Immersed Ultrafiltration Membranes for Treatment of Organically Laden Surfice Water


Ultrafiltration membranes are becoming increasingly prevalent in potable water treatment applications. This trend can be attributed to the improved cost effectiveness of membrane systems as compared to conventional treatment technologies and to progressively more stringent water quality regulations. In particular, increased awareness related to the formation of disinfection by-products (DBPs) such as trihalomethanes (THMs) and halo-acetic acids (HAAs) has required utilities to improve the removal of their organic precursors.

Excellent removal rates of as high as 75% for TOC and 95% for colour have been achieved for at drinking water plants using ZeeWeed® immersed ultrafiltration membranes in combination with a coagulant, pH control, and/or powdered activated carbon (PAC). As compared to a conventional plant using coagulation-flocculation-clarification-filtration, a membrane system incorporating coagulant addition can be designed with a reduced flocculation hydraulic retention time and with the elimination of the clarification step. The process then uses coagulation-flocculation-ultrafiltration. Coagulant is added prior to a flocculation tank that flows directly into the membrane tank where suspended particles are filtered by the membranes. With the elimination of clarification, the floc need only be larger than the membrane pores to be removed, eliminating settleability concerns. This leads to a decrease in plant footprint due to lower flocculation retention time, as well as to decreased chemical consumption and residuals disposal costs. The addition of PAC can also be incorporated upstream of the membrane tanks to increase organics removal.

A large proportion of drinking water treatment plants in Alberta are designed for the treatment of surface water sources. With many of these water sources having highly variable organics, reaching seasonal peaks as high as 25 mg/L TOC, effective organics removal is essential prior to chlorine disinfection. For conventional water treatment plants, this can be particularly challenging during periods where turbidity peaks can exceed 1,000 NTU. This paper will describe the use of enhanced coagulation with immersed ultrafiltration membranes, its advantages as compared to conventional treatment plants, and will discuss details of coagulation, PAC dosing, pH adjustment, and treated water quality for several full scale plants in Alberta including: 1) Mountain View Regional Water Services Commission, Anthony Henday WTP – 6 MGD, polyaluminum chloride; 2) Municipal District of Lesser Slave River, Canyon Creek WTP – 0.25-0.33 MGD, aluminum sulphate addition; and 3) Municipal District of Lesser Slave River, Hamlet of Smith WTP – 0.16-0.19 MGD, aluminum sulphate and polyaluminum chloride addition. Data will also be presented for several pilot scale evaluations performed in Alberta.

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