39    SIDE-BY-SIDE EVALUATION OF ONE- AND
SIX-MICROMETER MICROSCREEN MEDIA FOR
REMOVING ALGAE FROM AERATED LAGOON
EFFLUENT
A. R. Abernathy, Professor
M. K. Rhoads, Graduate Student
Environmental Systems Engineering Department
Clemson University
Clemson, South Carolina 29634-0919
R. J. Hynek, Supervisor
Process Engineering
ENVIREX, Incorporated
Waukesha, Wisconsin 53186-7360
INTRODUCTION
The Camden, South Carolina Wastewater Treatment Plant has been using six Envirex microscreens
since 1980 for removal of algal solids and BOD5 from aerated lagoon effluent. The media in these
microscreens has been 1 /.m woven polyester mesh. Problems have been experienced with early
breaking of the polyester filaments along the supporting medium and with limited hydraulic throughput during periods of very high algal density in the influent to the microscreens. These problems led to
replacement of the 1 ^m media in one microscreen with 6 jim mesh material. It was hoped that the new
media would have a longer operating life and also allow greater hydraulic flux at approximately the
same removal rates for algae and BOD5. A side-by-side evaluation of these two media in full scale
plant operation was the object of this project.
Harrelson and Cravens1 have reported on the design of the Camden facility. The plant consists of
three aerated cells created by floating curtain partitions followed by a non-aerated cell. The current
design was a modification of an older facultative lagoon system. Design retention times are 20 hours,
43 hours, 43 hours, and 4.85 days in the four cells. The first cell was designed for complete organic
suspension and the next two aerated cells for partial suspension. The fourth cell serves as a settling
pond after which the pond effluent is lifted by two variable speed screw pumps to the microscreens.
The effluents from the six microscreens flow to a common channel for disinfection and final discharge. Screened effluent is used to backwash the microscreens. See Figure 1 for the flow diagram of
the wastewater facility.
The six microscreens are 3.05-m diameter x 4.87-m long (10 ft x 16 ft). The number of units
operated at any time depends upon the water level in the treatment ponds, algal density in the pond
effluent, and the flow rate of wastewater arriving at the treatment ponds. During this study, average
flow to the microscreens was approximately 4164 m'/day (1.1 mgd) although the facility was designed
for 7192 mVday (1.9 mgd).
METHODS
For this evaluation it was decided to sample the influent to the microscreens, the effluent from one
microscreen with 1 nm media, the effluent from the 6 /un media microscreen, and the backwash from
the two selected units. Flow was measured at the effluent from the two microscreens by use of 90° V-
notch weirs (4 notches per weir) installed at the discharge to the main effluent channel. Failure to get
accurate measurements of the backwash water deflected from the outside of the screen and the water
carried up into the backwash trough by the rotating screen forced the assumption that the influent
volumetric flow rate was equal to the effluent volumetric flow rate for the individual units.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Primed in U.S.A.
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