THE ROLE OF DISSOLVED ORGANIC MATTER ON PHOSPHOROUS SORPTION ONTO IRON-ENHANCED ACTIVATED ALUMINA MEDIA USING IN-FIELD AND FLOW-THROUGH COLUMN EXPERIMENTS

The Western Lake Erie Basin (WLEB) has been experiencing harmful algal blooms due to increases in dissolved reactive phosphorous (DRP) from agricultural land in the Maumee River watershed. Agricultural best management practices (BMPs) can be useful to mitigate the DRP loads; nevertheless, DRP is not always fully removed by in-field BMPs. Phosphorous (P) removal structures can be filled with phosphorus sorption materials (PSM) such as iron and aluminum oxides and can be placed at the junction of runoff and subsurface drainage to trap DRP from tile drainage. However, dissolved organic matter (DOM) from the agricultural farmland might compete with phosphate ions (PO₄^3-) at the adsorption sites in the media, reducing its lifetime and efficiency. Therefore, laboratory flow-through column experiments were conducted to determine whether DOM is affecting P sorption onto iron enhanced activated alumina media (Alcan). The experiments were informed by field data collected from a regional farm. Alcan (Al/ Fe (hydro) oxides) media was efficient in removing PO₄^3- coming into the filtering system and thereby, flow-through column experiments were able to determine a discrete P removal percentage efficiency of 83.32%, 68.26%, 66.54%, 57.16% and 41.27% by the end of treatment I (5mg L^-1 PO₄^3- only), treatment II (5mg L^-1 PO₄^3- and 5 mg L^-1 DOM), treatment III (5mg L^-1 PO₄^3- and 10 mg L^-1 DOM), treatment IV (5mg L^-1 PO₄^3- and 20 mg L^-1 DOM), and treatment V (10mg L^-1 PO₄^3- and 20 mg L^-1 DOM), respectively. Moreover, from exponential regression analysis of P removal curves for each treatment, it was measured that a total cumulative of 231.45 gm, 92.65 gm, 92.06 gm, 65.998 gm and 91.476 gm of P per kg PSM can be added to treatment I, II, III, IV and V, respectively, until the media gets fully saturated, i.e., concentration of influent PO₄^3- would be equal to the effluent PO₄^3- concentrations. It is evident that DOM is competing with PO₄^3- decreasing PO₄^3- sorption onto the Alcan media. Plausible geochemical mechanisms involved in the competitive sorption between DOM and PO₄^3- onto the media include surface protonation and ligand exchange. The change in pH, concentration of influent PO₄^3- and DOM throughout the length of the experiments was crucial on suggesting the adsorption mechanisms of both DOM and PO₄^3-.