"Modification of RO membrane by natural antifouling nano-material for water desalination"

Abstract

Biofouling is still a major problem hindering wider application of composite cellulose acetate (CA) reverse osmosis in water desalination process. Nanocomposite membranes having silver nanoparticle have been used widespread to control biofouling. Silver nanoparticles (AgNPs) can prevent the capability of bacteria permanently adhesion to the membrane surface. This study proposes an innovative biofouling control approach by surface modification of the cellulose acetate RO membrane with bio-AgNPs. Initially green synthesis of AgNPs was accomplished utilizing different extracts of four types of marine algae by different solvents through the reduction of silver nitrate and to evaluate the antibacterial and antioxidant potential. Aqueous extract of Ulva fasciata was selected among all algae species screened for the green synthesis of AgNPs. The characterization of synthesized AgNPs/UE was made through UV-visible spectrophotometry, FTIR spectroscopy, X-ray diffraction, scanning electron microscope equipped with energy dispersive X-ray spectroscopy and high-resolution transmission electron microscopy. Cellulose acetate composite membrane using green synthesized biogenic silver nanoparticles AgNPs with Ulva fasciata extract were prepared and tested for antibacterial activity. Phase inversion technique was used to prepare pure CA membranes and different parameters that affect the membrane performance such as evaporation time, annealing temperature, thickness of membrane, concentration feed

and applied pressure were studied. Different amounts of biogenic silver nanoparticles bio-AgNPs were embedded in cellulose acetate membrane. The effects of the bio-AgNPs content on the structure of the membrane and its filtration performance were systematically investigated. The results demonstrated that silver containing nanostructures were uniformly distributed on membrane surface. The prepared pure CA and modified membranes were characterized by Fourier transform infrared spectroscopy, contact angle, dynamic mechanical analysis, thermo-gravimetric analysis, elemental analysis and scanning electron microscopy techniques. The results of RO performance indicated that by addition of biogenic silver nanoparticles, the water flux largely increased with much slower enhanced effect on the salt rejection of the membranes. The water flux for modified CA membrane increased from 3.00 L/m2.h to about 7.00 L/m2.h by addition of 2.5 mg from biogenic silver nanoparticles and with increasing the salt rejection from 96.56 % to 97.2 % of 2000 ppm NaCl model solution at the same condition (10 bar, pressure). According to the CA/bio-AgNPs performance and microbial growth morphology, bio-AgNPs showed better resistance for bacterial adhesion in seawater desalination. Modified CA1/bio-AgNPs membranes were applied to test the desalination of real source of seawater such as, Mediterranean Sea water.