Florida Wastewater Practice Test 2026 - Free Wastewater Certification Practice Questions and Study Guide

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.