Cranfield Research Insights #5: Unlocking the Circular Economy – Realising the Potential of the Biological Cycle

Overcoming the Yuk Factor to make Productive use of Human Waste

Happy New Year to my LinkedIn Contacts! This continues my series of posts based on my PhD research. The first year of my PhD will be spent studying and reading, pulling together what is already known before I venture into new territory. I’m going to capture my insights in a series of short pieces shared on LinkedIn. I admit mainly this is to help my own writing and comprehension, but maybe they are helpful to others interested in the Circular Economy? I hope so and would welcome your comments, feedback, further contacts and references.

On 26 October 2020 readers of the British tabloid newspaper The Sun were greeted with this headline: “UN-POO-LIEVABLE Countryfile viewers ‘put off their dinner’ as farmer uses human poo to fertilise crops in revolting scenes.” (The Sun, 2020) Countryfile is a genteel, popular, Sunday evening BBC TV show about farming and the countryside, and the item in question had seen their resident farmer Adam Henson experimenting with using sewage sludge to fertilise his crops. Sun readers had complained that watching this had put them off their Sunday dinner.

This is an example of what sanitation experts call the yuk factor. In fact, returning human waste to the land is neither new nor unusual – Antille et al (2017) describe a major UK wastewater treatment operator who dispose of 70% of sewage sludge to farmland, and this is allowed under relevant legislation (eg the EU Sewage Sludge Directive 86/278/EEC) and practised in several European countries. The same paper cites economic reasons in favour of this practice, with alternative disposal routes for sludge being 30-50% more expensive. In developing countries return of human waste to the land exists widely, often as an informal practice without proper treatment, and indeed open defecation in rural communities often takes place on agricultural land. But these practices are not widely known and may still provoke a negative public reaction, and the fear of that reaction can provoke corporate policies barring such practices from the supply chains of their brands.

Why Would We Use Human Waste-derived Products in Agriculture?

Despite the yuk factor, there are (at least) three reasons to consider this practice:

a)    It may be beneficial to soil health and therefore to agriculture. This is the main focus of this piece, developed below.

b)    It may facilitate the provision of sanitation, which remains a major issue in many countries, with only 45% of people globally having safely managed sanitation in 2017  (UNICEF and World Health Organisation (WHO), 2019). Typical sanitation provision (predominantly pit latrines, or flush toilets with sewers) is not designed to recover nutrients, so innovation and investment are needed in toilets, collection systems, treatment and transport. This could provide a revenue stream to help fund sanitation (provided the revenues exceed the additional costs), and it could establish a business model for sanitation which incentivises the complete and continuing operation of the whole system, whereas there are many examples of sanitation systems which have been built but not sustained. This is relevant both within agricultural communities, (providing sanitation for local people and returning material to local farms) and on a bigger scale (returning material from towns and cities to farms in the surrounding countryside). Examples of companies trying this are Geneco, in Bristol, UK, and Sanergy, in Nairobi, Kenya. It is not straightforward to make these models work (Mallory, Holm and Parker, 2020), although the challenges are often in enablers like market development, retailer risk management policies, and regulation, which arguably could change if these models were pursued at scale.

c)     It may play a part within the wider Circular Economy, as part of a fully developed biological cycle.

“A Circular Economy is based on the principles of designing out waste and pollution, keeping products and materials in use, and regenerating natural systems.” (Ellen MacArthur Foundation, 2017) It could replace today’s linear “Take-Make-Dispose” economy (Ellen MacArthur Foundation, 2012). A key element of the Circular Economy is Cradle to Cradle’s two cycles, biological and technical (McDonough and Braungart, 2002), redefined (Ellen MacArthur Foundation, 2015) as “flows of renewable resources” and “stocks of finite resources” respectively. These definitions are based on the fate (not source), a biological material being safe to return to the biosphere, whereas a technical material would contaminate the biosphere and should remain in use cycles within the industrial system.

The biological cycle is far from circular in its current form, meaning that much material grown on the land leaves the biosphere permanently after production, yielding no flow of “waste” materials, containing organic matter and nutrients, returning to the soil.

