Making a splash for Net Zero

How the water sector is reducing carbon emissions

The water sector directly contributes around 1% of the UK’s greenhouse gas (GHG) emissions. This was previously estimated at 5 million tonnes of greenhouse gases.

For this reason, the water sector in England is planning to slash emissions in the next decade, a move which has focused the thinking of innovation teams in water companies – and their partners in the environmental, academic and industrial spheres – around the country.

A problem as big and urgent as tackling CO2 requires some different thinking and the following projects are examples of some exciting approaches that sector is exploring.

What’s great about these projects is not only will they reduce carbon emissions, but they also make use of the circular economy – recycling waste product into useful materials. Believe it or not, from what is flushed down the toilet can come very useful products!

These four projects are ideas that, if successful, could generate income for the sector as well as helping the planet – making both commercial, and environmental, sense to implement.

Creating chalk from waste

CHP (combined heat and power) engines are huge machines used on treatment works to generate renewable electricity from biogas (methane and carbon dioxide) produced in the sewage treatment process. CHP engines are a really positive technology, enabling the sector to produce a significant amount of renewable electricity from waste, but one of the drawbacks is that, just like a car engine, it produces exhaust which contains carbon dioxide. This CO2 is referred to as a ‘biogenic emission’ – it’s produced by burning what is effectively a renewable gas. Yet the CO2 produced has exactly the same effect on the environment as if it were produced by burning fossil fuels. If you run the numbers, the carbon footprint from CHP is significant for the water industry – 230,000 tonnes of carbon emissions per year from Severn Trent alone. Their innovation team are looking at future-proofing this technology by extracting the carbon and turning it into something useful.

The CECCU (CHP Exhaust Carbon Capture and Utilisation) team, led by Severn Trent, are working with a start-up that has developed technology that captures CO2 from the exhaust of a CHP engine and then converts it into chalk, also referred to as ‘precipitated calcium carbonate’. This kind of pure, fine chalk is a great material for a variety of uses including concrete and paint manufacture in the construction industry and also in agriculture to adjust the PH level of the soil. The process would effectively take something that is causing an environmental problem and convert it into something with real value. What’s more; producing chalk in this way means that there is no need to extract it through mining. The technology can be retrofitted, added on to existing CHP machines – it doesn’t require taking anything out of service or being replaced at high cost.

One of the challenges that the project faces is making sure the market is ready. Currently any products produced from waste needs to have a specific ‘end of waste’ certification from the Environment Agency in order to be sold on, the product created here would need to go through official certification before being made commercially available. However initial research shows that customers are overwhelmingly positive about the technology and its potential impact on reducing CO2. The team hope that by working together with the environment agency they can achieve certification quickly in order to start selling the chalk and prove the circularity of the project.

Once design is finished later this year, the team will start by installing the technology at a waste water treatment plant in the Midlands from early next year. If it proves successful, the plan would be to roll-out this technology all around the country between 2025 and 2030. The information on the tech will be shared with others in the water sector and any other sectors that use CHP machines – if every CHP machine was fitted with this technology the impact on reducing emissions would be massive for our planet. Results could save more than 1 million tonnes of CO2 per year in the UK in the water sector alone, and up to 5 million tonnes for all the UK sectors that use CHP.

Powered by poop? Turning sewage into biohydrogen

Every day 3,920 tonnes of organic material are taken away by sewers in England and Wales for treatment, that’s equivalent to the weight of 329 double decker buses. One method of treating sewage is via anaerobic digestion, this means using oxygen to break down organic contaminants and other pollutants. One of the by-products of this process is biogas- a naturally occurring mix of gases including methane, carbon dioxide and hydrogen sulphide.

Currently at the exploratory stage, Welsh Water’s project, named HyValue, is looking to investigate the practicalities of creating biohydrogen directly from biogas produced by sewage treatment. It’s hoped that the biohydrogen created will be used to power Cardiff’s fleet of 300 public buses, not only reducing the associated carbon emissions from diesel exhaust, but also reducing nitrous oxide emissions & particulate emissions in the region.

