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Silver compounds are the basic light-sensitive material used in most of today’s photographic films and papers. Each facility that processes silver-based images generates wastewater containing silver. During processing, particularly in the fixing bath or bleach-fix, silver is removed from the film or paper and is carried out in the solution, usually in the form of silver thiosulfate complex. If your facility uses photographic developing equipment, you may be discharging silver into the sanitary sewer system.
While there is no current legislation in the town’s by-laws which require that silver recovery equipment be installed on photo-processing equipment, the Town of Amherst’s Sewer Use Ordinance states that any discharge having a total silver concentration greater than 0.064 milligrams per liter (mg/l) is prohibited. To be in compliance with this limitation, however, it will likely be necessary you’re your businesses to utilize some form of silver recovery system.
What’s The Concern With Silver?
We wear silver jewelry, eat off silverware and carry silver fittings in our teeth. Then why is the silver in film processing solutions regulated?
The answer has to do with the different forms that silver can take. The metallic silver that we use in eating utensils and jewelry is nontoxic. But some forms of silver can be very toxic to aquatic organisms. In fact years ago, silver cation (Ag+) was used as a biocide in wastewater treatment. Even today, silver nitrate is sometimes added to the eyes of new infants in order to kill bacteria.
How Can Silver Recovery Benefit You?
Besides the obvious environmental benefit to aquatic environments, the silver discharged from photo-processing equipment is a valuable, finite natural resource, which can be captured and recycled. By using some form of silver recovery, dischargers will maximize the amount of silver they recover. In many cases, this will provide economic returns to the discharger.
How Does Silver Recovery Work?
The simplest and most cost effective form of silver recovery is a process called metallic replacement. Metallic replacement requires little capital expenditure for equipment and requires only a few simple plumbing connections. The equipment needed for a metallic replacement system includes a plastic container, a plastic-lined steel or stainless steel drum filled with metal (usually steel wool) and some plastic hose and plumbing connections. Silver is recovered when the silver bearing solution flows through the cartridge and makes contact with the steel wool. The iron goes into solution as an ion, and the metallic silver is released as a solid to collect in a sludge at the bottom of the cartridge or is deposited on the steel wool. When the cartridge can no longer effectively remove silver (approximately 6 months – 1 year, depending on frequency of use) the silver bearing sludge is sent to a refiner who will refine it and in most cases will pay the customer for the recovered silver.
The Town of Amherst Environmental Control Division is asking business owners and operators to take responsibility on themselves to limit the amount of silver discharged to the sanitary sewer systems. By taking steps to remove silver from wastewater discharges, your company will be participating in a town-wide effort towards a cleaner environment as well as avoiding unnecessary fines.
For more information on Silver and Silver Management Practices contact:
The Silver Council
550 Mamaroneck Avenue, Suite 307
Harrison, NY 10528-1612