Municipal Wastewater Plant Problems With Cyanide
Effluent Regulations
DAVID T. LORDI, Coordinator
Technical Studies and Services
CECIL LUE-HING, Director
Research and Development
EARL KNIGHT, Coordinator
Industrial Waste Division
The Metropolitan Sanitary District of Greater Chicago
Chicago, Illinois 60611
INTRODUCTION
The Illinois Pollution Control Board through its Water Pollution Rules and
Regulations has established a cyanide limit for effluents discharged to the waters of the
State at a concentration of 0.025 mg/1 (1). In addition, no industrial discharge to a
municipal sewer system can exceed 0.025 mg/1 of cyanide if the effluent of the municipal
treatment plant to which the industry discharges exceeds 0.025 mg/1. The Rule does not
specify whether the limit refers to free or complex cyanides.
The Metropolitan Sanitary District of Greater Chicago (MSDGC) has the
responsibility of providing sewage collection and treatment for an area of approximately
890 square miles including the City of Chicago and 116 surrounding communities. The
District maintains and operates three major treatment works, North Side (340 MGD),
West-Southwest (850 MGD) and Calumet (220 MGD). In addition, the District operates
four other smaller treatment plants, East Chicago Heights, Hanover Park, Lemont and
Streamwood with an additional combined flow of approximately 20 MGD. Figure 1 shows
the District's boundaries and treatment plant locations.
In order to evaluate its compliance with the IPCB cyanide standard of 0.025 mg/1 the
District has carried out several studies including the determination of cyanide levels present
in the treatment plant effluents and the raw sewages to each of the treatment plants, other
possible sources of cyanide not attributable to industrial wastes as well as known
industrial cyanide waste loads. An evaluation was also made of the precision of the
analytical procedures at the low levels which have been encountered (2).
This paper presents an evaluation of the cyanide levels which have been found in terms
of the compliance with the effluent standards of the State of Illinois and possible
contributions to those levels. In addition, some work is presented regarding the possible
identification of effluent cyanide as simple and/or complex cyanide.
REPRODUCIBILITY OF CYANIDE ANALYSES AT LOW CONCENTRATIONS
The analytical procedure used for the low cyanide concentrations encountered in
various wastewaters and treatment plant effluents was the colorimetric pyridine-
pyrazolone method recommended in Standard Methods (3). This method uses a distillation
step ahead of the colorimetric procedure to break down the complex forms of cyanide. The
method thus determines total cyanides which include both simple and complex cyanides.
Replicate samples of standard solutions at concentrations of 0.01,0.025, and 0.5 mg/1
of both potassium cyanide, as a measure of a simple cyanide, and of potassium ferri cyanide,
as a measure of a complex cyanide, were prepared and run. In addition, replicated analyses
were carried out  on samples of treated wastewater effluents.
338