It is commonplace for farmers to produce and use compost, leave organic material on the soil, and use manure, and also common for domestic gardeners to make compost from both food and garden waste. However more widespread collection of food and other organic waste is sporadic, and much organic material is incinerated or landfilled. Some products of agriculture and forestry receive chemical additives making them unsuitable for returning to the biosphere (chemicals used in paper manufacture or textile dying). In other cases biological materials are intentionally mixed with non-biological (eg in using a plastic nappy), leaving little prospect of recovering the biological component. All this limits the potential for a return flow of nutrients and organic matter to the soil.

Failure to use the biological cycle fully also includes excessive use of long-lived plastics for short-duration applications, often resulting in low value / unappealing items (eg used nappies, sanitary products, and small pieces of food packaging) which are unlikely to be recycled, increasing plastic waste. If these plastic items were instead made from compostable materials, then the nappy with the faeces, the packaging with the food, and so on, could be recovered together to produce compost and biogas.

Remedying all this could potentially alter the balance of the carbon cycle, increasing carbon content in the soil, reducing waste incineration (of plastic) while increasing use of biogas (ie switching from a fossil-based to a renewable fuel), and also reducing the need for carbon-intensive fertiliser production. However this needs more detailed Life-Cycle analysis to establish any net benefit after allowing for processing, transport etc.

The final note on this is that this is a heavily cross-sectoral viewpoint, challenging  established thinking even on sustainable approaches within agriculture, sanitation, renewable energy, solid waste management, and product/packaging design. My PhD research is therefore in part analysing the potential resource flows (particularly the carbon cycle) but mainly on the government and business decision making which could yield such a joined-up approach to the biological cycle.

What are the Research Findings on Fertilising Crops with Human Waste-derived Products?

Antille et al (2017) report on trials at Cranfield University, UK, in 2007-10, of organomineral fertilisers (OMF), produced from granulated biosolids coated with urea and muriate of potash, used on winter wheat crops. Two OMF formulations were compared with urea and biosolids granules, to assess the effect on crop responses and soil chemistry. The resulting yields were highest for urea, followed by the two OMF formulations, with the biosolids least effective, and this is explained by the available nitrogen. The management of nitrogen levels is discussed, one recommendation being to replace two applications of nitrogen fertiliser with one followed by an application of OMF. Supplementary potassium fertiliser might also be required. The authors note from literature the risks of high phosphate levels in fertiliser derived from human waste, but the formulations were designed to maintain (not increase) phosphate levels and the results confirmed this. Heavy metals were below permitted levels in all the trials. Overall the conclusion was that OMF can be used safely, partially to replace existing fertilisers, maintaining yields while meeting other objectives such as disposal of the sludge which would otherwise be waste carrying higher disposal costs. The study did not consider the net effect on carbon emissions.

Deeks et al (2013) also trialled OMFs in Cheshire, UK, in 2008-11, on a wider selection of crops (wheat, oilseed rape, barley, beans and forage maize). OMF was used, again with urea and muriate of potash, and this time compared with a conventional fertiliser (CF). The conclusion was the crop growth response was not significantly different between OMF and CF, nor did the trials lead to different nutrient levels in the soil. This was achieved with slightly lower application of nutrients with OMF, and the authors conclude that nitrogen uptake from OMF is efficient. They note that the variability in sludge chemistry can be compensated in the coating process to produce a consistent OMF, and also that conventional equipment can be used for application, while also noting that the trial was conducted with particularly closely controlled sludge conditions. Again carbon emissions were not assessed.

Pawlett et al (Pawlett, Deeks and Sakrabani, 2015) tried OMF on rye grass, again near Cranfield University, UK, with a study focused specifically on nutrient potential. This was explained in the context of global phosphate shortages, which in part might be mitigated by  recovery of phosphate from sewage sludge. This shows OMF producing comparable yield to urea, and the addition of biosolids increasing organic matter, in turn leading to increased microbial biomass – although there is a trade off, with increased urea leading to reduced soil carbon.

