Influence of aeration and media fill ratio on submerged aerated filter hydrodynamics and process performance

Submerged aerated filters (SAFs), are used to meet stringent ammonium (NH4+) and soluble organic consents. Current design follows a black box approach, whereby inlet and outlet contaminant concentrations are monitored, independently of internal hydrodynamic conditions. To investigate the influence of internal hydrodynamic conditions tracer tests were performed on a SAF with biofilm on the media surface, at 100, 75, 50 and 25% media fill ratios. Results indicate that SAF internal hydrodynamic conditions directly influence process performance. A 50% media fill ratio showed optimum hydrodynamic conditions for BOD5 removal, with a removal efficiency of 70% and a mean tracer retention time (¯t), exceeding the hydraulic retention time (HRT) by 68 mins. A 100% media fill ratio showed optimum conditions for NH4+, with a removal efficiency of 60%, but internal shortcutting was evident. The methods used can be applied to diagnose, underperforming SAF reactors and enable optimisation of internal hydrodynamic conditions for selective contaminant removal.