Septic System

From Antivist

Composting Toilets

There are two basic types of compost toilet, those that complete the composting process 'in situ' and those that are emptied to a separate compost pile remote from the toilet itself. The latter arrangement is sometimes referred to colloquially as a "bucket and chuck it" system, like a "humanure bucket system". This means that faeces is deposited into a plastic container to which soak material such as straw, sawdust, dry grass, etc, is added in order to absorb excess liquid, cover human waste materials, exclude flies, reduce smells and balance Carbon:Nitrogen ratios. When full, the bucket is removed and emptied onto a composting pile that is kept separate from other composting materials such as kitchen or garden waste.

Some composting toilets use electricity, while others do not. Some electrical systems use fans to exhaust air and increase microbial activity. Other systems require the user to rotate a composting drum or otherwise stir the composting humanure from time to time.

Some composting toilets are large with a significant space requirement in the room below the toilet. Others are not significantly larger than a traditional toilet. Those small systems generally do not claim to finish the composting on-site, but are preparing the human waste materials for secondary composting in another location (like a compost pile).

All composting toilets eventually need some end product removal. A full size composting toilet does not need to have solids removed for several decades if the active tank volume is at least three times the yearly addition. This is due to the dramatic reduction in volume over time -- after around 5 years only 1-2% of the original volume remains. It is then a mineralized soil which will not decompose any further. other smaller type systems need to remove solids several times a year.

A related device, though only by its stand-alone use and not for its sustainability, is the incinerating toilet, which uses natural gas or propane to reduce the waste material to ash in a process similar to a self


'DIY' compost toilet systems

Far more simple and basic DIY systems can also be constructed that require very little cost or maintenance, provided that attention is paid to a number of important factors. The toilet must control odors. This is achieved by ensuring adequate ventilation (sometimes simply by leaving a small gap between the top of the wall and the roof, more sophisticated systems may incorporate some kind of low voltage extractor fan). Odors can also be controlled by either ensuring that urine and faeces are kept separate or by adding sufficient high carbon content 'soak' material (see below) to absorb excess liquid. The design of the composting toilet should allow the material to remain aerated to prevent the compost from becoming anaerobic, which can result in unpleasant odors. It must also either heat the faeces to the point that pathogens are destroyed (a thermophilic process), or else allow sufficient time (up to a year) for such pathogens to break down and disappear naturally (a mesophilic process). The upside however is that they do not use any significant amount of water and they may produce fertilizer safe for small scale agricultural use.

Another variant is the Tree bog - a form of compost toilet which has willows, nettles and other nutrient-hungry plants planted around it. The faeces are held in a chamber open to the air which allows it to decompose rapidly, feeding the trees around it. Unlike a conventional compost toilet, a tree bog should never need emptying. Effectively, it is a system for converting human faeces to biomass.

Tree Bog

A Treebog is simply a controlled compost heap whose function has been enhanced by conscious management and the judicious use of moisture/nutrient-hungry trees. Treebogs use no water, purify waste as they create willow as a biomass resource, and also contain the organic waste, thus preventing the spread of disease - all whilst creating soil. A seating platform/cubicle is mounted at least one meter over an aerobic compost heap. The area beneath the seating platform should be enclosed by a double-layer of chicken wire - this acts as an effective rodent/small animal and child proof barrier, but allows air to circulate through the compost heap.

The space between the wire should be stuffed not too densely with straw which acts as a wick to help sop up excess urine preventing the likelihood of odour problems due to incomplete biological absorption of the nitrogen from the urine. The straw filled wire also enables the pile to be well-aerated whilst acting as a visual screen for the first year�s use. The structure is then surrounded by two closely planted rows of osier or biomass willow cuttings; this living wall of willow can then be woven into a hurdle-like structure and its annual growth can be harvested.

Treebogs can also be sited on the edge of existing stands of trees, woodlands or hedges: the mature tree roots will soon find the additional source of nutrients, so that the willow may be unnecessary, - or indeed, in the middle of a mature woodland, pretty well impossible due to shading.

The Treebog combines resource production and waste purification. The Treebog functions by transforming faeces and urine into growing trees and organic soil. The roots of the trees are host to soil micro-organisms which decompose and mineralise the materials in the compost heap, making the nutrients available to the tree roots. Thus the willow are able to grow more vigorously as these added nutrients become available.

Inputs, Costs and Maintenance

There are few costs apart from initial construction and planting. Under heavy usage it is advisable, once a week, to add a fine layer of non-chemically treated wood sawdust/wood chips, shredded newspaper or straw. Half a cup of dried soil and/or wood ash helps prevent odour if added every other day. It is also advisable to occasionally level the heap with a pole.


Benefits include:

  • Purification of waste without using water.
  • Soil is both generated & regenerated.
  • Earthworms proliferate within and around the compost contained within the Treebog.
  • Leaf mould from willow leaves.
  • Comfrey bed on leach field for nitrate/phosphate absorption.
  • Leaf matter and twigs for stock fodder.
  • No odour or fly problems.
  • Willow wands for baskets, fuel or structural use.

The Treebog is a simple and effective means of taking responsibility for wastes produced in your own day to day existence. It involves no secondary handling (shovelling or bucketing) of waste matter. Management is minimal, being an annual winter cutting and weaving of the willow. The wands can be used as polewood, for basket or hurdle making, or chipped for use for animal bedding or cut and bundled as fagots to use as fuelwood.

