Fluorescence in situ hybridizations were used to identify and determine the abundance of nitrifying bacteria and Anammox bacteria (recycling bacteria) in freshly settled sludge of biological nutrient removal (BNR) secondary clarifiers. An uneven distribution was observed for recycling bacteria in two BNR systems. Settling patterns suggest microcolony formation processes are sensitive to the internal recycle rate, which allow for rapid recycling bacteria microcolony growth by increasing circulation of flocs through the aeration and anoxic basins. Sludge containing high levels of recycling bacteria are selectively collected and separated from the remaining sludge, uncoupling the solids retention time (SRT) of the recycling bacteria from the wasting bacteria. Elevated recycling bacteria SRTs increase concentrations of nitrifying bacteria in the aeration basin and Anammox bacteria in the anoxic basin, improving nitrification and anaerobic ammonium oxidation. Uncoupling the SRT enhances aeration and/or anoxic basin utilization and reduces the overall hydraulic residence time.
Stroot, Peter G., "Solids retention time uncoupling by selective wasting of sludge" (2013). USF Patents. 239.
University of South Florida