Ultraviolet light has a proven track record of killing bacteria and viruses found in municipal wastewater. In addition, environmental concerns over the use of chemical disinfectants, coupled with improvements in ultraviolet-lighting technology, have led to the development of UV systems that treat spent metalworking fluids in the industrialized world; disinfect drinking water in developing countries; and clean aquaculture water, ballast water, and hospital air everywhere.

Typically, chlorine gas or liquid is injected by a high-speed inductor directly into wastewater to kill bacteria before the water is discharged. "The main advantage UV has over standard disinfection techniques is that the light-based system eliminates the transport and use of chlorine," said George Tchobanoglous, professor emeritus of civil and environmental engineering at the University of California, Davis. "Even though the water is dechlorinated by the addition of other chemical compounds such as sulfur dioxide, residues of these toxic compounds remain in the water, which is a matter of increasing concern." Tchobanoglous chaired a committee of academic, industrial, and environmental consultants who drafted guidelines on UV disinfection for California in 1994.

Another factor leading municipalities to reconsider chlorination is its increased cost due to the national Uniform Fire Code adopted in 1993. This specifies double containment of stored chlorine and chemical scrubbers in case of leaks—both of which are expensive propositions.

"There are no residuals left by UV-light systems, whose effectiveness has been improved with the development of more-intense ultraviolet lamps. Now, one lamp can do the work of 20," Tchobanoglous said.

Only about 5 percent of American wastewater is currently treated by UV before being discharged, but the Electric Power Research Institute (EPRI) in Palo Alto, Calif., expects that figure to grow to 25 percent within 10 years.

The Central Contra Costa Sanitary District (CCCSD) in Martinez, Calif., is an example of UV's growing acceptance by U.S. municipalities. The district's treatment plant, located 45 miles from San Francisco, treats approximately 40 million gallons of wastewater per day before discharging it into Suisun Bay and San Francisco Bay. The plant's old treatment system, dating from the early 1970s, involved adding 3,500 pounds of chlorine daily, along with 2,400 pounds of sulfur dioxide per day to neutralize the chlorine.

CCCSD reconsidered its chlorination strategy in 1990, when community groups expressed concern about the possible accidental discharge of chlorine gas into the air. In addition, provisions of the Clear Air Act required limiting worker exposure to chlorine fumes, and provisions of the looming fire code specified the installation of an expensive leak-containment system to prevent such discharges.

Water authorities are replacing chlorination by using banks of UV lamps, shown here being cleaned of sediment, to disinfect municipal wastewater

In 1991 CCCSD plant management compared the costs of continuing to use chlorine treatment with those of three other disinfection strategies: hypochlorite, ozone, or UV treatment. Hypochlorite cost about twice as much as chlorine on an annualized basis and ozonation was even more expensive, but three UV systems were comparable to the cost of chlorination and dechlorination. An additional factor favoring UV treatment was an unused concrete denitrification channel in which lamps could be installed.

A large-scale pilot plant capable of treating less than 1 million gallons per day was built on-site by Los Angeles-based Montgomery Watson and CCCSD in 1992. It demonstrated that UV was just as effective as chlorination in killing bacteria and slightly more effective in destroying viruses found in the Martinez plant's wastewater. It also showed the lamps would need to be cleaned of fouling every two to four weeks.

Montgomery Watson designed the UV system, which was installed in October 1996. Water is piped to a treatment channel that is covered by a clear plastic lid to reduce algae growth. Eighteen banks of low-pressure mercury ultraviolet lamps made by Bailey-Fischer & Porter Co. in Warminster, Pa., line the sides of the channel. Each bank holds approximately 400 lamps.

Overhead cranes raise and lower the 9-ton banks to clean the lamps and replace those that are damaged or burned out. Cleaning is accomplished with dilute acids, such as 2-percent citric or phosphoric acid, in the lamp maintenance building. Both cleaning acid and replacement lamps are stored in this structure.

