By Dr. D. Roy Cullimore and Lori A. Johnston
Summary: Bacteria are threatening the water sources that supply the populations around the world. First and foremost, identifying the problems is always the first concern. Next, selecting the right options to more effective prevention will include in-depth, comprehensive testing. The following describes but one method toward safeguarding the water that is so vital to our existence.
The supply of fresh and clean water is essential to the survival of both flora and fauna, and healthy habitation of areas around the world. The environment contains many different species of bacteria. Many of these bacteria perform very useful functions in recycling nutrients within the water. Some species can, however, cause problems. These problems range in ground and surface waters that range from slimes, plugging, discoloration and cloudiness to corrosion and infection.
One particular concern is the plugging problems that limit the life span of water wells and the pumps, fittings, tanks and other equipment designed to deliver water to end-users. In the Canadian prairies, up to 70 percent of wells are impacted by these events leading to an average life span of 15 years before failure. In water storage, treatment and distribution systems, it’s often formation of slimes, discoloration and cloudiness that causes concern. There is, of course, a universal concern about the presence of pathogenic bacteria that’s generally addressed using coliform bacteria as the indicator group for health risk.
Such a wide variety of bacteria aren’t easy to detect and identify using a single test. Yet, their impact can make water unsafe, unacceptable or unavailable due to flow losses through plugging or equipment failure from corrosion. Often, the events they cause are ignored, considered inevitable or put down to simple physical and chemical effects. In such cases, ignorance may be bliss—but it’s also expensive in terms of greater operating costs in storage, treatment and distribution systems.
A considerable lack of attention has been paid to nuisance events caused by bacteria other than those associated with potential health risks. In groundwater, it was a common practice until almost 10 years ago to consider the environment to be essentially sterile. Bacterial events weren’t considered important. In surface waters, larger and more obvious organisms such as algae and pond weed received more attention as potential indicators of biological fouling than bacterial slimes and clouds. Today, it’s recognized that microbes are present in all waters and their nuisance impact needs to be managed if sustainability is to be maintained. Remember, there’s no such natural water that’s totally sterile. In reality, all waters—including drinking water—contain bacteria that can have very positive or negative impacts on the water quality.
Beyond the direct and recognized hygiene risks in water, there are many other challenges posed by the various bacteria commonly found in drinking water processes. While these microbes can cause water plant operators grief, they may not get routinely investigated for their impacts nor are rigid standards necessarily applied in all cases, i.e., small systems account for the large majority of violations of federal drinking water standards. While non-microbial regulations continue to move forward to address issues such as pesticide contamination and by-products of the mining and petroleum industries, bacterial drinking water regulations remain in a state of relative stasis by comparison. The reason for this is partly due to a lack of robust, reliable and validatable methods compared to the much more defined methodologies applicable in chemical testing. Progress is also slow in this arena simply because of a lack of practical knowledge on the true impact that microbes have on water quantity and quality, the water systems, as well as on the consumers. Studies are often vague or contradictory. These problems become more complicated by the fact that most bacteria causing problems cannot easily be detected unless they’re growing as slimes (or biofilms), encrustations or tubercles at a site that can be readily seen. This means a single water sample may not contain any bacteria if, at the time of sampling, the large majority were growing in biofilms. This adds to the difficulty of testing for bacteria in water because a single sample may not reflect those bacteria biofouling the surfaces (e.g., walls of a pipe, dead-end areas in distribution systems, impellers of a pump, gravel pack and filter beds). A sequence of samples taken over time is required to assure validity of data being obtained.
Health risks posed by a few species of bacteria growing in water become more difficult to assess because these species are “opportunistic” pathogens. This means such species are more likely to cause disease under certain conditions, commonly where the victims’ health already is stressed in some way. These circumstances are often associated with the elderly, very young or immune impaired. In ground and surface waters, such opportunistic pathogens aren’t normally in a majority but can form a small part of the heterotrophic waterborne bacterial community. The net result is bacterial issues haven’t been extensively monitored or regulated beyond common routine requirements for the control of the fecal and/or total coliform bacterial populations in water.
