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Technical Papers
OPERATIONS & MAINTENANCE
Figure 1. Plant production rate (L/s) with raw water true colour (HU) and chemical dosages.
Figure 2. Dual media filters run time, hr (Source: SCADA).
NON-IONIC POLYMER DOSE OPTIMISATION At Nepean WFP immediately after coagulation, non-ionic polymer is dosed in the pipeline upstream of the roughing filters. Trials were conducted to optimise non-ionic polymer dosing to improve the floc strength. This was carried out from September 2013 while having raw water higher true colour. Eventually, non-ionic polymer dose rate was optimised to an average of 0.32 mg/L (maximum 0.35 mg/L) in September–October 2013 for the raw water true colour 25–30 HU, and 0.19 mg/L in March–May 2014 for the raw water, also with true colour 25–30 HU. Optimisation of non-ionic polymer dose rate depended on the variability of
WATER DECEMBER 2014
the nature of raw water (variation of floc strength) in the same colour range and optimum dose rate of two coagulants (floc size optimisation). The result of nonionic polymer dose increase was positive; better floc strength was achieved, which improved performances of both the roughing filter (higher solids adsorption) and dual media gravity filter (run time, head-loss before backwash and UFRV).
ROUGHING FILTERS BACKWASH TIME OPTIMISATION After non-ionic polymer dose optimisation backwash water from the roughing filters contained higher solids, which proved higher solids holding in the roughing filters during operation
with increased floc strength. To improve roughing filter media regeneration, air– water wash time was increased from 360 sec to 420 sec in mid-October 2013 and then to 540 sec in January 2014. Water wash time was also increased from 15 min to 20 min in January 2014. The combined effect of increased non-ionic polymer dose and increased air-water and water wash time improved the roughing filters’ solids adsorption performance, improved the water clarity of roughing filter discharge, reduced solid loading to dual media gravity filters (DMF), and further improved the performance of the DMF.