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Evers M.,University of Wuppertal | Evers M.,Luneburg University | Jonoski A.,UNESCO IHE Delft | Maksimovic C.,Imperial College London | And 10 more authors.
Natural Hazards and Earth System Science | Year: 2012

This paper presents an approach to enhance the role of local stakeholders in dealing with urban floods. The concept is based on the DIANE-CM project (Decentralised Integrated Analysis and Enhancement of Awareness through Collaborative Modelling and Management of Flood Risk) of the 2nd ERANET CRUE funding initiative. The main objective of the project was to develop and test an advanced methodology for enhancing the resilience of local communities to flooding. Through collaborative modelling, a social learning process was initiated that enhances the social capacity of the stakeholders due to the interaction process. The other aim of the project was to better understand how data from hazard and vulnerability analyses and improved maps, as well as from the near real-time flood prediction, can be used to initiate a public dialogue (i.e. collaborative mapping and planning activities) in order to carry out more informed and shared decision-making processes and to enhance flood risk awareness. The concept of collaborative modelling was applied in two case studies: (1) the Cranbrook catchment in the UK, with focus on pluvial flooding; and (2) the Alster catchment in Germany, with focus on fluvial flooding. As a result of the interactive and social learning process, supported by sociotechnical instruments, an understanding of flood risk was developed amongst the stakeholders and alternatives for flood risk management for the respective case study area were jointly developed and ranked as a basis for further planning and management. © Author(s) 2012. Source

Alhadidi A.,MESA Institute for Nanotechnology | Kemperman A.J.B.,MESA Institute for Nanotechnology | Schippers J.C.,UNESCO IHE Delft | Wessling M.,MESA Institute for Nanotechnology | van der Meer W.G.J.,MESA Institute for Nanotechnology
Desalination and Water Treatment | Year: 2012

The ASTM considers the silt density index (SDI) test as a standard test for fouling potential of RO and NF feed waters. Up to date, the SDI is used at many full- and pilot-scale installations. The design and choice of the applied RO pretreatment is to a large extent based on the SDI test on the raw feed water. Comparing and monitoring UF/MF membrane performance is another SDI application. From a practical point of view, the SDI of RO feed water preferably should be lower than 3. The SDI has several disadvantages making it an unreliable test. The SDI has a non linear relationship with the colloidal concentration in the water and it is not corrected for the feed water temperature. Besides that, the SDI is not based on any filtration model. SDI is trying to simulate the RO fouling using dead-end MF membrane. The modified fouling index (MFI) is another fouling index. The MFI is based on the cake filtration model, can be corrected for pressure and temperature and is therefore used as a promising alternative for the SDI. Nevertheless, the procedure of measuring a MFI is more difficult and not directly suitable for carrying out "in the field". The objective of this study therefore is to determine a theoretical relationship between SDI and MFI, and to validate this with experimental results. This relationship can be used to investigate the influence of membrane and testing parameters on SDI under cake filtration conditions, implying this model is valid for cake filtration mechanism and a particle rejection of 100%. In order to calculate the SDI, the times t1 and t2 for collecting the first and second sample are predicted using the measured MFI value and the MFI definition. In this research, the influence of several parameters (such as temperature, membrane resistance, etc.) on the SDI will be shown. The experimental results show a good agreement with the theoretical work, but only if the cake filtration start builds up directly at the beginning of the experiment. In general, this work clearly demonstrates that SDI currently is not reliable test for RO fouling. Either corrections for the SDI are necessary to give a more reliable index, or a new index has to be developed. © 2012 Desalination Publications. All rights reserved. Source

Di Baldassarre G.,UNESCO IHE | Montanari A.,University of Bologna | Lins H.,U.S. Geological Survey | Koutsoyiannis D.,National Technical University of Athens | And 2 more authors.
Geophysical Research Letters | Year: 2010

