Dissolved fraction

Radionuclides are usually extracted from filtrates of discrete samples (from the Rosette sampler, Gerard bottles or from the ship s seawater supply) by coprecipitation as Fe(OH)3, Mg(OH)2, Mn02, BaS04, PbS04 or Co-APDC. If quantitative recovery cannot be guaranteed, yield tracers are used. The sample volume has to be known accurately. Large volumes can be metered with a water meter (approximately 1 % error). Samples of approximately 25 L can conveniently be weighed on board with a balance (precision approximately 50 g). 

A widely used method to extract radionuclides is to run the sample through columns filled with Mn02-coated fibres. Such columns or cartridges can be made to remove Th, Pa, Ra, Ac (not U) with high efficiency from large volumes (several m ) of seawater. As the efficiencies are seldom 100 %, two identical cartridges are used in line. The efficiency, E, can then be calculated from the ratio of activities A and B measured in the two cartridges  

Preparation of Mn02-Cfiated acrylic fibre Moore, 1976) 

Several batches of Mn-fibre may be prepared from the initial solution. As the MnOj activity of the solution is reduced, the reaction speed slows and each batch requires more time. To compensate, additional solid KMn04 may be added to the original solution. However, the common ion effect will ultimately render the solution ineffective. The decision when to discard the solution is a trade off between the rate of preparation and the cost of preparing a new solution. 

Preparation of Mn02-coated polypropylene filter cartridges Buesseler et ai, 1992 Hartman and Buesseler, 1994) 

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A simple experiment with a coffee-cup calorimeter shows that when one gram of NH4N03 dissolves, fraction = 351 J. The calorimeter is open to the atmosphere, the pressure is constant, and... 

Efforts to apply Equations (6) and (7) to distributions of Th isotopes in the oceans showed that the situation was more complex. For example. Bacon and Anderson (1982) measured vertical distributions of Th in the deep sea and found that both the particulate and dissolved fractions increased linearly with depth. While the former observation is predictable from Equation (7) if sinking particles continue to scavenge Th during their descent, the latter is inconsistent with Equation (6). Bacon and Anderson (1982) suggested that the data could best be explained by a reversible scavenging equilibrium maintained between dissolved and particulate Th. Thus Equation (6) must be modified to ... 

If this binding does occur, then one would expect very strongly bound compounds to show an unusual affinity for the aqueous phase. This could increase the mobility of these compounds in the environment. It is likely that the bound fraction will undergo phase transfers and degradation at different rates than the free truly dissolved fraction of a dissolved pollutant. If this is the case, then an observed equilibrium between a pollutant in the free and bound states could significantly affect its environmental behavior. 

In a dialysis experiment, a dialysis bag containing the dissolved humic materials is placed in a solution of a pollutant (preferably radiolabeled). The dialysis tubing is chosen so the pollutant is free to diffuse through the bag while the humic materials are retained inside the bag. The solution is shaken at constant temperature until it comes to an equilibrium point. At equilibrium, the pollutant inside the dialysis bag consists of two fractions that truly dissolved and the bound to the humic materials. The concentration of pollutant on the outside of the dialysis bag consists only of the free, truly dissolved fraction. Any increase of the pollutant concentration on the inside of the dialysis bag is due to binding by dissolved humic materials. A series of dialysis experiments, therefore, can measure the bound fraction concentration as a function of the free concentration. 

Average dissolved fractions of carbohydrates and proteins are shown in Table 3.4. Protein only exists in a dissolved form after transport in a sewer network, whereas lipids, per definition, are nondissolved. 

Although the investigations of both Raunkjaer et al. (1995) and Almeida (1999) showed that removal of COD — measured as a dissolved fraction — took place in aerobic sewers, a total COD removal was more difficult to identify. From a process point of view, it is clear that total COD is a parameter with fundamental limitations, because it does not reflect the transformation of dissolved organic fractions of substrates into particulate biomass. The dissolved organic fractions (i.e., VFAs and part of the carbohydrates and proteins) are, from an analytical point of view and under aerobic conditions, considered to be useful indicators of microbial activity and substrate removal in a sewer. The kinetics of the removal or transformations of these components can, however, not clearly be expressed. Removal of dissolved carbohydrates can be empirically described in terms of 1 -order kinetics, but a conceptual formulation of a theory of the microbial activity in a sewer in this way is not possible. The conclusion is that theoretical limitations and methodological problems are major obstacles for characterization of microbial processes in sewers based on bulk parameters like COD, even when these parameters are determined as specific chemical or physical fractions. 

