Can desalination plants solve Africa’s water crisis?

Due to the marked precipitation seasonality in many regions in Sub-saharan Africa, widespread failure of the previous rain season would lead to the occurrence of drought which threatens food security. For instance,  Southern Madagascar has experienced agricultural losses of up to 60% in the most populated provinces, 70% of crops in the capital city of Angola are allegedly affected by drought. 

Climate-induced food security is forced towards the top of the political agenda.  In the previous blog, we explored GMMR that transfers from areas of surplus to areas of deficit. However, not all countries have ample groundwater aquifers to allow huge amounts of water to be transported. In this post, we will explore the technology of desalination that turns seawater, into clean, usable water. 

What is desalination? 

Source: Youtube

There are two leading desalination technologies (Shatat and Riffat, 2012),

Reverse osmosis, where seawater is fed through a fine membrane under high pressure that produces brine (salts and minerals).

Thermal evaporation, where saline water is evaporated and condensed to form freshwater, similar to the process of distillation. 

In short, desalination removes salts and minerals from seawater, making it safe to consume. 

Diagram of reverse osmosis. Source: City of Cape Town

Desalination in Algeria 

Algeria, like other southern Mediterranean countries, is facing the problem of water and food scarcity. It has an uneven distribution of rainfall - mainly distributed in the northern coastal region but drops to less than 100 mm/year in southern Sahara  (Bessenasse et al. 2010). The existing balance of water resources is destabilised by continuous droughts exacerbated by climate change, in addition to pollution from industrial and agricultural activities close to the 1200km coastline (Mitiche et al., 2010). Furthermore, groundwater levels in the northern region where 80% of the population lives have been significantly affected by the high pumping rates - and the use of groundwater has essentially reached its limit (Drouiche et al., 2011). 

Algeria is a successful example that turns to desalination to meet its water needs. It currently has 11 desalination plants with a combined capacity of over 2,100.000 m3/day, producing about 20% of the national drinking supply. The city of Magtaa is home to the continent’s largest RO plant, providing a whopping 500,000 m3/day of drinking water for its citizens. Thus, desalination stands out as an efficient solution to compensate for major water shortages for drinking water, and rising demands for agricultural, industrial sectors and to tackle Africa’s timely water scarcity issues (Hamiche et al., 2018). 

However, desalination also has its drawbacks  (Djoher, 2020; Lattemann, 2007) 

Economic costs 

• High energy costs due to the large quantity of energy consumed by the desalination plant 

• Desalinated water is 2-3 times more expensive than natural water sources. Therefore it may not satisfy the needs of the poorest who are most affected by the water crisis 

Environmental concerns  

• Disposal of hot and concentrated brine may damage fragile marine ecosystems 

• Energy production unit accompanied by the desalination plant runs on fossil fuels which emit greenhouse gases, contributing to climate change

Desalination for agriculture? 

Desalination might have a role in food security by alleviating water constraints for irrigated agricultural near coastal areas threatened by water scarcity, though its major purpose will be for drinking water supplies (Martinez et al., 2020). 93% of African agriculture is rainfed, but with rainfall on the decline and becoming more inconsistent, desalination could be a tool to support agriculture during periods of low rainfall (Mitiche et al. 2010). 

Algeria is positioned in a difficult situation with regard to agriculture as it cannot achieve food self-sufficiency due to low endowments in renewable resources (Lipper,2011). Therefore, Algeria heavily relies on 45% of imported food (virtual water trade) that costs an average of 9 million USD (Salim,2021). This indicates an utmost priority for Algeria to better exploit its agricultural potential by utilising its desalination technology to expand cultivated while adapting to hydro-climatic constraints to minimise the dependency on food exports. 

While the cost of desalinated water may be too high for irrigated agriculture,  there are still  successful examples in Spain, where brackish water is processed in small-medium sized plants to adapt to local farmer requirements whilst ⅕  of the total desalinated water is used for irrigated agriculture (FAO, 2004) 

In conclusion, even there is a case to be made that desalination is energy-expensive and environmentally harmful, desalination has shown potentials for water-scarce countries to meet their urgent requirement for extra sources of water to increase water and food access. However, it remains clear that desalination potential has not been fully recognised in terms of agricultural uses in Algeria and it can be a useful tool in managing long-term water uses