Makers of OilSorb™ and Other State-of-the-Art Filtration Media
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Makers of OilSorb™ and Other State-of-the-Art Filtration Media
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Stormwater Treatment Organoclays are a cost-effective, easy-to-use method for removing oil from water in a variety of applications George R. Alther Because stormwater runoff from parking lots, paved streets, and asphalt-covered roofs often is contaminated with oil; benzene, toluene, ethlybenzene, and xylene (BTEX); and fuels that have leaked from vehicles or leached from asphalt, it is unacceptable for discharge into the sewerage system. Some states now limit the concentration of oil that can be discharged into surface waters to 10 mg/L. Industries and municipalities, therefore, are installing systems that can remove these contaminants from stormwater. Typical systems include oil-water separators and ultrafiltration systems -- both of which have limitations. Oil-water separators cannot reduce the oil level to less than about 15 Mg/L and do not remove BTEX; ultrafiltration units' membranes quickly become fouled by oils. Using organically modified clays (organoclays) to remove oil from stormwater is a less common, but more effective method that typically removes oil to concentrations less than 3 mg/L. Organoclays have been modified with quaternary amines to remove oils and other non-polar compounds with low water solubility from water by means of a partitioning mechanism. Typically, the clays are used in a granular form, blended with anthracite, and placed into activated-carbon adsorber columns through which stormwater flows are directed. A treatment combination in which activated carbon follows the organoclay typically is most effective. Organoclay removes seven times more oil than activated carbon (an oil content equivalent to 50% of its weight). Therefore, in this treatment combination the organoclay removes the oils and the carbon removes the BTEX. Description of Organoclay Organoclays are manufactured by modifying bentonite - chemically altered volcanic ash that consists primarily of the clay mineral montmorillonite - with quaternary amines, a type of surfactant that contains a nitrogen ion. The nitrogen end of the quaternary amine (the hydrophilic end) is positively charged and ion exchanges onto the clay platelet for sodium or calcium. The bentonite has a charge of 70 to 90 milliequivalent per gram (meq/g). After it is treated with the quaternary amine, approximately 30 to 40 meq/g remain, which gives the organoclay the capability to remove small amounts of common heavy metals, including lead, copper, cadmium, and nickel. Organoclay can be used in granular form in carbon vessels or as powder in batch-treatment systems. As the organoclay is introduced into water, the quaternary amine is activated and extends perpendicularly off the clay platelets into the water. A chlorine or bromine ion is attached loosely to the carbon chain. The positively charged sodium ions replaced by nitrogen bond with this chlorine ion, causing the sodium salt to wash away, leaving behind a neutral surfactant - the organoclay. The hydrophilic end of the amine dissolves into the oil, removing it from water. Because the partition reaction takes place outside the clay particle, in contrast to adsorption of oil inside activated carbon pores, the organoclay does not foul quickly like activated carbon does. The anthracite that is blended with the granular organoclay also has oil removal capabilities, and has about the same bulk density [56 lb/ft3 (897 kg/m3)] as the organoclay to prevent the interstitial pores from filling with oil immediately. Organoclays also are effective in removing chlorinated phenols and other hydrophobic, chlorinated compounds that are sparingly soluble, including polynuclear aromatic hydrocarbons and polychlorinated biphenyls. When combined with activated carbon, organoclays remove BTEX much more economically, because the organoclay removes low-solubility compounds, including xylene and toluene, while the carbon removes benzene. Figure 2 (p. 33) compares the costs of using activated carbon, alone, to remove oil from water versus using organoclay-anthracite to remove oil. Organoclay reduces operating costs by approximately 50%. Application Options One of the most common uses of organoclays is for stormwater cleanup. Various application methods are available, depending on the facility setup and the volume and chemistry of the stormwater being treated. When local authorities required a facility in New York state to capture stormwater runoff from its parking lot and treat the water before discharging it into the city sewer, the facility constructed a collection and storage pond, and used organoclay to treat stormwater effectively. At the lowest point of the pond, a trench was dug and 10-ft-long x 6-in.