Biologically intensified filtration (dual-media dry bed filter) for advanced waste water treatment

The dry-bed filtration process had been used in water treatment, and pilot-scale experiments had been carried out on its application to sewage treatment. In this process, the sewage trickled through the filter bed and simultaneously air was sucked down through the bed to provide adequate oxygen for increased metabolic activity. The performance of different materials as filter media was investigated. The development of biofilm on the medium reduced the backwash velocity required to achieve the necessary filter bed expansion of 15-20 per cent. Using a basalt/anthracite dual-media bed, the dry filtration process was very effective in achieving nitrification. Results obtained using this process on a large scale at a municipal sewage works are presented. The process had also been tested at full scale for treatment of waste waters from the paper industry, food processing, and a brewery.