Which metric is commonly used to evaluate digestion effectiveness in terms solids reduction?

• A. DO concentration
• B. Gas production rate
• C. Percent solids reduction
• D. TSS in influent

Answer: (C)

Measuring digestion effectiveness by how much solids are reduced. Percent solids reduction directly quantifies the amount of solids removed or transformed during digestion, giving a clear indication of how well the process is breaking down solids. It’s calculated by comparing the solids content before digestion (initial solids) with the solids content after digestion (final solids) and expressing the difference as a percentage of the initial amount. This metric, often using total solids or volatile solids, shows the actual mass reduction from the digestion process.

Why this is the best fit: it links directly to the goal of digestion, which is to lower the solids load by digesting organic matter. The other metrics measure related aspects but not the solids reduction itself. Dissolved oxygen concentration reflects aerobic conditions and oxygen demand, not how much solids were reduced. Gas production rate indicates how actively digestion is producing biogas, not the mass of solids removed. TSS in influent measures incoming solids, not the effectiveness of digestion in reducing solids.