Water Supply (Aug 2022)
Comparative evaluation of pilot-scale reactors based on pulsating floc blanket clarification and conventional clariflocculation technologies in simultaneous treatment of natural organic matter and turbidity
Abstract
Simultaneous treatment of synthetic raw water containing natural organic matter (6 mg L−1) and clayey turbidity (0–20 NTU) was carried out with PACl on continuous upflow type pilot-scale models of pulsating floc blanket clarifier (PFBC) and conventional clariflocculator (CC) each designed for a capacity to treat about 8,000 liters per day, to understand mechanistic differences in their functioning. Fluidized bed of pre-flocculated particles prompted contact flocculation and enmeshment which lowered the residual turbidity for PFBC (0.07 ± 0.09 NTU) compared to CC (2.48 ± 1.71 NTU). Fine particles suspended in water clarified from PFBC and CC were hetero-disperse with Zavg as 2,341 nm and 5,693 nm respectively. On average, total residual aluminum was found to be 147 ± 33 ppb and 141 ± 51 ppb, while dissolved residual aluminum was found to be 31 ppb and 59 ppb for PFBC and CC respectively. Average total organic carbon reduction by PFBC and CC was 70.4% and 67.7% respectively. Size, structure and fractal dimensions of flocs were studied and average settling velocity of PFBC flocs was calculated to be 37% higher than CC flocs. Distinctness in characteristics of sludge formed in the two reactors has been highlighted by means of SEM micrographs and FT-IR spectra. HIGHLIGHTS PFBC gives better colloidal destabilization and turbidity removal than CC; Total residual aluminum comparable but dissolved fraction higher for CC than PFBC; Significant aluminum demand raised from NOM satisfied foremost by PACl; Average settling velocity of PFBC flocs found to be 37% higher than CC flocs; Zone of pre-flocculated particles in PFBC abets nucleation and contact flocculation;
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