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| December 2007 |
Feature |
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Waterless Toilets come of ageBy Dr Garth CambrayWe are flushing our environment down the sewer. Dry loos are increasingly becoming an option to solve this problem. This article takes a peak under the "bonnet" of a uniquely African answer to the call for a better toilet system. In many cases wasting things is likened to flushing something, like money, down the toilet. One of the strangest things about the way we think is that very few of us see water as money, and that we flush a lot of that down the loo every year. In fact, to flush away the 50 litres of feaces and 500 litres of urine we produce per year the average water borne sewerage user spoils nearly 15 000 litres of water. In most cases, that sewerage is poorly treated and pollutes an additional 50-100 000 litres of water. To put this in perspective - if that water were filtered and bottled it would be worth R20 000 for the flush water and at least R130 000 for the water polluted by the discharge. To treat 15 000 litres of spoiled water will cost quite a lot of money - hence something about the way we run our toilets stops us seeing that we are literally flushing away our money - or more precisely, every year we go to the toilet is the equivalent water value of one pretty decent family car. Dry toilets occupy a similar niche in the market to solar panels. Both dry toilet technologies and solar panel technologies tend to be seen by most people as a good idea for other people to use, and once the technology has become cheaper, or better, we smugly think we will use it too. And because not enough people use niche market technologies, the profitability of such companies is low, and hence the products don't evolve very fast. In South Africa it appears the age of the dry toilet has arrived. In designing a toilet system there are certain very important things to bear in mind. Human waste products tend to stink and we don't like to know that, hence a toilet system has to have ways of ensuring that when a user enters the toilet there are no odours - waterborne sewerage uses a "P" lock system that keeps a little bit of water in the bowl and ensures that no vapours from the sewerage system can find their way to the toilet user. Human wastes are comprised of a certain amount of solid matter and quite a lot more liquid urine. With waterborne sewerage these are mixed together making for more expensive processing at the sewerage works. In the 1980's I remember as a child hearing of the work of Dr Brian La Trobe when he still lived in Grahamstown. This boundlessly creative and enthusiastic scientist has since the 1980's been involved in projects to convert waste into products, and to produce waterless toilets. In the 1990's he and Gavin La Trobe formed various companies to market and develop waterless toilet systems. In 2000, Gavin initiated research and development on the system reported on in this article - which bases its functionality on the so called "Conveyance/Diversion" system. If one looks at the composition of normal human waste material we have faeces and urine. Faeces is rich in complicated organic molecules and bacteria and other potential pathogens. Faeces is therefore an incompletely degraded chemical mixture - things can live in it as it has lots of unused energy in it, and if they do, many will use up oxygen - so if we dump faeces into water we mix pathogenic bacteria into it and add complicated organic nutrients that will allow those and other bacteria to grow and use up all the oxygen in the water rendering it foul and polluted, and also making it rather expensive to treat. Urine on the other hand has very few pathogenic bacteria in it, and very few complicated chemicals in it - it is in fact a rather good fertilizer containing nitrogen and other useful elements for plant growth. If we dump it in water it will provide an ideal nutrient source for algae to grow messing the water up in an entirely different way to the way faeces does.
From a process design perspective, current waterborne sewerage systems are very flawed in that urine and faeces are mixed, creating a difficult to treat mixture. The La Trobes "Conveyance/Diversion" system uses a clever method to separate dry and liquid wastes, thus streamlining waste treatment. The toilet system has a normal looking toilet pedestal.
Upon sitting on the toilet a trap door is opened to expose a conveyer belt below. An air extraction system ensures that air is constantly drawn through the toilet, hence no odours escape upwards. The conveyer belt is tilted slightly upwards. Any solid matter entering the toilet falls on the conveyer, while liquid matter runs forwards and exits the toilet through a pipe and can either go into a pebble bed in a hole, or into a lined trench with plants in it. The plants absorb the nutrients from the urine and transpire clean water vapour into the air. Solid matter moves in the opposite direction - after each use, the "flush" lever is depressed causing the conveyer to move forward one click. Solid matter migrates slowly along the conveyer, and as it goes it dries due to the airflow drawn constantly through the system by the vent pipe. Solids are removed from the conveyer by a scraper function and end up in a collection point. The collector requires emptying every 8 or so months, with decomposed faecal matter rendered safe for burial as a soil improver for trees, or disposal by municipal solid waste disposal systems. All in all, this dry toilet system, is a clever way to
provide the average toilet user with an alternative to waterborne sewerage that
is convenient, low maintenance and effective. More information:
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