re: killing bacteria

A standard way of killing bacteria in liquids is to use short wavelength UV:
a bacteriacidal (?) lamp. These are little mercury vapor tubes, with no
fluorescent lining. They efficiencly turn electrical power into 257 nm
wavelength radiation, which kills just about anything. Don't look at them
directly, or let the radiation contact you! They also have a green and a
few other Hg line outputs, so you can seem when they are running. A UV
absorbing glass or plastic is enough protection, or anything opaque.
They should be available by special order at lighting distributors.
Electrically they are the same as a fluorescent lamp, and so will start and
run in a normal fixture.

My guess is that these should kill any bacteria, if the liquid is at all
transparent.

If not, try ozone.

The UV or ozone might break down the organics in you coolant.

Elliot Burke