New Science
October 2021
Advancing sustainable sanitation and agriculture through investments in human-derived nutrient systems. Environmental Science & Technology 54: 9217–9227
Lohman, H., Trimmer, J., Katende, D., Mubasira, M., Nagirinya, M., Nsereko, F., Banadda, N., Cusick, R., Guest, J. 2020.
Summary by Dobermann, A.
The new paradigm for plant nutrition calls for increasing the recovery and recycling of nutrients from different waste streams in the entire food system, including human excrements. As this paper nicely shows, the latter presents both a problem as well as an opportunity. Particularly in big cities of low- and middle-income cities, poor collection and disposal of sewage causes massive water sanitation issues. On the other hand, recovering nutrients from such waste streams could generate income to offset sanitation costs while also enhancing agriculture through increased access to nutrients. Using the example of Kampala, Uganda, the authors evaluate whether such resource recovery sanitation could in fact have a profitable business model. They evaluate two nutrient recovery systems – a simple system of urine storage and a more advanced system with struvite precipitation and ion exchange – and show that profitability can be achieved at a nutrient selling price at or below fertilizer market value in Uganda. They estimate, that in 10 sub-Saharan African countries the recoverable nutrients from the total population without at least basic sanitation services are of the same magnitude as nutrients distributed in fertilizer subsidy programs. Considering the low use of mineral fertilizers in most of Sub-Saharan Africa, capturing and recycling more of these nutrients could make a substantial contribution to increasing crop yields. Realizing this potential requires innovative sanitation strategies and the development and financial support of human-derived fertilizer markets in areas with poor fertilizer and sanitation access.
Classic Plant Nutrition Paper
On the composition, value and utilization of town sewage. Journal of the Chemical Society 19: 80-128
Lawes, J.B. and Gilbert, J.H. 1866.
Summary by Dobermann, A.
The industrial revolution in the 19th century led to a rapid rise of town sewage that needed to be collected and disposed off. City administrators, engineers and scientists needed to look for new solutions that were both safe and economical. Here, John Bennett Lawes and Henry Gilbert, the founders of the Rothamsted Experimental Station in England, summarize their research on this subject. They begin by stating: “It is no less true than strange that, after so many centuries of advance in regard to almost every other requirement of civilized life, the lesson should not have been learnt of how to dispose of the excretal matters of large populations, in such a manner as to secure both their collection and removal without nuisance and injury to health, and their economical utilization for the reproduction of food.” They review how others have tried to dealt with these problems, and follow with detailed discussions of the composition and value of town sewage and its applications to agricultural land. They calculated, for example, that in the town of Rugby every individual contributed about 60 tons of sewage per year, containing 12.5 pounds of ammonia from urine and feces. They also realized that the usage of water per head of population was increasing, resulting in more liquid sewage of lower nutrient value to crops. Their main conclusions were: (i) removing the refuse of large populations requires liberal amounts of water; (ii) the discharge of town sewage into rivers renders them unfit as a water supply to other towns, is destructive to fish, causes diseases, and is a great waste of nutrients; (iii) the proper mode of both utilizing and purifying sewage is to apply it to land; and (iv) considering the great dilution of town sewage, it is best fitted for application to grassland, which can receive it the year around, which would also lead to an enormous increase in the production of milk, butter, cheese and milk, whilst also producing more manure that can be applied to cropland.
We have of course come a long way since then in our understanding of sewage, engineering better collection and processing systems in towns, and regulating the use of sewage in agriculture. Sewage has also changed over time and nowadays also contains pollutants that were not known at that time. Nevertheless, this paper is early circular economy thinking in action, and it is as relevant today as it was 150 years ago.