Multi-Objective Optimization Algorithm for Sewer Network Rehabilitation Using Life Cycle Cost Analysis and Semi-Markov Deterioration Models

Effective, budget-conscious renewal strategies that improve sewer network conditions and reduce the risk of pipe failure are essential for municipalities in order to maintain acceptable performance and service levels for their wastewater infrastructure assets. Developing such strategies is a challenging task because the wastewater system is a complex system that consists of many non-heterogeneous components. This complexity stems from the fact that the behaviors of these components are impacted by many external factors such as the asset deterioration process. The deterioration of wastewater assets creates significant risks to the surrounding environment due to infiltration and exfiltration processes, and the increased risk of their failure. This creates a pressing need for an accurate deterioration prediction model to forecast the current and future conditions of wastewater systems. Therefore, this paper proposes a multi-objective optimization approach for wastewater network rehabilitation that utilizes both a life-cycle analysis approach and a semi-Markov deterioration model. The main purpose of this model is to answer the following question: how and when should we intervene to optimize the allocation of the renewal budget—by maximizing the average network condition and minimizing the average risk of failure—that is subject to minimum condition limit, minimum risk of failure limit? And how do we prevent maximum from exceeding the available budget within the specified planning horizon?