Which type of organisms are primarily used in secondary sewage treatment?

In secondary sewage treatment, the primary goal is to remove organic matter and nutrients from the wastewater after primary treatment has removed solids. Bacteria and other microorganisms play a critical role in this process. These microorganisms are essential because they break down organic compounds, essentially consuming them as food, which leads to the reduction of pollutants in the effluent.

Bacteria are particularly effective at decomposing organic materials due to their metabolic processes, which can occur under aerobic (with oxygen) or anaerobic (without oxygen) conditions, depending on the specific treatment method used. In addition to bacteria, other microorganisms, including protozoa and fungi, may also contribute to the degradation of organic material. However, the primary agents of this transformation during secondary treatment are indeed bacteria, highlighting their vital role in maintaining water quality and supporting environmental health.

The other options do not play a significant role in secondary sewage treatment. Algae and fungi are not the main organisms used, as they typically participate in different ecological processes. Viruses and parasites are generally not beneficial in this context and can even pose risks to human health. Large invertebrates and protozoa, while present and sometimes helpful in certain treatment systems, are not the primary organisms responsible for breaking down sewage in secondary treatment. Thus