In a study involving several contaminated freshwater streams in New Jersey Pinelands, Ross and Sherrell [8] have used CFF, with a 10 kDa (ca. 3 nm) cutoff, to separate the filtrate (<0.45 pm) into colloidal and truly dissolved fractions in freshwater systems. The colloidal fraction,/cou, was calculated by difference ... 

Environmental chemicals occur as pure liquid or solid compounds, dissolved in water or in nonaqueous liquids, volatilised in gases, dissolved in solids (absorbed) or bound to interfaces (adsorbed). Figure 5 gives a schematic view of the different physical states at which substrates are taken up by microbial cells. There is a consensus that water-dissolved chemicals are available to microbes. This is obvious for readily soluble chemicals, but there is also clear evidence for microbial uptake of the small dissolved fractions of poorly water soluble compounds. Rogoff already had shown in 1962 that bacteria take up phenanthrene from aqueous solution [55], In the intervening time many other researchers have made the same observation with various combinations of microorganisms and poorly soluble compounds [14,56,57]. 

Uptake occurs from the bioavailable fraction, which in almost all cases corresponds to the dissolved fraction. Sorption and binding to suspended solids, sediments, and DOM have a great effect on bioavailability [71,72] therefore the more hydrophobic surfactants tend to be less bioavailable. Thus, for the same initial concentration, the bioavailable fraction of C12LAS, compared with that of the Cn... 

The practice of free-phase NAPL recovery, soil vapor extraction, and hydraulic containment at remediation sites almost always generates some volume of water contaminated with dissolved fractions. Depending on the size of the facility and the scale of the recovery and restoration project, the amount of groundwater coproduced can possibly exceed 1000 gal/min. Handling of these volumes of contaminated water can be very expensive if treatment is required prior to disposal or reinjection. Treatment of water derived from sites contaminated by other organic chemicals will involve adaptations of these procedures to the specific situation. 

The primary concern with coproduced water during NAPL recovery operations will normally be removal of the dissolved fractions of hydrocarbons. As previously indicated, there are many treatment technologies available for the removal of dissolved hydrocarbons. The commonly used processes are discussed in the following sections. 

The issue of dissolved fractions, in terms of aquifer restoration objectives, would be more appropriately addressed at a phase of the remediation program after the source of the dissolved contamination is controlled. Of course, containment of the dissolved plume remains a priority throughout the program. For large-scale recovery programs, requiring treatment prior to reinjection would place an excessive economic burden on the overall remediation effort without technical justification, at least during the course of NAPL recovery. 

When released to surface waters, mirex will bind primarily (80-90%) to the dissolved organic matter in the water with a small amount (10-20%) remaining in the dissolved fraction, because mirex is a highly hydrophobic compound (Yin and Hassett 1989). Mean mirex concentrations in sediments, collected at four basins in Lake Ontario between 1982 and 1986, ranged from 30 to 38 pg/kg in three of the basins within the water circulation pattern of the lake. A fourth basin outside the pattern showed much lower concentrations (6.4 pg/kg), indicating that mirex was being transported with the lake water (Oliver et al. 1989). The residence time for mirex in Lake Ontario water was estimated to be 0.3 years. This indicated that mirex was either scavenged by particles or was chemically reactive and, therefore, was rapidly removed from the water column (Arimoto 1989). 

Figure 17 Volume dependent in vivo dissolution of micronized felodipine FCDNa indicates the dissolved fraction of felodipine aspirated at mid-jejunum of Labradors. The orally administered dose of 10 mg was suspended in 200 mL saline 0.9% (Experiments E and F) or glucose 20% (Experiments B, D, and S). VR represents the recovered fluid volume. Source From Ref. 10, Figure 16.12.

