Bioresource Technology, Vol.224, 229-235, 2017
Granulation of activated sludge under low hydrodynamic shear and different wastewater characteristics
Five reactors were operated with low upflow superficial air velocities (0.41 cm min (1)) in order to observe granulation on synthetic wastewaters with different characteristics: 1) 340 mg-COD L (1); 2) 630 mg-COD L (1); and 3) 1300 mg-COD L (1). Stable granulation was only observed under low hydrodynamic shear for low-strength wastewater. 55-70% of soluble chemical oxygen demand (COD) was utilized before aeration and 91% COD, 62% total nitrogen (TN), and 96% total phosphorus (TP) were removed from the low-strength wastewater. Although medium-strength wastewater did generate granules they rapidly acquired a filamentous surface layer that resulted in decreased performance and loss of nitrification. 94% COD, 30% TN, and 85% TP were removed from the medium-strength wastewater. The high-strength wastewater did not develop granules and 85% COD was removed. Results demonstrated that high shear force was not required for granulation. Rather, granulation depended on multiple parameters to out-select rapidly growing aerobic microorganisms. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords:Aerobic granular sludge;Biological nutrient removal;Superficial upflow air velocity;Hydrodynamic shear force;Wastewater treatment