Which of the following substances can negatively affect the operation of a wastewater treatment plant?

Excessive oil and grease can negatively affect the operation of a wastewater treatment plant due to their properties that disrupt the biological processes essential for effective treatment. When oil and grease enter the wastewater system, they can coat the microorganisms that break down organic matter, hindering their activity. This can lead to reduced efficiency in the treatment process and increased difficulty in managing the sludge, ultimately impairing the plant's overall function.

Furthermore, high levels of oil and grease can lead to issues such as pump failures, clogging in pipes and equipment, and the formation of scum on the surface of treatment basins, which can prevent adequate oxygen transfer necessary for aerobic treatment processes. Managing these substances requires additional treatment measures, increasing the operational costs and complexity of the facility.

The other substances listed, while they can pose challenges, typically have a different impact. Soluble nutrients are generally required for the biological treatment processes, organic waste is the primary feedstock for the treatment system, and clean rainwater is usually a non-issue when it comes to treatment unless it carries contaminants. Thus, excessive oil and grease stands out as a substance that can severely hinder the efficient operation of a wastewater treatment plant.