MUNICIPAL WASTEWATER PLANT PROBLEMS WITH MERCURY
AND MERCURY EFFLUENT STANDARDS
David T. Lordi, Coordinator of Technical Services and Studies
Cecil Lue-Hing, Director of Research and Development
Stanley W. Whitebloom, Coordinator of Industrial Wastes
The Metropolitan Sanitary District of Greater Chicago
Chicago, Illinois 60611
INTRODUCTION
Mercury has been found to be ubiquitous in the environment and has received much
attention since the beginning of the  1970s.    The recognition and concern for the potential environmental hazard from increases in mercury have led to the promulgation of
various mercury standards and control of the uses of mercury compounds.
The Illinois Pollution Control Board (IPCB) through its Rules and Regulations
established a limit of 0.0005 mg/1 (0.5 /ig/1) on mercury concentrations in wastewater
treatment plant effluents discharged to the waters of the State of Illinois [1].   In
addition, the 0.5 jug/1 limit is applied to industrial dischargers into a municipal system
if the municipal plant effluent exceeds 0.5 /ig/1.    These regulations are currently under
review by the IPCB.    The United States Environmental Protection Agency has established a criterion of 2 /ig/1 for use in monitoring potable water supplied [2].
A series of studies was undertaken by the Metropolitan Sanitary District of Greater
Chicago (MSDGC) to develop information with regard to an evaluation of the District's
compliance with the IPCB's mercury effluent standards and for use in hearings held by
the IPCB in review of the mercury standards.    The occurrence of mercury in the
wastewater treatment plants and possible sources and control are discussed in this
paper.
MERCURY LEVELS AT MSDGC TREATMENT PLANTS
The MSDGC provides sewage treatment for an area of approximately 860 square
miles and treats an average of 1.4 billion gallons of sewage per day in six sewage
treatment plants ranging in size from 2 mgd to 1200 mgd.   The levels of mercury and
the compliance of the District's treatment plant effluents and effluents from other
publicly owned treatment plants with the numerical limit of 0.5 Mg/1 mercury were
determined.   The possible sources contributing to mercury found in the wastewaters of
these plants were also investigated.   Evaluation of plant operational data covers a period
of five years from 1972 through 1976.
Final Effluent Mercury Levels
The mercury levels found in the effluents from the MSDGC treatment plants have
been compiled for the years 1972 through 1976.   Table I presents the annual average
effluent mercury concentrations observed for this period.   These values are the averages
of daily composited samples collected at each of the treatment plants.
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