IT IS time to go back to basics and examine what toilets and sewerage systems are supposed to do. The point of all these systems is the safe disposal of human waste matter. Flush toilets and sewerage transfer the problem elsewhere; they are complicated ways of spreading pathogens away from the user to the public at large. Toilets and sewerage can be split up into two, since there really is no logical connection between the two, just a historical one. The safe disposal of wastes can be undertaken in two ways:
Off-plot systems in which excreta are collected from houses and then transported away. This is what the modern sewerage system is. On-plot systems in which safe disposal of excreta takes place on or near the household.
If sewerage and flush toilets are considered indispensable, the way to reduce their environmental and financial impact is controlling how much water they waste. What options are available to reduce water use in sewage systems?
In the flush system, the water is used not just to clean the toilet bowl, but also to transport the excreta. A family of five who uses a water toilet contaminates more than 150 thousand litres of water to transport 250 litres of excrement in one year. We must recognise that:
Water is a precious resource and should not be used to transport faeces.
Waste should be managed as close as possible to its source.
Faeces and urine are resources rather than waste products.
The first step is seeing our biological "waste" as resources. All organisms need nutrients to grow; plants get these nutrients from the soil. Sewage systems bypass the natural flow of nutrients back to the soil and instead dump these nutrients into water. On an average, a healthy person discharges 100 to 400 grammes of faecal matter and 1-1.31 kilogramme of urine per day, which has nitrogen, phosphate and potassium.
So with this first step, toilets can be seen as collection devices rather than methods of getting rid of wastes. The problem is cultural - a society is "civilised" if it has access to flush toilets; faeces and urine are used only by less developed ones. But if these cultural blinkers are thrown away, progress can be made towards solving the problem of polluted rivers and groundwater, waterborne diseases and the enormous cost of sewage treatment.
The second step is recognise that water is a precious resource and should not be used to transport faeces. And since we know excreta contains dangerous pathogens, it makes very little sense to dilute pathogens in water. Even if a small amount of pathogen-carrying material is mixed with a lot of pure water, the result is still a dangerous mixture. Unless treated properly, human waste is hazardous waste and "civilised" society puts it into drinking water sources.
The third basic principle is that waste should be managed as close as possible to its source. Ignoring this principle is one of the reasons centralised sewage systems are so unsustainable both financially and environmentally.
One way to do this would be change sewerage tactics. The condominial sewerage system was developed in Brazil as a low-cost option as they cost about 50-80 per cent less than standard systems. Households are connected to small-bore pipes rather than directly to sewers. These smaller pipes meet up and connect to the main municipal sewer. Smaller bore pipes need less water and at far lower pressure, making an immediate savings in the volume of water used to carry faeces.
Another possibility is decentralised effluent treatment. A block of houses or a housing colony can have its own sewage treatment plant. Again this means that compared to centralised systems, far less water is used, as wastes do not have to be transported very far. Treatment plants can be smaller in size since the volume of wastes they will deal with will be comparatively small. Any sludge produced is used locally as fertiliser.
A high-tech system is to do away with water-based sewerage and have vacuum-based sewer system like the one developed in Germany. If these can be coupled with vacuum toilets there is virtually no need of water. The outflows from toilets, kitchens, and baths are sucked by a local pump into a household vacuum station, from where they are sucked into a central treatment point. Vacuum sewer network can work up to a 4 km radius with one vacuum station. The collected sludge can then be conventionally treated or used in a biogas digester. However, these systems as yet are expensive and energy intensive.
A place where this is being tried is a pilot housing project in Lbeck-Flintenbreite in Germany where an integrated system with vacuum toilets, vacuum sewers and a biogas plant for blackwater as well as greywater treatment in reed-bed filters is under construction.
Instead of focussing on the sewerage and treatment plants, flush toilets themselves can be modified to the amount of water they use. Low flush toilets that use just one litre per flush have been designed. Quite a large amount of water can be saved and recognising this, many cities, like Los Angeles, USA, are giving rebates to people willing to change their toilets to low water systems, and in some cases, provide them free.
These possibilities make a large difference to the problem of water pollution. But again they presuppose sewerage lines, however small. On-plot sanitation solves this problem.
Toilets originally designed for ships and airplanes are now being adapted for houses. The vacuum toilets mentioned earlier also reduce the amount of water. Electric incinerator toilets fall into this category where the faeces and urine mixture is dried by electric fans and then burnt.
Of low-tech versions the standard on-plot solution seems to be pit latrines. These are merely holes dug into the ground and covered with superstructure that contains the toilet seat or pan. When the pit is full, it is either emptied or another pit dug and the superstructure moved to it. The old site with a topping of soil is suitable for growing trees. Instead of a straight drop, an "s" bend is attached just below the toilet pan, a water seal can be included which cuts off most of the odours.This is basically a simplified version of the septic tank. In terms of the environmental impact, both pit and septic tank toilets pose risks to groundwater. The US Environment Protection Agency has also expressed concern about the amount of groundwater contamination that is caused by septic tanks: they pose the greatest risk to groundwater in the US.