As shown in Figure 5.3, chemicals, such as iron, can be present in a rariety of species and phases that span a large size spectrum. The dissolved fraction can include inorganic complexes, organometallic molecules, and the uncomplexed ions. In the case of iron, two oxidation states are possible, so the free ion can be in the form of Fe (aq) or Fe " (aq). In the colloidal and particulate phases, iron can be present as part of a mineral (inorganic) or an organic molecule. Within the particulate phase, a distinction is often made between the fraction that is adsorbed, usually electrostatically as an ion, onto the surface and the fraction that is covalently bound into the crystal lattice. 

One way that contaminants are retained in the subsurface is in the form of a dissolved fraction in the subsurface aqueous solution. As described in Chapter 1, the subsurface aqueous phase includes retained water, near the solid surface, and free water. If the retained water has an apparently static character, the subsurface free water is in a continuous feedback system with any incoming source of water. The amount and composition of incoming water are controlled by natural or human-induced factors. Contaminants may reach the subsurface liquid phase directly from a polluted gaseous phase, from point and nonpoint contamination sources on the land surface, from already polluted groundwater, or from the release of toxic compounds adsorbed on suspended particles. Moreover, disposal of an aqueous liquid that contains an amount of contaminant greater than its solubility in water may lead to the formation of a type of emulsion containing very small droplets. Under such conditions, one must deal with apparent solubility, which is greater than handbook contaminant solubility values. 

Relationship Between Nodular and Rejecting Layers. Nodular formation was conceived by Maler and Scheuerman (14) and was shown to exist in the skin structure of anisotropic cellulose acetate membranes by Schultz and Asunmaa ( ), who ion etched the skin to discover an assembly of close-packed, 188 A in diameter spheres. Resting (15) has identified this kind of micellar structure in dry cellulose ester reverse osmosis membranes, and Panar, et al. (16) has identified their existence in the polyamide derivatives. Our work has shown that nodules exist in most polymeric membranes cast into a nonsolvent bath, where gelation at the interface is caused by initial depletion of solvent, as shown in Case B, which follows restricted Inward contraction of the interfacial zone. This leads to a dispersed phase of micelles within a continuous phase (designated as "polymer-poor phase") composed of a mixture of solvents, coagulant, and a dissolved fraction of the polymer. The formation of such a skin is delineated in the scheme shown in Figure 11. 

Fig. 16.18 Relationship between dissolved frac- tribution of the metal in the Fe oxide curve I lotion of various metals and dissolved fraction of cation of the metal at the Fe oxide surface curve...

A correction for the dissolved fraction of the less sol component must be established experimentally. Approx qualitative analysis by framing is described. Fcoin the amt of solv just insufficient to dissolve a known wt of sample and the addnl amt reqd to effect soln, identity of the sample is deed. Other tests used are mp, colors obtd in acetone soln with NaOH. NHa and the crystn form See also Refs given below Refs 1) M. Thomas, MP 36, 133—62(1952)... 

When kdesorb is very slow (or even zero as when the compound is encapsulated in an authigenic mineral), [z]sorbed Ald[z]w so we can neglect the second term in the gradient driving transfer. In this case, we refer to the compound as experiencing sequestration. The parameter, (1 -fw), quantifies the extent of a compound s sequestration in a particular case of interest when we are justified to assume that the dissolved fraction is equal to the bioavailable fraction. Quantitative evaluation of desorb is taken up in Section 19.5. 

Dissolved fraction and equilibrium partition coefficient, at sediment-water interface ... 

Eq. 11) we found that the open-water diffusivity is reduced by the dissolved fraction fw. Adapted to diffusion in the particle aggregate, we get the effective diffusivity ... 

To calculate the (macroscopic) distribution coefficient Kd(t) from Eq. 19-69 we have to remember that Cs(/) is defined as the total mass of the chemical in the dried particle divided by the particle mass. This includes the dissolved fraction of the chemical in the pore water when the particles are dried. Thus from Eq. 19-71 ... 

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