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1.
The goals of the study were to determine the effectiveness of a laboratory-scale biofilter on the removal of methyl tert-butyl ether (MTBE) and investigate the operating parameter effects on biofilter performance. The experimental results show that average MTBE removals of 53.6–93.2% were observed at loads of 2.5–20.1 gm?3 h?1 and an empty-bed residence time of three minutes, after continuous operation for four months throughout the biofilter acclimation period. After a one-day recovery period operation, the biofilter system recovered from the introduction of a shock load. More than 99% removal efficiencies were achieved for the inlet MTBE concentration at 50 ppmv and with the highest residence time. MTBE removals at the bottom section of the biofilter were consistently lower than for the top section, which was attributed to insufficient microorganism growth in the bottom section. The parameters estimated by using the Michaelis-Menten equation were 1.116 ± 0.51 ppmv s?1 for the maximum removal rate (V m ), and 26.38 ± 17.21 ppmv for the half-saturation constant (Ks), evaluated at the biofilter exit.  相似文献   

2.
The objective of this study was to test the effectiveness of a nitrate-rich nutrient solution and hydrogen peroxide (H2O2) to enhance in-situ microbial remediation of toluene in the unsaturated zone. Three sand-filled plots were tested in three phases (each phase lasting approximately 2 weeks). During the control phase, toluene was applied uniformly via sprinkler irrigation. Passive remediation was allowed to occur during this phase. A modified Hoagland nutrient solution, concentrated in 150 L of water, was tested during the second phase. The final phase involved addition of 230 moles of H2O2 in 150 L of water to increase the available oxygen needed for aerobic biodegradation. During the first phase, measured toluene concentrations in soil gas were reduced from 120 ppm to 25 ppm in 14 days. After the addition of nutrients during the second phase, concentrations were reduced from 90 ppm to about 8 ppm within 14 days, and for the third phase (H2O2), toluene concentrations were about 1 ppm after only 5 days. Initial results suggest that this method could be an effective means of remediating a contaminated site, directly after a BTEX spill, without the intrusiveness and high cost of other abatement technologies such as bioventing or soil-vapor extraction. However, further tests need to be completed to determine the effect of each of the BTEX components.  相似文献   

3.
A sampling programme was set up to measure 1,3-dichloropropene and methyl isothiocyanate in air in a region with intensive agricultural use of these soil fumigants. In two consecutive autumns, 6-hour air samples were taken at two locations in that region with charcoal tubes using automatic samplers. Most (81%) of the 6-hour concentrations of 1,3-dichloropropene measured in both years were below 3.2 μg m?3 and a few percent could not be measured with a detection limit of around 0.3 μg m?3. Only 4% of the 6-hour concentrations exceeded 10 μg m?3, almost all of which were measured at a location where a field just upwind of the measuring site had been treated. For methyl isothiocyanate, 73% of the 6-hour concentrations of both years could not be measured with a detection limit in the two years of 1 and 2 μg m?3, respectively. A small fraction (3%) of the concentrations were in the range of 3.2 to 10 μg m?3 and only 1% exceeded 10 μg m?3. The rates of emission of 1,3-dichloropropene and methyl isothiocyanate into air were estimated for weeks with many applications in the region studied. Using the PAL model, the concentration of fumigant in air at a receptor site was computed for representative fumigations at different upwind positions. The computed concentrations in air ranged up to 9.9 μg m?3 for 1,3-dichloropropene and up to 2.5 μg m?3 for methyl isothiocyanate.  相似文献   