The entire system consumes 700 kilowatts of power, translating to 70 to 80 watts per lamp. In case of emergencies, auxiliary power is generated by a 7-megawatt natural-gas-fired power station on-site.

The aim of the UV system at Martinez was to achieve effluent concentrations of fecal coliform (bacteria) of 200 per 100 milliliters. CCCSD reported that the UV system has far exceeded this goal, measuring effluent concentrations of fecal coliform below 30 per 100 milliliters.

Machining fluids—used to lubricate and cool parts and tools or to remove the chips from grinding, milling, and other metalworking tasks—are a breeding ground for bacteria. These microbes attack the fatty acids that provide the fluid's desired cooling and lubricating properties, thus shortening fluid performance life. The traditional solution has been to add chemicals such as triazine—a widely used biocide manufactured by several chemical companies—to kill or inhibit the growth of bacteria.

The use of biocides poses its own problems, however, because metalworking fluids become aerosols that contact workers. These mists are a stew of bacteria, highly toxic bacterial by-products known as endotoxins, and the biocides themselves.

Recent studies have shown a correlation between exposure to these mists and an increased incidence of gastrointestinal cancer, acute pulmonary disease, occupational asthma, dermatitis, and other health problems among the 1.3 million American workers exposed to these fluids. The Occupational Safety and Health Administration underscored the seriousness of the problem by designating exposure to metalworking fluids as one of the top five workplace health hazards in the United States.

This has led machine-working companies to seek alternative disinfection solutions, including UV, from research and development companies such as Triton Thalassic Technologies Inc. (T3I) in Ridgefield, Conn. The company was first approached in February 1995 by a major automotive manufacturer interested in adapting T3I's UV technology to treat machining fluids, according to Barry Ressler, T3I's chairman and CEO.

Ressler and his colleagues have designed a specialized ultraviolet-lamp geometry, combination of gases, and fluid dynamics that enable their technology to emit a monochromatic wavelength that is highly fatal to bacteria but does not affect the fatty acids in the fluids. "We first proved that our technology could penetrate the opacity of machining fluids as well as that of water, then joined forces with scientists at the Los Alamos National Laboratory to optimize the technology," Ressler said.

Much of this work was done at T3I's research and development laboratory in Ship Point Business Park, located in Lusby, Md. The scientists used a 500-gallon closed-loop and flow-through demonstration system to conduct tests of various lubricants and coolants. The T3I staff also performed chemical and microbiological experiments using the site's gas-chromatography and mass-spectrometry instruments. They used the Powersim modeling/simulation package made by Powersim Corp. in Herndon, Va., to create computerized models of the treatment application.

The result was the Fluid Application Specific Treatment and Control (FASTAC) System, which was first installed and field-tested in a major automotive powertrain plant over a two-week period in February. FASTAC was installed in-line on a 1,240-gallon soluble-oil machining sump, and within 24 to 48 hours it was able to reduce the presence of bacteria from 106 to 107 per milliliter down to 103 to 104, a destruction rate of 99.9 percent.

In addition to the lower bacteria counts and the elimination of biocides, Ressler indicates that FASTAC should also extend fluid life. "This will reduce the volume and cost of waste disposal, which industry estimates put at three times the cost of the fluid itself, along with the downtime associated with dumping, cleaning, and recharging a fluid sump," Ressler said.

The next step in developing FASTAC's machining potential is scaling the technology down to treat the smaller volumes of fluid used by machine shops, medical-equipment manufacturers, and the like.

Another major market for FASTAC is the closed-loop aquaculture systems used to breed bigger fish faster than nature does. Aquaculture involves raising fish in a controlled environment; closed-loop aquaculture systems use a fraction of the space and water required by traditional fish-farming ponds because they filter and recirculate water in growing tanks and runways that can be located in underused industrial facilities, waterfronts, and other such places. (see "Like Growing Fish in a Barrel," Input/Output, April).

