Results Hailed in Lab Tests on Contaminants in Drinking Water

Responding to “extremely favorable” tests of a new process for removing chemicals from drinking water, Los Angeles water officials plan to build an experimental water treatment plant at one of the contaminated ground water wells in the San Fernando Valley, scientists and water officials said.

The tests, conducted at UCLA, have consistently cleansed water samples of 95% of various chemical contaminants, including two hazardous solvents that are the main pollutants found in more than 40 of the area’s 110 drinking-water wells, said William Glaze, a UCLA professor of public health and project manager for the study.

Reductions of that magnitude would purify water from the contaminated wells to be within the limits that are considered safe.

The new process, called advanced oxidation, will soon be tested on other pollutants, including pesticides, and could have worldwide applications as a treatment for water contaminated with a wide array of chemicals, Glaze said.

Four techniques for producing advanced oxidation are being compared in the study, but the city Department of Water and Power has already chosen one--treatment of water with ozone and hydrogen peroxide--for its experimental plant.

The San Fernando Valley well fields supply 15% of Los Angeles’ drinking water--more in dry summer months. The well water is pumped over the Santa Monica Mountains to customers in Hollywood, the central city and East Los Angeles. Water officials have shut the most polluted wells and have blended water from others with clean supplies to keep contamination levels within health guidelines.

Currently, the only system planned for cleaning water from the contaminated San Fernando Valley wells is an aeration tower, which blasts air through a cascade of pumped ground water to evaporate the solvents. Construction of a $2.8-million tower in North Hollywood may begin this spring, according to DWP officials.

The water department has also been studying the use of granulated activated carbon filters to purge pollutants from well water, said Duane Georgeson, DWP assistant general manager. But in that technique, the carbon must either be treated periodically to remove built-up contaminants or be discarded--both of which would be cumbersome, costly operations, he said.

Georgeson predicted that the new ozone-hydrogen peroxide process will easily outperform carbon filtration and should be “at least comparable both in terms of cost and effectiveness to aeration towers.” But he said: “There’s always a big difference between bench-scale tests and results in the field.” The pilot plant should provide the necessary data, he said.

Glaze said the research grew out of meetings held two years ago with officials of DWP, which was assigned by the federal Environmental Protection Agency to be the lead agency for the cleanup of the contaminated Valley ground water. The EPA is providing most of the $263,350 cost of the laboratory-scale experiments.

A commercial water purification firm had approached DWP with a system that cleansed water with a combination of ozone and ultraviolet light, but the city wanted an independent appraisal of the technique, Georgeson said.

“We had run some field tests with the ultraviolet light process and they fell far short of producing the results they promised,” Georgeson said.

Glaze proposed a comparison of that and several other related processes. Ultraviolet light works well in the laboratory, but if such a process were scaled up to the size of a treatment plant, it would not work, he said.

He and the research team are comparing four processes: the ozone-ultraviolet combination, ozone combined with hydrogen peroxide, hydrogen peroxide and ultraviolet, and ozone alone.

Hydrogen peroxide was included because Glaze had found in previous studies that it is formed during the ultraviolet-ozone reaction. By starting with the hydrogen peroxide, the researchers may have a shortcut, obviating the need for ultraviolet light, he said.

Ozone Key Ingredient

The key to the advanced oxidation process is ozone, an unstable, highly reactive gas made up of molecules containing three oxygen atoms. High in the atmosphere, it shields the Earth from some forms of radiation; near the surface, it is a noxious component of smog.

Around the turn of the century, French scientists discovered that, when ozone was bubbled through water, it killed bacteria. It has been used since then as an alternative to chlorination.

Most widely used in Europe, disinfection with ozone is catching on in the United States, where chlorination has recently been found to produce cancer-causing compounds when it combines with other substances in water, Glaze said. Moreover, when ozone is bubbled through water, it makes suspended particles in the water more easily filterable--the result being clearer water.

A recently completed $146-million water filtration plant in Sylmar--which Glaze said is the most sophisticated filtration plant in the world--is using ozone to cut by half the amount of chlorine needed to treat water brought by aqueduct from the Owens Valley to Los Angeles.

In the new process, ozone is used in an entirely different way, Glaze said.

Oxidation Reaction

Several years ago it was discovered that, when water was exposed to ozone bubbles in combination with ultraviolet light, a powerful oxidation reaction took place that seemed to destroy almost every organic compound in the water, Glaze said.

