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

Abstract

The fate of trace concentrations of cupric sulphate (< 0.4 mg/L) dosed into chloraminated distribution systems to inhibit nitrification has been shown in this study to be controlled by at least two crucial factors: the character of natural organic matter (NOM) and iron hydroxide corrosion products present at low concentrations (< 2 mg/L). This research quantified the removal of Cu(II) ions added into waters containing trace Fe(OH) 3 flocs and the effect of NOM of different character on this removal. The dominant dissolved copper species in NOM-containing waters were found to be Cu(II)-NOM complexes.Both intramolecular chelation and intermolecular complexation can occur, with the latter occurring preferentially and resulting in the aggregation of smaller organic molecules to form larger molecules.The presence of ferric hydroxide flocs when Cu(II) ions were added into NOM-containing waters was shown to result in removal of Cu(II) ions, presumably as Cu(II)-NOM complexes. This removal was through adsorption processes obeying Freundlich isotherms, although the presence of larger NOM molecules and heterogeneous copper species (e.g. Cu(OH) 2(s) and CuO (s) ) appeared to shield smaller Cu(II)-NOM complexes from adsorption to some extent. For the strategy of inhibition of nitrification in distribution systems by the addition of Cu(II) ions, complexation of Cu(II) ions by NOM and adsorption of Cu(II)-NOM complexes by ferric hydroxide flocs released from pipe walls pose significant operational challenges to maintaining the concentration of Cu(II) ions through the distribution system.

Modelling combined effect of chloramine and copper on ammonia-oxidizing microbial activity using a biostability approach

“…In chloraminated systems, Cu speciation will be controlled by various factors, including pH, NOM concentration and its complexing ability, and free ammonia. For example, in the case of Mundaring water used for this study, Cu-NOM complexes were the major species present (Zhan et al, 2012). Therefore, future studies should concentrate on understanding Cu speciation and its impact on nitrifiers in the chloraminated environment.…”

“…Following the Australian Drinking Water Quality Guidelines (ADWG, 2004) and authorized by the Department of Public Health, Western Australia, copper doses of 0.25e0.40 mg-Cu L À1 were applied in a part of the distribution system. The results showed that nitrification could be controlled by dosing copper into service reservoirs and pipelines, although an impediment was the significant loss of copper during transport through the corroded iron pipeline (Zhan et al, 2012). Several processes can significantly affect the copper concentration in the pipelines compared to the reservoir.…”

“…Zhan et al (2012) noted that the majority of the inorganic copper added as copper sulfate (up to a concentration of 0.4 mg-Cu L À1 ) existed as Cu-NOM complexes in Mundaring weir water in Western Australia at pH 8. Sarathy and Allen (2005) had similar findings for surface water.…”

“…Several processes can significantly affect the copper concentration in the pipelines compared to the reservoir. Copper could be bound as cations into the biofilm matrix, and sulphide produced in anaerobic pockets can lead to CuS (Kristiana et al, 2010) or by other iron corrosion products of the pipelines (Zhan et al, 2012). Therefore, the success of the copper dosing depends on short time dosing into service reservoirs rather than into the pipelines where biofilm or corrosion is significantly present.…”

Legionellosis and Recent Advances in Technologies for Legionella Control in Premise Plumbing Systems: A Review

“…While pH plays an important role in the speciation of copper (i.e., copper ion levels decrease significantly under alkaline pH), silver ions are relatively stable in the pH range of 6-9. Some chemical parameters (e.g., chloride and phosphates added for chlorination and corrosion control, respectively) react with copper and silver ions, and consequently these metal complexes diminish their microbiocidal power [111][112][113]. Moreover, the latter metal complex chlorargyrite (AgCl (s) ) contributes to the purple/grey stains in bathroom porcelain [114].…”