Effect of Flocculation in Membrane‐Flocculation Hybrid System in Water Reuse

Abstract

Preflocculation reduces the fouling of membranes in cross‐flow microfiltration (CFM) thus leading to high quality product water at economic filtration flux. As such, this hybrid system will have a major impact in treating the biologically treated sewage effluent. The preflocculation achieved through the floating medium flocculation (FMF) was found to increase the phosphorus removal up to 96%. The decline in microfiltration permeate flux with time was reduced by the incorporation of flocculation. However, the improvement in the removal of dissolved organic carbon (DOC) was marginal (from 20% with membrane alone to 46% with the membrane‐flocculation hybrid system). The flocculation followed by adsorption as pretreatment helped to increase the DOC removal as high as 98%. Flocculation was found to remove more than 66% of colloidal effluent organic matter (EfOM). An attempt was also made to quantify the hydrophobic fraction in the pretreated effluent and to identify the molecular weight (MW) range of organics removed by the flocculation. The pretreatment of flocculation was found to remove 68.5%, 61.8%, and 62.9% of hydrophobic, hydrophilic, and transphilic organic matter. The MW size distribution analysis indicated that flocculation with ferric chloride removed a majority of organic matter in the MW range of 300–5000 Da.

Keywords:

• Cross‐flow microfiltration
• Flocculation
• Floating medium flocculation
• Hydrophobicity
• Molecular weight size distribution
• Biologically treated sewage effluent
• Effluent organic matter

Acknowledgments

This research was funded by an Australian Research Council (ARC) discovery grant. The support of Brain Pool Korea for the visit of S. Vigneswaran during the period of March–June 2003 is greatly appreciated.