The 40-mgd Nick C. DeGroot Water Treatment Plant, operated by South San JoaquinIrrigation District (SSJID) of Manteca, is the largest existing membrane drinking watertreatment plant in California to date. The SSJID treatment plant, dedicated on July 14,2005, employs the processes of coagulation, flocculation, high-rate dissolved air flotation(AquaDAF™), stabilization with lime and carbon dioxide, submerged ultrafiltration(ZeeWeed® 1000 membrane), and disinfection with sodium hypochlorite. This is thefirst low-pressure membrane plant using the high-rate AquaDAF™ process aspretreatment. The AquaDAF™ process can operate at surface overflow rate as high as 18gpm/ft<sup>2</sup>, which is super-high when compared to conventional clarification.A 4-month pilot testing program was conducted prior to the design of the treatment plantto verify design assumptions of the pretreatment (coagulation, AquaDAF™, andstabilization) and membrane filtration systems, and to seek regulatory approval forpermitting. The full scale plant has been operating satisfactorily for more than a year.This paper compares the performances of the pilot- and full-scale plants. Water quality,chemical coagulant (ferric chloride) dosages, surface overflow rates, turbidity and total organic carbon (TOC)removal of the AquaDAF™ and ZeeWeed® 1000 systems, fluxes, backwash frequencies,recovery rates, etc., will be reviewed and compared. Operating problems encounteredand suggestions for design improvements are discussed. Includes tables, figures.