Beams from these louvered UV lamps draw in tuberculosis germs by air convection, thus preventing the disease's spread in hospitals and homeless shelters

While recycling tank water reduces the environmental impact of closed-loop aquaculture sites, operators face the challenge of controlling bacteria and breaking down the ammonia produced by fish breeding. T3I is working closely with the Biotechnology Center at the University of Connecticut in Storrs, anticipating a state-funded project to adapt its UV technology to treating aquaculture water. Ressler said his company will be field-testing FASTAC in tilapia, flounder, and salmon aquaculture facilities this fall.

T3I originally aimed its UV technology at dealing with industrial-plant zebra mussel fouling and treating contaminated ballast water discharged by cargo ships and tankers, and it has continued to develop these applications. Discharged ballast water has introduced nonindigenous species into countries, including the United States, where they have no natural enemies. As a result, these foreign creatures often proliferate to the point where they pose an environmental and economic problem. The best-known example is the zebra mussels that have clogged industrial and power-plant intakes along the Great Lakes (see "Power Plant Pest," Input/Output, March 1991).

T3I was first approached by its automotive client when it presented its UV technology as an alternative to using chemical biocides to kill the zebra mussel at the Zebra Mussel Conference in February 1995, according to Ressler. Since that time, a congressional task force supporting the National Invasive Species Act and the United Nations' International Maritime Organization have become interested in using FASTAC in conjunction with prefiltration to kill virtually all the microorganisms in ballast water without using chemical biocides.

Ressler's company is in the design phase, and is lab-testing a FASTAC system to serve the typical commercial freighter plying the Pacific Ocean between the United States and the Far East. "The prototype system can treat the required 4,000-gallon-per-minute loading and discharge flow rates through a 12-inch-diameter pipe, and we can easily scale up the system for larger vessels," Ressler said.

In developing nations, 400 children under five years old die every hour from diarrheal diseases, including cholera and typhoid, that are transmitted by contaminated drinking water. Although UV treatment can kill these waterborne pathogens, such systems are often too expensive for third-world villages. Scientists at the Lawrence Berkeley National Laboratory in Berkeley, Calif., developed UV Waterworks, an inexpensive, low-maintenance UV treatment system specifically geared for developing nations (see "Cleaning Water with Light," News & Notes, August 1996).

The Berkeley design team was led by Ashok Gadgil, an ASME member and a physicist at Berkeley. "There was a lot of mechanical engineering involved in designing the UV Waterworks system," Gadgil said. "For example, we performed radiometrics calculations to ensure that the proper light intensity is maintained. We also analyzed the hydrodynamics of the flow to prevent a wide distribution of residence time for water flowing under the lamp. This ensures high efficiency."

UV Waterworks can be connected to the pumps common to most villages in developing countries in two ways. In the case of hand pumps, the unit is connected to a surge tank, typically holding 30 liters, that collects water from the pump. For electrical borehole pumps, the disinfecting unit is connected to a tank mounted on a small pedestal.

Water from either tank enters a stainless-steel chamber, and is bathed by UV light at 254 nanometers—the optimum frequency for killing bacteria—emitted by a single 36-watt standard mercury-vapor lamp positioned above the water without contacting it. This eliminates the need for and expense of the UV-transparent sleeve used on many disinfection lamps, which are typically immersed in water. "Over time, biological and chemical deposits build up on the sleeves, rendering them opaque and requiring cleaning," Gadgil said.

UV Waterworks is designed to be gravity-fed, reducing electrical consumption to the 40 watts that power the lamp. This can be provided by a car battery and a photovoltaic panel, or by a small wind turbine in more remote locations.

Gadgil and his fellow engineers field-tested the system in India from 1994 to 1995. They found that the flow rate of 30 liters per minute they originally designed was excessive for local needs. The designers then scaled down the system to handle half that flow, building a unit that measures 28 inches long, 16 inches wide, and 11 inches high, and weighs 15 pounds.

