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61.
采用曝气生物滤池与二氧化氯相结合的工艺处理医院污水。主要对曝气生物滤池去除COD、氨氮的效果进行了研究,并且在实际应用中证明了用这种相结合的处理方法具有一次投资小、运行费用低、年经济效益高等优点,有良好的技术经济性。 相似文献
62.
It is quite rare to find biodegradation in rapid sand filtration for drinking water treatment. This might be due to frequent backwashes and low substrate levels. High chlorine concentrations may inhibit biofilm development, especially for plants with pre-chlorination. However, in tropical or subtropical regions, bioactivity on the sand surface may be quite significant due to high biofilm development—a result of year-round high temperature. The objective of this study is to explore the correlation between biodegradation and chlorine concentration in rapid sand filters, especially for the water treatment plants that practise pre-chlorination. In this study, haloacetic acid (HAA) biodegradation was found in conventional rapid sand filters practising pre-chlorination. Laboratory column studies and field investigations were conducted to explore the association between the biodegradation of HAAs and chlorine concentrations. The results showed that chlorine residual was an important factor that alters bioactivity development. A model based on filter influent and effluent chlorine was developed for determining threshold chlorine for biodegradation. From the model, a temperature independent chlorine concentration threshold (Clthreshold) for biodegradation was estimated at 0.46-0.5 mg L−1. The results imply that conventional filters with adequate control could be conducive to bioactivity, resulting in lower HAA concentrations. Optimizing biodegradable disinfection by-product removal in conventional rapid sand filter could be achieved with minor variation and a lower-than-Clthreshold influent chlorine concentration. Bacteria isolation was also carried out, successfully identifying several HAA degraders. These degraders are very commonly seen in drinking water systems and can be speculated as the main contributor of HAA loss. 相似文献
63.
Aranda A Díaz-De-Mera Y Bravo I Morales L 《Environmental science and pollution research international》2007,14(3):176-181
Goal, Scope and Background Within the non-methane hydrocarbons, alkanes constitute the largest fraction of the anthropogenic emissions of volatile organic
compounds. For the case of cyclic alkanes, tropospheric degradation is expected to be initiated mainly by OH reactions in
the gas phase. Nevertheless, Cl atom reaction rate constants are generally one order of magnitude larger than those of OH.
In the present work, the reaction of cyclooctane with Cl atoms has been studied within the temperature range of 279–333 K.
Methods The kinetic study has been carried out using the fast flow tube technique coupled to mass spectrometry detection. The reaction
has been studied under low pressure conditions, p=1 Torr, with helium as the carrier gas.
Results The measured room temperature rate constant is very high, k=(2.63±0.54)×10−10 cm3molecule−1s−1, around 20 times larger than that for the corresponding OH reaction. We also report the results of the rate coefficients
obtained at different temperatures: k = (3.5±1.2)×10−10 exp[(−79±110)/T] cm3 molecule−1 s−1 within the range of 279–333 K. This reaction shows an activation energy value close to zero.
Discussion Quantitative formation of HCl has been observed, confirming the mechanism through H-atom abstraction. The reactivity of cyclic
alkanes towards Cl atoms is clearly dependent on the number of CH2 groups in the molecule, as is shown by the increase in the rate constant when the length of the organic chain increases.
This increase is very high for the small cyclic alkanes and it seems that the reactions are approaching the collision-controlled
limit for cyclohexane and cyclooctane.
Conclusions These results show that gas-phase reaction with Cl in marine or coastal areas is an efficient sink (competing with the gas
phase, OH initiated degradation) for the Earth’s emissions of cyclooctane, with a Cl-based lifetime ranging from 11 to 2000
hours, depending on the location and time of day.
Recommendations and Perspectives Cl and OH fast reactions with cyclooctane are expected to define the lifetime of cyclooctane emissions to the atmosphere.
The degradation of cyclooctane occurs in a short period of time and consequently (under conditions of low atmospheric mass
transport), close to the emission sources enabling a significant contribution to local effects, like the formation of photochemical
smog.
ESS-Submission Editor: Prof. Dr. Gerhard Lammel (lammel@recetox.muni.cz) 相似文献
64.
Díaz-de-Mera Y Aranda A Bravo I Rodríguez D Rodríguez A Moreno E 《Environmental science and pollution research international》2008,15(7):584-591
Background, aim, and scope The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort
to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated
alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number
of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve
our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation
of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase.
Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present
work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF3CF2CF2OCH3) (1) and its isomer CF3CF2CF2CH2OH (2).
Materials and methods Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr
of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order
kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K
for reactions of HFE-7000 and CF3CF2CF2CH2OH, respectively.
Results The measured room temperature rate constants were k(Cl+CF3CF2CF2OCH3) = (1.24 ± 0.28) × 10−13 cm3 molecule−1 s−1and k(Cl+CF3CF2CF2CH2OH) = (8.35 ± 1.63) × 10−13 cm3 molecule−1 s−1 (errors are 2σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k
1(266–333 K) = (6.1 ± 3.8) × 10−13exp[−(445 ± 186)/T] cm3 molecule−1 s−1 and k
2(298–353 K) = (1.9 ± 0.7) × 10−12exp[−(244 ± 125)/T] cm3 molecule−1 s−1 (errors are 2σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl
radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2σ) were obtained for CF3CF2CF2OCH3 and CF3CF2CF2CH2OH, respectively.
