Contaminated soil is crushed and conveyed into a reaction vessel at GeocleanÕs plant in Lorraine, France, where solvents will extract pollution from the soil.

For instance, IT Corp. of Monroeville, Pa., designed a system to inject ozone into the ground to treat groundwater laden with hydrocarbons in Long Beach, Calif. United States Filter Corp. of Naperville, Ill., has adapted a Finnish evaporating system to decontaminate groundwater containing dissolved uranium in Tuba City, Ariz. In France, a number of engineering companies have developed chemical and thermal processes to remove pollutants from soil.

Ozone is a powerful oxidizer that is generated by strong electric fields, such as lightning. Engineers have employed the principle to generate ozone to treat wastewater for many years, and are now putting it to work in cleaning groundwater, such as at the Long Beach site.

This property is now co-owned by the Los Angeles Flood Control District and the City of Long Beach, but from 1902 to 1913 it was home to a manufactured gas plant operated by Southern California Edison. Gas manufacturing was widespread in the years before World War II, when utilities heated oil or coal to produce a synthetic gas. This process generated tar, oil, and lampblack residues that were typically buried on-site, contaminating the soil and groundwater with hydrocarbon wastes.

Samples of soil analyzed by Southern California Edison showed concentrations of benzopyrene at 4,820 milligrams per kilogram, naphthalene at 20,000 mg/kg, and benzene at 4,820 mg/kg. Conventional remediation, involving excavating the soil and pumping out groundwater for treatment, was complicated because the site has been overtaken by the growth of modern Long Beach.

The Hadwaco evaporator shown treating leachate at a landfill in Lahti, Finland, provided the basis for the system that will treat uranium-laden groundwater at Tuba City, Ariz.

The 340x230-foot strip of land where gas was synthesized when Theodore Roosevelt and William Howard Taft lived in the White House is now wedged between the Long Beach Freeway and the Los Angeles River. The property is crisscrossed by an extensive system of power transmission cables, underground utilities, and elevated bridges.

The challenging nature of the Long Beach site led the California Environmental Protection Agency to select it as a pilot project for its Expedited Remedial Action Program. The program was established by the California legislature in Sacramento to test regulatory policies for the remediation of contaminated properties.

"It is unique for Southern California Edison as a non-owner to want to clean the property, but they identified the site as a liability and approached us for remedies," said Megan Cambridge, unit chief of the Expedited Remedial Action Program. "The dense subsurface infrastructure of the site made the conventional practice of extracting the contaminated groundwater very difficult, so we suggested injecting ozone into the soil to promote degradation of the polyaromatic hydrocarbons as an alternative."

In the Solvis process, polluted soil is passed through these pipes by endless screws in a countercurrent of solvent that strips them of contaminants, which are combusted elsewhere.

Southern California Edison chose IT Corp. to build the remediation system, because of the environmental engineering company's experience in building four full-scale ozonation systems and six pilot scale systems to treat similar contaminants under similar site conditions. In October 1998, IT Corp. engineers sank 31 vertical sparging points throughout the plume of contamination at the Long Beach site. The sparging points are made of corrosion-resistant Teflon tubing for most of their length, with the lower 25 feet made of 316 stainless steel rods wrapped with stainless steel wire mesh. Ozone is distributed through the screened portion of each point. The company also placed four horizontal sparging points through the center of the plume approximately six feet beneath the water table.

In a trailer on the surface, IT Corp. engineers installed two ozone generators made by Ozonia North America of Elmwood Park, N.J. Using a pure oxygen gas source, these machines generate an electric corona around ceramic dielectric components to produce a total of 52 pounds of ozone daily.

The injection gas, containing five to 10 percent ozone and 90 to 95 percent oxygen, is delivered through the sparging points into the ground at rates as fast as 7.5 cubic feet per minute, at 20 pounds per square inch pressure.

"We also installed 25 vertical monitoring wells with two-foot screens [similar in design to the ozone-injection wells] at Long Beach to measure the amount of dissolved oxygen in groundwater, which indicates whether ozone is dispersed," said Jay Dablow, a geologist at IT Corp. Dablow managed the design, construction, and operation of the Long Beach on-site ozone treatment system. Monthly groundwater and quarterly soil samples are extracted from the monitoring wells for off-site laboratory analysis.

