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1.
Different pelagic areas of the Mediterranean Sea have been investigated in order to quantify physical and biological mixing processes in deep sea sediments. Herein, results of eleven sediment cores sampled at different deep areas (> 2000 m) of the Western and Eastern Mediterranean Sea are presented.210Pbxs and 137Cs vertical profiles, together with 14C dating, are used to identify the main processes characterising the different areas and, finally, controlling mixing depths (SML) and bioturbation coefficients (Db). Radionuclide vertical profiles and inventories indicate that bioturbation processes are the dominant processes responsible for sediment reworking in deep sea environments.Results show significant differences in sediment mixing depths and bioturbation coefficients among areas of the Mediterranean Sea characterised by different trophic regimes. In particular, in the Oran Rise area, where the Almeria-Oran Front induces frequent phytoplankton blooms, we calculate the highest values of sediment mixing layers (13 cm) and bioturbation coefficients (0.187 cm2 yr−1), and the highest values of 210Pbxs and 137Cs inventories. Intermediate values of SML and Db (~ 6 cm and ~ 0.040 cm2 yr−1, respectively) characterise the mesothrophic Algero-Balearic basin, while in the Southern Tyrrhenian Sea mixing parameters (SML of 3 cm and Db of 0.011 cm2 yr−1) are similar to those calculated for the oligotrophic Eastern Mediterranean (SML of 2 cm and Db of ~ 0.005 cm2 yr−1).  相似文献   

2.
To investigate the potential role of ammonia in ion chemistry of PM2.5 aerosol, measurements of PM2.5 (particulate matter having aerodynamic diameter < 2.5 µm) along with its ionic speciation and gaseous pollutants (sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3) and nitric acid (HNO3)) were undertaken in two seasons (summer and winter) of 2007-2008 at four sampling sites in Kanpur, an urban-industrial city in the Ganga basin, India. Mean concentrations of water-soluble ions were observed in the following order (i) summer: SO42− (26.3 µg m− 3) > NO3 (16.8) > NH4+ (15.1) > Ca2+ (4.1) > Na+ (2.4) > K+ (2.1 µg m− 3) and (ii) winter: SO42− (28.9 µg m− 3) > NO3 (23.0) > NH4+ (16.4) > Ca2+(3.4) > K+(3.3) > Na+ (3.2 µg m− 3). The mean molar ratio of NH4+ to SO42− was 2.8 ± 0.6 (mostly >2), indicated abundance of NH3 to neutralize H2SO4. The excess of NH4+ was inferred to be associated with NO3 and Cl. Higher sulfur conversion ratio (Fs: 58%) than nitrogen conversion ratio (Fn: 39%) indicated that SO42− was the preferred secondary species to NO3. The charge balance for the ion chemistry of PM2.5 revealed that compounds formed from ammonia as precursor are (NH4)2SO4, NH4NO3 and NH4Cl. This study conclusively established that while there are higher contributions of NH4+, SO42− to PM2.5 in summer but for nitrates (in particulate phase), it is the winter season, which is critical because of low temperatures that drives the reaction between ammonia and HNO3 in forward direction for enhanced nitrate formation. In summary, inorganic secondary aerosol formation accounted for 30% mass of PM2.5 and any particulate control strategy should include optimal control of primary precursor gases including ammonia.  相似文献   

