BLANKETmaster: clarifier-by-clarifier sludge blanket control
BLANKETmaster is a real-time control system for the sludge blanket in clarifiers. In secondary clarifiers it sets the return activated sludge flow of each clarifier from its own measured blanket depth, instead of dividing a plant-wide flow equally. It sends its setpoints to the plant's SCADA system.
Why blanket depth matters
A blanket that rises too high increases the risk of solids leaving with the effluent and, in extreme cases, washes active biomass out of the process. A blanket held lower than necessary wastes pumping energy and sends thinner sludge to thickening and digestion. Return sludge held constant, or as a fixed ratio to influent flow, works in steady dry weather but cannot follow daily load changes, differences between clarifiers or wet weather.
How it works
- Operators set two values: the blanket depth target and the maximum blanket depth.
- The return sludge flow of each clarifier is set from its own measured blanket.
- The system learns the daily pattern of loading, so that it acts ahead of regular rises such as the morning peak, and changes to a wet-weather mode when influent flow is well above its usual level for that time of day.
- Return sludge flow is never commanded to zero.
- During commissioning, an advisory mode calculates and records the flows the system would command without sending them, so that operators can compare them with current practice.
What a high blanket costs: a full-scale study in primary clarifiers
In a full-scale study at the 167 MGD San Jose/Santa Clara Water Pollution Control Plant, primary clarifiers were operated at different blanket depths. At peak flow, the clarifier with the blanket above 2.0 m produced effluent with 25% more suspended solids, 23% more soluble BOD, 46% more BOD and 75% more dissolved hydrogen sulfide than the clarifier with the blanket held at 1.4–1.7 m. Manual blanket monitoring and pump adjustment took an estimated 16.1 operator hours per week.
No measured results for secondary clarifiers have been published.
Operators keep authority
Operators set the target and maximum blanket depths and can override BLANKETmaster at any time. Every reading is checked before it is used. Faulty readings are detected and not acted on, and operators are alerted.
Instruments
BLANKETmaster uses a sludge blanket depth measurement in each clarifier together with the existing return sludge valves, pumps and flow meters. These can be bought from any supplier; Ekster & Associates sells none of them, but provides recommended performance specifications.
Where it is used
The Los Angeles County Sanitation Districts awarded Ekster & Associates a contract for BLANKETmaster on the secondary clarifiers at the Pomona Water Reclamation Plant in October 2026.