Role of organic fouling layers on the transport of micropollutants in forward osmosis membrane processes

In this study, the impact of organic fouling layers on the transport of micropollutants (MPs) during the operation of the forward osmosis (FO) process was investigated. The rejection of MPs after the formation of organic fouling layers with three model foulants (bovine serum albumin (BSA), sodium alginate (SA), and humic acids (HA)) showed that the electrostatic and hydrophobic interactions governed the transport of MPs. The negatively charged functional groups in the organic fouling layers increased the rejection of negatively charged MPs, while the rejection of positively charged and neutral MPs with high Kow was significantly decreased in the presence of an organic fouling layer. The adsorption analysis showed that the positively charged and hydrophobic MPs were preferably adsorbed into the organic fouling layers, and the elevated concentration of MPs in the organic foulant layer accelerated the diffusional transport of adsorbed MPs across the FO membranes. The SA showed higher adsorption capacities of MPs than HA or BSA, and thus a dramatic decrease in the rejection of MPs was observed. Our findings indicate that the rejection efficiencies of MPs might be overestimated when experiments are conducted without organic fouling layers. The rejection of MPs thus should be carried out in the presence of foulants in the FO process.

Automated summary

This study investigated the impact of organic fouling layers on the transport of micropollutants (MPs) during forward osmosis (FO) process. The results showed that the transport of MPs was governed by electrostatic and hydrophobic interactions. The presence of negatively charged functional groups in the organic fouling layers increased the rejection of negatively charged MPs, while the rejection of positively charged and neutral MPs with high Kow was significantly decreased. Adsorption analysis revealed that positively charged and hydrophobic MPs were preferentially adsorbed into the organic fouling layers, and the concentration of MPs in the fouling layer accelerated their diffusion across the FO membranes.