Environmental Engineering Reference
In-Depth Information
Cl
2
Rotating biological contactors
Secondary
settling
tanks
Primary
settling
tank
Euent
Influent
Solids disposal
figure 7.7 Rotating biological contactor (RBC) treatment system.
7.4.1 rbC equipment
The equipment that makes up an RBC includes the rotating bio-
logical contactor (the media, either standard or high density), a center
shaft, drive system, tank, baffles, housing or cover, and a settling tank.
The rotating biological contactor consists of circular sheets of synthetic
material (usually plastic) mounted side by side on a shaft. The
sheets
(media) contain large amounts of surface area for growth of the biomass.
The
center shaft
provides the support for the disks of media and must
be strong enough to support the weight of the media and the biomass;
experience indicates that a major problem is collapse of the support
shaft. The
drive system
provides the motive force to rotate the disks and
shaft. The drive system may be mechanical or air driven, or a combina-
tion of each. When the drive system does not provide uniform movement
of the RBC, major operational problems can arise.
The tank holds the wastewater in which the RBC rotates. It should
be large enough to permit variation of the liquid depth and detention
time. Baffles are required to permit proper adjustment of the loading
applied to each stage of the RBC process. Adjustment can be made to
increase or decrease the submergence of the RBC. RBC stages are nor-
mally enclosed in some type of protective structure (
cover
) to prevent
loss of biomass due to severe weather changes (e.g., snow, rain, tempera-
ture, wind, sunlight). In many instances, this housing greatly restricts
access to the RBC.
The
settling tank
is removes the sloughing material created by the
biological activity and is similar in design to the primary settling tank.
The settling tank provides 2- to 4-hr detention times to permit settling
of lighter biological solids.
7.4.2 rbC operation
During normal operation, operator vigilance is required to observe
the RBC movement, slime color, and appearance; however, if the unit is
covered, observations may be limited to that portion of the media that
can be viewed through the access door. Slime color and appearance can
indicate process condition; for example:
