Wet or Dry Ecological Sanitation - or - To mix or not mix, is that the question?
by Bjorn Brandberg
How much potential has the WC?
A massive stream of food (nutrients) from the rural areas to the cites is impoverishing the soil in the rural areas, and threatening the health of both urban and rural populations. Urban growth has made sullage systems polluting rivers and lakes. Even the oceans are at risk because of the popularity of flush water toilets. An evaluation of alternative sanitation technologies in Luanda low-income areas in Angola caused the author think twice. May be waterborne sanitation using WCs actually is the solution which can save the cities.
Presently there is a massive stream of food (nutrients) from the rural areas to feed the urban population, which is producing excreta (urine and faecal matter) in corresponding quantities, resulting in a more or less serious sanitation problem. The challenge is to create a corresponding stream of nutrients back to the productive soil without creating new problems.
The great success (or disaster?) in sanitation was the introduction of the water toilet. Urban faecal born diseases were reduced to fractions of what it was before the introduction of waterborne sanitation. The WC became a reality, or a dream, for the entire urban population, worldwide. Improved sanitation has been intensively promoted for at least two decades with focus on the poor and the underserved, with too little result. It is therefore with hesitation many of us embark on the very difficult but very important subject of ecological sanitation, especially as we know that we are entering an area of cultural taboos. The great success of the WC was the reduction of faecal borne diseases in urban areaas and the disaster was that it was not affordable economically or environmentally –– or is it still in the pipeline for further developments.
Why did the WC become so popular
Because of its excellent hygiene? I dare to say no. Because of its high costs? May be. It was the status of the white porcelain and the clean water and the rapid “elimination”, out of view, of that unpleasant matter that had to leave the body, which made the WC so popular among the higher income groups that they were willing to spend money on it. A business developed to the extent that municipalities had to spend more and more money to extend the necessary sewers until they reached the “final” destination, a nearby river where the untouchable excrements became invisible –– but not harmless.
What are the lessons learnt?
We have learned a lot. For example:
- That invisible does not mean harmless. The bill that landed on the Mayors desk and from there dug into the taxpayers’ wallets had to be increased with an ever-increasing cost for treatment of the polluted water.
- That the popularity of the system made it spread into communities where the majority of the population and the municipalities could not carry the costs, and that the world is facing severe problems of water supply to the cities and that the rural areas gradually are deprived of their soil fertility to the point that the soil is poisoned by chemical fertilizers and pesticides.
- That the example of the rich has a tremendous force, which is difficult to stop.
The introduction of the WC was an expensive lesson, which we will continue to pay for during many years to come. What we are starting to learn is that the ecological price may become even higher, not only for the rural population but also the people in the cites who depend on the healthiness of the soil in the countryside where their food is produced.
For the low income population (in developing countries) conventional dry latrines are the most common type of sanitation. It has the advantage of not polluting the streams and the impact on the ground water is less than for example WC with conventional septic tanks. It also bears its own costs, as the municipality normally does not subsidize construction. Still, it does not return the fertile value of the food to the plants. Only a fraction may be found by roots of trees and returned to nature and men in terms of cleaner air, shadow and beauty. –– For sustainable ecological development we need new ecological solutions.
Dry or wet ecological sanitation
Ecologically we are getting poorer and poorer as we are wasting our waste. On long term there is a need of some form of returning the nutritional value from the human waste to the soil. There are principally two solutions:
- Dry ecological latrines
- Wet flush toilets with ecological treatment.
The two systems have advantages and disadvantages, possibly making them suitable for different areas. Eventually an ecological sanitation system for urban areas will need some sort of transport facility returning the nutritive value to nature. –– Dry or wet?.
Dry systems may include urine diversion, where the urine can be stored in separate tanks and taken to rural areas to be used as fertilizers. Urine is normally safe but unpleasant to handle. The faecal matter can be treated locally or centrally. In its fresh form it is dangerous to handle and local treatment with ash or lime can not always be trusted. With a wet system you flush and the system takes over. –– Good or bad?
Are we at a crossroad?
Just now we may be standing at a crossroad as we did once when the WC was introduced in our homes.
- Should we choose a dry system, which would save a lot of water, or a waterborne system, which seems to be much easier for people to accept?
- Are we going the dry path for introduction ecological sanitation where individual households may need to be trained (against their will and culture?) to manage the first part of the system or should we go waterborne with ecological recovery of fertilised water?
- Can we chose both systems and let people chose to see who is he winner?
One thing is for sure: We must find a solution which attracts the relatively rich and from there work ourselves down through the social strata eventually reaching at least the families ing the low income periurban areas in developing . If we do not get the enthusiasm and the example from the pattern setters and the decision makers we will have the to well known problem that sanitation, in this case ecological sanitation, stays at the bottom of the list of priorities. In that perspective, what is happening in Europe and the united states is very important.
Wet ecological sanitation
Wet (low volume pour flush) toilets are very common in southern Asia and are rapidly gaining popularity in periurban areas in Africa. The need for water for flushing has been criticized, as water supply in the fast growing periurban areas is a major concern and a political problem. In spite of this the population in for example periurban Luanda is practically refusing dry latrines. This in spite of that water, in general bought from water vendors, may cost up to 50% of the already strained household budget. Reasons are weak except one: Style and status. Dry latrines are rural and have a poverty stigma while the homemade pour flush latrine is mimicking the famous WC. A visible septic tank (soakaway) with a vent pipe, which not is necessary, adds to the status.
Also low water flushed latrines can become ecologically sound. The water can be filtered through ecological wetlands for compost and energy production before it is used as irrigation for fruit trees and possibly other products.
Dry ecological sanitation
Dry ecological latrines will produce two products, the urine, which is rich in nutrients and microbiologically sufficiently safe for immediate use as a fertilizer, and the faecal matter which either should be burnt in the toilet (incineration toilets) or treated with lime (or ash) and used as compost. In urban areas the demand for urine and compost will be limited and of little value for the rural soil unless collection and distribution systems are put in place. The handling of urine (storage and transport) can become both expensive and smelly. The smell of urine, though harmless is rarely appreciated.
Unless burned in the toilet the faecal matter will need to be collected or composted on site. On site treatment with lime or composting is difficult to control and the microbiological quality of the human manure may be doubtful. Local handling of human excreta may be difficult for the families to accept.
A way forward?
Waterborne systems require water, which is a limited recourse. We have however generations of experience of transporting human excreta with water, and it is very well accepted by municipalities and the urban population. Ecological treatment can be made locally with solids separation and drain fields (sub surface irrigation with evapotranspiration beds) or centrally in treatment plants (wetlands) for production of wood fuel, compost and eventually food. Recent developments of the flushing systems have reduced the water demand to the point of ecological soundness. A one litre flush dilutes the urine to the concentration the plants like. Retention tanks allows tube dimention to be reduced to fractions of what normally is used today. With ecological treatment of the sullage we are no longer wate the water we return it to nature as a fertilizer. What was received is given back. Where sewers and treatment facilities not are available the septic sullage can be treated locally in evapotranspiration beds where both water and fertile value is used for sub surface irrigation. To which extent the evapotranspiration bed can be used for legumes and other vegetables may need further studies, but as the possible contamination is limited to the family level epidemical risks are minimal.
For the poor; huge pits, which often collapse, may no longer be required but a little tank that retains the solids until suspended in the water. Family level pour flush latrines can later be connected to a small-bore sewer system, which can be connected to ecologically sound wetland treatment. Kitchen and bath water can go the same way helping to ransport nutrients (and the water) to a place were plants grow.
For a long time we have said: Don’t mix water, urine and faecal matter. May be we were wrong. May be we should have a second look on our waterborne systems. May be they can be improved to become ecologically sound. May be we should promote both systems and compare –– giving both of them a fair chance.
Is this a competition between two technologies?
If it is, may it be good for development of excellence in performance as long as we do not forget the objective: Ecological sanitation; Healthy for people and healthy for sustainable development in urban and rural areas.