Florida Wastewater Practice Test

What is the liquid effluent called that is removed from an anaerobic digester?

1. Sludge

2. Supernatant

3. Effluent

4. Settled solids

The correct answer is: Supernatant

The liquid effluent removed from an anaerobic digester is referred to as supernatant. This terminology is used specifically in the context of wastewater treatment to denote the liquid phase that remains above the settled solids after a period of settling or digestion. In anaerobic digestion, organic matter is decomposed without oxygen, resulting in the production of biogas and the separation of solids and liquids. The supernatant is generally clearer than the sludge below it and contains dissolved and suspended organic matter that has not settled. Understanding the role of supernatant is essential in wastewater treatment processes, as it is part of the treatment cycle and can be further processed or treated for various uses. The distinction between supernatant and other waste forms like sludge or settled solids also highlights different aspects of waste management and treatment stages crucial for effective wastewater treatment operations.