To address the practical aspects of monitoring and detecting the various bacteria, a simple and easy test is needed. One such water testing system involves a series of double-sealed 4-inch vials with a floating ball and selective medium to create an environment to measure bacterial activity. These tests detect the level of activity—or aggressivity—of various nuisance bacteria by a time lag, measured in the number of days from the start of the test to when the first reaction is observed. The greater the level of activity, the shorter the time lag to observing a reaction and the more aggressive the bacteria are in that water sample. Conversely, the longer the time lag before any activity is observed then the less aggressive are the bacteria. This test, therefore, determines bacterial activity levels in a water sample rather than numbers of bacterial cells. This is based on the premise that bacteria can be more aggressive in water if the cells are active rather than passive. For example, one thousand active cells in one milliliter of water could achieve a higher aggressivity than one million passive cells that aren’t aggressive.
This biological reactivity test detects the bacterial presence by looking for reactions as well as aggressivity (by the activities and through the time lag). Reactions relate to growth events such as formation of colors, clouds, slimes and gels. Reactions relate to the manners in which the microbes interact within the vial. These reactions may also involve development of gassing and/or precipitation. The unique nature of the test makes it very different—and possibly superior—to the agar culture techniques. This premise is based on the fact that water used in the test is an undiluted sample and contains the microbes still within their natural environment. Figure 1 illustrates how the process functions, creating a vertical redox gradient coupled to a gradual increase of nutrient loading (from the base up). As a result, a greater variety of environments are created than in standard agar spreadplate techniques such as heterotrophic plate counts.
Again, bacteria can be “missed” in monitoring using a water sample if they’re all contained in biofilms, encrustations or tubercles. To compensate for this, it’s necessary to stress the environment prior to sampling to cause some of these bacteria to be released to the water. In water wells, this is done by shutting the pump down for a prolonged time (e.g., one day) before taking a set of samples, which would then reflect the bacteria sloughing into the water from the growth sites. In water treatment, storage and distribution systems, frequent sampling will detect the bacteria at times when they slough into the water. Routine sampling and testing gives a more accurate picture of the bacterial activities in a system than a single sample.
How it works
The biological reactivity test uses a unique system for encouraging selected groups of microbes to grow in the test. First, there’s normally no dilution of the sample. Microbes that can be active and/or react with selective conditions created within the vial can be targeted to a select group of bacteria (e.g., iron related bacteria, sulfate reducing bacteria, etc.). These conditions are created using two practices. The first is a floating ball—a floating intercedent device (FID)—that restricts entry of oxygen into the sample below. The second practice is use of a crystallized deposit of selective nutrients, which sit in the bottom of the tube and encourages the actions and reactions by the specific group of microbes. In the first practice, oxygen enters around the floating ball to allow oxygen-requiring (aerobic) microbes to grow. They’ll use all of the oxygen diffusing down and causing the lower portion of the sample to become devoid of oxygen. This volume underneath becomes suitable for growth of microbes that don’t require oxygen (anaerobic). Thus, a single biological activity test provides environments that are aerobic (oxidative) and anaerobic (reductive). Essentially this forms into a reduction-oxidation gradient with a transitional zone (redox front) in the middle.
The key to determining the presence of different groups of microbes is the crystallized selective medium attached to the floor of the test vial. This medium will begin to slowly dissolve when the water sample is added. As the medium dissolves, a series of chemical diffusion fronts become established and move slowly up the test vial. This slow with upward progression and can take as long as two days, which gives the microbes in the sample time to adapt to the increasing concentration of nutrients and, if suitable, begin to become active. Even very sensitive microbes that would normally fail to grow on any agar media are better able to adapt and grow within a test vial if the crystallized medium is suitable for their growth. It’s the selective nature of this medium that restricts growth and activities of the bacteria to only those belonging to the targeted group. Other bacteria fail to become active and grow. The location of the growth itself gives an early indication of the type of microbes involved. The system therefore can provide a considerable amount of information on the bacteria in the water sample without requiring the facilities of a full microbiology laboratory.
