Fuzzy‐Set Approach for Optimizing Sludge Application Land Selection

Abstract

Cost and environmental protection are primary considerations when developing a land application scheme for wastewater sludge disposal. Although cost is not difficult to determine, environmental impact is much more difficult to assess. Currently, there is no established relationship between the many environmental factors involved and the quality of the application site. This paper presents an approach in which fuzzy sets and mathematical optimization are used in concert to develop and evaluate land application schedules for wastewater sludge. The six environmental factors considered in this model are: soil pH, cation exchange 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 driven 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 wastewater sludge.