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Sistema PLUVALOR nelle aree urbane

ECOSAN di Eautarcie nelle aree urbane

EAUTARCIE nei paesi in via di sviluppo
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In the gigantic cities of developing countries, there are serious water problems, both in the fields of sanitation and water supply. Solutions proposed by water multinationals are too expensive and not within the reach of poorer countries. Despite this, under pressure from these multinationals, major infrastructures (sewers, water treatment plants, water supply systems, etc.) are realized – seriously indebting these countries.

In short, EAUTARCIE restores domestic water-related activities within Nature's great cycles: water, carbon, nitrogen and phosphorus.

The text within this page was first published in French on www.eautarcie.com: in 2008

The original text has since been adapted and first published in English on this page at www.eautarcie.org: 2009-06-15

Last update : 2016-10-25

EAUTARCIE nei paesi in via di sviluppo

Rainwater Harvesting

Homes without electric power

I am often asked if the PLUVALOR system can be installed in isolated villages of developing countries where there is no electric power.

In such situations, you obviously cannot pressurize the household water network. Nevertheless even here, rainwater can constitute a convenient asset for the home. In tropical regions, rainwater that is stored in an underground cistern made from concrete or masonry will conserve itself impeccably, commonly at temperatures of 18 to 20°C. The main challenge is to try to have water at your disposal year round, even during dry seasons. The longer the dry season, the greater the required cistern capacity.

Calculating the cistern capacity

The calculation is simple. You multiply the roof catchment area (expressed in m² and measured horizontally) by the local average annual rainfall (expressed in metres). You thus obtain the annual theoretical recoverable rainwater volume (expressed in m³).

Assuming regular water consumption throughout the year, you divide the volume by 12 to establish the monthly available water volume. The cistern's capacity will therefore be this monthly volume, multiplied by the dry season's duration, expressed in months.

As an example, take a house with a 50-m² (horizontally-measured) roof catchment area, located in a tropical region of Africa having an annual rainfall of 1400 mm or 1.4 m, with a dry season extending to 5 months annually. The water volume that can be harvested is thus 50 x 1.4 = 70 m³. If you take into account 10% loss to evaporation, maintenance, seasonal overflow, etc., you can count on about 63 m³. The household will therefore dispose of 63 000 litres divided by 365 days = 173 litres of water on a daily average. Considering average African water consumption at about 25 litres per person daily (especially in rural regions), rainwater harvesting of this quantity will cover the needs of about 6 to 7 people. There are seldom more people in a house of this size.

To calculate the cistern's holding capacity, you must take into account that for 7 months, the cistern will capture an average of 63÷7 = 9 m³ of water monthly. However, monthly water consumption is about 63÷12 = 5.25 m³. Therefore, the cistern's theoretical capacity to cover these 7 months (rainy season) as well as the other 5 months (dry season) will be 5 x 5.25 = 26.25 m³. In reality, rainfall will vary from one month to the next. On the other hand, either the dry season or the rainy season can overextend itself. This will obviously entail the need for a greater holding capacity. In our example, you can consider then that a 28- to 30-m³ cistern will provide sufficient volume to recover almost all precipitation and bridge the period between two rainy seasons.

Roof and gutter materials

Corrugated steel or plastic roofing materials are well adapted to rainwater harvesting. Conventional roofs tiles are also good. Thatch and straw roofs, wood shingles or palm leaves are not. For gutters, you can use galvanized steel, zinc, plastic or terracotta (preferably glazed on the inside). Eventually, you could consider bamboo or wood, but you'd need to make sure that water does not stagnate in the gutters in any way.

Drawing water from the cistern

Without electric power, the minimal solution is to provide a convenient access hatch in the cistern's top. Through this hatch, you can lower a bucket in the water on the end of a rope to draw water from the tank. The water will then be stored within the house, preferably in large earthenware jars where only the inside surface is glazed. To preserve the water's freshness, you need to periodically wet the unglazed outside surface of the jar.

Alternately, you can easily install a manual pump, or even an electric pump connected to a photovoltaic panel.

