Which of the following is NOT a level of the sewage treatment process?

The sewage treatment process consists of multiple stages designed to remove contaminants from wastewater. Primary settling, chemical coagulation, and activated sludge settling are all recognized levels of treatment.

Primary settling refers to the initial stage where solids settle out of the wastewater, allowing for the removal of larger particulates. Chemical coagulation involves adding chemicals to facilitate the aggregation of finer particles into larger clumps, which can then settle out more effectively. Activated sludge settling is part of the aeration phase, where microorganisms break down organic matter, and after this biological treatment, the mixture undergoes settling to separate the activated sludge from the treated water.

Filtration, while important in some water treatment processes, does not serve as a distinct level in the sewage treatment process specifically. It is typically considered a post-treatment step that can follow other treatment methods to further purify the effluent before it is discharged or reused. Thus, identifying filtration as not a level of the sewage treatment process is accurate within the context of standard treatment stages.