Final answer:
Microorganisms in the aeration tanks of an activated sludge treatment plant perform most of the work, decomposing organic matter and absorbing nutrients, aided by oxygen supplied through aeration.
Step-by-step explanation:
The "work" in an activated sludge treatment plant is primarily performed by microorganisms. During the secondary treatment phase, wastewater is exposed to air in an aerator to provide oxygen for aerobic bacteria and other microorganisms that break down organic contaminants.
The aerated effluent then moves to a secondary clarifier, where these microorganisms further decompose organic material and absorb nutrients. The resulting mixture, known as activated sludge, contains microorganisms that play a crucial role in the breakdown of organic matter.
Solids processing is another critical step where solid wastes, such as the sludge removed from the clarifier, undergo further decomposition in digesters.
These wastes can be reduced in volume, have odors minimized, and potentially harmful organisms destroyed. Secondary treatment systems can either use a fixed film or a suspended growth system to facilitate bacterial decomposition.
The three phases of wastewater treatment—primary, secondary, and tertiary—ensure that wastewater is thoroughly processed and treated before being released or repurposed.
Through this sequence of treatments, each with its specific processes like sedimentation, biological decomposition, additional filtration, and disinfection, the wastewater treatment plant effectively manages sewage and sludge.