ABSTRACT
At moisture contents 90% sludges behave as liquids, while below 90% they be have as non-Newtonian fl uids exhibiting plastic rather than viscous fl ow ( Fig. 21.1 ).
In sludges with a moisture content of 95% most of the water is in a free or readily drained form (70%) while the remainder is bound to the sludge and more diffi cult to remove ( Fig. 21.2 ). While most of the free water can be removed by gravity settlement, some of the bound water must also be removed if the sludge is to be mechanically handled rather than pumped. This is normally done by coagulation using chemicals and dewatering equipment which removes moisture by altering the particle formation of fl ocs and the cohesive forces that bind the particles together, thus releasing fl oc and capillary water.
