Contaminants removal treatment

A U.S. EPA study (41) showed that soil vapor extraction (SVE) is an effective treatment for removing volatile contaminants from the vadose zone. Sandy soils are more effectively treated than clay or soils with higher organic content because higher air flows are possible in sand and clays—organic soils tend to adsorb or retain more contaminants. Removal of volatiles is rapid in the initial phase of treatment and thereafter decreases rapidly thereafter-an important consideration in the design of air emissions control over the life of the project. 

Where small and/or single contaminant effluents are encountered, packaged treatment plants may be acceptable. Consideration should, however, be given to capital cost, payback period, reliability of equipment, maintenance, plant-life expectancy and contaminant-removal efficiencies. 

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. 

To meet the specified standard,4 wastewaters are often subjected to a series of treatment processes before they are discharged into the environment, particularly, water bodies. The treatment processes include physical, chemical, and biological processes that may be applied singly or collectively. The collective application of the processes can be employed in a variety of systems classified as primary, secondary, and tertiary wastewater treatment, to achieve different levels of contaminants removal.2... 

Wang, L.K. Kurylko, L. Wang, M.H.S. Contamination Removal System Employing Filtration and Plural Ultraviolet and Chemical Treatment Steps and Treatment Mode Controller. U.S. Patent No. 5,190,659, March 1993. 

Activated alumina is an ex situ contaminant removal technology that extracts metals from liquid and airstreams by adsorption. It is often used as a polishing treatment in conjunction with... 

If the source of contamination is not removed, treatment of the groundwater may be ineffective as a long-term sointion. 

For a project at Fort Richardson in Alaska, total treatment costs using SVE and SPSH were 967,822. Costs ranged from 189 to 288/yd of soil treated, or 726 to 2552/lb of contaminant removed. Because the site was in a remote location, diesel generators were used as a power source. This factor may have increased treatment costs (D21202S, pp. 34, 35). For additional information about this project, please see Case Study 3. 

The Stripperator was used as part of a pump-and-treat system installed at Camp Lejeune in North Carolina. This system, which was used to remove VOCs, had an average cost of 95,000 per pound of contaminant removed. According to the U.S. Navy, 175,000 was spent on the system to remove 3 lb of contaminants, and 325,000 was spent to remove an additional 0.5 lb. The Navy claims that the high cost of treatment at the site resulted from inefficiencies in groundwater extraction methods and was not caused by the use of the Stripperator (D22770N, p. ES-1, ES-3, 3-18-3-28). 

In the cost analysis, EPA stated that there was a correlation between SVE unit costs and the volume of soil treated. SVE was demonstrated to have a measurable economy of scale. Unit costs for the treatment of less than 10,000 yd of soil ranged from 60 to 350/yd. Unit costs for applications treating more than 10,000 yd of soil were as low as 5/yd treated. A similar correlation was noted for unit costs versus mass of contaminants removed. Unit costs for projects with less than 3000 lb of contaminants requiring removal ranged from 300 to 900/lb. Unit costs for larger projects were less than 15/lb, and costs for treating over 500,000 lb of contaminants were less than 2/lb (D22449H, pp. 4-1, p. 4-4). 

The efficiency of the system is dependent on the soil type, contaminant type, and contaminant concentrations. Many sites require that an impermeable barrier or containment wall be constructed to prevent the continued migration of pollutants through soil and water. The treatment area must be clear of underground obstructions. Treatment is generally limited to soil less than 40 ft deep. More energy may be required to achieve contaminant removal in saturated soils. 

At a Superfund site in Battle Creek, Michigan, DVE was nsed as part of a larger SVE system to treat 26,700 yd of VOC-contaminated soil. Excluding before-treatment cost elements, total remediation expenses at the site were 1,645,281. This valne translates to 62/yd of soil treated, or 37/lb of contaminant removed. Before-treatment costs at the site eqnaled 535,180. The EPA notes that overall costs at this site were higher becanse of the extensive sampling and analysis that were required (D13945R, pp. 225, 227 D125053, p. 871). 

TerraTherm Environmental Services, Inc., a subsidiary of Shell Technology Ventures, Inc., has developed the in situ thermal desorption (ISTD) thermal blanket technology to treat or remove volatile and semivolatile contaminants from near-surface soils and pavements. The contaminant removal is accomplished by heating the soil in sim (without excavation) to desorb and treat contaminants. In addition to evaporation and volatilization, contaminants are removed by several mechanisms, including steam distillation, pyrolysis, oxidation, and other chemical reactions. Vaporized contaminants are drawn to the surface by vacuum, collected beneath an impermeable sheet, and routed to a vapor treatment system where contaminants are thermally oxidized or adsorbed. 

Before one of the zero-valent iron treatment processes can be used at a site, extensive batch tests must be performed. Then, column tests are performed for several months to predict performance based on site conditions. Following pilot tests that take 6 months to a year, full-scale operation may begin. Thorough research of the site has to be conducted. For the treatment to be successful, the precise water velocity, depth of contamination, and soil matrix have to be known (Wilson, 1995). Errors in these calculations would cause the treatment to be ineffective in contaminant removal. From these results, the size of the barrier is determined by the least reactive contaminant. 

Electrochemical technique (also electrocoagulation) is a simple and efficient method for the treatment of potable water. This process is characterized by a fast rate of contaminant removal, a compact size of the equipment, simplicity in operation and low capital and operating costs. Moreover, it is particularly more effective in treating wastewaters containing small and light suspended particles, such as oily restaurant wastewater, because of the accompanying electroflotation effect. 

This section aims to explain the unique features of membrane separation methods, their superior performance in contaminant removal, and their operational sensitivities and limitations. We focus particularly on the factors that need to be carefully assessed when the membrane technology to be used in the treatment of liquid radioactive waste is being considered. These include membrane configuration and arrangement, process application, operational experience, data related to key performance parameters, and plant and organizational impacts. 

The type of activated carbon used for the treatment of groundwater depends upon the other organic compounds present. For example, humic acids will often compete with other contaminants for adsorption sites. Hence, for each situation, isotherms should be determined, and the efficiency of contaminant removal should be evaluated on a TOC basis (total organic carbon). As noted, the compounds most prevalent in groundwaters are chlorinated organics. Their removal by adsorption on GAC is the most effective treatment in liquid or gas phase processes [66]. 

Remove the by-products after they are formed this first approach, removing the by-products after they are formed, can be difficult and costly. Many books discuss the treatment technologies available for organic contaminant removal (1,2). 

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