> Does anyone have any data or can cite a source for the amount (%) of
> silver still remaining in a print or film which would leach or dislodge
> during the wash cycle?
I don't have the number, but the amount is actually quite small. Also, it is
not the actual amount only, but the dilution. Someone who worked in a
processing lab told me before that they diluted the used fixer before the
dumped it. I assumed that was done to satisfy the legal requirement. The
practice is debatable, however, since it actually waste water.
But remember that for a processing lab, they dump the chemical + only some
water when their employees use the bathroom. For a college darkroom, however,
you only dump a small amount of chemical + large amount of water (compared to
a lab) when the students use the bathrooms. This should also be taken into
consideration. So the amount of silver over total waste water is relative
small.
> I need to accommodate the safety folks on campus,
> they've come up with the notion there is sufficient silver in the rinse
> water to necessitate a system of recovery or abatement.
I know a college that used the silver recovery because they thought that
since the continue to use the chemical, they might as well use the recovered
silver to generate some "income." But if it is just for the safety folks on
campus, you can try to give them the explanation above and see if they would
accept it.
Dave Soemarko
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