Water Labs Ramp up to Handle Post 9-11 Testing

By Andrew L. Meyer

The events of Sept. 11, 2001, have significantly increased work loads in water laboratories throughout the country. Faced with a sudden and unprecedented demand for testing, water microbiology labs are refocusing their efforts to maximize productivity. Recently developed DST microbiology methods produce results in 18 hours with very little hands-on time. This offers lab managers a solution for handling the increased load that bioterrorism monitoring requires.

As a result of Sept. 11, some utilities are increasing their microbiological contamination monitoring throughout the treatment chain. Sampling is done at the source, in the treatment plant, and throughout the distribution system.

Source water monitoring can alert operators to changes in water quality. For example, a rain event can cause runoff to pollute a reservoir, or an upstream discharge can contaminate a river source. Armed with source water quality information, operators can respond in several ways. They can:

• Change the depth at which water is drawn from a reservoir.
• Switch to another intake point in a source.
• Draw from an alternative source.
• Modify treatment.

Likewise, microbiological monitoring throughout the treatment plant (influent, after pre-chlorination, after sedimentation, after filtration and after post-chlorination) can also help improve operations. Based on this information, operators can modify parameters such as flow rates, flocculent feed rates, settling time, backwash frequencies, and disinfectant feeds.

Most importantly, microbiological monitoring of the distribution system can highlight problems that introduce fecal pathogens such as inflows through leaks, cross contamination, and intentional contamination. Additionally, microbiological testing can identify trends in biofilm development, which could result in pipe corrosion, reduction in flows, disinfectant consumption and taste and odor complaints. Given this critical information, operators can bypass broken pipes, correct cross connections, increase disinfection residuals, flush lines and, if necessary, issue boil notices.

Testing methods

The vast majority of effort in a microbiological lab is typically devoted to coliform and E. coli testing. The presence of these organisms, especially E. coli, indicates fecal contamination that could introduce waterborne disease.

Coliform and E. coli tests vary considerably in their complexity and time-to-result. The Environmental Protection Agency has approved three approaches to coliform/E. coli testing: multiple tube fermentation (MTF), membrane filtration (MF) and Defined Substrate TechnologyRegistered (DST).

Multiple Tube Fermentation, invented in the early 1900's, involves pipetting each sample into a series of media-filled test tubes, incubating them for two to five days and examining them for turbidity and gas production. Due to the amount of labor required and the time it takes to get results, this test is rarely used.

Membrane Filtration, invented in the 1950's, replaced Multiple Tube Fermentation as a quicker and easier method. The traditional approach is to capture the bacteria on a filter and then incubate the filter on growth media for 24 hours. Bacteria grow into visible colonies that are counted and then confirmed over the course of 1-3 days with the same confirmation steps as Multiple Tube Fermentation.

Defined Substrate Technology, invented in the late 1980's, is now in use by over 90 percent of US state health labs. It involves adding a powdered reagent to the sample and incubating overnight. Samples containing coliforms turn color and samples with E. coli fluoresce. There is no need for confirmation and the test can be run as a presence/ absence or a quantitated test.

The main advantages of DST Methods (eg ColilertRegistered by Idexx) are ease-of-use and speed-to-result. Labs still using traditional methods may find it difficult to handle the increased testing that bioterrorism monitoring requires.

Colilert was first approved by the EPA in 1989. More recently, the EPA has approved a newer version of the test called Colilert-18. The new test provides results in 18 hours, versus the 24-hour incubation time required by older versions.

There are two advantages of this 18-hour test (available in either presence/absence or quantitative formats):

• The rapid time-to-results means that contamination can be found 6 hours sooner than any other approved test. This allows operators to correct a problem nearly a whole workday sooner.
• Laboratory workflow can be optimized with an 18-hour test. In most cases, sample collectors return to the lab at the end of the day. With an 18-hour test, samples can be processed as they arrive and then read the following morning, before the next samples arrive. With the typical 24-hour tests, the first day's samples have to be read precisely when the second day's samples have to be processed.

As bioterrorist threats (and new regulations) create an increasing burden for water testing laboratories, rapid microbiological methods offer improved productivity and time-to-results to handle the work without increasing staff.

About the Author:

Andrew L. Meyer is a Marketing Manager at Idexx Laboratories and has been working in the field of drinking water microbiology since 1993. He can be reached at [email protected]