AWWA MTC93002

The purpose of membrane pretreatment is to eliminate or minimize the fouling potential of the feedwater and thereby maintain membrane productivity. Fouling is caused by either plugging by materials in the feedwater or by chemical deposits formed on the membrane. Some problems are suspended solids, scaling, biological fouling, and metal oxides and hydroxides. This paper discusses causes of each, for example, sulfates, silica, and calcium carbonate for scaling; silt density index, turbidity measurements, and zeta potential, for suspended solids; and iron and aluminum for metals. Following an introduction to each problem the author suggests pretreatment solutions: a variety of filtering methods (cartridge filters; dual media filtration; coagulation, flocculation, clarification and filtration; microfiltration or ultrafiltration) for suspended solids; means of removing ions or inhibiting scale (removing ions via ion exchange or lime softening or adding a polymer scale inhibitor) for scaling; ultraviolet light for biological fouling (the author discourages the use of chlorine because it forms THMs and damages membranes); and oxidation and filtration (using greensand or other filters) for iron removal. The source of aluminum is generally alum used in the water treatment process and its precipitation can be controlled in part by pH adjustments.

Product Details

Published:

01/01/1993

ISBN(s):

0898677076

Number of Pages:

13

File Size:

1 file , 670 KB