The correct answer is (c), Both biogas and sludge.
Explanation:
Biogas:
This is a renewable energy source produced by the anaerobic digestion of organic matter present in wastewater.
Sludge:
This is a solid material that settles out of wastewater during the treatment process. It is composed of organic matter and solids that were separated from the wastewater.
Why other options are incorrect:
(a) Biogas: While biogas is a product of wastewater treatment, it’s not the only one.
(b) Sludge: Similar to (a), sludge is only one of the products of wastewater treatment.
(d) Aerator: An aerator is a device used in wastewater treatment to introduce oxygen into the water, which is necessary for the aerobic bacteria to break down organic matter. It’s not a product of the treatment process itself.