Phosphorus recovery and reuse from anaerobically digested dairy manure

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.