And, even later work was done using the new film and paper hardeners which restrain swell to a different amount. And much work was done with alkaline fixers with and without hardeners.
Yes, yes, I know all of that, but the salient point remains that any method puts the same amount of chemistry (within tiny limits) into the wash water if the wash is properly done! Therefore, both methods impact on the environment in roughly the same manner. Wash aids can increase this "pollution" to some extent, or at least change it.
The amount of chemicals both methods put into the environment may be the same.
Originally Posted by Photo Engineer
The amount of water that has to be cleaned (either before it is dumped into a river, or before it goes into the water grid, or both) however is not.
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.
When you use more water, more water needs to be treated.
And it will be, regardless of the concentration of chemicals in it.
See my edit of my previous post.
It is not merely the amount of water, but the concentration of ingredients at any given moment which enters the sewage system or the treatment plant.
Even when you dump clean water down the sewer, it has to be treated. First, to make it clean water fit to come out of your tap. Then to clean it up again before it is dumped.
When you dilute the filth in the sewage system, it may lead to cleaner, i.e. less concentrated, sewage, but still and also increase the volume of it, increase the volume that has to be treated.
So another conclusion we can safely draw is that the more water you use, the more water will be treated.
At a price. Which counts as environmental costs.
Well, I have been involved in some of these situations with photofinishers being shut down due to effluent, and also doing lab tests on the effluents and how to constrain them.
Yes, the volume of sewage is important, but the absolute concentration of ingredients is also important. As an extreme at one end, the sludge becomes so thick it is virtually impossible to treat. On the other end, the volume is so great that the holding tanks can overflow. Both are bad.
But, you miss the point that a huge "plug" of concentrated chemistry can do more damage as it enters the treatment area than a larger more dilute flow. The word here "CAN" is important, because actual tests around the median, not extremes is ambiguous. And, I hasten to add that most of us dump very little due to the size of our operations.
Now, for a specific example of something extreme but possible. A photographer wishes to dispose of his effluent and he lives in a desert area. If he decides to dump it in the desert, should he dump concentrated waste over a small area, or dilute waste over a large area? This hypothetical question has real import on the situation we are considering here. The interesting part is that the concentrated effluent has insufficient volume to be dumped over a large area, but the dilute effluent can be dumped over a large area. The same holds true in a wash. Successive dumps occur with plug flow in the pipes and enter the sewage treatment as blocks of contaminant, but the more dilute continuous wash takes place over longer times.
In practice, as I said, the results are ambiguous due to the low flow from our types of labs.
On another tack, when water is severely limited, then a whole new set of practices hold. In a true desert environment, water is precious for both incoming purposes and outgoing purposes. There are few studies on the exact nature of what should be done in these cases. There are ways to adapt to this using mixed bed resins in which the total water consumed and total effluent remains zero once the system is set up and charged with water. You put in your initial charge of water for all of the processing system and then just drain off the deionized water at the other end and re-use it. The problem is the cost of the resins and the cost of disposal. This was all worked out by myself and others at EK in the 70s BTW.
I'd choose dumping concentrated waste on a small area over dumping diluted waste over a large area.
Except when the dilution is so great that we're entering the domain of homeopathic 'concentrations'.
Yet, then still the idea of dumping over a huge are instead of keeping the smut contained in a small one appears to be wrong, the worst of the two choices.
But what concentrations are we talking about here?
When we use a few litres of water to wash our film, instead of many times that much, do we create a "huge plug of concentrated chemistry"?
Does having to treat those few litres contaminated with fix cause problems that having to clean many times that much of more dilute fix doesn't?
For me, the botom line is that, even though we may not think it, water is not 'free'. We all live in a 'desert', even when we don't.
It is taken from the environment in huge quantities, at a cost to that environment. And it needs to be treated before it is fit for use. And once again after we have flushed it down the drain.
The more we waste it, the larger the cost, both to the environment (and our health) and to our wallets.
QG, you are right, but then as few as we analog photographers are, we contribute very little to the impact on the environment. Even a photofinisher contributes little in terms of water usage when you get right down to it.
Many industries use far more water than the entire analog manufacturing and processing chain are concerned, or they introduce far worse pollutants. Photography is quite mature and the engineers working in the field have considered the questions I bring up. In fact, I think that consideration of some of these facts and questions have given rise to the ambiguity and sometimes to the apparent retractions in textbooks.
The bottom line is to use what gives you the right level of retained hypo and silver at the lowest level of pollution.
And remember, when you dump exhausted developer and/or fixer, this is hundreds of times worse than the wash water contamination.
You REALLY should be more concerned with the LOSERS at BP for destroying the worlds oceans and not so much with the water used by rinsing film or prints.
We in the USA pay a MAJOR amount for Water and Sewer processing and the amount of stuff that goes in the sewer is NOTHING compared to what goes down the drain just in household cleaners and washing cloths etc, So we PAY for this use and what we are depositing is a drop in the bucket.
And if you are REALLY freaked out, go buy some carbon offset credits (http://www.carboncatalog.org/) to off set your hazardous waste activity !!
Now you will be SUPER GREEN !!!