3.
Biocide-containing anti-fouling paints are regulated and approved according to the added active ingredients, such as Cu. Biocide-free paints are considered to be less environmentally damaging and do not need an approval. Zn, a common ingredient in paints with the potential of causing adverse effects has received only minor attention. Laboratory experiments were conducted in artificial brackish seawater (ASW) and natural brackish seawater (NSW) to quantify release rates of Cu and Zn from biocide-containing and biocide-free labeled eroding anti-fouling paints used on commercial vessels as well as leisure boats. In addition, organisms from three trophic levels, the crustacean Nitocra spinipes, the macroalga Ceramium tenuicorne and the bacteria Vibrio fischeri, were exposed to Cu and Zn to determine the toxicity of these metals. The release rate of Cu in NSW was higher from the paints for professional use (3.2-3.6 µg cm2 d− 1) than from the biocide leaching leisure boat paint (1.1 µg cm2 d− 1). Biocide-free paints did leach considerably more Zn (4.4-8.2 µg cm2 d− 1) than biocide-containing leisure boat paint (3.0 µg cm2 d− 1) and ship paints (0.7-2.0 µg cm2 d− 1). In ASW the release rates of both metals were notably higher than in NSW for most tested paints. The macroalga was the most sensitive species to both Cu (EC50 = 6.4 µg l− 1) and Zn (EC50 = 25 µg l− 1) compared to the crustacean (Cu, LC50 = 2000 µg l− 1 Zn, LC50 = 890 µg l− 1), and the bacteria (Cu, EC50 = 800 µg l− 1 and Zn, EC50 = 2000 µg l− 1). The results suggest that the amounts of Zn and Cu leached from anti-fouling paints may attain toxic concentrations in areas with high boat density. To fully account for potential ecological risk associated with anti-fouling paints, Zn as well as active ingredients should be considered in the regulatory process.  相似文献   

4.
Rhizosphere acidification of faba bean, soybean and maize   总被引:2,自引:0,他引:2  
Interspecific facilitation on phosphorus uptake was observed in faba bean/maize intercropping systems in previous studies. The mechanism behind this, however, remained unknown. Under nitrate supply, the difference in rhizosphere acidification potential was studied by directly measuring pH of the solution and by visualizing and quantifying proton efflux of roots between faba bean (Vicia faba L. cv. Lincan No.5), soybean (Glycine max L. cv. Zhonghuang No. 17) and maize (Zea mays L. cv. Zhongdan No.2) in monoculture and intercrop, supplied without or with 0.2 mmol L− 1 P as KH2PO4. The pH of the nutrient solution grown faba bean was lower than initial pH of 6.0 from day 1 to day 22 under P deficiency, whereas the pH of the solution with maize was declined from day 13 after treatment. Growing soybean increased solution pH irrespective of P supply. Under P deficiency, the proton efflux of faba bean both total (315.25 nmol h− 1 plant− 1) and specific proton efflux (0.47 nmol h− 1 cm− 1) was greater than that those of soybean (21.80 nmol h− 1 plant− 1 and 0.05 nmol h− 1 cm− 1, respectively). Faba bean had much more ability of rhizosphere acidification than soybean and maize. The result can explain partly why faba bean utilizes sparingly soluble P more effectively than soybean and maize do, and has an important implication in understanding the mechanism behind interspecific facilitation on P uptake by intercropped species.  相似文献   

5.
Experiments were performed to study the airflow rates (AFRs) in a naturally ventilated building through four summer seasons and three winter seasons. The AFRs were determined using heat balance (HB), tracer gas technique (TGT) and CO2-balance as averages of the values of all experiments carried out through the different seasons. The statistical analyses were correlation analysis, regression model and t-test. Continuous measurements of gaseous concentrations (NH3, CH4, CO2 and N2O) and temperatures inside and outside the building were performed. The HB showed slightly acceptable results through summer seasons and unsatisfactory results through winter seasons. The CO2-balance showed unexpected high differences to the other methods in some cases. The TGT showed reliable results compared to HB and CO2-balance. The AFRs, subject to TGT, were 0.12 m3 s−1 m−2, 1.15 m3 s−1 cow−1, 0.88 m3 s−1 LU−1, 56 h−1, 395 m3 s−1 and 470 kg s−1 through summer seasons, and 0.08 m3 s−1 m−2, 0.83 m3 s−1 cow−1, 0.64 m3 s−1 LU−1 39 h−1, 275 m3 s−1 and 328 kg s−1 through winter seasons. The AFRs are not independent values, rather they were estimated for specific reference values, which are: area, cow and LU as well as rates. The emission rates through summer seasons, subject to TGT, were 9.4, 40, 3538 and 2.3 g h−1 cow−1; and through winter seasons were 4.8, 19, 2332 and 2.6 g h−1 cow−1, for NH3, CH4, CO2 and N2O, respectively.  相似文献   

