AWWA MTC69762

The City of Camarillo, California is implementing a groundwater desalination facility to better utilize groundwater from an aquifer with continuing degradation in water quality. The city's wells have been increasing in total dissolved solids (TDS), chlorides, and sulfates, which will require desalination, but have also been increasing in iron and manganese, causing complications in selection of a desalination process. The city has been pilot testing various alternatives for iron and manganese control ahead of reverse osmosis, looking at methods of oxidation and filtration during a twelve month pilot study. Aeration plus media filtration was found to be an effective method for removal of iron, while not impacting the dissolved manganese, which is less likely to foul the reverse osmosis (RO) membranes. While iron oxidation through aeration is generally thought to be a rapid process, organic complexation of iron has slowed the oxidation process, such that complete oxidation of iron was not seen within a 37 minute pre-filtration contact tank. Membrane filtration and conventional media filtration were both tested to determine whether membrane filters could provide better removal of oxidized iron. However, it was found that the depth filtration achieved in conventional media filters enhanced both the oxidation and removal of iron, making it a more effective pretreatment process for reverse osmosis at this facility. This paper presents the impact of contact time, dissolved oxygen level, pH, and catalyzing agents on the complete oxidation and removal of iron ahead of reverse osmosis. Includes 4 references, table, figures.