For personal hygiene, hot water can be provided by means of a 50- to 200-litre metal or plastic drum, painted black and exposed to the sun, to be installed atop some sort of turret. After a few hours, the water will be sufficiently hot to supply a faucet or even a shower. This set-up should obviously be connected to another water source, other than harvested rainwater (such as water from a river). Personal hygiene does not require high quality rainwater; lesser quality water is quite satisfactory.

Nevertheless, if you have a sufficiently large roof, you can consider hot water production fed from the rainwater cistern.

Potable water production

A basic principle of sustainable water management consists in adapting water quality to the uses for which it is intended. A person's daily needs in strictly potable water do not exceed 5 litres. The main problem in developing countries is the shortage of good quality water and the undue persistence in using available potable water for all uses. The PLUVALOR system is inspired by a pragmatic approach: prioritize the production of high quality potable water from rainwater harvesting on the basis of 5 litres per day per person. For non-food uses, it is better to agree to lesser quality water from other sources. Without a doubt, this is the PLUVALOR system's major appeal, especially in countries where good quality potable water is rare, or unavailable. Hence, priority should go to reserving rainwater for potable water production.

Starting from the rainwater cistern, water intended for drinking will be prepared with the aid of a gravity microfiltration system. Such systems have been on the specialized market for some time. These consist in ±10-litre vessels with a lid, in which are held ceramic filter candles. Raw water drips down through the ceramic candles. Filtered potable water then collects in the lower chamber to be drawn off from a spigot.

Combining small-scale rainwater recovery cisterns for drinking water production with the use of domestic ceramic filters is by far the least expensive solution to providing high quality drinking water for everyone, worldwide.

Within a program for rural development, it would be easy to finance the mass purchase of domestic ceramic microfiltration systems for individual resale to the population at an accessible price.

Another option would be to finance the implementation of local industries to manufacture ceramic filters. This relatively simple technology can be brought under control and simplified by local earthenware or pottery craftsmen[1]. Such manufacturing installations could be set-up in Africa, for example, to cover the needs of the entire continent.

[1]
Pottery craftsmen could develop and perfect earthenware filtering jars where the inside's bottom would not be glazed. Tests would be required to analyse bacterial elimination efficiency. At the bottom of this jar, you could even add a layer of granulated charcoal (again, needs to be tested). This is to improve the filtered water's taste. Water would therefore slowly drip down through the porous portion of the jar to a second jar (a water storage vessel), fully glazed on the inside only. The unglazed outside surface of the storage vessel would be regularly wetted to lower the temperature of the stored filtered water. To draw drinking water, a spigot or faucet would be placed at the bottom of the storage vessel.

Start by educating the population

To resume, producing quality drinking water in developing countries is a priority. Everyone, without exception, could easily dispose of such water thanks to rainwater, and with truly moderate capital investment. For other uses, lesser quality water (from wells, rivers, springs) is adequate.

Generally speaking, harvesting rainwater is not a tradition or custom within the populations concerned. Using this rainwater harvesting system, however simple, therefore requires a certain education.

Filtering rainwater to provide drinking water in the home is simple to learn. You pour raw cistern water in the filtering unit's upper compartment and you recover filtered water from the lower compartment. After a few hours when there is insufficient filtered water, it's time to clean the ceramic cartridge or candle. Cleaning is done in a bucket containing non-potable water, using a clean nailbrush specifically set aside for this purpose.

Rainwater is a renewable resource. Nevertheless, the most difficult thing to learn is that it's also a limited resource that should be used with considerable moderation. Accordingly, acquiring responsible management practices becomes important to prevent that the cistern be prematurely emptied. The best means is to inform the users every day to be mindful of the water quantity available.

Safe non-potable water production

I must insist that persistence to want to use potable water for all daily uses is incompatible with the notion of «sustainable water management».

