BENEFICIAL BIOFILMSFrom: http://www.cs.montana.edu/ross/personal/intro-biofilms-s3.htmIn natural environmentsAs we have already pointed out, biofilms are all around us, on us, and in us. Obviously,then, not all biofilms are harmful. Many play an important role in the ecology of the earthand the sustainability of life in general. The report, "Global Environmental Change:Microbial Contributions, Microbial Solutions," points out: ". . .the basic chemistry ofEarths surface is determined by biological activity, especially that of the many trillionsof microbes in soil and water. Microbes make up the majority of the living biomass onEarth and, as such, have major roles in the recycling of elements vital to life." Imaginethat! "Microbes make up the majority of the living biomass on Earth," and, as we arelearning, those microbes often live in biofilm colonies on surfaces.For example, it is known that bacteria are early colonizers (in a biofilm) of initially cleansurfaces submerged in water. Scientists have been able to document a predictable patternof the way in which biofilms form on a clean surface under water. Whether the surface inquestion is a boat hull floating on top of the water, or a new deep sea vent at the bottomof the ocean, microbes are already present in the those environments and are capable ofrapid attachment to and community development as a biofilm on those surfaces (the boathull or the deep sea vent).It is important to recognize that microorganisms, such as bacteria, that colonize inbiofilms have evolved along with other organisms, including human beings. While somebacteria produce effects that are bad for other organisms, most bacteria are harmless oreven beneficial. When it comes to bacteria, higher organisms (like us) are just anotherenvironment to colonize. So heres a thought: humans, who are often thought to be thecolonizers of the world, are themselves the target of colonial powers, in the form of themany microorganisms that sneak into and inhabit our body!Water and wastewater treatmentOne of the best examples of successful, beneficial application biofilms to solve a hugeproblem is in the cleaning of wastewater. Think of it this way. We know thatmicroorganisms are the main agents that cause decay in dead plants and animals. Decayhappens (partly) as the microorganisms feed on the tissue of the dead organism. Sincethat is true, perhaps one could engineer a system that uses the proper microorganisms (inthe form of a biofilm) to process wastewater and sewage: if the contaminated water werepassed through such a biofilm, perhaps the microorganisms in the biofilm would eat (andthus remove) the harmful organic material from the water.Good idea! Indeed, even before biofilms were recognized and became the subject ofintense research, engineers were taking advantage of natural biofilm environmentalactivity (without knowing about biofilms) in developing water-cleaning systems.
Biofilms have been used successfully in water and wastewater treatment for well over a century. English engineers developed the first sand filter treatment methods for both water and wastewater treatment in the 1860s. In such filtration systems the the filter medium (i.e., sand) presents surfaces to which microbes that feed on the organic material in the water being treated can attach. The result? The formation of a beneficial biofilm that eats the "bad" stuff in the water, effectively filtering it. Of course, we dont want themicroorganisms in the biofilm to get into the filtered water, or for chunks of biofilm todetach from the colony and make it through the system. Ideally, the biofilm staysattached to the filtration system and can be cleaned when the system is flushed.Interestingly, scientists and water treatment engineers have discovered that drinkingwater and wastewater that have been processed with a biofilm system in a treatment plantare more "biologically stable" than water filtered by other types of treatment systems.This just means that there is likely to be less microorganism contamination in water thathas passed through a biofilm-based filter than there is in water that has passed throughsome alternative treatment system. This implies that biofilm treated water typically haslower disinfectant demand (e.g., use of chlorine) and disinfection by-product formation(e.g., that unsavory taste and smell of chlorine) potential than water treated in other waysif the water prior to treatment is high in the kind of nutrients the biofilm craves (which inthis case is organic carbon).People are finicky. We want our drinking water to be crystal clear, have no odd odor,and to taste, well, like pure water. Water that is safe to drink because of being treatedwith chlorine can still have an odd color, smell bad, and taste worse. So, drinking waterutilities go to great lengths to provide us with the kind of drinking water we want (usingozone in the primary treatment phase is one approach that is used). In any such system, abiofilm treatment phase may well be one approach that will help yield the desired result.Remediation of contaminated soil and groundwaterOne of the less obvious beneficial applications of biofilms is in cleaning up oil andgasoline spills. Thats right, certain bacteria will eat oil and gasoline. Remember that oilwas produced over many years by decaying vegetation, so it is an organic compound.We wouldnt recommend that you suck up any spilled oil or gasoline, but the fact thatsome of the naturally occurring bacteria in soil love the stuff leads to a new idea:
bioremediation. This is a term that refers to the engineering of a biofilm that can beintroduced into the area of an oil or gasoline spill to help clean up the mess, and all withnatural, non-harmful means.Indeed, bioremediation usingbiofilms has emerged as a technologyof choice for cleaning up groundwater and soil at many sitescontaminated with hazardous wastes.Bioremediation results in • the reduction of both contaminant concentration and mass for many subsurface contaminants (e.g., petroleum hydrocarbons and chlorinated organics) and/or • a beneficial speciation change in the bacteria in the biofilm that allow them to tackle other contaminants, such as heavy metals (such as mercury)In other words, bioremdiation is a great idea! How to actually make it work requires anunderstanding of biofilm processes and engineering systems for introducing a biofilminto the contaminated ground and providing the necessary environment below the surfaceof the ground to encourage the biofilm to do its job (illustrated in the diagram above).For students interested in this topic, the study of biofilms and engineering (e.g.,environmental engineering or chemical engineering). Just keep on truckin, and you willget there.Microbial leachingAs you probably know, mining for precious metals of various kinds (gold, silver, copperand so forth) is a messy job. The desired metal is not generally found in nice, big, purechunks. The largest gold nugget ever found was reputed to weigh about 70 Kilograms.But most gold, as with all other precious metals, is generally hard to see with the nakedeye, mixed in the ground with dirt, rocks, and other ground debris--the ore from whichthe gold must be extracted (note that the ore in a good copper mine, for instance, willtypically consist of less than 1% copper). The extraction process, when done withchemicals, is called "leaching." For years, the leaching of copper, for example, was donewith acid. Not good, very not good for the environment. In fact, most leachingtechnologies have resulted in toxic leftovers.
Well, guess what? Today approximately 10 to 20 percent of copper mined in the UnitedStates is extracted from low grade ore with the assistance of biofilms. And miningcompanies are making a considerable investment to extend this process to the extractionof other precious metals.How is a biofilm engineered to accomplish this job? Again, one must find a bacteria witha particular appetite--one that would eat the ore, say, that encased copper particles, thusreleasing the copper to be recovered. This idea has led to the most common biofilmsupported leaching process, called "heap leaching." Low grade ore is placed in a "heap,"and sprayed with a mildly acidified water solution that encourages the growth of aparticular bacteria that eats away at the ore, releasing water soluble cupric ion (copper)that can then be recovered from the water.Other biofilm technologies with promise...coming soon.Microbial fuel cellsBiofilm "traps”Microbial "canaries"From: http://www.cs.montana.edu/ross/personal/intro-biofilms-s3.htm