Maris Rusis, thanks for posting this!
So... I really shouldn't worry about the environmental impact of disposing my (quite minimal) used B&W chemicals?
I always bring my fixer and film developer to the cities recycling center, but according to your information, the CO2 impact of driving there might be more harmful than the disposal of the chemicals.
But what about the recycling? Silver is a precious metal so I would expect that recycling this will have a positive impact on the environment. On the other hand... recycling requires energy and materials, starting with me driving my car to the cities recycling center.
Considering the environmental cost of the handling, transport and recycling of photo chemicals on one side and the benefits of recycling and avoiding pollution on the other side.... what would be the bottom line balance for someone like me, disposing some 20 litres of developer and fixer per year?