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Riddles and answers for OWT operators and scientists
By Henry Vere
In the morning when you get up and wonder where the awful taste in your mouth and strange coating on our tongue came from, you can thank biofilms for the great start to your day. Biofilms are present on the teeth of most animals, where they may become responsible for tooth decay. Biofilms can develop on the interiors of pipes, floors, and counters but also be found in more natural settings, such as among the rocks and pebbles at the bottom of most streams and rivers or floating on the surface of stagnant pools of water. E coli can be a slimy biofilm lingering on the surface of a scratched chopping block. Biofilms grow in the heat or the cold; look for them in acidic pools in Yellowstone and on glaciers of Antarctica.
Biofilms are made up of bacteria, or other microorganisms, growing as organized groups in a self-produced, extra-cellular matrix. As a consequence of their growth mode, these bacteria take on special characteristics and have abilities that individual bacterial cells simply don’t possess. Aside from the way they affect humans, these organized bacteria are a critical component of wastewater treatment systems.
The word biofilms was coined in 1978 by J. William Costerton, now director of the Center for Biofilms at the University of Southern California’s School of Dentistry. Floating or planktonic bacteria populate less than 1% of wastewater treatment systems, according to Costerton. The rest are all biofilm bacteria. Floccules are simply biofilms floating on material in the water, not on the sides of pipes or treatment tanks, though floccules still behave completely like a Biofilm in any case.
The traditional method of sampling water has involved taking free-floating or planktonic bacteria and culturing it in the lab on a petri dish and studying it under the microscope. But according to Costerton, this gives you a limited picture of what you have.
“Individual bacterial cells floating around are simply not able to do much. But floccules and attached populations of biofilms result in a tremendous increase in efficiency when it comes to bacteria,” says Costerton. “This also means that test tube microbiology doesn’t translate at all well when it comes to water treatment. Bacteria floating around in a test tube just do not have the same cooperating properties as biofilms or floccules; it’s pretty artificial.”
Studying the bacteria in situ gives a more accurate picture. “Using a confocal microscope enables us to look at opaque surfaces and certain reagents; you can have much better luck chasing the chain of contamination intelligently,” says Costerton.
When it comes to testing, bacteria from biofilms in various locations should be studied to determine, as in the case of a serious infection, exactly where the source of the contamination is. “We’ve used such attribution techniques quite well,” says Costerton. “We used this method for corrosion bacteria, finding nothing for long stretches until we found a spot where someone had placed contaminated water into the system. It is rather graphic when the testing is done.
“Flowing water changes all the time, whereas these populations coming in from the source are extremely obvious if you look at surfaces. A problem in the study of biofilm bacteria is that they don’t grow very well when introduced onto a culture medium. This is one reason why direct study methods are used now. We have wonderful ways of having only 0157H E. coli lighting up like a beacon or little flashlight.”
The reagents used are called fluorescent in situ hybridization (FISH) probes. The process itself is called FISH-ing. “This makes the identification process much easier; you cannot argue with it at all. With a stream containing biofilm on an irrigation ditch above and then below, say, a ranch, if the location above has little 0157H on it but below a great deal, there is no argument about the source of the harmful bacteria.”
Enter Quorum Sensing
Biofilms may be good or bad when it comes to wastewater treatment, according to E. Peter Greenberg, a professor at the University of Washington, who feels as well that the term’s definition is still in the works.
Anamox are clusters of bacteria, which can take nitrogen levels very low in wastewater treatment plants. “These systems are used extensively in Europe,” says Greenberg. “I think biofilms may be manipulated to our benefit in wastewater treatment because bacteria in biofilms are resistant to killing by toxic compounds, which would otherwise kill them if they were not in biofilm arrangements.”
Biofilms, because they are aggregates, can also clog up a system. This can be an issue with some technologies, according to Greenberg, who has been a basic researcher since the late 1970s in social activities of bacteria. When he started, Greenberg learned bacteria did nearly everything that other organisms did and were ideal models for the study of genetics, physiology, or nutrient cycles. But many researchers failed to find any sensing properties, specifically termed “quorum sensing,” which are examples of social activity.
“There were even arguments about that; people said small creatures couldn’t benefit from social organizations and bacteria were the example pointed to in this ‘rule,’” says Greenberg. “But our lab and several others showed bacteria could communicate among individual cells in a given species. This was formal communication with specific signals and receptors enabling the bacteria to monitor their population densities and do things when there were enough of their buddies around.”
At the same time there was a small group of people working on biofilms. It became clear to them that these organized structured communities of bacteria in different places in a biofilm appeared to have different jobs. “To me this smacked of a social organization such as a small town,” says Greenberg. “The discovery was incorporated into my research. Now there are some other examples of social behavior in bacteria.
“Fundamentally what I am trying to know is what are the rules governing social behavior in biofilm bacteria. There are really good models for this study. We can control their environment in the lab, genetics is simple, and we know from my research that bacteria, such as Pseudomonas aeruginosa can control virulence by communication—it also infects the lungs of people with cystic fibrosis. We cannot get rid of it with antibiotics.”
