UFC 3-280-04
17 DEC 2003
the filter is maintained at a constant level or is varied during the filter run. Influent flow
splitting with constant level incorporates individual weirs in the header channel entrance
to each filter. An element in each filter communicates with a controller to keep the level
of water over the media constant. This is done with a modulating valve. No level ele-
ments, controllers, or modulating valves are necessary for influent flow splitting with
varying water levels. After splitting, the water level is based upon the head loss through
the filter. As the head loss increases, the water level increases to achieve a constant
rate established by an orifice plate in the effluent piping. The splitting allows flow varia-
tions to be equally distributed among the filters. Often influent flow splitting may not be
needed for low flow systems where the flow may be interrupted.
6-3.4
Variable-declining rate filtration controls the flow to the multiple filters by vary-
ing the upstream or downstream water level with centrifugal pumps. Each filter operates
under the same head, but at different flow rates, depending on degree of filter clogging.
The influent enters below the low water level of the filters, resulting in less head loss. As
one filter becomes clogged, the head loss builds, slowing the rate of filtration. The other
filters then pick up the capacity lost by the dirty filters. Variable-declining rate filtration
generally provides better effluent quality and higher unit filter run volumes.
6-4
OPERATIONS AND MAINTENANCE CONSIDERATIONS. Depending on the
variability of the wastewater characteristics, an equalization basin may be provided
ahead of the filters. The equalization basin results in less variation in influent character-
istics. A steadier stream can result in higher consistency in filtration and reduced opera-
tional problems.
6-4.1
Commonly encountered problems in the filtration of wastewater are described
in Table 6-1. These include turbidity breakthrough, mudball formation, buildup of
grease, oil and carbonates, development of cracks and contraction of filter bed, loss of
filtering media, air binding, and gravel mounding. Every attempt should be made to de-
sign the filter to avoid these problems. Suggestions are incorporated in the control
measures column. Additionally, upstream processes, such as an oil/water separator,
should be considered to control potential waste constituents that may cause operation
problems.
6-4.2
All prepackaged equipment should come with a list of O&M issues and
recommended spare parts. Patented equipment, especially traveling bridge filters and
continuous backwash filters, will have specific manufacturer's recommended trouble-
shooting guides. Similarly, control equipment will need to be maintained according to
the manufacturer's recommendations.
6-4
Previous Page
