COMPUTER CONTROL OF A SMALL
WASTEWATER TREATMENT PLANT
Rajendra Seksaria, Project Engineer
David B. Corkle, Senior Project Engineer
Peter F. Loftus Corporation (Illinois)
Chicago, Illinois 60606
Robert E. Schwab, Staff Engineer
Caterpillar Tractor Co.
Peoria, Illinois 61629
In an effort to meet stringent discharge requirements, wastewater treatment plans are
becoming more complex. In addition, labor costs are rising, processes are becoming more
complex, and conventional control systems have limited capability and reliability. These
factors will result in increasing emphasis on computers and microprocessors to monitor,
control and operate treatment processes. Because of their ability to operate a variety of
process equipment simultaneously, computers can release operators for other tasks and
reduce total manpower requirements. Computer simulation preceding construction can
significantly reduce the time and cost required for startup. Computers provide exceptional
controller versatility, replace conventional control room instrumentation and reduce operating costs through process optimization.
The computer has successfully operated two complex wastewater treatment processes—
an oily wastewater treatment using air flotation and a heavy metals treatment incorporating
chromium reduction, precipitation and clarification. Both of these systems operated
unattended, requiring approximately 10 min of operator time during startup or shutdown.
All monitoring and control is achieved through two adjacent CRT consoles.
This chapter shows how the computer was applied as a useful tool for operating these
treatment systems and discusses additional features that a computer can provide.
DESCRIPTION OF TREATMENT PROCESSES
Oily Wastewater Treatment System
All oily wastewater from the manufacturing processes except for coolants is collected
and pumped to the waste treatment facility. The oily wastewater is processed through a
corrugated plate separator before being stored in one of two 130,000-gal equalization
tanks. Waste coolants, which are segregated from the general waste stream, are stored in a
separate 130,000-gal tank and are metered into the oily wastewater stream for treatment.
When one of the equalization tanks is full, the contents are sampled and jar tests are performed to determine the amount of chemicals required for treatment. The wastewater
is recirculated through a chemical mix tank where acid, alum and caustic soda are added
in succession. The wastewater is then pumped through a flocculation tank to a dissolved
air flotation (DAF) unit. Polyelectrolyte is injected into the line before flocculation. The
DAF unit discharges treated water to the city sanitary system and scum to sludge-holding
tanks for dewatering using vacuum filters. Free oil is skimmed from the plate separator
and concentrated by decanting before being transported to another facility for reclamation.
841