Elimination of health-relevant heavy metals from raw waters of the drinking water supply in the PR China by means of weakly basic anion exchange resins

Abstract

The selective elimination of traces of heavy metals from raw waters of the drinking water supply by means of commercially available weakly basic anion exchangers has been investigated. Target species were heavy metal cations (of Hg, Cd, Zn, Ni, Cu, Pb) and chromate (Cr(VI)) anions. In the laboratory investigations, suitable anion exchangers were indentified. The phenol formaldehyde-based resin Duolite A7 revealed optimum properties for sorption of practically all heavy metal cations. Acrylic weakly basic exchangers provide optimum properties for chromate removal. Both kinds of exchangers also remove part of the natural organic matter. In parallel investigations in China Chinese anion exchangers were investigated. Further fundamental investigations comprised the sorption mechanism, the rate-controlling step and the conditions of optimum regeneration and rinsing. Furthermore, a mathematical approach for prediction of the filter breakthrough performance was tested. In the pilot scale experiments were carried out at several sites in China to demonstrate the processes and to obtain economic data about the application. Experiments at Shenyang showed that chromate concentrations of about 100 μg/L Cr(VI) can be decreased below the standard of 50 μg/L for about 4000 bed volumes. Experiments at Haikou showed that mercury concentrations of about 2 μg/L can be diminished below 1 μg/L for more than 15000 m 3 /m 3 of exchanger. The experiments at Huludao demonstrated that a simultaneous elimination of copper and mercury species, again at very large specific throughputs is achieved. In all cases only few m 3 of sulfuric acid, NaOH solution and rinsing water were required. Evaluation of the cost of chemicals and energy revealed that the specific operating cost of the selective elimination are in the range of? 0.02/m 3 to? 0.05/m 3 .