Some forms of hydrogen production aren’t sustainable as they rely on burning fossil fuels or produce large amounts of carbon dioxide. This project is much more environmentally friendly as the CO2 that is produced in the process can be captured and used to make food-grade CO2 for fizzy drinks. In terms of renewable fuel, there’s no doubt that as long as the human race continues the supply will not cease. The project exemplifies the idea of making use of waste, moving towards upcycling and circularity so that the water sector can make the best possible use of all resources.

The public are incredibly receptive to the idea. In South Wales, where the project is based there are significant issues with air pollution. Cardiff currently has 300 buses, 100 of these are electric but 200 of them operate on routes too long or hilly to do so and need to be powered by an alternative fuel. By replacing diesel and petrol buses with biohydrogen, not only would this project be dealing with waste management of sewage, but also creating health and environmental benefits for the local population by transitioning local transport to renewable fuel. The UK water sector has an ambitious target of being carbon neutral by 2030, and project like this, if successful, could have a huge impact on progress, as well as making a significant contribution to Welsh Water’s Journey to Net Zero.

Using bacteria to prevent emissions from laughing gas

On big plants where our wastewater is processed, water companies use a technology called ‘activated sludge’ – essentially big tanks full of bacteria – to break down pollutants in the wastewater. One of these pollutants, ammonia – which is toxic to fish –  is broken down into nitrate and nitrogen gas, but this process results in the production of a small amount of nitrous oxide. Nitrous oxide isn’t harmful to humans, it’s laughing gas used in medicine and catering, however it is a potent greenhouse gas that is really damaging to the environment. Currently it contributes to roughly sort of two thirds of Severn Trent’s scope one emissions, (that’s emissions generated directly by burning fuel). The equivalent of approximately 200,000 tonnes of CO2 is generated each year through nitrous oxide being emitted from the company’s wastewater treatment plants.

The Severn Trent team, Catalysing a Net Zero future, along with partners from a tech start-up in California, is trying to identify bacteria in nature that will remove ammonia without producing nitrous oxide as a byproduct. Scientists think they have identified the right types, but the challenge is capturing them and then getting them to live happily in sewage tanks so that they can work effectively in water treatment plants. Using encapsulation, the team plan to culture the bacteria of interest, and then capture it in little plastic chip, the size and shape of a tic tac. This would be introduced to the tanks and used to break down ammonia naturally without creating harmful byproducts. The next step is to run a pilot to test how well this works, before potentially scaling up, nationally and internationally. The team have strong links with leading academics in this area and are optimistic about results, but the pilot will build a clearer picture of its success rate and reveal how effective the bacteria really are.

A HERU for screenings

As wastewater is treated, it passes through filters which remove debris or ‘screenings’ such as plastic or old wet wipes – these capture an estimated 100,000 tonnes a year across the UK. Currently these are disposed of by sending the debris to landfill, but this project is exploring converting this waste to energy in what’s known as a HERU (Home Energy Recovery Unit) reactor. The technology was originally developed for household refuse, the idea being that most waste could be treated in an under-sink unit that burns waste, producing both biochar (like charcoal) and hydrogen rich gas.

An experimental project, the team from Severn Trent will use a 200 litre version of this HERU reactor, make sure that it’s designed for screenings and run tests at its resource recovery and innovation centre. The project also involves a team from Huddersfield University that is advising on how best to use the hydrogen produced by the process. It’s possible that microturbine technology could be employed to generate power. By processing screenings on-site with HERU rectors at treatment plants, water companies could also eliminate carbon emissions from transporting screenings between sites. In an ideal world the pilot will show that the project can not only remove this debris from landfill but also generate sustainable energy, or at least be energy neutral.

Government targets mean that the cost of sending materials to landfill is set to increase considerably in the next few year – so avoiding these costs could be beneficial to water companies that are able to pass savings on to the customer.

The journey to net zero

 With record temperatures experienced in the UK this summer, British people are more aware than ever before of how carbon emissions are contributing to climate change. Whilst there’s still a long way to go and much to do before the 2030 deadline, it’s really exciting to see innovative solutions from water companies and tech partners that could make a huge difference to the sector’s emissions, and therefore the environment.

Don’t work in the water industry but have an idea on how to cut emissions?
The Water Discovery Challenge will be welcoming groundbreaking innovations from organisations in any sector from January 2023 to win a share of £4 million – with further competitions planned in the future. Find out more here: waterinnovation.challenges.org/discovery