Which of the following is NOT a unit of wastewater pre-treatment?

Filtration units are not typically classified as a unit of wastewater pre-treatment. Wastewater pre-treatment primarily focuses on the removal of large solids, grit, and other materials that can hinder the effectiveness of subsequent treatment processes.

Grit chambers serve to remove sand, gravel, and other heavy particles from wastewater, allowing for more efficient treatment downstream. Equalization basins are used to balance out variations in flow and pollutant load, providing a consistent influent to downstream treatment processes. Bar racks function to screen out larger debris and solids, preventing them from entering the treatment facility and causing damage or operational issues.

While filtration is an important process within the overall scope of wastewater treatment—often applied in secondary or tertiary treatment stages to remove remaining solids or pathogens—it does not perform a pre-treatment function for the purpose of preparing wastewater for primary treatment processes. Therefore, filtration units do not fit into the category of pre-treatment units.