Sewage treatment is a critical process in modern sanitation systems, aimed at removing contaminants from wastewater before it is released back into the environment. One of the most vital components of this process is bacteria. These microorganisms play an essential role in breaking down organic matter, purifying water, and ensuring that the treated effluent meets environmental standards. This article explores the various roles that bacteria play in sewage treatment, the mechanisms through which they operate, and the significance of their activities in maintaining ecological balance.