What does "bioremediation" refer to in sewage treatment?

Bioremediation refers to the use of microorganisms, such as bacteria and fungi, to clean up or degrade environmental contaminants, including those found in sewage. This natural process harnesses the capabilities of living organisms to break down harmful substances into less toxic or non-toxic forms, effectively reducing pollution and restoring the environment.

In the context of sewage treatment, bioremediation plays a crucial role in breaking down organic materials and pollutants, thus facilitating the overall treatment process. By employing microorganisms, treatment facilities can effectively reduce the biochemical oxygen demand (BOD) and total suspended solids in sewage, leading to cleaner discharge into the environment. This method is often more sustainable and environmentally friendly compared to chemical treatments, which can introduce additional pollutants.

In contrast, other options like filtering water through sand primarily focus on physical processes, while chemical treatment of sludge involves specific reactions without the use of living organisms. The addition of nutrients to enhance plant growth does not directly relate to the degradation of contaminants within sewage but rather supports plant life that may indirectly benefit from cleaner water. Therefore, the option that accurately captures the essence of bioremediation in sewage treatment is the use of microorganisms to degrade environmental contaminants.