Aeration investigation of biological aerated filters using off-gas analysis

The bulk of the operating costs for biological aerated filters are associated with aeration, accordingly, any efficiency improvements which may be made to this aspect of the process could result in significant savings operationally. This study used off-gas analysis to determine the effects on oxygen transfer efficiency of variations to the air flow and substrate loading rates to two pilot scale granular media biological aerated filters (BAFs) treating primary settled sewage. The columns provided a good representation of full scale units, providing up to 99% ammonia reduction. Incremental increases in the mass transfer coefficient (KLa) were observed, as reported elsewhere and attributed to direct interfacial transfer between the bubbles and the biofilm. The OTE varied with flow rate but was far more sensitive at the lower end of the experimental range, rising sharply for air flow rates below 5 to 10 m/h. Increasing the organic loading rate also improved the OTE. The use of fine bubble diffusers did not improve the OTE, however, probably as a result of the packing media used.