Rehabilitation of water distribution systems following a cadmium contamination intrusion—A solution based on water quality and water distribution systems modeling

Contaminant(s) intrusion into water distribution systems (WDS) may have an adverse effect on large populations. The pipeline corrosion scale has the capability to adsorb the contaminant and thereafter release it to water once the system is returned to operation, causing secondary contamination. Therefore, overcoming contamination events should remove the contaminant from both aqueous and scale phases in a controlled fashion, while not jeopardizing the WDS integrity, nor causing red-water events. This study examined the adsorption and subsequent release of cadmium, as a representative heavy-metal ion, from representative pipeline corrosion scales. Adsorption/desorption batch experiments were conducted on corrosion scales peeled off from old domestic WDS pipes. The effect of water quality (pH, alkalinity, ionic composition, [Cd²⁺]) on Cd(II) adsorption and release was examined. The corrosion scale showed high Cd²⁺absorption capacity and linear relation between [Cd²⁺] and the adsorbed Cd. Desorption experiments included dosages of various acid types, Na2S, and KCl. HCl dosage to pH3 was found a suitable technique, releasing ~90% of the adsorbed Cd(II). The work conclusions will serve to design continuous adsorption/desorption experiments, with the aim of determining the optimal rehabilitation treatment.