Recent advances in simultaneous saline wastewater treatment and methane storage: A review

Water recovery and reuse are crucial strategies for addressing water scarcity and environmental pollution. Conventional wastewater treatment relies on pollutant removal or degradation; however, it often involves complex unit operations and high energy demand, with limited water recovery. Leveraging the unique structure and physicochemical properties of hydrate crystals, hydrate-based water treatment technologies enable direct extraction and reuse of water molecules through solid-liquid phase transitions, garnering increasing attention. Concurrently, hydrate-based methane storage offers distinctive advantages, including elevated storage capacity, moderate storage and transportation conditions, straightforward release mechanisms, and cost-effectiveness. Building upon this foundation, a dual-purpose strategy emerged, utilizing methane gas to form hydrates with water molecules in saline wastewater. Simple solid-liquid separation then isolates the hydrates from the wastewater. The subsequent decomposition of methane hydrates yields methane gas and pure water, achieving both water purification and recovery, as well as methane storage and release. The nucleation and growth process of hydrates, the exclusion of pollutants via crystal phase transitions, the slow growth kinetics of hydrates, and the difficulties associated with separating solids from liquids after formation have all limited the use of hydrate methods in wastewater treatment. This article provides a comprehensive overview of the application of the hydrate method in gas storage and treatment of saline wastewater, including the utilization of pure methane hydrates, thermodynamic and kinetic promoters, and the key role of porous media in the formation and decomposition of methane hydrates. This review offers valuable insights for practitioners engaged in methane storage and saline wastewater treatment.