Fixed bed column evaluation of phosphate adsorption and recovery from aqueous solutions using recycled steel byproducts.

Excessive phosphorus loading from anthropogenic sources is a major cause of eutrophication of natural waters. Phosphorus is also a non-renewable natural resource that cannot be substituted with other sources. The objective of this study was to determine the feasibility of using recycled steel byproducts to remove and recover phosphate from aqueous solutions. Laboratory fixed bed column experiments were conducted with recycled steel chips of different sizes to evaluate phosphate adsorption characteristics and phosphate recovery efficiencies using alkaline solutions. The results showed that phosphate adsorption onto steel chip filters was characterized by an initial fast breakthrough followed by a stable removal phase. The cumulative phosphate adsorption capacities of the steel chips were 8.43-10.4 mg P/g following 4800 empty bed volumes with a 3 min contact time and an initial concentration of 10 mg P/L. The phosphate adsorption onto steel chips was favored at low flow rates, low pH values, and low organic carbon concentrations. Sodium hydroxide solutions effectively desorbed phosphate from the steel chips. The total phosphate desorption percentages were 58.9%, 64.2%, and 83.4% after 120 empty bed volumes using 0.05 M, 0.10 M, and 0.20 M NaOH solutions, respectively. Steel chips also exhibited high phosphate adsorption and desorption capacities when treating agricultural subsurface drainage water, municipal wastewater, and stormwater runoff. Overall, the results of this study suggest that recycled steel byproducts are efficient and promising low-cost phosphate capturing materials for sustainable phosphorus management.

Evaluation of industrial by-products and natural minerals for phosphate adsorption from subsurface drainage.

Agricultural subsurface drainage has been recognized as an important pathway for phosphorus transport from soils to surface waters. Reactive permeable filters are a promising technology to remove phosphate from subsurface drainage. Three natural minerals (limestone, zeolite, and calcite) and five industrial by-products (steel slag, iron filings, and three recycled steel by-products) were evaluated for phosphate removal from subsurface drainage using batch adsorption experiments. Phosphate adsorption onto these materials was characterized by Langmuir isotherm and second-order kinetic models. The adsorption capacities increased by factors of 1.2-2.5 when temperature was increased from 5°C to 30°C. Industrial by-products exhibited phosphate adsorption capacities that were one order of magnitude higher than natural minerals. Medium-sized steel chips exhibited high phosphate adsorption capacities (1.64-3.38 mg/g) across different temperatures, pH values, organic matter concentrations, and real drainage water matrixes. The strong chemical bonds between phosphate and steel by-products prevented the release of adsorbed phosphate back to the solution. The steel by-product filter can be paired with a woodchip bioreactor for nitrate and phosphate removal. It is suggested that the phosphate filter be connected to a woodchip bioreactor after the startup phase to minimize the impact of dissolved organic matter on phosphate adsorption. The results of this study suggest that the low-cost steel by-products examined could be used as effective adsorption media for phosphate removal from subsurface drainage.