The role of a combined coagulation and disk filtration process as a pre-treatment to microfiltration and reverse osmosis membranes in a municipal wastewater pilot plant

Abstract

A pilot study was conducted to assess the performance of a municipal wastewater reclamation plant consisting of a combined coagulation–disk filtration (CC–DF) process, microfiltration (MF) and reverse osmosis (RO) membranes, in terms of the removal of water contaminants and changes in characteristics of effluent organic matter (EfOM). The CC–DF and MF membranes were not effective for the removal of dissolved water contaminants. However, they could partially reduce the turbidity associated with the cake layer formation by particulate materials on the membrane surfaces. Furthermore, most of water contaminants were completely removed by the RO membranes. Although the CC–DF process could remove approximately 20% of turbidity, the aluminium concentrations considerably increased after the CC–DF process due to the residual coagulants complexed with both carboxylic acid and alcohol functional groups of EfOM. Those aluminium–EfOM complexes had a lower negative charge and higher molecular weight (>0.1μm pore size of the MF membranes) compared to non-complexed EfOM. These results indicate that the control of the formation of the aluminium–EfOM complexes should be considered as a key step to use the CC–DF process as a pre-treatment of the MF and RO membranes for mitigation of membrane fouling in the tested pilot plant.