ISBN 978-3-8439-4873-9

978-3-8439-4873-9, Reihe Thermodynamik

Andreas Michael Kastl
Impact of Hydrodynamics on Initial Cake Layer Formation in Forward Osmosis

145 Seiten, Dissertation Technische Universität München (2021), Softcover, A5

Zusammenfassung / Abstract

Freshwater is a rare resource. Although it can be replenished by polishing wastewater with membrane processes, biofouling is a severe problem. Biofouling increases the costs of wastewater treatment by membrane processes and must be mitigated. The initial stage of cake layer formation is critical during biofilm formation and biofouling development in membrane

systems. However, the effects of hydrodynamic conditions on the deposition of bacteria remain unclear during the initial stages of biofilm formation. This dissertation investigates the impact of permeate water flux and crossflow velocity on fouling propensity in forward osmosis systems with spacers. Additionally, the fouling mitigation potential of pulsating flows is assessed.

Fluorescence microscopy was used to track Bacillus subtilis and inert beads in situ and in real-time in a forward osmosis system with spacers during the first hours of biofilm formation. The impact of permeate water flux, crossflow velocity, and pulsating flows on spatio-temporal deposition patterns was quantified. Subsequently, core mechanisms of particle deposition

were identified by computational fluid dynamics. The insights gained in steady-state and transient operating conditions were then applied to spiral-wound modules. Areas prone to fouling were identified at steady-state and pulsating flow conditions.

The results of this research indicate that an appropriate choice of hydrodynamic conditions can minimize bacteria accumulation before biofilm formation in forward osmosis. Another key finding is that the ratio of permeate water flux to crossflow velocity impacts all aspects of particle deposition. Concomitantly, pulsating flows are a viable technique to delay the onset of fouling in membrane processes. These insights are relevant in new or cleaned forward osmosis membrane systems used to treat water of high fouling propensity and could aid in designing new spacer geometries.