Waste activated sludge from three full-scale wastewater treatment plants was subjected to laboratory-scale sludge handling and dewatering procedures in a series of experiments designed to evaluate the effect of commonly used techniques on dewater-ability and to define the mechanisms responsible for changes in dewaterability. The results showed that the techniques used to handle waste activated sludge can have a drastic effect on the subsequent rate of dewatering. For optimum dewatering, the sludge organisms must be maintained in a viable, aerobic condition and metabolic activity must occur. The conditioning effects of synthetic polymers are strongly affected by handling techniques. Changes in the median particle size of the sludge floc strongly affects specific resistance and the compressibility factor. (Author)