GRAVITY FILTRATION FOR REDUCTION OF
SUSPENDED METALS IN A
LIME PRECIPITATION TREATMENT SYSTEM
Roy D. Knapp, Environmental Engineer
Harrison Radiator Division
General Motors Corporation
Lockport, New York 14094
Edgar G. Paulson, Vice President
Industrial Pollution Control, Inc.
Westport, Connecticut 06880
Increasingly stringent discharge limits are requiring facilities to provide processes for
upgrading their effluent quality. For a plant removing heavy metals by precipitation and
clarification, the addition of filtration is a logical consideration.
Although filtration is an accepted water treatment process that has been used for years,
it must be evaluated closely when applied to a wastewater. It is imprudent to assume that
conventional water filtration practices can be directly applied to treatment of a clarified
wastewater. The suspended solids to be removed from a wastewater may have different
characteristics than those generally removed in the treatment of supply waters. Also, other
constituents, such as organics, oils and detergents, may have an impact on the operation of
the filter installation. A study program should be conducted to confirm that filtration
will produce the desired improvement in effluent quality and that the developed design
and operating parameters are within practical limits.
The main items to be considered are the relationships between media configuration,
effluent quality, hydraulic loading rate, run length and pressure drop. There is a large
variety of media configurations. These include graded sand and/or coals in single, dual or
multimedia units. Also, unstratified sand or coal may be used in deep bed units. The first
step in the testing program is to screen potential media configurations based on effluent
quality and run length in order to select candidate media configurations that provide satisfactory performance and yet are as simple in configuration as possible. More extensive pilot-
plant work should then be conducted to finalize media selection and to develop design and
operating parameters.
Concurrently, various backwash procedures must be evaluated. The possibilities include
water, water with surface wash, air followed by water, and simultaneous air-water. The
desire is to use the simplest system possible consistent with maintaining the condition of
the filter bed.
The investigation must also evaluate whether the wastewater has a scale-forming tendency. This may identify potential long-range problems that otherwise may not have been
apparent during a short-term testing program.
Presented here is a case history of an installation where filtration was used to upgrade
the clarified effluent of a heavy metal removal treatment plant.
GENERAL
The Harrison Radiator Division of General Motors Corporation primarily manufactures
automotive radiators and air conditioners at their facility located in Lockport, New York,
approximately IS miles north of Buffalo. Typical manufacturing operations include metal
forming, assembly, degreasing, washing, chromium conversion coating and painting.
95