Best Performance in a self-composting waterless toilet

Posted by Bruce Loxton

Oct 11, 2017 8:57:23 PM

Kimberley started installing self-composting toilets in 2014 with an integrated ventilation system in Kimberley Karavans. Self-composting toilets are very successful in boats but relatively new to caravans and camper trailers.IMG_2067-1.jpg

In the 3 years since the first instalation, users have overwhelmingly given strong positive feedback: "it is the biggest change for cleaner and easier camping - no need for a dump point and no added weight".

The benefits of self composting toilets:

  • No odor (there really is none).
  • No Water needed.
  • No liquid sewage.
  • No need to find a dump point.
  • Similar size to conventional toilet.

The waterless toilet works by

  • Separating the urine from the solids waste (basic fundamental requirement)
  • Adding carbon to the waste (Coir or sphagnum peat moss)
  • Compost aerobically (good air flow and rotation of material)
  • Achieving a high internal temperature inside the compost pile. (kills the pathogens)

This is a "game changer" in camping.  Kimberley have designed the highest performance waterless toilet to give a longer life and easier wate removal.

See video on Toilet here:

Design changes for higher temperature

The two primary factors that destroys pathogens in the compost are temperature and time. A compost pile that is properly managed will destroy pathogens with the heat it generates. The higher the temperature, the faster the pathogens are destroyed and "happy campers".

Time and Temperature with Humanure .jpg

This is the relationship of the internal compost temperature and time. This is NOT the ambient temperature.

“Complete pathogen destruction is guaranteed by arriving at an internal compost temperature of 62° C for one hour, 50° C for one day, 46° C for one week or 43° C for one month. It appears that no excreted pathogen can survive a temperature of 65° C for more than a few minutes.”

So we set our design target to get an internal temperature as close as we could to 65° C.

The Kimberley Kruiser already had a system for added heat:

Air from the drying chalet passes onto the composting toilet and is vented out through the roof. This will heat the base of the toilet. Together with a good aerorobic process the thermophilic temperature will increase to the maximum of 65 degrees C. As you can see from the chart, at this temperature, pathogens are destroyed in just over an hour.


For general use with Kampers and Karavans and Kruisers without running the drying chalet, a different heating system is required.

An independent 12V membrane heater has been designed to increase the internal temperature of the toilet.

The 12V membrane heater sits between the removable liner and the base.  This is shown in the image on the right with the stainless steel handle and turner.

The membrane heater is 25W. (using 2 Amps approx.) 4 hours use generates 100W of heat and uses 8 amp hours of battery capacity.

This accelerates the composting process just before emptying or in ambient temperatures below 20 degrees c.

Image shows cut away design and the removable liner.

1 waterless liner IMG_0232.jpg
Waterless Toilet cut away profile.jpg

How you use the waterless toilet:

  • You slide open the “safety” cover and use. There is no water tank.
  • Two compartments: one for solids and a tank for liquids. You select which to use first with a quick release lever. 
  • No water flush; liquids or solids fall into tank through gravity.
  • Typically 80 uses for solids, less for the liquids tank. 
  • Couple should have 3-4 weeks before emptying
  • An automatic turner eliminates the manual cranking.
  • When you empty, just pust waste into a rubbish bin or scatter in the bush if fully composted.

Solids tank:

  • Start with a little peat moss or coconut coir.
  • Automatic timer turns a 12V motor to churn contents every day.
  • Moisture is kept low with a continuously-running fan. 
  • Constant air flow desicates the solids and accelerates the composting process.
  • In the event of an upset tummy, a second boost fan "super desicates" combined with a membrane heater built into the base.

When solids compartment is full:

  • Switch on the heater and the booster fan.
  • Wait 3-4 hours
  • Remove the inner liner and empty into a plastic bag for easy disposal.

After last use:

  • Leave in the caravan/ camper in automation mode. This keeps aeration operating. (remove and empty liquids tank though).
  • After a few days, it will be close to dust!
  • Discard in a plastic bag and place in rubbish bin.

Liquids tank:

  • Tank configured for easy removal and transport for emptying.
  • Adding brown sugar to tank will reduce any liquid odour.
  • Because of the automatic system, it can be left operational while in storage.

The last word in composting toilets critical in getting the best performance:

“A thermophilic (high temperature) compost pile will destroy pathogens, including worm eggs, quickly, possibly in a matter of minutes. Lower temperatures require longer periods of time, possibly hours, days, weeks, or months, to effectively destroy pathogens.”

"Although one need not strive for extremely high temperatures such as 65°C in a compost pile to feel confident about the destruction of pathogens, a higher temperature will shorten the time."

Read about the details in this handbook by clicking:




Topics: waterless toilet, compost toilet, self-composting toilet, membrane heater

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The Kimberley Karavan, a lightweight folding off road caravan that can go anywhere. Kimberley Karavans are unique with their internal shower and toilet, comfortable internal seating and luxury finishes.