Online measurement for quality improvement

During primary sedimentation, undissolved particles are brought to sedimentation. These are either transferred directly to the anaerobic digester or pumped to the thickener. This measurement makes it possible to determine exactly the primary sludge content pumped to the digestion tower and to control an optimal sludge discharge rate.    
Two main dewatering applications are known for the further treatment of sewage sludge: Thickening or decanting and centrifugation. When decanting, the focus is to provide an appropriate dry matter content for the digestion process. During the sludge dewatering, a flocculant is added to the sludge to be thickened to improve the efficiency of the separation of water and solids. Given that the polymers and flocculants used for this process are cost intensive, their dosage needs to be accurately adjusted to the solids content of the sewage sludge.

To achieve an effective dewatering by centrifugation, a sufficient water/solids ratio is required. The sludge for thickening is dewatered using a high-performance centrifuge. Before adding flocculants, the solids content is detected with the Berthold microwave measurement system, which was specifically developed for this application and not only determines the dosage of the flocculants, but also continuously monitors the feeding to the centrifuge with a constant solids throughput.

Technical Features

  • High accuracy < 0.2 wt.% dry matter content (standard deviation) 
  • Representative measurement results due to detection of the entire material flow in the pipeline
  • No wear of components as with other technologies 
  • Reliable measurement with only one calibration factor, even with different sludges
  • Suitable for industrial or municipal waste waters


Customer benefits

  • Determination of the total dry matter load to the digester
  • Optimisation of the anaerobic digestion process
  • Cost reduction through optimised use of flocculants
  • Optimised pump utilisation avoids blockages and ensures optimum efficiency
  • Non optical measurement, not sensitive to contamination therefore no maintenance required

Measuring principle and function

The MicroPolar measuring system uses the special dielectric property of water. It generates microwaves that interact with the water molecules. This interaction induces a weakening of the microwave energy, which can be detected as phase shift and attenuation. As the phase shift and attenuation change is directly proportional to the water content, this allows the determination of the concentration of the medium with high accuracy. Berthold's superior multi-frequency technology guarantees highly stable and reliable measurements that are unaffected by interferences caused by reflections or resonances. The microwave power of a MicroPolar system is so low (max. 10 mW) that the material to be measured is neither heated nor changed in any way.