The maintenance operation frequency and schedule of inspections for filtration equipment are shown in appendix III, table F.

Q15. Backwashing should be performed on gravity filters at what intervals?

Q16. When severe algae growth exists on filter sand or walls, what corrective action should be taken?

Q17. Sodium hydroxide is used in filter underdrain systems of porous plate to correct what condition?

Q18. What are the two types of flow rate controllers?

Q19. What is the major difference between a pressure filter system and a gravity filter?

Q20. To remove iron oxide in a diatomite filter, a solution of what chemical and at what percent should you use?

MAINTENANCE OF AERATION EQUIPMENT

LEARNING OBJECTIVE: Identify and understand basic maintenance for aeration equipment.

Proper maintenance of aerators is another important area in water treatment activities.

WATERFALL AERATORS

The recommended maintenance procedures for waterfall-type aerators (cascade or step, and tray or splash pan) is as follows:

Weekly, inspect the aerator surfaces for algae or other growths, precipitated iron oxide, and for nonuniformity of water distribution and staining. Clean when necessary. Treat with copper sulfate or hypochlorite solution to destroy growths.

Every 6 months, clean and repair tray aerators, removing the trays as necessary. Inspect the coke tray aerators for biological growths and coke deterioration. Replace the coke if the cleaning is not effective. Repair the screen and enclosures if necessary.

Annually, repair or replace the surfaces on cascade or step aerators.

INJECTION OR DIFFUSER AERATORS

Injection or diffuser aerators may be either porous medium design or injection nozzles.

Porous Ceramic Diffusers

The maintenance procedures for porous ceramic diffusers-plate or tube-is as follows:

1. Upon evidence of the nonuniform distribution of air or clogging that impairs operation, dewater the tank; inspect and clean diffusers if necessary.

2. Every 6 months, drain the aeration tank and inspect the diffusers for joint leaks, broken diffusers, and clogging. Porous ceramic diffusers may suffer clogging of either the waterside or the air side (underside).

For waterside (porous plate diffusers), use oxidizing acids to clean organic growths from the plate surface.

NOTE:

Chlorine gas introduced into the air line at intervals between inspections will help hold down organic growths.

Removable plates should be soaked in 50 percent nitric acid. Plates grouted in place cannot be treated with nitric acid; use chromic acid (made by adding 1 gram of sodium dichromate to 50 ml of sulfuric acid). Pour approximately 2 fluid ounces on each plate 2 days in a row.

WARNING

Acids must be handled carefully. DO NOT pour water into sulfuric or chromic acid, as it will explode or splatter. Such acid will cause severe burns to the skin and clothes. ALWAYS pour acid SLOWLY into the water, while stirring continuously. Acid treatment should only be done only upon the approval of the Public Works Officer under supervision of a chemist or other qualified personnel.

Air side (porous plate diffusers). When clogging is caused by iron oxide particles from pipes, treat this condition with a