Which statement correctly describes the Kraus process in the activated sludge family?

• A. Kraus process is listed as an activated sludge treatment type.
• B. Kraus process is a fixed-film trickling system.
• C. Kraus process uses high-purity oxygen in covered tanks.
• D. Kraus process is a chemical precipitation step.

Answer: (A)

The Kraus process is categorized as an activated sludge treatment type because it relies on suspended-growth biology to treat the wastewater. In this approach, air is bubbled through a mixed liquor of wastewater and microbial sludge, keeping the microorganisms in suspension so they oxidize the organic matter and pollutants. The key idea is biological treatment in a aerated reactor with return sludge to maintain an active biomass, followed by settling to separate treated water from the sludge.

This isn’t a fixed-film trickling system, which uses a bed of media for biofilm growth, nor is it a chemical precipitation step, which removes contaminants by adding chemicals. Some activated sludge variants may use different oxygen delivery or configurations, but the defining feature is the suspended-growth biological process, placing the Kraus method squarely in the activated sludge family.