The correct answer is B. Sludge.
Sludge is a by-product of sewage treatment. It is a thick, semi-solid material that contains solids from sewage, as well as bacteria, viruses, and other microorganisms. Sludge can be decomposed to produce biogas, which is a renewable energy source that can be used to generate electricity or heat.
Sewage is the wastewater that is produced by homes, businesses, and industries. It contains a variety of pollutants, including human waste, food scraps, and industrial chemicals. Sewage is treated in a wastewater treatment plant to remove these pollutants before it is released back
into the environment.A sewer is a pipe or tunnel that carries sewage from homes and businesses to a wastewater treatment plant.
Scum is a layer of solid material that forms on the surface of water. It is made up of dead algae, bacteria, and other microorganisms. Scum can be removed from water by skimming or filtering.