Graywater Solar Greenhouse

Working with the Land

Rather than spend about $15,000 on a standard septic system, Cindy Hale spent the same amount on an elegant advanced sewage system that produces flowers and vegetables year-round. Red clay underlies her farmstead 20 miles north of Duluth on the North Shore. A traditional septic system with drain field does not work in this geology, and she did not want to put in an above-ground "mound" system.
After doing some research she found Community Eco-design Network (CEN) of Minneapolis, who created the overall project design. The primary architect, Roald Gundersen, also worked on Biosphere 2 in Arizona.

The design plan uses a composting toilet for "blackwater." "Graywater" -- waste water from her shower, sinks and washing machine -- flows into a 300-gallon below-ground holding tank that supplies water and a few nutrients to six 3' x 9' foot raised beds in a 36' x 10' detached greenhouse. During the summer, rainwater is harvested from the greenhouse roof and stored in two 3' x 9' above-ground tanks in the greenhouse. The rainwater tanks are used for supplemental summer watering and store water during the winter to even out temperature swings.

A "water wall" system sends water from the rainwater tanks down grooves in the inside north metal wall to cool and dehumidify the greenhouse in summer, and warm the greenhouse during winter nights. Water is distributed subsurface to the growing beds via 4" perforated drain tile lines.

A Great Greenhouse

During the past two years flowers and vegetables have grown year-round with heat from the sun, heat from the graywater, and virtually no other heat source. Cindy plans to use insulated curtains for the greenhouse windows during winter nights to eliminate the occasional supplemental heating. During the first year Cindy had to experiment to determine what plants could grow when so as to use all the incoming graywater.

The greenhouse is built with "off-the-shelf" non-toxic materials and heavily insulated on its north sidewith straw bales and by 3' high soil berms around the entire foundation, which are great outdoorgardening locations. A pre-fabricated, lightweight concrete I-beam was used for a foundation, to hold heat and to make the frames for the growing beds and rainwater tanks. The cost for labor and materials was $24.62/sq. ft. A county permit for an experimental septic system was required.

Cindy feels fortunate to have discovered an economical and efficient system to run her greenhouse while utilizing available gray water and runoff from her home.