How It Works: Composting Toilet

System Purpose.  Receive and recycle humanure.

How It Works Summary.  Sawdust covered humanure hauled in buckets to outdoor bin and composted for two years before applying to garden.   All details can be found in Joseph Jenkin’s Humanure Handbook.

System Cost.  $1,000 including installation.  Our less elegant first model, used in the shed before the house was built, cost $100.  No major replacement costs.

System Components

Toilet like any other toilet, except ours is elegantly constructed of cherry and deploys a bucket rather than a watery bowl to receive humanure. 

Sawdust, the “water” of the composting toilet, minimizes odor and unsightliness, while adding valuable compostable material.   With a couple scoops, we “flush” with sawdust rather than clean water.  “Cover Your Stuff” says the butterfly adorning the attached sawdust bin.   This bin holds 15 gallons of sawdust which we obtain from an artist friend who turns beautiful wooden bowls and didn’t know what to do with all his sawdust until we came along.  Since running out of sawdust is the only failure mode (and a very serious one at that), we try to keep a 30 gallon barrel full at all times.    If the sawdust is too dry it generates dust when scooped.  To avoid dust we mix in a little water before filling the sawdust bin.  In theory, any scoop-able and compostable material could be used. 

5 gallon buckets for collecting, storing and transporting the sawdust-covered humanure.   The bucket replaces the toilet bowl , drain pipes and miles of sewer pipe of the conventional toilet system.  One bucket fits snugly beneath the toilet seat and is replaced with a clean bucket when full.    To replace the full bucket, simply lift the hinged top of the toilet, remove full bucket, replace with empty bucket and close.  Our black buckets hide the “skid” marks.    When four full buckets accumulate in the garage, we carry to compost bin where they are dumped, scrubbed, rinsed and dried.  Thus the sawdust toilet system does require two gallons of water per week for cleaning buckets.  We collect this water off the shed roof.  A standard toilet brush works well for scrubbing buckets followed by a spray bottle rinse.   Rinsed buckets hang upside down in the sun to dry.  The now clean buckets are lined with dried grass (to reduce splatter and ease dumping) then returned to the garage to await use in the toilet.

Compost Bin capable of processing two years worth of humanure.    The compost bin, which we call the "hacienda", replaces the sewage treatment facility of the conventional toilet system.  Our two-bin system requires no turning.   Bin size depends on number of people generating humanure and length of non-composting season (cold winter).  Our bins measures 5’ x 5’, easily large enough to process and store one year’s worth of humanure for our family of two in cold climate Minnesota.     The center bin stores straw and hay for covering the compost.   The cover minimizes odor and flies, while permitting vital oxygen to enter the composting process.   A bin is used for a year, then allowed to rest  for a year before emptying onto garden and used again.  The amount of garden compost produced is always less than hoped, perhaps only 10 cubic feet per year per humanure generator.   

System Maintenance.  Replace full bucket with empty bucket (1 bucket per person every 4 days).   Clean full buckets (Every four buckets seems about right).   Fill sawdust bin (every 3 weeks or so).   Obtain sawdust (as needed).   Empty compost onto garden (once per year). 

Report Card.   A / B+   (See blog post for details).

Biggest Challenge.  Big parties.  We rented a portable toilet for our Grand Opening Celebration to service 120. 

Biggest success factor.  Courage.  The composting toilet system is, by far, our most controversial alternative system.   The other systems ask little of a visitor.  Everyone gets used to it.  Eventually they may even appreciate the only toilet that never plugs, never leaks, is much less odiferous than a two year old’s diaper, keeps pharmaceuticals out of our lakes and streams, and feeds raspberries.

The Connection.    How better to “see” the cycle of life, death and life-renewed?  From food to you to food again.