Water Resources Research Act Program

Details for Project ID 2015MO147B

Removal of NOMs by Advanced Thin Film Composite Membranes for the Control of Disinfection Byproducts

Institute: Missouri
Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-29
Total Federal Funds: $22,000 Total Non-Federal Funds: $45,229

Principal Investigators: Zhiqiang Hu

Abstract: It is known that interactions of natural organic matters (NOMs) and chlorine generates a number of harmful disinfection byproducts (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs), and N-nitrosodimethylamine (NDMA). Among various methods used for the control of DBPs, removal of NOMs by membrane-based nanofiltration (NF) and reverse osmosis (RO) is considered one of the most effective approaches. The membrane treatment has merits because they are capable of removing NOMs and other contaminants simultaneously and easily adaptable to different scales with modular design. In addition, it has become increasingly cost-competitive in comparison with other approaches such as coagulation/flocculation and carbon adsorption. The overall goal of this two-year project is to develop high performance mixed matrix nano composite membranes (MMM) that could be used to effectively remove NOMs from the source water and thus decrease or eliminate the formation of DBPs during water chlorination. The key hypotheses are that the membrane removal efficiency for NOMs can be significantly enhanced by introducing more negative charges and higher hydrophilicity on the membrane surface via embedment of various silica nanoparticles. We will use polyamide as the thin-film layer on the polysulfone support to make thin-film composite, and select various silica nanoparticles as fillers. Specific objectives are to: 1) Fabricate mixed matrix nano-composite membranes (MMMs) with various silica nanoparticles; 2) Evaluate membrane performance in terms of water permeability and removal of NOMs; and 3) Assess the impact of NOM removal on the production of DBPs. This study addresses one of the most challenging issues facing many municipal water supplies in the State of Missouri, and the results may lead to the development of a more cost-effective membrane approach for the control of DBPs. In the first year, we have fabricated mixed matrix nano-composite membranes (MMMs) with silica and TiO2 nanoparticles and evaluated membrane performance in terms of water permeability and removal of NOMs. Two types of bimodal silica nanoparticles (~80 nm) with different internal pore structures were synthesized and incorporated into the polyamide (PA) thin-film layer during interfacial polymerization at concentrations varying from 0 to 0.1 wt%. The as-prepared membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, and their performances were evaluated in terms of the water permeability and salt rejection. The results showed the water permeability increased with increasing BSN concentrations, reaching a maximum of 53.5 L/m2h at a bimodal silica nanoparticle (BSN) concentration of 0.5 wt% (pressure at 300 psi, NaCl concentration: 2000 ppm). This represented a flux increase of approximately 40%, while maintaining a near constant salt rejection of 95%. The study demonstrated that the internal micro-mesoporous structures of bimodal silica nanoparticles contributed significantly to the membrane performance, which is consistent with previous studies with relatively uniform internal pores. In addition, nitrogen doped TiO2 (N-TiO2), a hydrophilic and visible light-active photocatalyst, was applied to prepare poly(vinylidene fluoride) (PVDF)/N-TiO2 mixed matrix hollow fiber membranes (HFMs) by the phase inversion method. The membranes were characterized by scanning electron microscopy (SEM), contact angle measurement and UV-Vis absorbance. In the second year of this project, we plan to 1) optimize the conditions that will result in maximal NOM rejection under fixed cross membrane pressure; and 2) assess the impact of NOM removal on the production of DBPs. The membrane performances for treating surface water will be evaluated based on the water flux and total organic carbon (TOC) rejection. The resistance of membranes against fouling will also be evaluated. It is expected that the thin-film nanocomposite membranes and hollow-fiber ultrafiltration membranes are quite different for NOM removal. The thin-film nanocomposite membranes are capable of removing NOM at a higher percentage but require a higher cross membrane pressure in comparison with the hollow-fiber ultrafiltration membranes. This study will assess the performance of these membranes for the removal of NOM and subsequent reduction of DBP. Such information could be used to select membranes that will result in adequate reduction of DBPs to meet regulatory standard but with least cost.