In response to requests from Plumbing Manufacturers Intl. (PMI) and its members, as well as from other supporters of the U.S....
Ground water is the most popular source for water in the United States. Now with growth of proven treatment methods and advances in treatment technologies for contaminated ground water, the future is bright for the ground water industry.
The United States uses over 79 billion gallons per day from 15 million plus wells and is the largest water well market in the world. Growth in proven treatment methods for drinking water is being accompanied by rapid technological advances in the treatment of contaminated ground water.
Carbon filters, reverse osmosis units, ion-exchange (water softeners), aeration units, ultraviolet units, non-carbon filters, and distillation units comprise the dominant treatment methods used by Americans.
Ultraviolet Units - Sunlight quickly destroys bacteria and viruses in water. The critical wavelength of the sun's rays for disinfection is the ultraviolet.
Since the early 1900s, man-made ultraviolet lights have been used for disinfecting water. In 1966, the U.S. Department of Health, Education and Welfare recognized the technology and issued guidelines which are still in place today. The guidelines provide for a minimum radiation level of 2,537 Angstrom units, minimum dosage of 16,000 micro-watt-seconds per square centimeter, a mechanical cleaning device or "wiper" to keep the glass clean without disassembly, an accurate intensity meter, flow control mechanisms, and automatic alarm for malfunctions. Technology in ultraviolet units has advanced considerably.
Today contact time is measured in seconds and units are capable of treating flows from 1 GPM to 2 million gallons per day. The treated water is free of most bacteria and viruses without chemical additives. For the destruction of Giardia, prefiltration is still needed. For water that is going into distribution systems, chlorine will still be added to give the disinfection holding time.
But according to Ann M. Wysocki of Atlantic Ultraviolet Corp, Hauppauge, N.Y., most domestic applications don't require any additional treatment.
Carbon Filtration - Still the undisputed king of organic treatment, carbon filtration is here to stay. Dating back to the 1700s, carbon adsorption is now one of the fastest growing components of the water treatment market, with growth since 1990 of 86 percent for domestic applications and 26 percent in industrial applications.
Homeowners who fear levels of gasoline in their well water use carbon filtration. This works nicely, but some studies have suggested cheaper diffused aeration to bring ground water contaminated with over 100 mg/L gasoline to drinkable quality. Dechlorination fever continues to drive sales for carbon adsorption units which are very effective for removal of trihalomethanes. Carbon units are also very effective for removing radon but can present a regulatory nightmare when it comes time to dispose of spent filter media containing low level radioactive waste. For the most part, carbon adsorption is not a viable treatment for bacteria and viruses.
Ozonation - Effective in treating deadly cryptosporidiosis, ozonation showed more promise than ultraviolet irradiation for treating what has become the most important newly recognized contaminant in American drinking water.
Fortunately for the ground water industry, one new study showed that cryptosporidium is six times more likely in surface water than in ground water. Ozone is a powerful oxidizing agent and has become the dominant disinfection technology for the bottled water industry.
Another tribute to the ground water industry is that bottled water is usually spring water, a type of ground water, or water from wells. Consumers don't often see "Bottled River Water" on the shelves.
Sales of residential point of use ozonators are up 113 percent since 1990. However, ozonators are not without drawbacks such as fumes, which need to be properly run through a catalytic filter. Another non-chlorine disinfection method, ozonation is on the upswing.
Ion Exchange - Ion exchange units, or water softeners, continue to be the most effective treatment option for that common treatment problem - iron. Industrial sales of softeners have moved up by 56 percent since 1990.
Also since that time, the residential point of entry (POE) market softener sales are up 37 percent, with a 25 percent increase for point of use (POU). Paper mills , textile mills, and laundries are heavy users of softeners for treatment of another dissolved metal - manganese.
Aeration - One of the oldest methods for ground water treatment, aeration is used for some new problems like radon gas. Aeration is effective for treating hydrogen sulfide gas with the advantages of no new chemical by-products resulting in the process. And since air is utilized as the oxidizing agent, the process is relatively inexpensive.
Diffused bubble aeration process with 60 minute aeration time at aeration rates of 50 cubic feet per hour, an air/water ratio of 3.4, removed 99 percent of radon.
Today, environmental engineers and hydrogeologists employ methods such as vapor extraction, air sparging, steam stripping, bioremediation, electromigration, free product removal, pumping and treating, bioslurping, UV/Ozone/hydrogen peroxide oxidation, oxygen enhancement, containment, and vitrification. Beyond these treatment options, evolving state-of-the-art includes many more.
Vitamin B-12 Catalyzed Dechlorination of Perchloroethylene (PCE) - One of the most common solvents to contaminate ground water as a dense non-aqueous liquid (DNAPL) is perchloroethylene. Low level thermal desorption, biodegradation, combining pumping and treating with UV, vapor extraction, and other options have been employed to treat PCE. Scientists are experimenting with a mixture of vitamin B-12 and titanium citrate to degrade the contaminant. Four advantages emerge for the biochemical system over the use of anaerobic bacteria: 1) rate is faster, 2) no need for careful balance of nutrients or additional carbon source, 3) no restriction in the range of concentrations of the compound to be treated, and 4) the remedial solution is mobile even in the presence of organic carbon. The system has promise for TCE and other contaminants also.
Phytoremediation - What started as a treatment for sludge from wastewater operations is now an exciting emerging technology for treating contaminated ground water and soils. For years uptake and detoxification of contamination by plant species, Phytoremediation has been a factor in designing land application of sewage projects and erosion control at strip mine sites. A number of exotic plants called hyper accumulators have been identified and used in pilot studies at industrial and natural settings to attempt to demonstrate plants' ability to absorb and sequester toxic metal contamination.
Two hyperaccumulators of note are the New Caledonia Rubber Tree and, more importantly, Indian Mustard Plant Brassica Juncea demonstrated the ability to accumulate metal concentrations at least equal to some high grade ores. Remarkably, metals may be more cheaply recovered from the plants than from mineral ores. The plants are incinerated or acid leached to recover the minerals, and the process vastly reduces the landfill burden.
Phytoremediation is showing promise for treating ground water contaminated by petroleum hydrocarbons like TCE at the U.S. Air Force Base in Carswell, Texas where over 100 poplar trees degrade petroleum-contaminated ground water. Garden variety plants like sunflowers, cottonwoods, junipers, rye grass, and cattails are all useful, but further demonstration projects are needed.