water in sewage sludge:

In a sludge suspension four water fractions can be distinguished on the basis of their binding form to the solids:

A free - unbound water  (free water)

B-D bound water (bound water)

No physical binding to the particles

  • Separable during mechanical dewatering
  • Release is accelerated by polymer flocculants
  • Quantity = total water - bound water

Physical and chemical binding to the particles

  • Not mechanically separable
  • cannot be influenced by polymer conditioning
  • quantity determines the flake structure


Supernatant water

  • for static thickening

Bulk water: (A*)

  • in large clusters of flakes


B: Internal water:

  • Water which is physically bound inside the flakes by capillary forces (pore size up to approx. 10 µm)

C: Surface water:

  • Water that is chemically or physically bound by adhesive forces

D: Chemical bound water:

  • Strongly bound water, chemically in gels and EPS, inner cell water and hydrate water

Source: KOPP 2001, DIN ISO/TC 308 2019

Through targeted thermogravimetric measurements the free water can be quantified.

  • Determining the water content enables an accurate prediction of the maximum achievable dewatering result DS(A)KBKopp
  • This measurement is ideally suited for determining guarantee values and as a reference value for optimizing sludge dewatering.
  • The forecast accuracy of the characteristic value is ± 0.5% DS points for operationally optimized drainage units.
  • The forecast parameter DS(A)KBKopp is included in the technical report DWA M-383 “Characteristic values of sewage sludge dewatering” (July 2019) and is therefore technically recognized.
  • Measurement of more than 1500 sludge samples for national and international expert reports based on the prediction parameter DS(A)KBKopp

If the optimum dewatering result is not achieved, it is recommended to carry out tests at a reduced or modified throughput rate and to check the machine parameters.

An improvement in discharge of 2-3 %DS points has already been achieved several times by reducing the machine feed rate (e.g. dewatering at 15 m³/h instead of 20 m³/h with centrifuge dewatering) and thus increasing the weekly operating time and adjusting the machine settings (including the differential speed and control start of the centrifuge).

KBKopp recommends using the DS(Mod-A) dewatering model to optimize sludge dewatering in order to achieve the operationally possible dewatering result over the course of the year (see navigation point DS(Mod-A) ).