I am a hydrogeologist using an optical brightnener for groundwater
tracing. We inject the tracer into a borehole/ soakaway/ sinking
stream. We then use small balls of cotton wool (approx. 5 cm
diameter) to detect the optical brightener in springs, boreholes and
rivers, to prove groundwater connections. I have found that in the
river we need to sample, the cotton wool becomes coated in a brown
slime, presumably a form of biofilm, preventing the absorbtion of the
fluorescent tracer. I have tried covering the cotton wool in netting,
cloth, plastic mesh and wire mesh, but the cotton wool still becomes
coated in the biofilm. I know absolutely nothing about biofilms but
wonder if there is any method of preventing the cotton wool becoming
coated in biofilm, yet still allowing the water to flow through the
cotton wool and the optical brightener to be absorbed. Perhaps there
is some treatment I could apply to the cotton wool? Any advice would
be greatly appreciated.
Louise Maurice
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