The Berkeley designers made the newer version of UV Waterworks cheaper to manufacture by reducing the number of components and eliminating the need for welded parts. "We also cut down on material costs by using stainless steel to fashion only those parts that contact the water flow. The rest of the unit can be made of engineered plastics, mild steel, or enameled aluminum," Gadgil said. The new model can provide 10 liters of clean water daily to 1,000 people at 7 cents per year per person, well within the reach of most third-world economies.

UV Waterworks is being manufactured and marketed in India by Urminus Industries in Bombay, which makes the exterior shell of the units out of coated aluminum. In the United States and other countries, the systems are being manufactured in City of Industry, Calif., and marketed by WaterHealth International Inc. in Napa, Calif., which fashions the exterior shell of the units out of engineered thermoplastics. In the United States and other industrialized nations, the UV Waterworks systems can be used by rural households that draw their water from wells, ponds, or lakes contaminated by bacteria.

"We've also received inquiries from ranchers, resorts, and campgrounds located in rural or remote locations that are not connected to a centralized water system," said Alice Hughey, vice president of WaterHealth. The systems can disinfect sufficient water for approximately 150 households at typical U.S. consumption rates of approximately 100 gallons per day for a four-person household.

Gadgil and his colleagues are continuing to refine the design of the UV Waterworks system in a project funded by the U.S. Department of Energy that began in February. They are currently field-testing the system to treat drinking water in South African rural areas and in the townships on the outskirts of cities, in partnership with the South Africa Center for Essential Community Services, a nonprofit agency cofunded by EPRI and the major South African utility, Eskom.

Another joint EPRI/Eskom health project is developing an ultraviolet-germicidal-irradiation (UVGI) technology to reduce the transmission of tuberculosis-causing bacteria in buildings such as homeless shelters, hospitals, prisons, jails, and morgues, where many people infected with TB but not necessarily diagnosed with the disease are found. Airborne TB microbes can infect without personal contact and pose a serious health threat, particularly from strains that are immune to antibiotics.

UV lamps were first used to kill airborne pathogens in hospitals back in the 1950s, but continuing infection and safety hazards earned the systems a bad reputation. "EPRI studied these older UV systems and found they were improperly designed or installed for this application," said Anne Kovalski, national health-care initiative manager at EPRI. "A major goal of the EPRI/Eskom project is to create engineering control guidelines that will make UVGI effective."

The key to effective UVGI systems is designing a lamp with louvers that will focus its beams only across the top portion of a room. "This protects the inhabitants from UV exposure as natural convection carries bacteria into the killing zone," said Kovalski, who has years of hospital experience in environmental health and safety and as a nuclear medicine specialist. These lamps are mounted on the ceiling or wall or in ventilating ducts.

EPRI has installed UVGI systems—designed by Atlantic Ultraviolet in Hauppauge, N.Y.; Lumalier Inc. in Memphis, Tenn.; and Nature's Quarters in Haddam, Conn.—at five Manhattan homeless shelters as part of an epidemiological study to demonstrate UVGI's effectiveness in killing airborne TB. This study is being cosponsored by Consolidated Edison Co. in New York; the New York State Energy Research and Development Authority; St. Vincent's Medical Center in New York; and Harvard University's School of Public Health in Cambridge, Mass.

The systems were installed in May, and are scheduled to run through 2002 as part of a larger five-city project that will include Birmingham, Ala., and other large U.S. cities with high rates of TB. Installations in South Africa include King George V Hospital in KwaZulu-Natal and other hospitals, clinics, schools, prisons, hostels, workplaces, and homes.

Researchers in both countries will take air samples to determine the concentration of TB-causing bacteria. "We will be establishing the effect of ventilation, humidity, and long-term UVGI lamp performance on transmission rates of TB," Kovalski said.

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© 1997 by The American Society of Mechanical Engineers