ENVIRO LOO
biological operational principles

Firstly it will be observed in the Enviro Options literature that we refer to our "dry or waterless sanitation system" and not strictly as a composting toilet. We do however at times, refer to the term, "composting" in reference to the system, as it is a term commonly associated with this form of sanitation technology. It is however our opinion that the form of treatment and stabilisation achieved within the Enviro Loo is more of a dehydrating process over lenghty retention period, with an ancillary, lesser composting process.

• Separation of liquid and solid wastes at the initial stage of the waste entering the container through the toilet pan.
• The liquid drains to the bottom of the container from where it is evaporated due to the design of the ventilation system
• Body waste falls onto a bed of organic matter on the plate
• Simple to use agitator “flush” breaks up the waste to ensure adequate aeration and dehydration
• As the waste migrates down the sloped, ridged, perforated drying plate, it is subjected to continuous ventilation.

• This forced extraction ventilation system results in a continuous air flow through the unit, allowing for rapid aerobic decomposition and evaporation of liquid waste. It also creates a negative pressure within the container, thereby preventing the escape of odours through the toilet pan.
• The airflow is assisted by the ventilation extraction unit positioned on top of the outlet vent pipe with air being drawn into the container via the inlet vent pipes.
• Sunlight absorbed by the black manhole cover increases the ambient temperature within the container.
  
  

Liquid and Solid Separation:
Faeces and urine drops directly through the toilet pan onto a sloping reception area.

The urine proceeds by gravity, to the liquid trap at the bottom of the tank, via drainage holes through the front portion of the plate. Any faeces that enters the system at the same time, is later swept onto the drying plate by a flat scoop attached below the toilet flap.

Migration of the Solid Waste down the Drying Plate:
The initial push of the solid waste via the scoop onto the drying plate, pushes the faeces onto a bed of organic and enzymes material that is loaded, on commissioning of the toilet. This organic additive helps kick-start the decomposition process. Any foreign material such as sanitary pads, and various forms of anal cleansing material is pushed along with the solid waste. Toilet paper ultimately breaks down, newspaper and other foreign materials merely dehydrate and are easily removed from the collection area, in the fullness of time. The solid waste slowly, but progressively moves down the sloping drying plate. This movement is aided by the scraping / pushing action of the flat scoop attached below the flap.

The surface of the drying plate has a number of ridges across the width of the plate, design to retard the progress of the solid waste plate, while the waste is constantly aerated, thereby stimulating a reduction in volume via the subsequent evaporation of liquid.

In order to avoid contamination of the dried waste, the waste material is periodically removed from the drying plate collection area and deposited into a hanging bag. This waste then remains in the bag for an approximate period of eighteen months to two years prior to removal from the system.

The waste contains a myriad of organisms contributed from the faeces itself and the starter organic material, in a symbiotic arrangement of survival of aerobic mechanisms, bacteria, protozoa, helminths, yeast cells, other commensals plus, of course, a high volume of dead cellular waste.

At various times the waste might contain evidence of maggots, larvae and grubs, which are all part the breakdown and stabilisation process. As the dehydrating material gradually moves towards the collection area, the microbiological activity will begin to slow down due to a lack of moisture.

The time frame (retention period) from entry of the solid waste, until the waste is removed from the collection area, depends on the number of users per day and according to the local climatic conditions namely; average wind velocity, ambient temperature and humidity levels.

After widespread utilisation of the system in South Africa, it has been the experience of Enviro Options that some of the dried humus like material, need only be removed approximately, every eighteen to twenty four months.

Aeration of the Waste:
The ventilation through the system is such that during the period that the waste moves down the drying plate it is constantly subjected to a large airflow.

For example with a relatively low wind speed of 4 kilometres per hour we can estimate an airflow of approximately 100 to 150 cubic metres per hour through the system.

This continual airflow has the following effect on the solid waste:

• A reduction in volume through evaporation of the high moisture content.
• The oxygen devitalises the pathogenic arganisms.
• The oxygen acts as a deodourising agent.

Biological Heat Within The Solid Mass:
It is a well known fact that in the course of the composting process, there is a build-up of heat within the mass of the composting material. Temperature of sixty five to seventy degrees celsius are not uncommon, particularly with "forced aeration composting".

This sort of scenario would never be achieved within the solid mass in an Enviro Loo. Temperature of 55 degrees celsius and above can be reached directly underneath the sealed manhole cover. Within the solid mass on the drying plate it is doubtful if the internal temperature would ever go above thirty five to forty degrees for the following reasons;

• The solid mass on the drying plate is too small to retain heat.
• Any heat build-up, no matter how small, is quickly dissipated by the incoming air.
• To reduce the in-flow of air could result in anaerobic conditions within the system.

"Radiant heat" therefore contributes to the operation of the system, via the heat build-up underneath the manhole cover and through the approximate ten degree increase in temperature, above ambient, within the ventilation pipe causes a convection current, which assists operation of the ventilation extractor and thereby positive ventilation extraction through the system. This creates a negative pressure within the container.

The other important aspect of the stabilisation process is the prolonged dehydration process, thereby retention period, resulting in subsequent bacteria attenuation and devitalisation.

See the graph over page by Feachem at al (1983),which depicts the elimination of pathogens related to temperature and time.

This demonstrates that at a temperature of approximately 35 degrees celsius most pathogens would be reduced below hazardous level within a retention period of one year. It is therefore self explanatory, that if the waste has a retention period of between 18 to 24 months, it very unlikely that a disease causing pathogens would survive at infective concentrations, apart from helminths.

Viruses from human waste will not survive outside the host body for longer than three month periods

The eggs of Ascaris worm cysts and other helminths are however capable of extended periods of survival at temperature below 65 degrees celsuis.