FUZZY-SET APPROACH FOR OPTIMIZING SLUDGE APPLICATION LAND SELECTION

Cost and environmental protection are primary considerations when deve loping a land application scheme for wastewater sludge disposal. Altho ugh cost is not difficult to determine, environmental impact is much m ore difficult to assess. Currently, there is no established relationsh ip between the many environmental factors involved and the quality of the application site. This paper presents an approach in which fuzzy s ets and mathematical optimization are used in concert to develop and e valuate land application schedules for wastewater sludge. The six envi ronmental factors considered in this model are: soil pH, cation exchan ge capacity, soil percolation-rate, site slope, nitrogen-loading rate, and cadmium-loading rate. The optimization model is used to determine sites that are to be used for wastewater sludge application, and is d riven by overall cost considerations. Using fuzzy membership functions for each environmental factor. a collective belief in the application sites is determined. This belief reflects the level of confidence in using the chosen sites with regard to the safe application of wastewat er sludge.