I am looking at ecotoxicity publications, and would also like to know how efficient silver recovery is.
The whole topic can get much deeper than you would probably imagine. There have been a number of silver recovery methods over the years, each with their own strengths and weaknesses. But these have to be part of a process "system."
For the most part, photo processing effluent is ruled more by regulatory bodies than by actual "ecotoxicity" effects (whatever that really is).
As a real brief introduction, the main concerns with common photographic effluent are mainly the "oxygen demand" (see either COD or BOD), and silver content. Now, if you dumped "enough" chemicals with a high oxygen demand into a stream, this is detrimental (it robs the aquatic organisms of oxygen). But if you dump the same thing into a sewage treatment plant, well, this is one of the main things that a treatment plant treats (human waste also has a high oxygen demand). Now, if you wanted to minimize your oxygen depleting waste, what would/could you do? Well, number one, you would reduce the total amount of chemical waste by using "replenishment" for everything, and in the case of fixer you would use multi-stage counter-current flow replenishment systems. By doing this you could reduce chemical waste by probably a factor of 5 or 10 times over the single-use processors. So the design of the "process" can have a major effect on the "ecotoxicity," again, whatever that really is.
With respect to silver-bearing waste, conventional internet lore is that this is toxic to micro organisms (as is ionic silver, such as dissolved silver nitrate). But photographic silver, in tests for "acute toxicity" in the environment, so to speak, is found to be relatively benign compared to ionic silver. In the US, at least, it is possible for a photo finisher to get a special sewering permit from local municipalities to handle their effluent. Yet it is subject to the same regulatory standards that were probably intended for ionic silver. And some of these standards are so low as to be crazy, in my view.