Gray Water Recycling Directly Through Hydroponic Systems

Task Question/Justification:

Can water be recycled in an ALS system through direct incorporation of gray water into the hydroponic system and using plant uptake / transpiration as a method of producing clean water?


Recycling water used for personal hygiene will be necessary in a closed, space-based system. Incorporation of human hygiene water (gray water) into hydroponic plant production systems, and subsequent recovery of the water transpired by the plants, is one potential means for water purification and recycling. The use of plants, and the active microbial community associated with their roots, for water processing would eliminate the need for physical-chemical treatment or a bioreactor and the concomitant resupply of physical components, (i.e., filters, etc.). Volunteers showered and washed clothes with predetermined amounts of soap (igepon) and deionized water to provide gray water with an approximate soap concentration of 1000 ppm. Gray water was added daily (1.5 L) to 20 L hydroponic tanks supporting wheat and soybeans (separate experiments). Tanks contained a) no gray water (control), b) soapy water additions (igepon and water), c) filtered gray water (0.2 µm filter to remove bacteria and skin cells), (soybean study only) and d) unprocessed (raw) gray water. Both the hydroponic solutions and the rhizosphere were sampled for microbial composition to determine the survival of human-associated bacteria. The rate of soap degradation was assessed throughout the plant growth cycle. Plant material was harvested and fresh and dry mass were determined. Preliminary findings demonstrated that soap degradation rates increased as plant root mass, and associated rhizosphere microbial activity, increased. Sodium levels increased in all gray water treatments over time.

Why recycle gray water through hydroponic systems?

Experimental Objectives:

Evaluate the effects of directly recycling human hygiene water through recirculating hydroponic systems on

Experiments to date
(these are preliminary experiments and analyses are currently being completed):

Wheat and Potato (day 57) - at left, front two trays,
control, back two trays, synthetic gray water
  Wheat and Potato (day 57) - at left, raw gray water
(back two trays infected with Pythium fungus)
Soybean experiment (day 33) - at left, front two
trays, control, back two trays, synthetic gray water
  Soybean experiment (day 33) - back two trays,
filtered gray water, front two trays, raw gray water


What soap was used?

Gray water production:
  • laundry (wheat only) and shower water
  • gray water stored at 4 C for up to 2 days (soybean) or 7 days (wheat)
  • both experiments used daily additions of 1.5 L gray water to a 20 L hydroponic system supporting 0.5 m2 growing area
  • experiment based on system in which plant growth provides 25% of food requirement (10m2 /person), but receives 100% of gray water (25 L /person /day)

Plant Growth:





Sodium Accumulation:


Soap Degradation:


Microbial Responses:

Soap degraders


Total and respiring cell numbers


Human-associated bacteria



These are two preliminary gray water studies that have not yet had a chance to be replicated. From these studies, new experiments will be designed to better answer the questions that arose from gray water additions.

Author: Colleen Loader and Cheryl Mackowiak /Previously Dynamac International, Inc., Jay Garland, Lanfang Levine, Kim Cook, and Hollie Vivenzio /Dynamac International, Inc.
A service provided by the Biomedical Office, NASA/Kennedy Space Center: Dr. William Knott, Chief Scientist, Biological Programs.