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Continuous upflow pilot plants based on conventional clariflocculation (CC) and pulsating floc blanket clarification (PFBC) technologies were designed and fabricated for a capacity to treat about 8,000 L/day, to understand the fundamental differences in their functioning and assess their relative performance, especially under low turbidity conditions. Influent turbidity varying from 2 to 10 NTU was treated using coagulant alum, and efficiency of CC and PFBC in terms of average turbidity removal was found to be 23% and 48%, respectively. On observing this vast difference, it was postulated that total residual aluminum should also be lower in water treated from PFBC. Experiments and MLR analysis confirmed the hypothesis, with residual aluminum ranging from 0.055 to 0.040 mg/L and 0.036 mg/L to below detectable levels for CC and PFBC, respectively. These findings are of high significance, since minimization of residual aluminum in drinking water is a priority of WHO due to its reported neurotoxicity and can be complied with simple replacement of CC with PFBC. Practitioner points Pulsating floc blanket clarifier (PFBC) performed better than conventional clariflocculator (CC) in terms of turbidity removal. Pulsating floc blanket allowed more effective utilization of coagulant alum, resulting in significantly lower residual aluminum in clarified water. Turbidity levels of influent and effluent are related to residual aluminum in treated water. PFBCs are more compact and modular, and can facilitate a good alternative to CCs.

A pulsating floc blanket clarifier (PFBC) employing cyclic contractions and rarefactions to a bed of densely concentrated suspension of flocculated particles in fluidized state, was compared with conventional clariflocculator (CC) at pilot scale (8,000 L/day) in continuous mode of operation. For influent turbidity varied from 2 to 20 NTU, coagulation-flocculation behavior exhibited under the two fundamentally different treatment processes with PACl influenced inter-related performance parameters. The residual turbidity was found lower by 74%, flocs and fine colloids in suspension larger by 73 and 75% respectively, and the total and dissolved residual aluminum lower by 50 and 49% respectively on average for PFBC compared to CC. Particulate form comprised major fraction (≈72%) of total residual aluminum for both. PFBC abetted formation of a more consolidated floc structure which rendered the shape, size and morphology such that the settling velocity was 50% to 410% higher than that of the CC flocs. Reaction-limited aggregation (RLA) process and inter-particle bridging were dominant and the resulting floc structure and its formation mechanism have been presented.

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.

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