Phosphorus removal from irrigation return flow using an iron oxide filter and denitrifying pine bark bioreactor treatment train

Development of low-cost aqueous P removal methods is imperative for water resource protection. This study assessed the contribution of an iron oxide (FeOx) filter for P sorption paired with a denitrifying pine bark bioreactor, quantifying the effect of treatment order on P removal. FeOx filters were placed upstream (order 1) or downstream (order 2) of pine bark bioreactors receiving a continuous flow of simulated irrigation return flow after constructed floating wetland treatment. The FeOx filters removed 0.095 ± 0.01 g P·m^-3·d^-1 and 0.21 ± 0.01 g P·m^-3·d^-1 in the spring and fall, respectively. P concentration was reduced from 5.08 to 3.8 mg·L^-1 and from 6.72 to 4.5 mg·L^-1 in the spring and fall experiments, respectively. The FeOx substrate sorbed 1.49 ± 0.08 mg P·g FeOx^-1 in spring and 3.18 ± 0.2 mg P·g FeOx^-1 fall experiments. P sorption varied by season due to differences in the load presented to the FeOx filters. Reclaimed FeOx substrates were viable P removal filters, especially during cooler months when the nutrient uptake capacity of constructed floating wetland plants was limited. Overall, findings indicate that FeOx filters can be used as a substrate for P sorption in conjunction with constructed floating wetlands or other plant-based treatment technologies that can be limited by seasonality.