Author: Bernadette Ballantyne
Partner: Mott MacDonald
Something very interesting is happening with wastewater in East Anglia. “Last week, we began planting 300,000 baby tomato plants across the two greenhouses,” says Andy Allen, director and co-founder of developer Oasthouse Ventures. Heat for the greenhouses is actually coming from wastewater treatment works and to make sure there was enough heat Andy and his team examined every major sewage treatment works in the UK looking for facilities with large enough flow rates to generate the heat required and at the same time having plenty of space nearby for developing these massive glass structures.
The temperature of the wastewater leaving the sewage works is about between five and 15 degrees. “What we do is we capture only a few degrees of that water, but at very large volumes of flow. So we’re capturing large amounts of heat, which was transferring into the greenhouse, via heat pumps, which are, of course, electrically driven. And in doing so, we’re providing 90 odd percent of the heat that the greenhouse requires solely from the waste heat from the sewage works. So it’s very sustainable.”
In addition to the heat pumps, Andy also says that there are combined heat and power engines, which provide the carbon dioxide and electricity for the greenhouse as well. Just to be clear the wastewater itself is not used in the growing process, its role is purely as a heat source for the greenhouses 2.5km away. Wastewater is taken right at the end of the treatment process when it is cleaned but still warm. “At that point, we are taking that heat from that water via heat exchangers. And on a hydraulically separated unit, we are pumping that heat in a heat transfer fluid, two and a half kilometres in a 450 mm pipe to our energy centre at our greenhouse, where that heat is put through our heat pumps and the heat transfer fluid, flows back to the sewage works to pick up more heat and comes back. So it just is constantly going around in a loop.”
Even better Andy says that the experience on this project could act as a template for the use of heat pumps, which have much lower carbon emissions than gas boilers, at both residential and industrial scale. “I think the largest heat pumps used in the UK to date are roughly around the six megawatt mark. And we’ve done a step change in terms of scale, our heat pumps are in the mid 30s for megawatt hours in terms of capacity of heating. So it is a real standalone flagship project, showing what can be done with heat pumps and electric heating as a whole.
Boosting UK supply
The greenhouses will supply somewhere between 9,000 and 16,000 tonnes of tomatoes per year and this use of waste heat is an example of how water companies can benefit other industries in their quest towards net zero by 2030. A quest that is two decades ahead of the UK’s national target which was set in June 2019, when it was written into law that UK greenhouse gas emission would be net zero by 2050. Meaning that we must find the right balance between the emissions that we produce and the amount that we remove.
In that same year, 2019, we emitted 435 million tonnes of greenhouses gases. And it is exactly why initiatives like the water industry’s Net Zero 2030 Routemap are important in helping the water industry itself to decarbonise.
But before we learn more about that, we are going back to East Anglia and these super sustainable greenhouses, whoch could not have happened without collaboration with the owner of the wastewater treatment works.“Hats off to Anglian water, who we work in collaboration with. And obviously, it was a sensitive discussion point because we’re putting pieces of equipment on their site, essentially. And what happens if our equipment breaks? What happens if we affect their, their regulated utility? What happens if we affect them? So, there was lots of discussion points around that and lots of protections built in. But no, I can see that other water companies are looking to do similar things.”
Beyond the greenhouse
Anglian Water are excited about the project too. “The greenhouse thing is wonderful, because it means that the greenhouses are emitting far less CO2 in doing what they need to do to supply food,” says Richard Buckingham, climate change and carbon manager for Anglian Water. “We’re benefiting because our previously warm effluent will be discharged, when it comes back from the greenhouse has been cooled. So it’s discharged cooler. So the environment, benefits from that, in terms of a carbon benefit.”
So although Anglian Water isn’t getting a direct carbon saving from this project, this is a collaboration that is helping farming and agriculture to lower their carbon footprint, and Richard echoes Andy’s thoughts on potential for expansion beyond agriculture.
“Now this, this particular one is greenhouses. But there’s no reason why this what we currently termed waste heat couldn’t become a valuable resource to another user. Now, in this case is greenhouses. But there’s no reason why it couldn’t be in buildings.”
For Anglian Water, helping other entities lower their carbon footprint through projects like re-use of waste heat is an extension of the work that they are doing to lower their own. Richard is also responsible for the net zero carbon route map – the plan for all water companies to have net zero operational emissions by 2030. “The roadmap to net zero is essentially a sector level plan, showing different pathways of how the water sector in the UK could reach net zero by 2030 by summarising different decarbonisation options of how to get there,” says Maria Manidaki, technical lead for net zero from Mott MacDonald. The consultant worked with Ricardo to create this routemap for the whole industry at the request of water industry trade association, Water UK.
