Seedlings powered by recycled sludge


Safi Sana Circular Model

Short summary and update of the Safi Sana facility in Ghana and the connected Via Water project:
Safi Sana collects urban faecal and organic waste from poor communities to produce energy and organic sludge. This sludge is processed into nutrient rich process water and nutrient rich dry compost. The compost is high in organic matter and nutrients and is safe for use in vegetable production. It is also essential for soil fertility improvement and hence providing a much needed boost to the local crop production. The Safi Sana model is cyclical (see illustration below) and should sustain itself by selling the energy to the grid and compost to local farmers.
Impact: Improved environmental sanitation for 125,000 people. 25 tons of faecal sludge and solid organic waste processed daily. Producing 2,500 kg of organic fertiliser serving 50 hectares of farm land 2,200 kWh to serve 3,000 people with green power on a daily basis.
Below a schematic overview: We collect organic material from the community (bottom left), this is fed into the digester via mixing pits. Biogas is converted to electricity and connected to the grid (yellow line) and compost and seedlings (orange and green lines) go to the farmers who in turn produce for the local markets (dark green line).
In the connected ViaWater pilot, the produced compost and water is used to grow seedlings in a nursery. We expect that there is a better market for seedlings which can help farmers increase their yield even further. It also helps us to make better use of the irrigation water which is difficult to transport. This way, the treatment of waste becomes self-sustaining. The pilot is assisted by Wageningen University, East West Seeds International and Tikola Ltd.

But before we can start seedling production, the waste treatment centre needs to be completed, so let’s start there:

Inoculation stage:
The Safi Sana waste treatment factory is situated in Ashaiman, an urban slum at the edge of Accra in Ghana. The centre piece is a 27x27m square digester with a capacity of roughly 1800m3. We are now rounding off the inoculation phase. The digester can be compared to a stomach; bacteria convert organic waste into methane gas through the process of anaerobic digestion. The initial ‘feeding’ of the Safi Sana digester – or inoculation - consists of faecal sludge from nearby public toilets and indigested content from animal intestines – also called ‘unborn manure’ which we get from the local abattoir. When the Methane production is high enough, we can connect to a CHP – a Combined Heat and Power generator which can generate electricity. Safi Sana has a contract with the Electricity Company of Ghana to deliver electricity to the grid.

This is also the point where we can start fertilizer production. Digestate, or the material remaining after the anaerobic digestion of biodegradable feedstock, will be pumped from the digester to drying beds. The drying beds are covered with permeable material allowing water to sift through and the solids to remain on top. We expect this process to begin in September, which will allow us to start the production of organic fertilizer.
In parallel we have selected the greenhouse technology and also expect this to be built on the Safi Sana property in September.

More on that in the next blog.