SLUDGE PRODUCTION IN ROTATING BIOLOGICAL CONTACTORS WITH SUPPLEMENTALAERATION AND AN ENLARGED FIRST-STAGE

A full-scale rotating biological contactor (RBC) was used to study the effectiveness of supplemental aeration and an enlarged first stage in improving the performance of an RBC system. These experimental studie s suggest that generally the sludge production was higher in the first stage because of the higher soluble COD (SCOD) removal rates. However the sludge production in the first stage was significantly higher in the presence of supplemental air than without the air. At lower organi c loadings, the first-Stage sludge production was 1 . 09 kg SS/kg (2 . 40 Ib SS/lb) and 0 . 572 kg SS/kg (1 . 26 Ib SS/lb) SCOD removed with and without supplemental ail; respectively. In addition, with supplem ental air there was an increasing stabilization of volatile solids in the subsequent stages when the substrate was limiting in the succeedin g stages. Overall sludge production was the same with and without supp lemental aeration at low and high organic loading rates. However overa ll sludge production decreased substantially with the use of an enlarg ed first stage, particularly with supplemental aeration, which results in lower operating costs for sludge stabilization and disposal. This occured despite higher first-stage sludge production rates with the us e of supplemental air. Also, the overall performance of the RBCs recei ving supplemental aeration was significantly better when compared to t he RBCs receiving no supplemental air, both in terms of SCOD or SBOD5 removal and ammonia nitrification.