Effectiveness of ferric salts in removing low levels of dosed copper from NOM-containing natural water

Abstract

Water utilities dose copper in drinking water systems to inhibit/kill microorganisms including algae. Under conditions observed in the systems, the majority of dosed copper is reported to be in dissolved forms of Cu-NOM and inorganic compounds. High concentrations (40 mg/L) of ferric salts are reported to be able to remove large amounts of copper. However, the fate of dissolved copper when a small amount of ferric salts (,2 mg/L) is present in natural water or in the distribution pipes when they are released from the corroded iron pipes are not known. The current paper investigates the mechanisms behind the dissolved copper removal in NOM-containing bulk water.When copper was dosed from 250-800 mg-Cu/L, relatively high solubility was demonstrated in Mundaring water, with dissolved copper increased from 250-720 mg-Cu/L. Both ferric chloride and ferric hydroxide were found to have a considerable ability to remove dissolved copper while the former showed higher capacity. Ferric chloride showed a linear relationship with copper removal (R 2 ¼ 0.99) and the removal by ferric hydroxide showed excellent agreement with either the Freundlich (R 2 ¼ 0.98) or Langmuir (R 2 ¼ 0.99) adsorption isotherm.

Impact of NOM character on copper adsorption by trace ferric hydroxide from iron corrosion in water supply system

“…Chlorine and chloramine are also strong oxidizing agents which can compete with Cu 2+ to react with iron. Our earlier study [26] and studies by others [8,10] found little dissolved copper existing in natural water in the form of cupric ions, as most of the copper existed as Cu-NOM complexes. This finding further excludes the possible reaction between free cupric ions and iron.…”

“…as a nitrification inhibitor), little research has been conducted on dissolved Cu(II) removal by low concentration (< 2 mg/L) iron pipe corrosion products released from corroded or damaged pipes in distribution systems like the G&AWSS. Preliminary experiments using water from Mundaring Weir showed adsorption of dissolved Cu(II) by Fe(OH) 3 flocs present at trace concentrations, with the adsorption obeying Langmuir or Freundlich adsorption isotherms [26].…”