The gas phase addition of NOx to olefins

The addition of N₂O₅ to 1-hexene in synthetic air results in 1,2-hexanedioldinitrate and 2-hexanon-1-ol-nitrate as the main products and some -hydroxy-1-ol-nitrate. In the reaction with cyclohexene, cis/trans-1,2-cyclohexanediol-dinitrate and cyclohexene-1-on-2-ol-nitrate have been detected. The addition of NO₃ to isoprene produces 4-nitrato-3-methylbutenal-2. The reaction of NO₃ with methylenecyclohexane and sabinene in air results in 1-(methylnitrate) cyclohexane-1-ol and both epimers of 1-(methylnitrate)-4-(isopropyl) cyclo-hexene-4-ol, respectively. The main products of the addition of NO₃ to - and β-pinene were probably rearranged compounds of the limonene type: -pinene produces 1-(methyl)-2-(nitrato)-4-(2-propane-2-ol)-cyclohex-1-ene and β-pinene produces 1-(methylnitrate)-4-(2-propane-2-ol)cyclohex-1-ene. Other rearrangements give rise to a variety of nitrates and ketonitrates of structures as yet unknown in the - and β-pinene systems.

The probably particle-borne addition of NO₂ to -pinene, β-pinene and camphene in air produces 2-nitrolimonene, 7-nitrolimonene and nitrocamphene as the main reaction products.     

Processes involved in uptake and release of nitrogen dioxide from soil and building stones into the atmosphere

Atmospheric NO₂ was taken up by samples of various soils and building stones. The NO₂ uptake rate constants were highest in soil samples taken during the summer months. However, the NO₂ uptake rate constants of the soils and building stones were not significantly correlated with any of the following variables: moisture, pH, ammonium, nitrite, or nitrate. NO₂ uptake by soil and stone was not abolished by autoclaving indicating a chemical uptake process. NO₂ uptake by acidic and air-dry soils and stones resulted in nearly stoichiometric reduction of NO₂ to NO. This reduction was enhanced by the addition of ferrous iron and was further enhanced by incubation under 1 ppmv SO₂. The results suggest that NO₂ reduction may be coupled to oxidation of ferrous to ferric iron which may be reduced again by atmospheric SO₂ thus regenerating the ferrous iron content of the soil or stone. Conversion of NO₂ to NO was not observed in neutral or/and moist soils and stones. NO₂ was also taken up by purified and sterilized quartz sand moistend with water. This uptake was enhanced by addition of humic material but not by addition of bacteria which both had been extracted from genuine soil. Under most conditions, only uptake but no release of NO₂ was observed. However, NO₂ was released in air-dry soils that were heated to 45–65°C, or in ammonium-fertilized soil or stone that was drying up at room temperature. Under the latter conditions mimicking field practice, the NO₂ release reached rates that were similar to the NO release rates.     

Characteristics of roadside air pollution in Korean metropolitan city (Daegu) over last 5 to 6 years: temporal variations, standard exceedances, and dependence on meteorological conditions

The present study performed a roadside data analysis to provide baseline data for exploring associations between environmental exposure to four gaseous pollutants and health effects on residents living near roadways. The yearly roadside concentrations of CO and SO₂ showed a well-defined decreasing trend, whereas those of NO₂ and O₃ exhibited the reverse trend. In most cases, the diurnal trends of the roadside concentrations were well-defined for all seasons, plus the daytime concentrations were higher than the nighttime concentrations. In contrast to the other target pollutants, the daytime O₃ concentrations observed at the roadside sites were lower than those observed at the residential site, likely due to high-levels of fresh NO from traffic emissions that rapidly react with O₃, thereby reducing the O₃ roadside level. The Sunday roadside concentrations of CO, NO₂, and SO₂ were similar to or somewhat lower than the weekday concentrations. Conversely, for O_3, the Sunday roadside concentrations were similar to or somewhat higher than the weekday concentrations. The higher O₃ concentrations on Sunday may be due to the reduced titration from a decrease in NO_x emissions under VOC-limited conditions (low VOC/NO_x conditions). The monthly averages of O₃ concentrations exhibited the reverse seasonal variation to the other target compounds, with peak O₃ concentrations between April and June, and the second peak between August and October. It is also suggested that for O₃, the 8-h standard is more stringent than the 1-h standard, while for NO₂ and SO₂, the 1-h standard is more stringent than the 24-h standard. The multiple regression equations obtained from the relationship between the concentrations and five meteorological parameters indicated that the number and type of meteorological variables in the equations varied according to the pollutant, monitoring station, or season.     

