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Apeldoorn, Netherlands

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. Source

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). Source

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. Source

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. Source

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. Source

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