On-line monitoring of floc formation in various flocculants for piggery wastewater treatment

Abstract

In this study photometric dispersion analyzer (PDA) was used to monitor floc size variation during the flocculation process for piggery wastewater treatment. Three types of flocculants, alum, Fe2(SO4)3 and FeCl3, were used to investigate the effects of flocculant type and dosage, mixing intensity and temperature on floc formation. From the analysis of the floc size index (FSI) at the optimum dosage, FeCl3 was proved to produce the larger floc formation and better settling efficiency than Fe2(SO4)3 or alum. It took 7.5 min in FeCl3, 18.5 min in Fe2(SO4)3 and 22.0 min in alum for complete floc settlement. FeCl3 produced the most easily settled flocs. As the mixing intensity increased from 200 to 400 rpm, FSI value reduction rate was 50% in alum, 21% in Fe2(SO4)3 and 10% in FeCl3. As well, floc formation produced by FeCl3 had lower degree of disaggregation at high mixing intensity. Alum and Fe2(SO4)3 were less effective in floc settling at low temperature while FeCl3 showed no significant effect related to temperature. It could be concluded that FeCl3 flocs did not affect from high shear force and low temperature due to the unaltered characteristics of turbulent flocculation, fluid dynamics and solubility of FeCl3. It made FeCl3 a better flocculant compared to alum and Fe2(SO4)3. In terms of particle removal, turbidity and TP removals increased with the decrease of mixing intensity and with the increase of temperature. Mixing intensity and temperature have shown no significant effect on the removals of COD and NH3-N in piggery wastewater.