4.
Eutrophication of ponds for agricultural use has begun to adversely affect rice production and the residential living environment in Japan. Cultivation of useful terrestrial and aquatic plant species in plant-bed filter ditches enables to treat domestic wastewater in addition to resource recycling and amenity functions. We evaluated the ability of several plant species, Italian ryegrass (Lolium multiflorum Lam.), hanana (Brassica campestris L. var.), African marigold (Tages erecta L.), sorghum (Sorghum vulgare Pers.), kenaf (Hibiscus cannabinus L.), papyrus (Cyperus papyrus L.), and reed (Phragmites communis Trin.), to remove nitrogen and phosphorus from polluted pond water whose N and P concentrations were much lower than those in domestic wastewater. Artificial pond water containing 2.5 mg L-1 of N and 0.5 mg L-1 of P was supplied to ditches at a loading rate of 1.1 g m-2 d-1 for N and 0.21 g m-2 d-1 for P. Italian ryegrass, papyrus, or kenaf in ditches removed N and P more effectively than other plants. The average removal rate of Italian ryegrass in ditches was 0.62 g m-2 d-1 for N and 0.10 g m-2 d-1 for P, that of papyrus 0.81 g m-2 d-1 for N and 0.15 g m-2 d-1 for P, and that of kenaf 0.73 g m-2 d-1 for N and 0.11 g m-2 d-1 for P. The influence of N and P concentrations on the removal rates of Italian ryegrass, papyrus, and kenaf was studied. Concentrations at a removal rate of zero were 0.2–0.3 mg L-1 for N and 0.01–0.03 mg L-l for P. At low concentrations, the plant removal rates increased sharply with the rise in the concentration. When N concentrations exceeded 0.3–0.6 mg L-1 and P concentrations 0.10–0.45 mg L-1, the removal rates were high and less affected by the concentration. It was considered that these plant species could be used most efficiently at the concentrations where removal rates are less restricted.  相似文献   

5.
Indoor air-borne loads of volatile organic compounds (VOCs) are usually significantly higher than those outdoors, and chronic exposures can cause health problems. Our previous laboratory studies have shown that the potted-plant microcosm, induced by an initial dose, can eliminate high air-borne VOC concentrations, the primary removal agents being potting-mix microorganisms, selected and maintained in the plant/root-zone microcosm. Our office field-study, reported in the preceding paper, showed that, when total VOC (TVOC) loads in reference offices (0 plants) rose above about 100 ppb, levels were generally reduced by up to 75% (to < 100 ppb) in offices with any one of three planting regimes. The results indicate the induction of the VOC removal mechanism at TVOC levels above a threshold of about 100 ppb. The aims of this laboratory dose-response study were to explore and analyse this response. Over from 5 to 9 days, doses of 0.2, 1.0, 10 and 100 ppm toluene and m-xylene were applied and replenished, singly and as mixtures, to potted-plants of the same two species used in the office study. The results confirmed the induction of the VOC removal response at the lowest test dosage, i.e in the middle of the TVOC range found in the offices, and showed that, with subsequent dosage increments, further stepwise induction occurred, with rate increases of several orders of magnitude. At each dosage, with induction, VOC concentrations could be reduced to below GC detection limits (< 20 ppb) within 24 h. A synergistic interaction was found with the binary mixtures, toluene accelerating m-xylene removal, at least at lower dosages. The results of these two studies together demonstrate that the potted-plant microcosm can provide an effective, self-regulating, sustainable bioremediation or phytoremediation system for VOC pollution in indoor air.  相似文献   

6.
Peat was employed as a biological filter material for the removal of hydrogen sulphide (H2> S) dimethyl sulphide (Me2S) and methyl mercaptan (MeSH) from odorous ventilation air. Removal of H2S was possible without the need to inoculate the filter material with oxidizing microbes whereas Me2S required inoculation for degradation. The removal of Me2S was decreased as a result of MeSH addition. Liming of the filter material, i.e., addition of calcium hydroxide, increased removal efficiency and activated the oxidation of H2S without any adaptation period. As a consequence of the poor Me2S removal efficiency of natural peat, a limed and inoculated biofilter was needed to purify mixtures of gases containing sulphur. The highest H2S load tested with limed but otherwise natural peat was 136 g-S m-3 day-1, yielding a 99 % reduction. The maximum Me2S elimination capacity with limed and inoculated peat was 175 g-S m-3day-1, but removal became unstable when the load exceeded 150 g-S m-3day-1. The maximum MeSH load tested was 107 g-S m-3day-1, yielding 98 % removal.  相似文献   