In the desperate race for environmental sanitation, more radical designs are emerging which take ecological thinking to its logical conclusion. Why not then just get rid of the water? This is "ecological sanitation" or ecosan for short, works on the principle Don't mix faeces, urine and water. One need not look towards other countries for successful ecosan design. In India, people in Ladakh have been using such toilets for centuries (see box: Return to nature). Modern versions of ecosan have also been tried and tested in India too (see box: Thinking clean).
Urine is nearly sterile. Faeces, which is 10 times smaller in volume than urine, contain most of the pathogens. If the two are kept separate, urine can be directly used as fertiliser while faeces can be sanitised and used as soil conditioner. This is why ecosan is described as "closing the loop". We eat plants that get nutrients from the soil. We urinate and defecate and return the nutrients back to the soil.
Ecosan works by separating the urine and faeces at source and putting both the urine and faeces back into the local nutrient cycle. Designing a toilet pan where the urine and faeces go in different directions ensures this. The faeces drop straight down in a small storage chamber made of concrete or other impervious material. The urine goes to a tank. The faeces is stored and allowed to decompose by a process of aerobic digestion. Ash or other organic absorbing material like sawdust is used to cover the faeces to aid in the drying out process. Time allows heat, given of by decomposition, and normal soil bacteria to kill all the disease carrying organisms. Within six months, the faeces is reduced to humus.
The process used to sanitise faeces can be simply split up into two types; with urine it is a composting, without; a dehydrating process. In both, the action of time and soil microbes destroys pathogens.
Modern ecosan toilets are already in use where laying sewage lines is a problem. In Sweden composting toilets were first introduced more than 50 years ago. Though a wide variety of models are being used, the 'Clivus' Multrum model is one of the most popular ones (See diagram: the Clivus Multrum composting toilet).
The Clivus Multrum is a single vault-composting toilet where urine, faeces and organic household wastes are combined and processed together. The model is available as a unit and consists of three main components: a composting vault with a slanting floor; air conduits; and a storage space at the lower end. Besides these, a tube connecting the toilet seat riser with the receptacle and a sloping channel for the kitchen waste.
Faeces, urine and toilet paper along with all kinds of kitchen and organic household wastes go into the multrum. The contents slide down slowly along the multrum sloping floor with the fresh deposits at the upper end down to the storage part of the vault. The heap decomposes, reducing to less than 10 per cent of its original volume and gradually forms humus. The humus produced has similar bacterial count as that of soil and is directly used as a fertiliser and soil conditioner. The humus produced in this process is only taken out after five years for the first time and later once a year. In Sweden, this model is used in houses, weekend houses, institutions and as public toilets. One problem is that since there is no diversion of urine the slanting floor poses a risk of liquid accumulation at the lower end of the composting vault. To stop this a container for liquid storage below the composting vault has been provided in a newer version.
Urine separating toilets can be designed for multi-dwelling environment too. Gebers Housing Project is a cooperative housing project - a two-storied building with 32 flats - located in a suburb south of Stockholm. This project involves community participation and was started in 1998 with the primary aim of recycling all nutrients of the human waste to agriculture.
The urine is flushed with a small amount of water and is carried by gravity to large tanks under the building from where it is transported to a farm and stored in large reservoirs.There is a natural rise to a high ph of urine and it is considered to be disinfected after six months of storage. Faeces on the other hand are handled dry and fall straight down into individual bins under the house. The faeces is taken out after one year and composted collectively for later use in agriculture.
There are working examples in less developed countries too. China has a large ongoing ecosan programme. In the Guangxi Zhuang Autonomous region in southeast China, Yongning county has 1440 ecosan toilets in 45 villages. In the same region, another county, Beiliu, has 3,316 dry toilets. Most of these are in houses but some are in public use like schools. The faeces are dried in the toilets themselves and are collected and used in three ways. They are put into a biogas digester and the gas made is used provide lighting and cooking facilities for the village. The leftover sludge is applied to fields as a soil conditioner along with the urine. Faecal sludge is also used for aquaculture. The circle is complete.
CHASING A DREAM
It is the poor who cannot afford sanitation systems and are paying the cost of flush toilets and sewerage. We pump our disease-laden effluents towards them. The medical interventions possible for the rich may be out of the reach of most poor people. Most deaths from waterborne diseases are not caused not by the pathogens themselves, but because of dehydration, the victims do not have enough clean water to drink. Malnutrition is also exacerbated by lack of clean drinking water. Flush toilets hijack natural resource like water that the poor depend to meet their daily needs.
Whether donor agencies or government subsidy, there is a lot of money to be made in sanitation and those in power will not easily give up that power. So governments will continue to build flush toilets and keep chasing the impossible dream of sewerage. Sanitation engineers have no interest in changing the technology paradigm. Water pollution is not their problem in any case.
There is no need to import expensive technological fixes. Ecological sanitation shows that there are new approaches, and that these are based on traditional understanding of the human-environment relationship. These are not really new technologies just a new way of looking at things. Alternatives to the flush toilets and sewerage are needed and an understanding of basic environmental cycles shows us the possibilities. Put back what you take out.
But most important need is a change in mindset. The flush and forget attitude is not working. The faster we realise this, the better.
With inputs from Priyanka Chandola