Generating designs for wastewater systems

Optimization models have been used in the preliminary design of wastewater treatment systems to obtain a least cost design. However, this may not produce the best design if other unmodeled issues and incomplete information of the cost and performance data of the treatment processes are considered. Optimization models may be more useful in the design of wastewater treatment systems, if they can be used to generate “good" but “different" design alternatives for evaluation. A study was conducted to examine two modeling-to-generate-alternatives (MGA) methods (the generating and screening, G&S, method and the efficient random generation, ERG, method) for the purpose of generating good and different preliminary designs for a typical wastewater treatment system design problem. The results showed that various attractive designs, which are good with respect to the objectives specified but widely different with respect to the treatment processes, could be generated by the two MGA methods. In comparing the alternatives produced by the two methods with those derived from the original optimization model and a constraint method, it was found that the MGA methods were more effective for the development of various preliminary wastewater treatment system designs, which not only met minimal requirements but were also widely different from each other.