UPGRADING OF A WASTE-WATER TREATMENT-PLANT UTILIZING EXISTING TRICKLING FILTERS AND A NEW FILTER STAGE

The upgrading of wastewater treatment plants with the objective of enh ancing the elimination of nitrogen and phosphorus is a demanding under taking as regards the choice of process technology, especially if the basic function of existing treatment systems is to be retained. With r eference to an existing two-stage biological sewage plant with trickli ng filters in the second stage, the present paper illustrates how the volume of the activated sludge stage that is being enlarged can be min imized by exploiting the benefits of a primary treatment stage with hi gh BOD5 elimination and by integrating the trickling filters in the ma in stream of the treatment chain. This requires that the extremely cos tly filtration stage that is essential for eliminating the phosphorus also fulfils other tasks, in this case residual denitrification.