CAPACITY EXPANSION FOR REGIONAL WASTE-WATER SYSTEMS

A simple yet effective approach is presented for solving regional wastewater treatment system capacity expansion problems. The approach decomposes a model into two levels, upper and lower. The lower level treats the subproblems related to separate facilities of a regional treatment system. These subproblems are solved independently by dynamic programming. The upper level is used to coordinate the sub-problems in the lower level and is updated using a random polyhedron search algorithm that identifies progressively superior solutions. Constraints imposed on treatment plant or transfer capacities are considered first, and then constraints relating to the in-stream quality of the receiving water are incorporated. The procedures developed are tested in a hypothetical problem with seven communities along a river and its tributary. The results obtained indicate that it is economically attractive to consider time-staging of capacity whenever possible. It is also observed that the model with in-stream quality constraints required more computational resources, the amount of which is somewhat dependent on the level of in-stream quality requirement imposed. However, the incremental computational efforts required might not be excessive. © ASCE.