Activated Sludge Process - Wastewater Operators - page 309

• Sludge bulking occurs when solids are evenly distributed through-

out the tank and leaving over the weir in large quantities.

• Sludge solids washout occurs when the sludge blanket is down but

solids are flowing over the effluent weir in large quantities. Control
tests indicate good-quality sludge.

• Clumping occurs when large clumps or masses of sludge (several
inches or more) rise to the top of the settling tank.

• ashing occurs when fine particles of gray to white material are flow-
ing over the effluent weir in large quantities.

• Straggler floc is comprised of small, almost transparent, very fluffy,
buoyant solids particles (1/8 to 1/4 inch in diameter) that rise to the
surface, usually accompanied by a very clean effluent. New growth
is most noted in the early morning hours. Sludge age is slightly
below optimum.

• Pin floc is comprised of very fine solids particles, normally less
than 1/32 inch in diameter, that are suspended throughout lightly
turbid liquid; usually the result of an overoxidized sludge.

8.13 ProCess ConTrol saMPling and TesTing

The activated sludge process generally requires more sampling
and testing to maintain adequate process control than any of the other
unit processes in the wastewater treatment system. During periods of
operational problems, both the parameters tested and the frequency of
testing may increase substantially. Process control testing may include
settleability testing to determine: (1) the sett led sludge volume; (2) influ-
ent and mixed liquor suspended solids; (3) return activated sludge sol-
ids and waste activated sludge concentrations; (4) volatile content of
the mixed liquor suspended solids; (5) dissolved oxygen and pH of the
aeration tank; and (6) BOD 5 and chemical oxygen demand (COD) of the
aeration tank influent and process effluent. Microscopic evaluation of
the activated sludge is used to determine the predominant organism.
The following sections describe most of the common process control
tests.

8.13.1 aeration Tank influent and effluent sampling

8.13.1.1 pH

pH is tested daily with a sample taken from the aeration tank influ-
ent and process effluent. pH is normally close to 7.0 (normal), with the
best pH range being 6.5 to 8.5 (although a pH range of 6.5 to 9.0 is sat-
isfactory). A pH of >9.0 may indicate toxicity from an industrial waste
contributor. A pH of <6.5 may indicate loss of flocculating organisms,
potential toxicity, industrial waste contributors, or acid storm flow. Keep
in mind that the effluent pH may be lower because of nitrification.