Once a serious problem has been confirmed (e.g., the presence of highly aggressive bacteria), then the relationships between these aggressive bacteria and the problems in the water system can be considered. Generally, the more aggressive a particular group of bacteria is determined to be then the more probable it is that those bacteria would have the potential to be causing problems. Figure 2 illustrates the manner in which connections are made between reaction patterns, time lag and the aggressivity of different bacterial groups. For example, highly aggressive sulfate reducing bacteria (SRB) are likely to be associated with a corrosion event and/or a black sulfide problem. Very aggressive iron related bacteria (IRB) are more likely associated with encrustations and iron-rich slime formations.
Figure 3 defines the target bacterial groups commonly found in water. In each case interpretation has to be limited to the water system from which the sample was directly taken and shouldn’t be over interpreted as a general condition in all water systems. Bacteria are normally present in all waters in low numbers and simply their presence doesn’t indicate a problem exists. Where a very aggressive group of bacteria are determined to be present then problems created by that group may exist at, or upstream from, the sampling point. Those problems would be limited by the nature of the group detected (e.g., SRB would mean corrosion or sulfide problem). Opportunistic pathogens, where there’s a concern, should be directly isolated by the standard techniques already available and the species confirmed before a serious health risk can be considered to be present.
The next stage is to control the problem by some form of management usually in the form of a chemical treatment. If a treatment has been successful then subsequent testing should reveal longer time lags before a positive reaction is recognized. Generally, every extra day of delay added to the time lag means the aggressivity of the bacteria has been knocked back significantly. Interpretations of shifts in the time lags can be achieved using Figure 2.
The bacterial reactivity system can be used to determine serious biofouling events in water that can be linked to hygiene risk. In terms of drinking water monitoring, there are some conditions in which the system may detect when a sample has an unacceptably high bacterial aggressivity. Threshold limits for biofouling are proposed to set the stage for the use of this method in the routine management and decision making processes applicable to drinking water. These proposed limits are given in Figure 5. This method represents a convenient and easy detection technique that can be applied in the field, office and laboratory. Results are quickly gathered and interpretation allows the user to rapidly begin to get a true understanding of the level of biofouling that’s occurring within the system. The aggressivity level can be quantitatively interpreted to some degree through the time lag using Figure 2. It also can be monitored over time by routine sampling and data interpretation.
Bacteria haven’t been considered as a major concern traditionally in the water industry beyond those that are recognized as opportunistic, pathogens or indicators of health risk. Today, bacteria have been found to be major “players” in the generation of various problems in the water industry relating to corrosion slimes, quality issues associated with degenerating chemistry, discoloration and/or cloudiness as well as to losses in production due to plugging or equipment failure. The aforementioned detection method provides a simple and yet sophisticated way to diagnose and monitor these changes with effective treatment and control. When used routinely and interpreted fully—with effective treatment (confirmed by subsequent testing)—there now exists an opportunity to extend the life of a water system with improved performance. In the water well industry, such tests are aiding in a campaign to extend the useful life of wells in Canada.
About the author
D. Roy Cullimore, Ph.D., is president of Droycon Concepts Inc., which is based in Regina, Saskatchewan, Canada. Droycon is the maker of the BART™—Biological Activity Reaction Test—that’s discussed in this article. Additional tests for nitrates and algae have been added to the program. Related software, BARTTSOFT™ version 4.0, offers a simple data collection and interpretation program that can be downloaded off the Droycon’s website. This system is part of a sustainable water well initiative that originated with Canada Agriculture PFRA-TS seven years ago and is now being adopted as a standard approach to water well management across North America. Cullimore can be reached at (306) 585-1762, (306) 585-3000 (fax), email: firstname.lastname@example.org or website: http://www.dbi.sk.ca
Unacceptable biofouling risk means that the bacterial group detected at these levels presents an unacceptable biofouling with a serious potential for a health risk could also be associated with the water. Immediate confirmation and treatment action is recommended. Serious biofouling risk means that the levels of aggressivity of the bacterial groups as listed is sufficiently high to believe that some very significant biofouling event is occurring upstream from the point at which the water sample was taken. Determination of the location of the site and nature of the biofouling is recommended by further testing, prior to treatment of the affected region.