How Composting Toilets work

How composting toilets work

Composting toilets provide a hygenic method of recycling human waste. They avoid the need to waste and pollute precious water.

The waste is collected in a small chamber directly beneath the toilet pedestal. A low-powered 12 volt electric fan continually circulates air through the composting chamber, evaporating liquids, speeding the composting process and eliminating odours.

The working principle of Nature Loo batch-type composting toilets

The batch-process Nature Loo models come with at least two composting chambers. Fill one, put it aside to continue composting, and put the second chamber into use. When it’s time to change chambers again, the contents of the first chamber should be well and truly composted. You then remove the compost, put it on your garden or bury it, and re-use the cleaned chamber.

The modular Nature Loo batch system means that capacity is virtually unlimited. If usage increases, buy an additional chamber and rotate the chambers more often.

The continuous process toilet, the Sun-mar Excel, completes the composting process in situ. Once finished, the humus is removed from the tray at the base of the unit and disposed of, as per the batch process models.

Good composting is achieved by ensuring correct levels of moisture, oxygen, temperature and carbon/nitrogen ratio. All Nature Loo systems use the same type of ventilation and drainage to take away excess liquids from solids and provide adequate oxygen. Warmth is developed inside the pile itself and by exposure of the chamber to direct sunlight, or in the case of the Sun-mar Excel, by a heating element. Carbon-rich mulch is added when necessary, to develop the correct carbon to nitrogen balance.

Keeping your Nature Loo clean and fresh is incredibly simple. Every so often, just as with a conventional flush toilet, you might need to give it a scrub with a toilet brush. When you do, use a biodegradable detergent, vinegar solution, or better still use Nature-Flush enzymes.

The Nature Loo system is completely free of chemicals and odours.


Even a complete novice can install a Nature Loo in about half a day.

All you need is a clearance of 750mm for the Classic 650 and around one metre beneath your toilet room for the larger Classic 750 model. In the cases of using the self-contained single units, the Excel & the Compact, the entire unit sits directly on the slab floor.

You can place an upstairs unit almost anywhere you want, completely independent of your downstairs unit. Some manufacturers of composting toilets have systems which allow two pedestals to feed into one chamber. Whilst this is cost effective it limits the design of the house to back to back toilet pedestals. With a Nature Loo you are free to locate the second loo wherever you want it. We also offer discounts on second units destined for the same home.

A Nature Loo does not need to be installed on the north side of a home because all chambers eventually get exposed to direct sunlight, once full.


The moisture content of a compost pile is very important. Below 40%, the organic matter will tend to dry out and not decompose rapidly. Over about 60%, not enough air can get into the pile, and it can become anaerobic {no oxygen}, and may smell.

A moisture content of approximately 50% is ideal for composting. Nature-Loo reduces the naturally high moisture content of human waste by separating the escess liquid waste from the solid waste by displacing it through a perforated floor into the liquid chamber. This prevents the process from becoming anaerobic.

Subsequently when the chamber is full and left to stand in the sun, no additional liquid is being added and the moisture content falls rapidly. Direct exposure to sunlight further reduces the moisture level. Unlike most other commercial composting toilets, with Nature Loo there is no requirement to only position the toilet on the sunny side of the building.

With the Excel in normal use, the thermostatically controlled heater and fan evaporate all excess liquid.


Micro-organisms that require oxygen to survive are called aerobes. Organic materials are decomposed most rapidly by aerobes ~ much more rapidly than the anaerobes used in septic systems.

Aerobes need many cubic metres of oxygen per day for rapid breakdown. A small ventilation fan in the Nature Loo provides up to 420 litres of air per minute, more than enough to keep the process going at optimum levels. This has the added advantage of acting as a highly efficient extractor fan to remove any rising odours from the toilet room.


The heat coming from piles of organic material is generated by the feeding and multiplication of millions of microorganisms. Technically, the stage of the temperature cycle below 40 °C is termed mesophilic, above 40 °C is thermophilic.

Composting is most rapid in the thermophilic stage. As the temperature rises over 40 °C, mesophilic organisms die out and are replaced by an upsurge in the population of thermophilic organisms; the agents of fastest decomposition.

Nature Loo functions well in both thermophilic and mesophilic stages, but in most cases it operates in the faster, thermophilic stage. This happens for a couple of reasons:

Air is drawn into the Nature Loo through the toilet pedestal. As the air inside a house is usually warmer than the air outside, the Nature Loo chamber is also kept warmer. In colder climates, the chamber may also be insulated with a thermal insulation material, to maintain the composting rate.

