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991.
992.
石灰湿法脱硫过程中pH条件对结垢的影响研究 总被引:8,自引:0,他引:8
针对石灰湿法脱硫中存在的结垢问题,在鼓泡床中模拟了石灰湿法脱硫过程,通过分析液相的组成,结合反应机理探讨了pH对结垢的影响。结果表明,当pH控制在6.0~4.0时,既能避免结垢,又能获得较高的脱硫率。提出了实际中预测结垢倾向的方法。 相似文献
993.
Background Worldwide, large amounts of sediments have to be dredged annually from waterways and harbours. These sediments are sometimes
polluted with a variety of toxic compounds. In some countries, including Belgium, the load with the biocide tributyltin (TBT)
from ship coatings prohibits the dumping of harbour sludge into the sea. Land-based dumping is a commonly used alternative.
Objective This research investigated the feasibility to use land-deposited harbour sludge for plant production. In a field trial, the
growth of 38 more or less salt-tolerant plant species on low and high TBT-contaminated sediments was studied. The elimination
of TBT from sludge with and without vegetation was compared. The uptake of TBT and its degradation products di- and monobutyltin
(DBT and MBT) into harvest products under field conditions was determined.
- Experimental Set-up. Sediments dredged in May 2003 from the brackish waters of the port of Antwerp were analysed in the laboratory
for soil texture, pH, electroconductivity, sodium, magnesium, potassium, calcium, ammonium, nitrate, total nitrogen, chloride,
sulphur and the organotins TBT, DBT and MBT. The sediments were lagooned for one year to dewater, desalinate and improve their
structure. Salt-tolerant domestic and wild plants were selected and sown in May 2004. In August 2004, plants were harvested
and the produced biomass was determined. Samples were taken from vegetated and non-vegetated top and bottom sediments and
from plants growing above soil and analysed for TBT, DBT and MBT.
Results The fresh sediments showed a good supply with nutrients and a neutral pH, but were rather saline (EC 14 mS cm-1 of the saturated
paste extract). The salinity decreased to 3.7 mS cm-1 during lagoonation. The high and the low contaminated sediment had initially
43 and 1.6 mg TBT kg-1 dry weight, respectively. Besides TBT, several other contaminants were present in the sediments at
critical levels. The biomass production of the plant species from the field trial ranged from 0.2 to 13 tons dry mass per
hectare. Plants performing excellently were barley, sorghum, rape seed, a clover/grass mix and reed. If at all, a positive
influence of TBT on plant growth was seen. TBT was degraded significantly faster (>40%) below barley. The uptake of TBT, DBT
and MBT into stem and leaves of reed, grass and clover was very low, but measurable and not related to concentrations in soil.
No uptake of TBT or its metabolites into corn of barley was found.
Discussion This study confirmed former results: the toxicity of TBT to higher plants is low, and even high levels in soils would not
be a hindrance for crop production. The removal of TBT seemed to be increased by both lagooning and plant growth, although
the target values for sea dumping in use in certain European countries were not reached. A plausible explanation for the faster
degradation of TBT under vegetation is that oxygen is a limiting factor, and plants dewater the soil, thus aerating it. The
uptake of the organotins TBT, DBT and MBT into harvest products is probably due to attached soil particles.
Conclusions To summarize, barley was the optimal species: it grew very well despite the salinity of the dredged sediments, it had a significantly
positive effect on TBT removal; it showed no measurable uptake of TBT or the other butyltins into the harvested product; and
it is a cash crop well established in European agriculture.
Outlook The amounts of dredged sediments are high, and good soils are becoming increasingly rare. The feasibility of using dredged
sediments for non-food production, such as energy crops, should be investigated by a critical risk assessment. 相似文献
994.
Seasonal Fluctuation in Heavy Metal Pollution in Iran´s Siahroud River - A Preliminary Study (7 pp) 总被引:1,自引:0,他引:1
Charkhabi AH Sakizadeh M Rafiee G 《Environmental science and pollution research international》2005,12(5):264-270
Background The management of its available water resources has become a key issue for Iran. During the last few decades, the water quality
of Siahroud River in the coastal plain of the Caspian Sea in Gilan Province in Northern Iran has significantly degraded. The
scarcity of water has been compounded by rapid population growth and increasing pollution from fertilizers, pesticides, and
municipal and industrial wastes. One of the sources of this degradation is the movement of heavy metals from the river's watershed
into the various water systems supported by the river, including the water system for Rasht City.
Methods To study the magnitude of heavy metal pollution in the Siahroud River, seven heavy metals including Zn, Cu, Pb, Cd, Mn, Fe,
and Ni were measured in duplicate from replicated water samples collected over five consecutive seasons and analyzed by Atomic
Absorption Spectrometry. In situ measurements of pH were taken with the samples and total organic carbon (TOC) was analyzed
by IR gas measurement.
