MOST commonly used to determine stabilization of solids in an aerobic digester?

• A. VSI
• B. Methane gas production
• C. Specific oxygen uptake rate
• D. Volatile acid alkalinity ratio

Answer: (C)

In an aerobic digester, stabilization of solids is judged by how actively the solids are being biologically degraded, which is best shown by the rate at which the microbial community consumes oxygen. This is captured by the specific oxygen uptake rate, a respirometry measure that expresses oxygen consumption per unit mass of solids (per hour). It directly reflects the biodegradability of the solids: a higher uptake rate means the material is readily biodegradable and the system is actively stabilizing it, while a lower rate indicates the solids are more stabilized and less prone to further degradation. Because it provides a direct, rapid readout of microbial respiration and potential for further stabilization, it’s the most commonly used metric for assessing stabilization in aerobic digestion.

Methane gas production is tied to anaerobic processes, not appropriate for aerobic digester stabilization. The volatile acid/alkalinity ratio is also a parameter more relevant to anaerobic digestion stability and acidification dynamics. VSI is not the standard metric used for this purpose.