AWWA JAW30368

Dissolved-air flotation (DAF) was compared with conventional gravity settling (CGS) in laboratory experiments using synthetic water and in field studies using alum and polyaluminum chloride. DAF produced significantly lower residual turbidities than did CGS, particularly at colder temperatures. The difference in performance between DAF and CGS is explained using the particle size, particle density, temperature, and settling-rate relations described by Stokes' law. In addition, the large bubble volume concentrations released during DAF provided adequate opportunities for collisions between particles and bubbles, thus reducing the need for long flocculation periods. DAF achieved good performance with flocculation periods of 5 min, whereas CGS required at least 20 min of flocculation. In both processes, dissolved organic species and organic halide precursors were removed to the same degree, and similar levels of residual dissolved aluminum were found. Includes 35 references, tables, figures.

Product Details

Edition:

Vol. 83 - No. 9

Published:

09/01/1991

Number of Pages:

6

File Size:

1 file , 1.8 MB