Introduction for prospective compost toilet installers/makers/purchasers

Trev Miller

1-2-2016 ed.1.2 html/pdf 7-3-2016/22-4-2016


Compost toilets come in a wide spectrum of forms: from little more than "appointed places" with a platform to perch in a field... And maybe even some privacy or protection from the weather!...to extensively engineered, proven, mass-produced systems that would grace any residence. A compost toilet has provision for the removal of the accumulated material, often for horticultural use. A simple pit-toilet is *not* a compost toilet, nor is any system which uses a water supply to store or transport the contents. A finer distinction also exists between usually large, dual-chambered compost toilets in which the entire decomposition process takes place, and more compact toilets which only begin the decompostion process before it is continued elsewhere.

Consider the important criteria that apply to *all* human toilet systems:

Specifically for all *compost* toilet designs:

Types of compost toilet.

Some of the constraints that shape the design of compost toilets.

This constructor's range of designs.

It is not practical for a small producer to offer a wide range of very different systems, so I have concentrated on one particular design I consider most matched in ease of installation and maintenance to local DIY single-households. The system offered here is: 1] -constructed using only low-environmental-impact materials - recycled in some cases - and assembled by local labour. Environmentally costly or risky materials - such as PVC - are reduced or avoided, as are timbers of unspecified origin. 2] -designed and evolved by an artist-engineer, who has used this design out of preference since 2008. The system is self-contained, compact, modular, and may be used indoors, outdoors, or in mobile application. It allows no odours to escape to the internal environment, therefore attracting no vermin, also excluding them by means of screens on the ventilation. 3] -only for situations where they will be maintained by, or by arrangement by, the user. The constructor may be available to perform repairs and service to the structure of the system, but will not receive or handle material in the composting process. It is strongly advised that the systems are installed only at locations where the material collected may be stored, composted and used as fertiliser. 4] The products offered are of the **separator** type. There are numerous advantages to this design but also one significant disadvantage. Separator type means that the urine and feces are collected and stored separately. If the toilet is used carefully, they don't come into contact with each other. The main "con" of this design therefore, is that if a proportion of (potential) users cannot or will not pay some attention to position and aim while they are using the toilet, then the toilet will not function well, and will require excessive and inefficient remedial management. A few splashes of urine accidentally entering the solids collector through poor initial aim is not usually a problem, as long as the toilet is not used by people who do not aim at all. It is therefore unsuitable as the *only* toilet where frequent users are likely to be :

The advantages of the separator system:

Most normal, motivated adults have no problems in using the toilet, once they *understand* the concept Urine is effectively sterile when excreted, so if it can be collected without significant contamination with fecal organisms, can (at the discretion of the user) be sparingly used after a short fermentation on soils near parts of crops which may be consumed by humans. It may also be immediately applied to active compost heaps of sufficient size, to accelerate decomposition and improve the nutrient value of the vegetable compost. Urine accumulates significantly faster than feces, particularly if the toilet is regularly used only as a urinal (though this is not advised) but the urine is much easier to handle, in 25 litre drums, than the solids, and can be used much sooner, if required. Separation allows the feces volume to reduce by drying, if the toilet is used on average once a day or less, meaning that the period between changes of the solids bin is considerably extended. An 80L (traditional domestic) bin will typically last at least 6 months between changes if this is the case. The full solids bin may easily be removed from the toilet assembly and loaded onto a barrow or trolley by a normally fit, active adult. It will typically weigh 20-25kg. Thus no mechanisation or external labour will be required for maintenance in most private applications.

Further functional details of this specific separator system:

A small internal fan is required to keep a slightly lower pressure in the chamber. This prevents odours escaping into the room the chamber is located in, including while in use, prevents attraction of vermin to the chamber, and if used on a once-a-day basis or less, allows significant drying of the solids and extension of the period between collection vessel changes. The 3 Watt fan consumes less than £10 per annum of electricity if connected to the grid, or may be powered by a local renewable energy source. The fan vents into a stack, similar to that on a "wet" toilet, 3m or more above ground level. During very still weather conditions, especially when very warm, a slight "farmyard" smell may be detected in the vicinity of the vent pipe - however it *does not* smell like raw sewage or feces. No additions of any material to the chamber are required, maximising its operational time. Toilet paper may be added freely, consuming negligible volume. Sawdust may be added for cosmetic purposes if desired, but will substantially reduce the period between collector changes, and number of bins required. In a system used for a holiday-let, leveling and lightly covering with sawdust was recommended as part of the cleaning between user changes - typically weekly. When filled, the solids collector vessels are sealed and stored for approximately 6 months outside. This allows the most recent surface to decay to a state where vermin are no longer attracted to it. After this, the contents are mixed with a normal horticultural/garden compost heap containing plenty of fibrous material and allowed to continue decomposition. After a further 6-12 months, the result is indistinguishable from loam. The emptied bins are left open to weather for several weeks, then washed out and stored for re-use. A set of 3-5 bins is adequate for approx. once-daily use. There is a trade-off between the height at which the user is above the collection vessel, giving a sense of "separation" from the contents, and the convenience of access to the appliance and installation. In the specific design, this has evolved to a seat/squat height of approx. 30cm above the absolutely full collection vessel, with the collection vessel sunk 30cm into the floor and seat/squat height of 60cm. These may be adjusted slightly on a custom basis, if required. The constructor has built about 10 units of this design, all hand-made, advised on others made by their diy users, and grown abundant salads for several years on his own personal compost. If all users are aware of their own intestinal health and if the time for secondary and tertiary decomposition guidelines are followed, pathogens should not be an issue. Parasitic worm eggs are likely to present the only problem, and for this reason, cat or dog feces should not be placed in the toilet, but in any case would constitute a smaller risk than the animal defecating directly on the beds to which the compost is eventually applied. If the toilet is to be used by children who may carry threadworm, it is advised the compost be only used on crops whose edible parts are well above the ground - eg. fruit trees and bushes.

Costs and construction:

So far, all have all been built in situ, but this is may not be necessary. Some have been for internal use in bath/shower rooms, which were built at the same time; others were installed in modified garden shed kits, others for festival use in a tent; at the time of writing, one is being constructed for fitting within a highly-specified camper van. Photos may be attached. Site visits to existing installations can be arranged. All completed units have good user satisfaction reports and no unsolved technical issues. The costs of the system are as follows: End of document.