Florida Wastewater Practice Test

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Prepare for the Florida Wastewater Exam. Study with multiple choice questions and detailed explanations. Ensure your readiness with our comprehensive test materials!

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What is the best adjustment to make if solids are rising in a secondary clarifier with small gas bubbles?

Increase aeration DO
Decrease aeration DO
Increase chemical dosing
Decrease chemical dosing

The correct answer is: Decrease aeration DO

In cases where solids are observed to be rising in a secondary clarifier accompanied by small gas bubbles, decreasing aeration dissolved oxygen (DO) is typically the best adjustment to make. When the DO levels are too high in the aeration basin, it can lead to excessive growth of microorganisms, particularly filamentous bacteria, which can produce gas under certain conditions. These gas bubbles can attach themselves to the solids, causing them to float rather than settle correctly in the clarifier. This results in rising solids, which is not desirable for effective wastewater treatment. By decreasing the aeration DO, you can help to reduce the proliferation of these filamentous organisms and promote a healthier balance of microorganisms that are better suited for settling. Lowering the DO levels can also reduce the tendency for gas production within the treatment process, helping solids to remain suspended longer and settle appropriately in the clarifier rather than rising. Therefore, this adjustment addresses the immediate issue of solids rising in the clarifier and aims to restore optimal settling and overall treatment efficiency.