Which of the following tasks does preliminary treatment NOT perform?

Preliminary treatment in wastewater treatment plants is primarily focused on the removal of large solids and debris that can interfere with subsequent treatment processes. This stage typically involves processes such as screening, which effectively removes bulky items and large debris from the influent wastewater. Additionally, measuring influent flow is a crucial part of this stage, as it helps operators understand the volume of wastewater entering the treatment system.

However, primary biological treatment is not a function of preliminary treatment. Instead, primary biological treatment occurs later in the treatment process, typically following preliminary treatment and primary clarification. This stage involves biological processes where microorganisms degrade organic materials in the wastewater. Therefore, stating that preliminary treatment provides primary biological treatment is inaccurate, making it the correct choice for the task that preliminary treatment does not perform.