Well Water Iron Removal using DMI-65 filtration medium
Southport Power Plant, North Carolina, installed three wells for iron removal to provide an alternative water supply to address the increased costs associated with the use of city water for drinking applications. The well water quality required the addition of two 300 gpm reverse osmosis (RO) units as pretreatment for the ion exchange demineralizers. The original well water design, however, did not include measures to address iron in the water. The iron contained in the well water supply resulted in fouling to the cartridge filter elements and Reverse Osmosis (RO) membranes.
Early RO operation during 2004 noted lower than expected well water flow. As a result, the original two RO arrays were derated from 9:5 to 8:4 arrays with product flow reduced from 300gpm to 250 gpm. RO operation was often performed with only one unit in service in order to lower the iron fouling rate (iron removal) and to increase the membrane cleaning interval. During these times, well supply from the best well flowed to the unit in service with the option to change over to the standby unit when the performance dropped off. Chemical cleanings for each RO were performed once per month with the post cleaning restoring the unit back to baseline.
A well water study was performed in December 2004 and it was determined that multimedia filters, chlorine and filter aid continuous additions were required for iron removal as well as lowered SDI (silt density index) of the well water supply. The pretreatment was installed in early 2006 based on the findings of the well water study. The system included chemical injection of chlorine for iron oxidation, filter aid to accumulate iron particles for removal by multimedia filters and a filtrate storage tank to allow for constant RO water flow and for post filter backwash return to service rinse. After the filtrate tank the filtered water has sodium bisulfite and antiscalant added for removal of residual chlorine and to control against scale formation on the RO membranes.