7.
The concentration of methyl bromide and bromide-ion was determined in irrigation water, drainage water and surface water during the leaching periods of two glasshouse soils after application of methyl bromide. The maximum concentrations in drainage water was 9.3 g m?3, and 72 g m?3 for bromideion. These concentrations were determined within 24 h after the start of leaching. During the leaching procedure fish mortality was observed in the ditches around one of the glasshouses. The average half-life for the decline of methyl bromide in surface water under field conditions was calculated to be 6.6 h at a water temperature of about 11°C. Methyl bromide and bromide-ion concentrations were determined by gas chromatography.  相似文献   

8.
Summary The influence of the photosynthesis-inhibiting herbicides Goltix and Sencor on growth and nitrogenase activity of Anabaena cylindrica and Nostoc muscorum was studied. The cyanobacteria were grown under N2-fixing photoautotrophic conditions. A. cylindrica was entirely inhibited even in the presence of low field concentrations (Sencor 10 ppm, Goltix 50 ppm). In contrast, Goltix (50 ppm and 100 ppm) and Sencor (10 ppm, 20 ppm, 50 ppm and 100 ppm) did not exert an inhibitory influence on growth and nitrogenase activity of N. muscorum. In the presence of normal field rates of the studied herbicides increased light intensities during incubation had no detrimental effect on N. muscorum. Only at 20 W/m2 light intensity did the higher concentrations of Sencor (50 ppm and 100 ppm) cause partial inhibition for the first 10–12 days, which was compensated during subsequent incubation. The delayed inhibitory effects caused by higher concentrations of Goltix (200 ppm and 500 ppm) are supposed to be due to degradation product(s). In the natural environment other species of cyanobacteria may occur which are able to tolerate photosynthesis-inhibiting herbicides.  相似文献   

9.
Extracts of particulate organic matter were examined for discrete rainfall events from metropolitan Los Angeles, California, using an in situ filtration technique. Filtration efficiency was 98 % for the collection of extractable organic C associated with particles having nominal diameters greater than 0m22 μm Organic background levels of less than 260 ng per sample were determined. Rainwater particle samples were extracted with repeated hexane and benzene: isopropanol (2: 1) solvent additions using ultrasonic agitation. Extract mixtures were quantified by high-resolution gas chromatography (HRGC) and were adjusted for component losses with perdeuterated recovery standards. Yields for the neutral fractions ranged from 130 to 669 μg with flux rates corresponding to 371 to 1097μg m?2 day?1. Aliquots of the neutral solvent extracts were derivatized with diazomethane to convert acidic hydroxy and carboxylic acid groups to the respective methyl ether and methyl ester analogs. This step produced increased yields of 8 to 188 %, and resulted in yields for the acid +neutral extracts that ranged from 374 to 8681μg with flux rates of 591 to 2343 μg m?2 day?1. Source identification was conducted by high-resolution gas chromatography/mass spectrometry (HRGC/MS) analyses. Molecular analyses indicated major anthropogenic contributions from petroleum and combustion sources, and for some samples, the significant input of microbial lipid components as well. Minor amounts of vascular plant waxes were also present in most cases. These mixed inputs of both anthropogenic and biogenic materials compared closely with previous source determinations for carbonaceous aerosol particles in the Los Angeles air basin.  相似文献   

10.
The biofilter system containing tire-derived rubber particle (TDRP) filter media was utilized to treat the odorous gas contaminant, hydrogen sulfide, in consideration of the economic advantage of reusing discarded tire materials and the high potential of TDRP media for biofilm attachment. The pilot-scale system having 0.38 m3 of bed volume operated with synthetic hydrogen sulfide gas on continuous basis from a range of 0.34 to 1.15 m3/min. This bioreactor system achieved over 94% removal efficiency at 20?C90 ppm of inlet H2S concentration while operating in 20?C67 s of empty bed retention time, indicating that overall effective operation was performed at mass loading rates of H2S ranging from 19.6 to 28.5 g H2S/(m3?h). It was apparent by the effectiveness of the system??s performance that this system had the capability to effectively remove hydrogen sulfide with high efficiency over a range of concentrations. A maximum elimination capacity was not found for the biofilter during this study, which tested loading rates between 0 and 30 g H2S/(m3?h).  相似文献   

