The US Environmental Protection Agency first called the intimate tie between the provision of water and the production of energy “the Water/Energy Nexus.” Then, the name evolved to “the Water/Energy/Food Nexus.” Energy and agriculture are the two largest users of water. Without water, energy and food supplies fail.
There is also another, deeper water/energy nexus that underlies the provision of water: the energy required to separate small contaminants from water. The contaminants of concern in the 1800s and early 1900s were bacteria and viruses – larger and easily removed at low energy. The contaminants of concern today are small, both naturally-occurring and resulting from industry, agriculture, or the contaminants from daily living. The smaller the contaminant, the more energy needed to remove it. As water shortages drive increasing use of desalination, the removal of salt – a very small contaminant – will drive global energy use.
The decades-long goal of membrane researchers has been to find a way to break this iron grip of the rising energy requirement when removing small contaminants: achieving low energy and high specificity separation. This is Agua Via’s focus.
The Agua Via energy savings work by making sure that all the elements of the system are designed to operate at the lowest energy possible under the laws of nature while meeting all the operational constraints of the aqueous environment. Gravity – the weight of the water alone – provides the driving force for Purification. For Desalination, a Forward Osmosis system increases the yield.
Two major energy-saving components in the Agua Via system are:
- the 1-atomic layer thick membrane. At 0.5nm, the 1-atomic layer thick membrane is as thin as possible under the laws of nature – thinner than carbon nanotubes. Physics calculations indicate that the energy expenditure for a water molecule to enter and pass through the membrane is near zero.
- the aquaporin-inspired design for the pores. Each pore is a modification of the natural aquaporin structure, the water superhighway in the membranes of cells. These modifications allow the pores to transport water at a flux rate 1,000 times that of the natural aquaporin.
Building with atomic precision gives the opportunity to add in many other energy-saving tricks from Nature in addition to the aquaporin-inspired design. One example is to encourage “water ordering.” Left to their own devices, water molecules going through a membrane’s pore act like a crowd of people jostling and bumping into each other as they try to go through a gate to leave a football stadium. With water ordering, the water molecules line up neatly and speed their own passage through the pore by traveling quickly in an orderly line rather than losing speed and energy to jostling.
We hope that the ability of these membranes to clean virtually any feedstock to high purity will contribute to another major energy savings: the energy of moving water. Moving water is a major consumer of energy. In California, 19% of all electricity goes to moving water. Globally, commercial energy consumed for delivering water is more than 26 Quads, 7% of total world consumption.
By considering the use of distributed systems for purifying water or recycling water, the possibility exists for even greater energy savings through avoiding moving large volumes of water into and out of centralized plants.
Physicists characterize “energy” as the ability to do “work.” We want to provide better quality water without all the work or the energy expenditure.