Settling and Dewatering Characteristics of an A-stage Activated Sludge Process Proceeded by Shortcut Biological Nitrogen Removal

The waste solids settling and dewatering characteristics of an A/B process pilot study were evaluated using standardized characterization methods, like sludge volume index and zone settling velocity, and recently developed characterization methods that measure settleability and dewaterability. The test results indicated that the A/B process had similar settling, thickening, and dewatering characteristics when compared to four full-scale water resource recovery facilities. Sludge volume index values of 85 ± 26 mL g-1 over an 18-month operating period were obtained in the pilot A-stage. The centrifuge cake solids obtained from undigested A/B pilot waste activated sludge dewatered to an average value of 25.7% dry solids with a range of 23.2-28.0%. Settling, thickening, and dewatering performance of the undigested A/B waste sludge indicated that the A/B process is a viable process from a solids handling standpoint with similar characteristics to full-scale single-sludge activated sludge processes.