Cody L. Ritt’s research while affiliated with North Dakota State University and other places

Phosphorus (P) is a non-renewable natural resource which is used extensively in agriculture as a fertilizer. Phosphate (PO 4³⁻ ) rocks are mined to meet growing agricultural demands induced by rising global populations. Much of the P used in agricultural fields finds its way into surface waters where it permanently resides, leading to devastating effects on the aquatic ecosystem through eutrophication of the waterbodies. This research was aimed at developing a sorbent that can engender a P reuse cycle by utilizing eutrophic surface waters as viable P sources (mines). The goal was to develop a sorbent which can selectively recover low concentration (≤100 P μg L ⁻¹ ) typical of eutrophic waters. Molecularly imprinted polymers (MIPs) were identified as a potential technology for accomplishing this goal. Three MIPs were screened for viability by assessing their sorption capacities. After the initial screening, one MIP was selected for further studies. The selected MIP was found to have partial PO 4³⁻ selectivity and tunable P sorption capacity. Adjusting the template:monomer ratio resulted in an increase in P sorption capacity from ∼11 to ∼28 mg PO 4³⁻ -P g ⁻¹ , making this MIP competitive with existing technologies. The MIP was characterized to understand the polymer chemistry and mechanisms of P-removal. The possible mechanisms of aqueous P removal by the MIP were identified as selective chemical binding to the imprinted recognition sites and electrostatic attraction.

Novel iron (Fe) cross-linked alginate (FCA) beads were used for phosphate removal from synthetic water, lake water, and wastewater. Batch experiments were conducted with the beads (0.118 g dry weight) using three different initial concentrations of phosphate (C0=5, 50, and 100 mg PO43 - P/L) as well as environmentally relevant (eutrophic lakes) concentration of 100 μg PO43 - P/L. Approximately 97% of phosphate (C0=5 mg PO43 - P/L) was removed by the beads in 360 min from an aqueous solution. In 360 min, beads removed ∼76% of phosphate from water with C0=50 PO43 - P/L and ∼46% from water with C0=100 mg PO43 - P/L. For 100 μg PO43 - P/L, 80% removal was achieved within 20 min. The second-order reaction fit well for all the concentrations with reaction rate constants (k) of 0.076 and 0.2027 L/mg/min (C0=5 mg and 100 μg PO43 - P/L, respectively). The maximum phosphate sorption capacity was found to be ∼79 mg PO43 - P/g of dry beads. No change in phosphate removal was observed in the presence of Cl-, HCO3-, SO42-, NO3-, and natural organic matter (NOM). To investigate the feasibility of using the FCA beads in a real-life situation (e.g., in eutrophic lakes), actual lake waters (11-69 μg PO43 - P/L) were used and 81-100% phosphate removal was observed in 24 h. Results presented here demonstrate the potential for the use of the FCA beads for the reclamation of eutrophic lakes (removal of excess of phosphate).

Novel metal cross-linked alginate beads (MCA) were successfully used for aqueous phosphate removal. Batch experiments were conducted using three different concentrations of phosphate (5, 50, and 100 mg PO4 3--P/L) with 0.11812 gm (dry weight) iron cross-linked beads. About 94% phosphate was removed in 6 h from the aqueous solution having an initial phosphate concentration of 5 mg PO4 3--P/L. With 50 mg PO4 3--P/L, the beads were found to remove only ~41% in 6 but achieved 89% phosphate removal in 96 h. The second order reaction model fitted better for all the concentrations, and observed reaction rates were found to be 0.2979, 0.083, and 0.0181 per h for 5, 50, and 100 mg PO4 3--P/L, respectively. Interference of Cl-, HCO3-, SO4 2-, NO3-, and natural organic matter (NOM) was investigated, and no change in the removal efficiency of phosphate was observed. To investigate the feasibility of using the MCA beads in real-life situation (e.g., eutrophic lakes), "pouch experiments" were conducted in two conditions, namely shaking and static where MCA beads were introduced into the water in pouches. The efficacy of beads in pouches was found to be the same as free beads (used in earlier batch experiments). The successful sorption of phosphate by MCA beads is expected to have enormous implications for nutrient removal and recovery.