The composition and compression of biofilms developed on ultrafiltration membranes determine hydraulic biofilm resistance.
This study aimed at identifying how to improve the level of permeate flux stabilisation during gravity-driven membrane filtration without control of biofilm formation. The focus was therefore on understanding (i) how the different fractions of the biofilms (inorganics particles, bacterial cells, EPS matrix) influence its hydraulic resistance and (ii) how the compression of biofilms impacts its hydraulic resistance, i.e., can water head be increased to increase the level of permeate flux stabilisation. Biofilms were developed on ultrafiltration membranes at 88 and 284 cm water heads with dead-end filtration for around 50 days. A larger water head resulted in a smaller biofilm permeability (150 and 50 L m(-2) h(-1) bar(-1) for biofilms grown at 88 cm and 284 cm water head, respectively). Biofilms were mainly composed of EPS (>90% in volume). The comparison of the hydraulic resistances of biofilms to model fouling layers indicated that most of the hydraulic resistance is due to the EPS matrix. The compressibility of the biofilm was also evaluated by subjecting the biofilms to short-term (few minutes) and long-term variations of transmembrane pressures (TMP). A sudden change of TMP resulted in an instantaneous and reversible change of biofilm hydraulic resistance. A long-term change of TMP induced a slow change in the biofilm hydraulic resistance. Our results demonstrate that the response of biofilms to a TMP change has two components: an immediate variation of resistance (due to compression/relaxation) and a long-term response (linked to biofilm adaptation/growth). Our results provide relevant information about the relationship between the operating conditions in terms of TMP, the biofilm structure and composition and the resulting biofilm hydraulic resistance. These findings have practical implications for a broad range of membrane systems.
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Process Engineering, CH-8600 Dübendorf, Switzerland; ETH Zürich, Institute of Environmental Engineering, CH-8093 Zürich, Switzerland. Electronic address: Nicolas.derlon@eawag.ch.
Nicolas
N
Derlon
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Process Engineering, CH-8600 Dübendorf, Switzerland.
Alexander
A
Grütter
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Process Engineering, CH-8600 Dübendorf, Switzerland.
Fabienne
F
Brandenberger
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Process Engineering, CH-8600 Dübendorf, Switzerland.
Anja
A
Sutter
Helmholtz Centre for Environmental Research - UFZ, Magdeburg, Germany.
Ute
U
Kuhlicke
Helmholtz Centre for Environmental Research - UFZ, Magdeburg, Germany.
Thomas R
TR
Neu
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Process Engineering, CH-8600 Dübendorf, Switzerland; ETH Zürich, Institute of Environmental Engineering, CH-8093 Zürich, Switzerland.
Eberhard
E
Morgenroth
D018441:Biofilms; D005374:Filtration; D008567:Membranes, Artificial; D011312:Pressure; D014462:Ultrafiltration
D008567:Membranes, Artificial
Biofilm; Compression; Extracellular polymeric substances (EPS); Hydraulic resistance; Permeability; Ultrafiltration membrane