Full Description

The East Bay Municipal Utility District (EBMUD) operates six water treatment plantsthroughout the East Bay in California. The primary source water is snowmelt from theSierra Nevada collected at the Pardee Reservoir. The water travels from the reservoirthrough 90 miles of aqueduct before reaching either immediate treatment or subsequentstorage at one of several terminal reservoirs. EBMUD is interested in lowering totaltrihalomethane (THM) levels and haloacetic acid (HAA) levels in its treated water. Animportant mechanism leading to the formation of these disinfection byproducts (DBPs)is the application of chlorine in aqueduct water to suppress biofilm. Biofilm control iscritical to mitigate headloss and biocorrosion in the aqueduct. A potential method ofcontrolling biofouling while minimizing THM and HAA formation would be to replacefree chlorine with ultraviolet (UV) light as primary disinfection. There is potential that UV treatmentwould reduce chemical dose, thereby decreasing THM and HAA formation.The focus of this project was to determine the effectiveness of UV treatment on its ownand in combination with free chlorine (Cl2) and chlorine dioxide (ClO2) in suppressingbiofilm growth in aqueduct water. The study also assessed DBP concentrations andassessed the potential for UV to reduce chemical disinfectants. The technical approach involved eight annular reactors (ARs) set up at the Pardee Reservoir to simulate the aqueduct. Two trains of water, one treated with UV light and one un-treated, enteredseparate clearwells and were dosed with a sodium tetraborate solution to adjust pH to alevel similar to the full-scale aqueduct. The adjusted water was then pumped into eachAR, which represented the first section of the aqueduct where residual disinfectant is stillmeasurable. One of the ARs was used as a control for the UV train and one AR was acontrol for raw water. Two ARs were dosed with ClOsub2/sub, one that was pre-treated with UVand one that was not. The final four ARs were dosed with Clsub2/sub, two having been pretreatedwith UV and two without. The ARs were set at a rotational speed that created the same shear stress at the outer wallof the AR's cylinders as that which would be seen at the outer wall within the aqueduct. Chlorine dioxide was generated according to Method 4500-ClOsub2/sub of Standard Methods forthe Examination of Water and Wastewater, 19th Edition. Free chlorine was measured using the DBP colorimetric method. Heterotrophic plate counts (HPC) were performed using a spread plate technique on R2Aagar (BD, Franklin Lakes, NJ). Includes 5 references, table, figures.

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Edition: Vol. - No. Published: 06/17/2005 Number of Pages: 7