Microfluidic colloid filtration

Abstract

Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.

Transition-state theory predicts clogging at the microscale

“…Clogging is encountered at many length scales, ranging from the deposition of marginally-soluble asphaltenes at pipe walls in oil recovery1, the formation of protein fouling layers in waste water treatment23, particle clogging during membrane filtration4 or microfluidic operations567. Similar phenomena are encountered at much larger length scales such as in blockades of granular hopper flows8, the emergence of traffic jams on merging lanes910 or in crowds swarming through narrow escape routes1112.…”

Dynamics of pore fouling by colloidal particles at the particle level

“…Fouling by colloidal particles remains a major issue in many industrial processes including particle synthesis and solid handling in microreactors, membrane filtration, and liquid chromatography, often leading to complete stoppage of the process [1]. Even though this clogging issue is specific to each application, some generic features have been identified thanks to the use of microfluidic technology coupled with various imaging techniques such as confocal microscopy [2][3][4][5][6][7]. This technology enables the design of microdevices with complex geometries [8] that mimic industrial processes, in particular membrane filtration, and inside these devices we can follow the capture or deposition of colloidal particles over time, at the pore scale level, using diverse microscopy techniques.…”

“…Studies have determined the influence of pore geometry (width, shape, length, varying or fixed cross section) [3,5,[9][10][11], the confinement, i.e. the ratio between the particle radii and the smallest dimension of the pore [4,5,10], the polydispersity of the colloidal suspensions [12,13], the stability of the suspension with respect to the DLVO interaction potentials, between particles and the pore walls and between particles themselves [3][4][5][14][15][16], and the deformability of the particles [6].…”

“…Despite these efforts to visualize the fouling process inside model membranes, the dynamics inside a pore at the particle level remain completely unexplored. Almost all the work that has used either microfluidic setups or various kinds of membranes or microsieves onlyfocus on pores that are already partially or completely clogged, thereby ignoring the particle deposition history [3,6,[17][18][19][20].…”

Design Optimization for a Microfluidic Crossflow Filtration System Incorporating a Micromixer

“…Thus, concentration polarization becomes a serious drawback in microfluidic membrane filtration. As in conventional macroscale filtration, membrane fouling is also a factor to be considered when designing a microfluidic filtration system [33][34][35]. In previous studies [36,37], it was demonstrated that, with a micromixer incorporated with a microfluidic membrane filtration system, the permeate flux could be significantly improved via chaotic mixing that reduces the amount of fouling on membrane surfaces.…”