Layered double hydroxide membranes for advanced removal of phosphate from wastewater

Abstract

With the increasingly stringent effluent requirement for phosphate worldwide, the demand for advanced phosphorus removal is rising. Although conventional flocculation-filtration is a reliable way for achieving low phosphorus concentrations, floc accumulation on the membrane will create additional resistance requiring greater operation pressure in practical applications. Here, we fabricated a layered double hydroxide (LDH) membrane for advanced removal of dissolved phosphate without pre-flocculation. The permeability of the LDH membrane can reach 32337.2 L/(m2·h·bar), which is 10–100 times higher than conventional adsorption membranes with embedded active sites. In addition, the LDH membrane yielded a strong phosphate retention capacity and could reduce the phosphate to <0.05 mg/L at a load of 1146.5 mg/(m2·h). And if 0.1 mg/L is selected as the target, the LDH membrane can treat 4400 bed volumes of wastewater at the above load. Moreover, actual wastewater experiments have demonstrated the advantage of LDH membranes in alleviating the rapid growth problem of transmembrane pressure. The intra-membrane kinetic analysis revealed the rate basis of LDH membranes to capture phosphate in an instant hydraulic residence time. Stoichiometric and characterization analyses indicated that the main phosphate retention mechanisms were ion exchange (56.7%), ligand exchange and electrostatic attraction. This study proposes new insight into the design and fabrication of membranes for advanced phosphate removal, which is enlightening for the development of tailored membranes with different functions.