What is a problem that can occur when suspended solids in effluent are too high?

The correct answer highlights the potential presence of contaminants in the effluent, which is a significant problem when suspended solids exceed acceptable levels. High concentrations of suspended solids can indicate that there are not only particulate matter but also attached contaminants, microorganisms, and other harmful substances. This increases the risk of pollutants entering the environment, which may affect aquatic ecosystems and pose health risks to humans and animals.

Suspended solids can also interfere with various treatment processes. For example, they can hinder the effectiveness of biological treatment methods, as the solids may shield pathogens from exposure to treatment chemicals or microorganisms meant to break them down. Therefore, the presence of excess suspended solids suggests that there may be associated contaminants that compromise the quality and safety of the effluent.

The other options do not accurately reflect the consequences of high suspended solids in effluent. For instance, a decreased chemical oxygen demand would indicate lower organic pollution, which is not the case when suspended solids are high, as it often suggests more organic material present. Increased oxygen levels in treated water typically point toward improved treatment conditions, which is inconsistent with the issues raised by high suspended solids. Lastly, improved effectiveness of the treatment process would suggest it is working efficiently, which is unlikely in the presence of significant amounts of suspended solids.