Covalently Functionalized Sawdust for the Remediation of Phosphate from Agricultural Wastewater

Phosphate remediation from wastewater is rapidly becoming an ever more attractive process due to a combination of both the economic pressure of increasing phosphate scarcity and the environmental damage caused by untreated agricultural runoff. Ideally, remediated phosphate will be recoverable and would be able to be reused as fertilizer. Many different resins have been investigated, but due to the scale of the challenge, any feasible solution will involve the use of very inexpensive waste products as the solid support. Sawdust, functionalized with iron-binding ligands, is such a potential resin. Sawdust alone binds 0.3 g/kg of phosphate which is insufficient. Iron has a strong affinity for phosphate, making the formation of iron-phosphate bonds a promising avenue for the development of recyclable resins. Previously prepared iron-chitosan complexes bound 8.2 g/kg. However, as the price of chitosan has rapidly increased, alternatives are required. In this current study, the covalent modification of the sawdust using either carboxymethylcellulose-supported ligands, or direct functionalization of the sawdust can increase this to 40 g/kg using ethylene diamine as the iron-binding ligand. Binding decreases over repeated cycles of phosphate exposure and elution, but can be fully restored through regeneration using iron salts. The simple green synthesis of this material, and the iron-binding capability of the investigated ligands is discussed. These sawdust-based resins show promise as potential candidates for industrial-scale phosphate recovery efforts in the future