AWWA MTC53883

The use of microfiltration (MF) and ultrafiltration (UF) membranes for municipalwater treatment has traditionally been limited to high quality surface watersources. Despite the recent, significant increase in the acceptance andapplication of both MF and UF membrane systems in North America, UF and MFmembranes have typically not been applied on waters having an average turbidityand total organic carbon (TOC) level greater than 20 NTU and 10.0 mg/L,respectively without extensive pretreatment. The applications of membranes atfacilities with moderate to poor quality raw water have generally been limited toeither settled or filtered water for polishing treatment; particularly for watertreatment plants with capacities greater than 5 million gallons per day (MGD). Inthis context, recent advances in the configuration and application of immersedmembrane systems offers an opportunity to economically apply UF membranes totreat high turbidity, and organic laden water sources on a large scale withoutconventional pretreatment by using a new combined treatment process. With thisprocess, vacuum/suction driven, hollow fiber membranes are directly immersed incoagulated and flocculated raw water. The membranes provide a positive barrier toparasites such as Giardia and Cryptosporidium, as well as high concentrations ofboth organic and inorganic solids, which are either suspended in the raw water ordeveloped by coagulation and co-precipitation. This integratedcoagulation/membrane process eliminates the need for sedimentation and rapidgravity sand filtration and is not negatively impacted by high turbidity and TOClevels. In addition to turbidity and pathogen reduction, the process can also beoptimized for natural organic matter (NOM), color and TOC reduction and can beused in combination with powdered activated carbon (PAC). This efficientcombination of membrane and coagulation/adsorption pretreatment processes hassignificantly reduced the economic considerations associated with construction ofnew and retrofitting existing water treatment facilities to meet increasinglystringent drinking water quality guidelines. As a result, pre-design and pilotstudies have been completed for immersed ultrafiltration treatment facilitiesranging in size from 2-40 MGD treating poor quality raw water directly. Theresults of these studies described in this paper indicate that immersedmembranes, either directly or with a coagulant, can be applied on low qualitywater sources while providing drinking water that meets current and proposedregulatory guidelines including the Disinfectant- Disinfection By-product(D/DBPR) Rule and the Interim Enhanced Surface Water Treatment Rule (IESWTR).Pilot test results and treated water quality data for applications in CentralAmerica, Montana,U.S.A., and Alberta, Canada are presented. Includes 5 references, tables, figures.