Effects of sodium bicarbonate and co-amine monomers on properties and performance of thin film composite membrane for water and wastewater treatment

Abstract

Polyamide (PA) thin film composite (TFC) nanofiltration (NF) membranes are widely used for the treatment of water and wastewater treatment. However, they still experience lower permeability and rapid flux decline within short period of time particularly in the case where the feed solutions contain high levels of organic pollutants. To solve this problem, a co-amine monomer in the presence of an inorganic additive can be introduced during interfacial polymerization process to alter the PA layer properties of membrane, aiming to improve its water flux and antifouling properties without affecting salt rejection. The main objective of this work is to determine the effects of sodium bicarbonate (NaHCO3) additive loading (0.5, 1.5 and 0.25 wt.%) and piperazine (PIP)/2-(2'aminoethoxy) ethylamine (AEE) co-amine weight ratio (2:0, 1.75:0.25, 1.50:0.50, 1.0:1.0 and 0:2) on the properties and performance of TFC membranes for water and wastewater treatment, respectively. The chemical composition and morphology of the resultant TFC membranes were characterized by field emission scanning electron microscopy (FESEM), surface chemistry through attenuated total reflectance Fourier transform infrared analysis (ATR-FTIR) and hydrophilicity through contact angle measurement. Results showed that polymerization successfully took place forming a thin PA layer on the support membrane pore size within the range of NF. 0.5 wt% NaHCO3 was the best loading to improve membrane water permeability without really affecting Na2SO4 rejection. This modified membrane showed 37% higher water permeability than that of membrane without additive. In the presence of 0.5 wt% NaHCO3, it is found that the introduction of AEE into PIP solution at PIP:AEE ratio of 1:1 could more greatly improve the salt rejection of PIP-based membrane from 97.1% to 98.5%, producing a permeate of better quality. The improved separation rate was due to the formation of denser and rougher PA layer upon AEE incorporation. Further characterization on the selected TFC membranes for aerobically treated palm oil mill effluent (AT-POME) treatment indicated that the membrane made of PIP:AEE of 1:1 was able to achieve improved performance, recording 79.15%, 94.26% and 89.3% rejection for conductivity, colour (ADMI) and COD reduction. This work demonstrated the importance roles of additive and co-amine monomer in improving characteristics of TFC membrane for water and wastewater treatment.