WitteveenBos

Deventer, Netherlands

WitteveenBos

Deventer, Netherlands

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PubMed | Netherlands Institute of Ecology, WitteveenBos and Wageningen University
Type: | Journal: Environmental management | Year: 2017

Submerged macrophytes play an important role in maintaining good water quality in shallow lakes. Yet extensive stands easily interfere with various services provided by these lakes, and harvesting is increasingly applied as a management measure. Because shallow lakes may possess alternative stable states over a wide range of environmental conditions, designing a successful mowing strategy is challenging, given the important role of macrophytes in stabilizing the clear water state. In this study, the integrated ecosystem model PCLake is used to explore the consequences of mowing, in terms of reducing nuisance and ecosystem stability, for a wide range of external nutrient loadings, mowing intensities and timings. Elodea is used as a model species. Additionally, we use PCLake to estimate how much phosphorus is removed with the harvested biomass, and evaluate the long-term effect of harvesting. Our model indicates that mowing can temporarily reduce nuisance caused by submerged plants in the first weeks after cutting, particularly when external nutrient loading is fairly low. The risk of instigating a regime shift can be tempered by mowing halfway the growing season when the resilience of the system is highest, as our model showed. Up to half of the phosphorus entering the system can potentially be removed along with the harvested biomass. As a result, prolonged mowing can prevent an oligo-to mesotrophic lake from becoming eutrophic to a certain extent, as our model shows that the critical nutrient loading, where the lake shifts to the turbid phytoplankton-dominated state, can be slightly increased.


Mulling B.T.M.,University of Amsterdam | van den Boomen R.M.,WitteveenBos | van der Geest H.G.,University of Amsterdam | Kappelhof J.W.N.M.,Stichting Waternet | Admiraal W.,University of Amsterdam
Water Research | Year: 2013

Constructed wetlands (CWs) have been shown to improve the water quality of treated wastewater. The capacity of CWs to reduce nutrients, pathogens and organic matter and restore oxygen regime under normal operating conditions cannot be extrapolated to periods of incidental peak discharges. The buffering capacity of CWs during peak discharges is potentially a key factor for water quality in the receiving waters. Therefore, the aim of the present study was to investigate the behaviour of peak discharges of suspended particles, (associated) physiochemical parameters and pathogenic organisms from a wastewater treatment plant (WWTP) in a full scale constructed wetland (CW). By mixing clarified water and sludge rich water from the settlement tank of the WWTP, the suspended particle concentration was increased for 8 h from ±3.5 to ±230 mg L-1, and discharged into a full scale horizontal surface flow constructed wetland. An increase of suspended particle concentration following the peak discharge concurred with increases in turbidity and oxygen demand, total nutrient load (nitrogen, phosphorus and carbon) and pathogens (Escherichia coli and Enterococci). Temperature, pH, conductivity and dissolved nutrient concentrations (nitrogen, phosphorus and carbon) were however unaffected by the initial peak discharge. After retention in the unvegetated ponds (the first CW compartment) the applied suspended particle peak with a total load of 86.2 kg was reduced by >99%. Similar peak buffering was observed for the turbidity, oxygen demand and settable volume. Simultaneously dissolved nutrient concentrations increased, indicating partial mineralization of the suspended particles during retention in the unvegetated ponds. The peak buffering of pathogens was lower (40-84%), indicating differences in removal processes between other suspended particles and pathogens. The results indicated that the suspended particles were probably mostly removed by sedimentation and mineralization, where pathogens were more likely buffered by biofilm retainment, mortality and predation, mainly in reed ditches. After passing through the total CW the residuals of the suspended particle peak discharge were temporal increased concentrations of inorganic carbon (IC), NH4 and E. coli (respectively 11%, 17% and 160% higher than steady state concentrations). The observations support the positive role of CWs for effective buffering of wastewater discharge peaks. © 2012 Elsevier Ltd.


