Role of Bioflocculation on Chemical Oxygen Demand Removal in Solids Contact Chamber of Trickling Filter/Solids Contact Process

The trickling filter/solids contact (TF/SC) process was developed in the late 1970s to improve the quality of the final effluent from existing trickling filter plants, to be able to meet stricter Environmental Protection Agency effluent requirements. Although this process has successfully achieved this objective, it is still not completely understood, there is limited information regarding the flocculation phenomena occurring in the solids contact chamber (SCC), and no information could be found on the relationship between flocculation and organic matter removal kinetics. To better understand the kinetics of biological flocculation in a continuous flow SCC, a long-term experimental program was conducted using a TF/SC pilot plant constructed at the Marrero, La., wastewater treatment plant. This program started in January 1998 and has continued through date. The present article will focus on two major areas: (1) the kinetics of bioflocculation in the SCC; and (2) effect of bioflocculation on chemical oxygen demand (COD) removal. Analysis of the wastewater composition revealed that, on the average, only 18.7% of the total COD in the SCC influent is truly dissolved. Therefore, most of the total COD removal observed in the SCC must be due to a physical process, such as flocculation. The experimental data confirmed that flocculation of the particulate COD contained in the trickling filter effluent explains the high total COD removal observed at the SCC. Both total and colloidal COD removals are well explained by the first-order flocculation model.