We must insist that once your drinking water needs are addressed by a proper rainwater harvesting system, all other uses (personal hygiene, cooking, laundry and dishwashing) can rely on other sources of water (wells, rivers, lakes and springs) without necessarily needing to make this water legally potable. You must avoid at all cost resorting to chemical disinfection (with chlorine or «disinfectant tablets» for example). Chemically disinfected water undermines a person's immune system, even when used externally. Infants and young children are particularly sensitive to chemical disinfection. It inhibits the proper development of a functional immune system. If during the first three years of life, a child's immune system cannot develop due to water disinfection, it will malfunction lifelong. The first signs of this is the increased sensitivity to viral disease and the early emergence of allergy problems of all kinds. Thereafter, the tendency to degenerative disease also increases.

So bathing young children (especially infants) in chemically disinfected water such as city tap water sets the stage for more serious health problems down the line. Such problems usually occur after long years of using disinfected water.

Water that is contaminated by faecal bacteria is normally inappropriate for domestic uses. Fortunately, such water can easily be improved thanks to the natural process that we’ve called photo-purification, like what we recommend for greywater. This involves setting up two or more artificial ponds in a serial link-up, to create a series of wetlands. The ponds are shallow depressions dug in the ground, about 30 to 40 cm deep near the edges and 80 to 120 cm deep at the centre. The ponds must be made impervious at their bottom with a waterproofing membrane. You need to install aquatic plants and prevent access to ducks, geese and other animals. The inclusion of fish (or better, frogs and salamanders) is recommended, to destroy mosquito larvae.

Polluted water (from a river for example) will go through what we call « tertiary » treatment whereby nitrates and phosphates (often from faeces) are eliminated by the plants. Thanks to daylight, organic pollutants (detergent residues, un-decomposed faecal matter, bacteria) are subjected to natural phenomena called coagulation and flocculation. You then observe sedimentation of the pollutants and an often-spectacular regression of the water's turbidity as it becomes clear. The flocculated pollutants settle at the bottom where bacteria then complete their elimination (generating water an carbon dioxide in the process). In the clarified water, the sun's UV completes the purification process by eliminating the last remaining pathogenic bacteria. To help out these different purifying processes, you can also include a fountain that could be powered by photovoltaic panels. To help out these different purifying processes by oxygenating the water, you can also include a fountain that could be powered by photovoltaic panels or a windmill aeration system that needs no power.

I have had the opportunity of experimenting with the purifying power of such ponds. After receiving household grey wastewater that has first gone through a batch reactor and planted trench filter, the pond's effluent often complies with drinking water standards. Nevertheless, each set-up will be a distinct case study. When you want to purify river water that contains too much nitrate (from faeces or agricultural runoff) or phosphate (from faeces or laundry), filamentous algae quickly develop. These must be regularly removed. After composting, they provide excellent agricultural amendment of organic origin.

The size of such a system depends not only on the quality of the water that needs to be treated, but also on the quantity of filtered water that you want to draw daily. In most cases, a holding capacity of 3 to 4 weeks worth of water gives remarkable results.

After drawing filtered water (with a pump for example), it may become necessary to convey the water through a filter bed composed of gravel, sand, charcoal and limestone granules. With such a set-up, you can supply hundreds, even thousands of people with non-potable, yet innocuous «risk-free» water for non-food purposes.

The system described above uses the self-purifying capacity of natural water and is an alternative to the chemical treatment commonly applied to river water to produce mains water.

Note: in the long term, once there is a generalized application of ecological sanitation principles, the housing sector ceases to pollute watercourses. In the absence of agricultural and industrial pollution, river water returns to its original purity. Water can then be drawn from rivers to supply water distribution networks or to be used directly in homes for non-food uses, without any health risk. The transition to organic farming would eliminate pollution from the agricultural sector (i.e. from fertilizer and pesticide residues).

Rainwater harvesting in desert regions

Rainwater can constitute the only source of water in the desert. Take for example the central region of the Sahara where annual rainfall is about 20 mm. In reality, we are looking at one single 40 mm rainfall every 2 years. This would mean that you need to recover the water from that single event, and keep it fresh for up to 2 years.

Some of the natural water stops along caravan routes are actually underground grottos or rock cavities where precipitation accumulates naturally and water conserves itself very well. You can recreate such water stops. Fortunately, there is no lack of space in these regions. With a catchment area of 1 hectare, you can theoretically recover an average 200 m³ of water annually. Accounting for a 2-year wait between rainfalls, you would thus need a cistern capacity of at least 400 m³ per hectare of catchment area. This could provide about 500 litres of water per day.

