ABSTRACT
(Received May 31, 1988)
This article compares the two different approaches that are commonly used for modelling the optimal expansion of a wastewater treatment system, namely constant degree of treatment over time (approach 1) and varying degree of treatment over time (approach 2). The models formulated in these two different approaches are solved via dynamic programming techniques. The results of this study indicate that approach 1 yields an optimal cost that is significantly higher than that obtained from approach 2. However, approach 2 is found to call for a very frequent upgrading of the treatment facility. To assess the merit of having a very frequent expansion schedule, a setup cost is imposed on upgrading work. The result of this part of the study indicates that the optimal frequency of upgrading a treatment facility decreases drastically as the magnitude of the set up cost increases. Besides, it is also found that an optimal plan may call for more than one upgrading in spite of a very high setup cost being imposed.
