AWWA ACE56356

To minimize disinfection byproduct (DBP) formation three optimization options are available to conventional treatment plants that chlorinate prior to or at the rapid mix and include: lower the level of chlorine dosed at the rapid mix and re-chlorinate; move the point of chlorination to after the sedimentation basin; or, switch to a different pre-disinfectant/oxidant. However, implementing these optimization objectives cannot compromise the pathogenic barrier achieved by effective filters. The objectives of this study are to: assess and evaluate the conditions under which optimizing preoxidation is effective in controlling DBPs; and, determine the conditions under which preoxidation impacts filter performance. Tests were conducted with a pilot-scale system. Results indicated that lowering the pre-chlorination dose and re-chlorinating after the sedimentation basin such that a target distribution system residual (1 mg/L at 24 hours) is maintained, yielded lower chlorine consumed (up to 50%) and lower total trihalomethanes (TTHMs) formed after 24 hours (up to 29%). Two aspects of filter performance were monitored: the ripening period; and, steady-state turbidity. For all dose scenarios, steady-state turbidity averaged 0.06 ntu. Trends in increasing steady-state turbidities were observed as the preoxidant dose location for chlorine was moved from the rapid mix to mid-flocculation to post sedimentation. Chlorine also yielded lower steady state turbidities compared with chlorine dioxide and potassium permanganate dosed at the rapid mix. Includes 11 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/16/2002

Number of Pages:

20

File Size:

1 file , 420 KB