Comparison of Treatment Capacities of Swim-bed and Activated Sludge Processes for Domestic Wastewater

Abstract

Some operational problems remain unsolved for the conventional activated sludge (CAS) process, such as the large space requirement, high operational cost and large excessive sludge production. Swim-bed technology using a novel acrylic-fiber material biofringe (BF) material for biomass attachment is considered as a solution to some of these problems. In lab-scale tests, the CAS and BF processes were operated in parallel while contaminant removal efficiencies and sludge productions were compared. The study was conducted in two runs with BOD volumetric loading rates of 0.5 kg-BOD/m³/d for the Run I and 1.0 kg-BOD/m³/d for the Run II, corresponding to hydraulic retention times of 7.2 h and 3.6 h, respectively. Overall, superior contaminant removal efficiencies were demonstrated for the BF process. Average COD removal efficiencies for the BF and CAS processes in Run I were 92% and 86%, respectively, and in Run II, 90% and 83%, respectively. High nitrification efficiencies were obtained for both processes throughout the study; however, during Run II, the BF process had a significantly improved nitrogen removal efficiency of 44% versus 34% for the CAS process. After increasing the volumetric loading rates in Run II, sludge washout occurred in the CAS process, while high biomass levels were maintained in the BF process, demonstrating the retention capacity of the BF carrier. Sludge yields were calculated to be 0.12 kg-MLSS/kg-COD_removed for the CAS process versus 0.081 kg-MLSS/kg-COD_removed for the BF process in Run I and 0.22 kg-MLSS/kg-COD_removed versus 0.12 kg-MLSS/kg-COD_removed, in Run II, respectively. A large amount of protozoa and metazoa were found in the BF process, which could have contributed to the observed reduction of excess sludge.