While the Long Beach installation used long-established ozone generation chemistry, it pioneered automating the process to deliver the optimum amount of ozone to particular points of the contaminant plume. "We accomplished this by designing a manifold in the ozone-generating trailer that leads to 35 solenoid valves, each one regulating the flow of ozone to a specific sparging point," Dablow explained. Based on the findings of the monitoring wells and daily operational monitoring data, an Allen-Bradley programmable logic controller opens each solenoid valve in sequence for varying amounts of time, from 15 minutes to two hours.

As part of the remediation system, the IT Corp. engineers designed a soil vapor extraction system to capture unreacted ozone gas and lightweight hydrocarbon vapors that might seep from the ground. This system consists of 10 separate wells, screened for 10 feet, which are put under vacuum by a blower. The extracted stream of ozone, oxygen, and hydrocarbons is sent through a catalyst that destroys ozone before sending the gases into canisters filled with activated carbon. "We remove the ozone first because it can react with lighter hydrocarbons such as benzene, and when mixed with oxygen, can become explosive in carbon canisters," Dablow said.

After a second round of sampling, the ozone treatment system reduced dissolved hydrocarbons in groundwater by 80 to 90 percent, and reduced the presence of benzopyrene, a cancer-causing agent, from 600 parts per billion to undetectable levels. "We also have found that soil contaminants have migrated into our monitoring well samples," Dablow said. "This leads us to believe the ozone system will continue to strip the contaminants from the soil into the groundwater, where they can also be treated by ozonation."

The Long Beach ozone system is expected to run until next year. IT Corp. is designing an ozone treatment system similar to the Long Beach project for the site of another Southern California Edison manufactured gas plant.

An abandoned uranium mill in Tuba City, Ariz., is a reminder of the Cold War's hidden costs. The mill processed aproximately 800,000 tons of uranium ore from 1956 to 1966 for use in national defense programs and as fuel for nuclear power plants. The tailings left after the leaching of the uranium from the ore contaminated the groundwater.

The U.S. Department of Energy, which is responsible for the site and its cleanup, has commissioned United States Filter Corp. in Naperville, Ill., to design an evaporation system to treat nearly one billion gallons of contaminated groundwater over 20 years. USFilter is a subsidiary of Vivendi in Paris, a leading European environmental treatment company.

USFilter formed a joint venture with Hadwaco Ltd. OY of Helsinki, Finland, to market the latter company's mechanical vapor recompression evaporator technology in new markets, primarily North America. The MVR system that USFilter and Hadwaco designed for Tuba City will process contaminated groundwater, by distilling clean water, for reinjection into the aquifer.

Like other MVR systems, the Hadwaco evaporator compresses the evaporated process fluids to raise their temperature and pressure. The compressed vapor is then condensed, transferring its heat to the wastewater in a heat exchanger to create more evaporation. The condensed vapor, or distillate, is clean water that exceeds drinking water standards in many cases.

Environmental cleanup crews install the Tredeco equipment on-site to heat soil in a rotary furnace so that the pollutants can be removed by desorption and evaporation.

Unlike most MVR systems, the Hadwaco relies on two parallel, falling film heat exchangers made of a proprietary polymer compound, rather than metal, plastic-coated metal, or graphite shell-and-tube heat exchangers.

Hadwaco found that plastic heat exchangers are less expensive to manufacture, operate, and maintain than those other materials. Because the falling film plastic heat exchangers provide larger heat transfer areas, they reduce the temperature differential required to achieve the desired evaporation capacity. Thus, the Hadwaco evaporator uses a low-speed fan rather than a costlier, high-speed, high-maintenance mechanical compressor. In order to retain sufficient mechanical integrity within the polymeric heat exchanger, the Hadwaco evaporator operates under vacuum to make process liquid boil at 130° to 140°F. As a result, the Hadwaco evaporator can treat 1,000 gallons of wastewater while consuming 30 to 40 kilowatts per hour. Evaporators equipped with conventional heat exchangers require 60 to 300 kilowatts per hour to treat the same amount of wastewater.

A circulation pump provides a constant flow of process fluid to the upper portion of the heat transfer element, assuring uniform distribution to the heat transfer surfaces through a proprietary liquid distributor. A portion of the circulated wastewater evaporates on the outer surface of the heat transfer element. The water vapor flows through a fan compressor to increase heat and pressure before being directed to the inner surface of the heat transfer element, where it condenses.

The latent heat from condensation is transferred to the wastewater side of the heat transfer element. Clean condensate is collected for reuse, while concentrated wastewater falls to the bottom of the vessel to be removed and treated further.

