Electrochemical oxidation of iron and manganese in groundwater

Groundwaters in the Waikato region are often naturally contaminated with iron and manganese at levels of up to 20.0 mg/L and 0.9 mg/L respectively. When present with elevated levels of silica and/or organic matter, these waters upon oxidation can form highly stable and difficult to filter brownish colloidal suspensions. Usual treatment methods involve either ion exchange to remove the metal, when present at low concentrations, or chemical oxidation using calcium hypochlorite to remove the metal as hydrous oxide precipitate. An electrochemical method using a novel porous electrode flow through (PEFT) cell design was found to be 100% effective in oxidizing iron and manganese after a single pass through the cell providing 3 g/L sodium chloride was added. Without sodium chloride addition the 10 to 12 mg/L of naturally occurring chloride gave 47% instant oxidation at 25 V. This percentage was increased to 70% when the chloride concentration was raised to 250 mg/L (well below the chloride drinking water standard). Complete oxidation and rapid settling was achieved by four passes through the cell at voltages as low as 10.5 V. The power consumption required to produce drinkable water was 18 kWh/m3 .