Rubbish, trash, garbage, junk – are some of the terms used to describe the waste products we produce in huge quantities everyday. A big part of it goes to the landfills or gets dumped in other ways. But it’s important to be aware that most of it, including even human waste, can be recycled.

Composting toilets achieve a lot in that direction. The primary objective of the composting process is to contain, immobilise, or destroy organisms that cause human disease and to not contaminate the immediate or distant environments. It occurs in a controlled environment with plenty of air and moisture where bacteria, actinomycetes, and fungi combined with the action of worms reduce the matter into a stable oxidised form.

These toilets contain and control the composting of excrement, toilet paper, and added carbon material in a controlled aerobic environment. The material is broken down in a completely natural process to 10 to 30 % of its original volume over a number of months. The end result is a stable soil like material called humus.

Human waste enters from the top with the addition of some form of added carbon material such as sawdust. Over a period of time due to the action of gravity and the weight of additional material on top the pile slowly works its way down the inclined slope of the chamber. When it finally gets to the bottom it has been completely oxidised and is in a stable form ready for removal.

Air is provided by inlet holes at the bottom of the chamber and slotted pipes inside the chamber. The movement of air through the system results in the majority of the moisture in the system being removed as water vapour out of the flue. Excess liquid collects and is removed at the bottom of the vault and is piped to its own mini leach field or into the grey water system.

The toilets if used within their design parameters have a retention period of at least one year and all solid material is fully oxidised well within this period and all pathogens have been virtually destroyed. Liquid is removed mainly by evaporation up the flue which is fan assisted.

Nitrogen removal:

Nitrogen entering the composting toilet is virtually all in organic form in the urine. The urine enters in the top and enters the oxygen and organic rich environment of the compost pile.

At this stage most of the nitrogen is lost as ammonia gas and dissipates up the flue. The rest of the nitrogen then slowly seeps through the compost and converts to its nitrite form. The urine/compost liquid is trapped successively for a few days in a series of steps on the chamber floor and then onto the bottom of the composting chamber where it is held in an anaerobic environment (anoxic environment) also high in organic carbon and converts to nitrate.

During this process the nitrogen is reduced to nitrogen gas and again dissipates up the flue. After all this, any excess liquid is drained through a stainless mesh filter out of the chamber and dealt with in various ways.

Phosphorus removal:

Phosphates are mainly present in the grey water system as a result of phosphate levels in cleaners and detergents. Dispersal pipes with breathers are used in the upper organic layers of the soil wrapped in geo textile cloth to provide an environment high in biological activity in a wide variety of soil conditions. These biological aerobic conditions result in a discharge of highly treated liquid.

The long retention time and the binding effect of the carbon material result in a very low level of phosphorus in the end liquid. The resulting excess fluid is again put into the grey water system or put through the separate biological filter.

Biological filter:

This filter is connected via a 20mm pipe to the composting unit and is gravity trickle fed as new fluid enters the composter and displaces retained fluid at the bottom. The liquid enters the top and slowly filters down through the media and out via a series of holes drilled in the bottom.

The media consists mainly of coir dust and particles. This pre-treated product is used because coir has a much greater surface area and biological mass and lasts much longer than most other products; and is much more efficient in binding elements such as nitrogen and phosphorus. It also retains moisture better and has a better capillary action than peat and is more resilient and will not compact when wet.

All this provides a stable aerobic environment very rich in biological activity and with good binding properties that ensure that the liquid leaving the filter is very low in potential pollutants.

Unlike a septic tank system and long drop type toilets that have anaerobic bacteria and a distinct strong smell, composting toilets use aerobic bacteria that do not produce the sulphides etc that produce strong odours. Composting toilets usually have a slightly earthy forest humus type smell.