11.
Seven experimental pilot-scale subsurface vertical-flow constructed wetlands were designed to assess the effect of plants [Typha latifolia L. (cattail)], intermittent artificial aeration and the use of polyhedron hollow polypropylene balls (PHPB) as part of the wetland substrate on nutrient removal from eutrophic Jinhe River water in Tianjin, China. During the entire running period, observations indicated that plants played a negligible role in chemical oxygen demand (COD) removal but significantly enhanced ammonia–nitrogen (NH4–N), nitrate–nitrogen (NO3–N) total nitrogen (TN), soluble reactive phosphorus (SRP) and total phosphorus (TP) removal. The introduction of intermittent artificial aeration and the presence of PHPB could both improve COD, NH4–N, TN, SRP and TP removal. Furthermore, aerated wetlands containing PHPB performed best; the following improvements were noted: 10.38 g COD/m2 day, 1.34 g NH4–N/m2 day, 1.04 g TN/m2 day, 0.07 g SRP/m2 day and 0.07 g TP/m2 day removal, if compared to non-aerated wetlands without PHPB being presented.  相似文献   

12.
Anthropogenic and biogenic high molecular weight (C12–C32) hydrocarbons (HC) were deposited from the atmosphere in association with both wet and dry deposition. Wet deposition generally removes HC at a faster rate (22 to 670 μg m?2 day?1) than dry deposition (4 to 189 μg m?2 day?1). However, due to longer periods during which dry deposition occurred, the removal of atmospheric HC by wet and dry deposition is almost equal during this sampling period. Atmospheric HC concentrations ranged from 0.8 to 4.1 μg m?3 and show no simple relationship to wet or dry deposition rates. Large variabilities in deposition rates for individual events were found, but long-term average deposition was relatively constant.  相似文献   

13.
Catalytic oxidation of benzene, toluene, and ethylbenzene (BTE) on virgin zeolite, nZnO-coated zeolite, with and without UV?+?O3, at 300 °C bed temperature was investigated using laboratory experiments. The coating was done at three weight ratios of Zn (estimated Zn content in nZnO) to zeolite (0.2:1.0, 0.5:10, 1.0:1.0). The coated adsorbents were examined by scanning electron microscopy, wavelength dispersive X-ray spectroscopy, and Brunauer Emmett Teller analyses. In the catalytic oxidation experiments, the adsorbents were first saturated with BTE by purging an air stream containing a mixture of BTE at 5 ppm each for 28 min. Introduction of UV?+?O3 on the coated 13X zeolite (0.5:1.0) bed improved the average removal efficiency (RE) of benzene, toluene, and ethylbenzene (with inlet concentration of 5 ppm each) to 68.7, 90.0, and 99.6%, respectively, from the corresponding values of 57.3, 79.9, and 98.5% when no UV?+?O3 was used. An increase in the coating weight ratio from 0.2:1.0 to 0.5:1.0 had produced a higher RE for benzene only, while a further increase to 1.0:1.0 witnessed a decrease in RE for all three compounds, and more for benzene. Avg RE of BTE decreased with the increase in their inlet concentrations, more significantly for an increase from 5 to 50 ppm and less noticeable for a further increase to 100 ppm. The final oxidation products and intermediate products in the outlet streams from the oxidation and thermal desorption were analyzed which showed predominant compositions of CO2 followed by BTE and some levels of CO and other volatile organic compounds.  相似文献   

14.
To develop a low cost and energy-saving wastewater treatment technique in combination with resource recycling and amenity functions, we constructed a plant bed filter ditch in which useful terrestrial and aquatic plants can be utilized for nitrogen and phosphorus removal from wastewater. Screening studies were conducted to evaluate and compare the effectiveness of 20 kinds of plant species which are economically important or exhibit on aesthetic value, including 13 terrestrial species, for domestic wastewater treatment. Artificial wastewater containing 20 mg L-1 of Nand 3.3 mg L-1 of P, was supplied to the ditch at the rate of about 1.41–2.08 g m-2 d-1 for N and 0.20–0.33 g m-2 d-1 for P. The experiments were performed in a glass house with windows opened from April to November. The ditches showing high Nand P removal rates were planted with plants which exhibited high biomass production rates. In the case of the papyrus ditch, Nand P removal rates exceeded 0.8 g m-2 d-1 for N and 0.15 g m-2 d-1 for P from late spring to autumn, in the case of the kenaf ditch and sorghum ditch, from summer to autumn and in the case of the Italian ryegrass ditch and barley ditch, in early spring. These findings indicated that efficient wastewater treatment can be performed consistently except in the winter season, by cultivating these plants in an appropriate combination in the ditches.  相似文献   

