Rapid population growth in Dakar has resulted in an increased demand for water and a growing pressure on an already stressed and inadequate water supply (Re et al. 2010). Public water supply in Dakar is sourced from a combination of groundwater (46%) and surface water piped from the Senegal River via hundreds of kilometres of underground pipes (Taylor 2016). The sanitation infrastructure is dominated by septic tanks that are attached to households and emptied periodically by tanker trucks.
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| Household Septic Tank in Dakar
Source: Professor Richard Taylor 2016
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A combination of challenges stand in the way of effective water supply and sanitation in this city. The main issue is groundwater contamination. In recent decades groundwater has been cited as the answer to water and sanitation provision across much of Africa (Taylor et al. 2009). Not only are groundwater resources in Africa plentiful and relatively simple to access in many regions, they also provide a comparatively high-quality supply of water that tends to require less or even no chemical treatment compared to surface water and also stand to be the only water resource that may benefit from climate change (Taylor et al. 2013). However, in Dakar groundwater may not be the solution. Although the city depends heavily on groundwater for its public water supply, the groundwater quality here is incredibly low.
The low-quality of the groundwater in Dakar is mostly due to contamination from human waste. Many of the septic tanks in the city are poorly maintained and as a result occasionally spill over allowing effluent to drain to the aquifer. Furthermore, during rainfall events, public toilets and sceptic tanks may flood and spill out onto the streets and also drain to the aquifer. Waste may reach the aquifer via a number of pathways. If it drains through the soil and there is a long enough distance between the surface and the water table, the harmful organisms in the waste may be removed and subsequently the aquifer will not be harmed. However, if the water table is shallow, some harmful organisms may reach the aquifer before effective filtration has taken place. Alternatively, waste may drain to the aquifer more directly via a macropore in the subsurface. This could either be a vertical crack in the ground or man made heterogeneity such as a poorly sealed well.
Aquifer contamination from human waste means that groundwater may contain harmful pathogens and have much higher levels of nitrates. The international guideline for the concentration of nitrate in drinking water is 50mg/l. This value is based on evidence for the development of methaemoglobinaemia in infants exposed to higher concentrations (WHO 2011). In Dakar, nitrate levels have been found to be as high as 500mg/l.
However, it is not only fecal contamination that threatens the quality of Dakar's groundwater. Due to its coastal location, the aquifer is at risk from salt water intrusion if too much groundwater pumping occurs. This means that even if the Dakar authorities prevented contamination from human waste, the aquifer may still not be able to provide the city with enough freshwater.
Dakar is in a difficult position and is in need of alternative water and sanitation solutions to those now being widely promoted elsewhere across Africa. Already a number of ingenious solutions are being proposed including waste treatment (shown in the video above) and the pumping of urban groundwater to peri-urban areas where it can be used to both irrigate and fertilise farmland. But it is clear that more needs to be done to improve water and sanitation provision in this city.
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ReplyDeleteVery interesting. Could coastal regions invest in desalination plants to provide fresh water?
ReplyDeleteHi Sarah,
ReplyDeleteGood question. Rainfall is the dominant source of freshwater in Sub-Saharan Africa (SSA) despite being highly variable in time and space. The erratic nature of rainfall patterns in SSA mean that for many parts of the year the region suffers from water shortages and therefore an alternative, more reliable source of freshwater would be highly desirable.
Global desalination capacity is growing at an annual rate of 13.6% and is expected to do so for at least the next 5 years. Many countries in the Middle East and North Africa (MENA) region are already turning to desalination plants to supply freshwater on a large scale (Algeria for example) however take up has been relatively slow in sub-Saharan Africa. Why is this?
For one, desalination technology is still a very expensive method of providing freshwater. Although major technological advancements have been made regarding new and ingenious membranes, it remains a complex and energy intensive process. One of the biggest problems facing water utilities in SSA is funding. The public sector is critically constrained by a lack of capital, and due to very low levels of cost recovery (in the city of Lagos only about 4% of water bills are paid!), expensive projects such as desalination plants are simply not economically viable. Low levels of cost recovery also mean that the private sector is very unlikely to step up to provide funding, especially in SSA which is perceived to be a relatively high-risk investment location.
However, some countries in SSA are investing in this technology. South Africa is the regions biggest user of desalinated water and has recently teamed up with Iran to develop a new generation of plants to "be built along all coastal communities" in the country (Reuters 2016). Ghana and Namibia also have operational plants. Yet even in South Africa, desalination only serves as a complimentary source of water to more traditional sources and it is by no means close to providing national coverage. Nor is it close to providing water at a price that could be afforded by all income groups.
Further challenges include the fact that this is a new and complex technology and therefore desalination plants rely on a local pool of experts, chemicals and materials to keep them operational. The supply chain for getting the necessary chemicals and materials to this region is long due to the lack of local industry and therefore materials have to be imported from afar at a high cost. Without training, local populations are also not able to operate and repair the plants themselves and therefore international experts are needed.
To sum up, desalination has proved to be a viable alternative source of fresh water for a few countries, particularly those that have an abundant supply of cheap energy from oil, such as Algeria, Saudi Arabia and Iran. However, for SSA, where for most countries public sector capital is low, private sector investment is unattractive, many of the population cannot afford to pay much for their water, and specific local knowledge and industry is lacking, this technology is not currently the answer. However, the speed at which this technology is progressing is very promising and perhaps at some point in the future, when the renewable energy capacity of SSA is greater and the desalination process is less expensive to set up and operate, this technology may be able to provide a large and reliable supply of freshwater to the region.
I hope this answers your question! Below are the links to the sources I used.
best,
Freddy.
http://www.prnewswire.com/news-releases/strategic-analysis-of-the-desalination-technologies-market-in-sub-saharan-africa-300232096.html
http://www.reuters.com/article/us-safrica-iran-water-idUSKCN0Y20PQ
Hi Freddy, thanks very much for your comprehensive reply.
ReplyDeleteIt is obviously a complex and expensive industry and perhaps waiting for advances in affordable technology is the only option. Very frustrating though as one senses that if the infrastructure and trained staff could be initially provided eventually local production of equipment and chemicals and a local source of trained workers would follow.