Composting Toilet

In early 2009, Greensgrow Farms expanded our sustainability features with the addition of a solar composting toilet. Previously, the farm lacked basic toilet facilities for staff and customers. Used for centuries throughout the world, composting toilets are simple and effective devices for dealing with human waste in a way that saves water, reduces waste and provide a useful finished product.

The Greensgrow design is based off a model developed by Larry Warnberg and further improved by the Dunton Family Farm in Oregon that uses a small passive solar greenhouse to accelerate the process of breaking down the waste into a finished sanitary product free of pathogens and bacteria. Each tub, or batch, will take about 3 months to decompose, at which point the finished compost can be used as fertilizer for our flower beds. We cure our compost for an additional 9 months to ensure complete digestion.

When properly used, composting toilets are odor and insect-free, and are a fantastic and more sustainable alternative to conventional plumbing. The end product is a homogenous and pathogen-free dry compost that does not in any way resemble the beginning product.

The Process

  • To begin a composting tub, or batch, we begin with a 4 inch layer of straw, finished compost and/or soil to introduce worms and other beneficial organisms into the mix.
  • After each “deposit” of human waste, a layer of wood shavings is added to the pile to cover the waste and balance the added nitrogen with an easily-digestible carbon source. The sawdust also helps to keep moisture – and therefore odor – minimized.
  • When the tub is full, a finish layer of sawdust and/or compost is added to the top and the lid is attached, and the batch is moved to the back of the chamber into the greenhouse for decomposition.
  • For the next three months, solar energy from the sun is used to keep the batch warm to facilitate microbial activity in the pile.
  • At the end of the initial composting period, the batch is transferred to an open “curing” bin for at least a year before being used for non-edible crops.