Abstract
Inorganic phosphate is a common nutrient that is applied as a fertilizer to both agricultural fields as well as urban settings such as private yards, public parks and other urban landscaping. While phosphate typically binds tightly to soil, movement of phosphate off of application sites can occur through soil erosion. The soil and its bound phosphate can then end up in surface waters such as rivers and lakes. Phosphate found in surface water bodies exists both as bound to the suspended clay as well as that free in solution. Elevated phosphate concentration in surface waters can lead to algal blooms and eutrophication. While the phosphate bound to clay in suspension in surface water bodies can be removed by commercially available polymer flocculants, the phosphate that is free in solution is more challenging as it is usually found in low concentrations and other anionic salts are generally present in higher concentrations. To remove phosphate from contaminated water systems, where other anions exist at higher concentrations, it is favorable to have a method of removal that is selective for phosphate. As a proof of principle, thiourea derivatized polymer flocculants were examined for the selective removal of phosphate in the presence of competing anions. The polymer flocculants exhibited selectivity for phosphate through hydrogen bonding and were effective at removing up to 43% of phosphate from simulated wastewater. Computational studies and 1H NMR were used to investigate the selectivity of the thiourea monomer for phosphate over competing anions such as chloride and sulfate.
Highlights
Phosphate is an essential plant nutrient that is applied as a fertilizer to agricultural crops and to urban landscapes
While the phosphate bound to clay in suspension in surface water bodies can be removed by commercially available polymer flocculants, the phosphate that is free in solution is more challenging as it is usually found in low concentrations and other anionic salts are generally present in higher concentrations
The study described show that the addition of thiourea to a polymer flocculent results in a material that can be used to remove both the sorbed and soluble phosphate from wastewater
Summary
Phosphate is an essential plant nutrient that is applied as a fertilizer to agricultural crops and to urban landscapes. While phosphate applied to a field benefits the crops being produced, it may move off site into rivers and lakes [1] [2]. Phosphate is generally a limiting nutrient for the microorganisms present. Phosphate that is applied to fields is generally bound tightly to the soil and will have little movement through the soil profile [3]. Once the soil moves into a surface water body it can become suspended and the phosphate will come to an equilibrium between the soil bound and aqueous portions based on environmental conditions such as pH and temperature of the water present [3]. Polymer flocculants as well as other coagulants are effective at removing the suspended solids and the phosphate bound to them; they remove little if any of the phosphate that is free in aqueous solution [4] [5]
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