Objectives
The aims of this Work Package are:
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Characterize the influence of membrane material properties on fouling sensitivity and permeate flux performance in activated sludge filtration
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Investigate the potential of altered membrane morphology on fouling prevention
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Investigate the influence of membrane filtration tank geometry on hydrodynamics by means of Computational Fluid Dynamics
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Investigate the influence of membrane filtration tank geometry on hydrodynamics experimentally by comparing different filtration tank geometries with identical feed solutions and modules
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Characterize the influence of membrane module geometry on fouling behaviour
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Compare mass transfer characteristics (sustainable flux levels) of different membrane module concepts
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Investigate capillary hollow fibre modules in terms of the influence of module packing density and fibre arrangement on hydraulic performance
Membrane process performance (measured as permeability level and evolution over time) in MBR applications is both determined both by the properties of the membrane material (particularly through the membrane permeability under severe fouling conditions encountered in activated sludge filtration) as well as through membrane module design and operation (particularly through hydrodynamic conditions determining local mass transfer and clogging sensitivity). Improvements in both sectors of membrane process engineering are required to achieve significant progress in the economic feasibility of MBR applications in municipal wastewater treatment.
The work package restricts its activity to submerged systems, applied at municipal wastewater treatment as those are most promising and widely applied due to low energy requirements and effect of cleaning procedures. Work will encompass three membrane configurations, HF, FP and tubular, with the tubular and hollow-fibre configuration studied both as air-lift submerged and pumped side-stream. The aims of the work package are defined as follows:
Methodology / work description
The tasks to be undertaken in the work package are:
WP2.1 Membrane characteristics
A comprehensive investigation of the properties of commercially available hollow-fibre and flat sheet membranes for MBR applications in terms of pore size distribution, hydrophilic properties, MWCO, surface morphology, surface charge, and adsorption affinity for fouling substances is intended. To identify fouling potential of dissolved matter like polysaccharides, proteins, humic acids and lipids, analysis by Size Exclusion Chromatography (SEC) and an analytical method for photometric determination of polysaccharides will be used. These techniques are well established and standardized approach will be applied. Determination of MWCO can be achieved by means of dextran filtration and gel chromatography. Charge properties of different membrane material and of fouled membranes with sludges and specific dissolved materials (i.e. EPS) will be characterized using the methodology of flow potential. Additional microscopic and spectroscopic techniques like, Scanning Electron Microscopy (SEM, REM), Atomic Force Microscopy (AFM) and Energy Dispersive X-ray Analysis (EDX) are available. Standardised methods for foulant isolation and characterisation will be employed across the study and coordinated with participating partners.
In order to compare the fouling sensitivity experiments will be performed where different membrane modifications in terms of polymers and blends with different material properties (i.e. surface charge and hydrophilicity) and with varying pore size distributions will be tested. Bench scale filtration experiments with activated sludge are intended using hollow fibres as well as flat sheet membranes. Investigations will be performed with single hollow fibre membranes in a special constructed “single-strand” test cell and in bench scale membrane module units available in the research group’s facilities. Membrane samples will be provided by the consortium partners.
WP2.2 Hydrodynamics in membrane filtration units
Investigate the hydraulic conditions in a filtration unit and the impact of specific alterations of the flow pattern on filtration performance. Alternative module design and operating conditions will be applied. Detailed analysis of hydrodynamic conditions will be done by application of computational fluid dynamic (CFD) tools. Comparisons of the impact on hydraulic performance due to filtration tank designs will be conducted in pilot scale using different geometries.
For this task – the detailed analysis of hydrodynamic system behaviour – a computational fluid dynamic model (CFD-model) will be used. This model bases on the program system FLUENT and is extended for this application field by own developments. The computation of the flow field for the two-phase-system water and air will be carried out using the Algebraic-Slip-Mixture-model, which allows a realistic approximation of the system behaviour. A special modification of the k-ε-model – the rng-k-ε-model – is used to describe the heterogeneous turbulence intensity distribution and is especially usable for density influenced flow. The flow resistance of the membrane modules is taken into account the computation by approximating these membranes zones as porous media. In this work package the following questions will be investigated regarding the system behaviour:
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influence of the module design
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influence of the module operation
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influence of the aeration elements
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influence of the filtration tank geometry
The generation of boundary conditions will be carried out by measurements in pilot plants, which will be used by the project partners. Equally, measurements will be taken in order to compare the computed results with the system conditions within the investigated systems.
WP2.3 Module design
Test different membrane systems to investigate the dependency of module geometry and operating conditions on sustainable flux levels. Membrane module geometries and designs to test will include different capillary hollow fibre modules with different packing densities. Modules to be investigated will include immersed systems and side-stream units where the membranes are placed outside if the biological reactor. This therefore includes the module designs commonly used today as well as novel membrane module designs and system configuration concepts. Experiments will be done on different pilot scale units and compared using normalised parameter values (WP1). Testing units capable of investigating different systems in parallel under comparable conditions will also be employed. Alternative membrane modules for testing will be supplied by the SME partners in the project.
Deliverables & Milestones
Month 6 Membrane materials selected and analytical tools established
Month 12 Membrane materials characterised and filtration tests performed
Month 18 Process system for module investigation set-up
Month 24 Membrane modules tested and mass transfer systems characterised
Month 30 Module investigation completed and optimisation goals defined
Month 36 Improved membrane module design and operation concept
Work package nr.
