Incorporating the water-energy ‘nexus’ into policy talks

The mining, processing, and burning of fossil fuels requires water. The uptake, transportation, cleaning, and use of that water also requires energy. This interdependency, known as the water-energy nexus, is now commonplace in high-level policy dialogues. Particularly in drought-prone areas, water can be a limiting factor for energy production, and energy inputs dominate the cost of water provision over long distances. Academia and major regulatory agencies acknowledge the vulnerabilities created by this nexus. However, industry has made little progress in considering energy-water interdependencies in the production process.

With globalization, growing populations, increasing standards of living, and the threat of climate change, the provision of energy and water is not only increasingly vulnerable but it is also complex. Mapping out the nexus to understand vulnerabilities and opportunities is an imprecise science. However, industry cannot make sound nexus decisions until it understands the cost and benefits of potential management choices. Therefore, managing the energy-water nexus with an optimization framework can lead to better outcomes for industries and their communities.

In a recent paper published in Current Opinion in Chemical Engineering, Peter Varbanov, of the University of Pannonia, Veszprém, explores the implications of the energy-water nexus management for industry. Particularly, he traces the capability of process integration (PI) and mathematical programing (MP) frameworks to optimize energy and water use. PI methodologies establish links among processes, simultaneously minimizing inputs (water and energy) and outputs (effluents and emissions). MP then seeks to optimize these processes. Over time, PI and MP frameworks have moved from simple models that consider water and energy, to increasingly complex systems that can account for water reuse and multiple possible contaminants.

Few decisions are clean-cut. Water conservation often means increased energy use or costs.  Therefore, industry decisions often involve trade-offs between water and energy goals. For example, carbon sequestration — used to mediate the greenhouse gasses emitted by energy consumption — requires large amounts of water. Similarly, water-scarce areas import water-intensive goods over long distances. This saves local water resources but requires additional energy for transportation. Depending on the current needs of the community, either energy or water conservation may be optimal. In some rare cases, neither may be the optimal outcome. The decision space is complex and demands the development of industry applicable PI and MP frameworks for optimal outcomes.

Recent developments in these frameworks include:

to account for heat flows, exchanges and storage

time slices' to account for variability in demand and supply

more precise site-wide heat recovery targets

methods for sustaining high energy efficiency in existing industrial processes

identifying  bottlenecks in multifunctional energy systems

algal biofuel production and waste water treatment optimization 

modeling simultaneous waste and water treatment or desalination and energy generation

supply chain integration

evaluation of industry outcomes under various policy scenarios

PI and MP frameworks are increasingly applicable to current industrial processes. These frameworks highlight the strong links between energy and water in industrial process — changes affecting one can easily affect the other. It is important to integrate nexus management and technology for sustainable practices. In an increasingly complex world, models can simulate industrial processes, even under uncertain conditions. This simulation produces understanding and promotes efficient industrial process and better conservation outcomes for communities.