Effect of extraction conditions on citrate-mediated phosphorus removal and recovery from intercepted particulate runoff

Abstract

Abstract Phosphorus (P) is a nonrenewable mineral resource that is critical to achieving food security for the growing world population. However, nearly half of total annual mined P is lost through nonpoint particulate runoff streams. Previously, we demonstrated inorganic phosphate extraction from runoff particulate mineral phases using P-solubilizing fungi (PSF) generating the organic acids citrate and oxalate. The objective of the current study was to investigate the effect of extraction process conditions on P extraction efficiency and kinetics from impounded urban storm water runoff sediments using citrate as the sole P solubilization agent. Abiotic extraction experiments were conducted according to a one-factor-at-a-time approach. High P removal and solubilization were favored at low sediment loading (5 g/100 mL), low initial pH (3), and high initial organic acid loading (75 mM), with P recovery efficiencies of 75% to 100% and 240 ppm solubilized phosphate levels achieved under these conditions. Initial and equilibrium extractant pH levels between citrate pK a1 (3.08) and pK a2 (4.74) appeared conducive for citrate ligand-induced particulate P release, possibly due to optimal balance of protonated and dissociated carboxylic groups. The results suggest that operating the extraction under fed-batch or semi-continuous modes with pH control can help maximize runoff particulate P recovery efficiency in PSF-mediated bioextractions wherein citric acid is the major fungal organic acid product.