Contaminant recovery

Surfactants have been widely used to reduce the interfacial tension between oil and soil, thus enhancing the efficiency of rinsing oil from soil. Numerous environmentally safe and relatively inexpensive surfactants are commercially available. Table 18.6 lists some surfactants and their chemical properties.74 The data in Table 18.6 are based on laboratory experimentation therefore, before selection, further field testing on their performance is recommended. The Texas Research Institute75 demonstrated that a mixture of anionic and nonionic surfactants resulted in contaminant recovery of up to 40%. A laboratory study showed that crude oil recovery was increased from less than 1% to 86%, and PCB recovery was increased from less than 1% to 68% when soil columns were flushed with an aqueous surfactant solution.74-76... 

During the later phases of remediation of an aquifer, it has often been suggested that the expense of continuing LNAPL recovery is not worth the effort, considering the remaining small quantities of recoverable product. The implication of this argument has been that the product will eventually go into solution and therefore will be recovered as part of the dissolved contaminant recovery. Experience has demonstrated that this is not usually a viable option, because the time required and treatment costs to accomplish the task are much greater than with respect to LNAPL product recovery efforts. 

In another example, urine samples were extracted with MIP phases imprinted with clenbuterol in order to determine the concentration of this (3-agonist, which is known to be misused in animal breeding and thus is occasionally found as a food contaminant. Recovery rates of up to 75% were observed for spiked samples when extracting the clenbuterol. However, in subsequent control experiments clenbuterol was detected also in non-spiked blank urine samples, and further experiments lead to the conclusion that the clenbuterol used as template permanently bled from the Mi-polymer. Consequently, the authors decided to use in the future a structural analogue as template instead of clenbuterol in order to avoid this problem [44]. 

In many studies, the slow fraction was underestimated due to incomplete contaminant recovery. This can lead to erroneous conclusions when some process of interest is being measured against the mass of contaminant believed to be present. 

The technology requires the site to have a barrier layer below the depth of contamination. Dependent upon the type of contamination, this layer can be either a high-permeabiUty layer, a low-permeability layer, or the water table. Low-permeabUity sods can isolate the contaminants from contact with the steam, and thus impede contaminant recovery. 

According to the vendor, typical subsurface contaminant recovery applications cost about 75 to 150/yd. In contrast, costs for removal and incineration can range from 200 to 300/yd (D14453G, p. 5). 

Special applications The environmental control and life support system on a spacecraft maintains a safe and comfortable environment, in which the crew can live and work, by supplying oxygen and water and by removing carbon dioxide, water vapor, and trace contaminants from cabin air. It is apparent that the processes aimed at the recycling of air and water are vital for supporting life in the cabin. These recycling processes include separation and reduction of carbon dioxide, removal of trace gas-phase contaminants, recovery and purification of humidity condensate, purification and polishing of wastewater streams, and are performed totally or in part by adsorption equipment (Dabrowski, 2001). ... 

In order to maintain wastewater discharges within permit conditions and reduce flows to manageable rates for contaminant recovery systems, a program to reduce rinsewater flows was initiated in September 1986. The thrust of this program... 

Despite the temperature limitations of thermal screw systems, there are some advantages. First, since thermal screws operate at a lower temperature, they require less fuel and do not combust the contaminants, thereby allowing for contaminant recovery. Second, since these systems are indirectly heated, the volume of off-gas generated is lower. Finally, the interlocking screws increase mixing of the feedstock, which improves treatment. ... 

An alternative to destroying contaminants in a thermal oxidizer is to recover them for further treatment. As shown in Fig. 3, the APC system for contaminant recovery also begins with a baghouse/cyclone to remove particulate matter. However, the off-gas is then directed to a condenser instead of a thermal oxidizer. 

Fig. 3 Off-gas treatment with system with contaminant recovery.

In addition to the minimum DRE and the limits on HCl for thermal oxidizers already mentioned, regulatory agencies will place emission limits on the exhaust gas depending on local regulations and the contaminants of concern. The most commonly regulated emissions for thermal oxidizer exhaust are particulate matter (PM), CO, HCl, sulfur oxides (SO ), VOCs, total hydrocarbons (THC), and nitrogenoxides (NO t). Alternatively, regulators typically place limits on PM, THC, and/or VOC emissions from contaminant recovery systems. ... 

There are mainly two proposed mechanisms for NOx contamination recovery NO reduction and NOx oxidation. Mohtadi et al. [35] proposed a NOx reduction mechanism [35] ... 

---