6.
Gross CO2 and CH4 emissions (degassing and diffusion from the reservoir) and the carbon balance were assessed in 2009-2010 in two Southeast Asian sub-tropical reservoirs: the Nam Ngum and Nam Leuk Reservoirs (Lao PDR). These two reservoirs are within the same climatic area but differ mainly in age, size, residence time and initial biomass stock. The Nam Leuk Reservoir was impounded in 1999 after partial vegetation clearance and burning. However, GHG emissions are still significant 10 years after impoundment. CH4 diffusive flux ranged from 0.8 (January 2010) to 11.9 mmol m− 2 d− 1 (April 2009) and CO2 diffusive flux ranged from - 10.6 (October 2009) to 38.2 mmol m− 2 d− 1 (April 2009). These values are comparable to other tropical reservoirs. Moreover, degassing fluxes at the outlet of the powerhouse downstream of the turbines were very low. The tentative annual carbon balance calculation indicates that this reservoir was a carbon source with an annual carbon export (atmosphere + downstream river) of about 2.2 ± 1.0 GgC yr− 1.The Nam Ngum Reservoir was impounded in 1971 without any significant biomass removal. Diffusive and degassing CO2 and CH4 fluxes were lower than for other tropical reservoirs. Particularly, CO2 diffusive fluxes were always negative with values ranging from - 21.2 (April 2009) to - 2.7 mmol m−2 d−1 (January 2010). CH4 diffusive flux ranged from 0.1 (October 2009) to 0.6 mmol m−2 d−1 (April 2009) and no degassing downstream of the turbines was measured. As a consequence of these low values, the reservoir was a carbon sink with an estimated annual uptake of - 53 ± 35 GgC yr−1.  相似文献   

7.
In the present study the degradation kinetics and mineralization of diclofenac (DCF) by the TiO2 photocatalysis were investigated in terms of UV absorbance and COD measurements for a wide range of initial DCF concentrations (5-80 mg L−1) and photocatalyst loadings (0.2-1.6 g TiO2 L−1) in a batch reactor system. A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Artemia salina) was performed to evaluate the potential detoxification of DCF. A pseudo-first-order kinetic model was found to fit well most of the experimental data, while at high initial DCF concentrations (40 and 80 mg L−1) and at 1.6 g TiO2 L−1 photocatalyst loading a second-order kinetic model was found to fit the data better. The toxicity of the treated DCF samples on D. magna and P. subcapitata varied during the oxidation, probably due to the formation of some intermediate products more toxic than DCF. Unicellular freshwater algae was found to be very sensitive to the treated samples as well as the results from D. magna test were consistent to those of algae tests. A. salina was not found to be sensitive under the investigated conditions. Finally, UV absorbance analysis were found to be an useful tool for a fast and easy to perform measurement to get preliminary information on the organic intermediates that are formed during oxidation and also on their disappearance rate.  相似文献   

8.
Vanadium (V) when ingested from drinking water in high concentrations (> 15 μg L− 1) is a potential health risk and is on track to becoming a regulated contaminant. High concentrations of V have been documented in lead corrosion by-products as Pb5(V5+O4)3Cl (vanadinite) which, in natural deposits is associated with iron oxides/oxyhydroxides, phases common in iron pipe corrosion by-products. The extent of potential reservoirs of V in iron corrosion by-products, its speciation, and mechanism of inclusion however are unknown. The aim of this study is to assess these parameters in iron corrosion by-products, implementing synchrotron-based μ-XRF mapping and μ-XANES along with traditional physiochemical characterization. The morphologies, mineralogies, and chemistry of the samples studied are superficially similar to typical iron corrosion by-products. However, we found V present as discrete grains of Pb5(V5+O4)3Cl likely embedded in the surface regions of the iron corrosion by-products. Concentrations of V observed in bulk XRF analysis ranged from 35 to 899 mg kg− 1. We calculate that even in pipes with iron corrosion by-products with low V concentration, 100 mg kg− 1, as little as 0.0027% of a 0.1-cm thick X 100-cm long section of that corrosion by-product needs to be disturbed to increase V concentrations in the drinking water at the tap to levels well above the 15 μg L− 1 notification level set by the State of California and could adversely impact human health. In addition, it is likely that large reservoirs of V are associated with iron corrosion by-products in unlined cast iron mains and service branches in numerous drinking water distribution systems.  相似文献   

