What is known about the transportation, fate and effects (TF&E) of silver for given wastewater treatment scenarios?
Silver is released from photoprocessing operations primarily as a thiosulfate complex. Any hydrated ion (Ag+) that may exist quickly (within seconds) binds to materials available at the point of release. Most photoprocessors discharge to municipal wastewater treatment facilities (also called “POTWs”) where sulfides and other organic materials bind the silver to form insoluble compounds. Generally 90% or more of all incoming silver is deposited into sewage sludge. Research has shown that less than 50% of the “total” silver in the water column of ambient and receiving waters is “dissolved” silver (“total” and “dissolved” are defined by EPA test methods). The ionic silver (Ag+) is found in the dissolved silver fraction, but a large proportion of this latter category is complexed with natural organic matter or bound to colloidal particles, so the concentration of ionic silver, and the resultant toxic effect, is very small indeed.
