doeHealth Care Waste & Toxics Reduction Tips

for small and medium size health care facilities

SILVER RECOVERY FROM DIAGNOSTIC IMAGING:

Approximately 20% of the silver used each year ends up in X-ray film.  When the X-ray film is processed, the silver is released into the fixer solution where silver in excess of five parts per million designates as dangerous waste.  Spent fixer typically contains between 3,000 and 8,000 parts per million.Dangerous waste generators may treat their own waste onsite, without a dangerous waste treatment permit, if they meet certain requirements.

On-site silver recovery is typically used for spent fixer. Due to the complexity of other silver recovery processes send film and paper off-site for recycling.  You can install a silver recovery unit at the end of the x-ray or film processing line.  The recovered silver can be sold to a metal reclaimer.  Properly treated fixer may be disposed of to the sewer with permission from the public wastewater treatment authority.  Never discharge silver into a septic system; even in small quantities it can harm the system. Facilities with septic systems should contract with an industrial wastewater disposal company to dispose of this waste. 

Local Issues

Some sewer districts in the state have set their own local silver discharge limits for businesses. This is to help the sewage treatment plant meet its discharge levels for silver into waters of the state. In some locations, sewer discharge levels are so low that businesses using on-site silver recovery systems will have difficulty meeting these levels. Similar low limits are continuing to be developed in other areas of the state. Businesses located in areas with strict local sewer limits may have no choice but to explore off-site recycling options.  To see your local sewer discharge limits click local sewer silver discharge limits

The Economic Case

The cost of setting up a silver recovery system can range from $200.00 to $1,800.00.  If you generate at least 2-3 gallons per week of spent fixer, treating on-site can save you money.  For example:

One gallon used fixer =                             0.25 troy ounces silver
10 gallons fixer used monthly x 0.25 =     2.5 troy ounces silver
12 months x 2.5 =                                    30 troy ounces silver
$12.00 per ounce (price fluctuates) x 30= $360.00 recovered annually

The recovered cost of not managing and disposing of the fixer as dangerous waste must also be considered, as well as the energy and maintenance cost of the recovery system.

 

chartChoose the Right System

Take the time to define your needs and then select the system that meets those needs. The process of choosing a system needs to include consideration of five main factors:

  • Your compliance situation: Check with your local wastewater utility for applicable regulations before purchasing a system. Do not dispose of treated silver waste into on-site septic systems.
  • Capital cost and projected revenue: Silver recovery systems may not be economical for businesses generating smaller quantities of silver bearing waste.
  • Ongoing maintenance: These systems require regular testing to ensure proper function.
  • Space requirements: A system needs to be easily accessible for testing and maintenance.  Some systems do not work properly with low or intermittent flow.
  • Waste volume: Make sure the system you choose will operate in the range of fixer solution you generate.
 

 

If Onsite Recovery is not Feasible:

  • Use a pickup-and-recycle service for the used fixer solution.

 

chart

 

Things to Keep in Mind:   

  • Keep developer and used fixer separated. Developer will ruin silver recovery systems.
  • Unused developer contains hydroquinone, a toxic substance, so unused developer cannot go down the drain. Because hydroquinone is used up in the developing process, used developer is non-hazardous and is safe to be disposed to sewer (not septic).
  • Do not dispose of any developer to septic systems.
  • Flush the drain thoroughly as you dispose of the used developer to the sewer, with permission from the local wastewater treatment authority

 

Operating a Silver Recovery Canister System

Businesses choosing to use silver recovery canisters for on-site silver recovery need to use 2 in a series, to consistently meet dangerous waste and local sewer silver discharge limits. Two canisters in a series can reduce silver concentrations to about 1 part per million (ppm). One canister, even of high quality, will show diminishing returns after being used a few times and will eventually discharge solution that exceeds allowable limits

Monitor the flow of used solutions into the canisters. If the flow is too fast, the proper reaction won’t happen inside the canister and you won’t meet silver discharge limits for sewer. If it is too slow, the canister may deteriorate too soon.

Monitor the flow of used solutions into the canisters. If the flow is too fast, the proper reaction won’t happen inside the canister and you won’t meet silver discharge limits for sewer. If it is too slow, the canister may deteriorate too soon. Use a metered pump system or a restricted gravity feed system and keep flow rates at manufacturers recommendations, usually between 1-3 gallons per hour.

Install a sample valve between the two silver recovery canisters.  Use this valve to sample effluent from the first canister. Using silver test paper strips, check the sample to see when the first canister is spent. Silver test strips can detect silver at levels between 200 and 500 parts per million (ppm). When your first canister reaches this level, it is time to rotate it out, putting your second canister first in line and adding a new, second canister. In addition, if the tubing between canisters is clear plastic, you can visually inspect the solution flowing through — if it is brown or has debris in it, this is a good sign that the working ability of the first canister is spent.

Test your outflow.  Take periodic samples of the wastewater leaving the system over the life span of a canister.  The sampling should be frequent enough to ensure you do not exceed discharge limits.  Have the wastewater sample analyzed for silver to see if it meets hazardous waste and local sewer silver discharge limits. Keep a file with all test data in it — you’ll have a starting point from which to make refinements to your on-site process.

Perform regular maintenance as recommended in the manufacturer’s instruction manual and keep a maintenance/changeover log. Work closely with your supplier for help in developing a changeover schedule based on your volumes of silver-bearing solutions. Ask your supplier if they provide a full service waste management arrangement.

Fill metallic recovery cartridges with water before initially putting them into service. This will extend the life of canisters by preventing the steel wool from dissolving as they fill with fixer.

Observe Strict Local Sewer Discharge Limits.  To see your local sewer discharge limits click here. Control discharges to sanitary sewer and do not exceeding your silver discharge limits.

Maintain all Records.  Keep operation and maintenance (O&M) logs for a minimum of five years.  Keep laboratory results and other documentation relating to dangerous waste in perpetuity. Here is a sample O&M Log and a sample Test Log.

Best Solution: Eliminate Fixer Waste

To eliminate generating waste fixer, switch to digital imaging.

Additional Resources


See an excellent technical information memorandum on treatment-by-generator rules.

If you do not know your generator status . view this quick information.

This document will provide assistance designating your wastes.

Get help determining how to count dangerous waste under the regulations.

Here are the complete regulations.

To check your local sewer discharge limits for silver.

View a slide show of a silver recovery effort, including contact information.

Answers to questions about mercury and silver dental office wastes.

RETURN TO HEALTH CARE HOME.

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This information is brought to you by the Washington Department of Ecology/Toxics Reduction Unit with assistance from the Pacific Northwest Pollution Prevention Resource Center (PPRC) . June 2010