15.
Abstract

Electrical conductivity (EC) methods were tested using combinations of surrogate irrigation (SI) waters, soil salinity levels, and soils ground or retaining aggregates. The EC varied in low-salinity soils saturated with SI; the sum of the baseline ECe and SI EC were not equal to the measured EC. The baseline ECe and the SI EC sum in the high‐salinity ground soils were not equal to the any measured ECs. Salt‐removal potential from gypsiferous soils was examined using multiple extractions from the same soil sample. Calcium concentrations remained consistent over 14 extractions, whereas Na concentrations decreased. The ECe decreased from more than 8 dS m?1 in the initial extraction, to approximately 4 dS m?1 by the 9th to 14th extraction. Multiple extraction data suggest that improved leaching will not lower soil ECs to less than approximately 4 dS m?1 because of gypsum and calcite reservoirs in the tested soils.  相似文献   

16.
Biological treatment systems such as biofilters offer a potential alternative to the existing physicochemical techniques for the removal of volatile organic compounds from gaseous emissions. In this experimental work, continuous phase biofiltration of xylene vapors were performed in a laboratory scale compost biofilter that was inoculated with a xylene-acclimatized consortium. The performance was assessed by continuously monitoring the removal efficiency (RE) and elimination capacity (EC) of the biofilter at loading rates varying between 2–220 g?m?3?h?1. The steady-state removal efficiencies were maintained between 60% and 90% up to a loading rate of 80 g?m?3?h?1. The removal efficiency decreased significantly at loading rates higher than 100 g?m?3?h?1. The pressure drop values were consistently less and insignificant in affecting the performance of the system. The present study also focuses in evaluating the stability of biofilter during shut down, restart, and shock-loading operations. An immediate restoration of biological activity after few days of starvation indicated their capability to handle discontinuous treatment situations which is more common to industrial biofilters. The sensitiveness of the biofilm to withstand shock loads was tested by abruptly increasing/decreasing the loading rates between 9–55 g?m?3?h?1, where, removal efficiencies between 60–90% were achieved. These results prove the resilience of the biomass and the stability of the compost biofilter. Anew, results from kinetic analysis reveal that, steady-state xylene removal in the biofilter can be adequately represented by Michaelis–Menten type kinetics, and the kinetic constants namely, ECmax (120.4 g?m?3?h?1) and K s (2.21 g?m?3) were obtained.  相似文献   

17.
Arsenic and antimony concentrations in water and sediment samples collected from Prestea, a gold mining town in the Western Region of Ghana and its environs were studied. The concentrations of these elements were measured using instrumental neutron activation analysis (INAA). INAA was preferred to other modern analytical techniques because of its relatively higher selectivity, sensitivity and high precision. Beside its multi-elemental nature, INAA is very fast and thus presents a very good analytical tool for the determination of elemental concentrations in various samples including water and sediment. The samples were irradiated using a 30 kW tank-in-pool Ghana Research Reactor-1 (GHARR-1) operating at a thermal neutron flux of 5 × 1011 n s?1 cm?2. The samples were irradiated and counted without any chemical treatment. Elevated levels of As and Sb were found in both water and sediment. Generally, As and Sb concentrations in the water samples ranged from 0.90–8.25 ppm and 0.09–0.75 ppm respectively. These values far exceed the WHO recommended values for As and Sb in water, 0.01 ppm and 0.005 ppm respectively. The levels of As in sediment ranged from 942–10,200 ppm, and that of Sb was 8.5–90.4 ppm. Arsenic concentrations in both water and sediment were generally higher than Sb concentrations. This is, however, not surprising as arsenopyrites (FeAsS2) are among the major pathfinder minerals associated with gold mined from Ghana. Our results show that the study area is polluted as far as the levels of As and Sb in water and sediment are concerned.  相似文献   

