anodes should be inspected for excessive disintegration.

2. Check terminals and jumpers of test leads for rust, corrosion, broken or frayed wires, loose connections, and similar deficiencies. Tighten all connections.

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 connections.

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.

WARNING

Do NOT bridge insulated couplings or break electrical connections without engineering advice.

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?

Q13. What are the two methods of cathodicprotection for sedimentation basins?

Q14. What cathodic method requires no external

power supply?

MAINTENANCE OF FILTRATION EQUIPMENT

LEARNING OBJECTIVE: Identify and understand basic maintenanee for filtration equipment.

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.

GRAVITY FILTERS

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 fig. 8-5.)

Filter Media

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 slime.

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.