Why dewaterabilty of sewage sludge occurs upstream- a model to quantify the effects

J. B. Kopp*, Sewage Sludge Treatment Consulting KBKopp, Germany

Mechanical dewatering of sludge is a key technology to reduce disposal costs. It can be observed that ignition loss of sewage sludge in the last ten years increase continuously and dewatering results decrease even if god degree of degradation are achieved in anaerobic digesters. This can be explained by change in organic compound in primary sludge (PS) itself and increasing amount of waste activated sludge (WAS).

To optimize sludge dewatering processes, the dewaterability of sewage sludge needs to be understood. There are two categories of water in a sewage sludge suspension: the free water content with no physical binding to sludge particles. By mechanical dewatering of sewage sludge only this free water content can be separated. The second category is the bound water, which is the sum of internal water, surface water and chemical bound water. The internal water is bound in the interstices inside flocs and particles physically by capillary forces in pores up to approx. 10 ┬Ám. Surface water is bound on the surfaces of particles by physical and chemical adhesive forces. At least chemical bound water is fixed in cells, gels, EPS and by hydration. The structure of flocs mainly determines the amount of bound water and dewatering results. Therefore dewaterability occurs upstream. A model was generated to explain the main influences on dewaterabilty in wastewater treatment plant. Further the effect of new technologies like vacuum degassing, thermal hydrolysis and phosphorus precipitation as struvite on the water binding will be quantified...

Session: L16 - Dewaterability of Sludges
Day: 24 October 2019
Time: 13:00 - 14:15 h

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