Improving resistance to fouling of aromatic polyamide thin-film composite reverse osmosis membrane by surface grafting of N,N'-Dimethyl Aminoethyl Methacrylate (DMAEMA)

Abstract

The treatment of wastewater is an essential option to solve the water deficiency issue and can help inhibit the harmful effects of algal blooms and eutrophication in the urban water system. Municipal wastewater presents a high potential for water reuse as it is available in large quantity. Treatment with membrane technology presents advantages over other treatment methods due to the low treatment cost, unit operations reduction, and constant operation. The membrane bioreactor (MBR) process is practically used as the appropriate technique to treat municipal wastewater; nevertheless, it requires an advanced treatment of the effluent such as reverse osmosis (RO), as some of the contaminants are not removed. However, treatment of wastewater using RO results in membrane fouling which causes degradation and poor performance. This study aimed to minimise fouling of an aromatic polyamide thin film composite (TFC) RO membrane through the graft polymerisation of N,N'- dimethyl aminoethyl methacrylate (DMAEMA) by redox initiation with sodium metabisulfite and potassium persulfate. Biofouling tests using a bench-scale RO system with a secondary membrane bioreactor (MBR) effluent were used to assess the impact of surface modification. Significant changes in chemical and morphological structures were observed through attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis and scanning electron microscopy (SEM). The salt rejection decreased as DMAEMA concentration increased. Furthermore, the flux recovery ratio increased from 68.61 to 83.57% and the flux decline ratio decreased from 38.21 to 25.54%. The modified membrane’s sterilisation ratios were far higher than the unmodified membrane, thus showing better anti-biofouling properties when using Escherichia coli (E. coli) bacteria as model biofoulant. The DMAEMA modified membrane with the highest sterilisation ratio (76.8%) showed better anti-microbial properties against microorganism tested, obstruct growth and multiplication. This was further confirmed with the pure water flux test, where the unmodified and DMAEMA modified membranes declined by 46.0 and 37.3%, respectively