A routemap for industry
Maria says that this means following a decarbonisation hierarchy in the pathways considered starting with reducing emissions and then displacing those emissions by using renewable energy to replace the fossil fuel electricity. And after you’ve done all these things, then you can consider removing those emissions by natural sequestration or other means. “So the removals bit is the ‘net’ in the net zero equation,” she says.
The pathways don’t just depend on efforts of the water companies. For example the greatest source of emissions today is electricity purchased from the grid. So the rate at which the UK continues to decarbonise its energy sector directly affects the rate at which water companies can reduce emissions. This different pace would also incentivise companies procure and/or generate their own renewable electricity. So a really ambitious pathway could see the water sector cut emissions by 10 million tonnes over the next decade, and two other scenarios show a lower rate of reduction.
Maria also points out that water companies have already lowered their carbon footprint by 45 to 50 percent over the past decade, and this has largely been driven by the gradual decarbonisation of the UK electricity mix.
Although the net zero routemap is written for the industry as a whole, the challenge facing water companies varies across the country. “Each water company will be producing their own net zero roadmap by July this year,” says Richard. “And I suppose from Anglian Water’s perspective, the key themes for us will be around energy efficiency and reducing consumption and around renewable generation.”
Not only will they be seeking efficiencies they will be generating their own cleaner power sources generating 44% of electricity using renewables by 2025, mainly using PV and CHP / biogas. That means developing well over 100 solar energy projects. Last year for example the company switched on its biggest array to date, 11.65MW of solar panels at the Grafham Water Treatment Works in Cambridgeshire. This alone will save 3,500 tonnes of carbon per annum. But it is not always as easy as simply placing solar cells alongside sources of energy demand. “There are areas of the network where demand is higher than others, but part of it revolves around where you can actually put solar installations. So how much land do you have around particular facilities? So at certain points of reservoirs, for example, we have large areas of land, we can put big solar arrays in, we have some covered reservoirs, which are already kind of flat hardstanding and again, we can put lots of solar in.”
This is an important point because all water companies are working with massive existing networks, some of which are over 100 years old, and they were set up to be as efficient as possible at the time. But times change.
Process emissions challenge
Moving away from grid electricity and developing their own renewable resources is an important step in decarbonising that water industry, but there is another emissions challenge that will be a lot more difficult to tackle. “So our process emissions, you know, how do we capture those? How do we record it? How do we capture those gases?” says Pete Stevens, manager of carbon neutrality at Yorkshire Water
Process emissions are the second biggest source of greenhouse gas emission for water companies and as Pete says this isn’t just about carbon. Nitrogen Dioxide and methane are emitted from wastewater treatment process and the subsequent sludge treatment, but until now this hasn’t really been analysed or accounted for.
Priyesh Depala, a senior investment advisor for low carbon infrastructure at Mott MacDonald says that our understanding of the scale of those emissions from different types of aeration processes and different setups is relatively limited. “So the two main processes that we use in treating wastewater in the UK are aerated processes and that’s activated sludge processes, which are in the presence of oxygen and air. And then the other ones are a kind of less intensive process, which is trickling filters. So we rely on ambient air to kind of grow on physical media.”
These forms of aerobic biological treatment all rely on specific forms of bacteria which in the presence of oxygen can digest the organic matter in the wastewater. As they do this they then begin to stick together and can be easily removed through simple settlement forming a sludge. Then there is the less common anaerobic wastewater treatment process, which uses a different type of bacteria and is in contained systems, to clean up the wastewater. Something which could play a more important role in the future as gases are captured and not emitted. However most of our legacy wastewater treatment involves the first kind of wastewater treatment, huge open aerated systems and capturing the emissions may cost more which is not likely to be the most efficient way to pass on to the bill payer. “So you kind of either have to look at advanced thermal treatments or you have to look at the idea of you’re going to encapsulate all your processes, and somehow clean the air before it goes out atmosphere, nothing’s going to be cheap. There’s a need for innovation,” says Pete.
Risk to net zero
Pete says innovation means considering these gases as a resource. “Certainly, if we can capture methane do we kind of split the carbon and hydrogen use the hydrogen as a fuel rather than the biomethane? So there’s lots of avenues to explore in there, and I don’t think anyone’s got a clear picture of how we’re going to deal with process emissions. And that’s probably quite a big risk to becoming net zero.”
