Drying of Sand-Digested Sludge Mixtures

An empirical design equation has been developed to estimate the drying rate during the falling rate drying period of a mixture of sand and centrifuged digested primary domestic sewage sludge to be used as a fill material. The drying rate is required to calculate the average moisture content of the mixture while drying. The design equation was developed from data collected over a nine-month period using three different sands with sand-to-sludge dry solids ratios from 0:1 to 30:1. The primary variables considered are sand-to-sludge dry weight ratio, ambient temperature, and ambient relative humidity. Mixture depth and sand particle size were not found to affect drying rates for ranges and distributions tested. The design equation has not been verified for polymer-treated sludges.