Reduction of Pb(II) in water to safe levels by a small tubular membrane nanofiltration plant

Dilute Pb(II) aqueous solutions were nanofiltered through a tubular membrane with good rejections. Retention was modeled using the Modified Spiegler–Kedem theory. The true retention, evaluated from concentration-polarization measurements, was similar to the observed value. The three characteristic parameters of the model: reflection coefficient σ , solute permeability P , and mass transfer coefficient K m were evaluated simultaneously. The reflection coefficient decreased with an increase in concentration until a plateau was reached at a concentration of 30 ppm. At low concentrations, the solute permeability increased with an increase in concentration, reaching a maximum at a concentration of 30 ppm. Subsequently, the permeability decreased with further increase in concentration, until at concentrations ≥ 100 ppm, it reached values close to those observed for very dilute solutions (