Van Veen B.A.D.,WitteveenBos | Vatvani D.,Deltares | Zijl F.,Deltares
Continental Shelf Research | Year: 2014

For implementation of a regional Tsunami Early Warning System (EWS) in Sumatra island in Indonesia, a set of detailed and accurate tsunami propagation and flooding models using Delft3D were developed. The purpose of the models was not only to reproduce the 2004 Indian Ocean tsunami, but also to determine tsunami flood hazard maps with different return periods. The model outputs have then been used to build a tsunami flooding database covering 1250 hypothetical sources for different earthquake parameters along the Sunda Trench for an EWS called RiskMap. The model simulations produced detailed information of near-shore tsunami wave height, tsunami inundation length and run-up. Smart storage of computational results, in a geo-referenced database, allows quick access to the requisite information. The result is a system capable of issuing a warning within few minutes after a detection of an earthquake. The system has been successfully installed and tested in the last two years at national and regional emergency coordination centres, National Agency for Meteorology, Climatology and Geophysics (BMKG) and at Tsunami Disaster Mitigation Research Centre (TDMRC) in Banda Aceh. © 2012 Elsevier Ltd.


Gil J.A.,Technical University of Delft | Krzeminski P.,Technical University of Delft | van Lier J.B.,Technical University of Delft | van der Graaf J.H.J.M.,WitteveenBos | And 2 more authors.
Journal of Membrane Science | Year: 2011

The filterability of the activated sludge is an important characteristic that offers valuable information about the filtration process in membrane bioreactors (MBR). MBR operators rely on permeability values to monitor the process. However, results obtained in this and other studies have demonstrated that permeability alone is a weak parameter, as it provides no specific information about which factors are determining it. Aiming to elucidate the causes affecting the filterability of the activated sludge, some research groups have quantified and correlated the filterability with different activated sludge parameters, mostly for municipal MBRs. This paper however, offers a different approach focusing on an industrial scenario. A representative sample of eleven full-scale industrial MBRs has been selected in centre-Europe to conduct a study, in order to quantify both, the impact of parameters and constituents of industrial activated sludge on filterability. Temperature, membrane configuration, hydraulic retention time, solids retention time, and the soluble organic fraction did not show any impact on filterability whereas the mixed liquor suspended solids and the food to microorganism ratio demonstrated a slight influence. Among all parameters analyzed, the colloidal fraction played the most important role in the fouling process indicating that for industrial activated sludge, the membrane acts as a biomass barrier merely, since a high percentage (>75%) of the soluble organic fraction is small enough to pass the membrane (0.03. μm). Finally, filterability measurements suggest that on the whole, an optimization in the operation of industrial MBRs is plausible. © 2011 Elsevier B.V.


Lousada-Ferreira M.,Technical University of Delft | van Lier J.B.,Technical University of Delft | van der Graaf J.H.J.M.,WitteveenBos
Journal of Membrane Science | Year: 2015

The relation between activated sludge filterability and mixed liquor suspended solids (MLSS) concentration in membrane bioreactors (MBRs) is framed in a single hypothesis, explaining results seemingly contradictory. A total of 44 activated sludge samples were collected and analyzed on a variety of parameters, i.e. filterability, MLSS concentration, soluble microbial products (SMP) concentrations and particle size distribution in the range of 2-100μm and of 0.4-5.0μm. The sludge filterability was assessed by using the Delft Filtration Characterization method (DFCm). In order to investigate the impact of MLSS concentration, identical samples were diluted with permeate. Results showed that dilution of the samples led to an increased activated sludge filterability, but only when the starting MLSS concentration was below the apparent critical value of 10.5g/L. As opposed, the filterability of sludge with MLSS concentrations above 10.5g/L, and which was characterized by a moderate to good filtration quality, i.e. δR20<1 [×1012m-1], worsened when diluted. The specific resistance times the particle concentration of a cake layer obtained when filtrating sludge of moderate to good filterability and MLSS concentration above the apparent critical value was 5.5 times smaller compared to the cake layer of sludge with MLSS concentration below the critical value. Results from SMP assessment and particle counting in the range 2-100μm showed that reduction in sludge mass and de-flocculation occurred, upon dilution of all samples. However, when diluting sludge samples with MLSS concentrations exceeding 10.5g/L and which were characterized by a moderate to good filtration characteristics, there was also release of particles below 0.4μm, opposite to dilutions of samples with MLSS concentrations below 10.5g/L. We postulate that sludge, which is characterized by a moderate to good filterability, having an MLSS concentration above the apparent critical value of 10.5g/L, is likely to retain particles smaller than 0.4μm in its mass, as opposed to sludge with MLSS concentration below the apparent critical value. Our work indicates that there are optimal MLSS concentration ranges in MBR technology, to promote good filterable sludge quality in order to avoid fouling. © 2014 Elsevier B.V.


