anodes should be inspected for excessive disinte-
2. Check terminals and jumpers of test leads for
rust, corrosion, broken or frayed wires, loose
connections, and similar deficiencies. Tighten all
3. Check the bushing supporting the anode for rust
and corrosion. Where resistors are installed in the
circuit, examine these units for corrosion, broken and
frayed wires, and loose connections. Tighten all
4. Check the anode suspensions for rust, corrosion,
bent or broken suspension members, frayed or broken
suspensions lines or cables, loose bolts, loose cable
connections, and frayed or broken wiring. Install new
anodes when necessary.
Do NOT bridge insulated couplings or break
electrical connections without engineering
The maintenance operation frequency and
schedule of inspections for clarification equipment are
shown in appendix III, table E.
Q12. Collector basins should never be cross
connected with what type of water system?
Ql3. What are the two methods of cathodicprotection
for sedimentation basins?
Q14. What cathodic method requires no external
MAINTENANCE OF FILTRATION
LEARNING OBJECTIVE: Identify and
understand basic maintenanee for filtration
Maintenance procedures on both gravity and
pressure filters are essentially the same, differing only
in detail. Some of the maintenance operations for
diatomite filters are similar to those for sand filters;
others are not.
Regardless of the type of filter medium used (sand
or anthrafilt), the material filtered out of the water must
be removed from the filter at regular intervals. (See
During daily backwashing, as an operating
procedure, the operator should observe any conditions
which may indicate a need for more complete
inspection. The MINIMUM procedures are as follows:
At monthly intervals, drain the filter to the
surface of the filter medium; inspect the surface for
unevenness, sinkholes, cracks, algae, mud balls, or
When depressions or craters on the surface are
of appreciable size, dig out the sand and gravel, and
locate and repair any break in the underdrain system.
When a filter bed is not backwashed correctly,
sand grains and foreign matter begin to stick together.
Over a period of time, large clumps, called mud balls,
are formed. They lower the efficiency of the filter bed
and must be removed. Surface washing usually breaks
down these formations, and they can then be removed
by backwashing. When the plant does not have surface
wash equipment, mud balls may be removed by the
steps of the procedure as follows:
1. Wash the filter bed completely clean at 2- to 3-
week intervals by using about twice the usual amount of
backwash to make sure the bed is cleaned thoroughly.
When the wash water is clear, reduce the rate
until the bed is expanded about 20 to 25 percent
to expose mud balls on the sand surface.
Remove the mud balls manually with a 10-mesh
screen attached to a long handle.
When sand shows evidence of algae,
prechlorinate ahead of filters. Where severe
algae growths exist on sand or walls, remove the
filter from service and treat the filter with a
strong hypochlorite solution. Add enough
hypochlorite to produce 2 to 4 ppm of free
residual chlorine in a volume of water 6 inches
deep above the filter surface. Draw down the
filter until the water level is just above the bed
surface. Allow it to stand for 6 to 8 hours, then
backwash the surface, and follow this by a
complete backwashing. Repeat if necessary.