9.
We analyzed benthic fluxes of inorganic nitrogen, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates in hypolimnetic sediments of lowland lakes. Two neighbouring mesotrophic (Ca' Stanga; CS) and hypertrophic (Lago Verde; LV) lakes, which originated from sand and gravel mining, were considered. Lakes are affected by high nitrate loads (0.2-0.7 mM) and different organic loads. Oxygen consumption, dissolved inorganic carbon, methane and nitrogen fluxes, denitrification and DNRA were measured under summer thermal stratification and late winter overturn.Hypolimnetic sediments of CS were a net sink of dissolved inorganic nitrogen (−3.5 to −4.7 mmol m−2 d−1) in both seasons due to high nitrate consumption. On the contrary, LV sediments turned from being a net sink during winter overturn (−3.5 mmol m−2 d−1) to a net source of dissolved inorganic nitrogen under summer conditions (8.1 mmol m−2 d−1), when significant ammonium regeneration was measured at the water-sediment interface. Benthic denitrification (0.7-4.1 mmol m−2 d−1) accounted for up to 84-97% of total NO3 reduction and from 2 to 30% of carbon mineralization. It was mainly fuelled by water column nitrate. In CS, denitrification rates were similar in winter and in summer, while in LV summer rates were 4 times lower. DNRA rates were generally low in both lakes (0.07-0.12 mmol m−2 d−1). An appreciable contribution of DNRA was only detected in the more reducing sediments of LV in summer (15% of total NO3 reduction), while during the same period only 3% of reduced NO3 was recycled into ammonium in CS.Under summer stratification benthic denitrification was mainly nitrate-limited due to nitrate depletion in hypolimnetic waters and parallel oxygen depletion, hampering nitrification. Organic enrichment and reducing conditions in the hypolimnetic sediment shifted nitrate reduction towards more pronounced DNRA, which resulted in the inorganic nitrogen recycling and retention within the bottom waters. The prevalence of DNRA could favour the accumulation of mineral nitrogen with detrimental effects on ecosystem processes and water quality.  相似文献   

10.
Secondary materials could help meeting the increasing demand of landfill cover liner materials. In this study, the effect of compaction energy, water content, ash ratio, freezing, drying and biological activity on the hydraulic conductivity of two fly ash-sewage sludge mixes was investigated using a 27-1 fractional factorial design. The aim was to identify the factors that influence hydraulic conductivity, to quantify their effects and to assess how a sufficiently low hydraulic conductivity can be achieved. The factors compaction energy and drying, as well as the factor interactions material × ash ratio and ash ratio × compaction energy affected hydraulic conductivity significantly (α = 0.05). Freezing on five freeze-thaw cycles did not affect hydraulic conductivity. Water content affected hydraulic conductivity only initially. The hydraulic conductivity data were modelled using multiple linear regression. The derived models were reliable as indicated by Radjusted2 values between 0.75 and 0.86. Independent on the ash ratio and the material, hydraulic conductivity was predicted to be between 1.7 × 10−11 m s−1 and 8.9 × 10−10 m s−1 if the compaction energy was 2.4 J cm−3, the ash ratio between 20% and 75% and drying did not occur. Thus, the investigated materials met the limit value for non-hazardous waste landfills of 10−9 m s−1.  相似文献   

11.
Pilot-scale struvite crystallization tests using anaerobic effluent from potato processing industries were performed at three different plants. Two plants (P1 & P2) showed high phosphate removal efficiencies, 89 ± 3% and 75 ± 8%, resulting in final effluent levels of 12 ± 3 mg PO43−-P L−1 and 11 ± 3 mg PO43−-P L−1, respectively. In contrast, poor phosphate removal (19 ± 8%) was obtained at the third location (P3). Further investigations at P3 showed the negative effect of high Ca2+/PO43−-P molar ratio (ca. 1.25 ± 0.11) on struvite formation. A full-scale struvite plant treating anaerobic effluent from a dairy industry showed the same Ca2+ interference. A shift in the influent Ca2+/PO43−-P molar ratio from 2.69 to 1.36 resulted in average total phosphorus removal of 78 ± 7%, corresponding with effluent levels of 14 ± 4 mg Ptotal L−1 (9 ± 3 mg PO43−-P L−1). Under these conditions high quality spherical struvite crystals of 2-6 mm were produced.  相似文献   

