Expected contaminant dispersion

Off-gassing is expeeted mainly for the eontaminant not adsorbed in the pores of the adsorbent. At low eontaminant loadings, most, or all, of the contaminant molecules are expected to be in the pores. As the contaminant concentration increases, the eontaminant eapacity of the pores is reached, and excess contaminant disperses on the rest of the substrate which is non-binding. These excess moleeules are free to evaporate. 

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

The dispersed phase fluid must circulate for large fluid particles in qualitatively the same manner as for small fluid particles. Because of the large values of Eo, surface-active contaminants are not expected to damp out internal fluid... 

Krey plotted the area within the isopleth (Fig. 5.7), and found that the area (km2) within the isopleths, Ap (Bq m-2), was proportional to A 0,824. Since the area increased less rapidly than A l, a summation was possible, and this gave a result 0.15 TBq (4 Ci) as the total deposit of Pu from the spill at Rocky Flats. The highest deposit was 7.4 x 104 Bq m-2 2fiC m-2). This greatly exceeded the peak off-site contamination at N.T.S., but the area involved was much less, as would be expected from the modes of dispersal in the two cases. 

One of the immediate applications of this model is to simulate advection and dispersion of contaminants in soil columns with low permeability and strong retention mechanisms. In these cases, the contaminant would not be expected to travel to the lowest layers of the soil profile very soon. In this chapter, results from two common contaminant-input conceptualizations were simulated. The first scenario consisted of a localized contaminant load (point source) located at the center of the topsoil column layer (point-source contaminant inputs may simulate localized leakages of chemicals on the surface of the earth). The second simulation consists of a linearly distributed contaminant load (line source) over the top surface of a soil column. Line sources are commonly used in groundwater contamination problems (e.g., see Mulligan and Ahlfeld, 2001). Additionally, a two-point source simulation is included for purposes of comparison. 

Type B agents normally are expected to be dispersed in liquid form to contaminate... 

For Fildes s successors at Porton Down, the problem is now beginning to look insoluble. As Rex Watson, the present Director of Porton Down, put it in an interview in 1981 The attraction of anthrax when it was used was that it was thought to be sufficiently resistant an organism to withstand being dispersed by a munition... I don t think at that time perhaps they understood as much as we do now about its persistence over very long periods. 7 Porton would expect there to be an area of contamination for the next tens, perhaps even hundreds of years. Until that area is clear, Gruinard will remain closed to the public. At the moment, to be sure of being safe, the Porton men who go back still have to wear protective suits and take a seven and a half month course of injections. I doubt, added Dr Watson, that we would do such an experiment now if we had to in those conditions. ... 

Let us point out two more aspects of this problem, which contribute to the preservation of a noticeable mobility of the bubble surface. It is expected that in the development of microflotation technology, increasingly deeper purification from dispersed particles and therefore from molecular contaminations can be attained under the condition of a remarkable residual mobility. 

Natural attenuation (NA) refers to the reduction of contaminant concentrations in environmental media by processes such as dilution, dispersion, sorption, volatilization, and biotic or abiotic transformations. As a passive remediation approach, NA is mostly applied in connection with organic contaminants which migrate from the source in groundwater. Naturally attenuating contaminant plumes show a decline in the dissolved contaminant mass as a function of time, and a decline in contaminant concentrations downgradient from the source. Before potential receptor exposure points are reached, natural attenuation is expected to reduce dissolved contaminant concentrations below regulatory standards (Wiedeme-ier et al. 1999). 

---