The Water–Energy Nexus: The Power of Commitment

Nov. 30, 2022
How green hydrogen, water utilities and wastewater by-products can deliver a more resilient future.

Accelerating the transition to low-carbon energy and better managing scarce water resources are two key pillars of a more sustainable future. But what are the intersection points between these critical enablers and where do the opportunities lay to better leverage the water-energy nexus?

What follows are the experiences of two leaders in different fields, living and working in different countries – on different continents – to compare and contrast their views.

A Thirsty Gamechanger: Green Hydrogen

The potential for the synergistic relationship between water and energy to deliver on global climate ambitions is particularly evident in the case of green hydrogen – touted as one of the key renewable energy ingredients required to achieve a Net Zero future. While hydrogen is the most abundant element in the universe, on Earth it exists only as a chemical compound, meaning it must be extracted from naturally occurring liquid, gas and solid materials and separated from other elements before it can be used as an energy source.

Traditionally, hydrogen has been produced using industrial processes that extract it from fossil fuels such as oil, natural gas or coal, emitting carbon dioxide as a by-product to varying degrees of intensity, depending on the feedstock used. This is where ‘green’ hydrogen comes in as a climate-friendly alternative. It is produced using any form of renewable power, such as wind or solar, to electrolyse water and separate H2O into its constituent parts; the big benefit being that oxygen is the only by-product.

While carbon capture and storage technologies are helping to decarbonise traditional hydrogen production processes by preventing CO2 emissions from entering the atmosphere, only green hydrogen offers a truly ‘zero emission’ option at present. Crucially, it also comes with the potential to rapidly scale as a global industry, to meet the world’s urgent need for clean energy – and lots of it.

But there is a catch. A recent analysis undertaken by GHD engineers indicated that vast quantities of high-purity water will be needed for green hydrogen production globally. Not only is water the primary input into the electrolysis process, it is also needed for other critical tasks such as cooling the electrolysers, which operate at very high temperatures. Once all the water requirements are factored in, it has been estimated that between 59 to 95 liters of water are required to produce 1 kilogram of hydrogen.

As the currently nascent but potentially game-changing green hydrogen industry gears up for global growth, sustainable management of already scarce water supplies will become increasingly critical. In some places, potable water for hydrogen will be readily available. In other locations, such as arid regions with big hydrogen ambitions — including the United Arab Emirates, California or parts of Australia — water may need to be purified at scale through recycling or seawater desalination to support the industry’s necessary expansion.

Balancing green hydrogen production aspirations with water scarcity issues will be a genuine challenge for the industry, particularly in the context of the increasingly severe drought events being experienced in many regions with stated green hydrogen goals.

Green hydrogen’s thirst for water is not an insurmountable obstacle but addressing it will take careful planning and design from the outset to ensure the utmost efficiency of equipment and production processes, along with the appropriate management of resulting wastewater, which must be disposed of in an environmentally sensitive manner to protect natural waterways. Getting this vital water-energy nexus right will put us in good stead to curb global warming while preserving the health and integrity of precious water sources and the wider environment.

The Untapped Potential Energy of Wastewater

A second interesting area of intersection between the water and energy industries is the untapped potential of wastewater as a renewable — and arguably infinite — energy source.

The process used to treat raw sewage, called anerobic digestion, produces energy-rich biogas, which can be used to decarbonise a water utility’s own energy-intensive operations and potentially, the wider gas network or electricity grid. It is a circular solution at the heart of the water-energy nexus that while mature in some parts of the world, is only just emerging as a viable opportunity in others.

Balancing green hydrogen production aspirations with water scarcity issues will be a genuine challenge for the industry.

In similar fashion, when biogas is refined into renewable natural gas (also known as green or biomethane), it can be used onsite by the water utility as an alternative fuel for its fleet of heavy vehicles (displacing diesel), sold to commercial off-takers, or fed into and blended with the local natural gas network. All of these applications have the benefit of reducing both the water utility and wider community’s reliance on fossil fuel-derived energy sources.

There also exists an exciting opportunity for water utilities to turn their hand to green hydrogen production, given the potential to harness biogas for clean electricity generation and ready access to treated water for electrolysis. This would usher in a transformational shift for both sectors and even more tightly bind the water and energy industries together on the road to Net Zero.

One final word on wastewater treatment plants potentially becoming net producers, rather than net users, of energy: biosolids. Biosolids are the often problematic by-product of treated sewage and are usually incinerated or relegated to landfill, neither of which provide satisfactory environmental outcomes. However, biosolids are full of energy, which can be extracted through new processes such as gasification and pyrolysis. The latter can also be used to convert biosolids into useful materials such as biochar, that in addition to permanently trapping carbon within the final product, can be used as a soil enhancer in agricultural applications.

Finite Resources, Endless Possibilities

The water-energy nexus has been a topic of discussion for many years, but the mature, utility-scale and highly regulated water and energy industries remain largely siloed. Achieving climate ambitions will require closer collaboration as traditional water utilities consider their role as future clean energy producers, and the energy establishment increasingly recognises the crucial role water will play in the low-carbon energy transition.

In addition to the intersection points related to green hydrogen and wastewater, many other examples of the water-energy nexus exist, at varying stages of exploration and development; pumped hydro solutions to deliver much-needed, large-scale energy storage, to smooth out intermittency issues associated with renewable energy, being just one. Indeed, the possibilities are only limited by our imagination as engineers, scientists and advisors to the industry.

However, all of these potential pathways will require the water and energy sectors to re-set their perspectives and business-as-usual approaches. How they view their role in the community; how nimbly they can adjust their business models; where they see value; how confident they are entering new supply chains; and how open they are to working with others are all important considerations.

It is also a question for regulators to ensure these industries are able to innovate beyond their traditional roles. One thing is for certain: working together to realize the potential of the water-energy nexus will be a critical enabler of tackling climate change and a positive step forward toward a more sustainable future.

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