12.
This work was designed to determine chemically inert mercury-selenium (Hg-Se) compounds formed in a culture of Pseudomonas fluorescens exposed to Hg2+ and SeIV (selenite). To isolate these compounds, different digestion methods were studied and sodium dodecyl sulfate (SDS) lysis was selected. The Hg0 and non-reactive Hg were determined in two series of cultures containing 0.0-6.00 μg L−1 SeIV (0.0-76.0 μmol L−1) in combination with low 5.00 μg L−1 (0.025 μmol L−1) or high 100 μg L−1 (0.500 μmol L−1) Hg2+. It was found that Hg0 formed in the culture decreased with the increase of initial SeIV, while the non-reactive Hg increased with the SeIV. In cultures with low initial [Hg2+], a median SeIV (2.0 μg L−1 or 25.3 μmol L−1) resulted in about 70% of the added Hg2+ sequestered as non-reactive Hg, and in culture with high initial Hg2+, about 40% was sequestered. P. fluorescens was proved to be indispensible for the formation of the non-reactive Hg-Se compounds. The Hg:Se molar ratio in the non-reactive Hg-Se compounds was close to 1, suggesting the existence of mercuric selenide in cells. Mechanisms for the formation of the non-reactive Hg-Se compounds are proposed.  相似文献   

13.
The photoassisted reduction of metal ions and organic dye by metal-deposited Degussa P25 TiO2 nanoparticles was investigated. Copper and silver ions were selected as the target metal ions to modify the surface properties of TiO2 and to enhance the photocatalytic activity of TiO2 towards methylene blue (MB) degradation. X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used to characterize the crystallinity, chemical species and morphology of metal-deposited TiO2, respectively. Results showed that the particle size of metal-deposited TiO2 was larger than that of Degussa P25 TiO2. Based on XRPD patterns and XPS spectra, it was observed that the addition of formate promoted the photoreduction of metal ion by lowering its oxidation number, and subsequently enhancing the photodegradation efficiency and rate of MB. The pseudo-first-order rate constant (kobs) for MB photodegradation by Degussa P25 TiO2 was 3.94 × 10− 2 min− 1 and increased by 1.4-1.7 times in kobs with metal-deposited TiO2 for MB photodegradation compared to simple Degussa P25 TiO2. The increase in mass loading of metal ions significantly enhanced the photodegradation efficiency of MB; the kobs for MB degradation increased from 3.94 × 10− 2 min− 1 in the absence of metal ion to 4.64-7.28 × 10− 2 min− 1 for Ag/TiO2 and to 5.14-7.61 × 10− 2 min− 1 for Cu/TiO2. In addition, the electrons generated from TiO2 can effectively reduce metal ions and MB simultaneously under anoxic conditions. However, metal ions and organic dye would compete for electrons from the illuminated TiO2.  相似文献   

14.
Radionuclides released to the atmosphere during dry weather (e.g. after a nuclear accident) may contaminate vegetable foods and cause exposure to humans via the food chain. To obtain experimental data for an appropriate assessment of this exposure path, dry deposition of radionuclides to leafy vegetables was studied under homogeneous and controlled greenhouse conditions. Gaseous 131I-tracer in predominant elemental form and particulate 134Cs-tracer at about 1 μm diameter were used to identify susceptible vegetable species with regard to contamination by these radionuclides. The persistence was examined by washing the harvested product with water. The vegetables tested were spinach (Spinacia oleracea), butterhead lettuce (Lactuca sativa var. capitata), endive (Cichorium endivia), leaf lettuce (Lactuca sativa var. crispa), curly kale (Brassica oleracea convar. acephala) and white cabbage (Brassica oleracea convar. capitata). The variation of radionuclides deposited onto each vegetable was evaluated statistically using the non-parametric Kruskal-Wallis Test and the U-test of Mann-Whitney. Significant differences in deposited 131I and 134Cs activity concentration were found among the vegetable species.For 131I, the deposition velocity to spinach normalized to the biomass of the vegetation was 0.5-0.9 cm3 g− 1 s− 1 which was the highest among all species. The particulate 134Cs deposition velocity of 0.09 cm3 g− 1 s− 1 was the highest for curly kale, which has rough and structured leaves. The lowest deposition velocity was onto white cabbage: 0.02 cm3 g− 1 s− 1 (iodine) and 0.003 cm3 g− 1 s− 1 (caesium). For all species, the gaseous iodine deposition was significantly higher compared to the particulate caesium deposition. The deposition depends on the sensitive parameters leaf area, stomatal aperture, and plant morphology. Decontamination by washing with water was very limited for iodine but up to a factor of two for caesium.  相似文献   

