Water availability in desert environments remain
a grave concern – and has always been a matter of survival. With climate change
this need will be further exacerbated as temperatures rise becomes more severe
and water resources more scarce. Renewable energy powered membrane filtration –
or desalination – cannot increase the quantity of water. The advanced treatment
can however make water that is unfit for consumption potable as is illustrated
in Figure 1 at the example of a site in Tanzania, East Africa.
Decentralized – or autonomous – treatment
systems are typically small, do not rely on infrastructure and need to be
robust to withstand operation in the harsh environment that characterizes
deserts. Providing the energy for operation, specifically the operation of the
high pressure pump required for nanofiltration or reverse osmosis, renewable
energy is an obvious choice. In deserts where solar irradiance is typically
abundant, photovoltaics or solar energy are suitable so long as sand storms and
dust as well as excessive heat can be managed.
The research on directly coupled renewable
energy powered membrane filtration system of the Schäfer-Richards teams began
in Australia two decades ago. Brackish groundwaters were treated in the
Australian outback that contained a wealth of contaminants ranging from salts
through to natural uranium. The direct coupling means that the renewable energy
resource is neither converted nor stored, resulting in a fluctuation of energy
with solar irradiance, while water is stored for periods of shutdown (bad
Treating brackish water is a significantly more
economic option to seawater desalination, because the salinity and hence the
pressure requirements are lower. Contaminants that occur in brackish groundwater,
in addition to salinity, may include nitrates, arsenic, fluoride, uranium and many
more. Organic matter contents is bound to increase with climate change, while
micropollutants, such as pesticides, are increasing in occurrence globally.
Nanofiltration and reverse osmosis can remove many of these contaminants, while
the generation of a concentrate remains a challenge in remote areas.
Evaporation ponds may be a viable option in desert environments. The formation
of inorganic scaling through salt precipitation is a further operational
This lecture intents to provide an overview of
renewable energy powered nanofiltration/reverse osmosis and inspire a
discussion about the suitability of such technologies in the desert context.
Issues may span from typical water contaminants to the operational issues such
as extreme temperatures.