Innovation has already found its way into the sludge treatment side of the water sector where the biogases emitted as the solids are broken down are captured to generate energy and then the solid waste itself is used in agriculture. Pete explains: “So all our sewage sludge goes into digesters to produce biomethane. Biomethane is then put into a combined team power plant to create renewable energy and heat and they’re both used on site. And then the spent digestate is used as a fertiliser. So it’s a really good example of the circular economy.”
In fact Yorkshire Water has been collaborating with a range of businesses to see how this biogas might be a low carbon fuel for other industries. In 2019 it used this gas to supply electricity to a pop-up pub in Leeds city centre. Much of its biogas comes from a new £72M anaerobic digestion plant which can treat 131 tonnes of sludge per day, almost all of the sludge produced from the city of Leeds. The biogas that it produces is enough to run 55% of the energy needed to treat the sludge and turn it into fertilizer.
It is this kind of thinking, around using our waste as a resource, and then collaborating with other industries, that is key in tackling the net zero challenge. Priyesh from Mott MacDonald explains: “So, going further on that we’ve got kind of anaerobic digestion kind of heavily embedded in the sector. But if we looked at Thames Water and their pyrolysis plant, they’ve got a demonstration pyrolysis plant that’s going through.
Pyrolysis goes further than anaerobic digestion. It heats the sludge up to 800degC in the absence of oxygen. Because no oxygen is present the sludge does not combust but the chemical compounds in the sludge thermally decompose into two end-products. Combustible gases and char. Extracting this gas results in capturing significantly more energy from the sludge, making the process energetically self-sufficient. The char contains key elements like nitrogen and phosphorous and even precious metals. Resources that could be of value to other industries. “So if we look at megawatt hours per tonne, dry solid that we can get through anaerobic digestion, a well operated pyrolysis plant can really have a step change in the amount of biogas and syngas that produces and can generate a big step change in the amount of power that we could be getting out of each tonne of dry solids that we have.”
These advanced thermal processes could see more biogas produced than the water companies need for powering their own operations, and again lead to more collaboration between water companies and other industries.
In the longer-term sewage also contains a wide range of chemicals such as phosphorus and volatile fatty acids that could be extracted and become a resource of the future. Hydrogen too is being considered as an operational fuel for the future.
Land use modelling progress
But there is another area where Yorkshire Water has made major progress that could benefit the whole sector and beyond, because when Mott MacDonald began working on the Water UK Net Zero Route map they realised that there needs to be a stronger market and guidance for accelerating the sequestration from land use changes. “One of the key challenges that we had up through kind of creating the water UK route map kind of part from natural sequestration perspective was that we didn’t have a baseline,” says Priyesh.
Natural sequestration, the ability of land to remove carbon emissions. Water companies are major landholders and the way that they manage this land can give them an important lever to remove their residual carbon emissions and reduce their reliance in purchasing offsets in a carbon market. Luckily Yorkshire Water had created a tool for this. “So we’ve created a model that takes all our land use types, its condition, and then we can run various scenarios to show what happens if we plant a million trees?,” says Pete. “The other thing I’ll say about some of the work we’ve done around this is for long term nature of carbon storage. So you might be doing projects now that are really good at reducing pollutants, increasing flood resilience, and storing carbon. But if you don’t register them, you kind of lose some of a carbon benefit that you can account for.”
With tree planting for example the carbon sequestration actually happens decades into the future and it peaks and then declines.
“So it’s making sure we’ve got the right strategy to plant the right trees in the right place” says Pete. “Restore the land properly, account for it transparently and openly for our customers sake, and have that very much longer-term view, you know, 25, 30, 50 years plus when we’re in a climate emergency now, so there’s all those tensions going on.”
Peatland for example has huge carbon storage potential but we need to better understand the science behind this storage potential and the permanency of any changes over time, especially when the effects of climate change will be more visible in the years to come.“So our model at the moment is telling us that there is there is, you know, is further development to be done here……but our model at the moment is saying trees are going to give us a long longer term, biggest storage potential, but what we need to be getting on with now is peatland restoration,” says Pete.
This could form a vital component of the UK plans to get to net zero by 2050. The Committee on Climate Change has advised government that peatland restoration could save 5 million tonnes of carbon emissions per year by 2050. It is another example of how getting to net zero requires collaboration across a wide range of stakeholders so that land can be better used, resources can be captured and shared, and the efforts of the water industry can benefit the rest of the country.
