Mathematical models were developed to investigate the characteristics of gaseous ozone transport under various soil conditions and the feasibility of in situ ozone venting for the remediation of unsaturated soils contaminated with phenanthrene. On the basis of assumptions for the mass transfer and reactions of ozone, three approaches were considered: equilibrium, kinetic, and lump models. Water-saturation-dependent reactions of gaseous ozone with soil organic matter (SOM) and phenanthrene were employed. The models were solved numerically by using the finite-difference method, and the model parameters were determined by using the experimental data of Hsu [The use of gaseous ozone to remediate the organic contaminants in the unsaturated soils, PhD Thesis, Michigan State Univ., East Lansing, MI, 1995]. The transport of gas-phase ozone is significantly retarded by ozone consumption due to reactions with SOM and phenanthrene, in addition to dissolution. An operation time of 156 h was required to completely remove phenanthrene in a 5-m natural soil column. In actual situations, however, the operation time is likely to be longer than the ideal time because of unknown factors including heterogeneity of the porous medium and the distribution of SOM and contaminant. The ozone transport front length was found to be very limited (< 1 m). The sensitivity analysis indicated that SOM is the single most important factor affecting in situ ozonation for the remediation of unsaturated soil contaminated with phenanthrene. Models were found to be insensitive to the reaction mechanisms of phenathrene with either gas-phase ozone or dissolved ozone. More study is required to quantify the effect of OH* formation on the removal of contaminant and on ozone transport in the subsurface. 相似文献
The effect of methanol of low concentration on adsorption and leaching of atrazine and tebuconazole was studied in this paper. The adsorption coefficients and the retardation factors (Rm) of pesticides on EUROSOIL 3# log-linearly decreased as volumetric fraction of methanol (fc) was increased in the binary solvent mixtures of methanol and water. These data are consistent with solvophobic theory formerly outlined for describing the adsorption and transport of hydrophobic organic chemicals from mixed solvents. Nevertheless, the adsorption of these pesticides in soil–water system slightly increased when the soil was pre-washed with methanol in comparison with that pre-washed with water (pure water system). Furthermore, their adsorption coefficients were still higher in binary solvent systems with methanol of very low concentrations, i.e. fc<0.03 for atrazine and fc<0.01 for tebuconazole, than those in pure water system. The adsorption coefficients (logKw) of atrazine and tebuconazole predicted by solvophobic theory were 0.5792 and 1.6525, respectively, and their experimental logKw were 0.3701 and 1.6275 in pure water system. Obviously, the predicted logKw of the two pesticides was higher than the experimental log Kw in pure water system. The predicted Kw and the retardation factor (Rw) in pure water system by solvophobic theory are thus possibly inaccurate. 相似文献
Activated sludges originated from wastewater treatment plants (WWTPs) play an important role in heavy metal removal from effluents. Extracellular polymers (ECP) form a major part of the activated sludge and are heavily involved in biosorption of heavy metals. The complexation of three heavy metals (Cd, Cu and Pb) with ECP extracted from six activated sludges, originated from different WWTPs, was investigated at pH 7.
ECP in the study were shown to be mainly composed of proteins, humic acids, uronic acids and polysaccharides along with smaller amounts of lipids and nucleic acids. IR spectra confirmed the presence of the functional groups usually found in the ECP and the content in each fraction was determined using colorimetric methods. The determination of surface charge was carried out on each ECP sample and allowed two pKa values characteristic of two distinctive functional groups to be determined. At the pH used in the study, the value of these constants indicates that only one functional group is under protonated form.
A polarographic method was used to determine the complexation parameters (number of binding sites and complexation constant) of ECP solutions towards metals. The following orders were established for the number of binding sites: Cu > Pb Cd and for the stability of the ECP–metal complex: Cd > Pb Cu.
A matrix of correlation between the composition of the polymers and the complexation parameters showed that the number of binding sites and the complexation constant were strongly linked to proteins, polysaccharides and humic substances content. 相似文献
In spite of increasing efforts to reduce nitrogen inputs into groundwater from intensive agriculture, nitrate (NO3) remains one of the major pollutants of drinking-water resources worldwide. Determining the source(s) of NO3 contamination in groundwater is an important first step for improving groundwater quality by emission control, and it is with this aim that we investigated the viability of an isotopic multi-tracer approach (delta15N, delta11B, 87Sr/86Sr), in addition to conventional hydrogeologic analysis, in two small catchments of the Arguenon watershed (Brittany, France). The main anthropogenic sources (fertilizer, sewage effluent, and hog, cattle and poultry manure) were first characterized by their specific B, N and Sr isotope signatures, and compared to those observed in the ground- and surface waters. Chemical and isotopic evidence shows that both denitrification and mixing within the watershed have the effect of buffering NO3 contamination in the groundwater. Coupled delta11B, delta15N and 87Sr/86Sr results indicate that a large part of the NO3 contamination in the Arguenon watershed originates from the spreading of animal manure, with hog manure being a major contributor. Point sources, such as sewage effluents, contribute to the NO3 budget of the two watersheds. 相似文献
Studies were conducted to quantify variability for pulp industry wastewater effluent, pulp and sludge analyses. Intralaboratory variability studies indicated that there is a potential for greater between batch variability in results than for within a batch. Intralaboratory relative standard deviations for replicate analyses ranged from 6% to 60%. Interlaboratory studies, using standard reference materials showed relative standard deviations from 4% to 135%. There appeared to be little dependance of variability on concentration, suggesting matrix effects were very important. In general, effluent variability was greater than observed for pulps or sludges. Analysis of reference standards indicated that 13% to 17% variability can be attributed to differences in calibration standards. A limited study of full congener PCDD/PCDF analysis variability showed it to be greater than observed for TCDD/TCDF. 相似文献