180 One of the principal technical constraints is the hydrochemical variability of mine waters, particularly their high salinity (30–60 g/dm³) and temporal fluctuations. For membranebased treatment systems, such variability necessitates the design of installations capable of operating over a wide range of pressures and flow rates. Salinity fluctuations of 20–30% may result in substantial changes in process efficiency and specific energy consumption. Under the assumed operating conditions, the energy demand of desalination processes is estimated at 2.5– 4.5 kWh per cubic meter of treated water, depending on feedwater composition and the selected NF/RO configuration. For an average flow of 10,000 m³/day, this corresponds to an annual electricity demand of approximately 20–25 GWh. These values confirm that mine water treatment systems remain energy-intensive even when supported by renewable energy integration. In this context, the methane capture and utilization module plays a critical systemstabilizing role. Assuming a capture potential of 0.5–2.0 million m³ CH₄ per year, the associated primary energy potential is approximately 5–20 GWh per year, depending on the efficiency of the cogeneration units. Even under conservative assumptions, this allows: ● coverage of approximately 10–40% of the water treatment system’s energy demand; ● reduction of peak electricity consumption from the external grid; ● significant mitigation of methane emissions, corresponding to several to tens of thousands of tonnes of CO₂ equivalent annually. Compared to photovoltaic generation, the methane module provides higher operational predictability and dispatchability, thereby serving as a balancing component during periods of reduced renewable energy output. From an economic perspective, capital expenditure constitutes a significant barrier to implementation. For a desalination facility with a capacity of 10,000 m³/day, investment costs may reach several tens of millions of euros, depending on the configuration of mineral recovery systems and auxiliary infrastructure. Photovoltaic installations of 5–10 MWp typically require investments in the range of 4–8 million euros, while methane capture and utilization systems involve additional dedicated infrastructure.
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