Ways to Remove Impurities from Drinking Water(Ref.#7)
NEWARK , August 19, 1999 - A new screening technique now being developed at New Jersey Institute of Technology (NJIT) promises to dramatically reduce the time and cost involved in targeting and removing so-called "problematic" organic matter in drinking water.
Such substances, which can range from natural humic (decayed plant and animal material) to non-humic (manmade organic matter such as dry cleaning fluid), can react with chlorine, the primary disinfectant used in water treatment, to form potentially carcinogenic byproducts.
The NJIT research project, under the direction of Assistant Professor Taha Marhaba, is funded by the New Jersey Department of Environmental Protection in participation with major New Jersey water utilities and sewage treatment plant authorities.
The new technique, known as Spectral Fluorescent Signatures (SFS), is much faster than conventional methods for screening for certain "fractions" that indicate the presence of problematic organic matter.
In a typical watershed, weather and other variables can alter the fraction mix within the space of a week. Changing conditions can also make it difficult for watershed managers to spot pollution sources.
However, because SFS is so fast - cutting a week or more off conventional screening methods - it promises to enable water treatment plants to keep abreast of watershed changes. With up-to-date information on problematic fractions plant managers could adjust and target their treatment to remove them before they change.
Faster screening should also help watershed managers locate pollution sources before weather alters them.
Moreover, better targeting and removal of problematic organic fractions via SFS will reduce the excessive need for coagulants - the chemicals used to induce particles suspended in water to fall out. Reduced coagulants in turn will mean less sludge production.
But perhaps the most significant benefit of SFS is its potential for targeting the problematic matter, allowing utilities to remove it prior to disinfection. By removing these precursors to potentially carcinogenic substances in drinking water, SFS could help water treatment utilities meet proposed tougher standards aimed at reducing these substances.
Chlorine has been used in water treatment since the early years of the century and has proven to be a highly effective disinfectant against disease-producing microbes. These microbes feed off of organic matter in water.
But since 1974, it has also been recognized that chlorine can sometimes react with certain types of organic matter to form potentially carcinogenic byproducts such as chloroform.
Concern over these by-products recently prompted the Environmental Protection Agency to propose tougher standards that would reduce levels of chlorine by-products allowed under existing regulations and place under regulation other chlorine by-products, plus the by-products of other water treatment disinfectants such as chlorine dioxide and ozone not currently regulated.
Moreover, the proposed standards would place a limit on the overall amount of disinfectants water treatment facilities would be permitted to use.
Such regulatory changes will be difficult to meet using conventional screening methods. Currently, water treatment systems base chemical treatment on measuring what's known as total organic carbon (TOC), a single, aggregate parameter of all organic matter in drinking water: the higher the TOC, the more coagulant is required.
But because it is such a broad parameter, TOC is less than accurate: water treatment managers don't know what part of TOC is problematic. As a result, they may use too much chemical treatment, which in turn could lead to higher levels of potentially carcinogenic by-products and sludge in drinking water.
There are existing methods to differentiate TOC into portions or fractions, but they are slow and time-consuming. Water samples from various locations in a watershed must be run through several isolation procedures to differentiate the fractions in each sample.
The process can take up to a week or more, enough time for the fraction mix in the watershed to change and cause a treatment plant to target the wrong fractions and overlook others that may be problematic.
The SFS technique takes just minutes to differentiate a TOC sample into six different fractions: "If you can rapidly find out what portion of the TOC is most problematic - most likely to generate potentially harmful byproducts-you can optimize your treatment by targeting and removing that portion," says Marhaba.
"In effect," says the researcher, "instead of treating all of the organic matter, SFS allows you to target the problematic portion. The result is you not only reduce by-product formation in drinking water, you generate savings in reduced chemical use and sludge production."
"SFS will enable a water treatment facility to strike a much better balance between the need for proper microbial disinfection, and the need to reduce potentially harmful by-product formation," he says.
SFS works like this: A fluorescent light that generates both visible and non-visible ultraviolet light excites the molecules in each roughly 15-milliliter water sample (about a thimbleful). The reflected light - actually the light waves from the "excited" sample - are then "read" by a computer.
The computer generates a three-dimensional "picture" or signature that measures six fractions - three kinds of organics (hydrophobic or humic)which separate from water, and three kinds (hydrophilic or non-humic) which don't separate from water and therefore, tend to be more problematic.
The SFS screening method also holds promise of rapidly pinpointing where various organic fraction sources are located within a watershed. "When analyzing different locations in a watershed, the three-dimensional picture or signature tells you that there's more humic input here, or more non-humic input there," says Marhaba.
"It enables you to find out if there are some non-point sources (polluted areas), or even point sources (specific pollution sources) in given locations in the watershed," he says.
Most important, it takes just minutes to analyze the samples instead of the week or more it would take using the standard screening method. "It's a rapid spatial and temporal technique: We are able to get an accurate idea of where the pollutants are today: not where they were a week ago," says Marhaba.
Ultimately, he hopes to use SFS in conjunction with the Geographical Positioning System to enhance pinpointing of pollution locations in rivers and other drinking water sources.
"After collecting samples at key locations in a river, we could feed in the "signatures" of each location and in minutes get a complete and ongoing picture of the level of organic fractions in that watershed area," notes the researcher.
Water treatment plant managers could then adjust their treatment accordingly to target the potentially harmful organic pollution in the given location, he says.
Marhaba estimates that the system is still several years from implementation. "We are working on refining the software used to generate the signature results, and verifying it in the field," he says.
NJIT is a public research university enrolling nearly 8,200 bachelor's, master's and doctoral students in 76 degree programs through its five colleges: Newark College of Engineering, School of Architecture, College of Science and Liberal Arts, the School of Management and the Albert Dorman Honors College. Research initiatives include manufacturing, microelectronics, multimedia, transportation, computer science, solar astrophysics, environmental engineering and science, and architecture and building science.
Yahoo! Internet Life magazine recently ranked NJIT the "most wired" public university in America, and has ranked it one of the top six "most wired" campuses among both public and private universities for three consecutive years. In addition, U.S. News and World Report's 1999 Annual Guide to America's Best Colleges ranked NJIT among the nation's top universities, and Money magazine's Best College Buys 1998 rated NJIT as the sixth best value among U.S. science and technology schools and among the top 100 overall.