The World Water Forum is being held until March 26 in Senegal. Thursday, the small company Filtre Plante presented with the UNHCR a sanitation project by phyto-purification of several refugee camps in the Sahel. This ecological process has recently been applied to the Dakar corniche where papyrus plants feed on dirty water to make it usable again. A first in West Africa. Follow the pipe.
From our special correspondent in Dakar,
Michael Orange disappears behind the trees and descends three meters below. We can hear the delicious sound of a waterfall whose bed plunges towards the sea, at the foot of the cliff. But it is a blackish pool that appears below a pipe: a municipal sewer. ” Much of Dakar’s wastewater flows into the sea. My children don’t bathe in Dakar, that’s for sure! exclaims the boss of Filtre Plante, created in 2020.
He then shows a pump and a black pipe that rises from the pond on the plateau to reach a patch of thick grass, papyrus. In the middle, a small jet delivers the water pumped below. In this basin, the water does not stagnate, it is drained by a succession of layers of gravel and emerges below. Beneath this plant mass, bacteria carry out the work of natural decomposition of the organic matter contained in the water. On arrival, this nourishes both the plant and the water that comes out clean and enriched with nutrients. However, it is not drinkable. ” Pathogens are 99% eliminated but this is enough for them to multiply again “, admits Michael Orange. As for its use for watering a vegetable garden, it still divides scientists. ” The reality is that the water that comes out of the planted filter is much better than that used for market gardening in Senegal. “, he sweeps.
Be that as it may, the treated and recovered water is not quite that which flowed from the domestic tap, the recycling of the water is therefore not fully completed. Another limitation is that only a very small part of the water flow is pumped for treatment.
That said, phyto-purification has undeniable advantages. It is first of all a basic, economical process – a little electricity, solar as much as possible – and ecological. Its development, in France for example, dates back to the end of the 1990s, particularly in the sanitation systems of local authorities. It is part of the range of nature-based solutions (SFN), or bio-mimicry, increasingly studied in the context of environmental preservation. Nothing revolutionary then, but it is a first in this tropical region.
The tropics, an ideal latitude for phyto-purification
” It is the perfect solution for the countries of the South “, says Michael Orange, who first highlights the space saving achieved: “ With the heat, the bacteria multiply and their concentration allows a more intense action on a smaller perimeter. Basically, it takes three times less floor space for the same amount of waste water [que sous des latitudes européennes, NDLR]. And space is often the major constraint in the development of a phyto project. In schools for example, which could connect their septic tank to a basin of plant filters.
The climate is also an asset, further argues the promoter of the concept: a phyto project is functional all year round when the plants do not die of cold. It also allows for a greater variety of plants. Finally, the planted filter does not require a large number of qualified maintenance personnel.
Michael Orange is therefore convinced, “ water treatment and reuse is part of the solution to global warming “: “Sif a village starts to not only treat but to recover wastewater, the system would be virtuous: less pollution, possibilities of cultivating all year round without waiting for the rainy season which lasts only four months maximum, less depletion of groundwater under demographic pressure… »
The rescue of the Corniche
Finally, the planted filter has an equally interesting economic and social component. Maha Baalbaki, and founder of the Ecolibri association, can attest to this. It was even she who came to find Michael Orange for his corniche greening project. This portion of cliff, still unbuilt, is the customary property of the Ouakam Fishermen’s Association, which closely monitors its land. “ The idea of planting to protect their site immediately interested them. They are seafarers and the coastline is one of them”, explains Maha Baalbaki. Many especially are also divers and the idea of treating the water suited them too “.
But all this greenery drinks a lot of water: 10,000 euros per year of clean water transported by tank truck, according to the accounts of this entrepreneur. For the same sum, the NGO was able to invest in these two 10 m² planted filters which have not generated any costs for a year. A planted filter of 10 m² offers a potential of 1750 liters of recycled water per day, or the watering of 350 trees.
Purified by the plants, the water resumes its circuit. The black pipe first meanders through a beautiful plot of various endemic species: here a young baobab tree, there a casuarina tree, further on a badamier which neighbors a shaded area and a palm tree. The ground slips gently towards the edge of the cliff. It’s hard to imagine that this future garden will resist winds and salt spray. In the meantime, it’s a reassuring island in the middle of the concrete.
A few more meters and you enter the tolou keur, a collective agro-ecological vegetable garden. The pipe irrigates lettuce, beets and chard drop by drop, which will be harvested by the fishermen’s wives. Third and last site visited by the tip: the urban forest, inaugurated almost a year ago by the Minister of the Environment and the EU, financial partner. ” 3 000 trees supposed to represent in 20 years a 100-year-old forest because they will capture 40 times more carbon than an oak forest for example says Maha Baalbaki.
The filter planted to clean up and green refugee camps
The planted filter seems to have a bright future in Senegal and perhaps beyond. Two humanitarian projects are already well underway. The first should be set up at the country’s large prison, located in Thiès, where prisoners wade through the overflow of their toilets.
The second will be tested in several refugee camps in Burkina Faso, Niger and Chad. “ Wastewater management is a critical issue in all refugee camps, explains Pierre-Yves Rochat, Water, Hygiene and Sanitation Advisor at UNHCR who will buy filters from Michael Orange. They come from family or community latrines and showers and accumulate inside pits that require frequent and expensive emptying services. The overflows also generate soil pollution and risks for the already fragile health of the exiles. The planted filter will have a double meaning here: sanitation and reforestation, which allows, among other virtues, to make the temperatures more bearable.