The City of Waco, Texas currently operates two conventional water treatment facilities, the 24 mgd
Riverside Water Treatment Plant (WTP) and the 42 mgd Mount Carmel WTP. The City has
historically experienced taste and odor episodes in its potable water supply related to algae growth in
Lake Waco, its sole source of raw water. Increased nutrient loadings due to a high concentration of
animal feeding operations in the Lake Waco watershed has led to an increased frequency and severity
of the algae blooms and subsequent taste and odor events.
Various treatment processes were screened to determine their suitability for meeting water quality
regulations and providing taste and odor control. These included various combinations of dissolved
air flotation (DAF), granular media filtration, granular activated carbon (GAC) contactors, ultraviolet
irradiation (UV), membrane filtration, and ozonation. The screening evaluated how each of the
processes could help the City meet treatment requirements in the areas of taste and odor control, Long
Term 2 Enhanced Surface Water Treatment Rule compliance and Disinfection Byproduct Rule
compliance. As a result of this screening it was determined that DAF produced significant benefits in
the area of taste and odor control and that the DAF/granular media filtration/GAC/UV combination
resulted 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 and
odor 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 quality
and saw algae concentrations in the treatment plant influent vary from 250 units/ml to over 5,000
units/ml.
The pilot studies showed that DAF facilities operating at 6 gpm/ft<sup>2</sup> followed by granular filters
operating at 4 gpm/ft<sup>2</sup> and GAC contactors provided excellent removal of algae, turbidity, and taste
and odor compounds. Algae removal through the DAF units averaged about 88% and when
combined with granular filters resulted in algae removals of over 99%. GAC contactors with an
empty bed contact time of 8 minutes proved effective at polishing the filtered water of residual
Geosmin to below human detection limits.
Design of the treatment facilities is currently underway. Among the issues being examined in the
design phase of the project are the effectiveness of high rate DAF which may allow the overflow rate
to be increased to as high as 15 gpm/ft<sup>2</sup>, solids handling for DAF float, control of odor emanating
from the algae laden float, and the suitability of the UV system when used in conjunction with
peroxide to provide additional taste and odor control. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 13 |
| Published : | 11/15/2004 |
