What term describes wastewater that contains no measurable DO and nitrate?

The correct term to describe wastewater that contains no measurable dissolved oxygen (DO) and nitrate is anaerobic. This condition indicates the absence of oxygen in the water, which is crucial for aerobic respiration—that is, the process where microorganisms use oxygen to break down organic material.

In anaerobic environments, different microorganisms thrive compared to those found in aerobic conditions. These anaerobic bacteria can decompose organic matter without oxygen, often producing byproducts like methane and hydrogen sulfide, which can create unpleasant odors and may be harmful if present in high concentrations.

Understanding the concept of anaerobic conditions is important for wastewater treatment processes. Effective management of environments with low or no DO is essential to ensure proper treatment and minimize odor problems and the release of harmful gases.

The other terms relate to different conditions: toxic substances might inhibit biological processes; autotrophic refers to organisms that generate their own food typically using light or chemical energy; and aerobic pertains to conditions where oxygen is present, allowing for a different group of microorganisms to thrive. Having clarity on these definitions helps in understanding the dynamics of wastewater treatment systems.