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Method of application in Drinking Water Treatment Plants
The filter media treatment process was conducted in one of the rapid filters at the CWFP. An electrical metering pump (PULSAtron Series MP) proportionally controlled by the CWFP flow-paced computer system was employed to inject PACl. The PACl injection port was in the settled water pipe before the water reached the test filter. The filter media treatment process included two stages: (1) A high concentration of liquid PACl was applied to settled water during the filter-to-waste stage of operation for 13 min. (2) After filter-to-waste when the filter was placed in operation, a lower concentration of PACl was continuously injected during filter run. PACl addition was terminated when the test filter head loss reached 115 cm (45 inch) according to the standard operating procedure for the facility, but the filter was not backwashed until the filtered water volume reached 1.5 million gallons, filter online time reached 90 hours, or filter water quality deteriorated. Different concentrations of PACl were applied at both stages to evaluate the effect of PACl on filter ripening and long term performance. Table 2 provides details of PACl concentrations used in each trial. The PACl concentrations reported at each stage were dependent on the plant flow rate during filter-to-waste (0.9 mm/s or 240 gpm) and the average flow rate during filtration.
A control filter in the CWFP was operated simultaneously with the test filter to compare the filter performance, head loss accumulation, and aluminum concentration in the filtered water.
Table 2. Summary of full-scale experiments
Trial PACl used during FTW *† (mg Al/L) PACl used in Filtration (mg Al/L) PACl metering time (hr) Total Al mass used (g/m2) Incremental head loss ** (cm) Average filtration rate (mm/s)
1 0 0 0 0 -10 1.28
2 4 0.43 32.5 59.6 80 1.11
3 4.2 0.19 65.9 52.2 65 1.13
4 0.23 0.19 60 44.9 71 1.09
5 0.14 0.12 70 34.9 63 1.15
6 0.06 0.056 77 19.2 30 1.23
- FTW: Filter to waste
† The test PACl was 5.5% Al by mass and the PACl density was 1260 kg/m3
**Incremental head loss = final head loss in test filter – final head loss in control filter
Facilities Currently Using the Technology
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