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Title:Mechanism study of virus removal in membrane filtration and the application to improve virus removal
Author(s):Lu, Ruiqing
Director of Research:Nguyen, Thanh H.
Doctoral Committee Chair(s):Nguyen, Thanh H.
Doctoral Committee Member(s):Espinosa-Marzal, Rosa M.; Guest, Jeremy S.; Herzberg, Moshe
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):membrane filtration
virus removal
permeate flux
Abstract:To overcome the severer droughts in recent climate change, direct potable water reuse has been in practice and a wider acceptance can be expected with a reliable control of the water quality. Pathogenic viruses in municipal wastewater can result in outbreaks of virus infection without sufficient removal. Membrane bioreactor (MBR) has shown its promise to remove virus in municipal wastewater treatment, but the major concern is the trade-off between the water permeate flux and the virus removal efficiency. The objective of this study is to understand factors controlling virus removal in low pressure membrane filtration. The virus transport in the membrane surface vicinity was investigated with the dynamic of virus removal. By filtering human adenovirus 2 (HAdV-2) with a 0.2 µm hollow fiber membrane, the virus removal efficiency was observed to be a function of the number of the total filtered virus (N_v). When N_v was low, the HAdV-2 removal efficiency decreased with N_v, while the permeate flux did not significantly change. The decrease of virus removal was attributed to the accumulation of rejected viruses in the membrane surface vicinity, leading to an increase of the local virus concentration. Further increase of N_v leaded to an increase of virus removal as a function of N_v, accompanied by a decrease of the permeate flux. By fitting the permeate flux decrease with the pore blockage-cake filtration model, it was determined that HAdV-2 fouled the membrane and decreased the effective membrane pore size, leading to the enhanced virus removal and the decreased permeate flux. It was also found that, the aim of high virus removal with the high permeate flux could be achieved by maintaining the pristine membrane and avoiding virus accumulation. To quantitatively evaluate the virus adsorption on membrane, the adsorption kinetics was investigated with a quartz crystal microbalance with dissipation (QCM-D). Both in the presence and absence of foulants, the HAdV-2 adsorption onto membrane was determined to be irreversible in 3 to 100 mM CaCl2 solutions. The kinetics of HAdV-2 adsorption could be explained with the random sequential adsorption (RSA) model. A decrease of the virus adsorption rate was observed over the adsorption time, because previously adsorbed virions would exert repulsive forces towards the virion approaching the membrane surface. Similar observation was found even in the HAdV-2 favorable adsorption. The knowledge of virus adsorption indicated that virus adsorbed onto the membrane formed a monolayer to decrease the effective pore size, which enhances the pore blockage and cake layer formation. The mechanism study illustrates the process of virus passage through the membrane. At the beginning of filtration, the observed high virus removal can be attributed to the virus adsorption onto the pristine membrane surface, and that the local concentration of suspended virus in the membrane surface vicinity is similar to the bulk solution. As filtration goes on, virions adsorbed on the membrane surface repel incoming virions and keep them suspended in the membrane surface vicinity. The convective transport and the diffusive transport jointly push the virus towards the membrane surface, increasing the local virus concentration in the membrane surface vicinity and decreasing the observed virus removal efficiency. In the long-term filtration, the virus adsorption facilitates foulant layer development, which translates into the improved virus removal with the decreased permeate flux. The mechanism study indicates that to avoid virus adsorption and approaching membrane surface could be effective in maintaining the high virus removal and the high permeate flux at the beginning of filtration. This hypothesis was tested with a zwitterionic polymer grafted membrane. The repulsive interaction forces between incoming particles and the membrane surface was validated with atomic force microscope (AFM) in the contact mode. The repulsive forces keep a distance between viruses and the membrane surface, where the convective force is low since the flow velocity decays with the distance away from the membrane pores. The enhanced virus removal by the grafted membrane was observed in our bench-scale filtration experiment. In the presence of foulants, the permeate flux of the ungrafted membrane significantly decreased while the grafted membrane only had minor decrease in permeate flux. The grafted membrane achieved both higher virus removal and higher membrane permeate flux than the ungrafted membrane in the presence of foulants. The mechanism knowledge is validated by the enhanced virus removal of the grafted membrane. Practically, the zwitterionic polymer grafting method shows its promise to control viruses in water reuse.
Issue Date:2016-11-22
Rights Information:Copyright 2016 Ruiqing Lu
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12

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