Phosphorus recovery and reuse from anaerobically digested dairy manure

Katherine Porterfield

University of Vermont

Co-Authors: J. Faulkner, R. Joblin, D. Neher, M. Curtis, S. Dvorak, D. Rizzo, and E. Roy

Anaerobic digestion of dairy manure generates clean energy, but alone falls short of meeting phosphorus (P) management goals on farms. We assessed the potential to recover and reuse P from anaerobically digested dairy manure using dissolved air flotation (DAF) to separate fine solids. Influent and effluent samples were collected from a DVO Inc. Phosphorus Recovery System accepting >95% dairy manure digestate three times per week for 15 weeks. A nutrient mass balance showed that 85 ± 12% of P is recovered in the fine solids. Fine solids were upcycled (i.e. transformed to a higher quality product) by drying and blending with other organic waste residuals to create a novel plant food product. At 6% v/v plant food, the dry biomass of tomato and marigold was 6-times greater than an unamended control group and not significantly different from a group amended with an organic market alternative as a positive control. The demonstrable agronomic value of recovered dairy manure fine solids indicates potential to improve P mass balance on dairy farms by exporting surplus P as a bagged horticultural product. Sustainable material drying and transport remains a key challenge to realizing this potential.

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2 thoughts on “Phosphorus recovery and reuse from anaerobically digested dairy manure

  1. Hi Katherine,
    I am wondering about several things in your study:
    a) at which time after seeding did you take the photos (Fig. 4) of the marigolds and tomatoes?
    b) the colour of both margigolds and tomatos looks a bit suspicious on the poster (rather yellowish). Did they really grow well?


  2. Hi Dr. Schönborn, thank you for your questions. These pictures were taken 5 weeks after seeding for both marigolds and tomatoes. The color of the photos has been edited so that the seedlings would stand out from the dark background. For this study, our only growth metrics were biomass and germination. We did not measure any plant health metrics related to color, though I think that could be a useful line of inquiry for future studies. You can find a more detailed overview of our methods in this article: Please let me know if I can answer any more questions about this study.


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