When I was in business, my silver recovery unit had a drum about 6" diameter which rotated at slow speed as one electrode. There were 2 carbon bars as the other electrode. I believe voltage was about 6VDC. When the silver coating on the drum was about 1/8" thick, I would break it off. Kodak made test papers to determine the silver content of the solution. It took about 3 days to remove enough silver so that it was safe to discharge into the sewer system. Acceptable level was around 50ppm.