Oxygen Uptake Rate Tests to Evaluate Integrated Fixed Film Activated Sludge Processes

The combination of biofilm and suspended growth processes is, to date, relatively novel and there is a need to develop tools to monitor the performance of IFAS systems. The recent start-up of a full-scale demonstration Integrated Fixed Film Activated Sludge (IFAS) process in Ontario was monitored for approximately 100 days, providing an opportunity to investigate analytical tools to assess process performance.The objective of this study was to understand the dynamic changes in physical and microbiological parameters in the process during and following plant start-up. More specifically, knowledge of the rate of biomass accumulation on the carriers, and the time to establish full nitrification activity was desired. Parameters such as total biofilm solids, in-basin nitrification rates, and batch nitrification rates were compared to an oxygen uptake rate (OUR) test modified by us for use with large polyethylene carriers. Samples were collected from both upstream and downstream ends of the plug flow aeration basin to enable profiling of the above parameters through the basin.As observed in other IFAS installations, the modified OUR test determined that the biomass carriers performed greater than 87% of nitrification. Nitrification activity of the carriers was observed to follow different trends than biofilm total solids during process start-up. The process reached high nitrification rates within weeks whereas the biofilm total solids required more than 50 days to attain a quasi-steady-state. This study illustrated that parameters in addition to biofilm total solids are required to assess activity in nitrifying IFAS processes and oxygen uptake rates can be a useful tool in this regard.