Facilitated Iron Reduction as a Possible Means of Rejuvenating Phosphorus Removal Performance of Filtration Substrates

Abstract

In order to mitigate nutrient pollution in surface runoff more sustainably, the finite capacity for phosphorus (P) sequestration in best management practices (BMP) that rely heavily on sorption processes must be addressed. These BMP include sand filters, bioretention cells, and several types of constructed wetland. This study investigated facilitated microbial reduction of iron-based filtration substrates to promote controlled release of P previously sequestered by the BMP, P harvest for recycling, and rejuvenation of the substrate sorption capacity. Total dissolved P was well correlated with total dissolved iron during the reduction process, indicating that microbial iron reduction was capable of releasing previously sequestered P from substrates. Furthermore, results indicated that a sufficient carbon source was necessary but addition of a microbial culture was not necessary to facilitate iron reduction. While a large percentage of the previously sequestered P was removed, the process was much slower than initial sequestration of P by adsorption, and further research is needed to promote a more rapid release of P in order to optimize the rejuvenation process for field application.

Field Application of a Renewable Constructed Wetland Substrate for Phosphorus Removal1

“…Comparison of the rate of Fe reduction in this study to the first 50 days of a previous bench‐scale study with the sand‐only cell type but with synthetic stormwater (Rosenquist et al. , 2011) revealed significant differences (Figure 7A; R 2 = 0.97) with field‐scale, sand‐only cells displaying higher reduction rates than bench‐scale cells.…”

“…Substrate type made a significant difference in the slope of this model, but not the intercept, with iron/sand cells releasing less P for a given amount of Fe dissolved. The coefficients were lower than in bench‐scale trials (Rosenquist et al. , 2011), possibly due to lower IC and therefore less P adsorbed.…”

“…While relatively little variation in pH occurred in prerejuvenation runs, larger pH fluctuation did occur during postrejuvenation runs and is probably a lingering effect of rejuvenation, which decreases pH by creating organic acids (Figure 4) (Rosenquist et al. , 2011).…”

“…Oxidized forms of Fe demonstrate large P‐sorption capacities (Shilton et al. , 2005) but once they are reduced, much of the adsorbed P is released back into solution (Peretyazhko and Sposito, 2005; Rosenquist et al. , 2011).…”

“…, 2011). This process has demonstrated the ability to release P that was sequestered in the wetland during filtration at high concentrations suitable for P recovery (Rosenquist et al. , 2011).…”