DON’T BE AS MAD AS A HATTER, PREPARE FOR ADDRESSING MERCURY IN YOUR
PLANT –
BACKGROUND AND CASE HISTORY
by
Ralph B. “Rusty” Schroedel, Jr., P.E., BCEE, Brown and Caldwell
Keith Hitzke, North Shore Environmental Construction, Inc.
Background
Mercury has been used for decades in many pieces of process and electrical equipment at wastewater
treatment facilities, as well as many other items. Two of the most common and largest users of
elemental mercury were manometers and trickling filter distributors. In 1972, the United States
Environmental Protection Agency banned the use of mercury except for special cases. However,
wastewater facilities have continued to use existing equipment that contains mercury. State and federal
regulatory agencies are considering requiring that water and wastewater treatment facilities complete
an audit for mercury and to address identified sources of elemental mercury, especially at facilities
where trickling filters have been in use for decades. It is important for wastewater facilities to address
elemental mercury and mercury added products. There are case histories where significant quantities of
historically retained and accidentally spilled elemental mercury required a major cleanup effort should
the history of mercury use at treatment facilities not be investigated and addressed properly.
The common design for trickling filter distributors for much of the 20th century included a mercury
seal. The seal used a combination of a reservoir, fill pipe, and the density of the mercury, as compared
to the low water head required to distribute the wastewater, to create a seal at the rotating center
column. A 10-inch unit would use about 30 pounds of mercury and a 15-inch unit would use about 40
pounds of mercury. (1) A technical paper cites distributors containing nearly 750 pounds of mercury. (2)
Often, mercury was lost from the center column due to high flows forcing the mercury out of the seal
onto the trickling filter media and center column support. Overfilling of the mercury seal during
maintenance also occurred. It was not unusual to see water leaking from a center column that had lost
its seal. Also, historical wastewater received at the plant and maintenance activities may have added to
the volume of mercury. In addition to trickling filter seals and historical flows, mercury manometers,
still seen in many older plants across North America, are another source for mercury spills.
A report by The Northeast Waste Management Officials’ Association (3) summarized the sources of
elemental mercury and mercury added products. The report also provides a detailed description of
mercury added items. Lastly, that report provides a table of mercury added products likely to be found
at wastewater treatment facilities and a checklist for those products developed by the Northeast Ohio
Regional Sewer District. All of this information supports the need to address the sources of elemental
mercury and mercury added products at wastewater treatment facilities, especially those with trickling
filters.
A “Case History”
As part of an upgrade at a wastewater plant, existing trickling filters were being renovated and
modified. Removal of the center pivot assemblies may require addressing unknown quantities of
elemental mercury. A far more substantial monitoring and cleanup effort may be required if careful
study, analysis, monitoring, and construction is not performed. North Shore Environmental
Construction, Inc. (NESC) has performed clean up at a wastewater plant. The quantity and extent of
elemental mercury on site requires a carefully planned and executed remediation effort.
Conclusions and Recommendations
Any wastewater facility with old trickling filters should anticipate the need to address historical
mercury issues as well as more recent mercury spills in, and possibly around, the area of the TFB’s.
Any upgrade or rehabilitation of existing trickling TFB’s should expect to address likely mercury
contamination. It also appears that mercury throughout wastewater treatment plants will need to be
investigated and audited in the near future.
This paper will be of interest to any operators of older, existing wastewater plants, especially those
operating trickling filters, and engineers designing rehabilitation of plants with trickling filters.
References:
(1)
(2)
(3)
USFilter (Envirex), Memorandum Dated October 10, 2005
“A Case Study of Mercury and Methylmercury Dynamics in a Hg-Contaminated Municipal
Wastewater Treatment Plant”, C.C. Gilmour and N.S. Bloom, Water, Air, and Soil
Pollution, 80: 799-803, 1995
“Mercury-Added Products Found at Drinking Water & Wastewater Treatment Facilities”,
The Northeast Waste Management Officials’ Association, June 30, 2010
Trickling filter rock with visible, elemental mercury
Visible mercury in area beneath rock media support