An energy free pump: nanoporous gels to passively lift subsurface water

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THE NEED. By 2030, a third of the population in developing countries will reside in areas where the gap between water demand and water supply is predicted to be over 50%. Meeting this shortfall by exploiting alternative water resources using traditional engineering technologies will deplete valuable energy resources and incur significant cost. Globally, drought-related economic losses between 2010 and 2015 had an estimated cost to agriculture of $29 billion.THE VISION: This project will develop a bioinspired pump capable of passively lifting subsurface water, from depths of tens-to-hundreds of meters, using only energy that is provided naturally by the atmosphere. This bioinspired system uses emerging materials and concepts in geotechnical engineering to mimic the wicking mechanisms plants use for transpiration. Through the injection of a colloidal silica-based hydrogel into soils and rocks, a soil-hydrogel network will be created that has an increased soil hydraulic conductivity and water retention capacity during periods of high negative soil water pressure (i.e. when the soil is very dry). The network will be designed to enable the passive lifting of water from a deep groundwater table to near-surface soils during periods of drought. PLANTS AND TREES. Water pressure in trees has been shown to reach values as low as -10MPa, which is theoretically equivalent to a capillary rise of 1 km. In such systems, high water tension can be maintained thanks to the presence of a capillary nanoporous interface that prevents the ingress of air thus inhibiting air seeding and cavitation (air bubbles). Nanoporous interfaces are found in different parts of the soil-plant continuum. In the leaves, such nanopores maintain the differential between the negative xylem water pressure and the surrounding atmospheric air pressure. In the stem, nanoporous networks segment xylem vessels, providing the trees with the capacity to isolate expanding air cavities and prevent diffuse embolism. Nanoporous soil-root interfaces also prevent the ingress of air.THE HYDROGEL CHALLENGE: The aim is to modify a soil/rock pore network via injection of nanoporous hydrogel to create a 'hydraulic extension' of a plant root system. Hydrogels are formed as a network of one or more cross-linked nanoparticulate polymers. They are characterised by high hydrophilicity and their properties are only recently being investigated for geotechnical applications. Preliminary experiments by the applicant, in preparation for this bid, have shown they can facilitate water transfer through their pores even at porewater pressures of -10 MPa. The project will tackle three different challenges, each vital to success of the system: to design a hydrogel with suitable hydraulic properties, that is injectable into the soil; to create a continuous, durable network of nanopores within the grouted soil that is resistant to repeated cycles of wetting and drying; to demonstrate that plants can thrive when connected to the "Energy-free water pump".