Memorandum

23 May 2011

Page 1 of 3

MEMORANDUM

TO: Carey Johnston, EPA/EAD

Damon Highsmith, EPA/EAD

FROM: Kimberly Landick, ERG 

DATE: 23 May 2011 Revised

SUBJECT: Polishing System for Removing Dissolved Mercury Review

EPA is initiating an effluent guideline rulemaking for dental facilities to reduce 

discharges of mercury to the environment. Mercury is a concern to human health because 

it is a persistent bioaccumulative toxic element. Mercury-containing amalgam wastes can 

enter the environment when new fillings are placed or old mercury-containing fillings are 

removed, and the wastes are flushed into the chair-side drains. Some of the waste 

amalgam particles settle out in the sewers, and some are carried to publicly owned 

treatment works (POTWs). Treatment processes at POTWs remove approximately 90 

percent of the mercury received in the wastewater. The mercury removed from the 

wastewater then resides in the biosolids or sewage sludge generated during treatment. 

Dentists can reduce mercury discharges by implementing best management 

practices, including the use of chair-side traps and vacuum filters to collect wastewater 

containing mercury, amalgam separators to remove mercury solids in the wastewater, and

a polishing system to remove dissolved mercury. This memorandum provides technology 

and cost information on the polishing system. 

Polishing System for Removing Dissolved Mercury Background

Approximately 2-3 percent of the total mercury in a dental office waste stream is 

dissolved mercury which can be removed with a polishing system. The polishing system 

is a pump and treatment system that is located after the amalgam separator. The amalgam 

separator used can be any standard amalgam separator as long as it is large enough to 

collect one full day of liquid used in the dental office. The waste stream initially enters 

the drain and goes to an amalgam separator. The amalgam separator removes all solids 

and then stores the liquid. At offices using a polishing system, the liquid is pumped to a 

secondary storage tank at the end of the work day. In the storage tank, oxidation and

mercury speciation occurs; this speciation must occur for the polishing system to remove 

the dissolved mercury from the waste stream. Additionally, in order for mercury 

speciation to occur through oxidation, all of the solids need to be removed, making the 

amalgam separator located before the polishing system necessary. The process of 

mercury speciation is a patented process owned by SolmeteX (ERG & Al Dube`, 2011).

After speciation of the mercury, the waste stream is pumped through a series of 

three filters which removes the dissolved mercury. The first filter is a granulated 
Memorandum

23 May 2011

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activated carbon (GAC) filter, the second is a Keyle:X resin contact bed and the third is a 

0.5 micron filter. The waste stream is then discharged to the sewer. According to 

SolmeteX, the dental waste stream is an extremely difficult waste stream to work with 

especially when removing mercury because there can be numerous constituents in the 

waste stream which can change from day to day. Therefore, the polishing system does not 

collect one hundred percent of the dissolved mercury every time, but it significantly 

reduces the amount entering the sewer (U. S. EPA & Al Dube`, 2011). 

Treatment Effectiveness 

An amalgam separator removes solid mercury and a polishing system removes 

dissolved mercury in the dental waste stream. SolmeteX has not collected any data on the 

percentage of mercury removed from the polishing system. A trial was completed in 

Colorado Springs, CO, where a polishing system was installed at two different dental 

facilities. The sewage treatment plant that collected the wastewater from these two dental 

offices measured the mercury in their waste stream before and after the polishing system 

was installed. They found a decrease in the mercury content of the wastewater after the 

polishing system was installed. Therefore, it was concluded that the removal efficiency of 

the polishing system is better than that of a stand-alone amalgam separator because it 

directly addresses a portion of the dissolved mercury released from the dental waste 

stream. However, according to SolmeteX, there is not a current technology that would 

completely solve the issue of total mercury removal. This lack of data is a limitation for 

evaluating the polishing system (ERG & Al Dube`, 2011). 

Dissolved Mercury Regulations

Currently there are no laws, rules or statutes in the Unites States that require a 

dental office to remove dissolved mercury. The ISO Standard 11143 and the EPA/ETV 

Standard used for amalgam separators do not include dissolved mercury. Toronto, 

Canada has a 10 parts per billion discharge limit but it is not enforced because again, 

according to SolmeteX, it is impossible for any dental office to meet the limit 

consistently (ERG & Al Dube`, 2011). 

Polishing System Costs and Maintenance Information

The polishing system has 3 components that need to regularly be maintained and 

replaced. The series of three filters needs to be replaced approximately twice a year 

depending on the dental waste stream. Chlorine tablets are used to clean the polishing 

system. These can be bought from a local pool vendor and typically 2-3 buckets are used 

annually per polishing system. Finally, there is also a standard collection container 

attached to the polishing system which needs to be replaced twice a year. This container 

has a fill line allowing replacement to be monitored by sight. Table 1 presents cost 

information for the polishing system model by SolmeteX.
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23 May 2011

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Table 1. Polishing System Costs ($2010)

Manufacturer Model Technologies MSRP Maintenance Requirements

Replacement 

Parts Costs

SolmeteX Polishing

System

Oxidation, 

Filtration $4000

Replacement parts include a 

series of 3 filters (GAC filter, 

resin contact bed, and 0.5 

micron filter), chlorine tablets 

(3 buckets annually), and a 

standard amalgam collection 

canister.

$2000-$2100

Total Average Cost for an Amalgam 

Separator

$1,213 -

$1,271 Varies by manufacturer. $506 - $527

Total Average Cost for Entire System $5213 -

$5271

$2506 -

$2627

Sources: EPA & Al Dube`, 2011 and ERG & Al Dube`, 2011.

References

U.S. EPA & Al Dube`. 2011. Email correspondence between Jan Matuszko, EPA and Al 

Dube`, SolmeteX, March 15, 2011: Subject Dissolved Mercury. 

ERG & Al Dube`. 2011. Notes from telephone conversation between Kimberly Landick, 

ERG and Al Dube`, SolmeteX, May 5, 2011: Subject Polishing System for Removal of 

Dissolved Mercury.