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911.
D R van der Vaart W M Vatvuk A H Wehe 《Journal of the Air & Waste Management Association》1991,41(1):92-98
The emission of Volatile Organic Compounds (VOCs) is attracting increasing concern both from the public and by government agencies. Among the many available control technologies for the treatment of VOC containing waste streams, incineration offers an ultimate disposal strategy rather than a means for collecting or concentrating the offending compounds. This paper describes the major, commercially available thermal and catalytic incinerator systems that are designed to treat dilute, VOC containing gas streams. Qualitative guidelines are presented whereby the technologies can be compared. In addition, an example waste stream is used to illustrate a simplified procedure for calculating the material and energy balances for each of the incinerators. The resulting parameters will be used in a companion paper to estimate the capital and operating costs associated with each design. In this manner, a first estimate can be obtained of the costs of cleaning a waste stream containing low levels of VOCs. 相似文献
912.
In long-term experiments lasting up to 73 days the effect of rather low levels of zinc, copper, lead and cadmium on the growth and metal uptake was studied by investigating four aquatic plant species: Elodea nuttallii, Callitriche plataycarpa, Spirodela polyrhiza and Lemma gibba. Except Elodea, which was already very sensitive to 5 μmol Cu 1?1, no differentiation in growth or mortality could be detected depending on species or elements. There was a clear differentiation between the uptake levels of the heavy metals with regard to the plant species, resulting in a higher heavy metal content in de submerged species in comparison to the floating ones. For zinc, lead and cadmium, an equal ratio was detected between the concentration in the medium and in the plant tissue independent of the plant species. The involvement of roots in element absorption by aquatic plants and the possibility of using aquatic plants as indicators of heavy metal pollution in Dutch waters are discussed. 相似文献
913.
914.
915.
El Niño is well known to affect marine fishery. The Southern Oscillation, however, may also have a strong effect on riverine fish production in floodplains via its effect on river discharge. In years with high river discharges larger parts of the floodplain are inundated, increasing the surface area of suitable nursery grounds for young fish stock. In this way high river discharges are thought to have a positive effect on fish production, while low discharges are thought to have a negative effect. The collapse of the sábalo fishery in the Pilcomayo River in Bolivia, for instance, can be attributed to the 1990–1995 El Niño event and subsequent overexploitation of the fish stocks. 相似文献
916.
Eelgras (Zostera marina L.) in the Dutch Wadden Sea historically covered an area varying from 65–150 km2 in the eulittoral as well as the sublittoral zones. At present, this area comprises less than 1 km2 eulittoral eelgrass stands, with an associated decrease in habitat diversity. The causes for this decline are presumably
connected with the ‘wasting disease’ and the closure of the former Zuiderzee in the early 1930s resulting in increased tidal
range and increased currents. After a slight recovery of the eelgrass populations on the intertidal flats a definite decline
started in the early 1970s, possibly connected to increased turbidity. The present water quality and turbidity do not negatively
influence eelgrass growth up to a depth of at least 0.6m below Mean Sea Level. Based on mesocosm experiments and field experiments
it is concluded that re-establishment of eelgrass should be possible in sheltered bays and on unexposed tidal falts. The most
suitable depths for a reintroduction are those between 0 and 20–40 cm below mean sea level. 相似文献
917.
The biochemical composition of the ovaries of the asteroid echinoderm Asterias rubens was studied, with emphasis on the changes which are manifest during the annual reproductive cycle. Ovarian dry weight displays only minor changes during ovarian development, constituting about 20% of the organ fresh weight. Levels of all constituents show some variation, but in general increase with ovarian growth. Only the free amino acid level is rather constant. Except for glycogen, the contents of other constituents (total lipids, other reducing sugars, free amino acids and proteins) show a rectilinear increase with ovarian growth. Glycogen content increases rectilinearly with time during early vitellogenesis, but remains constant during further development until ovarian maturity. By plotting constituent levels and contents against a non-linear gonad index axis rather than against sampling date, results can be correlated more easily with ovarian growth stages. The possibility of endocytosis of a vitellogenin-like yolk precursor by the ovary is discussed. 相似文献
918.
Wolterbeek HT Viragh A Sloof JE Bolier G van der Veer B de Kok J 《Environmental pollution (Barking, Essex : 1987)》1995,88(1):85-90
A Zn- and pH-buffered medium was used to study the accumulation of Zn in batch-cultured algae (Selenastrum capricornutum Printz.). All experiments were carried out using (65)Zn radiotracers, which were measured by gamma-ray spectrometry. Zinc was applied in the presence of nitrilotriacetic acid (NTA), leading to free Zn(2+) concentrations ranging from 4.2 x 10(-11) to 1.6 x 10(-7) mol litre(-1). During the 75-h experiments, the rates of Zn influx and efflux were determined, the latter with full consideration for algal growth rates. Algal growth stopped completely at a free Zn(2+) concentration of 1.6 x 10(-8) mol litre(-1). Initial Zn binding was determined and, based on free Zn(2+) concentrations, presented by the apparent dissociation constant K(diss) and capacity C as 4.6 x 10(-9) mol litre(-1) and 19.8 x 10(6) mol gDW(-1), respectively. The rate constant of Zn efflux could be calculated as a constant 0.021 +/- 0.003 h(-1), irrespective of the Zn concentrations applied. The rates of Zn influx were expressed by the V(max) and K(M) values as 3.3 x 10(-10) mol gDW(-1) s(-1) and 6.3 x 10(-9) mol litre(-1), respectively. These values, which are based on applied free Zn(2+) concentrations, are compatible with the operation of a high-affinity low-concentration carrier mechanism. The results suggest that, under the conditions applied, free Zn(2+) may be the most relevant Zn species for Zn uptake; furthermore, relative growth rate may be regarded as a relatively sensitive signal for Zn stress circumstances. 相似文献
919.
Oswald van Cleemput Annick Vermoesen Cornelis-Jan de Groot Karla van Ryckeghem 《Environmental monitoring and assessment》1994,31(1-2):145-152
Grazed grassland which received 295 kg ha–1 N-fertilizer (NH4NO3), split-applied, was used to measure nitrous oxide emission. The closed box method was used. At the same time, also soil cores were taken for incubation in the presence of acetylene. During 280 days in 1992, a total emission of 8.4 kg N2O-N ha–1 was found. This was close to 50 % of the total denitrification, which was 18.7 kg (N2O+N2)-N ha–1 over 280 days. A variability study on N2O emission was carried out on a surface of 1, 100 and 10,000 m2, respectively. This study confirmed the lognormal distribution of data with variation coefficients of 20 to 25%. It was also found that the effect of application of 200 kg KNO3-N on N2O emission was limited to 2 weeks upon fertilization. It more than doubled the emission rate during this period. 相似文献
920.
Walter Debruyn Gilbert Lissens Jan van Rensbergen Maria Wevers 《Environmental monitoring and assessment》1994,31(1-2):159-165
The estimation of nitrous oxide emissions is complicated by the high degree of uncertainty on the emission factors involved and by the limited acquaintance with all significant nitrous oxide sources. A potentially important source for which emission data are lacking is the sewage system transporting waste water from human activities. For this study an experimental measurement campaign has been carried out on waste water sampled at different sewage treatment plants. The nitrous oxide developing from the water samples was monitored by means of gas chromatography. The methodological analysis was based on the concentration/time curves obtained. Our results indicate that the formation of nitrous oxide from the waste water matrices results from microbiological denitrification. We deduced tentative emission factors for the waste water types studied. 相似文献