Effect of La3+ on the activities of antioxidant enzymes in wheat seedlings under lead stress in solution culture

In order to improve the plant ability to resist lead stress, effect of 0.05 mg/l La(NO₃)₃ on the activities of catalase (CAT), superoxide dismutase (SOD), the level of malondialdehyde (MDA) in wheat seedlings under lead stress was studied. The effect of La³⁺ on plant growth, chlorophyll content in wheat seedlings after adding 0, 50, 100 mg/l Pb(NO₃)₃ to the nutrient solution for 12 days was observed. The plants were grown in nutrient solution in a strictly controlled climate growth room. Effects of La³⁺ (with La treatment) compared with check groups was evidently observed. The activities of SOD and CAT in root were enhanced 0.45–1.69 times and 33.20–77.77% respectively and MDA content was reduced 11.05–27.49% in root after treatments from the second day till the end of the experiment. The activities of SOD and CAT was found to be increased slightly (P<0.05) and MDA content decreased in shoot and root of wheat seedlings by La³⁺ under lead stress within five days after treatments compared with Pb1 and Pb2 groups. It was assumed that antioxidant enzymes was found to be increased by La(NO₃)₃, the antioxidant potential of the wheat seedlings to resist lead stress enhanced. It is suggested that La³⁺ could be used to resist lead stress at the beginning under stress while the stress was not so serious.     

Nitrogen trace gas emissions from a riparian ecosystem in southern Appalachia

In this paper, we present two years of seasonal nitric oxide (NO), ammonia (NH₃), and nitrous oxide (N₂O) trace gas fluxes measured in a recovering riparian zone with cattle excluded and adjacent riparian zone grazed by cattle. In the recovering riparian zone, average NO, NH₃, and N₂O fluxes were 5.8, 2.0, and 76.7 ng N m⁻² s⁻¹ (1.83, 0.63, and 24.19 kg N ha⁻¹ y⁻¹), respectively. Fluxes in the grazed riparian zone were larger, especially for NO and NH₃, measuring 9.1, 4.3, and 77.6 ng N m⁻² s⁻¹ (2.87, 1.35, and 24.50 kg N ha⁻¹ y⁻¹) for NO, NH₃, and N₂O, respectively. On average, N₂O accounted for greater than 85% of total trace gas flux in both the recovering and grazed riparian zones, though N₂O fluxes were highly variable temporally. In the recovering riparian zone, variability in seasonal average fluxes was explained by variability in soil nitrogen (N) concentrations. Nitric oxide flux was positively correlated with soil ammonium (NH₄⁺) concentration, while N₂O flux was positively correlated with soil nitrate (NO₃⁻) concentration. Ammonia flux was positively correlated with the ratio of NH₄⁺ to NO₃⁻. In the grazed riparian zone, average NH₃ and N₂O fluxes were not correlated with soil temperature, N concentrations, or moisture. This was likely due to high variability in soil microsite conditions related to cattle effects such as compaction and N input. Nitric oxide flux in the grazed riparian zone was positively correlated with soil temperature and NO₃⁻ concentration. Restoration appeared to significantly affect NO flux, which increased ≈600% during the first year following restoration and decreased during the second year to levels encountered at the onset of restoration. By comparing the ratio of total trace gas flux to soil N concentration, we show that the restored riparian zone is likely more efficient than the grazed riparian zone at diverting upper-soil N from the receiving stream to the atmosphere. This is likely due to the recovery of microbiological communities following changes in soil physical characteristics.     

