Why are bacteria important in sewage treatment?

Bacteria are essential to sewage treatment because they are used to metabolize and break down organic contaminants in wastewater, a process that reduces the biochemical oxygen demand (BOD) of the effluent before it is discharged into the environment.12

Their role is primarily exploited in two ways:

• Aerobic Treatment: In systems like activated sludge, bacteria thrive in oxygenated tanks, where they absorb and metabolize dissolved organic materials. This process effectively cleans the water by removing the organic matter that would otherwise deplete oxygen levels in receiving streams and harm aquatic life.321
• Anaerobic Digestion: In the absence of oxygen, bacteria decompose organic solids into stable substances, reducing the total mass of sludge and destroying pathogens. This process also produces biogas—a mixture of methane and carbon dioxide—which can be captured and used as a renewable energy source to power treatment plants.41

Additionally, specialized bacteria are used in tertiary treatment to remove nitrogen through nitrification-denitrification, preventing the release of ammonia and nitrates that can cause environmental issues like algal blooms.5