41    COMPARISON OF PACT PROCESS TO COUPLED
PHYSICAL/CHEMICAL BIOLOGICAL TREATMENT
Alan W. Obayashi, Laboratory Director
Enos L. Stover, President
James A. Thomas, Project Manager
Jose A. Pereira, Project Engineer
STOVER & BENTLEY, INC.
Stillwater, Oklahoma 74076
INTRODUCTION AND BACKGROUND
A manufacturing plant in the paper coating industry was faced with one of two options for its
wastewaters: either use some form of pretreatment to meet recently proposed sewer discharge limits,
or haul the liquid wastes from the facility. The proposed sewer ordinance for the town in which the
plant discharged into, had limits on the BOD (300 mg/L), suspended solids (350 mg/L), metals and
other inorganics. Because of the nature of the wastewater characteristics, Zimpro's powdered activated carbon treatment (PACT) process was given a strong consideration for this plant's pretreatment
facility.
As part of an extensive conceptual engineering study at the plant, Stover & Bentley, Inc. compared
the PACT process with the two-stage activated sludge process (with and without physical/chemical
pretreatment) during bench-scale tests. In addition to providing a technical comparison, this chapter
also presents an economic evaluation of the two alternatives.
EXPERIMENTAL PROGRAM
The experimental program covered two major areas including: (1) the physical/chemical pretreatment tests; and (2) the biological treatability studies. Wastewater composite samples from the plant
were sent every week during the study to the Stover & Bentley, Inc. laboratory in Stillwater,
Oklahoma.
Physical/Chemical Pretreatment Tests
Two physical/chemical processes were evaluated for potential use: (1) chemical coagulation/
flocculation/gravity settling; and (2) Dissolved Air Flotation (DAF). In order to determine the optimum chemical doses for chemical coagulation flocculation. jar tests were run. The chemicals used
were alum, lime, and various polymers. Early in the study it became apparent that some of the
samples were too concentrated (> 10%) for effective DAF treatment. After several attempts in using
the DAF had failed, the process was no longer used in the study.
A portion of the composite samples were pretreated using chemical coagulation/flocculation and
solids separation. The supernatant was used as feed for the two-stage biological reactors (pilot unit #1,
see Figure 1) which received pretreated wastewater. The remainder of the untreated composite sample
served as feed for the other two pilot units which included the PACT reactor.
Biological Treatability Study
The treatability study consisted of three continuous flow bench-scale activated sludge reactors. A
schematic diagram of each unit is shown in Figure 1. Pilot unit #1 received the pretreated composited
sample, while pilot units #2 and #3 received untreated raw wastewater. Pilot units #1 and #2 were two-
stage activated sludge systems, with the first stage being a once-through system and the second stage
being a conventional activated sludge system with an internal clarifier. Pilot unit #3 was the PACT
activated sludge system and received powdered activated carbon (Hydro Darco, American Norit,
Jacksonville, Florida) on a daily basis at a dose of 2500 mg/L of influent flow. All systems were fed
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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