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Examination of intermediate compounds in anaerobic digestate and their effect on phosphorous removal using electrocoagulation

Principal Supervisor: Dr Marie Kirby

Secondary Supervisor(s): Dr Simon Jeffery

University of Registration: Harper Adams University

BBSRC Research Themes: Renewable Resources and Clean Growth (Industrial Biotechnology)

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Deadline: 4 January, 2024


Project Outline

Modern agriculture is required to produce ever increasing quantities of food, both for humans and livestock, from a reducing land area. Decades of intensive agriculture to meet the ever-increasing demand for food has led to soil degradation and reducing crop yields. To maximise crop production, agriculture relies on nutrient inputs, sourced from internationally traded artificially made fertilisers and through the re-use of locally available animal excreta (slurries and anaerobic digestates). The manufacture of artificial fertilisers requires a significant amount of fossil fuel, mined rock phosphorous and nitrogen removed from the air. Artificial fertilisers are moved across the globe to deliver crop nutrients, dramatically increasing the carbon footprint of the food we eat. Additionally, artificial fertilisers are commonly manufactured in politically unstable geographical regions, increasing food insecurity and economic costs. Their continued use is now considered unsustainable.

A considerable proportion of the phosphorous and nitrogen fertiliser nutrients applied to soils are captured in animal slurries, manures and anaerobic digestates. Legislation dictates when and how they can be applied to farmland to provide fertiliser nutrients for crop growth. Due to the high-water content of these slurries, their land application is time-consuming, increases soil compaction and if applied incorrectly, can result in leaching of nutrients into waterways causing eutrophication. Slurry and anaerobic digestates are typically applied to meet the crop's nitrogen requirement, causing an overapplication and accumulating of soil phosphorous, increasing soil erosion.

To reduce overapplication of phosphorous when animal slurries and anaerobic digestates are applied to soil, phosphorous can be removed prior to land application. Previous research at Harper Adams University has demonstrated that >98% of phosphorous can be removed and separated from cattle slurry and digestates using electrocoagulation technology (Reilly et al., 2021). A more recent study has demonstrated that this removed phosphorous from cattle slurry was bioavailable for crop uptake when applied to a grass crop (Innovate UK, FIP 10003082 Phosphate circularity: from dairy cow slurry to grassland agronomy, under publication), offsetting the need to use artificial fertilisers.

This project will develop this research further, concentrating on the phosphorous removal and reuse from a range of different anaerobic digestates. Due to the more complex bio-chemical composition of anaerobic digestates produced from different feedstocks, electrocoagulation could be a suitable technology for biochemical reduction in this product stream (Reilly et al., 2019). Understanding the bio-chemical interactions of differing anaerobic digestates on the performance of electrocoagulation, the subsequent speciation of phosphorous and its bioavailability for crop uptake are key discoveries required to achieve a ‘nutrient circular economy’ through extraction of phosphorous from renewable/sustainable sources (for example slurry and digestates).

References

M. Reilly, A. P. Cooley, B. Richardson, D. Tito and M. K. Theodorou (2021). Electrocoagulation of food waste digestate and the suitability of recovered solids for application to agricultural land. J. Water Proc. Eng., 42: 102-121. https://doi.org/10.1016/j.jwpe.2021.102121.

M. Reilly, A.P. Cooley, D. Tito, S. A. Tassou, M. K. Theodorou (2019). Electrocoagulation treatment of dairy processing and slaughterhouse wastewaters, Energy Procedia, 161, 343 – 351. https://doi.org/10.1016/j.egypro.2019.02.106.

Techniques

  • Biochemical analyses of different anaerobic digestates and their effect on phosphorous availability for removal via electrocoagulation
  • Phosphorous bioavailability for crop utilisation (glasshouse crop trials)