Dewatering model DS (MOD-A)

Purpose: Synchronization dewaterability to dewatering result, to save disposal costs through timely optimization!

Based on analysis data from recent years, a calculation model was derived to forecast the maximum achievable dewatering result DS(Mod-A) for the actual state of digested sludge.

The model quantitatively records the main influences on drainability and thus enables changes in drainability to be documented. However, the derived model cannot replace the measurement of drainability with predicted values in accordance with DWA-M 383 for the determination and monitoring of guaranteed values in the context of tenders, as the loss on ignition as a parameter cannot be used as the basis for a guaranteed value.

Instead, the model is intended to help operators understand the dewatering process and optimize it in real time based on operating data. The following figure shows the comparison between dewaterability and dewatering result. The DS(Mod-A) value is calibrated using DS(A)KBKopp measurement results for the respective sewage sludge.

Source: DWA, KA Korrespondenz Abwasser, Abfall - 2019 (66), Nr. 8

The derivation of the model has shown that the excess sludge content in the raw sludge, the concentration of dissolved phosphate and the loss on ignition of the digested sludge have the greatest influence on the achievable dewatering result.

The influences are briefly summarized below:

1 WAS/PS in Raw Sludge

As the proportion of excess sludge in the raw sludge load in influent odanarobic digesters, the dewaterability decreases due to the higherwater binding capacity of WAS. Against this background, dewateringcan only be improved by digestion if primary clarification is also integrated. The dewaterability decreases with an increasing proportion of WAS sludge load and is determined by the size of the primary clarifier.

Source: KB Kopp

2 Phosphate Concentration

Dissolved phosphate PO4Ph as an influence on the water binding of the EPS, with increasing concentration of dissolved phosphate the water binding capacity in the digested sludge increases and dewaterability decreases.

Quelle: DWA, KA Korrespondenz Abwasser, Abfall - 2019 (66), Nr. 8

For digested sludge from wastewater treatment plants with enhanced biological P-removal (dissolved PO4P in digested sludge > 100 mg/l), the dewatering result is ~ 4%DS points lower and the pFM requirement~ 3 kgAS/tDS higher than fordigested sludge with low PO4 Pconcentrations (< 30 mg/l).

3 Organic Content
(VSS, loss on ignition)

Water is mainly bound to organic particles. This results in a higherwater-binding capacity or reduced dewaterability with increasing VSS.

Process Diagrams for Operation (Example):

Which parameters need to be measured:


WAS load of the raw sludge load [%] input in anaerobic digester: frommonthly average values operation datas


Digested sludge: phoshate PO4 phosphate after filtration 0,45  µm(weekly)


Digested sludge: VSS & DS (weekly)


DS(A): 2x per year to calibrate the model (winter/summer) to start