Results The results demonstrated that four of the seven heavy metals including Pb, Fe, Cd, and Mn exceeded permissible safe levels
as established by the United States Environmental Protection Agency. Multivariate factor analysis suggested that industrial
land-use was the main contributing factor for the high levels of Fe and Mn in the Siahroud River, whereas, Cd was principly
from agricultural activities in the watershed. The data also suggested that pH and TOC had an important role in the behaviour
of Pb and Mn, and that the elevated levels of these two heavy metals in Siahroud River was the consequence of other anthropogenic
sources. Only negligible levels of Zn, Cu and Ni were detected. Finally, all the sampling stations were subjected to cluster
analysis. The results indicated that three different zones could be distinguished according to the levels of pollution. In
addition, it was shown that the urban areas did not have a significant impact on the heavy metal pollution in the river. This
observation stems from the fact that the data from the sampling stations before and after Rasht City were not significantly
different.
Recommendation . Preventive measures need to be undertaken in the land-use systems and watersheds of the Siahroud River to reduce the pollution
levels of Pb, Cd, Mn and Fe. 相似文献
995.
介绍了2种不同等离子体发生区和不同测量距离对等离子体发生区沿面蓝光中紫外光的波长和相对光强的影响,所测的臭氧发生量大的等离子体发生区的紫外光的相对光强高,测量距离与相对光强呈指数关系,并且等离子体发生区沿面蓝光具有光催化作用. 相似文献
996.
997.
活性炭纤维吸附废水中对硝基苯酚及其脱附研究 总被引:8,自引:0,他引:8
采用新型高效吸附剂——活性炭纤维吸附废水中对硝基苯酚,对其吸附和脱附影响因素进行了较详细的研究,确定了最佳工艺参数,并对动态吸附一脱附进行了稳定性实验。在最佳的吸附条件下,装填4g活性炭纤维可处理含对硝基苯酚1000mg/L的废水1400mL,出水对硝基苯酚浓度〈2mg/L,达到国家综合污水一级排放标准,活性炭纤维有效吸附量可达349.87mg/g。在最佳脱附条件下,脱附率〉99%,并可从高浓度脱附液中回收对硝基苯酚。稳定性实验表明,吸附-脱附性能稳定,采用活性炭纤维吸附处理对硝基苯酚废水是一种行之有效的处理方法。 相似文献
998.
Guy Mercier Patrick Drogui Jean-Fran?ois Blais Myriam Chartier 《Water environment research》2006,78(8):872-879
The objective of this research was to investigate the performance of the ferrous sulfate bioleaching (FSBL) process in a pilot plant for decontamination and stabilization of wastewater sludge. Batch and continuous experiments, conducted with two 4-m3 bioreactors using indigenous iron-oxidizing bacteria (20% v/v of inoculum) with addition of 4.0 g ferrous sulfate heptahydrate per liter of sludge initially acidified to pH 4.0, were sufficient for effective heavy metal (cadmium, copper, manganese, zinc, and lead) removal yields. The average metal removal yields during the FSBL process were as follows: cadmium (69 to 75%), copper (68 to 70%), manganese (72 to 73%), zinc (65 to 66%), and lead (16%). The FSBL process was also found to be effective in removing both fecal and total coliforms (abatement > 5 to 6 log units). The nutrients content (nitrogen, phosphorus, and magnesium) were also preserved in decontaminated sludge. 相似文献
999.
1000.
A digestive tract mass balance was performed on six men with high body burdens of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Intake via food was measured by analyzing duplicate portions of the food consumed by the volunteers and excretion via feces was determined by quantitative collection and analysis of the feces. Blood samples were taken to determine the current body burden. The results showed that the quantity of non-metabolized chemical excreted in the feces clearly exceeded the uptake via food for all of the 2,3,7,8-substituted PCDDs and some of the PCDFs, indicating a significant clearance across the gastrointestinal tract. The concentrations of these PCDD/F congeners in blood and feces were highly correlated (r > 0.8), demonstrating that the fecal PCDD/F content was determined by the body burden. The half lives in the test persons due to fecal clearance of non-metabolized chemical were estimated from the excretion rate and the current body burden and ranged between 10 years (Cl8DD) and 33 years (2,3,4,7,8-Cl5DF). These were compared with the overall contaminant half-lives due to all clearance processes which were calculated from the body burden and the decrease in blood concentrations measured over several years. The fecal clearance of non-metabolized PCDD/F contributed on average between 37% (2,3,7,8-Cl4DD) and 90% (Cl8DD) to the total elimination. This indicates that the gastrointestinal pathway plays a decisive role in the clearance of most 2,3,7,8-subsituted PCDD/F congeners. 相似文献