Oxidation works by breaking down complex compounds--anything from a pesticide to petroleum--into their constituent atoms, which then recombine into such innocuous substances as carbon dioxide and water.

But oxidation is a reaction that can greatly vary in speed and intensity. It is found in the slow rusting of a car body as well as the instantaneous flaring of a match head.

The processes being studied at UCLA are designed to speed up the oxidation of compounds dissolved in water--to “burn” them, Glaze said.

For instance, trichloroethylene, or TCE, one of the two solvents found in San Fernando Valley wells, is made up of carbon, hydrogen and chlorine atoms. Linked together in the TCE molecule, these elements are a probable carcinogen. But when TCE is oxidized, the reaction produces harmless carbon dioxide, water, and chloride ions--half of a salt molecule.

Visiting Scholars at Work

In a cramped laboratory on the seventh floor of the School of Public Health, Glaze and a research team that includes visiting scholars from Taiwan and Japan have been working since last summer on the laboratory-scale tests.

The tests take place inside a polished steel cylinder that stands shoulder high on three splayed metal legs, looking like a 1930s fantasy of a rocket ship. The tank is filled with 14 gallons of water drawn from North Hollywood wells.

The water is “spiked” with an extra dose of 500 parts per billion of TCE and 50 ppb of the second solvent that has been found in Valley water--perchloroethylene, or PCE. Levels of the two solvents in the ground water have never been higher than 50 ppb, but EPA and city goals are to reduce contamination to below 5 ppb.

Each polluted water sample is then treated with one of the four techniques.

At five-minute intervals, samples are withdrawn from the reactor and tested for the presence of the solvents and for any residual hydrogen peroxide or ozone. The hydrogen peroxide and ozone are nearly always completely consumed by the oxidation reaction.

Computerized Tests

The samples are analyzed in a computerized chemical analysis laboratory--three compact boxes that fit easily on a desk top. The system performs the duties of equipment that several years ago would have filled a large room.

The computer combines the information produced by a gas chromatograph, which separates the dozens, even hundreds, of chemicals in a water sample, and data from a mass spectrometer, which provides the chemical “fingerprint” of each of the separated chemicals.

The device is fed a sample of water hundreds of times smaller than a raindrop and can detect as little as 5 parts per trillion of a compound dissolved in the water, Glaze said.

Results Promising

The process that shows the most promise is the combination of ozone and hydrogen peroxide. About 95% of the contamination in most cases has been removed. This translates to a drop from 500 ppb of TCE, for example, to 25 ppb. The removal rate is the same--95%--for lower concentrations, such as those found in the contaminated Valley wells, Glaze said.

For instance, water containing TCE at the maximum concentration found in Valley ground water, around 50 ppb, would come through the test with a concentration of 2.5 ppb, well below the currently recognized maximum allowable level.

Although the city has chosen the ozone-hydrogen peroxide combination for its pilot plant, the UCLA team plans to continue detailed testing of all four techniques. The study is to be completed in 18 months.

Glaze said the impact of the research will extend far beyond regional problems. “Although the focus is on L.A.’s water, we want to know if this process will work for Hackensack, New Jersey too,” he said.

In fact, the advanced oxidation process may have worldwide applications, allowing nations with limited water supplies to cleanse water from sewage treatment plants or contaminated sources, Glaze said.

Not a Cure-All

It is not a cure-all, though, he said. Metals such as mercury are not purged by the process. But in many cases, the advanced oxidation technique could be combined with other methods to guarantee purity.

The key now will be to develop a method for treating water with the ozone-hydrogen peroxide mixture in what is called a “flow-through” process, Glaze said. The laboratory technique of treating 14 gallons at a time--a “batch” process--could never work in a situation where thousands of gallons of water are being pumped each minute. Three or four designs are being studied, he said.

The cost of the process will probably be competitive with the cost of aeration and cheaper than carbon filtration, Glaze said. Two advantages over aeration towers would be that the advanced oxidation process is in theory not limited by scale; and, unlike aeration, which produces hazardous vapors that must themselves be caught in a filter, oxidation is not expected to produce any hazardous byproducts.

Glaze and the DWP are considering designs for the pilot plant, which will be set up to test a number of flow-through processes, Georgeson said. As soon as the equipment can be assembled, perhaps within three months, construction may begin, he said.

Between $25,000 and $50,000 has been earmarked for the facility, which would be built above a well in North Hollywood, Georgeson said. The money would come from funds that have been approved by the Los Angeles Board of Water and Power Commissioners, he said.