(434c) Novel Copper-Charged Anti-Microbial Reverse Osmosis Membranes

Water is essential for the survival of life on Earth, but the pollutants in water can cause dangerous diseases and fatalities. The provision of clean, drinkable water to people is a key factor. Over the years, natural sources of water have been falling short while, so the need for purified water has been increasing with increasing population. Reverse osmosis (RO) is a membrane-technology filtration technique that helps in the desalination and purification of water from lower quality sources, such as brackish water, seawater and wastewater. During the filtration of such sources, materials that are rejected by the membrane may accumulate on the surface of the membrane to foul it. Such materials include organic matter, colloids and microorganisms. The former two can be controlled via pretreatment; however, the accumulation of microorganisms is more problematic to membranes. Biofouling is the accumulation and growth of microorganisms on the surface of membranes and on feed spacers. After attachment, microorganisms excrete extra cellular polymeric substances (EPS), which form a matrix around the organism’s outer surface as biofilm. These biofilms are detrimental and result in irreversible membrane fouling.

The purpose of this project is to investigate the charging of membrane surfaces with copper (Cu⁺²) to control biofouling, and develop anti-biofouling membranes. The use of anti-biofouling membranes would reduce the cost associated with chemical additions as well as chemical storage. Copper and silver ions inactivate the bacterial cells and prevent the DNA replication in microbial cells. Previous studies using copper-charged feed spacers have shown the ability of copper to control biofouling without a significant amount of copper leached from the anti-biofouling polypropylene (PP) during crossflow filtration. Also, filtration using unmodified speed facers experienced almost 70% flux decline, while filtration using copper-charged feed spacers displayed only 25% flux decline. These intriguing results led to the hypothesis that the polymer chemistry can be extrapolated to produce membranes with increased biofouling resistance. To this end, glycidyl methacrylate (GMA), an epoxy, was used to attach a chelating agent, iminodiacetic acid (IDA), to membranes to facilitate the charging of copper to the surface. Cellulose acetate and polysulfone membranes were cast using the phase-inversion method. The membranes were then charged with copper ions to make them resistant to microbial growth. The pore size distribution analysis of cellulose acetate membranes, were conducted using various molecular weights of polyethylene glycol (PEG). The treated and original membranes were characterized for contact angle measurement, microbial resistance, chemically using Fourier Transform Infrared (FTIR), structural morphology using atomic force microscope (AFM) and copper dispersion on the membrane surface using scanning electron microscope (SEM).

The membranes were characterized with filtration of DI water and then subjected to protein rejection measurements. The permeation data over the five and a half hours of testing is shown in Figure 3. The permeation of the copper-charged membranes (treated) is initially lower than the non-treated membrane for the first two hours during the filtration of DI water.  The membranes were then subjected to bovine serum albumin (BSA) and lipase filtration. The permeation of the BSA for both membranes was lower than the lipase because the particle size of lipase is significantly smaller than BSA. The non-treated membrane shows a decrease in permeation over time for both proteins.