(150e) Recovering Runoff Particulate-Bound Phosphorus Via Fungal Bioextraction

Phosphorus (P) loss is a key issue affecting food-energy-water nexus sustainability. P in fertilizers is critical for ensuring food security for the continuously growing world population. Currently, P is obtained via energy-intensive mining and processing of phosphate rock, which is becoming more scarce and concentrated in a few geographical areas. Excessive fertilizer application due to slow diffusion and heavy fixation of P in soils have led to massive P losses amounting to almost half of all mined P due to agricultural soil erosion and runoff. P-rich runoff streams discharging into surface water bodies can cause eutrophication, toxic algal blooms, and overall quality deterioration of freshwater resources. In this work, we propose capturing and processing runoff sediments using a low-energy and inherently benign fungal bioprocessing method to unlock a previously untappped source of recoverable phosphorus for nutrient recycling and closing the loop of P use. This can potentially reduce the demand for mined sources while at the same time help protect watersheds from the devastating effects of eutrophication.

This paper presents the preliminary findings of our work involving the use of phosphorus-solubilizing fungi (PSF) for extracting and recovering particulate-bound phosphorus in erosion and runoff streams. PSF species can generate organic acids and phosphatase enzymes that can induce mobilization of matrix-associated or surface-adsorbed phosphate ions on inorganic minerals in runoff particulates, and degrade phosphate ester bonds in sedimentary organic phosphorus compounds to facilitate the release of phosphate ions, respectively. Samples of runoff sediments discharging into a eutrophic lake in Kalamazoo, MI were collected and characterized for total P content and P speciation. P extraction experiments on runoff sediment samples were performed using model organic acids and spent culture broth Aspergillus niger ATCC 15475. Phosphate solubilization and changes in P speciation of the runoff sediments during treatment were measured using a sequential chemical extraction method and colorimetric analysis. Changes in runoff sediment mineralogy was analyzed using X-ray Diffraction (XRD) spectroscopy. The results indicate that oxalic and citric acids can extract and solubilize a significant fraction of phosphates bound to the iron, aluminum, and calcium mineral components of the runoff sediments. A kinetic model describing phosphate mobilization via ligand-exchange and induced desorption mechanisms was developed and fitted into the experimental data. We also observed a significant reduction in the organic P fraction of sediments treated with spent fungal culture broth, indicating the possibility of phosphatase enzyme production and activity. Thus, changes in organic P speciation in the sediments were monitored using solution ³¹P nuclear magnetic resonance (NMR) spectroscopy. The findings demonstrate the feasibility of the proposed technology for P recovery from nonpoint nutrient pollution sources such as runoff sediments. It will help develop an effective, efficient, economical, and environmentally benign system that will benefit the community, agriculture and food production systems, and the environment in terms of resource security and environmental sustainability.