Which type of sludge is produced from trickling filters?

The production of humus sludge from trickling filters is rooted in the process by which these systems operate. Trickling filters involve microorganisms that grow on a substrate as they degrade organic matter in wastewater. This growth results in a biologically-rich material, which is predominantly composed of dead microorganisms and particulate matter – what we classify as humus sludge.

The key characteristics of humus sludge are that it is largely composed of settled biomass that originated from biological activity within the filter but is not a result of the activated sludge process, which is different in its operation and biological dynamics. In contrast to the other types of sludge mentioned, such as activated sludge, primary sludge, and waste activated sludge, humus sludge has its own distinct formation process linked directly to the trickling filter system and its method of treating wastewater.

Activated sludge and waste activated sludge are both associated with processes involving aeration tanks where microorganisms are kept in suspension. Primary sludge comes from the sedimentation of raw sewage solids during the primary treatment phase and does not originate from biological treatment via trickling filters. Thus, identifying humus sludge as the correct answer is based on its specific ties to the trickling filter process, differentiating it from the other sludge types produced in various wastewater treatment stages.