magnitude of these externalities is not known. We quantify the net value of ES lost in tropical countries as a result of cropland, forestland and pastureland absorption for exports after deducting ES gains through imports (“land displacement”). We find that net ES gains occur only in 7 out of the 41 countries and regions considered. We estimate global annual net losses of over 1.7 x 10¹² international dollars (I$) (I$1.1 x 10¹² if carbon-related services are not considered). After deducting the benefits from agricultural, forest and livestock rents in land replacing tropical forests, the net annual losses are I$1.3 and I$0.7 x 10¹², respectively. The results highlight the large magnitude of tropical ES losses through international trade that are not compensated by the rents of land uses in absorbed land.

Electronic supplementary material

The online version of this article (doi:10.1007/s13280-016-0768-7) contains supplementary material, which is available to authorized users.     

Electrochemical destruction of p-chlorophenol and p-nitrophenol -- Influence of surfactants and anode materials

The electrochemical oxidative removal of p-chlorophenol and p-nitrophenol was studied by cyclic voltammetry (CV) and constant current electrolysis on commercially available graphite and titanium substrate insoluble anodes (TSIA). The effect of cationic cetyl trimethylammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and non-ionic polyoxyethylene(23)lauryl ether (Brij-35) surfactants, which prevent adherent film formation on the electrode surface were also studied. CV experiments indicate that p-chlorophenol exhibits a relatively higher tendency for film formation on graphite and that sodium chloride is a better medium for the destruction of phenols. The electrochemical oxidation of phenols under galvanostatic conditions in chloride medium with CTAB enhanced the detoxification process with significantly lower fouling effects on TSIA. The surfactants, however, did not improve phenol removal on graphite under identical experimental conditions. A charge of 2.5F per mol was found to be sufficient to achieve 44-48% removal of phenol on both the electrodes in the absence of the surfactants. A 55-65% removal was achieved in the presence of the cationic surfactant on the TSIA electrode. Phenol was removed as a low molecular weight polymer (MW approximately 4450).     

Catalytic destruction of chloramine to nitrogen using chlorination and activated carbon--case study.

The paper presents the results of laboratory and pilot studies on the removal of chloramine from potable water using chlorination with a less-than-breakpoint dosage of chlorine, followed by treatment with catalytic activated carbon. The effect of the chlorine-to-nitrogen ratio, temperature, and carbon contact time were investigated to optimize conditions for chloramines removal and minimize the production of ammonia. Results demonstrated that prechlorination of water, followed by treatment with catalytic activated carbon, can degrade monochloramine to nitrogen gas as a main product. For all chlorine-to-ammonia ratios studied, the observed rates of monochloramine removal were higher at a temperature of 20 degrees C than they were at 5 degrees C. Generation of ammonia was slightly higher at the lower temperature. However, at both temperatures, practically all monochloramine was destroyed, and only insignificant amounts of ammonia were formed when a chlorine-to-ammonia ratio of 7:1 was applied. The described method is simple and cost-effective, because it eliminates the requirement of removal of ammonia, typically formed during the treatment of chloramines with activated carbon.