Modified Fenton reaction for trichlorophenol dechlorination by enzymatically generated H2O2 and gluconic acid chelate

Glucose oxidase is a well-known enzyme that catalyzes the oxidation of β-d-glucose to produce gluconic acid and hydrogen peroxide. Fenton reaction is a powerful oxidation technology used for the oxidation of groundwater pollutants. For the application of Fenton reaction in groundwater remediation, successful operation of Fenton reaction near neutral pH, and on-site generation of both H₂O₂ and chelate will be beneficial. The focus of this experimental study was to couple the glucose oxidation reaction with chelate-based Fenton reaction. The idea was to use the hydrogen peroxide and chelate gluconic acid generated during glucose oxidation for the dechlorination of 2,4,6-trichlorophenol (TCP) by Fenton reaction. The oxidation of glucose was achieved using the enzyme in free and immobilized forms. The rate of production of hydrogen peroxide was determined for each system, and was used to estimate the time required for complete consumption of glucose during the process, thus avoiding any traces of glucose in the Fenton reaction. In the case of free enzyme reaction, separation of the enzyme was achieved using an ultrafiltration membrane before initiating the Fenton reaction. The oxidation of TCP by Fenton reaction was performed at varying ratios of gluconic acid/Fe, and its effect on the decomposition of TCP and H₂O₂ was studied. TCP degradation was studied both in terms of parent compound degradation and free chloride generation.     

Nitration and hydroxylation of benzene in the presence of nitrite/nitrous acid in aqueous solution

This paper studies the nitration and hydroxylation of benzene in the presence of nitrite/nitrous acid in aqueous solution, both in the dark upon addition of hydrogen peroxide and under 360 nm irradiation. In both cases the detected transformation intermediates were phenol (P), nitrobenzene (NB), 2-nitrophenol (2NP) and 4-nitrophenol (4NP). P and NB directly form from benzene, and the initial formation rate of P is at least an order of magnitude higher than that of NB. In our experiments nitrophenols arise from P nitration, as can be inferred by their time evolution and isomer ratio (2NP:4NP=60:40, 3NP below detection limit). Nitrophenols may also form upon hydroxylation of NB, but in a different ratio (2NP:3NP:4NP=45:30:25). The detection of 3NP is thus a marker for the hydroxylation of NB, since this isomer is not formed in P nitration processes. The formation rates of P and NB increase with decreasing pH, both in the presence of HNO₂ + H₂O₂ in the dark (which produce HOONO) and in the presence of NO₂⁻/HNO₂ under irradiation. In the former case the pH dependence reflects the formation rate of HOONO. In the case of the irradiation experiments the pH effect can be accounted for by the higher molar absorbivity and photolysis quantum yield of nitrous acid when compared with nitrite. Interestingly, benzene does not react with HNO₂ alone in the dark. An important feature of benzene nitration in the presence of NO₂⁻/HNO₂ under irradiation is that the process is not inhibited by the addition of hydroxyl scavengers, differently from the case of phenol nitration. This finding indicates that nitrite irradiation might lead to the nitration of certain aromatic compounds in natural waters even in the presence of natural hydroxyl scavenging agents, which are usually thought to limit the environmental role of many photochemical processes.     

Preparation of agricultural residue anion exchangers and its nitrate maximum adsorption capacity