15.
The influences of various geochemical constituents, such as humic acid, HCO3, and Ca2+, on Cr(VI) removal by zero-valent iron (Fe0) were investigated in a batch setting. The collective impacts of humic acid, HCO3, and Ca2+ on the Cr(VI) reduction process by Fe0 appeared to significantly differ from their individual impacts. Humic acid introduced a marginal influence on Fe0 reactivity toward Cr(VI) reduction, whereas HCO3 greatly enhanced Cr(VI) removal by maintaining the solution pH near neutral. The Cr(VI) reduction rate constants (kobs) were increased by 37.8% and 78.3%, respectively, with 2 mM and 6 mM HCO3 in solutions where humic acid and Ca2+ were absent. Singly present Ca2+ did not show a significant impact to Cr(VI) reduction. However, probably due to the formation of passivating CaCO3, further addition of Ca2+ to HCO3 containing solutions resulted in a decrease of kobs compared to solutions containing HCO3 alone. Ca2+ enhanced humic acid adsorption led to a minor decrease of Cr(VI) reduction rates. In Ca2+-free solutions, humic acid increased the amount of total dissolved iron to 25 mg/l due to the formation of soluble Fe-humate complexes and stably dispersed fine Fe (oxy)hydroxide colloids, which appeared to suppress iron precipitation. In contrast, the coexistence of humic acid and Ca2+ significantly promoted the aggregation of Fe (oxy)hydroxides, with which humic acid co-aggregated and co-precipitated. These aggregates would progressively be deposited on Fe0 surfaces and impose long-term impacts on the permeability of PRBs.  相似文献   

16.
Oxidative removal of aqueous steroid estrogens by manganese oxides   总被引:2,自引:0,他引:2  
Xu L  Xu C  Zhao M  Qiu Y  Sheng GD 《Water research》2008,42(20):5038-5044
This study investigated the oxidative removal of steroid estrogens from water by synthetic manganese oxide (MnO2) and the factors influencing the reactions. Using 1 × 10−5 M MnO2 at pH 4, estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2), all at 4 × 10−6 M, were rapidly removed within 220 min, indicating the effectiveness of MnO2 as an oxidizing agent towards estrogens. E2 removal increased with decreasing pH over the tested range of 4-8, due most likely to increased oxidizing power of MnO2 and a cleaner reactive surface in acidic solutions. Coexisting metal ions of 0.01 M (Cu(II), Zn(II), Fe(III) and Mn(II)) and Mn(II) released from MnO2 reduction competed with E2 for reactive sites leading to reduced E2 removal. Observed differential suppression on E2 removal may be related to different speciations of metals, as suggested by the MINTEQ calculations, and hence their different adsorptivities on MnO2. By suppressing the metal effect, humic acid substantially enhanced E2 removal. This was attributed to complexation of humic acid with metal ions. With 0.01 M ZnCl2 in solutions containing 1 mg l−1 humic acid, the binding of humic acid for Zn(II) was determined at 251 mmol g−1. An in vitro assay using human breast carcinoma MCF-7 cells indicated a near elimination of estrogenic activities without secondary risk of estrogen solutions treated with MnO2. Synthetic MnO2 is therefore a promising chemical agent under optimized conditions for estrogen removal from water. Metal chelators recalcitrant to MnO2 oxidation may be properly used to further enhance the MnO2 performance.  相似文献   