Accordingly, you would need to bury a concrete cistern of the desired capacity at the low point of the (sloped) catchment area. On a finely planed sand base, you then lay out large sheets of PVC welded together to form a very large and impervious surface. To protect the PVC from deterioration by the sun's UV, you cover the membrane with a 20 cm layer of washed pebbles or gravel. A protective perimeter fence will prevent intruders from walking on the catchment area. Rainwater will then seep through this gravel layer to runoff to the central drain or gully towards the underground cistern.

With vast set-ups comprising many km² of catchment area, you could even create an oasis. To limit evaporative water loss in artificial oases, you would need to pay close attention to maintain ground cover with dead plant matter (leaves, cut grasses, etc.).

The main threat to this type of set-up is sand storms.

Sustainable Urban Wastewater Management

In tropical regions

A growing share of the population lives in (shanty)towns where hygiene is often dubious. The absence of sewers is often invoked as the main cause for this sanitary plight. Equating the lack of sewers to sanitary problems is somewhat misleading. On the other hand, rivers that cross through these cities – often enormous and overpopulated – convey considerable faecal contamination, thus compromising the quality of distributed water.

A new approach to wastewater conveyance

The implementation of a sewerage network including wastewater treatment plants is always presented as the only solution to sanitize the urban milieu. However, this requires important capital investment that is unfortunately not within reach of many of these populations. And even then, not all problems tied to wastewater disposal are resolved. Experience has shown in hundreds of cities that during the rainy seasons in tropical regions, sewers are incapable of absorbing the precipitation. When overloaded, sewers discharge their contents on city streets with all its faecal contamination, a vector of disease. What's more, the treatment plans are often overloaded by torrential tropical rains (e.g. monsoons) leading the sewers to spill out their untreated pollutant load into the closest river, which usually provides the population downstream with its drinking water!

In these conditions, how can one find a proper solution to urban wastewater management?

To start, you must divide the city into residential zones that include high-density vertical housing districts (core urban centres) and individual family housing districts. In the first case, you maintain status quo for now, i.e. centralized conveyance and treatment of wastewater. On the long term, you can arrange for the eventual transformation of the wastewater conveyance network as per the recommendations under EAUTARCIE's ECOSAN in an urban setting. Fortunately, vertical housing districts represent a proportionately weaker share of the overall cityscape. The majority of the population lives in family district homes serviced by small yards or gardens.

In terms of wastewater collection for family housing districts, only roadway stormwater will need to be collected and conveyed in a system of drainage gutters and/or covered chases (e.g. topped with perforated concrete covers, grates, etc.).The implementation of such chases is much less expensive than that of underground sewers. To a certain extent, these could also accept greywater discharged from the homes. (What must absolutely be prevented is the discharge of black water (containing faecal matter) into these chases.) If the chases were used to convey greywater, then they should not be watertight to permit the water's infiltration into the ground. But we shall see that by adopting sustainable techniques, stormwater networks will only partly receive greywater – and only during the rainy season (when irrigation is not needed for gardens). It will mostly collect only stormwater.

A new approach to urban waste reuse for urban agriculture

Residential districts having their own yards or gardens constitute in these countries an appreciable potential for foodstuff production. When setting up new neighbourhoods, urban planning should even provide enclaves within the urban fabric reserved for intensive gardening, with small plots made available for families (i.e. community gardens). With the foreseeable increase of food costs, urban agriculture will become a viable economic activity as well as an essential ecological endeavour. To facilitate the growth of such a vital activity, we must abandon, once and for all, the altogether erroneous notion that considers flush toilets as the basic requirement for good domestic hygiene. The biolitter toilet or BLT offers as much convenience and hygiene as a conventional flush toilet. Its acceptance is a question of education with regards to the environment and good citizenship.

