The big question everyone wants to know is…do dry composting toilets smell?

Composting toilet

Rota Loo

Some people think that all composting toilets smell, however, despite not having to flush once you’ve used a composting toilet, there is no smell at all.

The smell often associated with sewerage or septic tanks is actually caused by anaerobic bacteria, which forms when too much water or liquid is mixed with urine and faecal material, displacing oxygen.

Radiant Energy supplies Rota-Loo dry composting toilets – and as this is a waterless system, it is designed not to replicate the same conditions as a septic system. Each of the six internal composting bins has geo-textile filter material in the bottom which is porous to a rate of 300 litres per second per square meter. This material also has a mesh density of 175 microns. While that might all sound confusing, what it means is that liquids and oxygen can pass through while not allowing any solids (larger than 0.175 mm) to get through. So, all solids are retained in the bin, allowing liquids to separate. Therefore the process is completely aerobic and smells are minimised.

The Rota-Loo also allows you convenience of being able to install an extraction fan. Air, continuously pulled through the Rota-Loo to the vent creates a negative pressure at the pedestal. This means that a small amount of air is being taken from the bathroom (which is an obvious advantage, especially when you have to go straight after someone else!). So, with the Rota-Loo system, the air in the bathroom is always nice and fresh because odours are ‘sucked’ down the waste chute.

Evaporation and Rates of Composting

The second advantage of having a continuous airflow is its ability to evaporate liquid. One of the design criteria for the Rota-Loo installation is that the air inlet is placed diagonally opposite the vent pipe. The air inlet is placed as close to the base of the system as possible with the vent coming off closer to the top. This allows for the air to pass directly over the liquid, which has drained through the bin and is stored in the base of the Rota-loo under the turntable.

Complete evaporation is achieved through a combination of factors. A high differential between the ambient temperature of the liquid inside the system and the air temperature which passes over the surface of the liquid as well as the volume and rate of air change. For every 10 degrees of heat that can be generated or brought in to the system the composting rate can be doubled and the evaporation rate significantly increased. The site and installation of the Rota-Loo is therefore very important. The air inlet for the Rota-Loo should be placed in an area or position where naturally warmed air occurs and the system should be insulated, preferably in a dedicated room.

Where possible, we can incorporate small Soltran modules into the building design to provide the ultimate environment for the composting system. Not everyone is able to provide the best possible environment for their composting toilet so our distributors are able to advise on the best place for your Rota-Loo to be installed…after all, they have over 25 years experience in the business!


One of the latest innovations to come from years of experience and research is the development of the “Separating Pedestal”. The importance of this pedestal is quite significant; the separating pedestal can help in the elimination of odours whilst increasing the rate of decomposition (regardless of the temperature range) and produce a reusable product. This development increases the range of installation possibilities and can ensure a high degree of operating efficiency.

This system works because when urine is taken out of the composting process the carbon to nitrogen ratio is much closer to its optimum relationship. The amount of liquid in the pile will be significantly reduced leaving the system in an aerobic condition and the urine can be stored separately to be used as a natural organic fertiliser.