And again, that depends.
Originally Posted by Q.G.
We can all agree that our film and paper must have a certain minimum of hypo and silver in them for good keeping. The rate at which it is removed depends on the chemistry, the photomaterial and the local water used.
The discreet stepwise wash method decreases this retained level in a series of sawtooth steps down towards the minimum and the last wash is in equillibrium with the photomaterial in terms of retained materials.
With the continuous wash, the function is a linear decrease in retained materials and can reach near zero at the end due to the fact that fresh, uncontaminated water can be put in contact with the photomaterial at the very end.
Either of these methods can work as long as you test for retained silver and hypo in your photomaterial.
But, as for the question of concentration of materials / unit volume of effluent, you are right but studies on this are ambiguous. In fact, the first dump of wash water has a high concentration of hypo and silver salts whereas the first wave of running water has a lower concentration of hypo and silver salts.
I'm adding an afterthought here.....
The several washes method seems to behave in a manner similar to Plug Flow, so I suggest reading up on this. You get waves of decreasing concentration of contaminants. In a steady wash, there is a gradual decrease in contaminants. There is some argument that an instantaneous jump in contaminants, at a certain level, can be more harmful than a more dilute and spread out introduction of contaminants. But, as I note below, this is ambiguous depending on study.
Therefore, at any given time, with any given liter of wash water, it should be tested for contaminants to see which is better or which is worse. Due to the rapid dilution in most sewer systems results that I have heard of have been ambiguous either way.
The only conclusion is that the amount of chemicals dumped is equivalent.
Last edited by Photo Engineer; 07-19-2010 at 02:36 PM. Click to view previous post history.
Reason: See note above.