Studies of Bore Water Oxidation Using a Multi Electrode-Perforated Electrode flow Through Cell

Abstract

Anoxic groundwaters in the Waikato region are naturally contaminated with iron and manganese at levels of 25.0 mg/L and 0.9 mg/L respectively and above. Often these contaminants can be removed by simple aeration and clarification and/or filtration. However when present with elevated levels of silica and/or organic matter, these waters, upon oxidation, can form highly stable brownish colloidal suspensions that are difficult to filter. Typical treatment methods for these waters usually involve expensive ion exchange to remove the metal ions in their reduced forms or chemical oxidation, using strong oxidising agents such as calcium hypochlorite, to precipitate the metals as their respective hydrous oxides. An improved multiple electrode perforated electrode flow through (ME-PEFT) cell has been developed for in-line electrochemical oxidation of these problem waters. In initial work, using low cost graphite anodes and with added sodium chloride (250 mg/L), 40% instant oxidation at 16 V was achieved. When dimensionally stabilised anodes (DSA) consisting of titanium metal coated with TiO₂/RuO₂/IrO₂ were used in a dual electrode pair ME-PEFT cell, 100% oxidation of the iron was obtained after a single pass through the cell using only the naturally available chloride (10 to 12 mg/L). Power consumption was 3.80 kWh/m³.

The oxidised iron clarified readily yielding a clear solution containing less than 0.2 mg/L of iron and having a turbidity of 1.5 NTU after 5 hours settling time. Preliminary tests for an inline flotation clarifier have yielded promising results.