-wide (3-m-long x 150-mm-wide) slotted polyvinyl chloride pipes were placed inside, vertically, in a zigzag manner that caused each pipe to overlap the next one. The pipes were surrounded with soil to keep them in place and then filled with a granular organoclay-anthracite blend (30% and 70%, respectively). When stormwater fills the pond, it passes through the pipes at a rate of approximately 10 gal/min (38 L/min), and the organoclay in the pipes removes oil and gasoline from the stormwater. The water flows through the organoclay-anthracite barrier directly into the sewer system. The system also could have been constructed by filling the entire trench with an organoclay-anthracite blend. However, installing the piping system saved the facility money in the long run, because less material is needed to fill the slotted pipes than to fill the entire trench. The piping system also simplifies maintenance. Removing the pipes from the trench, replacing the organoclay, and returning the pipes to the trench is easier than emptying the entire trench. While the trench configuration is ideal for cleaning stormwater that is collected in a pond; other application methods are available for facilities that encounter large volumes of stormwater runoff and want to reuse treated stormwater - as boiler feed water, for example. Photo 1 (p. 31) shows two adsorption vessels, the first one filled with organoclay-anthracite, the second one filled with activated carbon. The vessels are preceded by bag filters and an oil-water separator. Setups like this one are particularly effective for utility companies and other large processing facilities that have serious problems with stormwater runoff, particularly in states like Florida and Texas, which experience frequent heavy rainfall. Another way to apply the technology is to install a trailer-mounted system equipped with an adsorber vessel filled with organoclay-anthracite, followed by a system filled with activated carbon. An oil-water separator could be added by constructing a larger trailer. Cities use configurations like this as mobile treatment systems that can be driven from one city-owned parking lot to the next to clean up stormwater. Case Histories The case histories below illustrate how organoclay-anthracite has been used to remove oil and grease from water efficiently, and to protect activated carbon from fouling. Hill Air Force Base (Ogden, Utah). Stormwater runoff and wastewater from paint stripping, degreasing, electroplating, and other airplane cleaning operations contained oil, grease, trichloroethylene, tetrachloroethane, chloroform, methylene chloride, and heavy metals including lead, cadmium, nickel, and zinc. The combined wastewater stream was collected in a sump system, treated in a secondary clarifier and a dissolved air flotation unit, and then treated in three organoclay vessels, followed by four carbon vessels. This system operated for more than 3 years without requiring a changeout of the organoclay or activated carbon media. Alaska industrial site. When groundwater contaminated with diesel fuel was treated with three activated carbon filters, breakthrough occurred within 2 days. Placing three filters filled with organoclay in front of the carbon solved this problem. The cleanup project was completed in 3 months; neither the organoclay nor the carbon beds were exhausted at that point. Florida power plant. A Florida utility installed a stormwater treatment system consisting of several 50-gal/min (189-L/min) adsorption vessels filled with 1600 lb (726 kg) of organoclay. Stormwater is routed through the vessels and given a 5-minute retention time. When it rains, water entering the system exhibits sheen and contains about 10 mg/L of oil. The organoclay removes 60% of its weight in oil, is performing as expected, and requires minimum maintenance. Since installing the system, the facility's runoff has met all local discharge specifications. Arkansas residential community. When a 10 000-gal (37.9-m3) underground storage tank leaked diesel fuel into the aquifer surrounding a small community, the contaminated water plume threatened to infiltrate a municipal water supply well located several hundred feet down-gradient from the tank. A contractor drilled four interceptor wells to withdraw the contaminated water before it reached the municipal well. The total extraction rate was 50 gal/min (189 L/min), and average oil and grease concentrations were 35 mg /L. The extracted groundwater was passed through an oil-water separator and then a column of organoclay adsorption media, and the treated effluent was re-injected into the aquifer upgradient of the tank. The final treated effluent recorded oil and grease concentrations of less than 1 mg/L. No hydrocarbons ever were detected in the municipal drinking water well. California refinery. A California refinery installed a temporary system to treat stormwater runoff to meet local regulations requiring that no more than 10 mg/L of oil be discharged into the sewer system. The existing system included equalization tanks, bag filters, and a flocculant-addition tank. A huge 2,000-gal/min (7600-L/min) adsorber was installed that contained 72,000 lb (32,000 kg) of organoclay. As soon as the system went on-line, the facility became compliant with the regulations - the oil content in the treated water dropped to less than 5 mg/L. As the above examples show, whether it is used in combination with activated carbon or, by itself, organoclay is an effective filtration media to remove small amounts - 200 mg/L or less - of oil and grease from water. The system has proven itself reliable and cost-effective in municipal and industrial applications throughout the United States, and is an ideal stormwater treatment solution. |
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Biomin, Inc. P.O. Box 20028 Ferndale, MI 48220 Phone: 248-544-2552 Fax: 248-544-3733 E-Mail: biomin@aol.com See Master Mind Marketing Inc with questions or comments regarding this web site. |