Jeliazovski evaluated mixtures of vermicompost or compost with mineral fertilisers in Madagascar, the compost being derived from the faecal component from Loowatt’s urine diverting toilets. Vermicompost combined with synthetic fertiliser achieved parity with synthetic fertilisers alone, and double the growth of organic fertilisers alone. Although not stated this may be related to nitrogen content which may be lower (relative to the UK studies) due to the removal of the urine component. Urine can be processed separately to produce a nitrogen rich fertiliser.

McNicol et al (2020) address the carbon / climate change aspects of disposing of human waste as compost, with data from Haiti as well as literature from other locations. This concludes that this approach has significantly lower (by multiples ranging from x1/4 to x1/27) net GHG emissions compared with alternative waste treatment options.

Conclusions

Taken together these studies confirm that the use of fertilisers based on human waste can be safe (in terms of heavy metals), and that there are formulation and application regimes available which fully or partly replace the use of nitrogen fertilisers, maintaining the balance of N P and K. There are positive indication in terms of carbon, organic matter, and microbial biomass. And all this is achieved while solving a waste problem in the sanitation sector, less expensively than with alternative disposal options. Additionally, the reduction in carbon-intensive nitrogen fertiliser use, and the increased carbon in the soil, plus the McNicol et al conclusions, are encouraging pointers towards a positive climate change impact, but this needs further research.

Overall, it seems Adam Henson was doing the right thing on his farm, and the bigger question may be how to achieve wider public understanding that this is actually the best thing to do with our waste, and perfectly safe – just another kind of recycling.?

References

Antille, D. L. et al. (2017) “Field-scale evaluation of biosolids-derived organomineral fertilizers applied to winter wheat in England,” Agronomy Journal, 109(2), pp. 654–674. doi: 10.2134/agronj2016.09.0495.

Deeks, L. K. et al. (2013) “A new sludge-derived organo-mineral fertilizer gives similar crop yields as conventional fertilizers,” Agronomy for Sustainable Development, 33(3), pp. 539–549. doi: 10.1007/s13593-013-0135-z.

Ellen MacArthur Foundation (2012) TOWARDS THE CIRCULAR ECONOMY - Economic and business rationale for an accelerated transition.

Ellen MacArthur Foundation (2015) Growth within: a circular economy vision for a competitive europe, Ellen MacArthur Foundation.

Ellen MacArthur Foundation (2017) WHAT IS THE CIRCULAR ECONOMY?, WHAT IS THE CIRCULAR ECONOMY? Available at: https://www.ellenmacarthurfoundation.org/circular-economy/what-is-the-circular-economy (Accessed: November 30, 2020).

Mallory, A., Holm, R. and Parker, A. (2020) “A Review of the Financial Value of Faecal Sludge Reuse in Low-Income Countries,” pp. 1–13.

McDonough, W. (William M. & P. and Braungart, M. (EPEA) (2002) Cradle to Cradle. North Point Press.

McNicol, G. et al. (2020) “Climate change mitigation potential in sanitation via off-site composting of human waste,” Nature Climate Change, 10(6), pp. 545–549. doi: 10.1038/s41558-020-0782-4.

Pawlett, M., Deeks, L. K. and Sakrabani, R. (2015) “Nutrient potential of biosolids and urea derived organo-mineral fertilisers in a field scale experiment using ryegrass (Lolium perenne L.),” Field Crops Research, 175, pp. 56–63. doi: 10.1016/j.fcr.2015.02.006.

The Sun (2020) “UN-POO-LIEVABLE Countryfile viewers ‘put off their dinner’ as farmer uses human poo to fertilise crops in revolting scenes,” https://www.thesun.co.uk/tv/13024816/countryfile-viewers-put-off-farmer-human-poo-fertilise-crops/, 26 October.

UNICEF and World Health Organisation (WHO) (2019) Progress on household drinking water, sanitation and hygiene I 2000-2017. New York. Available at: https://washdata.org/sites/default/files/documents/reports/2019-07/jmp-2019-wash-households.pdf (Accessed: November 19, 2020).