The correct answer is D. Toilets.
Sludge is a semi-solid or solid material that is produced as a byproduct of wastewater treatment. It is a mixture of organic and inorganic matter, and it can contain a variety of contaminants, including bacteria, viruses, and parasites.
Wastewater from toilets is the most contaminated type of wastewater, and it is the primary source of pathogens in sludge. Therefore, sludge from toilets is typically treated separately from other types of wastewater, and it is not used in agriculture or other applications where it could come into contact with people.
Wastewater from bathrooms, wash basins, and kitchen sinks is less contaminated than wastewater from toilets, and it can be treated and reused in a variety of ways. For example, it can be used to irrigate crops, to generate electricity, or to produce biogas.
In conclusion, the sludge does not contain wastewater from toilets because it is the most contaminated type of wastewater.