EVALUATION OF 4 DIFFERENT TERTIARY FILTRATION PLANTS FOR TURBIDITY CONTROL

The County Sanitation Districts of Los Angeles County operate 10 water reclamation plants (WRPs) for wastewater reclamation and reuse. To comply with State of California's stringent wastewater reclamation criteria, tertiary filtration systems are required at seven of these WRPs. Four types of filters, including mono-medium gravity (activated carbon or anthracite coal), dual-media gravity, and dual-media pressure filters, are used. A study has been conducted to evaluate and to compare the filters' performance. The study started with evaluating turbidity and suspended solids (SS) removal by using plant operational data. Ratios of SS to turbidity were determined and found comparable among the plants. Although all filters provide good turbidity control, removal efficiencies are different among the filtration systems. Some plausible explanations for the apparent differences in removal are provided. Particle size distribution (PSD) measurements were made on samples from various locations at the WRPs to provide insights into particle removal. Typical particle size and volume distributions in the wastewater streams were established. Although turbidity and PSD could not be well correlated, particle removals by the four filtration systems were determined for better understanding of their removal mechanisms.