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 manag ement practices, including the use of chair

- sid e 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 sys tem, 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. Addit ionally, i n order for mercury speciation to occur through oxidation, all o f 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 Solmet eX (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 granulatedMemorandum 23 May 2011 Page 2 of 3

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

0.5 micron filter. The waste stream is then discharged to the sewer. According to SolmeteX, t he 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`, 2 011)

.

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 Solm eteX, 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 statu t es in the Unites States that require a dental office to remove dissolved mercury. The ISO Standard 11143 and the EPA/ETV

Standa rd used for a malgam s eparators d o not include dissolved mercury. Toronto,

Can ada has a 10 parts per billion disc harge 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 component s that need to regularly be maintained and replaced. The series of three filters need s 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 need s to be replaced twice a year. This container has a fill line allowing replacem ent to be monitored by sight. Table 1 presents cost

information for the polishing system model by SolmeteX.Memorandum 23 May 2011 Page 3 of 3

Table 1. Polishing System Costs ($2010)

Manufacturer Model Technolog ies 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 Po lishing System for Removal of Dissolved Mercury

.