- where it is cost-competitive with other treatment

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2 High costs associated with new technologies and fear of the unknown tend to slow the emergence of innovative ideas into the marketplace. None of the technologies discussed in this section are new ideas; they are however, technologies whose time has come. In some cases, it is because the ideas have been retined, proven, and made more affordable. In other cases, the traditional technologies have become less attractive, thereby making room for the newcomers. let there be light Natural photolysis, via sunlight, follows the laws of nature to cleanse the earth s water supplies. Man, in his quest to speed up the process to meet the laws of federal, state and local regulatory agencies, expenments with other sources of radiant energy. The most well-known and understood of-these i s ultraviolet (UV) light, commonly used with hydrogen peroxide, ozone or some other catalyst to enhance the oxidation process. The UV energy reacts with the oxidant or catalyst to create a hydroxyl radical, a powerful oxidizing agent that destroys contaminants. This technology is available commercially for applications in municipal and industrial wastewater treatment as well groundwater remediation. The electron beam is another energy source being tapped to disinfect and detoxify contaminated water and sludges. The technology has been studied for years but its comparatively high cost has kept it from widespread commercial application. Researchers at the Electron Beam Research Facility in Miami, Fla., believe the technology is now ready for the marketplace. Initial funding for the research was provided by the National Science Foundation and more recently through EPA s Superfund Innovative Technology Evaluation (SITE) Emerging Technology program. Where UV relies solely on hydroxyl radicals, explains researcher William Cooper, electron irradiation generates an aqueous electron, in addition to hydrogen and hydroxyl radicals, which he says makes it effective in destroying a wider range of compounds, including carbon tetrachloride and chloroform. Electrons are accelerated to approximately 95 percent the speed of light and shot into a thin sheet of contaminated water or sludge. As the electrons penetrate the waste stream, treatment occurs in about onetenth of a second. Cooper, along with the project s two other researchers, Thomas Waite and Charles Kurucz, believe the technology has a bright future in groundwater remediation and in treating industrial waste streams - where it is cost-competitive with other treatment technologies. They have started their own company to commercialize the technology. Karol Bialy, chairman and CEO of Nutek Corp., Palo Alto, Calif., has been in the irradiation business since the 196Os, using the technology primarily for sterilizing medical supplies. In 1968, Bialy patented the use of irradiation to treat sewage sludge, which kills the pathogens and bacteria but retains the organic nutrient value of the sludge. Nutek recently installed a pilot plant at a wastewater treatment facility in Palo Alto, with funding from the Electric Power Research Institute (EPRI) and the city of Palo Alto, to investigate the effectiveness, reliability and operating costs of high energy electron beam disinfection. A preliminary cost comparison shows a slight cost advantage of the electron beam over a chlorine/ sulphur dioxide system. A major benefit to the process would be the elimination of chlorine and sulfur dioxide stored and used at the plant, as well as transportation of these chemicals to the plant. A shining star Significant advances in solar detoxification over the past decade should secure it a place in the commercial marketplace by the mid- 1990s, according to researchers at the Lawrence Livermore National Laboratory (LLNL), Livermore, Calif. LLNL is collaborating with Electrons are accelerated and shot into a thin sheet of contaminated water or sludge. As the electrons penetrate the waste stream, treatment occurs in about one-tenth of a second. (Source: Electron Beam Research Faci I i t y ) Sandia National Laboratory (SNL) in Albuquerque, and the National Renewable Energy Laboratory (NREL, formerly the Solar Energy Research Institute), in Boulder, Colo. Funding is being provided by the Department of Energy s Office of Technology Development and Office of Conservation of Renewable Energy. Potential markets include groundwater remediation and industrial wastewater treatment. Solar detoxification harnesses the natural process of photodegradation to break down hazardous materials into non-hazardous substances. Sunlight s ultraviolet radiation promotes photochemical reac- APRIL 15, 1992 POLLUTION ENGINEERING 39