Anion exchangers were prepared from different agricultural residues (AR) after reaction with epichlorohydrin and dimethylamine in the presence of pyridine and N,N-dimethylformamide (EDM method). Agricultural residues anion exchangers (AR-AE) produced by the EDM method were inexpensive and showed almost the same NO₃⁻ removal capacities as Amberlite IRA-900. AR-AE produced from AR with higher hemicelluloses, lignin, ash and extractive contents resulted in the lower yields. Sugarcane bagasse with the highest -cellulose contents of 51.2% had the highest yield (225%) and lowest preparation cost. The highest maximum adsorption capacity (Q_max) for nitrate was obtained from rice hull (1.21 mmol g⁻¹) and pine bark natural exchangers (1.06 mmol g⁻¹). No correlation was found between Q_max and -cellulose content in the original AR. AR-AE produced from different AR demonstrated comparable Q_max due to the removal of non-active compounds such as extractives, lignin and hemicelluloses from AR during the preparation process. Similar preparation from pure cellulose and pure alkaline lignin demonstrated that the EDM method could not produce anion exchangers from pure lignin due to its solubilization after the reaction with epichlorohydrin.     

A novel ortho-dehalogenation reaction of 2-chlorocinnamic acid catalyzed by the pink yeast Rhodotorula rubra Y-1529

In the present study, a resting cells suspension of Rhodotorula rubra Y-1529 was shown to have the capacity to perform an ortho-dehalogenation reaction on 2-chlorocinnamic acid. The results from the biodegradation of U-[¹⁴C]benzoic acid, cinnamic acid, 3-chlorocinnamic acid and 4-chlorocinnamic acid suggest that the first step of the ortho-dehalogenation reaction occurred during the oxidation of the unsaturated C3 side chain of 2-chlorocinnamic acid to 2-chlorobenzoic acid. None of the 2-chlorobenzoic acid was found in the biodegradation system, suggesting that this step was a highly regulated step. After the side-chain oxidation reaction, the hydroxylation of the benzene ring was determined to be at the para-position first, followed by the meta-position. The occurrence of 3:4-position ring fission reactions and the production of the final product, CO₂, was proven by the biodegradation of U-[¹⁴C] benzoic acid. This oxidative dehalogenation reaction catalyzed by R. rubra was found to be regiospecific for 2-chlorocinnamic acid; the chloride ion was probably removed after the ring fission reaction. A pathway of the ortho-dehalogenation reaction of 2-chlorocinnamic acid catalyzed by R. rubra was proposed based on these data.     

Study on the formation and transport of ozone in relation to the air quality management and vegetation protection in Tenerife (Canary Islands)

An experimental study on the formation and transport of ozone in ambient air was performed in Tenerife (Canary Islands) in order to investigate the processes affecting ozone levels and air quality. The special features of Tenerife (prevalence of the trade wind pattern (NE), orography and the specific location of the local ozone sources) permit to quantify the role of the ‘long-range transport from northern latitudes' versus the ‘formation and transport of ozone downwind of the main urban areas' of Tenerife. Levels of O₃, NO₂ and O_X were monitored in different types of environments to achieve this purpose. The results showed that: (1) upwind of the urban areas ozone is mainly transported from the ocean by trade winds, (2) local ozone titration (by NO) and ozone replenishment from the ocean are the main causes of ozone variations in urban and suburban areas, and (3) photochemical ozone production occurs downwind of the urban areas. Photochemical production causes daylight O₃ and O_X levels downwind of urban areas to be frequently (60% and 35% days/year, respectively) higher than upwind of the urban sites (O₃ and O_X excess frequently in the range 5–20 ppbv). Due to the above processes, different daily ozone cycles occur in short distances (<30 km), with maximum O₃ levels during daylight or night depending on the site. Ozone phytotoxicity was assessed by calculating the AOT40 index upwind and downwind of the main urban areas. The critical value for the 5-day-AOT40 index was simultaneously exceeded at the two sites (few times/year) during long-range transport events. During the additional exceedances of the critical value downwind of the urban area, relatively high 5-day-AOT40 values were recorded upwind of the urban site. Thus, long-range transport from northern latitudes may produce relatively high 5-days-AOT40 levels in the oceanic boundary layer. These results are important for the protection of the large number of endemic plants in the Canaries. The conceptual model discussed in this study may be qualitatively applied to other islands which possess features similar to those of Tenerife.     

