Which term describes an oxygen-deficient condition (less than 0.5 ppm)?

• A. Anaerobic
• B. Anoxic
• C. Alkalinity
• D. Baffle

Answer: (B)

Anoxic describes an environment with very little or no dissolved oxygen, typically with DO near zero and often defined as less than about 0.5 mg/L. In wastewater treatment, this low-oxygen zone enables denitrification because nitrate becomes the electron acceptor when oxygen isn’t present. This differentiates it from truly anaerobic conditions, which imply no oxygen and often different microbial processes. Alkalinity is a chemical capacity to neutralize acids, and a baffle is a physical tank component, so neither describes the oxygen level.