A biolitter toilet's effluent, when correctly composted, supplies an organic soil amendment that will generate high gardening yields. Urban composting [2] would also absorb the fermentable component of household garbage and cellulose-based waste materials (cardboard packaging, soiled paper, green wastes from private gardens and public parks, etc.). With this option, the volume of garbage would decrease spectacularly, by over 50% of total mass. Without smelly organic waste to treat, the selective cull of other waste would be made easier: metals, plastics, and glass for reuse or recycling.

[2]
Contrary to established notions, correctly done composting of urban waste combined with BLT effluent does not generate odours. As soon as the carbon/nitrogen ratio (C/N) is appropriately adjusted, odours disappear.

The shredding of cardboard waste and the collecting of dead leaves and other green waste offer a potential to supply appropriate litter for the BLT's in each home. Grass clippings and shredded branch cuttings from public spaces in and around cities provide an excellent mulch (and organic soil amendment) to reduce crop or garden irrigation needs. All these activities require the implementation of certain measures relative to the concept of permaculture.

Without black water (faecal water) production, greywater (soapy water) is perfectly appropriate, during the dry season, to be used for manual irrigation of small gardening plots, all without prior treatment or any health risk. Thanks to ground cover, greywater production has a good chance of satisfying these garden crops' water needs. The stormwater chase network will be dry at this time. During the rainy season, greywater that is not used for gardening irrigation will be conveyed towards natural wetlands due to the abundant rainfall, before rejoining the closest watercourse. The wetlands should be sized for a water holding capacity of up to 3 weeks. During this time, daylight will coagulate the soaps and detergents, as well as bacteria. The clarified water that will reach the watercourse will contain no detergents, and no potential faecal contaminant.

In dry or desert regions

As already mentioned on this website, in dry regions, where every litre of water « is worth its weight in gold », the use of a flush toilet and its inherent offshoot, black wastewater treatment pose a grave ethical problem. The water wastage that goes with the elimination of our excreta, and the destruction of precious organic matter for purposes of wastewater treatment reduce humanity's foodstuff production capacity. Therefore, forget flush toilets and black water treatment. The first consequence of eliminating WC water flushes is a substantial reduction in household water needs, by 25 to 30%.

Here again, you subdivide the city in high-density vertical housing districts and single-home family housing districts. In the first instance, people will continue to use flush toilets, but of the low-flow type. Toilet effluent will be selectively collected and treated by means of the infrastructure described at EAUTARCIE'S ECOSAN in an urban setting. The collected greywater would be conveyed directly to irrigate farmland, without going through a treatment plant. In this way, all city wastewater becomes available for agriculture.

For family district homes, flush toilets should be strictly forbidden[3]. In light of low rainfall in these regions, there shouldn't even be a sewerage network. Soapy greywater would simply be reused for irrigating family gardens. Litter for the BLT would essentially be made of used packaging cardboard. Plant wastes and other cellulose-based matter would be used as needed and when available. Composting of toilets' effluent would be done in the yard, using kitchen and garden waste, and including the fermentable part of household garbage. The resulting compost would provide fertilizer for gardening or farmland.

[3]
About the flush toilet’s environmental footprint: the quantity of human dejecta produced by one person (and transformed into nitrate pollution by conventional sanitation) is sufficient to fertilize – after proper composting (with plant matter) – the portion of land that sustains food crops for that one person. If that person uses a flush toilet, the water that he flushes to evacuate his dejecta is most often enough to irrigate the said portion of land. It follows that all flush toilet users annually destroy their own food base. Food for thought in an already overpopulated world…

We tend to underestimate the quantity of compost that can be produced in a city. Considering the extensive infrastructure required for the treatment of black water, it is not exagerated to assert that cities will become the umbilical cord of food production. Generalized use of this valuable organic matter for soil amendment has numerous advantages. First, you increase the soil's water holding capacity by increasing its humus content. This leads to a reduction in crop irrigation needs, chemical fertilizers, herbicides and pesticides, meaning less pollution and expense. In arid and desert areas, increased humus content also reduces the soil's reflectance (albedo), resulting in a reduction of ascending warm air currents, progressively leading to improvements in the rainfall regime. Desert reclamation is within our power, but it takes the political will to set up worldwide biomass management projects that would comply with techniques developed by Jean Pain and Paul Moray.

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