Comparison of Biological Aerated Filter (BAF) performance using two granular sunken media at low organic and hydraulic loadings

Biological treatment forms an integral part of wastewater treatment. Biological aerated filters (BAFs) are submerged attached growth bioreactors which provide biological treatment as well as filtration in a single unit. The packing media used in BAFs plays an important role in the system performance and determines the ability of the system to meet treatment objectives. The performance of upflow BAFs was compared using North American clay media and Severn Trent monomedia at low organic and hydraulic loads (0.18 kg tCOD/m3d – 0.6 kg tCOD/m3d and 0.1 m/hr – 0.38 m/hr, respectively). Two identical, two stage, bench scale, upflow BAFs were constructed using PVC pipes with an internal diameter of 0.11 m. The system was operated at the Peppers Ferry Wastewater Treatment facility for two months and was fed with effluent from the primary clarifier. Grab samples of influent and effluent from the BAFs were collected thrice a week to evaluate carbon oxidation, solids removal and nitrification. In order to evaluate system recovery when BAFs are operated intermittently, a drying cycle of eleven days was introduced. Both media performed satisfactorily with respect to carbon oxidation and nitrification. On average, total COD and total suspended solids (TSS) removal rates were, respectively greater than 80% and 55%. Conversion of ammonia to nitrate was greater than 90% throughout the study. It was concluded that additional factors like media properties and economic factors need to be considered in selection of the media.