Which statement describes the activated sludge process?

• A. The binding to a surface
• B. A process to upgrade treated wastewater for reuse
• C. A biological wastewater treatment process which speeds up decomposition of wastes in the wastewater being treated. Activated Sludge is added to wastewater and the mixture (mixed liquor) is aerated and agitated. After some time in the aeration tank, the activated sludge is allowed to settle out by sedimentation and is disposed of (wasted) or reused (returned to the aeration tank) as needed, the remaining wastewater then undergoes more treatment.
• D. A pump that lifts water

Answer: (C)

Activated sludge is a biological wastewater treatment process that speeds up the decomposition of organic wastes using microorganisms. In this method, wastewater is mixed with a population of microbes (the activated sludge) and aerated to supply oxygen. This aeration keeps the mixed liquor well oxygenated and encourages the microbes to oxidize the organic matter rapidly. After aeration, the mixture goes to a sedimentation tank where the heavier solids settle out. Some of the settled sludge is returned to the aeration tank to maintain the microbial population, while excess sludge is wasted. The clarified liquid then moves on for further treatment or discharge. This description matches the statement because it highlights the biological oxidation, the mixed liquor in the aeration tank, the subsequent settling, and the return or disposal of sludge. The other options don’t describe this biological, aerated, solids-separation process.