A Comparative Analysis of Simultaneous Nutrient Removal in Two Full-Scale Advanced SBR-based Sewage Treatment Plants

Two full-scale pre-anoxic selector-equipped SBR based wastewater treatment systems were analyzed in this study to determine the role of storage products in simultaneous nutrient removal (TN and TP) via simultaneous nitrification and denitrification (SND) and enhanced biological phosphorus removal (EBPR) mechanisms, respectively. For nutrient removal, it was observed that there are specific wastewater parameters that influence the plant's performance considerably, i.e., the concentration of readily biodegradable COD fraction, soluble BOD5, which can be quickly taken up by the denitrifiers and polyphosphate accumulating organisms (PAOs) for their metabolism and stored in the form of Poly-?-hydroxybutyrates (PHB) in anaerobic phase and subsequent storage of polyphosphates (poly-P) in the aeration phase. The TN removal was ~71% (SND ~78%) and ~85% (SND ~94%), and TP removal was ~41% (EBPR ~18%) and ~68% (EBPR ~51%) in Roorkee, Uttarakhand (India) and Varanasi, Uttar Pradesh (India) SBR plants respectively. Both of them are working well in performing high SND, which requires optimized management of dissolved oxygen (DO) levels and C/N ratios. The Varanasi SBR plant is working more efficiently for the EBPR process because of the several conditions prevailing in the plant. It comprises of anaerobic/ anoxic selector compartments (nine selector compartments per basin, which diminishes the effects of RAS falling in the anoxic zones and maintains ORP < -200 mV to ferment the rbCOD into acetates) along with six aeration basins (ORP > +150 mV and DO ranges from 0-2.4 mg/L for effective SND). It has optimized rbCOD/ TP ratios (10-20) in the raw sewage and good TP storage (as poly-P) in the biological sludge (>3%), leading to effective Bio-P removal.