The containers are black. This means they are an excellent absorber of heat, especially if located in natural sunlight as is recommended once they are full. Unlike most other composting toilets where the chambers are located under a house, the full Nature Loo chambers are exposed to natural sunlight for at least 50% of the composting cycle. In the case of the Excel the optimum temperature is maintained by the thermostatically controlled heater in colder climates.


An important function of the composting process is the destruction of pathogens. Most are killed in the thermophilic stage. Composting at temperatures above 55 °C for one day kills almost all pathogens.

As the Nature Loo chamber is in use for around 6 months, and is composting by itself for another 6 months, there is little chance of any pathogens surviving, even if the composting process does not reach thethermophilic stage. In addition, the unique use of isolated chambers ensures no recontamination from fresh waste.

Since a Nature Loo chamber’s internal temperature can reach 45 degrees centigrade in winter in Northern NSW, there is little chance of any pathogen surviving a number of months under such conditions, even in cooler climates. The temperature profile of the Excel is controlled thermostatically so as to ensure that any pathogens do not survive. A typical analysis of the humus from a Nature Loo shows no traces of Faecal Streptococci, Faecal Coliforms or Salmonella sp.

Click here for Nature loo Composting Toilet prices


The working principle of Sun-mar continuous-type composting toilets

Composting is Nature’s Way. Every living organism consumes nutrients and creates waste. To transform waste back to nutrients and complete this cycle, nature uses the processes of decomposition and evaporation. As is often the case, nature seems to be doing business in the best way possible.

That’s why Sun-Mar toilets are designed not only to harness these natural processes, but to optimize and accelerate them.

Toilet waste is over 90% water content. This can be evaporated and carried back to the atmosphere through the vent system. The small amount of remaining material is recycled into a useful fertilizing soil.

Wherever there is a poorly working septic system, a Sun-Mar can take care of the toilet waste; where there is an outhouse we offer the luxury of an indoor facility; and where there is no toilet at all, a Sun-Mar provides the right environmental choice. Sun-Mar units are economical, quick to install and easy to use.

Because no chemicals and no septic systems are used, fragile environments can be protected. A Sun-Mar composting unit is an environmentally healthy choice for recycling human waste. The Sun-Mar system produces no pollutants, while collecting nutrients. With a Sun-Mar, recycling is made easy!

Odour Free

As well as ensuring an aerobic breakdown in the Bio-drum, Sun-Mar ensures an odour free environment by engineering the air flow within the unit to maintain a partial vacuum at all times. Air is being drawn in either by a fan (or on non-electric units by the vent chimney) over the evaporating chamber and up the vent stack. Not only does this evaporate excess liquid, but by continuously pulling air in we ensure no smell escapes from the unit.

Evaporation is assisted on electric units by a thermostatically controlled heater in a sealed compartment underneath the evaporating chamber.

Sun-Mar’s Unique Bio-Drum

The ideal way to compost waste would offer operational simplicity and an environment where there is warmth, moisture, organic material, and oxygen. Sun-Mar creates this ideal environment in the patented Bio-drum.

The unique Sun-Mar Bio-drum ensures aerobic microbes flourish and work much more quickly to break down waste and convert it back to earth.

Operational Simplicity

Waste and peat mix bulking material enter through the waste inlet port at the top of the drum. To mix and aerate, rotate the drum periodically, simply by turning the handle on the front of self-contained units or on the side of central units. During rotation the inlet door closes automatically keeping the compost in the drum.

To empty compost from the Bio-drum simply release the drum locker and rotate the drum backwards. Now, the inlet port in the Bio-Drum opens automatically and compost drops directly into the compost finishing drawer.

After rotating, the Bio-drum locks itself in a top dead centre position ready to receive new material.

Supplying Oxygen

Sun-Mar’s unique Bio-Drum design is the easiest and best possible way to thoroughly and completely mix and oxygenate the whole compost. Rotate the drum, and the entire compost pile is tumbled and infused with oxygen. Oxygen is one key ingredient which allows aerobic bacteria to break down waste quickly and without odor.

Controlling Moisture

Moisture control, the other basic requirement for good composting, is one of the outstanding benefits offered only by Sun-Mar’s Bio-drum.

