Jl. Garland et al., Graywater processing in recirculating hydroponic systems: Phytotoxicity, surfactant degradation, and bacterial dynamics, WATER RES, 34(12), 2000, pp. 3075-3086
Incorporation of human hygiene water (graywater) into hydroponic plant prod
uction systems, and subsequent recovery of the water transpired by the plan
ts, is one potential means for water purification and recycling in bioregen
erative life support systems under development for long duration space miss
ions. Surfactant phytotoxicity and the potential for growth of human-associ
ated microorganisms were assessed in studies of wheat and lettuce in contro
lled environmental chambers to provide baseline information for future stud
ies with actual graywater streams. Igepon TC-42 (sodium N-coconut acid-N-me
thyl taurate), a surfactant designated for use on the International Space S
tation and a common ingredient of soaps and detergents, was added to plant
systems in three different modes: (1) pulse addition of 875 mg m(-2) growin
g area once a day, (2) continuous addition of 875 mg m(-2) over the course
of a day, and (3) variable addition of 0-3000 mg m(-2) d(-1) based on plant
water demand. The survival of three human-associated bacteria (Escherichia
coli, Staphylococcus aureus, and Pseudomonas aeruginosa) in the plant nutr
ient delivery systems were monitored following introduction 6 (wheat) or 3
(lettuce) days after planting (DAP). Igepon rapidly disappeared (i.e., a ha
lf-life of less than 1 h) following an initial adaptation period lasting le
ss than 2 days. Microbial degradation of Igepon was supported by appearance
of the degradation intermediate methyl taurine and an increase in the numb
ers of bacteria able to grow on media containing Igepon as the sole carbon
source in the Igepon treated systems relative to the control. Wheat growth
was not significantly affected by any of the Igepon treatments, but lettuce
yield was significantly reduced in the pulse and continuous treatments. E.
coli and S. aureus decreased below detection limits within 3-5 days within
the systems, but P. aeruginosa persisted in the rhizosphere, nutrient solu
tion, and nutrient delivery system biofilm for the duration of the wheat (7
0-day) and lettuce (28-day) experiments. (C) 2000 Elsevier Science Ltd. All
rights reserved.