Augustijn D.C.M.,University of Twente | van den Berg M.,University of Twente | de Bruine E.,WitteveenBos | Korving H.,WitteveenBos | Korving H.,Technical University of Delft
Water Resources Management | Year: 2011

The Volkerak-Zoom Lake is an enclosed part of the estuarine delta in the southwest of the Netherlands and exists as such since 1987. The current freshwater lake experienced a deterioration in water and ecological quality. Especially cyanobacteria are a serious problem. To solve this problem it is proposed to reintroduce salt water and tidal dynamics in the Volkerak-Zoom Lake. However, this will affect the water quality of the Mark-Vliet River system that drains into the lake. Each of the two branches of the Mark-Vliet River system is separated from the Volkerak-Zoom Lake by a lock and drainage sluice. Salt intrusion via the locks may hamper the intake of freshwater by the surrounding polders. Salt intrusion can be reduced by increasing the discharge in the river system. In this study we used the hydrodynamic SOBEK model to run different strategies with the aim to minimize the additional discharge needed to reduce chloride concentrations. Dynamic control of the sluices downstream and a water inlet upstream based on real-time chloride concentrations is able to generate the desired discharges required to maintain the chloride concentrations at the polder intake locations below the threshold level and to reduce the amount of water required by more than 50% compared to a situation with a constant discharge. Other effective measures consist of relocating the most downstream polder intakes more upstream, reducing the downstream cross section of the Vliet to increase flow velocities and measures that reduce the inflow of salt water via the locks. This study shows that dynamic control is a promising technique in regulated streams to alleviate water quality problems by controlled flushing of the system. © 2011 The Author(s).


Lengkeek H.J.,WitteveenBos | Besseling F.,WitteveenBos
Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions, POAC | Year: 2013

Structures in ice-infested waters are subject to horizontal and vertical ice actions. These actions will be transferred to the base of the structure and the subsoil. For gravity based structures (GBS) various verifications need to be performed in a stability analysis. These verifications are similar to the stability of a shallow foundation, such as sliding, overturning and bearing capacity. The methods presented in most handbooks are basically 2D and consider actions in the x-z (vertical) plane. This paper however focuses on actions in the x-y (horizontal) plane. The effect of eccentric loading in the x-y-plane, causing both rotational and translational effects, is investigated. The method is applied to circular structure and rectangular structures. Furthermore these structures are modelled in a 3D FEM model to verify the results.


Krzeminski P.,Technical University of Delft | Iglesias-Obelleiro A.,University of Santiago de Compostela | Madebo G.,UNESCO-IHE Institute for Water Education | Garrido J.M.,University of Santiago de Compostela | And 3 more authors.
Journal of Membrane Science | Year: 2012

The main objective of this study was to investigate the influence of seasonal temperature fluctuations on raw domestic wastewater composition and MBR sludge filterability. The influent and sludge samples were collected from a full-scale MBR in Heenvliet. All samples were analyzed in terms of filterability, particle size distribution, respirometry, fractionation and were further characterized by an extensive set of physicochemical measurements. Typical seasonal fluctuations and deterioration of activated sludge filterability during low temperature periods were observed. Filterability deterioration at low temperatures was linked to the incoming organic load, reduced MBR biomass concentrations, increased VSS/TSS ratio and reduced biodegradation of wastewater in the mixed liquor. Biological activity of the biomass was concomitantly decreased with temperature to reach a minimum during the winter period. Results show that the colloidal and soluble fraction (<1μm) represents the majority of the constituents, contains most of the COD, and plays an important role in the membrane resistance increase. © 2012 Elsevier B.V.


