A Branch and Bound Method for use in planning regional wastewater treatment systems

Abstract

A branch and bound method is presented for evaluating alternative regional wastewater treatment systems, taking into account economies of scale in constructing treatment plants and interceptor sewers. A branch and bound tree is ‘grown’ by using an algorithm which is very efficient computationally because it uses a powerful inspection step and a network algorithm to solve subproblems. Each infeasible solution found by using the method is converted to a feasible regional configuration of plants and interceptors. The alternative plans can be compared to examine tradeoffs between cost and other qualitative and quantitative planning objectives. Also the tree itself can be extended to generate additional planning alternatives. Rather than to find mathematically optimal solutions, the principal uses of the method are to generate systematically attractive alternative plans and potentially to assist in evaluating tradeoffs between different planning objectives.