On activated sludge systems operators have to balance their setpoints to get a ‘good settleable’ sludge continuously. Sludge to be separated from the water. If for that separation final clarifiers are used it’s important that the sludge settles quick enough to not get washed out into the final effluent. Such washout would otherwise result in a non-compliancy on the TSS discharge limit of often about 35 mg/l TSS.

For different types of bioreactors we have solutions to improve sludge settling.

Activated sludge systems

• Bacteriological selection mechanisms. With a contact tank or selector. In such case it’s to favour the conditions for the ‘floc forming bacteria’ above the ‘unwanted filamentous bacteria’. By having less filamentous bacteria in the sludge the sludge volume index (SVI) improves, giving it a better settleability.
  Result: effluent TSS will become compliant again.
• Gravimetric selection mechanisms. Or in our case to use the inDENSE technology to get more densified biomass, for very good settleability characteristics.

Granular sludge systems

• To aim for such system could intrinsically benefit for sludge settling ability. Or even better to use that improved settling to reduce the size of the WWTP. For the BIOCOS® technology it also improves the possibility for BNR Biological Nutrients Removal.

Attached growth systems

• For such systems like Moving Bed BioReactor (MBBR) of Fixed Bed BioReactor (FBBR), sludge settling could also become an issue if not designed correctly.

General and Other

• Pre-treatment. Without a proper pre-treatment it will always be more difficult to get the wanted behaviour of bacteria and sludge. Therefor at least fat, oil, grease (FOG) and particles (TSS) must be removed as much as possible. Also to balance (buffer/equalise) the water quality and quantity over time will give benefits.
• Chemicals solutions.