Water Treatment Using High Performance Antifouling Functional Polymer Membranes in Combination with Activated Carbon Filtration

Abstract

According to world population studies, by 2050 population exceeds 10 billion and water scarcity will affect more than four billion people. In Pakistan, water quality has been compromised because of rapid urban expansion, exponential growth in population, lack of infrastructure, poor management and socio-economic policies. The only way to reuse water and alleviate the water deficit is through water treatment, which often involves getting rid of dangerous impurities like inorganic, organic, and biofouling. Currently, polymer membranes with various pore diameters are used in water treatment operations. These membranes enable the removal of impurities down to the angstrom scale. Membranes serve as a barrier to remove chemical and biological pollutants that could deposit on their surface during the purification process and cause fouling. Membrane surface engineering reduce the membrane fouling and increase the water flux by electrostatic repulsion. In consideration of above, the work carried out with the objective to address the challenge of overcoming biofouling in polyethersulfone (PES) ultrafiltration (UF) membrane for water treatment through incorporation of antifoulant functionalities to improve function of membrane filtration. In the absence antifoulant functionalities, microorganisms can continuous to grow or attach to the surface of membrane and turns out to be uneconomical because of the frequent shutdown time, insignificant water flux and biofouling. In this research, innovative approach was adopted by addition of low to high modified activated carbon (mAC) concentrations into polymer membranes. To introduce antifouling characteristics, activated carbon (AC) was functionalized with amine (-NH2) functional group known as mAC. These mAC polymer membranes inhibit bacterial growth, control of other crucial properties including surface energy, surface area, porosity and fouling. In comparison to pristine membranes, the fabrication of low to high concentrations of mAC membranes induced notable changes in antifouling behavior. Thus, pure water flux (PWF) and BSA rejection (%) was improved up to 78 LMH and 15.8 %. This work elaborates the reduction of fouling in PES UF membranes by blending the polymer with antimicrobial Vancomycin. A broad spectra drug with a lot of hydroxyl groups at the edges and readily makes hydrogen bonding. It prevents N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG), the two core structural peptide subunits of xviii bacterial cell wall, from combining into the peptidoglycan. It also, affects RNA production and cell membrane permeability. This type of blend structure can be easily fabricated and scaled to reduce fouling in PES UF membranes. The concentration of Vancomycin has exponential effect on antibacterial activity of fabricated membranes. The large number of hydroxyl (-OH) groups at the edges of Vancomycin structure has increased the PWF up to 635 LMH. The improved fouling rejection rate was observed for drug added membranes i.e., up to 26 %. The growth of stimuli responsive polymer brushes has significant effects on antifouling properties of PES UF membranes. The work described here involves the growth of poly(acrylic acid) (PAA) brushes by surface-initiated atom transfer radical polymerization (SI-ATRP). To grow PAA hydrophilic polymer brushes, poly(t-butyl acrylate) was first polymerized and then hydrolyzed by acid. Various parameters have been altered in order to grow gradient polymer brushes and properties of the length or density gradient brushes have been investigated. The surface modified membranes showed very high contact killing rate studied under fluorescence microscopy. The highest PWF was calculated for length gradient polymer bushes containing membrane i.e., 629 LMH as compared to pristine i.e., only 82 LMH. The highest flux recovery ratio was observed up to 85 % for surface modified membranes.