Biological Aerated Filters (BAFs) are wastewater treatment systems which contain support media for biofilm development and provide oxygen at the base of the reactor to sustain aerobic microbial treatment processes. The aims of this study were to characterise and quantify the treatment capability of non-backwash BAFs used in small sewage treatment works, and therefore establish design recommendations. Three full scale trial BAFs, a field operational small sewage treatment plant, and a full scale aeration testing facility were studied. The trial BAFs, with simulated secondary settlement, provided carbonaceous stabilisation under various hydraulic loadings and airflow rates. Nitrification showed no relationship with airflow rate, but was inhibited at high hydraulic loadings. Sludge production in the BAFs was less at higher airflow rates, due to improved stabilisation of organic solids. Media specific surface area had little effect on treatment performance. Downflow operation generally provided better treatment than upflow operation, with high levels of suspended solids stabilisation, considered a function of longer residence times. The mean BAF residence times determined empirically were considerably shorter than the design residence times, and may have inhibited treatment potential. The oxygen transfer efficiency (OTE) of coarse bubble diffusers was enhanced in a simulated BAF, due to the effects of the support media. Fine bubble diffuser OTE was inhibited by the media. Coarse diffusers may be more appropriate than fine diffusers for small non-backwash BAFs, a function of performance and cost efficiency. A small packaged sewage treatment plant incorporating BAFs produced a well nitrified effluent with reasonable organic stabilisation, and showed little diurnal or seasonal variation in effluent quality. The plant compared well to other small sewage treatment systems, providing treatment in a small footprint. Design recommendations for non-backwash BAFs and small sewage treatment plants incorporating BAFs have been established, based on the knowledge gained during this study. It has been demonstrated that non-backwash BAFs are appropriate for use in small sewage treatment works.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:368839 |
| Date | January 1997 |
| Creators | Hodkinson, Brenden James |
| Publisher | University of Portsmouth |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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