Abstract

Fouling of rotating disk membranes as function of operating conditions and feed suspension characteristics was investigated in a series of laboratory experiments. A single-disk laboratory unit was operated over a range of disk rotation speeds and permeation rates (as controlled by the global transmembrane pressure drop) that were calculated to favor various conditions of particle transport and deposition. Permeate flux was found to be relatively insensitive to particle concentration in the feed stream. Thus, this membrane configuration appears to be well suited to the treatment of suspensions at high concentrations. However, the interplay between appropriate operating conditions to maintain permeate flux and the size of particles in the feed suspensions must be taken into account. Fouling was found to decrease with rotation rate and increase with transmembrane pressure (and therefore the initial permeate flux). Reductions in fouling observed at higher rotational speeds are attributed primarily to a high centrifugal force and radial component of drag on particles near the membrane surface. However, a trade off exists between the generation of high shear rates and centrifugal accelerations via high rotation rates and the radial distribution of the transmembrane pressure drop across the membrane that may locally reduce or reverse the flow of permeate across the membrane.

Author Keywords: membrane; filtration; rotating; fouling

Nomenclature

l/k_D (nm)

Debye length

a_p (μm)

particle diameter

e_o (C²/mJ)

permittivity of a vacuum

e_r

dielectric constant of water

f

volume fraction

g(m/s²)

gravitational acceleration constant

h

shear-induced diffusion characteristic height

J(l/m² h)

permeate flux

J_O (l/m² h)

clean water permeate flux

J_SS (l/m² h)

steady state permeate flux

k_B (J/K)

Boltzman’s constant

T(K)

temperature

Ω (rpm)

rotation rate

γ_w (s⁻¹

shear rate

μ(N·s/m²)

viscosity

ρ_p (kg/m³

particle density

ρ_w (kg/m³

water density

ψ_s (mV)

surface potential

Article Outline

Nomenclature

1. Introduction and background

2. Materials and methods

3. Experimental conditions

4. Experimental procedures

5. Results and discussion

6. Particle fouling experiments

7. Membrane fouling under constant operating conditions

8. Conclusions

References