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Clean water and fertilise soil with vegetable carbon
Solve waste water problems and at the same time gain a fertiliser for depleted soils. A new type of small sewage treatment plans will soon improve living conditions for people in Burkina Faso in western Africa. With the help of vegetable carbon, vital phosphorus can be recovered from waste water and used as soil fertiliser.
The concept was developed and implemented by the company Ökoservice GmbH in Denkendorf, together with the Hamburg University of Technology (TUHH), Germany, and local partners in Burkina Faso, such as ClimateSol. The German Federal Environmental Foundation (DBU) is providing technical and financial assistance of some EUR 121,000.
“Project results show impressively that the phosphorus cycle can be closed with smart environmental technology – in Germany and worldwide. This is a crucial issue, requiring appropriate cooperation to maintain our shared basis for life,” as DBU Secretary General Alexander Bonde said when presenting the project.
Waste product as fertiliser
This type of small sewage treatment plant generally does not require preliminary treatment, which is why no heavily contaminated faecal sludge is produced. This also eliminates the need for subsequent treatment, and the plant can also be significantly more compact than others, resulting in clear cost benefits and a smaller ecological footprint, as explained by project leader Jörg Fingas from TUHH.
In the project, an existing plant was adapted to the specific needs in Burkina Faso. “The special feature is that we added regional vegetable carbon to the sewage sludge. This left over from cooking, is extracted from the husk of the desert date tree, and is a waste product from oil production,” Fingas notes. The phosphorus and biomass contained in the waste water are deposited on the carbon, and they can subsequently be used as fertiliser to make impoverished soil fertile again. At the end of the process, the water is cleaned to the point where it can be used to irrigate fields.
Research is continuing: reaching drinking water quality
The project partners attached great importance to consideration of ecological and economic aspects. “This is why we designed the plant so that it can be built by local craftsmen, as a contribution to local value creation,” says Ökoservice’s Thomas Czoske. The goal is to use as many locally-available parts as possible, with only a small share coming from Germany.
The tested plant is designed for a household with up to twelve people, but it is also possible to scale the sewage treatment plants for up to 5,000 people. This makes them suitable for individual housing and also hotels, schools or camps.
According to DBU expert Franz-Peter Heidenreich, negotiations are already in progress with the first interested parties. Operation of the test plant is already secured for the next two years.
During this period a PhD thesis will investigate if the small sewage treatment plant can be used with e.g. moringa seeds as a disinfectant to reach drinking water quality. “We’re strengthening several cycles with this project, not only phosphorus but also water and local value creation,” is how DBU expert Franz-Peter Heidenreich summarises the project’s results.
The background – phosphorus as a raw material
Phosphorus is an important component of agricultural fertiliser. It is released in strip mining, with corresponding impact on the environment. This is frequently in countries with difficult political situations and takes a great deal of energy.
Much of the phosphorus ends up in sewage sludge from food. However, it cannot be reused directly in agriculture, as it often contains to many pollutants.
However, if phosphorus is not reused, there is a risk of exceeding one of the contamination limits for the global ecosystem defined by international experts, and missing the opportunity to meet the UN global sustainable development goals adopted in 2015 in the long term. These are intended to ensure sustainable development at the economic, social and ecological level.
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