"The situation, then, is that neither smoothness of surface, materials of construction, nor flow velocities long delay the advent of biofilm formation." (Meltzer 1994)
Bacteria constitute a very successful life form. In their evolution, they have developed successful strategies for survival which include attachment to surfaces and development of protective biofilms where they behave very differently than free-floating bacteria. Their successful strategies make it difficult for us to control biofilm growth in automated watering systems.
How biofilm bacteria evade our attempts to eliminate them:
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We purify water to remove nutrients and ask, "How could anything live in it?
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They use their polymer web to concentrate nutrients. They can live on nutrient levels we can’t even measure.
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We flush water lines trying to scour them off the pipes.
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They cement themselves to surfaces with their sticky polymers under the laminar layer where shear forces are too weak to remove them. |
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We smooth the inside surfaces of fittings so they can’t take shelter in crevices and crannies.
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It doesn’t matter. They will attach themselves speedily and inevitably anyway.
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| We sanitize piping with chlorine.
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They shield themselves in slime.
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So what is the solution?
Purify anyway!
It will limit nutrients somewhat, especially nutrients for microbes like sulfate-reducing bacteria which cause corrosion problems. Nutrient-poor RO water will support less bacteria than tap water. This means a thinner biofilm. Besides, the animals will be getting better quality drinking water.
Flush anyway!
Periodic flushing will minimize the thickness of the biofilm. Thinner biofilm have less anaerobic zones and sanitizing chemicals will have a shorter distance to diffuse through to reach the pipe surface.
Minimize crevices anyway!
Maybe surface finish doesn’t matter much as far as total biofilm accumulation, but eliminating large crevices (like o-ring joints) will eliminate deep pockets of biofilm which are harder to sanitize and are more corrosive. Also, electropolishing will aid in resisting corrosion.
Sanitize anyway!
If biofilm recovers in say 3 days after sanitization, knock it back down by sanitizing every 1-2 days. This could be done by automating chlorine or ozone sanitization.
There is no one easy answer. Unless a continuous chlorine level is allowed in a water supply, it will take a combination strategy. But, if we use every weapon we’ve got, it should result in a bacterial water quality which will satisfy the needs of our customers and the research animals.
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