TraceElement Removal in Distributed Drinking WaterTreatment Systems by Cathodic H2O2 Productionand UV Photolysis

摘要

As water scarcity intensifies, point-of-use and point-of-entry treatment may provide a means of exploiting locally available water resources that are currently considered to be unsafe for human consumption. Among the different classes of drinking water contaminants, toxic trace elements (e.g., arsenic and lead) pose substantial operational challenges for distributed drinking water treatment systems. Removal of toxic trace elements via adsorption onto iron oxides is an inexpensive and robust treatment method; however, the presence of metal-complexing ligands associated with natural organic matter (NOM) often prevents the formation of iron precipitates at the relatively low concentrations of dissolved iron typically present in natural water sources, thereby requiring the addition of iron which complicates the treatment process and results in a need to dispose of relatively large amounts of accumulated solids. A point-of-use treatment device consisting of a cathodic cell that produced hydrogen peroxide (H2O2) followed by an ultraviolet (UV) irradiation chamber was used to decrease colloidstabilization and metal-complexing capacity of NOM present in groundwater.Exposure to UV light altered NOM, converting ∼6 μMof iron oxides into settable forms that removed between 0.5 and 1μM of arsenic (As), lead (Pb), and copper (Cu) from solutionvia adsorption. After treatment, changes in NOM consistent with theloss of iron-complexing carboxylate ligands were observed, includingdecreases in UV absorbance and shifts in the molecular compositionof NOM to higher H/C and lower O/C ratios. Chronoamperometric experimentsconducted in synthetic groundwater revealed that the presence of Ca²⁺ and Mg²⁺ inhibited intramolecular charge-transferwithin photoexcited NOM, leading to substantially increased removalof iron and trace elements.