The Hadwaco evaporators were originally designed to treat low-concentration wastewater with little or no dissolved solids. For example, units are processing landfill leachate in Lahti, Finland; Borgotaro, Italy; and Pierola, Spain, as well as industrial effluent at the Stora Paperboard pulp mill in Gruvon, Sweden. However, USFilter, which has years of experience in treating wastewater with crystallizing solids, such as cooling tower water, saw opportunity in adapting the evaporators to treat wastewater high in dissolved solids.

Tuba City was a logical place to test the idea because the groundwater there contains 5,000 parts per million of total dissolved solids.

USFilter engineers at the company's research and development center in Plainfield, Ill., devised a recipe of anti-scaling chemicals that could be added to the wastewater to prevent crystals from clogging small passages in the evaporator.

"We operated a pilot plant unit at Tuba City to treat two gallons of contaminated groundwater per minute in October 1998. We ran three weeks of trials under different operating conditions to fine-tune the design," said Kevin Dunn, a chemical engineer and sales manager at USFilter heading the Tuba City project.

The 100-gallon-per-minute system being designed for Tuba City is approximately 13 feet in diameter and 50 feet in length, and is modular in design to minimize field installation time and cost. The unit's horizontal cylindrical arrangement allows the system to provide its own enclosure for the pumps and other process equipment and instrumentation, without the added cost of a building. The systems are fully insulated and can be operated remotely via telemetry. "After less than four weeks of field installation time in November, we expect to begin commissioning the unit in early December," Dunn said.

The clean condensate from the unit, accounting for about 95 percent of Tuba City's groundwater, will be reinjected into the aquifer. The remaining 5 percent, containing more than 100,000 parts per million of dissolved solids, will be directed to double-lined ponds where the hot Arizona sun will evaporate it continuously until the solids precipitate out.

A number of French environmental engineering firms specialize in designing systems to remove pollutants from soil. When the contamination is relatively low, contaminated earth can be treated on-site, a more economical approach than removing it for treatment. For example, Chassieu-based Geoclean treated the soil for 10 months in 1997 at a former oil depot in eastern France that was contaminated with hydrocarbons on the order of 500 to 4,000 parts per million. That site is now used for municipal technical services. "In order not to prevent use of the site during its treatment, we moved all the moderately contaminated soil into mounds," said Franck Leclerc, a chemical and process engineer at Geoclean. Leclerc and his colleagues fitted each mound with drains and connected the drains to a central pump. The pump created a vacuum of 5,800 pounds per square inch with a flow rate of 35,000 cubic feet per hour.

Aprochim uses solvents to remove PCBs from soil, and then distills the solvent to regenerate it for reuse.

The pump's exhaust was sent to an air/liquid separator to remove hydrocarbon fumes that were destroyed in a catalytic oxidation furnace. A gas chromatograph monitored the elimination of the hydrocarbons.

Frequently, soil contamination is too severe for on-site treatment, and requires excavation and removal. Geoclean developed its Solvis process to treat soil containing organic pollutants in concentrations up to 100,000 parts per million. The company built a Solvis plant in Lorraine that processes 15,000 metric tons of polluted soil annually.

Soil is brought to the Lorraine plant and passes through pipes by means of endless screws that reduce particles to a uniform size. The plant runs a stream of dichloromethane solvent in the opposite direction to remove contaminants. Steam is used to remove residues of solvent that are regenerated, like the spent solvent. The pollutants are sent to disposal plants for combustion and the treated soil is returned to the original site.

"On a clay soil, for example, we have reduced the concentration of polychlorinated biphenyls from 170 milligrams per pound of soil to less than 5 milligrams per pound," Leclerc reported.

Aprochim in Grez-en-Bouere adapted its process for removing PCBs from electrical equipment to clean soil contaminated with these compounds. The Aprochim process involves using solvent to extract contaminants, and then sending it to a distillation column. This regenerates the solvent for reuse and removes the pollutants so that they can be destroyed at high temperatures.

The most polluted soil in France and other industrialized nations is incinerated. However, incineration produces solid residues, or clinker, that must be disposed of at specifically designated sites. This is an expensive disposal method.

Tredi, headquartered in Paris, has developed its Tredeco thermal decontamination process as an alternative to incineration. This process involves installing the Tredeco equipment on-site. Up to 10 metric tons of soil per hour is heated to 932°F in a rotary furnace to remove pollutants by desorption and evaporation. The gaseous pollutants then are sent to a postcombustion chamber, where they are destroyed at more than 1,800°F. Effluents of the Tredeco process are cooled and treated in a washing unit.

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