Lousada-Ferreira M.,Technical University of Delft | Van Lier J.B.,Technical University of Delft | Van Der Graaf J.H.J.M.,WitteveenBos
Separation and Purification Technology | Year: 2016

Wastewater is increasingly used as a viable water source. Reclamation schemes rely on membranes technologies, such as Membrane Bioreactors (MBR) and subsequent membrane filtration steps to achieve the discharge or reuse limits. However, membrane technology is only effective if the membranes are intact. Moreover, growth or regrowth of particles between membrane filtration steps should be restricted, to guarantee a stable water production. Membrane integrity tools are being developed for the drinking water industry with high sensitivity and accuracy. However, such standards are not required for MBRs, where the produced permeate is not used for consumption without further treatment. In this research, we focused on permeate quality and particle counting measurements in the range 2-100 μm. A total of 433 samples of permeate and process water were measured at 8 full-scale and pilot-scale MBR locations, which were compared with 43 de-mineralized water samples measured at TU Delft. Only at one full-scale MBR the membrane integrity was compromised, which was successfully assessed by counts and shapes of the permeate particle counting distributions. All permeate samples had particles about a 100 times larger than the membrane pore size. Our results allowed us to define the relevant steps of a methodology to assess membrane integrity, particle or biomass growth and aggregation in MBR permeate. The latter two are of particular interest to determine whether growth in permeate lines is still acceptable or whether a cleaning action of the permeate collection system is required. © 2016 Elsevier B.V. All rights reserved.


Gil J.A.,RWTH Aachen | Dorgeloh E.,RWTH Aachen | van Lier J.B.,Technical University of Delft | van der Graaf J.H.J.M.,WitteveenBos | Prats D.,University of Alicante
Desalination | Year: 2012

This paper aims to be a quick reference guide to start-up decentralized membrane bioreactors (MBRs). The first part of this study focuses on the impact of different operational parameters on the start-up of decentralized MBRs, which can be easily reproduced in the field. Whereas wastewater is not an option to start-up decentralized MBRs, domestic activated sludge has shown to handle the input of wastewater in a better way than the municipal one. Starting-up at low mixed liquor suspended solids (MLSS) concentration is feasible, and a possible optimum concentration (~1gL -1) has been suggested. In turn, particle size distribution has shown how determined conditions release fine particles in the sub-micron range (0.1-1μm), impacting negatively the filterability of the initial inoculum and thus the operation. However, in the case of the air scouring rate, even releasing sub-micron particles to the media, high rates demonstrated to extend the operation. Regarding ambient conditions, low temperatures and associated deflocculation processes should be avoided. Chemical oxygen demand and NH 4 +-N removal efficiencies showed values over 87% and 75% respectively whereas suspended solids and removal of pathogens maintained low values (50mgL -1 and absence respectively) in the permeate, allowing the reuse of regenerated water since the first day of operation under the different conditions imposed. None of the analyzed parameters (i.e., MLSS, sludge volumetric index and dissolved organic carbon), influenced significantly the filterability of the initial inoculum. Contrarily, the input of wastewater has demonstrated to be the most important factor governing the fouling process of the membrane rather than the changes in the microbiology. As a final consideration, an efficient pretreatment and both low hydraulic retention time and fluxes can help to extend the operation and reach an easy transition between the start-up and the steady-state. © 2011 Elsevier B.V.

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