A Centrifuge-Based Procedure for Suspended Solids Measurements in Lagoon Sludge

Abstract. Concentration of suspended solids (SS) is an important parameter in wastewater analysis that is used to understand handling characteristics and to evaluate treatment options and efficiencies. Samples from anaerobic lagoon sludge often have high levels of SS that are difficult to measure by standard filtration techniques. A measurement technique developed in the Environmental Analysis Laboratory of the Department of Biological and Agricultural Engineering at North Carolina State University (NCSU) uses centrifugation to separate solids from liquid samples and quantifies dissolved solids (DS) in the supernatant. The value of SS is then calculated as the difference between total solids (TS) and DS. The method is based on the assumption that dissolved material is not affected by centripetal force up to 10,000 A— g and therefore partitions equally between the liquid phase and the water remaining in the centrifugal pellet. The method was compared to the standard filtration method and another centrifuge-based method using lagoon sludge with TS concentrations from 61,000 to 100,000 mg L -1 . The NCSU method was the only method that gave the reasonable result of SS less than the corresponding TS level. The variability of the NCSU method was significantly lower than that of the other methods as well.