Flyash as a Filtering Aid for Dewatering
Industrial Waste Plant Sludge
FRED W. MOEHLE,    CHIEF POWER ENGINEER
Uniroyal, Incorporated
Mishawaka, Indiana 46544
INTRODUCTION
Dewatering industrial waste plant sludge using flyash as a filtering aid has
proven successful at the UNIROYAL, Inc. U. S. Rubber plant located in Mishawaka, Indiana. This treatment plant located on the St. Joseph River was put into
operation in December 1964. It is designed to handle only contaminated industrial waste; all sanitary waste is discharged to the city sewer system.
To fully understand where the sludge comes from, how it is collected and how
the dewatering is accomplished, it might be well to briefly describe the entire
waste treatment plant operation. Briefly stated this facility can be considered a
filtration plant accomplishing its objective by means of chemical filtration as
opposed to mechanical filtration.
The industrial waste upon entering the plant is deposited in an equalizing
basin. From the equalizing basin the waste is pumped to a weir box which is at
the highest elevation in the treatment process. The waste flow through the clarifying process, therefore, is accomplished by means of gravity. From the weir box
the waste water flows through the first stage mixing tank where Ferri-Floc (ferric
sulfate), a flocculating agent, is added. The waste then flows through the second
stage mixer where a small amount of Separan, a flocculating aid, is added. Passing from this tank the waste water enters the first stage flocculator where a high
speed mixer brings the Ferri-Floc into intimate contact with the various waste
particles entrained in the water. From the first stage flocculator, the water enters
the clariflocculator which in effect is the second stage flocculator located in the
center of the clarifier. In the second stage flocculator, a slow moving mixer
allows the floe to form and precipitate down through the bottom of the flocculator
together with the water in which it is entertained. This flocculation process appears much like the curdling of near sour milk when poured into a cup of hot
black coffee. The clear water rises into the clarifier portion and is allowed to
flow over a weir plate around the periphery of the clarifier.
The floe remains at the bottom of the tank. The settled floe is hereafter referred to as sludge. The sludge build-up in the bottom of the clariflocculator is
periodically allowed to flow or is "blown-down" into a sludge collecting tank.
The "blow-down" is set on a time basis by the plant operator. The operator decides on the time setting after daily checking the level of the sludge blanket by
means of a sampling bottle.
It is the purpose of this paper to expound on the method of dewatering this
sludge using flyash as a filtering aid.
SLUDGE DEWATERING
Equipment
In the process of dewatering the sludge, six major pieces of equipment are
involved    (Figure 1).
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