E-Andrew Sindt Creative Component S11.pdf

Denitrification using biomass decay as the carbon source during React 2 converts the NO 3 - to N 2 gas withsome NH 4 + release due to cell decay. This NH 4 + is converted to NO 3 - through nitrification during React 3.Next, the reactor is in a quiescent mode in order to allow the solids to settle in preparation for decantmode. During decant mode, the settled water on top of the reactor is syphoned off and discharged(Rittman and McCarty, 2001).Complete denitrification is difficult to achieve due to deficient readily biodegradable organic carbon inthe final anoxic stage prior to decanting. As a result, numerous strategies have been investigated toachieve nearly complete N removal in SBR processes. Alleman and Irvine (1980) found through lab-scaleexperiments that cellular storage products can provide the necessary electron equivalents that arerequired by the denitrification process. Other strategies to ensure a suitable amount of carbon fordenitrification rely on feeding raw wastewater during the final anoxic stage.Figure 2.5-Typical SBR cycle for 90% N removal (Rittman and McCarty, 2001)2.2.2 Phosphorus RemovalPhosphorus accumulating organisms (PAOs) achieve luxury phosphorus uptake by anaerobically takingup carbon substrates and storing energy as poly-β-hydroxyalkanoates (PHA). The degradation ofinternal polyphosphate (poly P) which releases phosphorus in the anaerobic process and glycogenprovides energy and reducing power. Under aerobic conditions, the internally stored PHA is oxidizedand used for growth, polyphosphate synthesis and glycogen production (Li and Irvin, 2007).Phosphorus is removed from the liquid phase and stored in the biomass as poly P during the aerobicprocess. Alternating aerobic and anaerobic conditions are required by PAOs in order to gain acompetitive advantage over other microorganisms (Rittman and McCarty, 2001).The following objectives need to be completed to achieve significant phosphorus removal in EBPRsystem. First, PAOs should be selected. Second, storage of poly P is induced. Third, solids rich in poly Pshould be wasted (Rittman and McCarty, 2001). Four principal components, shown in Figure 2.6, arerequired in order to complete these three key points. First, the influent wastewater and mixed liquor19