Biosolids: the greatest story never told at COP26

Guest blog

Dr Peter Matthews, past president of CIWEM and former Chair of Natural Resources Wales, picks on biosolids as the industry’s opportunity for a great COP26 story.

COP26 is fast approaching, bringing with it – we hope – all the attention and urgency the climate crisis requires. We see it in the news, we read it in IPCC reports – but it’s not (exclusively) through academic study, flip charts and ‘men in grey suits’ that we will deliver the change required to address the crisis.

Instead, we need to turn to an under-rated weapon – storytelling. It might just be our most powerful ally against this particularly fearsome foe.

And with that in mind, let me add a chapter to water industry’s story of climate action – a chapter that perfectly highlights the mutual benefits possible when addressing the climate challenge.

I recently wrote a CIWEM post about the importance of aligning policy with priority when it comes to biosolids, building on a longer exposition on the future of biosolids which is on Linkedin. Both of those are built on a story that is as old as the hills themselves – literally. Namely, the carbon cycle.

We know almost all the planet’s carbon is locked in the ground – carbonates, oils, coal and the like – things often referred to as ‘hard carbon’. What remains is split between the biosphere including oceans, and the air – ‘soft carbon’.

Basic science tells us the carbon cycle incorporates a series of processes by which carbon compounds are interconverted in the environment. This involves the incorporation of carbon dioxide into living tissue by photosynthesis, and its return to the atmosphere through respiration and the decay of dead organisms, expelling both methane and carbon dioxide.

The oceans also absorb atmospheric carbon. However, there are concerns that as CO2 absorption increases, so does the acidity of water, which can negatively impact marine life. Coral being a case in point.

Disruptions to the carbon cycle

The challenge is that the hard carbon/atmospheric carbon/soft organic carbon interface has been disrupted. Hard carbon is being converted rapidly to atmospheric carbon and the capacity of a diminishing wild biosphere and oceanic water cannot absorb the excess atmospheric carbon and intensive food production tilts the interface towards atmospheric carbon.

At present (in the UK) about 20 per cent of our personal carbon footprint comes from the food we eat, hence the increasing focus on the provenance of our food, the ways in which it is produced, and the connection made between the environment and our health outlined in the recommendations to government in the recently published National Food Strategy.

Let’s look at some numbers to illustrate the point. We consume about 2kg of food each day (roughly 500g dry weight…for the’ non-biosolidsistas’ we use dry weigh of organic mass per person per dayto provide a basis for comparison). This is converted into body mass, energy, and atmospheric carbon – ultimately leaving about 50g dry solids as faeces.

This is flushed, then makes its way to one of almost 10,000 sewage works in the UK, where (in combination with other sources of solid material in the sewerage network and the by-product of treating the wastewater itself) it adds up to about 65 grammes of dry solids per equivalent head of population served by the wastewater treatment works.

And that’s when the magic happens. Anaerobic digestion (or a similar process) converts those dry solids into biosolids, generating renewable energy along the way. Those biosolids are destined (in most cases in the UK) to be supplied to agriculture as a soil improver. These biosolids are sewage sludges, quality controlled to remove chemical hazards, treated to remove pathogenic hazards, and used sustainably in an assured manner in agriculture.

We have long understood that conserving the innate value of sewage sludge in this way is good for soil fertility and agri-economics, and avoids what is the less acceptable and more carbon intensive disposal alternatives of landfill and incineration. There’s also the obvious benefit that it keeps its soft carbon out of the atmosphere for much longer, thus tilting the carbon cycle balance of food back away from the atmosphere.

This has been studied most extensively in King County in the US, but the best and most recent figures for the UK were provided by McLeod and Lake of Jacobs in 2020 (UK Water Net Zero Carbon), drawing on work by UKWIR.

Counting carbon costs

It is clear that as far as the final product is concerned, even after allowances are made for minor carbon emissions during the process (such as transport), the biosolids’ soft carbon is returned to the equilibrium of the natural organic cycle of decay and sequestration i.e. locking up in plants and soil biomass in crop production. The good news is, is that the latter has a more dominant, and more beneficial, impact on the carbon cycle.

There is an argument for claiming this is a ‘net zero process’, even when you take account of the energy needed for dewatering. The products have to be digested to ensure pathogen safety (and to remove any malodours).

The process of digestion produces gas which is converted into energy, and which can be used to power the dewatering process, and even the wider sewage treatment facility. The alternative – incineration – may produce some energy – but even then, the soft carbon in the sludge is converted into atmospheric carbon.

The Water Industry is committed to Net Zero by 2030. I have used McCleod and Lake’s publication to estimate that if we do not maintain the type of sustainable biosolids use illustrated here, it could add between ten and twenty per cent to the industry’s current carbon footprint.

What’s more, as I alluded to above, this story doesn’t have just one happy ending. In addition to the climate recovery benefits, biosolids create healthier soils leading to ecosystems that boost crop productivity, and they provide nutrient sources which reduce the need for chemical fertilisers. Abundant crops help remove carbon from the atmosphere, and so the cycle persists!

Making the story of biosolids heard at COP26

So if COP26 is the stage, these are the stories that we need to act out on it:

• The wastewater cycle can be harnessed as a sustainable resource, and hence is an important part of the circular economy agricultural use of treated sewage sludge brings benefit to our efforts to rescue the climate from further change
• We can work with nature rather than against it; we must be natural friends and not foes in water management
• We can harness advanced bio-technologies, working with nature in processes, such as anaerobic digestion
• We need strategic commitment to the notion that using biosolids is good, and is the best environmental option when allied with practices that ensure safety and avoid hazard. This needs a ‘can do, must do attitude’, rather than one of ‘can’t do unless…’.
• Regulation should not hinder this. It needs to ensure that good practice happens and importantly that the wider community is comforted and assuredthat the practice is sustainable and safe.

As with all good stories, we need to choose our words carefully. While the water industry knows that biosolids use is a combination of good operational practice and responsible science, it takes a degree of poetic, even artistic support to understand, empathise with and assuage the public’s innate reservation about all matters faecal.

If we get our words right, responsible use will resonate with an increasingly discerning public who no longer tolerate an ‘out of sight, out of mind’ mentality. And who wouldn’t want to be the author of the next chapter in such a good news story?

Governments can make policy and the public can confront their individual habits, while the responsible actions of bodies like, water companies, sensible controls by regulators, and focussed research from academia and active supporting professional bodies like CIWEM, can really turn this narrative into a blockbuster.

If the history of successful biosolid use in the UK is already written, it’s our innovation that will spark the imagination that fills the pages of the next episode.

Let’s take to the COP26 stage, proclaim our story, and get our message heard!

Continue the conversation: why not consider joining CIWEM's Wastewater and Biosolids Network?