Building your own Treebog

To create a Treebog with adequate volumetric capacity for domestic, year round use it is best to allow a minimum of at least 0.75m3/person/year. For annual events the minimum number of Treebogs required should be at least one Treebog/200 people/day: the overall volume of the Treebogs should be based on 350g per person per day. (Assume 1 tonne of faeces has a volume of 1m3.) Do not site your Treebog closer than 10m to a watercourse or spring and always provide handwashing facilities close by.

If you do not know what the soil/subsoil profile is in the area where the Treebog is to be situated, speak to people who are familiar with it, or dig a trial pit and if possible do a percolation test by filling this pit with water and seeing how long it takes for this to drain (percolate) away. The type of structure that can be built to house the Treebog is limited only by imagination. As a DIY project or the result of a professional carpenter�s labour a Treebog can look like a tent, a bender on stilts, a shed, gazebo or fanciful folly. Rainwater from the Treebog�s roof can be collected in a water butt for handwashing.

The Treebog can be created over a number of years to include a living, growing willow framework and surrounded with a range of fragrant perennial flowers (e.g. sweet rocket) and herbs (e.g. lemon balm). Current interest in living willow sculpture is inspiring the use of woven willow wands to create a living hurdle around the platform, which can also be covered with climbers (e.g. honeysuckle) to create a dense screen of foliage.

When planting the willow around the Treebog any existing vegetation, such as grasses, whose roots would compete with the willow sets, should be cut back and thoroughly mulched - either with black polyethylene sheet (silotop) or multiple layers of newspaper covered with straw. This will ensure rapid rooting of the willow in the first growing season which will be of benefit to the composting processes as well as giving maximum growth which will act as an effective visual screen for the platform.

Guidelines for building a Treebog

A seating platform/cubicle is mounted at least 1m over an aerobic compost heap... the rest is up to you. There is no one method; the chosen structure is often dependent on the materials and budget available; each builder is free to interpret the basic Treebog principles in their own way. For example, a summer camp Treebog will differ from an all year round domestic version.


The Treebog must be sited where the surrounding willow and other planted species will have plenty of sunlight otherwise photosynthesis will be limited and the plants will not thrive. To keep the Environment Agency happy Treebogs should always be situated more than 10m from any water courses or springs. Treebogs should not be located where the site is liable to flooding, and if placed close to a badger sett the Treebog must be badger proof or the contents will be snaffled away by these inquisitive creatures! Fencing may also be required to prevent livestock from eating the willows and other planted species.

Willow planting

Although not a requirement for an effective Treebog we would recommend that, ideally, the willow wands be planted at least one growing season prior to the Treebog being used for the first time. This is so that the willow roots are mature and the wands have grown up to a reasonable height before the platform is constructed - as the platform shadow can hinder the growth of the planted willow sets on the shade side.

The best time to plant out the willow for a Treebog (in the northern hemisphere) is from October to March, as then the willow has a chance to get established before the onset of summer. However it is possible to construct and use a Treebog at any time and then plant it out at the appropriate time of year. The straw mentioned in the information sheet will act as the visual screen for the compost pile until the willow is in place and growing. Unrooted willow sets/cuttings should be of a vigorous variety, and if they are planted out after the middle of April they should be well mulched and watered every day for the first month or they will not take (i.e. the roots will not develop and they will wither away). If possible use named osier or biomass types since these will grow vigorously and can tolerate the annual coppicing as well as being suited for use in basketry and hurdle making. If you are gathering local wild osier or other willow to plant your Treebog, use willow that has been coppiced or pollarded recently, because young wood makes the best cuttings.

Willow management

The willow can be coppiced annually or left to grow for more than one year, though you will find it grows quite large. Cut the willow between November and early March and don't be afraid to cut it right down to the ground or to the top of your living woven willow hurdle - as long as it is not smothered with weeds and has sufficient sunlight it will regrow vigorously, using the nutrients and moisture within the Treebog.


Sawdust is useful to aid the correct carbon-nitrogen ratio, but beware - some scatophobic campers have been known to fill an entire Treebog with sawdust, or straw, in just a few days - bucketing the stuff in to cover every trace of the poo! Use untreated sawdust only,in small quantities, or add a daily or weekly layer to the compost pile. Wood ash is helpful in keeping the compost pile sweet, but make sure all the embers have gone out and the ash is cold or you may end up with a Treebog bonfire! In normal use the pee drains away from the compost pile by gravity and soaks into the soil where it is rapidly broken down, but if large quantities of urine are entering your Treebog (perhaps because it is next to the beer tent!) you should consider separating the inputs - composting liquids and solids separately - e.g. a separate Treebog or simple straw urinal, for liquids only.

The 'gravity powered' separation of solids and liquids prevents the smells caused by the compost pile going anaerobic. The through-flow of air below the platform is also important as a boxed-in pile with no ventilation may well go anaerobic and start to pong.

Some Treeboggers have installed in their Treebog the urine separating system from a conventional compost toilet this enables pipework to take the urine directly to the planted willow and surrounding straw mulch and so the liquids and solids do not mix to any great degree - it is not clear if this is advantageous/necessary in that Treebogs, if well aerated, do not smell.

It is worth noting that any design used should prevent splashes of misdirected pee from soaking into wooden seating or seat support structures as this will decompose and cause a smell, a metal splash plate or plastic sheet pinned into place can prevent this from occurring.


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