Composting toilet

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As we planned the renovation of the house on the property that we purchased in El Ocotal, Yuscarán, El Paraíso, Honduras, we searched online for ideas that would reduce our ecological footprint.  It turned out to be a great exercise in learning by doing in which we made many mistakes along the way but which, in the end, we found to be very satisfying. 

Since we depend on stored rainwater from the roof, it was imperative that we conserve water.  And since we also have an orchard in which we are trying to restore badly degraded soil, a composting toilet seemed like a good option for us.  After reviewing the abundant online literature on composting toilets, we opted for a modification of the Clivus Minimus design, adapted to our own needs.  This toilet is now in its fifteenth year of use, and we are very pleased with it.

The toilet seat in the bathroom is at the top of a chamber made of ferrocement.  The compost chamber extends through the wall of the bathroom.  Its bottom is a smooth concrete slab inclined at a 30-degree angle and painted with an epoxy sealer. 

 To separate the urine from the feces, there is a ferrocement bowl, also painted with epoxy sealer, at the top front of the toilet.

There is a 6-inch diameter chimney that ventilates the top of the chamber to the outside. 

For the first two weeks that we used the toilet, the odors in the bathroom were so bad, we thought that our effort and investment were a terrible mistake.  I sprinkled a couple of cups of soil dug up from the nearby forest over the top of the waste, and like magic, within a couple of days the bad odors disappeared, and we haven’t been troubled with them since. 

After each urination, the urinal is rinsed with a brief spray of water, which then flows into the drainage system, where it is diluted by all the water from the other drains. 

After each bowel movement, a cup of pine sawdust is sprinkled over the solids.  The toilet paper is thrown directly into the toilet.  We experimented with different additives before settling on sawdust.  Kitchen waste and garden waste did not reduce the odors and tended to attract flies.

At the lower end of the composting chamber there is a door that allows access to the finished compost.  The openings to the ventilation pipes are covered with screen to keep out vermin.  To prevent the accumulation of water, there is a drain in the bottom of the collection chamber that drains into the house drainage system.

Above it on the lower wall of the chamber there is a small door to allow inspection of the contents of the chamber.  

As they accumulate, the solids slide slowly downward, decomposing as they go.  In our experience, it takes about two years from the time of deposit for the solids to reach the bottom of the collection chamber. 

The finished compost is dry and crumbly with an earthy odor.  We remove some once a year to fertilize our fruit trees and ornamentals. 

For good decomposition, it is important to maintain the moisture at the proper level—moist but not wet.  During the dry season, it may be necessary to spray water over the top of the compost from time to time.  Good aeration is also important to sustain aerobic microorganisms rather than anaerobic ones that produce unpleasant odors.  At first, we used the inspection port to stir the compost, but several insect species invaded and began to colonize the compost, and they turned out to be great helpers, turning the compost as they feed and helping to aerate it, making unnecessary for us to stir it. 

Black soldier fly adult

One of the helpful species is Hermetia illucens, the Black Soldier Fly.  Its larvae colonize the fresh waste, mixing it with the sawdust and toilet paper as they feed.  Occasionally it becomes a bit of a nuisance when some of the pre-pupae crawl out of the toilet in search of a place to pupate.

Soldier fly pre-pupa

Darkling beetle adult

Another of the helpful species is Zophobas morio, the darkling beetle, whose larva is called the Superworm.  It tends to colonize the drier, partially decomposed waste, complementing the soldier fly larvae and further stirring and aerating the compost.

Superworm