17.
Design parameters for sludge reduction in an aquatic worm reactor   总被引:3,自引:0,他引:3  
Reduction and compaction of biological waste sludge from waste water treatment plants (WWTPs) can be achieved with the aquatic worm Lumbriculus variegatus. In our reactor concept for a worm reactor, the worms are immobilised in a carrier material. The size of a worm reactor will therefore mainly be determined by the sludge consumption rate per unit of surface area. This design parameter was determined in sequencing batch experiments using sludge from a municipal WWTP. Long-term experiments using carrier materials with 300 and 350 μm mesh sizes showed surface specific consumption rates of 45 and 58 g TSS/(m2 d), respectively. Using a 350 μm mesh will therefore result in a 29% smaller reactor compared to using a 300 μm mesh. Large differences in consumption rates were found between different sludge types, although it was not clear what caused these differences. Worm biomass growth and decay rate were determined in sequencing batch experiments. The decay rate of 0.023 d−1 for worms in a carrier material was considerably higher than the decay rate of 0.018 d−1 for free worms. As a result, the net worm biomass growth rate for free worms of 0.026 d−1 was much higher than the 0.009-0.011 d−1 for immobilised worms. Finally, the specific oxygen uptake rate of the worms was determined at 4.9 mg O2/(g ww d), which needs to be supplied to the worms by aeration of the water compartment in the worm reactor.  相似文献   

18.
A novel and straight forward method is adopted to segregate the contribution of primary and secondary sources of formaldehyde based on the rates of its formation and removal at different times in the urban atmosphere of Kolkata. To achieve the above objective, the diurnal and seasonal mixing ratios of formaldehyde were measured during dry season at two busy roadside locations. The maximal secondary formation fluxes of formaldehyde during summer and winter were found to be 6.63 × 107 and 1.23 × 107 molecules cm− 3 s− 1, respectively. Apart from formaldehyde (C1), several other carbonyls were quantified in this study. An overall good correlation between acetaldehyde (C2) and propanal (C3) indicates the contribution of vehicular emission to the carbonyl budget. The secondary formaldehyde contributions in summer and winter were about 71% and 32%, respectively. The relative mean contributions of C1, C2 and ozone towards generation of OH fluxes in summer were found to be 1.56 × 107, 6.96 × 105, and 1.29 × 107 molecules cm− 3 s− 1, respectively, which were 3.2, 3.4 and 1.6 times higher than those in winter.  相似文献   

19.
Pure and 0.25% Ni2+ ion doped goethite samples, prepared by the coprecipitation method, were characterized for pH of Point of Zero Charge (pHpzc), Surface area, XRD, TG-DTA, FTIR and TEM. Effect of Ni2+ ions doping on the adsorption of chromate on goethite was investigated at pH-3, -5 and -7 in the temperature range 303-323 K. It was found that adsorption of chromate increases with decreasing pH and increasing temperature on both pure and Ni2+-doped goethite. Adsorption of chromate was found to increase from 61.4% to 82.92% with Ni2+ ion doping in goethite matrix at the lowest pH (pH-3) and highest temperature (323 K), using 1.02 mmol L−1 chromate solution. Langmuir isotherm was found applicable to the experimental data. The values of (isosteric heat of adsorption) calculated for both the samples of goethite were positive, showing endothermic nature of the adsorption process.  相似文献   

20.
Kinetic of benzotriazole oxidation by ozone and hydroxyl radical   总被引:3,自引:0,他引:3  
Ozonation experiments were performed in batch reactors in order to determine the rate constants for the reaction of molecular ozone and OH radicals with benzotriazole (BT) at different pHs. The first group of ozonation experiments was carried out for the determination of the rate constant for the direct reactions between ozone and BT. Two different kinetic models were used for the determination of kinetic rate constants: (i) the log-reduction of BT with ozone in excess, (ii) the competition kinetic model. The second-order rate constants for BT with molecular ozone were determined to be 36.4 ± 3.8 M−1 s−1 and 18.4 ± 0.8 M−1 s−1 at pH 2 from the two methods respectively. With the competition method, the value at pH 5 was found to be 22.0 ± 2.0 M−1 s−1. In a following stage, the reaction of BT with OH radicals was investigated at pH values ranging from 2 to 10.2. Using a method involving two probe compounds during the ozonation, the second-order rate constants of the BT reaction with hydroxyl radicals were determined. The rate constants were found to vary from 6.2 × 109 M−1 s−1 at pH 10.2 to 1.7 × 1010 M−1 s−1 at pH 2.  相似文献   

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