Which process is NOT typically part of secondary wastewater treatment?

Secondary wastewater treatment primarily focuses on the biological removal of dissolved and suspended organic matter, utilizing naturally occurring microorganisms to decompose the waste. The methods commonly employed in this stage include aerobic digestion, the activated sludge process, and trickling filters.

Filtration, while a crucial part of the overall wastewater treatment process, is primarily associated with tertiary treatment, which aims to further polish the effluent and remove additional contaminants, nutrients, and pathogens. Thus, it does not belong to the secondary treatment process.

Aerobic digestion involves using aerobic microorganisms to degrade organic material, the activated sludge process incorporates aeration tanks where microorganisms feed on organic matter, and trickling filters consist of a fixed bed of media that supports biofilm growth, all of which fall under the category of secondary treatment methods. Therefore, filtration is the correct answer, as it does not typically belong to this phase of treatment.