Laboratory experiments on the sand samples separated from sludge have been carried out to study their uncertainty associated with dose response and calibration. The uniformity of absorbed dose in a batch of sludge in a large-scale liquid sludge gamma irradiator has been examined by using sand samples separated from sludge as an in-situ dosimeter. Statistical analysis of the data, by applying ANOVA test, has been used to evaluate uniformity of dose. The re-circulation time for irradiation of sewage sludge to a dose of 3 kGy for its disinfection has been optimized using the data obtained.