Below 40% moisture content, composting slows and eventually stops completely. By not applying direct heat to the compost, Sun-Mar ensures that it does not dry out. In addition, the tumbling action during periodic mixing distributes moisture evenly throughout the compost.

At above 60% moisture content, liquid starts to drive out the oxygen in the compost, and the compost becomes increasingly anaerobic,- like a septic system. Sun-Mar’s unique Bio-drum optimizes composting speeds by automatically draining any excess liquid through a screen at the bottom of the drum directly into the evaporation chamber.

Maintaining Warmth

The microbes generate their own heat as they work. This warmth is held in the compost by the mass of material inside the drum, supported by indirect heat from the base heater (in electric units). By avoiding direct heat, Sun-Mar ensures that composting will not slow down as the material gets dried out.

The Ideal Environment For Aerobic Bacteria

Uneven distribution of oxygen and moisture allows anaerobic bacteria to take over. These microbes produce bad odors and do not allow the waste to break down quickly.

The superior oxygenation and moisture control provided by the Bio-drum provides the ideal environment for aerobic bacteria to odorlessly break down organic material. They quickly convert organic material into water and carbon dioxide, and leave behind simple salts which are ideal for uptake by plants.


Use and ongoing maintenance

Operating a Sun-Mar is easy. There are two things that you have to do on a routine basis – rotate the drum and add bulking material, at the rate of a cupful per person per day.

Add 1 cupful (or 2 handfuls) of Sun-Mar Compost Sure (or 50/50 mixture of peat moss and non-cedar wood shavings) to the Bio-Drum after every bowel movement. This usually represents one cupful per person per day of use.

If you have a central unit, peat mix only needs to be added when you do your rotations at the end of the weekend (cottage use) or once every 2nd day (residential/weekly use).

Why? Maintains the carbon/nitrogen balance, Absorbs Liquid, Helps oxygen penetrate for aerobic composting

Turn Handle to rotate the drum 4-6 complete revolutions, three times a week when in use, or, if used only at weekends, only on departure.

Why? Mixes and oxygenates the compost

Unplug the unit if you are leaving for a period of more than a few days. If you are leaving one weekend and coming back the next, you may unplug the unit.

Consider installing a timer to shut the unit off after 48 hours to evaporate excess liquid. If you are leaving for a period of more than few days, or the compost appears dry, add approximately 1/2 gallon of warm water before leaving to keep the compost moist.

Why? unplugging unit will conserve power and keep compost from drying. Addition of water helps keep the compost moist

Empty some compost into the finishing drawer when the drum is 1/2 to 2/3 full. It is 2/3 full when the compost reaches a level about 2-3 inches below the drum door when the door is open.

To empty some compost into the drawer, pull the drum locker button and rotate the handle counter-clockwise (to turn the drum clockwise). Turn at the same speed you would normally do for mixing.

If necessary, use the rake to level the compost in the drawer. If there is not enough compost in the drawer, turn the drum backwards (clockwise) again 1 rotation.

Leave the compost in the finishing drawer to finish for 3-4 weeks or until you next need to remove compost from the drum.

If your unit is used seasonally and is not used heavily, you may not have to remove any compost at all during the season. If so, follow “Annual Startup”.

Why? Moves some compost to the next stage for finishing, ensures that the drum does not get too full, provides Extra Time for composting to be completed.

Annual system start-up – What to do at the beginning of the holiday season

Empty any compost that had been left in the finishing drawer, and use the rake to clean out the evaporation chamber, paying special attention to the back two corners of the unit (or left hand side if it is a Centrex family unit).

Why? Your fertilizer is ready. This is a good time to remove peat debris from the evaporation chamber.

Remove additional drawers of compost (if there is more than 6 to 8 inches of compost in the drum). This is done by releasing the drum lock, and rotating the drum opposite from the usual direction (turn handle counter-clockwise) to extract compost into the drawer.

Since it will have been sitting over the winter and decomposing in the fall and spring, it will be finished and may be removed immediately, without any extra time needed to finish the compost in the drawer. Several drawers may be removed in this fashion if necessary.

Be sure to leave 6-8 inches of compost in the bottom of the drum to start off the season with a “starter batch” of compost.

Why? Frees space in the drum for the new season’s composting

Add 1/2 gallon of warm water. Why? Raises moisture level as an option for optimal composting:

Add SUN-MAR “Microbe Mix” or unsterilized black earth from a garden center. We do not recommend using topsoil as it may contain fly larvae, and may not contain all of the bacterium required.