Greenberg’s group has provided a key piece of data showing a lot of the Pseudomonas growing in cystic fibrosis grew as biofilms. They’ve taken things further, in reasoning this may be an important reason why cystic fibrosis cannot be cured simply with antibiotics.
“We know when bacteria are in biofilms they’re protected from such destruction,” says Greenberg. “It’s a complicated process. No one quite understands how biofilms are able to do this; though some of the film may die with some treatment, you can never quite rid yourself of all of it.”
Wastewater Service Company Optimizes Biofilm Use
Industrial Fluid Management Inc., in Defiance, OH, is a water and wastewater treatment service company. It operates numerous plants of various sizes and technologies. In the course of its work it works with a lot of attached growth, or biofilm systems, according to Tom Horn, technical director with the company. Horn oversees operations from a biological standpoint as well as working in sales and service for other wastewater treatment systems.
Industrial Fluid Management Inc. calls its work with biofilms bio-augmentation. “I consider that just one of the many services we provide,” says Horn. “Typically, depending upon the application, we diagnose problems, either at our facility or at those of our clients, to determine if bio-augmentation is a suitable application. It’s basically one of the ‘tools’ in my operations toolbox and often makes use of microscopic evaluation to see what’s present at a location.”
Bio-augmentation is the practice of enhancing the performance of indigenous bacterial populations of wastewater treatment systems through the addition of bacterial cultures with specific degradative abilities. Bio-augmentation does not replace an existing bacterial population but augments its ability to respond to certain situations or its ability to degrade components of the wastestream, resulting in improved treatment.
The benefits of wastewater bio-augmentation may be broadly categorized as follows: upset recovery/plant startup, improved response to degradable organic shock loads, recovery from toxic shock loads, recovery from pH excursions, recovery from hydraulic washouts, and recovery from process interruptions, such as electrical power loss.
Bio-augmentation helps with new plant startups, scheduled or nonscheduled plant shutdowns, nitrification startups, recovery and stability, and seasonal businesses (resorts, food processing). For issues related to stability, biological and chemical oxygen demand removal rates are increased, and statistically significant reductions in effluent variability, shock load resistance, degradation of pass-through compounds, targeted degradation of specific organics, and improved stability in nitrification are all common results from routine bio-augmentation programs.
Control of oil and grease in collection systems, lagoons, scum pits, and digesters is also accomplished, as is improved solids settle-ability in secondary clarifiers and improved cold-weather operation. Bio-augmentation has been successful in improving wastewater treatment performance in fixed film, activated sludge, lagoons, and industrial systems.
Industrial Fluid Management Inc. services small OWT systems all the way up to the system employed by Campbell’s Soup Corp., one of the largest industrial wastewater plants in the Midwest. For Horn, the term biofilm tends to be something beneficial or a structure the company would usually be encouraging the growth of. “If there is a trickling filter in place or we are supplementing such equipment or there is a lagoon with an aeration system for their wastewater, we’re well aware that often anything to encourage increased biofilm growth is beneficial and helps us with our work,” says Horn. “We simply supplement with a nutrient or a bacteria once we’ve studied the problem. From there, environmental factors take their course and the biofilms come into play as they would in the natural world.”
Aeration’s Connection to the Biofilm Picture
When you have wastewater you would like to use the bacteria naturally found in the liquid to help treat that wastewater. Naturally occurring organisms, as we’ve known for some time, can help accomplish that feat. The efficient way is to introduce oxygen into the film and then the bacteria in the water will remove the organic material such as the biochemical oxygen demand (BOD), and in some company’s setups it removes the oxygen with the idea of bringing oxygen to the bacteria.
What is the best method of bringing oxygen to the bacteria so that they will survive and end up removing or eating up the BOD? Aeromix Systems Inc. is attempting to give more oxygen to the bacteria in a wide variety of ways, according to Elie Dick, corporate director of marketing and general manager for Europe and the Middle East.
“Other companies tend to pick one technology and try to tell everybody that that’s the way to do it,” says Dick. “We don’t think there is one way which is perfect all the time in every application. For example, you can improve water quality in a pond in front of a hospital or even in the backyard of your house simply by installing a small fountain, which throws the water into the air. As it goes up it picks up oxygen, and as it returns it sits in the water and the bacteria will digest the organic material.
“As you bring more oxygen into the water the aquatic life of the pond improves. We also have systems bringing air directly into the water through surface aerators, in addition to mixing systems such as our Tornado, which brings air from the outside down into the water below the surface where it’s mixed with the water. In that case oxygen is injected right down into the water.”
Aeromix’s fourth approach is to have air enter the water at the bottom of the pond or tank. In the company’s submersible units everything, even the motors, is under water. The blowers are on the outside of the tank or pond. This method also causes the oxygen to mix with the water.
