Research Projects

Charged particles pose a complex challenge that can significantly impact the performance of membrane-based systems. Charged particles that create major challenges are: silica; iron hydroxides; alumina; clay and slit; organic colloids (humic acid substances) bio-colloids (bacteria) etc. Conventionally, mitigating charged fouling involves pre-treatment of the feed stream, optimization of operational parameters, and the development of fouling-resistant membrane materials. The research gap in this context is highlighted in Fig. 1. Here, a self-cleaning membrane module is being proposed that can counter the charged fouling dynamically during the process. The self-cleaning mechanism is triggered due to the long-range repulsion force that is generated on application of an AC (alternating current) electric field on the surface of a membrane fitted with a mesh-type electrode near its surface. Hence, the main scientific objectives of the proposed work are summarized as follows: To fabricate a smart, real-time self-cleaning membrane module to counter charged foulant particles, which is needed in varied applications ranging from water desalination to high bio-medical applications such as cleaning of dialyser membranes. Above is the schematic (Fig.2) of the underlying mechanism of the proposed system. In the above figure, an external AC field is applied to an electrode attached to an ultrafiltration membrane, which contains a solution of electrolyte. A charged foulant particle is advecting towards the membrane surface and is being repelled by the force generated because of the applied AC field. The governing equations to model the system are the well-known Poisson-Nernst-Planck equations (PNP), describing ion transport under the action of the AC field applied within the system. These may be written as (∂c_±)/∂t=-v (∂c_±)/∂y+D_± (∂^2 c_±)/(∂y^2 )+(FD_±)/RT ∂/∂y (c_± z_± ∂ψ/∂y) , and -ε (d^2 ψ)/(dy^2 )=e(z_+ c_+-z_- c_- ), where, c_± and c_ are the concentration of the anions and the cations, respectively, z_± and z_ are the valence of the cation and the anion, Fis the Faraday constant, Ris the universal gas constant, Tis the temperature, ψ is the electric potential all other symbols have their usual meaning. Time-averaged field (E ̅) is calculated as ¯E=-1/2π ∫_0^2π▒〖(∂ψ^*)/(∂y^* ) dt^* 〗 The force exerted by this generated electric field on the charged foulant particle shall experience competition with the permeation drag at the wall, which is given in the following equation 6πε_0 ε_∞ Rξ_p ¯(E(x))-6πμRu=0 Based on the background discussed above, the outline of the methodology of the proposed scheme is delineated as: 3.1 Experiments to be conducted: The main objectives of the present proposal are listed below: 1. Preparation of flat sheet membrane (conductive and non-conductive) 2. Fabrication of a crossflow module by incorporating a mesh-type electrode as the membrane support 3. Spinning of the hollow fibre membranes (inner diameter 220-250 μm outer diameter 400-600 μm, conductive and non-conductive). 4. Fabrication of the hollow fiber membrane module, potting the fibers in a casing with the mesh electrode glued to the inner periphery. 5. Quantification of membrane fouling using the model charged foulant bovine serum albumin (BSA) based on estimating the time-averaged electric force due to the AC field. The outcome of the proposed work will be a longer, usable membrane module with a smart self-cleaning assembly that would drastically reduce the operating cost in membrane industries.