A dispersant or a dispersing agent can be a polymer or a surfactant based suspension, depending upon the nature of application. A dispersant has an objective of breaking down particles to prevent settling or clumping.
A biodispersant is used in water systems for removing or preventing biofilms. The micro-organisms behave very differently when living within a biofilm than when the same species are floating freely. In water treatment, biofilms are undesirable because they harbor pathogenic organisms such as Legionella, they reduce heat transfer, they cause increased friction or complete blockage of pipes, they foul probes and they contribute to corrosion.
In terms of corrosion to the system metal: Biofilm contributes to MIC (Microbiological Induced Corrosion). In addition to it, biofilm allows accumulation of most of acidic metabolic products near the metal surface, which accelerate the cathodic reaction. One such metabolic product, hydrogen sulphide will also promote the anodic reaction through the formation of highly insoluble ferrous sulphide.
The corrosion products of MIC also interfere with the performance of biocides, resulting in a vicious cycle. The microorganisms themselves may make up from 5 to 25% of the volume of a biofilm. The biofilm allows enzymes to accumulate and act on food substrates, without being washed away, as they would be in the bulk water. The presence of the biofilm causes often-acidic metabolic products to accumulate within 0.5m or so of the colony. When one species can use the metabolic products of another, their colonies will often be found adjacent to one another within the biofilm. The thickness of the biofilm thus increases. The biofilm matrix can also protect organisms within it from the grazing by larger protozoa such as amoeba, from antibodies or leucocytes of a host organism, or from antibiotics. Due to such multiple advantages that microbes can derive from biofilm, almost all of them are capable of producing some amount of biofilm.
Biofilm is most stable when conditions in the ambient water are stable. Changes in ionic strength, pH or temperature will destabilize biofilm, and release them in dispersed form into water. A biofilm may grow exponentially at first, until the thickness of the film either interferes with diffusion of nutrients to the organisms within it, or the flow of water causes matrix material to slough off at the surface as fast as it is being produced below.
Biofilm development is most rapid when consortia of mutually beneficial species are involved. In the absence of antimicrobial agents, biofilms in cooling tower typically take 10 to 14 days to reach equilibrium. In order to enter biofilm bacteria cells, chemical species in the water must contain biodispersant that range in properties from strongly anionic and hydrophilic to hydrophobic. This is so, as almost all species of microorganisms accelerate the production of enzymes, as a protective mechanism, in response to stress including that caused by biocides. Thereafter, there is a considerable amount of time and often a high concentration of multiple biocides required for those biocides to diffuse into the biofilm bacterial cells and act. The shredding of the biofilm organisms into the bulk water by the action of a biodispersant results into spread of a species of microorganisms from one region of the system to another. Once such spread occurs, the biocide added to the system is expected to reach the concentration of the microorganisms somewhat easily, but still biocide may not be effective,
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