Fenton''s type reaction and chemical pretreatment of PCBs

This study evaluates the effects of Fenton's reagent (FR) on the rate and extent of the oxidative degradation of individual mono, di-, tri- and tetrachlorobiphenyls in the commercial mixture DELOR 103, equivalent to AROCLOR 1248. The oxidation effect of FR strongly increased with increasing the molar ratio of Fe²⁺/H₂O₂. The most effective oxidation of DELOR 103 (10 μg.ml⁻¹) was achieved in a solution containing 1M H₂O₂ and 1 mM Fe²⁺. The FR elimination rate constants of PCB congeners decrease with increasing number of chlorine substituents in the biphenyl molecule and show a good correlation with the values of molecular weights of the PCB congeners and their 1-octanol/water partition coefficients.     

Model reactor for photocatalytic degradation of persistent chemicals in ponds and waste water

A laboratory scale flow-through model reactor for the degradation of persistent chemicals using titanium dioxide (TiO₂) as photocatalyst immobilized on glass beads is presented. In the test system with a volume of 18 L contaminated water is pumped to the upper part of the floating reactor and flows over the coated beads which are exposed to UV-radiation. The degradation of two dyes of different persistance was investigated. Primary degradation of methylene blue did not fit a first order kinetic due to coincident adsorption onto the photocatalyst and direct photolysis, resulting in a half-life of 6 h. A filtrate of a green algae suspension accelerated the colour removal. In contrast, reactive red 2 was degraded only by photocatalysis; neither adsorption nor direct photolysis led to a colour removal. The course of primary degradation followed a first order kinetic with a half-life of 18 h and a rate constant of 0.04 h⁻¹. Analysis of the degradation products indicated mineralization by detection of NO₂⁻ and NO₃⁻, accompanied by a decrease of pH and an increase of conductivity. A successful adaptation of the model reactor (scale 1:10) to dimensions required for surface waters and waste water treatment plants would be a costefficient and environmentally sustainable application of photocatalysis for the treatment of industrially polluted water and could be of relevance for third world contries, particularly those favoured by high solar radiation.     

Reaction pathways of dimethyl phthalate degradation in TiO2-UV-O2 and TiO2-UV-Fe(VI) systems

The photocatalytic degradation of dimethyl phthalate (DMP) in aqueous TiO₂ suspension under UV illumination has been investigated using oxygen (O₂) and ferrate (Fe(VI)) as electron acceptors. The experiments demonstrated that Fe(VI) was a more effective electron acceptor than O₂ for scavenging the conduction band electrons from the surface of the catalyst. Some major intermediate products from DMP degradation were identified by HPLC and GC/MS analyses. The analytical results identified dimethyl 3-hydroxyphthalate and dimethyl 2-hydroxyphthalate as the two main intermediate products from the DMP degradation in the TiO₂–UV–O₂ system, while in contrast phthalic acid was found to be the main intermediate product in the TiO₂–UV–Fe(VI) system. These findings indicate that DMP degradation in the TiO₂–UV–O₂ and TiO₂–UV–Fe(VI) systems followed different reaction pathways. An electron spin resonance analysis confirmed that hydroxyl radicals existed in the TiO₂–UV–O₂ reaction system and an unknown radical species (most likely an iron–oxo species) is suspected to exist in the TiO₂–UV–Fe(VI) reaction system. Two pathway schemes of DMP degradation in the TiO₂–UV–O₂ and TiO₂–UV–Fe(VI) reaction systems are proposed. It is believed that the radicals formed in the TiO₂–UV–O₂ reaction system preferably attack the aromatic ring of the DMP, while in contrast the radicals formed in the TiO₂–UV–Fe(VI) reaction systems attack the alkyl chain of DMP.     

