EVALUATION OF TERTIARY FILTRATION AND DISINFECTION SYSTEMS FOR UPGRADING HIGH-PURITY OXYGEN-ACTIVATED SLUDGE PLANT EFFLUENT

The Joint Water Pollution Control Plant (JWPCP) of the Sanitation Dist ricts of Los Angeles County provides advanced primary and partial seco ndary treatment for 15.3 m(3)/s (350 MGD) of wastewater. A 7-mo pilot plant study evaluated several tertiary treatment alternatives for in-p lant water reuse. The influent to the tertiary treatment system was th e high-purity oxygen-activated sludge plant effluent. Three filtration systems were evaluated: a deep-bed anthracite filter, a shallow-depth pulsed-bed sand filter, and a continuous backwash deep-bed sand filte r. Chlorination and ultraviolet (UV) disinfection were also compared. All three filters were capable of consistently meeting the State of Ca lifornia's effluent turbidity limit. The differences in turbidity remo val efficiencies were insignificant. Changes in hydraulic loading rate , up to 0.2 m(3)/m(2) . min (5 gpm/ft(2)), had insignificant effects o n the quality of all filter effluents when filtering normal secondary effluent. The effect of chemical filter-aids on turbidity removal depe nded strongly on the characteristics of the filter influent and the fi lter design configuration. Breakthrough of alum might occur with an ex cessive dosage of alum. The estimated costs for filtering the secondar y effluent by the three filters were similar. A high-UV dose of 300 mW -s/cm(2) would be required to reduce the total coliform concentrations less than or equal to 2.2 MPN/100 mL, mainly because of the low UV tr ansmittance (40-63%). The 2.2 MPN/100 mL coliform standard could be me t either by a chlorine residual of 5 mg/L with a contact time of 120 m in or 10 mg/L for 60 min.