NAMS 2002 Workshop - ICOM 2008

Membrane Fouling III - RO & Biofouling – 1 – Keynote
Thursday July 17, 2:15 PM-3:00 PM, Maui
Biofouling of Spiral Wound Nanofiltration and Reverse Osmosis
Membranes: A Feed Spacer Problem
J. Vrouwenvelder (Speaker), Wetsus, Delft University of Technology, Delft, The Netherlands -
hans.vrouwenvelder@wetsus.nl
D. Graf von der Schulenburg, University of Cambridge, Cambridge, United Kingdom
J. Kruithof, Wetsus Centre of Excellence for Sustainable Water Technology, Leeuwarden, The
Netherlands
M. Johns, University of Cambridge, Cambridge, United Kingdom
M. Van Loosdrecht, Delft University of Technology, Delft, The Netherlands
Biofouling - growth of biomass, i.e. biofilms - is a major fouling type in
nanofiltration and reverse osmosis membrane systems. Biofouling increases the
pressure drop, thereby increasing the process costs [1,2]. In spiral wound
membrane elements, two types of pressure drops can be discriminated: the feed
spacer channel pressure drop and the trans membrane pressure drop. The trans
membrane pressure drop is related to the membrane flux (permeation rate).
The objective of this study was to determine (i) the effect of biofouling on the feed
spacer channel pressure drop and trans membrane pressure drop and (ii) the
role of feed spacer on the pressure drop.
The development of feed spacer channel pressure drop and biofouling was
investigated with monitors (named membrane fouling simulators [3]), single
membrane element test rigs, a pilot and a full scale membrane filtration
installation, operated with NF and RO membranes with and without permeate
production. Additionally, the development of pressure drop and biofouling was
determined in monitors without feed spacer. The feed water used for the
laboratory studies was tap water with or/and without dosage of biodegradable
compounds to stimulate biofouling. The development of fouling was monitored by
(i) the pressure drop, (ii) in-situ real-time non- destructive observations such as
nuclear magnetic resonance (NMR [4]) and using the sight glass of the
membrane fouling simulator and (iii) analysis of coupons sampled from the
monitor or membrane modules. The parameters determined were adenosine
triphosphate (ATP), total direct cell counts and total organic carbon (TOC).
Biofilm accumulation affected the feed spacer channel pressure drop without
influencing the trans membrane pressure. The same feed channel pressure drop
development in time was observed in nanofiltration and reverse osmosis
membrane modules. Apparently, the membrane type was not influencing
biofouling development. From the observations it can be concluded that the
pressure drop increase due to biofouling is a feed spacer problem. This