Visual Indicators For Influent Or Aeration Tanks

Wastewater operators are required to monitor or to make certain observations of treatment unit processes to ensure optimum performance and to make adjustments when required. When monitoring the operation of an aeration tank, the operator should look for the three physical parameters—turbulence, surface foam and scum, and sludge color and odor—that aid in determining how the process is operating and indicate if any operational adjustments should be made. This information should be recorded each time operational tests are performed. The following sections summarize aeration tank and secondary settling tank observations. Remember that many of these observations are very subjective and must be based upon experience. Plant personnel must be properly trained on the importance of ensuring that recorded information is consistent throughout the operating period.

15.10.1 Turbulence

Normal operation of an aeration basin includes a certain amount of turbulence. This turbulent action is, of course, required to ensure a consistent mixing pattern; however, whenever excessive, deficient, or nonuniform mixing occurs, adjustments may be necessary to the airflow or diffusers may require cleaning or replacement.

15.10.2 Surface Foam and Scum

The type, color, and amount of foam or scum present may indicate the required wasting strategy to be employed. Types of foam include the following:

• Fresh, crisp, white foam—Moderate amounts of crisp white foam are usually associated with activated sludge processes producing an excellent final effluent (normal operation; no adjustment necessary).

• Thick, greasy, dark tan foam—A thick, greasy dark tan or brown foam or scum normally indicates an old sludge that is overoxidized, a high mixed liquor concentration, and too high of a waste rate (old sludge; more wasting required).

• White billowing foam—Large amounts of a white, soap-suds-like foam indicate a very young, underoxidized sludge (young sludge; less wasting required).

15.10.3 Sludge Color and Odor

Though not as reliable an indicator of process operations as foam, sludge colors and odor are also useful indicators. Colors and odors that are important include the following:

• Chocolate brown/earthy odor indicates normal operation (no adjustment necessary).

• Light tan or brown/no odor indicates sand and clay from infiltration/inflow (extremely young sludge; decrease wasting).

• Dark brown/earthy odor indicates old sludge with high solids (increase wasting).

• Black color/rotten-egg odor indicates septic conditions, low dissolved oxygen concentration, and too low of an airflow rate (increase aeration).

15.10.4 Mixed Liquor Color

A light chocolate brown mixed liquor color indicates a well-operated activated sludge process.

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