Population Balance Model (PBM) for flocculation process: Simulation and experimental studies of palm oil mill effluent (POME) pretreatment

The present study is intended for the first time to completely replace the inorganic coagulants with organic polymers in palm oil mill effluent (POME) pretreatment by using direct flocculation of single and dual polymer systems under applied shear. The efficiency of direct flocculation of POME was investigated by using the Population Balance Model (PBM) which considered the charge neutralization and bridging attraction under applied shear. The collision efficiency was calculated based on the Derjaguin Landau Verwey Overbeek (DLVO) theory which considered the effect of adsorbed polymer layers on van der Waals attraction and bridging attraction. This is the first attempt to correlate the floc size distribution from PBM to the indirect indicators of COD, suspended solids, oil and grease. The model predictions are in close agreement with the experimental results for both single and dual polymer systems. The interaction energy curves based on PBM shows that the flocculation using cationic polymer is by charge neutralization and bridging attraction whereas flocculation using anionic polymer is by only bridging attraction. At the optimum flocculation conditions, 99.66%, 55.79%, 99.74% and 80.78% of suspended solids, COD, oil and grease removal and water recovery are achieved, respectively. The direct flocculation process significantly reduced the treatment cost by a factor of 3.6 compared to the conventional coagulation–flocculation process.