Fixed Activated Sludge Process for
Industrial Waste Treatment
KENJI KATO, Director of the Laboratories
YASUHIRO SEKQCAWA, Chief Researcher of Sanitary Engineering
Kurita Central Laboratories
Hodogaya, Yokohama
Japan
INTRODUCTION
Operational performance of the activated sludge process is not always simple
in practice. It has been pointed out that an appropriate performance by a skilled
operator is certainly required for meeting any unfavorable changes occurring in
practical operation. Bulking of activated sludge is surely one of the most unfavorable changes. Accordingly, care should be taken in operational control of
the activated sludge process for maintaining the sludge loading value appropriately constant in order to prevent sludge bulking.
If bulking of activated sludge takes place, it usually becomes difficult to
make the mixed liquor separate into supernatant and flocculated sludge in the settling tank. The bulky sludge, then, would be carried over out of the settling
tank. Subsequently, not only would the effluent properties become worse, but
also the sludge concentration in the aeration tank would be decreased under the
level as appropriate to achieving a preferable performance.
As to the bulking of activated sludge, many investigations have been available, but clarification has not always been satisfied of the causes of bulking phenomena. Various techniques also have been considered for purpose of preventing
the sludge from bulking. Now, a series of experimental studies have been carried
out with success for purpose of maintaining the sludge concentration appropriately
constant. Maintenance of the concentration of sludge has been achieved by fixing
the suspended floes of activated sludge on the meshwork of plastic net panels arranged vertically into the aeration tank. The present improvement would like to
to be called, "Fixed Activated Sludge Process, " or, briefly, "FAS process. "
In the progress of development on the FAS Process, the following items have
been considered in particular:
1) The design of aeration tank employed is almost similar to a usual aeration
tank equipped with air diffusing pipes. Since most of the activated sludge
is fixed on the net panels in the aeration tank, return of activated sludge
from the settling tank does not become necessary.
2) Displacement of sludge-fixing body is to be as minimized as possible in
order to keep the effective capacity of tank from decreasing.
3) It is also desirable that a detention period of waste water in aeration tank
be almost as long as that in the usual aeration tank.
4) Water movement attributed by aeration from diffusers should pass through
downward over all the surface of the fixing body. While a slight portion
of biological growth covering the fixing body gradually is sloughed off and
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