Flood-related fatalities in Africa, as well as associated economic losses, have increased dramatically over the past half-century. There is a growing global concern about the need to identify the causes for such increased flood damages. To this end, we analyze a large, consistent and reliable dataset of floods in Africa. Identification of causes is not easy given the diverse economic settings, demographic distribution and hydro-climatic conditions of the African continent. On the other hand, many African river basins have a relatively low level of human disturbance and, therefore, provide a unique opportunity to analyze climatic effects on floods. We find that intensive and unplanned human settlements in flood-prone areas appears to be playing a major role in increasing flood risk. Timely and economically sustainable actions, such as the discouragement of human settlements in flood-prone areas and the introduction of early warning systems are, therefore, urgently needed. © 2010 by the American Geophysical Union. Source

Alhadidi A.,MESA Institute for Nanotechnology | Kemperman A.J.B.,MESA Institute for Nanotechnology | Schippers J.C.,UNESCO IHE Delft | Wessling M.,MESA Institute for Nanotechnology | van der Meer W.G.J.,MESA Institute for Nanotechnology
Journal of Membrane Science | Year: 2011

The Silt Density Index (SDI) is commonly applied as a measure for the fouling potential of particles in RO and NF feed waters. The accuracy and reproducibility of the SDI test is increasingly questioned. In this work, the influence of membrane properties on the SDI value is investigated. Eight commercial '0.45 μm' membrane types made of different materials (PVDF, PTFE, acrylic copolymer, nitro cellulose, cellulose acetate, nylon 6,6, and polycarbonate) were used to measure the SDI. Three samples were randomly chosen from each membrane type (same lot), and several membrane properties were studied (pore size distribution, pore shape, surface and bulk porosity, thickness, surface charge, contact angle and surface roughness). SDI values for an artificial feed, composed of a solution of α - alumina particles of 0.6 μm diameter, were determined. The characterization of these membranes shows variation between the membranes used in this study (M1-M8), and within a batch of one membrane type. Substantial differences were found in the SDI values for the different types of membrane filters used. Pore size, porosity and thickness are the most important membrane properties and determine the membrane resistance. Using a membrane with high a membrane resistance results in a low SDI value. The variations in measured SDI values between batches and within a batch are large and explain, at least partly, the problems encountered in practice with unacceptable variations in SDI values. These observed differences make the test unreliable. The variations are attributed to differences in properties of the membranes used. In order to make the SDI a reliable fouling index, there is a very strong need for membrane filters with uniform and constant properties. © 2011 Elsevier B.V. Source

Alhadidi A.,University of Twente | Kemperman A.J.B.,University of Twente | Blankert B.,NORIT X Flow | Schippers J.C.,UNESCO IHE Delft | And 2 more authors.
Desalination | Year: 2011

Particulate matter present in feed water of reverse osmosis and nanofiltration membrane elements tends to deposit on the membrane surface and spacers. This type of fouling results in permeate flux decline, loss of product quality and membrane damage. To characterize the fouling potential of RO feed water the Silt Density Index (SDI) and the Modified Fouling Index (MFI0.45) are commonly applied. SDI is applied worldwide for many years on a routine basis by operators since it is a simple and cheap test. Unfortunately, the SDI has several deficiencies e.g. it is not based on any filtration mechanism, has no linear relation with particulate matter and is not corrected for temperature, pressure and membrane resistance. This might explain the frequently reported erratic results obtained in practice, e.g. water treated with ultrafiltration showed in several cases high SDI values, which could not be attributed to failures of the UF membrane elements or systems. To overcome these deficiencies the MFI0.45 has been developed. This test is based on the occurrence of cake filtration during a substantial part of the test, has a linear relation with particulate matter content, and is corrected for pressure and temperature. However the manual procedure of measuring an MFI0.45 is somewhat more complicated and for this reason less suitable for application on a routine basis in practice. Fully automated equipment, measuring SDI and MFI0.45 at the same time is on the market. In this study a mathematical relation between SDI and MFI0.45 has been successfully developed, assuming that cake filtration is the dominant filtration mechanism during the tests. Based on the developed mathematical relation and experiments with an artificial colloidal suspension of aluminum oxide spheres (0.6 μm) as model water, it could be demonstrated that the SDI depends on pressure, temperature and membrane resistance. The effect of temperature and membrane resistance explains to a large extent the erratic results from the field. It is recommended to correcting SDI for temperature and membrane resistance and/or to making the guideline formulated by ASTM for the allowable range of membrane resistances much more stringent. © 2010 Elsevier B.V. Source

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