3 Researchers are evaluating solar detoxification S ability to clean up groundwater. tions. Researchers claim the process destroys more than 80 toxic chemical compounds, including industrial solvents, pesticides, wood preservatives and dyes, and some fuels. LLNL, NREL and SNL researchers are evaluating solar detoxification s ability to clean up groundwater at a Superfund site contaminated by trichloroethylene and tetrachloroethylene from World War I1 aircraft and machine maintenance activities. The experiments have shown that solar detoxification reduced the level of solvents in the groundwater by 99 percent - from 106 parts per billion (ppb) to less than 0.5 ppb. Contaminated water is treated by the combined action of sunlight and a light-activated catalyst, in this case titanium dioxide (TiO?) added to the water in slurry form. The catalyst absorbs the sunlight and reacts fobreak down them inants intu carbon dioxide, water and low concentrations of simple mineral acids, which are neutralized before being discharged. The LLNL system used curved parabolic mirror troughs to reflect the sun s ultraviolet rays onto a glass tube, called a reactor, through which the contaminated water is pumped. Recent developments in photoreactor design suggest that nonconcentrating, or one-sun, photoreactors are even more efficient than the parabollc trough, which could accelerate the time to commercialize the technology. Researchers are also investigating ways to afix the catalyst to support structures, such as glass, fiberglass, ceramic or metal. When added in slurry form, the catalyst particles must later be filtered out, which can be difficult and costly. The intermittency of solar resources is also a concern. Where overall flow is small enough (as in groundwater remediation) water can be stored overnight or when cloudy for processing during the next sunny period. Since this may not be practical in all applications, researchers are looking at combining solar with a backup UV-lamp system for 24-hour treatment. Perhaps they should talk with... Nutech Environmental of London, Ontario, Canada, has developed an ambient temperature photocatalyst technology that uses artificial light and ;t TiOt. catalyst to destroy organic pollutants, including PCBs and dioxins, in industrial effluent and contaminated groundwater. Nutech uses a supporting structure for the catalyst, according to Brian Butters, general manager, to elimi- 0 Contaminated water is treated by the combined action of sunlight and a Ti0 catalyst. Curved parabolic mirror troughs refikct the sun s rays onto a glass tube through which the water is pumped. (Source: NREL)

4 I i SCWO Process Cryogenic oxygen pump nate the problem of removing catalyst particles from the water. Contaminated water is piped into a reactor where it flows over a Ti02 coated mesh. This mesh is exposed to a very low dose of ultraviolet-a light, causing the catalyst to form reactive radicals that break down the organic compounds to carbon dioxide and water. The technology offers benefits in energy cost, oxidation rates and total organic carbon (TOC) reduction. The elimination of an offending chemical from detection does not necessarily mean the water has been detoxified, says Butters. The offending contaminant may have just been changed from one compound into another, without changing the TOC content. The company is concentrating now on designing commercial systems, said Butters, and has planned several demonstration projects over the next year. Super stuff When water is put under pressure (3200 psi) and heated to 705 F, it becomes supercritical, meaning it is now a single-phase fluid that is neither liquid nor gas. Organic compounds dissolve readily at the supercritical level, and when oxygen is added they oxidize quickly. Supercritical water oxidation (SCWO) provides ultra-high destruction efficiencies, 99.9 percent or better,. of organic and biological wastes, including dioxins, PCBs, halogenated solvents and pesticides. The reaction occurs in a matter of minutes. Dr. Earnest Gloyna, who Supercritical water oxidation can oxidize organics very effectively at moderate temperatures and high pressure. (Source: Modec) has been studying SCWO at the University of Texas at Austin since 1985, reports excellent destruction results on toxic organic wastes. SCWO has the greatest destruction potential and worldwide environmental benefit of any development in my 45 years in the field, Gloyna