Optimal Operation Strategy for Island Multi-Energy Microgrids Considering the Water-Energy Nexus of Wastewater Treatment and Desalination

Island regions face dual challenges of renewable energy accommodation and freshwater scarcity, severely constraining operational economy and reliability. However, existing research regards wastewater treatment and seawater desalination as isolated subsystems, overlooking the significant synergistic potential in their water-energy nexus. This paper proposes a novel optimal operation framework for standalone island multi-energy microgrids, constructing a water-energy coupled system that integrates wastewater treatment, seawater desalination, hydrogen electrolysis, methanation, and diversified energy storage. A hierarchical collaborative dynamic weighting mechanism is proposed to facilitate system coupling coordination. At the system macro-level, a Sigmoid-based adaptive strategy responds to real-time operating conditions by dynamically adjusting the weighting ratios of four-dimensional objectives; at the water system micro-level, the load allocation between wastewater treatment and seawater desalination is optimized through a continuous regulation mechanism. This method establishes a framework to maximize the coupling coordination between wastewater treatment and seawater desalination, fully exploiting the flexible load characteristics of water treatment facilities to mitigate renewable energy fluctuations. Simulation results from a case study validate the effectiveness of the proposed strategy; the method achieves collaborative and efficient system operation alongside water-energy security assurance and significantly reduces the total system operating cost by 76,259.14 CNY compared to traditional methods.