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PhD Defense by Søren Lorenzen

Søren Lorenzen, Department of Chemistry and Bioscience, will defend his thesis on "Influence of surface charge density on filterability of organic model particles during cross-flow and dead-end filtration"


18.01.2017 kl. 13.35 - 16.35



"Influence of surface charge density on filterability of organic model particles during cross-flow and dead-end filtration"


Regardless of what the name suggests, filter cakes are not a new type of baked goods. They are the result of the accumulation of solid material during separation processes and are found in a variety of applications, ranging from the coffee grindings that makes the plunger on your French press hard to move to the mixture of sand, dirt, and decaying plant material that tends to clog your outdoor drain during heavy rainfall. Generally speaking, a filter cake occurs as an unavoidable consequence of the use of filters for separation purposes, as the nature of filtration is to let some components pass while leaving others behind, some of which could become the filter cake.

During filtration and dewatering of suspensions of biological origin, compressible filter cakes with high specific resistances are often formed. The properties of these filter cakes are significantly different from what might be expected based on classical filtration theory derived from inorganic suspensions, not only by having a higher specific resistance, but also by being highly compressible, even at low applied pressures.

One area in which this becomes an issue is in the processing of activated sludge from wastewater treatment plants, where a significant amount of operational costs are associated with either dewatering of sludge in conventional activated sludge plants, or in the prevention and/or removal of fouling in membrane bioreactors.. 

A key factor in sludge filtration is thought to be related to the charged groups on the surfaces of the sludge flocs, single cells, and exopolymers. Due to the complexity of sludge and other suspensions of biological origin, it becomes difficult to isolate and vary only one property (such as charge) without affecting several others, all of which can affect filterability. Therefore, a set of model particles has been synthesized to allow the variation of surface charge density while keeping other properties constant.

The objective of this PhD project is thus to gain knowledge about the influence of particle surface charge on filter cake behaviour during filtration of well-defined organic model particles, specifically made to simulate the particles found in activated sludge and other suspensions with similar properties. The main focus will be on specific filter cake resistance, compressibility, porosity, and osmotic effects. Even though model particles have previously been used extensively for similar purposes, the ability to vary particle charge without varying other properties has not existed until now.


  • Associate Professor Morten Lykkegaard Kristensen, AAU


  • Associate Professor, Donghong Yu (Chairman), Department of Chemistry and Bioscience, AAU, Denmark
  • Research Professor Bart Van der Bruggen, Department of Chemical Engineering, Leuven, Belgium
  • Maître de conférences, Dr. Patrick Loulergue, Institut des Sciences Chimiques de Rennes, France





Department of Chemistry and Bioscience, AAU, Section of Chemistry


Fredrik Bajers Vej 7H, 9220 Aalborg Ø, room number: To be announced

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