Venturi Aeration, Inc.

Supernatant Aeration Using the Venturi Aeration Process

Supernatant from anaerobic digester can now be treated so that the supernatant can be returned to the plant headworks without causing any deterioration to the plant effluent. This direct method of supernatant treatment utilizes the venturi aeration process for odor control and conditioning which removes imbedded and clinging hydrogen sulfide gas bubbles from the solids inherently found in the supernatant. This permits odor free and degassed solids to settle rapidly in the primary clarifier.

To control the usual high BOD5 associated with the supernatant, dilution with secondary sludge from the intermediate and final clarifiers can be utilized. Secondary sludge withdrawal from the final clarifier can be adjusted to obtain the desired BOD5 level of the treated supernatant. Dilution rates of 4:1 to 10:1 should be considered depending on the strength of the supernatant. The wetted volume of the supernatant aeration basin should be sized for a minimum of 60 minutes detention time of the combined influent. The venturi aeration process equipment should be sized to pump at least twice the maximum rate of the combined influent. To operate the system with a minimum of energy, the entire operation can be placed on inexpensive timers. Primary, intermediate and final clarifier sludge withdrawals and the venturi aeration equipment can all be synchronized to operate together with a minimum energy cost.

When properly designed and constructed, this supernatant treatment method will return to the headworks an odor free liquid high in dissolved oxygen (DO) and BOD in the same range of the raw influent sewage. The supernatant odors will be controlled throughout the entire plant.

In some designs the venturi aeration equipment can be installed at a septage receiving area for odor control and conditioning and when not in use for septage treatment, typically up to 14-16 hours per day, it can be used for supernatant aeration during non-septage receiving hours. Supernatant liquids extracted from plate and frame pressings can also be aerated using the venturi aeration equipment. This increases the flexibility of the equipment when it can be multi-tasked.

For additional information on the venturi aeration equipment or process please contact Venturi Aeration, Inc. at 800-439-2610.