Terra-Loo : designing and building a portable composting toilet

Design challenge: Develop and implement a portable composting toilet, optimized for small-scale events, transportability, and sustainable product lifecycle.

Tools used: CAD (Rhino), graphic design (Adobe), Textile design, Business planning, metal and wood fabrication.

I spent a year on an organic family farm in rural France, living in a yurt without internet or phone. There I was introduced to the practical eco-agro technology of composting toilets, which turn human waste into pathogen neutral soil amendment by means of passive thermal composting. By the time I returned home to coastal California, I had decided to try to bring this resource-conscious technology to the public fore by starting a portable composting toilet project. We have all used the prototypical porta-potty, and it is always brutal (*for a deeper explanation of composting toilets, and a comparison with conventional portable toilets, please see the bottom of this page). My objective was to create a better user experience — light, odor free, visually unoffensive — that was also educational and thought-provoking about what is “waste”. The project was dubbed Terra-Loo.

The logo and graphics were designed by hand to have a natural feel, and prepared in the Adobe Suite. Here is the principal logo:

The portable toilet itself consisted principally of three parts: the pallet-compatible and one-person manageable frame; a weather-resistant organic canvas covering (itself eventually compostable); the toilet-urinal unit itself.

Prototype. Hand-built, hand-sewn, hand-welded (with human for scale)

The fastener-free frame was designed in Rhino and welded in Oakland, CA.

CAD drawing of frame

The fabric covering was hand-sewn by myself, which I really enjoyed doing.

Designing the toilets turned out to be the easier part. Getting regulatory approval to pilot a new, unaddressed technology in California was the real challenge and ultimately my applications to do such were denied. However, it was a great experience in design and business and bureaucracy, and I have plans to continue to work on this project later on in life as there are many iterations and ideas yet to be explored.

*When humans produce waste (urine and feces), this waste must go somewhere. In the developed world, this usually means to a localized septic tank or to a centralized wastewater treatment facility, where the waste is processed before being released either into waterways as semi-neutralized effluents or as biosolids sludge deposited on farmland or in landfills. When it comes to portable toilets — like the ones seen at construction sites, music festivals, etc. — the waste, held in the toilet in a pool of sanitary chemicals, is emptied from the toilet into a truck, and then deposited at a wastewater treatment facility. The ecological consequences and challenges of such treatment are dubious at best and possibly disastrous for both human health and the natural environment at large.

Ecological questions aside, the typical chemical-based portable toilet presents another issue : an unpleasant user experience. Portable toilets are often foul-smelling and the accumulation of chemicals and waste in the holding tank is unsightly.

There is a solution, on all fronts : composting toilets. A composting toilet is any kind of toilet that prepares human waste to be composted (degraded in a semi-controlled environment by microbial flora and fauna) so that it becomes decomposed, pathogen-neutral organic matter, ready to be reincorpotated back into the soil-nutrient cycle. Some compost toilets do the composting directly in the toilet unit itself while others simply hold or prepare the waste in some way before it is taken to be composted elsewhere. For operating a composting toilet rental business, the best option seems to be a variation of this latter system, namely a biolitter toilet. A biolitter toilet, or BLT, works by covering the humanure with a carbonaceous material such as sawdust or woodchips, after each use. This not only helps to eliminate odors by inhibiting enzymes in urine from digesting nitrogen into ammonia and by limiting methane-producing anaerobic bacterial activity, it also eliminates the problem of unsightliness common in portable toilets — the only thing a new user will see in the receptacle is a layer of woody material, a far-cry from the soggy, chemical-blue pyramidal mass in the tank of a conventional portable toilet. When a BLT receptacle is full, it can be removed and replaced and the mix of carbonaceous material, nitrogen-rich humanure, and moisture is ready to be stored, transported, and deposited in an area suitable for proper composting.