Abstract: Phosphorus (P) is critical for sustaining food security for the growing world population. However, nearly half of total mined P from non-renewable phosphate rock is lost through nonpoint particulate runoff annually, which cause eutrophication and harmful algal blooms in surface waters. Recovering these losses is considered a significant step toward closing the loop in the disjointed global P cycle for nutrient and water sustainability. Our long-term research goal is to understand and adapt biogeochemical P cycling processes mediated by P-solubilizing fungi (PSF) for reclaiming substantial P losses in particulate runoff for sustainable recycling and reuse. Previously, we demonstrated P extraction from runoff particulates using cell-free cultures of PSF containing citric and oxalic acids. Abiotic extraction tests showed that pure citrate and 2:1 (mM ratio) oxalate-citrate extractant solutions provided the best runoff particulate-bound P removal efficiency. In this paper, we discuss the findings of further investigations on the factorial effects of process conditions on phosphorus recovery efficiency indicators and extraction kinetics. Batch abiotic extractions using impounded urban stormwater runoff particulates and aqueous 2:1 mM oxalate-to-citrate solutions demonstrated high P removal and solubilization favored at low sediment loading (5 g/100 mL), low initial pH (3), and high initial organic acid loading (75 mM). P recovery efficiencies up to 99.6 % and 200 ppm solubilized P levels were achieved under these conditions. Initial and equilibrium extractant pH levels near oxalate and citrate pKa2s (4.19 and 4.74, respectively) appeared conducive for optimal and/or synergistic oxalate ligand exchange and citrate ligand-induced particulate-bound P release. Parallel tests using pure citrate extractants showed similar factorial effects but slightly higher recovery efficiencies than mixed oxalate-citrate extractants due to Ca-bound P increases observed in the latter. However, the latter showed higher reductions in redox-sensitive Fe-bound P, which when released could fuel harmful algal blooms. The results suggest operating fed-batch or semi-continuous extractions to maintain higher organic acid ligand-to-particulate ratios and pH control. Further studies using instrumental analysis (i.e., FTIR and x-ray absorption spectroscopy) will help elucidate the molecular-level extraction mechanisms governing the extraction process.

Phosphorus sequestration from nonpoint particulate runoff via extraction using fungal carboxylic acids: Factorial effects on recovery efficiency and extraction kinetics

255th National Meeting (2018)

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