MICROBIOLOGY OF AN ANOXIC TRICKLING FILTER

As biological nitrogen removal is introduced at municipal treatment pl ants, existing trickling filters can be used for either nitrification or denitrification. In the latter case, the trickling filters must be operated in an anoxic mode. A pilot-scale study of the use of tricklin g filters for post-denitrification has been carried out at Ormanas Sew age Works, Sweden. The pilot trickling filter (4.5 m high and 0.4 m in diameter) was fed clarified effluent from a full-scale activated slud ge process, and crude syrup (a by-product from sugar refining containi ng mainly sucrose) was added as energy and carbon source for the denit rification. Furthermore, sodium nitrate was added at times when the ni trification in the activated sludge process was poor. The pilot plant was operated for over one year and was found to denitrify at a rate of 0.7 g nitrate-N/m(2), day. The aim of the present investigation was t o study the microbiology of the anoxic trickling filter.