ABSTRACT This study compared a standard Direct Filtration process (DF STD ) with a similar process that incorporated dissolved air flotation into a flocculation basin (DF DAF ) to mitigate the effect of particle loading events on filter run time and water quality. Pilot tests evaluated coagulant (0–20 mg/L as FeCl 3 ) and cationic polymer (0–1 mg/L) dosing under varied influent turbidity conditions (0.5–20 NTU) at a fixed DAF recycle ratio (9.5%–10%) and hydraulic loading rate 2.2–2.4 gpm/ft 2 (5.4–5.8 m/h). With an influent turbidity of 20 NTU, DF DAF consistently extended filter run times (48–55 h) compared to DF STD (< 18 h), while meeting filter effluent water quality goals. Polymer addition during DF DAF resulted in a thicker sludge blanket, enhanced solids removal (NTU, Fe, and TSS), organics removal meeting enhanced coagulation requirements (TOC and UV 254 ), and floc/particle accumulation in the upper filter layers rather than throughout the media. Continued development could prove the DF DAF process as feasible for full‐scale implementation.
Abada et al. (Sun,) studied this question.
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