Abstract
To address global fresh water scarcity, a novel hydrogel based seawater desalination technique using a
superabsorbent starch based polymer is proposed. Current approaches rely on thermal, membrane, or
hybrid approaches to desalinate water and impose high energy and environmental costs. Approximately
only 3 percent (by weight) of seawater contains dissolved solids (including salt) that are bonded to less
than 10 percent of seawater. This study harvested the remaining water using saponified starch-gpolyacrylamide’s hydrophilic properties. This required a) the creation of a hydrogel to separate fresh
water from seawater, b) the separation of the hydrogel from the brine solution, c) the dewatering of the
gel resulting in aqueous sulfuric acid and d) the recovery of fresh water from the aqueous solution. The
study demonstrated that a) It is possible to use such a hydrophilic starch based polymer to desalinate
water without thermal or electrical energy, b) that the extracted water’s conductivity is comparable to
fresh water indicating that the salts have been separated, and c) that this approach has promise in
mitigating the problems of pre-treatment and post-treatment during desalination. Mass and
conductivity analysis confirmed that the extracted water had a total dissolved solids concentration of
513 mg/L, within the WHO guidance for good drinking water (<600 mg/L). Sustainable and accessible
means for desalination have potential to improve millions of lives; the implementation of the proposed
hydrogel based desalination technique can address this need with very low infrastructure investments
and a high yield for irrigation needs (90%) and potable water needs (73%) with no chemical
contaminants, while producing a commercially useful fertilizer (Gypsum) as inert byproduct.
Rationale:
Water scarcity is a global crisis affecting over a billion people. 70% of the fresh water demand globally is
for irrigation and the increasing demand has caused the depletion of ground water tables in many parts
of the world.
Sea water is abundant, and current approaches to desalination are cost prohibitive in many parts of the
world, in economic, energy and environmental terms. There is a worldwide need for a less energy
intensive means for desalination. Current approaches to desalination primarily focus on membrane
based technologies or thermal technologies or a hybrid of these techniques. These attempt to physically
separate the salt from water. The amount of salt dissolved in seawater is only 3% by weight which bonds
with less than 10% of water, and yet these processes must subject the entire volume of water to the
current energy intensive desalination treatment. Dissolved salt forms an ion-dipole interaction with
water molecules. An alternative approach that selectively separates the water that has not formed such
an ion-dipole interaction by using a hydrophilic substance is highly attractive because it is a passive
chemical approach compared to the active energy intensive approach of thermal or membrane
technologies. Such an approach opens a new avenue of scientific investigation of desalination
technologies, and can potentially provide cheaper and abundant access to fresh water both for irrigation
and domestic use with much lesser infrastructure and capital commitments.