Currently, many rural economies are locked in subsistence farming and are vulnerable to food insecurity due to lack of access to water, technical know-how and feasible revenue streams, further aggravated by unsustainable farming practices and resulting in migration from rural areas to cities. Climate change negatively affects agricultural production in water-scarce regions of Africa, which makes water use efficiency one of the key factors for agricultural and rural livelihoods. Agriculture is still the most important economic sector in rural Africa and pathways of transition to a circular bioeconomy bears significant potential for socio-economic and environmental sustainability of rural communities in the long term. Revenue diversification pathways in Africa through bio-based and circular agricultural innovations (DIVAGRI) is an EU Horizon2020 funded research projects which includes 39 direct partners. The DIVAGRI consortium (https://divagri.org) has identified a range of major challenges in its target regions and identified solutions to address them within the scope of the project.
The Solar Desalination Greenhouse (SDGD) is a technology that transforms saltwater into freshwater, which can then be used for irrigation or mineralized for drinking. This desalination process is facilitated by halophytes, plants that have adapted to grow in saline conditions. As these plants grow, they humidify the air within the greenhouse. The SDGH then uses passive and active dehumidification to produce freshwater from this humid air, without the need for energy. The SDGH also offers additional benefits such as the production of high-value halophytes and sea salt. It’s a flexible system with moderate installation and operating costs, and it can utilize renewable energy sources like solar or geothermal power.
At the Welgevallen Experimental Farm in Stellenbosch, the University of Stellenbosch has adapted the SDGH to include aquaponics. The system has two water tanks with 1 000 Mozambique Tilapia (Oreochromis mossambicus) that are linked to 8 raised media beds, deepwater culture and an NFT system. The tilapias that are fed daily provide nutrients for the halophyte plants called Salicornia (Salicornia meyeriana). The water circulates between the plants and the fish in the tanks. The Salicornia grow in the brackish saline water at 20 ‰ (ppt), extracting the salt and producing water vapour that condenses on the sides of the greenhouse. The Salicornia plants can be harvested to produce a natural salt and are also used for fodder for livestock. The water can be harvested for drinking or other agricultural purposes.