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Filter Loading Evaluation for Water Reuse

Project: 02-03
Type: Report
Year Released: 2011

Program: Principal
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board
Total Investment: $952,000 (Cash: $400,000, In-Kind: $552,000)

Principal Investigators: Kara L. Nelson, Ph.D., University of California, Berkeley, Gordon Williams, Ph.D., University of California, Berkeley, Bahman Sheikh, Ph.D., P.E., Water Reuse Consultant, Bob Holden, P.E., Monterey Regional Water Pollution Control Agency, James Crook, Ph.D., P.E, Monterey Regional Water Pollution Control Agency, and Robert C. Cooper, Ph.D., BioVir Laboratories

Background

The California Water Recycling Criteria allows a maximum filter loading rate of 5 gpm/ft2. Higher loading rates would allow more water to be recycled with minimal cost implications. The impact of filter loading rate on filter performance and effluent quality was evaluated at a pilot-scale facility at the Monterey Regional Water Pollution Control Agency (MRWPCA) water recycling facility in Marina, California, and subsequently at two full-scale facilities in California. While the study evaluated filter loading rates ranging from 5 to 10 gpm/ft2, a loading rate of 7.5 gpm/ft2 was selected for detailed comparison to the regulatory limit of 5 gpm/ft2.

Goals and Objectives

The project, called the Filter Loading Evaluation for Water Reuse (FLEWR), addresses scientific, engineering, and regulatory gaps related to the impact of filter loading rate on granular media, rapid depth filtration of wastewater.

Research Approach

The FLEWR project was divided into two phases of activities. The goals of Phase I were to

  • Investigate the impact of filter loading rate (5, 6.25, 7.5, 8.75, 10 gal/ft2-min; 12.2, 15.3, 18.3, 21.4, 24.4 m/h) on filter performance and effluent quality at the pilot scale.
  • Characterize filter performance and effluent quality sufficiently to seek approval from regulatory agencies to operate full-scale tertiary filters higher than 5 gal/ft2-min during Phase II (as determined by the California Department of Public Health Equivalency criteria).

The goals of Phase II were to

  • Investigate the impact of filter loading rate (5 and 7.5 gal/ft2×min; 12.2 and 18.3 m/h) at five full-scale treatment plants.
  • Conduct additional laboratory and pilot-scale experiments on virus removal mechanisms during filtration.

Because of the regulatory implications of the project, the California Department of Public Health (CDPH) was consulted on a regular basis and was directly involved in establishing equivalency criteria for filter effluent quality.

Findings and Conclusions

  • When the coagulant dose was the same for all loading rates (at 5, 6.25, 7.5, 8.25, and 10 gpm/ft2), the removal efficiency of the filters decreased for all metrics (turbidity, particle counts in the 2-15 µm size range, total coliforms, E. coli, and MS2 coliphage) as the loading rate increased.
  • Detailed comparison of 5 gpm/ft2 and 7.5 gpm/ft2 filter loading rates, where the coagulant dose was optimized for each loading rate to produce an effluent turbidity of 1.9 NTU, determined there was no statistical difference in filter effluent quality between the loading rates with respect to turbidity, particle counts, and removal of indicator bacteria.
  • Viruses removed by filtration were primarily associated with particles in the 0.4 to 12 µm range.
  • Full-scale tests at two facilities (MRWPCA and Santa Rose, California) found that equivalent effluent quality was produced at the filter loading rates of 5 gpm/ft2 and 7.5 gpm/ft2, as determined by criteria defined by the California Department of Public Health (CDPH). To achieve equivalent performance at the MRWPCA facility, the average coagulant dose was about 50 percent higher when operating at 7.5 gpm/ft2 than when operating at 5gpm/ft2.
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