AWWA ACE61853

This paper discusses an expansion of the Chandler Surface Water Treatment Plant (CWTP) that included the following: added 15 mgd of firm production capacity; maintained filter effluent turbidity of < 0.15 NTU (95% of the time) in each filter; improved removal of disinfection byproduct precursors, i.e. total organic carbon (TOC); and, increased reliability of taste and odor compound removal (geosmin and methyl isoborneol). Bench and pilot testing were used to evaluate the alternative technologies that would best help the plant meet its treatment goals. The objectives of the bench-scale investigation were to determine the water quality impacts from coagulation with different coagulants and the impacts of pH adjustment on TOC removal. The following primary coagulants were evaluated with the addition of coagulant-aid polymer: aluminum sulfate (currently in use by the plant); ferric sulfate; and, poly-aluminum chloride. Aluminum sulfate (alum) achieved slightly higher TOC removal than ferric sulfate (ferric), whereas ferric achieved slightly better settled water turbidity. Poly-aluminum chloride performed well for turbidity removal but not for TOC removal. The results of the jar testing did not suggest that a change in primary coagulant would result in improved performance, so pilot testing proceeded using alum. The objectives for the pilot plant investigation were as follows: determine water quality impacts of biofiltration using differing media configurations; determine water quality impacts of ozonation and biofiltration; and, compare filtered water quality impacts between conventional sedimentation and ballasted flocculation. The study was performed in three phases, which were as follows: Phase I - filtration study using CWTP settled water; Phase II - filtration study using CWTP settled water with ozone; Phase III - filtration study using ballasted flocculation with and without ozone.