Which process characterizes secondary sewage treatment?

Which process characterizes secondary sewage treatment?

• A. Mechanical filtration
• B. Bacteria break down organic matter using biological processes
• C. Chemical disinfection
• D. Sedimentation

Answer: (B)

Secondary sewage treatment relies on microorganisms carrying out biological oxidation of organic matter. In this stage, processes like activated sludge or biofilm reactors keep the water in contact with air so aerobic bacteria can consume dissolved and suspended organics, turning them into biomass, carbon dioxide, and water. This biological degradation lowers the wastewater’s biochemical oxygen demand and overall organic load, which is the key goal of secondary treatment. Seeing the other options in this light: mechanical filtration is about physically removing larger solids before or after treatment, chemical disinfection targets pathogens and is typically a later polishing step, and sedimentation is the primary treatment that removes settleable solids by gravity. The biological, microbe-driven approach is what defines secondary treatment.

Secondary sewage treatment relies on microorganisms carrying out biological oxidation of organic matter. In this stage, processes like activated sludge or biofilm reactors keep the water in contact with air so aerobic bacteria can consume dissolved and suspended organics, turning them into biomass, carbon dioxide, and water. This biological degradation lowers the wastewater’s biochemical oxygen demand and overall organic load, which is the key goal of secondary treatment.

Seeing the other options in this light: mechanical filtration is about physically removing larger solids before or after treatment, chemical disinfection targets pathogens and is typically a later polishing step, and sedimentation is the primary treatment that removes settleable solids by gravity. The biological, microbe-driven approach is what defines secondary treatment.