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WP2
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Start date or starting event:
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3
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Activity Type
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RTD/Innovation activities
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Participant id
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NTNU
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CU
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RWTH
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INSA
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EAWAG
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UNITN
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UKZN
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Polymem
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KMS
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Fl.Co
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MILL
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Person-months per participant:
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6
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9
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24
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9
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3
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9
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3
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18
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18
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14
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4
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Objectives
- Characterise the influence of different membrane materials utilised in MBR applications on fouling
- Characterise the influence on module geometry on sustainable flux levels and fouling in MBRs
- Characterise the influence of filtration unit geometry on membrane module performance in MBRs
- Investigate optional membrane module designs and operating conditions
- Develop set of membrane material and module design criteria for improved MBRs
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Description of work
2.1 Membrane characteristics
(NTNU, CU, RWTH, INSA, UKZN, Polymem, KMS, MILL,)
Investigation of the influence of membrane material on fouling in MBRs.
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Investigate the properties of commercially available hollow-fibre and flat sheet membranes for MBR applications in terms of pore size distribution, hydrophobicity (using the contact angle measurement), MWCO, surface morphology, surface charge (zeta potential by methodology of flow potential), and affinity to potential foulants (i.e. polysaccharides, proteins, humic acids and lipids) and EDX analysis.
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Conduct comparisons of fouling sensitivity of different membrane materials (hollow fibre and flat sheet) in terms of membrane material characteristics by filtering activated sludge or biomass (test cell experiments, single-fibre test cells).
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Test modified membrane materials provided by SME partners with different pore size distributions (respectively with different MWCO) in terms of fouling behaviour, including fouling tests with model solutions (polysaccharides/proteins/humics) and real wastewater.
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Characterize new/used membranes fouled by different compounds (i.e. sludge, biological supernatant, proteins and polysaccharides) in order to determine how the surface properties are modified by fouling. Identify membranes fouled under controlled conditions and compared with membranes sampled from autopsied modules send by different partners involved in the project.
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Fouling characterisation techniques applied to compare the fouling sensitivity of different modules include:
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High-performance size exclusion chromatography with UV detection (HPSEC-UV) for identification of patterns in organic foulants.
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Fractionation of SMP and EPS, and quantitative analysis of their carbohydrate and proteinaceous content according to standard methods.
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Surface analysis of the fouled membranes using SEM with EDAS for identification of inorganic foulants.
Membrane materials and lab scale modules will be provided by partners (Polymem, KMS, MILL) for tests
Investigations will be set up with parallel procedures using the same methods but different materials as well as utilising the range of capabilities of project partners to characterise membranes with different methods.
2.2 Hydrodynamics in membrane filtration units
(NTNU, RWTH, UKZN, KMS, FlowConcept)
Investigation of the influence hydrodynamics on the process performance will include;
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Comparison of the impact on hydraulic performance due to filtration tank designs on basis of experiences gained with existing pilot and full-scale installations. Development of phenomenological relations and alternative design concepts. Combinations of different module and filtration tank designs will be tested in pilot units and compared to experiences from existing plants in operation. The impact of different configurations and designs related to aerobic, anaerobic and biofilm MBR processes will be compared.
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Investigate the hydraulic conditions in a filtration unit and the impact of specific alterations of the flow patterns on filtration performance by application of CFD-tools. Different plant configurations will be simulated based on membrane modules and process concepts under investigation by partners. Plant simulation results will be compared to experimental results achieved with different configurations (see task above).
Membrane modules will be supplied by partners and CFD simulation studies will be undertaken by FlowConcept.
2.3 Module design
(NTNU, CU, RWTH, INSA, EAWAG, UNITN, UKZN, Polymem, KMS, MILL,)
Partners will investigate the influence of membrane geometry on flux performance and fouling behaviour;
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Test different membrane systems to investigate the dependency of module geometry and operating conditions on sustainable flux levels. Tests will be conducted in pilot scale, different systems in parallel under comparable conditions, with “standard” monitoring and measuring methods (WP1). Variations in operating modes will be included, i.e. air and liquid flow rates, TMP ranges, permeate flows, continuous or pulsed/intermittent aeration, intermittent permeation (relaxation), and backwashing (WP3, WP4). Partners will operate different module systems in parallel and supplement with conclusions from previous pilot studies.
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Membranes investigated in WP2.1 will be included. Module geometries and designs to test will include different capillary hollow fibres modules with different packing densities and fibre arrangements. Tests will be carried out at different levels from small-scale test plants to semi-industrial scale pilot plants. Modules will be provided by the project partners. Applications will include aerobic, anaerobic and biofilm MBR concepts. The studies include the module designs commonly used today as well as novel membrane module designs and system configuration concepts. Results will enable further development of better membrane module designs and optimal operating conditions.
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Deliverables
D4 – Definition of membrane materials and analytical tools selected
D10 – Report - Membrane materials characterization and filtration tests performed
D17 – Process system for module investigation set-up
D19 – Report - Membrane modules tests and characterization of mass transfer systems
D26 – Definition of module investigation and optimization goals
D34 – Report - Improved membrane module design and operation concepts
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Milestones and expected result
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M2.1 +6 Membrane materials selected and analytical tools established
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M2.2 +12 Assessment of characterization and filtration tests performed
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M2.3 +18 Membrane pilots with different geometries set-up
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M2.4 +30 Module investigation completed and optimisation goals defined
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M2.5 +36 Final report: Improved module design and operation concepts
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