says. The University s Balcones Research Center now has six batch and continuous flow SCWO units and a 40 gpm pilot unit built under a joint research grant program with Eco Waste Technologies, Austin, Texas. We re very excited about it, says Jack Davis, president of Eco Waste Technologies. The company plans to bring SCWO to the commercial marketplace this year. Davis sees a large initial market for treating hazardous industrial effluent and as the technology develops, a huge market for treating military waste such as propellants, fuels and nerve gas. Basically, pressurized waste is mixed with heated, pressurized liquid oxygen. The mixture is fed to the preheater and somewhere between C, the single-phase occurs and oxidation begins. The mixture then moves on to an insulated reactor where the remaining organics are oxidized. The mixture is then cooled and the effluent is separated into gas, liquid and solid phases. The gas phase is separated into oxygen and carbon dioxide; the oxygen is recycled back to the process and the carbon dioxide can be liquified and sold. The technology meets EPA guidelines for a Totally Enclosed Treatment Facility for hazardous waste. Unlike an incinerator, a supercritical water reactor is a closed system that has no emissions to the atmosphere. Its relatively low operating temperatures will not produce nitrogen oxides (NO,), according to test results at the Balcones Research Center and other SCWO R&D companies. The high pressure and temperature required, however, makes supercritical water corrosive - not a small problem. Corrosion can eat away at the costly reactor vessel and cause particles to clog the system. Modell Development Corp. (Modec), Framingham, Mass., claims to have solved this and other technical APRIL 15, I992 POLI UTION ENGINURIN(; 41

5 ... EERING Rising costs and limited availability of conventional disposal options make new technologies viable. Li uid effluent -101 eadworks Solid end-product to reuse 0 Pressure and temperature combine to oxidize organics in sludges. The process takes place in a series of vertical tubes. (Source: Air Products & Chemicals Inc.) problems that plagued SCWO in the past. They have simplified the equipment, eliminated the need for auxiliary fuel, and demonstrated commercial operating conditions without clogging or corrosion. And, according to Modec estimates, costs are less than 50 percent those of incinerating comparable wastes. Some of this advantage occurs because SCWO requires very little dewatering, a costly, energyintensive step. Slightly less critical Another technology, available in the U.S. from Air Products & Chemicals Inc., Allentown, Pa., uses pressure and temperature below the supercritical state, says Robert Freudenberg, to oxidize organics in municipal sludge and less complex industrial sludges. You don t need to go supercritical with most municipal or wastewater treatment sludges because the organics generally found in these will oxidize readily without going supercritical, explained Freudenberg. For hazardous waste and for more complex sludges there may be a need to go to that level. The VerTech process, licensed from VerTech Treatment Systems b.v. of The Netherlands, uses aqueous-phase oxidation - basically, wet oxidation 42 POLLUTION ENGINE[ RING APRIL. 15, 1992 in a below-ground, vertical reactor. Oxygen and high pressure convert wastewater and sludge into water, carbon dioxide, a small amount of organic acids, and recyclable residuals. This is done in a series of vertical tubes, 4000 to 5000 feet deep. Sludge is pumped into the tubes, mixed with oxygen and then flows to the bottom of the oxidation vessel where it achieves a peak pressurization of 1500 pounds per square inch, and temperatures of 550 F. Under these conditions, the organics are oxidized. The stream returns to the surface as an odorless, sterile effluent. Remaining inorganic solids settle out in a separator tank. This residual material can be landfilled or used in construction materials. The separated liquid is returned to the wastewater treatment plant for reprocessing. A full-scale evaluation of the technology was done by EPA at a Colorado wastewater treatment plant in 1985, and construction began last fall in The Netherlands on the first commercial VerTech plant. But, Freudenberg explained, with the rising costs and limited availability of some conventional sludge disposal options, the economics are becoming such that this is now a viable solution. Reader Interest Review Please circle the appropriate number on the Reader Service Card to indicate the level of interest in the article. j