18.
Characterization of carotenoids in juice of red navel orange (Cara Cara)   总被引：10，自引：0，他引：10  
High-performance liquid chromatography with photodiode array detection was applied for the separation and characterization of carotenoids from a red-fleshed navel orange (Cara Cara). Carotenoid pigments were extracted using hexane/acetone/ethanol and saponified using 10% methanolic potassium hydroxide. More than 29 carotenoid pigments were separated within 60 min using a ternary gradient (75% acetonitrile/25% methanol, methyl tert-butyl ether, and water) elution on a C(30) reversed-phase column. The presence of lycopene (3.9 +/- 1.1 ppm) and a relatively large percentage of beta-carotene were distinct differences in the pigment profile of this red navel orange juice as compared to the profile of standard navel orange juice. The juice color in the red navel was much deeper orange than that from navel orange; hue angle ranged from 84.1 to 89.4 for red navel compared to 98.2 to 100.5 for standard navel.  相似文献   

19.
This study compared the tolerance limits of selected bacterial (Bacillus licheniformis, Brevibacillus lactosporus and Pseudomonas putida) and protozoan (Aspidisca, Trachelophyllum and Peranema) species to V5+ in wastewater systems. The isolates were exposed to various concentrations of V5+ (from 10 to 240?ppm), and their tolerance limits to this heavy metal were assessed at different temperatures (25, 30, 35 and 40°C) and pHs (4, 6, 7, 8 and 10) for 5?days. Chemical oxygen demand (COD), dissolved oxygen (DO) and die-off rate of the isolates were measured using standard methods. The results indicated that test isolates were tolerant to V5+, with a gradual decrease in their colony/cell counts when V5+ concentration gradually increased. Bacterial species were found to be more significantly tolerant (MIC: 110?C230?ppm?V5+) to V5+ than protozoan species which showed an earlier total inhibition/die-off rate (100%) at 60?C100?ppm?V5+ (MIC) (p?<?0.001). P. putida was the most tolerant bacterial species (MIC: 230?ppm?V5+) and Aspidisca sp. the most sensitive protozoan species (MIC: 60?ppm?V5+). An increase in COD and DO removal was observed throughout the experimental period. The highest COD increase (up to 237.11%) and DO removal (almost 100%) were observed in mixed liquor inoculated with P. putida after exposure to 10?ppm?V5+. Changes in pH and temperature affected the tolerance limits of all isolates. This study suggests the use of these tolerant bacterial and protozoan species in the bioremediation of V5+ from domestic and industrial wastewater under the control of pH and temperature.  相似文献   

20.
To improve domestic wastewater treatment for total nitrogen (TN) removal, a full-scale constructed wetlands combining an artificially aerated vertical- (AVCW) and a horizontal-flow constructed wetland (HCW) was completed in July 2007. The system covered a total area of 7,610?m2. From 2 July 2007 to 7 August 2008, the treatment capacity was 2,076?m3?day?1 with an aeration quantity of 7,400?m3?day?1. The system effectively reduced the average annual output of BOD5 (52.0?%), NH4?CN (58.41?%), and TP (41.61?%), although the percentage reductions of other pollutants, including chemical oxygen demand (34.1?%), suspended solid (38.9?%), and TN (31.05?%) were lower. The purpose of the HCW was for denitrification of the effluent from the AVCW, and annual average of 34.27?% of NO3?CN was removed compared with the reading at the AVCW outlet. With hydraulic loading increased to 4,152?m3?day?1 from 9 September to 23 November 2007, the removal rate for NO3?CN from the HCW decreased substantially from 48.80 to 18.86?%. The total removal rates of NH4?CN showed significant positive correlation with DO content in the AVCW and with total TN removal rates for the combined system (P?<?0.05). The study indicated that, even with limited artificial aeration, nitrification was very effective for NH4?CN removal.  相似文献   

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