No-one can doubt the benefits that have accrued as a direct result of the Industrial Revolution. The driving force of this revolution has, however, unlocked unimaginable quantities of fossil carbon that, unless an alternative can be found, will eventually result in unstoppable climate change. Hydrogen has, for many years, been recognised as a way in which the objective of clean energy production can be achieved.
The most abundant element in the universe, hydrogen was created during the big bang, continues to power our sun, and on earth, is mostly found in water. As a gas, hydrogen is tasteless, colourless, has no smell, and when it burns in air, which it does easily, forms water.
It is, therefore, no wonder that hydrogen is attracting increased interest as a major weapon in the fight against climate change as engineers seek to find viable, environmentally neutral alternatives to continue powering our energy hungry society. The chemical properties of this abundant gas make it an ideal substitute for energy production and, as innovative technology such as fuel cells and gasification technology are improving with every iteration, it is clearly seen as an efficient, clean mechanism in which net zero carbon emissions can be achieved within a relatively short time scale.
One of the major stumbling blocks to the implementation of a hydrogen driven society is that over 95% of hydrogen is currently produced by the reforming of natural gas. Known as ‘grey’ hydrogen, it is neither cost-effective nor environmentally friendly and investigations continue as to a source of hydrogen that can be classified as ‘green’, i.e., it is produced by renewable energy from a non-fossil source.
A characteristic of hydrogen is that it forms bonds with many other elements. In wastewater it forms a bond with nitrogen to produce ammonia, a chemical compound that, if not treated properly, can be highly damaging to the environment. Until recently, it has not been commercially advantageous to separate and recover ammonia from wastewater and treatment technologies have focused on removing and destroying ammonia, usually at significant cost. However, apart from being valuable as a fertilizer (amongst many other applications), ammonia can be reformed to produce hydrogen.
Wastewater treatment usually involves some form of anaerobic digestion; this to break down the organic material to a state in which it can be safely released to the environment. A natural by-product of anaerobic digestion is not only ammonia but also methane gas, the main component of natural gas. During anaerobic digestion, the gas, or biogas, produced is either flared or collected and used to provide fuel for engines to drive the wastewater treatment process. Methane, however, can also be reformed to produce hydrogen.
Technological development now ensures that both ammonia and methane can be successfully recovered from wastewater and, as both are more stable than hydrogen, they can either be reformed on site or transported before being cracked and used as fuel in places removed from where they are recovered.
The recovery of methane from anaerobic digestors is well understood and is now an integral part of most wastewater treatment plants. The recovery of ammonia is not as commonly undertaken in wastewater treatment plant but, as it is recognised as being a valuable compound in its own right, technologies that can recover and concentrate ammonia are being developed and tested around the world.
The challenge to wean our society off fossil fuel is significant and governments around the world are applying sterling efforts to facilitate the process. In the UK, the government water regulator Ofwat has launched a competition to encourage innovation in water treatment. The objective is to promote new technology in the treatment of water, and the Organics Group, together with Anglian Water Services Ltd, Cranfield University, Warwick University, and Wood Group UK Ltd has won a 250,000 grant to directly convert ammonia recovered from wastewater and generate a green hydrogen fuel – a first for the industry.
The project will take advantage of the experience obtained by Organics in the recovery of ammonia from wastewater from landfill sites in Hong Kong using heat as the agent of separation. The first project using this technology for the separation of ammonia from wastewater was built in 2000. Since then, 16 ammonia recovery units have been constructed and, with the increase in demand for alternative fuels, as well as the growing emphasis on a circular approach to waste management, the technology is well positioned to provide a viable means of hydrogen production from waste materials.
With climate change placing increased pressure on governments to find credible alternatives to fossil fuel, many countries now have substantial budgets that are aimed towards developing the hydrogen economy, and consequently, there are several initiatives underway around the world to find viable ways for the large-scale production of clean hydrogen.
Technological developments to date are highly promising and, with forward-looking legislative encouragement, it is highly likely that wastewater may be a key component for ensuring the future of the fuel.