Phosphorus (P) is a fundamental element for biochemistry and life as we know it. In nature, it exists as its oxidized form, phosphate (PO43-), it is a structural component in both DNA and RNA and is an essential nutrient for humans, animals, and plants. Even though PO4 is essential to life, however, its excess level in water has a detrimental effect on water bodies. Elevated amounts of PO4 in water bodies resulting from anthropogenic activities such as agricultural runoff, urban runoff, and wastewater discharge leads to water contamination and death of aquatic life. Nutrient pollution is a worldwide phenomenon and it is imperative to deal with the problem at the source, which necessitates new technologies for treatment in small-scale wastewater systems. Iron hydroxide minerals are chemically reactive, possess adsorptive properties, and have been shown to be involved in a variety of reactions. These minerals can occur naturally in the environment and can be synthesized in a lab. In this work, iron minerals were synthesized and studied for their applications to remove phosphate from water. Three different iron minerals were tested: completely reduced (100% Fe(II)), completely oxidized (100% Fe(III)), and partially reduced/oxidized (50% Fe(II): 50% Fe(III)). We also tested how the presence of organics would affect the phosphate adsorption reaction by doping phosphate solutions with histidine, arginine, and cysteine. We observed a maximum adsorption of 45% without organics, but the presence of organics enhanced phosphate adsorption by an additional ~30%. This work reveals an alternative technique to concentrate and remove phosphate from water and demonstrates how environmental conditions (redox state, pH, presence of organics) influence adsorption in a simulated mineral system.

Phosphate removal from contaminated waters via iron hydroxide adsorption

ACS Fall 2021

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