Decomposition of chlorinated dioxins, odourous compounds and NOx from MSW incineraton plant by oxidizing catalyst

An experiment was carried out to decompose chlorinated dioxins (PCDDs, PCDFs) Chlorobenzenes, NOx and odourous compounds (H₂S, CH₄S, C₂H₆S₂, C₈H₈, C₂H₆S, C₂H₄O, NH₃) simultaneously using a catalyst in the MSW incineration plant. The experiments were conducted at temperatures from 200°C to 400°C and from 3000h⁻¹ to 6000h⁻¹ at space velocity. A catalyst containing V₂O₅ and WO₃ on the basis of TiO₂ is used, an oxidizing catalyst of the honeycomb type. The average decomposition efficiencis were 95%, 98%, 92% for PCDDs(48CDDs), PCDFs(48CDFs) and Chlorobenzenes(36CLBs) at a reaction temperature of 350°C and a space velocity of 3000h⁻¹, more than 90% for NOx at a reactiont temperature of 300°C and more than 80% for odourous compounds at the reaction temperature of 300°C and a space velocity of 6000h⁻¹. All those compounds were decomposed successfully with increasing contact time and surface. The rate-determing step was the chemical reaction of catalyst surface.     

Photochemical oxidation of reduced sulfur compounds in an urban location based on short time monitoring data

This study examines the oxidation of reduced sulfur compounds (RSCs) in urban ambient air. The photochemical conversions of RSC (such as DMS, CS₂, H₂S, DMDS, and CH₃SH) to a further oxidized form (e.g., SO₂, MSA, and H₂SO₄) were assessed using a photochemical box model. For our model simulation of RSC oxidation, measurements were taken at an urban monitoring station in Seoul, Korea (37.6° N, 127° E) during three separate time periods (e.g., Sept. 17–18, Oct. 23, and Oct. 27–28, 2003). The results indicate that DMS and H₂S were the dominant RSCs with concentrations of 370 ± 140 and 110 ± 60 pptv, respectively. The photochemical conversion of DMDS to SO₂ was found to occur more efficiently than other RSCs. The overall results of our study suggest that photochemical conversion of RSCs accounted for less than 15% of the observed SO₂ during the measurement period. The SO₂ production from DMS oxidation (mainly by the reaction with OH) was found to be affected primarily by the abstraction channel due to high NO_x levels during the experimental conditions.     

Reaction of arsenic vapor species with fly ash compounds: kinetics and speciation of the reaction with calcium silicates

In coal combustion systems, the partitioning of arsenic between the vapor and solid phases is determined by the interaction of arsenic vapors with fly ash compounds under post-combustion conditions. This partitioning is affected by gas–solid reactions between the calcium components of the ash particles and arsenic vapors. In this study, bench scale experiments were conducted with calcium compounds typical of coal-derived fly ash to determine product formation, the extent of reaction and reaction rates when contacted by arsenic oxide vapors. Experiments conducted with arsenic trioxide (As₄O_6(g)) vapors in contact with calcium oxide, di-calcium silicate and mono-calcium silicate over the temperature range 600–1000 °C indicated that these solids were capable of reacting with arsenic vapor species in both air and nitrogen. Calcium arsenate was the observed reaction product in all the samples analyzed. Maximum capture of arsenic occurred at 1000 °C with calcium oxide being the most effective of the three solids over the range of temperatures studied. Using a shrinking core model for a first order reaction and the results from intrinsic kinetic experiments conducted in air, the reaction rate constants were found to be 1.4×10⁻³exp(−2776/T) m/s for calcium oxide particles, 7.2×10⁻³exp(−3367/T) m/s for di-calcium silicate particles and 5.5×10⁻³exp(−3607/T) m/s for mono-calcium silicate particles. These results therefore suggest that any calcium present in fly ash can react with arsenic vapor and capture the metal in water-insoluble forms of the less hazardous As(V) oxidation state.     