Discussion The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into
account the error limits. Comparing the obtained results at room temperature, k
1 and k
2, HFE-7000 is significantly less reactive than its isomer C3F7CH2OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers
with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and
alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF2– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties
for a given application by changing the number of –CF2– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated
and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C3H7CH2OH, respectively.
Conclusions The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average
contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the
marine boundary layer, τ
Cl values as low as 2.5 and 0.4 years for HFE-7000 and C3H7CH2OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes
under such conditions may constitute a relevant sink. In the case of CF3CF2CF2OCH3, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would
result in underestimations of lifetimes and GWPs.
Recommendations and perspectives The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge
of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development
of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject
to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature
dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate
lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution
is still required. 相似文献
65.
In this work assays involving chlorinated water samples, which were previous spiked with humic substances or algae blue green
and following the production of the THMs for 30 days is described. To implement the assays, five portions of 1,000 ml of water
were stored in glass bottles. The water samples were treated with solutions containing 2, 3, 4 and 5 mg l−1 chlorine. The samples aliquots (60 ml) were transferred into the glass vials, 10 ml were removed to have a headspace and
100 μl of the 10 mg l−1 pentafluortoluene bromide solution was added to each vial. The extraction step was performed by adding 10 g of Na2SO4 followed by 5 ml of n-pentane. The vials were stopped with a TFE-faced septum and sealed with aluminum caps. The generated THMs were determined
by gas chromatography with electron capture detector using reference solutions with concentration ranging from 8 to 120 μg
l−1 THMs. Three assays were monitored during 30 days and chloroform was the predominant compound found in the water samples,
while other species of THMs were not detected. The results showed that when the chlorine concentration was increased in water
samples containing algae the concentration of THM varied randomly. Nevertheless, in water samples containing humic substances
the increase of the THM concentration presented a relationship with the chlorine concentration. It was also observed that
chloroform concentration increased with the elapsed time up to one and six days to water samples spiked with humic substances
and algae blue green, respectively and decreased along 30 days. By other hand, assays performed using water samples containing
decanted algae material showed that THM was not generated by the chlorine addition. 相似文献
66.
67.
The migration and transformation of dissolved organic matter during the freezing processes of water 总被引:1,自引:0,他引:1
This study investigated the partitioning behavior of dissolved organic matter (DOM) in liquid and ice phases, as well as the changes in the optical properties and chlorine reactivity of DOM during the freezing processes of water. DOM was rejected from the ice phase and accumulated in the remaining liquid phase during water freezing. Moreover, the decrease in freezing temperature, as well as the increase in dissolved organic carbon (DOC) concentration of feed water, caused an increase in DOM captured in the ice phase. The ultraviolet-absorbing compounds, trihalomethane precursors, as well as fulvic acid- and humic acid-like fluorescent materials, were more liable to be to be rejected from the ice phase and were more easily retained in the unfrozen liquid phase during water freezing, as compared with organics (on average) that comprise DOC. In addition, it was also found a higher accumulation of these organics in the unfrozen liquid phase during water freezing at higher temperature. The freeze/thaw processes altered the quantity, optical properties, and chlorine reactivity of DOM. The decrease in ultraviolet light at 254 nm as well as the production of aromatic protein- and soluble microbial byproduct-like fluorescent materials in DOM due to freeze/thaw were consistently observed. On the other hand, the changes in DOC, trihalomethane formation potential, and fulvic acid- and humic acid-like fluorescence caused by freeze/thaw varied significantly between samples. 相似文献
68.
Weiying Li Yu Tian Jiping Chen Xinmin Wang Yu Zhou Nuo Shi 《Frontiers of Environmental Science & Engineering》2022,16(6):72
69.
我国工业区布局与城市规划建设间存在矛盾的分析 总被引:1,自引:0,他引:1
针对我国东部某沿海城市化工园区的建设和规划情况,分析目前的环境风险水平与周边地区建设发展规划存在的矛盾,并提出应尽快开展区域规划环评的建议。 相似文献
70.
Computational fluid dynamic (CFD) simulations were performed to assess the potential chlorine leak scenario in the super-urban area of South Korea, where the human population density is very high and numerous buildings exist near operational water treatment facilities. Flame acceleration simulator (FLACS) was used to predict the consequence from accidental chlorine releases out of one of the water treatment facilities for the nearby area having a size of 5 km × 3 km approximately. The ability to precisely implement 3-D geometries is crucial for a successful 3-D simulation. Thus, a method was proposed to rapidly and accurately implement geometry by importing computer aided-design (CAD) files provided by a government agency, and processing them using Auto CAD and MicroStation software programs. An accidental release from an 18-ton tank was simulated with three different wind directions to determine the expected evacuation distances. Results from the study showed that the endpoint distances varied depending on the density and arrangement of the buildings. Moreover, we employed physical barriers with varying heights for mitigating the effects of toxic gas releases and simulated how effectively they decreased the concentration of released chlorine. 相似文献