AWWA ACE58136

The Santa Clara Valley Water District (SCVWD) receives approximately 150,000 acre-feetof water per year from the Central Valley Project through the San Felipe DivisionUnit of the San Luis Reservoir. When water levels in the San Luis Reservoir fall below300,000 acre-feet, algae-rich waters in the upper 20 to 30 feet of the reservoir can bedrawn into the intakes. In the future, the San Luis Reservoir may be drawn down belowthe "low point" as much as 50 percent of the time due to proposed CALFED changes inwater management. These conditions can cause taste, odor and filter clogging problemsfor SCVWD as well as line and emitter clogging problems for San Felipe agriculturalcustomers using drip irrigation systems.In order to better quantify the treatment and supply problems associated with reservoirdrawdown to "low point" conditions, SCVWD conducted a pilot study of the impacts ofhigh algae feedwater on flocculation, sedimentation, ozonation, and filtrationprocesses. The pilot study included collection of algae from the reservoir surface waterduring the peak algae growth season. This collection allowed for testing of feedwaterswith high algae concentrations (on order of 5,000 to 10,000 cells per mL and up to 1,000fluorescence Rhod-equivalents). Blue-green algae (i.e. Aphanizomenon, Microcystis,Anabaena) are the dominant species in the San Luis Reservoir.Two pilot treatment trains were run side-by-side to compare water treatmentperformances for: algae-laden surface water collected from the top 3 ft., containing algae concentrationsthat may be anticipated under "low point" conditions; and,intake water withdrawn from the reservoir bottom, representing current withdrawalpractices from San Luis reservoir.Side-by-side pilot testing of these two waters allowed evaluation of treatmentperformances including: filter clogging, filter run length, headloss development, unitfilter run volume (UFRV), filtered water turbidity, filtered water particle counts, waterproduction capabilities, taste and odor control, and impact on intermediate ozonation.Pilot-scale evaluation compared filtration performance for the two water sources and twodifferent filter media designs: anthracite and sand dual-media design; and, granularactivated carbon.This paper focuses on the pilot study results that demonstrate and correlate the impact ofvarious algae count feedwaters with shorter filter runs. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/15/2003

Number of Pages:

15

File Size:

1 file , 800 KB