“With our equipment we tend not to use the term biofilm as we are encouraging growth throughout the water,” says Dick. “Some people use a trickling filter, typically rocks with gaps in between, with water thrown on the top. As it descends through the rocks the water is exposed to the air and a thin film sits on each rock, digesting materials in the stream of water as it passes.”
The Aeromix system would be closer to the model with the bacteria dispensed throughout. Another method is biologically rotating reactors, which are basically many disks separated by a short space, that are rotated in the water. As they move around they rotate, going up out of the water for a time and then back below again. As the disk is below water a film grows on the disk, and this biofilm goes to work eating the BOD. Then up into the air it receives its oxygen to survive, all the while still rotating.
“But as a technology, this rotating system appears to be fading,” says Dick. “It seems to use too much energy for the production of the desired results. Our Aeromix system is perhaps more energy-efficient.”
When Biofilm Removal Is the Goal
In the case of water distribution systems, biofilms are more of a hindrance than a help. Not only does RE-Ox LLC, a Basehor, KS, company, have disinfection capabilities, but it’s also able to remove the scale and biofilm building up in water distribution pipes. When those are removed, the system is cleaned up, resulting in a lowered chlorine demand in the distribution system. Consequently there is also less disinfection byproducts such as total chloromethane and haloaceydic acids regulated under the Safe Drinking Water Act.
“All in all you basically rejuvenate your distribution system, getting better flows through your pipes when the scales and biofilms have been removed, as well as obtaining higher water quality,” says Ray Northcutt, senior technical director for RE-Ox.
“When that scale, calcium carbonate, calcium silicate, or calcium phosphate is removed, what we call harborage is also removed. This is a place for microorganisms. Once evicted from that safe haven, they cannot thrive and multiply. I consider the biofilms something of a blanket the organisms place over themselves for protection. Our product simply wipes out that scale and the biofilms.
“People tend to find it hard to believe that a dilute bleach solution can have the incredible performance characteristics that this product has. They’re always a bit skeptical at first, but I’ve seen the results with my own eyes and know it works exactly as we say it will.
“There’s a whole lot of movement with scaling and biofilms with pressure changes and surges and it will dislodge much. You have regrowth down the line, not just bacteria but mold, slimes, and all sorts of different microorganisms. In short there’s a whole lot you can do for your distribution system if you get rid of the place where they live.”
The product works in systems with chloramines as their residual disinfectant and it works in chloranimated disinfection systems and in municipal systems containing free chlorine in their distribution systems.
“From a chemist’s point of view this shouldn’t be possible,” says Northcutt. “But it does work.”
Center for Biofilms Study
Phil Stewart, director of the Center for Biofilm Engineering at Montana State University in Bozeman, does extensive industrial interface in working with water companies in the area of BIOFILM study. In addition to sponsoring members, the center also runs project work for companies, which approach the center with a specific technology or chemistry to test on a BIOFILM. The center runs projects for the American Waterworks Association Research Foundation too.
“There is no ‘silver bullet’ when it comes to biofilms,” says Stewart. “They’ve been around for a couple billion years and have a good survival strategy which they’ve evolved. In the more open environments, such as medical applications, it’s easier to imagine targeted strategies to focus on particular microorganisms.”
Stewart also sees huge opportunities in taking the biofilm concept and seeing it through to new technologies. He sees this happening little by little, first in medicine, where more can be afforded and individual “bad” bacterial or yeast actors can be targeted as opposed to the virtual zoo of mixed species present out there.
“Much depends on the specific situation or process that one is dealing with when it comes to issues,” says Stewart. “In some instances we don’t really care if we kill the organisms or not; we just want them off the surface, just want to clean that up.
“Then we could relax our fixation with biocides and the idea of killing every germ so we can focus more on the idea of breaking up the biofilm matrix or studying the glue holding it together; how do we interdict that cohesion? There’s a lot of opportunity there to learn to break the film apart as opposed to killing the bugs. We have a lot more experience killing microorganisms—because you can do that to a free-floating organism—and a lot less experience understanding what holds them together and how that can be targeted.”
Work at the Center for Biofilm Engineering ranges from the study of biofilm in chronic wounds to dental plaque, oilfield operations, and household products. “When we think about microorganisms in environmental systems or water treatment systems, we’re really dealing with biofilms on the surfaces,” says Stewart. “We have to let go of thinking about free-flowing or planktonic organisms and really engage the biofilm concept and use biofilm methods if we’re going to get the right answers.
“You can’t get the right answers, can’t develop the right technology without having the biofilm in there from the beginning. One of our principal initiatives is to develop standard methods for working with biofilms.
“There is a hole there, and we need methods people can recognize as the standard approach. Regulatory agencies such as the EPA or even the FDA [Food and Drug Administration] can identify those as ways to study biofilm that are repeatable, consistent, and standardized. This is something industry is quite enthusiastic about.”
Henry Vere writes extensively on engineering and scientific subjects.
OW - July/August 2007 |
