Simulation of hydrodynamics and contaminant transport in artificial wetlands for partial gravity applications

Abstract

Wastewater treatment and reuse are vital for sustainability on Earth, and now that long-duration space missions are being planned, developing compact, self-sufficient wastewater treatment systems is a pertinent challenge. This study explores the conceptual feasibility and simulation of a bioregenerative life support system (BLSS) based on a vertical flow constructed wetland (VFCW) for treating highly concentrated wastewater (up to 3000 mg/L COD), including solid waste, under partial gravity. Using the HYDRUS-2D model with the CW2D module, the study simulates variably unsaturated water flow and reactive solute transport through sand and lunar regolith simulant beds in a VFCW, under Earth and lunar gravity. Results show that the low permeability and high air-entry suction of lunar regolith in partial gravity significantly reduce infiltration rates and dissolved oxygen availability, which limits treatment efficiency. However, an optimized intermittent feeding strategy with extended resting periods (10-day downtime) enabled the lunar regolith system to achieve up to 95% COD removal. Comparative analysis revealed that sand outperforms lunar regolith simulant in continuous feeding scenarios but accumulates more inert sludge. The findings suggest that substrate selection, hydraulic properties, and feeding strategy are more critical than gravity alone in determining treatment success. The study provides recommendations for using lunar resources to build and operate a VFCW to treat the waste from a 4-astronaut base and offers insights for minimizing the footprint of CW installations on Earth.