Radiolysis of aqueous 4-nitrophenol solution with Al2O3 or TiO2 nanoparticles

Aqueous 4-nitrophenol solutions containing TiO₂ or Al₂O₃ nanoparticles were irradiated with electron beam. 4-nitrophenol was decomposed by the ionizing radiation process in the absence of the nanoparticles. The addition of TiO₂ or Al₂O₃ (2 g l⁻¹) before irradiation improved the removal of 4-nitrophenol, total organic carbon (TOC) but also nitrogen (TN). To identify the origin of the loss (catalysis or simply adsorption), TiO₂ or Al₂O₃ nanoparticles were added after irradiation. Experiments show that the effect of the presence of TiO₂ or Al₂O₃ during irradiation is just due to adsorption.     

The binding of three PCB congeners to dissolved organic carbon in freshwaters

The binding of three polychlorinated biphenyl (PCB) congeners to natural levels of dissolved organic carbon (DOC) was measured in 12 lakes and streams using Sep-Pak C₁₈ columns. The association coefficients calculated on the basis of DOC (i.e. K_DOC mL/g C), varied by over an order of magnitude among the different freshwaters and ranged between 2.05 × 10² and 8.86 × 10³ mL/g C for PCB 52 and 1.03 × 10⁴ and 1.70 × 10⁵ mL/g C for PCB 153. In general, there were no significant correlations (p > 0.05) between the K_DOC values and various chemical parameters in the study lakes and streams.

A relationship was derived between the fraction of bound PCB and the octanol-water partition coefficient. While this relationship explained almost 50% of the variation in the observed data, it is apparent that other factors influence K_DOC values and that in natural freshwaters, only a small fraction of the DOC is involved in the binding of PCBs and other hydrophobic pollutants.     

Biological elimination of H2S and NH3 from wastegases by biofilter packed with immobilized heterotrophic bacteria

Biotreatment of various ratios of H₂S and NH₃ gas mixtures was studied using the biofilters, packed with co-immobilized cells (Arthrobacter oxydans CH8 for NH₃ and Pseudomonas putida CH11 for H₂S). Extensive tests to determine removal characteristics, removal efficiency, removal kinetics, and pressure drops of the biofilters were performed. To estimate the largest allowable inlet concentration, a prediction model was also employed. Greater than 95% and 90% removal efficiencies were observed for NH₃ and H₂S, respectively, irrespective of the ratios of H₂S and NH₃ gas mixtures. The results showed that H₂S removal of the biofilter was significantly affected by high inlet concentrations of H₂S and NH₃. As high H₂S concentration was an inhibitory substrate for the growth of heterotrophic sulfur-oxidizing bacteria, the activity of H₂S oxidation was thus inhibited. In the case of high NH₃ concentration, the poor H₂S removal efficiency might be attributed to the acidification of the biofilter. The phenomenon was caused by acidic metabolite accumulation of NH₃. Through kinetic analysis, the presence of NH₃ did not hinder the NH₃ removal, but a high H₂S concentration would result in low removal efficiency. Conversely, H₂S of adequate concentrations would favor the removal of incoming NH₃. The results also indicated that maximum inlet concentrations (model-estimated) agreed well with the experimental values for space velocities of 50–150 h⁻¹. Hence, the results would be used as the guideline for the design and operation of biofilters.     

A combined plasma photolysis (CPP) method for removal of CS2 from gas streams at atmospheric pressure

A combined plasma photolysis (CPP) reactor that utilizes a dielectric barrier discharge (DBD) plasma and 207 nm UV radiation from discharge-driven KrBr^* excimers was designed and constructed. Gas streams containing CS₂ were treated with stand-alone DBD and CPP at atmospheric pressure. In comparison to DBD, CPP greatly enhanced the removal efficiency at the same applied voltage, waste gas concentration and gas residence time. Thus the applied voltage could be reduced to a certain extent in the plasma processing of industrial wastes. Influences of the KrBr^* radiation, inlet CS₂ concentration and gas residence time on CS₂ removal by CPP were also studied. In addition, the likely reaction mechanisms for the removal of CS₂ by CPP are suggested based on the byproducts analysis. The enhanced removal efficiency and reaction mechanisms implied that the CPP process would probably be suitable for the removal of a large number of gaseous pollutants.