A CETP operator observes frequent foaming, poor settling and fluctuating MLSS. The most likely underlying cause is
- AHigh suspended solids
- BVariability in influent composition and possible surfactantsCorrect
- CExcessively low organic loading
- DHigh grit concentration
Solution
Concept
Operational disturbances and foaming in CETPs
Formula
NONE
Step-by-step solution
1. CETPs receive wastewater from multiple industries with varying chemical composition. 2. Influx of detergents/surfactants and intermittent toxic shocks induce filamentous bulking and foam formation (Nocardia foaming). 3. Filamentous growth traps air and prevents flocs from compacting, causing poor sludge settling. 4. Therefore, variable influent and surfactants are the primary cause. Answer: B
Explanation
Common Effluent Treatment Plants (CETPs) handle mixed effluents from diverse industrial sources. Severe variations in influent composition, combined with synthetic surfactants, oils, and toxic shocks, stimulate the proliferation of actinomycetes (like Nocardia) and filamentous bacteria. These cause persistent biological foam, sludge bulking, poor settling in secondary clarifiers, and fluctuating MLSS.
Why the other options are wrong
A) High inert suspended solids cause sludge accumulation, not chemical/biological foam. C) Low organic loading generally causes pin-point flocs rather than heavy surfactant foaming. D) High grit causes equipment wear in headworks, not biological clarifier foaming.
Shortcut
CETP Foaming + Poor settling = Influx of surfactants and fluctuating industrial influent.
Common mistake
Attributing foaming and poor settling solely to grit or inorganic suspended solids.
Correct answer: B) Variability in influent composition and possible surfactants