Question

Activated sludge should have the ability to settle quickly so that it can:

A. be rapidly pumped back from the sedimentation tank to an aeration tank
B. absorb pathogenic bacteria present in wastewater while sinking to the bottom of the settling tank
C. be discarded and anaerobically digested
D. absorb colloidal organic matter.

Answer 1

Hint: The activated sludge is a process with a high concentration of protozoa, microorganisms, bacteria, and fungi, which are present as a loose clumped mass of fine particles that are kept in suspension by stirring, with the aim of eliminating the organic substance from wastewater.

Complete step-by-step answer:
The activated sludge process (ASP) is a process that was developed for the treatment of sewage and industrial wastewater. There are many distinctive designs, but generally, all ASP has three major components: an aeration tank that functions as a bioreactor; a settling tank to separate AS solids and treated wastewater; and a return activated sludge (RAS) equipment that transfers settled AS from the clarifier to the aeration tank's influent. The activated sludge must settle fast so it can be pumped back into the aeration tank. The concentration of biodegradable elements in the influent is reduced in all activated sludge plants because of biological (and sometimes chemical) processes in the aeration tank. Various boundary conditions, like the hydraulic residence time (HRT) in the aeration tank, which is defined as the aeration tank volume separated by the flow rate, control the removal efficiency.
The activated sludge process in wastewater treatment includes injecting oxygen or air into raw, unsettled sewage. The solids are broken during this process. The sewage is bubbled, and the sewage liquor is dumped into a chamber with activated sludge. Live bacteria sink to the bottom of the tank, while dead bacteria float to the surface. While the live bacteria get back to the digestion chamber, clean water is released into a watercourse or soaked away.

Therefore the correct answer is Option A.
Note: The activated sludge process is designed to accelerate the rate of decomposition of waste substances in water and was first established in 1914, as per the International Water Association.