The Greensgrow Solar Composting Toilet

We all have to go sometimes...And what to do when there's no "flush"....

The Project

In early 2009, Greensgrow was excited to expand its sustainability features with the addition of a solar composting toilet for the main farm.

The farm lacked basic toilet facilities for staff and customers, and this new addition adds an essential amenity to our operation.

Used for centuries throughout the world, composting toilets are simple, yet 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 "humanure" into a finished sanitary product free of pathogens and bacteria.

Each tub, or batch, takes about 6 months to fully cure and break down, at which point the finished compost can be used as fertilizer for our flower beds. When properly used, composting toilets are odor and insect-free, and are a fantastic and more sustainable alternative to conventional plumbing.

The Process

To begin a composting tub, or batch, we begin with a 1 inch layer of finished compost or soil to introduce worms and other beneficial organisms into the mix.

After each "deposit" of human waste, a fine 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 "curing".

For the next month or two, solar energy from the sun is used to keep the batch warm to facilitate microbial activity in the pile.

At the end of the curing time, the end product is a homogenous and pathogen-free dry compost that does not in any way resemble the beginning product.

This finished product is safe for fertilizing any non-edible crops.