I guess it depends on when one got interested. B&W research may have largely ended a long time ago, but color went on much longer.
Originally Posted by Michael R 1974
The C-41 process was developed about the mid-1970s, I think. It's fixer was near-neutral pH, running about 6.5. When the RA-4 process came out, 6-hour mini-labs were close behind, followed in a year or two by 1-hour systems. Somewhere around 1980 effluent regulations in the US meant that finishers had to get good control over things. Kodak supplied a good deal of published research information on process and treatment methods, which was then used by specialist companies who built equipment such as ion-exchange systems used in developer regeneration and silver recovery from wash water. And in fact, Kodak had it's own Environmental Services group, which also worked with the photofinishing industry on these things.
I think the main thing, from the hobbyist perspective, is that no significant books on these things (as far as I know) were published after Haist. And there is probably not much further market for such books.
ps; in the other thread, I suggested a replenished fixer, which would really be the only sensible way to handle things commercially, where effluents are regulated.