AWWA WQTC60674

The City of Waco, Texas currently operates two conventional water treatment facilities, the 24 mgdRiverside Water Treatment Plant (WTP) and the 42 mgd Mount Carmel WTP. The City hashistorically experienced taste and odor episodes in its potable water supply related to algae growth inLake Waco, its sole source of raw water. Increased nutrient loadings due to a high concentration ofanimal feeding operations in the Lake Waco watershed has led to an increased frequency and severityof the algae blooms and subsequent taste and odor events.Various treatment processes were screened to determine their suitability for meeting water qualityregulations and providing taste and odor control. These included various combinations of dissolvedair flotation (DAF), granular media filtration, granular activated carbon (GAC) contactors, ultravioletirradiation (UV), membrane filtration, and ozonation. The screening evaluated how each of theprocesses could help the City meet treatment requirements in the areas of taste and odor control, LongTerm 2 Enhanced Surface Water Treatment Rule compliance and Disinfection Byproduct Rulecompliance. As a result of this screening it was determined that DAF produced significant benefits inthe area of taste and odor control and that the DAF/granular media filtration/GAC/UV combinationresulted in the highest level of total benefits to the City.Four pilot tests were conducted to prove the effectiveness of the DAF system to remove the taste andodor causing algae. These occurred in the Summer of 2000, the Winter of 2000, the Summer of 2002,and the Spring of 2004. The pilot tests were operated over the range of expected raw water qualityand saw algae concentrations in the treatment plant influent vary from 250 units/ml to over 5,000units/ml.The pilot studies showed that DAF facilities operating at 6 gpm/ft² followed by granular filtersoperating at 4 gpm/ft² and GAC contactors provided excellent removal of algae, turbidity, and tasteand odor compounds. Algae removal through the DAF units averaged about 88% and whencombined with granular filters resulted in algae removals of over 99%. GAC contactors with anempty bed contact time of 8 minutes proved effective at polishing the filtered water of residualGeosmin to below human detection limits.Design of the treatment facilities is currently underway. Among the issues being examined in thedesign phase of the project are the effectiveness of high rate DAF which may allow the overflow rateto be increased to as high as 15 gpm/ft², solids handling for DAF float, control of odor emanatingfrom the algae laden float, and the suitability of the UV system when used in conjunction withperoxide to provide additional taste and odor control. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

13

File Size:

1 file , 510 KB