Gravity Dewaterability of Pulp and Paper Mill Primary Wastewater Sludges

Primary sludges from three paper mills were subjected to gravity drainage in 25cm by 25cm laboratory columns under a variety of test conditions, including the nature of underdrain system, depth of application, single vs. multiple application, polymer dosage and application of low vacuum. It was possible to dewater these sludges to a cake solids content in the 11 to 15 percent range. Lower depths of application resulted in higher drainage rates, but varying depths, did not significantly affect the percentage of total volume of leachate drained. The type of underdrain system did not affect the sludge drainability. The leachate drained from the deposited sludge deteriorated with time in terms of COD and turbidity, due to degradation of the sludge solids. Attempts made to correlate the column performance with the bench scale drainage test, specific resistance and capillary suction time(CST), were partly successful