APPLICATION OF A NEW GENERATION OF IMMERSED ULTRAFILTRATION MEMBRANES FOR IRON AND MANGANESE REMOVAL

摘要

It is understood that the presence of iron and manganese in drinking water distributionsystems reduces the aesthetic quality of the water. When dissolved iron and manganeseare oxidized, they form insoluble compounds that precipitate and cause yellowish toreddish-brown to black staining, depending on the relative abundance of each metal. Inorder to improve the aesthetic quality of drinking water, the US EPA National SecondaryDrinking Water Regulations suggest maximum concentrations of 0.3 mg/L and 0.05mg/L for iron and manganese, respectively.During the last decade, microfiltration and ultrafiltration (MF/UF) membranes havebecome widely accepted as a viable alternative to conventional drinking water treatmenttechnologies such as coagulation, settling and sand filtration. Over the past few years,continuous advances in cost and reliability, coupled with an increasing concern aboutpathogens such as Cryptosporidium have made MF/UF membranes the preferredalternative to conventional technology for new plants.The ZeeWeed? Ultrafiltration Membrane system can remove particles that are greaterthan 0.1 microns in size, including iron and manganese precipitates. For the removal ofdissolved iron and manganese, an oxidation step is added prior to the membrane, whichconverts the dissolved species into their insoluble forms. Oxidation may be achieved byaeration or by the addition of oxidizing chemicals such as chlorine, chlorine dioxide orpotassium permanganate. This technology has been proven through numerous pilotstudies using the first three generations of ZeeWeed? 500 series immersed membranesystems, as well as the operation of a full-scale plant in New Brunswick, Canada that hasbeen operating since 1996.The ZeeWeed? 500c module was recently developed to improve the air distributionwithin the membrane fiber bundle such that the thickness of the cake layer could bemaintained or reduced during permeation. The improved design of the 500c module alsoallows for higher fluxes to be sustained. The ultrafiltration membrane used in theZeeWeed? 500c system has the same membrane chemistry and absolute pore size as itspredecessors and therefore also removes suspended solids, protozoa, bacteria and mostviruses. The ZeeWeed? 500c membrane can also be coupled with a pre-oxidation step toachieve the removal of dissolved iron and manganese. Pilot studies have recently been