Contaminants removal rate

The contaminants removal rate RIem can be calculated by multiplying the flow rate of air extracted from all the wells by the concentration of contaminant in the soil air Ca ... 

An advantage of the CURE process is the ability to achieve high contaminant removal rates. Also, floe, a by-product of the CURE process, tends to be stable and settle rapidly. Electrocoagulation will not remove metals that do not form precipitates. In addition, electrocoagulation will not remove nonreactive, soluble organic compounds nor desalinate water. 

Typically, the air-stripper manufacturer will supply liquid flow ranges acceptable for a particular tower. Selecting an air stripper for which the design flow is at the lower end of the tower s rated capacity will produce high contaminant removal rates, but may not optimize power requirements. For large-scale systems where significant operational costs may be incurred by overdesigning the system, the use of pressure-drop curves and calculations such as Eqs. (1)-(13) are required. 

The effect of the plume airflow rate and the turbulent mixing airflow rate through the zone boundary is presented in Fig. 8.35. The heat removal effectiveness and contaminant removal effectiveness are presented as functions of the relative airllow rate. 

The effect of the local exhaust airflow rate in the lower zone is presented in h ig, 8.37. The heat removal effectiveness e and contaminant removal effectiveness Cf (determined by extract air) are presented as functions of the local exhaust airflow rare. The total heat load is 60 W m - and the power of one heat source is 500 W. The supply airflow rate is 8 L s m . ... 

We recently demonstrated that photocatalyzed destruction rates of low quantum efficiency contaminant compoimds in air can be promoted substantially by addition of a high quantum efficiency contaminant, trichloroethylene (TCE), in a single pass fixed bed illuminated catalyst, using a residence time of several milliseconds [1-3]. Perchloroethylene (PCE) and trichloropropene (TCP) were also shown to promote contaminant conversion [2]. These results establish a novel potential process approach to cost-effective photocatalytic air treatment for contaminant removal. 

Removal Rate of Contaminants and Required Cleanup Time... 

Equations 14.17 and 14.18 are very simple, but the accuracy of the predictions depends greatly on the realistic estimation of Ca, which varies with time during the operation of the SVE system. For the start of the SVE project and considering that the free organic phase, NAPL, is present in the subsurface, a hrst approximation is to calculate Ca from the vapor pressure data of the contaminants (equation 2 in Table 14.3 or Equation 14.1). The actual concentration, however, will be lower than this value for two main reasons (1) the extracted airstream does not pass only through the contaminated zone and (2) limitations on mass transfer exist. An effectiveness factor q should be considered to take into account the effect of these phenomena on removal rates. The value of this factor can be determined by comparing the calculated concentration with data obtained from the preliminary pilot tests at the site ... 

Practical experience from the application of SVE at sites contaminated with a single type of contaminant (e.g., trichloroethylene, TCE) indicates that the removal of contaminants follows a trend in two distinct phases. During the initial phase, which covers the period from the project startup to the exhaustion of NAPL in the subsurface, the removal rate is almost linear. The second phase is characterized by a constant decrease in removal rates. 

This trend can be explained with the following mechanism. In the presence of NAPL, the extracted vapor concentration depends mainly on the vapor pressure of the contaminant. After the disappearance of free NAPL, the extracted vapor concentration becomes dependent on the partitioning of contaminants among the three other phases (see Table 14.3). As the air passes through the pores, the dissolved contaminants volatilize from the soil moisture to the gas phase, causing the desorption of contaminants from the surface of soil particles into the aqueous phase. As a result, the concentration in all three phases decreases, with a consequent decrease in removal rates. 

As this site is contaminated with a single compound, the removal of free NAPL is expected to follow a linear trend with constant removal rate. The required time can be calculated from Equations 14.17 and 14.18 ... 

The vacuum extraction method has been effectively applied to removing VOCs with low organic carbon content from well-drained soil, although it may also be effective for finer and wetter soils, but with comparatively slower removal rates. There are generally significant differences in the air permeability of various strata, which can influence process performance. Contaminants with low vapor pressure or high water solubilities are difficult to remove. 

When a recovery well is located within a contaminant plume and the pump is started, the initial concentration of contaminant removed is close to the maximum level during preliminary testing. As the pump continues to operate, cleaner water is drawn from the plume perimeter through the aquifer pores toward the recovery well. Some of the contaminant is released from the soil into the water in proportion to the equilibrium coefficient. For example, if the Kd is 1000, at equilibrium, 1 part is in the water and 1000 parts are retained in the soil. If the water-soil contact time is sufficient, complete equilibrium will be established. After the first pore volume flush (theoretically), the concentration in the water will be 0.9 and that on the soil will be 999. With each succeeding flush, the 1000 1 ratio will remain the same. If the time of water-soil contact is not sufficient to establish equilibrium, the recovered water will contain a lesser concentration. A typical decline curve is shown on Figure 9.2. Note the asymptotic shape of the curve where the decline rate is significantly reduced. 

Environmental contamination by pharmaceutical compounds (PhCs) has become an issue of great concern to many countries in recent years. Hence, the European Community has recently funded several projects to quantify their presence in water bodies and wastewaters, to evaluate the removal rates of compounds from major therapeutic classes during conventional and advanced treatments and to assess the risks they pose to the environment. Notable examples of these studies are ... 

Adsorption onto both powdered and granular forms of activated carbon, PAC and GAC, respectively, shows great potential for the removal of trace emerging contaminants, in particular, non-polar compounds with a log Xqw >2. PAC dose or GAC regeneration and replacement are critical for excellent removal rates [85]. 

Laboratory-scale studies indicate that the aqueous biphasic process is well suited to the recovery of ultrafine, refractory material from soils containing significant amounts of sUt and clay. The main advantages of the aqueous biphasic system in treatment of uranium-contaminated soils are that the process achieves a high removal rate for the uranium contaminant and that such removal is highly selective. Laboratory studies indicate that approximately 99% of the soil is recovered in the clean fraction. 

The PF system creates a fracture network by forcing compressed gas into a formation at pressures that cause stress failure. These fractures increase the formation s permeability. Increased permeability can greatly improve contaminant mass removal rates. PF can also increase the effective area that is influenced by each extraction weU and can intersect new pockets of contamination that were previously trapped in the formation. The ARS PF technology is patented and is commercially available. According to the vendor, it has been used at over 135 federal and private sites in the United States, Canada, Japan, and Belgium. 

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