The battle of the water networks (BWN-II): Padds based solution approach

The three objective BWN-II problem was solved using a multi-stage approach. Stage 1 consisted of identifying a feasible solution to the problem under nominal conditions (no power failure). Based on Stage 1 results, a total of 23 modifications to the network were defined as decision variables for Stage 2 of the design process which utilized a multi-objective optimization algorithm (Pareto- Archived Dynamically Dimensioned Search, PADDS). The non-dominated solutions from Stage 2 were then polished with another stage of optimization (Stage 3), where 49 new decision variables to adjust the pumping schedule were optimized with PADDS. The new non-dominated solutions after Stage 3 were then evaluated in the power failure scenarios to determine what pumps should be backed up by diesel generators Stage 4. Finally, Stage 5 involved selecting one of the remaining 159 non-dominated feasible solutions. Based on a total of 20,000 designs enumerated by PADDS, the eventual solution selected for the design has costs, greenhouse gas emissions and water age objectives equal to $356,368, 1,922,532 kg CO2-e/year and 0.15, respectively.