H023-10
Numerical Simulation of Hydrodynamics and Bio-Chemical Membrane Fouling in Porous Media

Monday, 7 December 2020: 17:57
Virtual
Reshma Mohan T, Indian Institute of Science, Bangalore, India, Seetha N, Assistant Professor, Department of Civil Engineering, IIT Hyderabad, Hyderabad, India, Lakshminarayana Rao, Indian Institute of Science, Center for Sustainable Technologies, Bangalore, India and Mohan Kumar, Indian Institute of Science, Department of Civil Engineering, Interdisciplinary Centre For Water Research, Indo French Cell for Water Sciences, Robert Bosch Centre for Cyber Physical Systems, Bangalore, India
Abstract:
Membrane Bioreactors have been widely used for the treatment of domestic and industrial wastewater to produce high-quality effluent with smaller footprints. One of the limitations of the membrane filters is their fouling. Membrane fouling is mainly caused by two factors namely, accumulation/precipitation of particulates on the membrane pores/surfaces (cake formation or reversible fouling) and bio-chemical reactions leading to bio-films (internal or irreversible fouling) inside the pores. Fouling reduces pore size and increases transmembrane pressure (TMP) leading to reduced productivity of membranes.

The flow dynamics and transport of water, air, and particulates have a direct effect on membrane fouling. In this work, a multiphase CFD model (water, air, and solid phase) is developed to model hydrodynamics and fouling in a porous membrane with outside-in-flow. A hollow membrane tube of 6 mm inner diameter, 0.6 m length and permeability of 10-8, immersed in a tank of 0.15 m3 with water and suspended particulates (1% volume fraction, density of 2000 kg/m3 and average particle diameter of 0.005 mm) is modelled. The airflow rate is varied from 0.002-0.006 m3/min (average air bubble diameter 2 mm). A combined set of Navier-Stokes and Darcy’s equation is solved. Turbulent viscosity is calculated using standard k-𝜺 turbulence closure equations. The reduction in the permeate flux due to cake resistance and internal fouling resistance is calculated. The velocity distribution, wall shear stress, turbulent characteristics, and TMP along the membrane is investigated. A sensitivity analysis is carried out to understand, the influence of rate of biofilm growth and cake growth on the reduction of the permeate flux.

The model results are validated using literature data. Results indicate that, increase in airflow rate cause an increase in the shear stress resulting in resuspension of deposited particles from the membrane surface. The fouling due to cake formation occurs at a rate of 0.1 to 1 mbar/min for 10 minutes time frame and agrees with literature results. The irreversible fouling rate due to biofilm growth occurs at a rate of 10-3 to 10-1 mbar/min. The developed multiphase model is being extended to a bundle of membranes.

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