Which parameter is NOT directly monitored for maintaining optimal anaerobic digestion?

Maintaining optimal anaerobic digestion involves monitoring several critical parameters to ensure efficient operation. The organic loading rate, temperature, and pH are all directly monitored because they significantly impact the activity of anaerobic microorganisms.

The organic loading rate refers to the amount of organic matter introduced into the digester in relation to its volume, influencing the rate of digestion and biogas production. Temperature affects the metabolic rates of the microorganisms; different temperatures can optimize or hinder the digestion process. pH is also crucial because anaerobic bacteria thrive in specific pH ranges, and deviations can lead to process instability.

Hydraulic retention time (HRT), however, is not directly monitored in the same manner as the other three parameters. HRT is a measure of the average time that the wastewater stays in the anaerobic digester. While it is an important design parameter that influences the overall treatment process, it is not something that is continually monitored or adjusted in real-time during the digestion process like the organic loading rate, temperature, or pH. Therefore, while the HRT can indirectly influence digestion efficiency, it does not require direct monitoring for optimal operation.