What is the normal range for the VA/ALK ratio in a well-operated digester?

The VA/ALK ratio, which stands for volatile fatty acids to alkalinity ratio, is a critical parameter in assessing the health and stability of anaerobic digesters. A normal range of this ratio in a well-operated digester indicates a balance between the production of volatile fatty acids during the digestion process and the buffering capacity provided by alkalinity.

The correct answer of 0.1 to 0.35 reflects the ideal condition for maintaining optimal microbial activity, preventing acid accumulation, and ensuring efficient digestion of organic matter. Keeping the ratio within this range helps to minimize the risk of digester upset, such as volatile fatty acid inhibition, which can occur if the ratio becomes too high. This is vital for achieving successful digestion, as excessive volatile fatty acid concentrations can be detrimental to the microbial population that facilitates the anaerobic digestion process.

In this context, options outside this range would not support the necessary conditions for effective digestion, leading to potential operational issues. For instance, too low a ratio could indicate insufficient acid production, while too high a ratio would signal an imbalance favoring acid accumulation, which could destabilize the digestion process. Therefore, the range of 0.1 to 0.35 is essential for optimal performance in wastewater treatment digesters.