Direct recycling of human hygiene water into hydroponic plant growth systems

Direct recycling of gray water (human hygiene water) through plant production systems would reduce the need for additional space, mass, and energy for water reclamation in Advanced Life Support (ALS) systems. A plant production system designed to produce 25% of crew food needs could theoretically purify enough water through transpiration for 100% of crew water requirements. This scenario was tested through additions of shower and laundry water to recirculating hydroponic systems containing either wheat or soybean. Surfactant (Igepon TC-42) did not accumulate in the systems, and both the rate of surfactant disappearance and the proportion of Igepon-degrading microorganisms on the plant roots increased with time. A mechanism of surfactant degradation via the microbially ally mediated hydrolysis of the amide linkage and subsequent breakdown of fatty acid components is proposed. Fecal coliforms present in the human gray water were not detectable on the plant roots, indicating that human-associated microorganisms do not grow in the system. Overall plant growth was unaffected by gray water additions, although preliminary evidence suggests that reproduction may be inhibited.