title: Optimization of gravity-driven membrane (GDM) filtration process for seawater pretreatment.
abstract: Seawater pretreatment by gravity-driven membrane (GDM) filtration at 40 mbar has been investigated. In this system, a beneficial biofilm develops on the membrane that helps to stabilize flux. The effects of membrane type, prefiltration and system configuration on stable flux, biofilm layer properties and dissolved carbon removal were studied. The results show that the use of flat sheet PVDF membranes with pore sizes of 0.22 and 0.45 μm in GDM filtration achieved higher stabilized permeate fluxes (7.3-8.4 L/m(2)h) than that of flat sheet PES 100 kD membranes and hollow fibre PVDF 0.1 μm membranes. Pore constriction and cake filtration were identified as major membrane fouling mechanisms, but their relative contributions varied with filtration time for the various membranes. Compared to raw seawater, prefiltering of seawater with meshes at sizes of 10, 100 and 1000 μm decreased the permeate flux, which was attributed to removal of beneficial eukaryotic populations. Optical coherence tomography (OCT) showed that the porosity of the biofouling layer was more significantly related with permeate flux development rather than its thickness and roughness. To increase the contact time between the biofilm and the dissolved organics, a hybrid biofilm-submerged GDM reactor was evaluated, which displayed significantly higher permeate fluxes than the submerged GDM reactor. Although integrating the biofilm reactor with the membrane system displayed better permeate quality than the GDM filtration cells, it could not effectively reduce dissolved organic substances in the seawater. This may be attributed to the decomposition/degradation of solid organic substances in the feed and carbon fixation by the biofilm. Further studies of the dynamic carbon balance are required.
authors.affiliation: Singapore Membrane Technology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One #06-08, 637141, Singapore. Electronic address: wubing@ntu.edu.sg.
authors.forename: Bing
authors.initials: B
authors.lastname: Wu
authors.affiliation: Institute of Environmental and Process Engineering, HSR University of Applied Sciences Rapperswil, Oberseestrasse 10, 8640 Rapperswil, Switzerland.
authors.forename: Florian
authors.initials: F
authors.lastname: Hochstrasser
authors.affiliation: Singapore Membrane Technology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One #06-08, 637141, Singapore.
authors.forename: Ebrahim
authors.initials: E
authors.lastname: Akhondi
authors.affiliation: Institute of Environmental Engineering, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: Noëmi
authors.initials: N
authors.lastname: Ambauen
authors.affiliation: Institute of Environmental and Process Engineering, HSR University of Applied Sciences Rapperswil, Oberseestrasse 10, 8640 Rapperswil, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Tschirren
authors.affiliation: Institute of Environmental and Process Engineering, HSR University of Applied Sciences Rapperswil, Oberseestrasse 10, 8640 Rapperswil, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Burkhardt
authors.affiliation: Singapore Membrane Technology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One #06-08, 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Fane
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Duebendorf, Switzerland. Electronic address: wouter.pronk@eawag.ch.
authors.forename: Wouter
authors.initials: W
authors.lastname: Pronk
mesh_terms: D018441:Biofilms; D057219:Biofouling; D019149:Bioreactors / Q000382:microbiology; D002244:Carbon / Q000737:chemistry / Q000302:isolation & purification; D056890:Eukaryota / Q000302:isolation & purification; D005374:Filtration / Q000295:instrumentation / Q000379:methods*; D006112:Gravitation; D008567:Membranes, Artificial; D009930:Organic Chemicals / Q000737:chemistry / Q000302:isolation & purification; D011145:Polyvinyls / Q000737:chemistry; D016062:Porosity; D015203:Reproducibility of Results; D012623:Seawater / Q000737:chemistry*; D041623:Tomography, Optical Coherence; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*; D005465:Fluorocarbon Polymers
chemical_list: D002244:Carbon; D008567:Membranes, Artificial; D009930:Organic Chemicals; D011145:Polyvinyls; C024865:polyvinylidene fluoride; D005465:Fluorocarbon Polymers
keywords: Biofilm layer; Gravity-driven membranes; Optical coherence tomography (OCT); Seawater pretreatment; Stabilized flux