SUN-MAR “Compost Quick” enzyme can also be used as a compost accelerant. Even though the compost still has microbes in it, you may want to start the year by replenishing microbes.

Compost Quick helps to accelerate the action of the microbes

Evaporation chamber

Compost must be kept moist but not saturated. Excess liquid from the drum strains through a stainless mesh screen into the evaporation chamber. The ideal environment for evaporating any excess liquid is a large surface area combined with heat and moving air. Sun-Mar meets these criteria in the evaporating chamber.

Any liquid not absorbed by the compost in the drum drains through the screen directly into the evaporating chamber.

On all central units the liquid falls first onto an evaporating tray and then to the main evaporating surface. The tray not only helps oxygenate this liquid, it also traps any peat mix debris, and almost doubles the evaporating surface. Evaporating trays can be removed and cleaned if necessary, through the door opening on Centrex 1000 and 2000 units, and through the drawer access port on Centrex 3000 units.

For optimum results evaporation is assisted on 110 Volt electric models by a thermostatically controlled heating element. Sealed in a compartment underneath the evaporating chamber, the heater warms the floor of the evaporating chamber without drying out the compost.

In non-electric units, although some liquid is evaporated by passive venting, the overflow drains must always be connected.


Finishing drawer – Advantages of a separate compost finishing drawer

Composting can be completed in the drawer without contamination by fresh waste. Compost in the drawer is gradually dried until ready for removal. Finished compost can be simply and safely removed

The finishing drawer serves two functions: to receive the compost in an easily accessible isolated container, and complete the composting and sanitation processes.

All Units Except CENTREX 3000 Series

Compost drops directly into the finishing drawer when the drum is rotated backwards. Composting is completed in the drawer, where it is isolated from fresh waste and possible contamination. While in the drawer, the compost is surrounded by a stream of drying air, and gradually dries prior to removal.

The pull out finishing drawer is removed by hand (no tools or screws are needed), and the sanitized compost may be emptied whenever more compost is to be extracted from the drum.

For seasonal units, several drawers may be removed in the Spring, reducing the compost level in the drum to 6-8″ to make room for next year’s operation.

CENTREX 3000 Series Units Only

There are two compost finishing drawers in the CENTREX 3000 series units. Both are easily removed by hand and are interchangeable.

The first drawer is inside the collection housing at the side of the unit. This is where the finished compost automatically falls after leaving the second section of the Bio-drum.

The second drawer is located inside the unit. Moving compost from the first drawer to this second station allows the composting cycle to be extended if necessary. This can help ensure the compost is safe to handle.

For seasonal units, the second section of the drum can be emptied in the Spring by rotating the drum backwards and dropping compost into the second drawer.

Click here to see Sunmar Composting Toilet prices


Nature Clear Greywater systems

Grey Water Treatment: How it works?


Nature Clear provides an odour free method of filtering and cleaning grey water with no moving or electrical parts. The water from all grey water outlets flows into a polymer tank where it is progressively filtered and biologically cleaned. From the tank the treated water flows under gravity into an application area. The application area materials should be supplied and installed by your plumber. It may consist of trenches or 150mm sub surface irrigation depending on local conditions and regulations.

Because the dwell time of the water in the tank is short, there is no time for bacteria to build up as there is in anaerobic septic tanks. Consequently the system should be odour free.

Filtering of the water takes place in several layers of naturally occurring materials separated by progressively finer grades of geofabrics. A biofilm is established near the centre of the tank where aerobic bacteria clean the water. The resulting water quality is typically of secondary treatment quality.

There is no disinfection process and consequently most authorities will not allow the water to be disposed of above ground. Whilst it is unfortunate that the water cannot be disposed of above ground, no chlorination process has been used to disinfect the water. Please also note that during periods of drought some councils will permit the use of a diverter to allow discharge of the treated water at the surface.

If the application area cannot be fed by gravity, or the local authority insists on a pressurised irrigation system being installed, a pump well and submersible pump will be required.

The maintenance of the system is enhanced if a grease trap is installed on the kitchen waste outlet. Normal maintenance involves replacing the top layer of organic coarse filtration material twice a year and annual cleaning of the top two layers of geofabric. The old materials can be disposed of in your composting toilet or into a suitable area in your garden. The annual cost is less than $10. Using worms to clean the material for you can reduce the frequency of changing the top layer of material.


Print Friendly, PDF & Email