Each comprises coagulation / flocculation / sedimentation / filtration.

Key to each is proper coagulation to prepare the water for filtration.

Coagulation treatment goal for each is removal of turbidity, particles, and DPB precursors (TOC).

Effectiveness depends on coagulant dose, polymer dose, alkalinity, pH, and TOC concentration.

Actiflo and Conventional Treatment:Similarities….

Actiflo uses microsand as a “ballasting” agent in the flocculation (i.e. maturation) process step.

The use of microsand results in a more robust floc which is significantly denser and has a higher settling velocity. This reduces the treatment time significantly compared to conventional treatment.

Actiflo systems have a much smaller footprint than conventional clarification systems of similar capacity.

Actiflo and Conventional Treatment:. . . and Differences

Settled water turbidity

Filtered water turbidity

Filter run time

TOC removal

Criteria for Coagulation Effectiveness

Alum dose

Polymer type and dose

Sand size

Sand concentration

Filter aids

Factors that Affect Actiflo Performance

City of ChandlerWater Treatment Plant (WTP) History

Plant original start up was in 1989 at 30 MGD. 3 conventional trains at 10 MG each.

Expansion in 1997 bringing production up to 45 MGD. 3 conventional trains at 15 MG each.

Expansion in 2008 completed, bringing production up to 60 MGD. 3 conventional trains at 10 MG each, and 2 Actiflo trains at 15 MG each.

In April 2008, the City received approval for normal operation of the Actiflo system from Maricopa County.

Raw water turbidities during startup ranged from 14 to 35 NTU.

Alum was used for coagulation through startup, typically at doses between 25 and 30 mg/L.

Startup was with a anionic polymer with a -10% charge.

Actiflo was started with a 65-grade sand.

Actiflo Start Up

The settled water NTU’s from the Actiflo system were high, causing shorter filter run hours. Moved 2/3 of our flow back to conventional treatment.

Made changes in dosages to the alum, polymer and amount of sand addition.

With assistance from Black & Vetch and Kruger, Plant staff began looking into the problems surrounding the Actiflo system.

Trouble in Paradise

Bench-scale and full-scale plant tests were conducted to evaluate the following:

Alum dose

Polymer type and dose (19 different polymers at charges from +35% to -47% were tested)

Sand size

Filter aids

Actiflo Study

The optimal alum dose depends on Actiflo influent turbidity.

Jar testing produced a graph that Operations could use to estimate the alum dose needed for various influent turbidity conditions.

Alum Dose

Polymer Testing

The greatest challenge in optimizing Actiflo is finding the range of polymer dose that effectively reduces turbidity without significantly shortening filter run times.

Balancing these goals proved to be the most significant challenge for the Pecos Water Treatment Plant.

Compare anionic and cationic polymers.

Anionic polymers worked better than cationic polymer for this water. Operations will continue to use the anionic polymer that Actiflo was originally started up on.

Polymer Testing

During the summer of 2008, a complete investigation was done on all components of the Actiflo by Chris Kincaid with the City of Chandler, and Tim White with Black & Vetch. The following is a list of items that were looked at:

Injection and Maturation basins, including mixers and collectors Sand piping Hydrocyclone

The findings were that everything appears to be in good shape and functioning, as suggested by Kruger. At this point we were at a loss as to what else to investigate.

Structural Integrity of the Actiflo

Actiflo jar tests were conducted to evaluate the effect of sand size on turbidity and filtration times. Four sand sizes were tested: grades 65, 70, 80 and 110.

At a polymer dose of 0.1 mg/L, turbidity was 0.6 NTU for 110-grade and compared with 1.5 for 65-grade sand. We were able to cut our polymer dose by more than half by switching from grade-65 sand to grade-110 sand.

Actiflo Sand

After being tested, we removed all of the Grade 65 sand and replaced it with the Grade 110 sand, and moved the majority of our flow over to the Actiflo system.

BOOM . . . all of the filters immediately began to go south with filter runs of only 8 hours. We shut the Plant down and on the recommendation of Kruger, began feeding alum as a filter aid at a dose of 2.5 mg/L. This brought the NTU’s down and the filter runs up.

NIRVANA!!!???

Switching to a smaller sand size had the greatest impact on Actiflo performance of any of the parameters evaluated.

The optimum alum dose for Actiflo depended on feed water turbidity.

Anionic polymers provided better treatment and caused less filter head loss than cationic polymers. Polymers with -10 and -15% charge performed well.

Actiflo treatment performances, as measured by settled water turbidity, improved as Actiflo sand concentration increased.

Conclusions

Victoria Sharp

Water Systems Operations Superintendent

City of Chandler / Water Treatment

PO Box 4008 MS 912

Chandler, AZ 85244-4008

480-782-3628

Contact Information