American Water College Complete Practice Test 2025

A thick zoogleal mass in trickling filters can indeed lead to anaerobic conditions. The zoogleal mass consists of microorganisms that form a biofilm on the filtering media. When this mass becomes excessively thick, it can obstruct the flow of water and limit the exchange of oxygen and nutrients within the biofilm.

In trickling filters, the presence of aerobic bacteria is crucial for the breakdown of organic matter. When the mass is too thick, the inner layers of the biofilm may not receive sufficient oxygen, which can foster anaerobic conditions—where oxygen levels are insufficient to support aerobic microbial activity. This shift to anaerobic conditions can hinder the overall treatment process, as anaerobic bacteria do not effectively degrade the pollutants in the same way that aerobic bacteria do.

Hence, the thick zoogleal mass ultimately disrupts the intended function of the trickling filter and can lead to reduced efficiency in the treatment of wastewater.