WasteWater Operator Certification - Grade 2 Practice Test 2025: The All-In-One Guide for Exam Success!

For the digestion of sludge to be considered effective, it is essential that the volatile solids content is significantly reduced. The effective range for this reduction is typically around 50-60%. This level indicates that a sufficient amount of organic material has been broken down by the microbial activity during the anaerobic or aerobic digestion process. A reduction in this range not only signifies that the process is functional but also that the microorganisms are actively consuming the organic material, which is crucial for stabilizing the sludge.

If the reduction were lower, such as in the 20-30% or 30-40% range, it would suggest that the digestion process may be inadequate or that the system is not operating as efficiently as it should be. These lower reductions could indicate potential issues, such as insufficient retention time, suboptimal temperature, or inadequate mixing, which could prevent effective digestion from occurring. On the other hand, reductions higher than 60-70% could be indicative of over-digestion, leading to operational challenges and possibly undesirable byproducts.