High rate and low rate digestion normally refer to which aspect of digesters?

The concept of high rate and low rate digestion primarily relates to the digestion time that organic materials spend in the digester rather than the flow rate. In high rate digestion, the retention time of the material is shorter, allowing for a more rapid breakdown of organic solids. This method typically utilizes higher temperatures, specific mixing conditions, and the addition of microorganisms that enhance the digestion process.

In contrast, low rate digestion involves a longer retention time, which allows for a more gradual breakdown of solids. This is often done in systems where there is more stable, lower-energy input but also tends to take longer for volatile reductions to occur.

The correct emphasis on digestion time helps clarify the operational characteristics of the digesters, such as how the microbial populations behave, the efficiency of volatile solid reduction, and the overall treatment effectiveness of the system. Understanding this distinction is integral for wastewater professionals as it affects design considerations and operational management of digester facilities.