Wim T.M. Audenaert

Environmental Chemistry, Chemical Kinetics, Physical Chemistry

Ph.D. Environmental engineer
25.17

Publications

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    ABSTRACT: The aim of this study was to determine an appropriate combination for effective and economical COD and nitrogen removal from landfill leachate. Biological (nitrogen) treatment was performed with the autotrophic nitrogen removal (ANR) process. The (post-) treatment performances of (i) ozonation alone, (ii) adsorption to granular activated carbon (GAC) alone, (iii) the combination of O3 and GAC and (iv) an integrated approach with continuous recirculation of ozonated ANR effluent were investigated. It was observed that ANR post-treatment with ozonation was able to remove only 15.2% of residual COD and 14.0% of total nitrogen in the effluent whereas using activated carbon a 73.6% removal efficiency of COD and 17.3% of total nitrogen was achieved. The best performance was obtained for an ANR post-treatment combination of ozonation and GAC, ensuring a high removal for both COD and total nitrogen. When different ratios of ozonated effluent were mixed with the influent of the ANR, it was found to be possible to reach COD removal as high as 40% in the ANR with a slightly decrease in nitrogen removal of around 70–80% compared to respectively 5.31% (COD) and 85.9% (total nitrogen) when no ozonated leachate was recycled to the ANR reactor. Taking the overall performance and operational expenses into account, a combination of ANR biological treatment and its different (post-) treatments (ANR + ozonation + GAC) results in a good performance and a lower cost compared to traditional treatment.
    Chemical Engineering Journal 09/2015; 275. DOI:10.1016/j.cej.2015.04.012 · 4.32 Impact Factor
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    ABSTRACT: The present work investigates the potential of coagulation-flocculation and ozonation to pretreat biologically stabilized landfill leachate before granular activated carbon (GAC) adsorption. Both iron (III) chloride (FeCl3) and polyaluminium chloride (PACl) are investigated as coagulants. Better organic matter removal is observed when leachate was treated with FeCl3. At a dose of 1mg FeCl3/mg CODo (CODo: initial COD content), the COD and α254 removal was 66% and 88%, respectively. Dosing 1mg PACl/mg CODo resulted in 44% COD and 72% α254 removal. The settle-ability of sludge generated by PACl leveled off at 252mL/g, while a better settle-ability of 154mL/g was obtained for FeCl3 after dosing 1mg coagulant/mg CODo. For ozonation, the percentage of COD and α254 removal increased as the initial COD concentration decreased. Respectively 44% COD and 77% α254 removal was observed at 112mg COD/L compared to 5% COD and 26% α254 removal at 1846mg COD/L. Subsequent activated carbon adsorption of ozonated, coagulated and untreated leachate resulted in 77%, 53% and 8% total COD removal after treatment of 6 bed volumes. Clearly showing the benefit of treating the leachate before GAC adsorption. Mathematical modeling of the experimental GAC adsorption data with Thomas and Yoon-Nelson models show that ozonation increases the adsorption capacity and breakthrough time of GAC by a factor of 2.5 compared to coagulation-flocculation. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Waste Management 06/2015; DOI:10.1016/j.wasman.2015.06.014 · 3.16 Impact Factor
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    International Conference on Industrial Waste and Wastewater Treatment and Valorization, Athens, Greece; 05/2015
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    Michael Chys · Wesley Declerck · Wim T. M. Audenaert · Stijn W. H. Van Hulle
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    ABSTRACT: BACKGROUND Landfill leachate requires rigorous treatment to limit environmental impact. Often, granular activated carbon (GAC) filtration is part of the treatment train. Little is known on how a preceding (advanced) oxidation process (AOP) could modify the adsorption properties. As such, different AOPs were compared as preceding step to GAC filtration for treatment of biologically stabilized landfill leachate.RESULTSColumn tests showed that the GAC filters could be used substantially longer (> 14 times compared with untreated leachate) after Fenton treatment. This is in contrast to leachate treated by UV/H2O2 (no improvement) and ozone. For UV/H2O2, most likely, the significant UV absorption of the leachate hindered the production of hydroxyl radicals. Ozonation (65% BOD increase), on the other hand, showed that there might be the potential to reduce costs related to external carbon source dosing by recycling part of the oxidized stream to the biological treatment unit.CONCLUSIONS The lifetime increase was mostly due to higher removal of COD (up to 63%) as it was clearly indicated that the oxidation processes did not alter the adsorption properties to any great extent. A clear overview of the operational expenses indicated that using a coupled treatment (oxidation + GAC) could lead to a significant cost reduction. © 2014 Society of Chemical Industry
    Journal of Chemical Technology & Biotechnology 03/2015; 90(3). DOI:10.1002/jctb.4344 · 2.49 Impact Factor
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    ABSTRACT: A major concern for landfilling facilities is the treatment of their leachate. To optimize organic matter removal from this leachate, the combination of two or more techniques is preferred in order to meet stringent effluent standards. In our study, coagulation-flocculation and ozonation are compared as pre-treatment steps for stabilized landfill leachate prior to granular activated carbon (GAC) adsorption. The efficiency of the pre treatment techniques is evaluated using COD and UVA254 measurements. For coagulation-flocculation, different chemicals are compared and optimal dosages are determined. After this, iron (III) chloride is selected for subsequent adsorption studies due to its high percentage of COD and UVA254 removal and good sludge settle-ability. Our finding show that ozonation as a single treatment is effective in reducing COD in landfill leachate by 66% compared to coagulation flocculation (33%). Meanwhile, coagulation performs better in UVA254 reduction than ozonation. Subsequent GAC adsorption of ozonated effluent, coagulated effluent and untreated leachate resulted in 77%, 53% and 8% total COD removal respectively (after 6 bed volumes). The effect of the pre-treatment techniques on GAC adsorption properties is evaluated experimentally and mathematically using Thomas and Yoon-Nelson models. Mathematical modelling of the experimental GAC adsorption data shows that ozonation increases the adsorption capacity and break through time with a factor of 2.5 compared to coagulation-flocculation.
    NATIONAL SYMPOSIUM OF APPLIED BIOLOGICAL SCIENCES, Leuven La Nueve, Belgium; 01/2015
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    ABSTRACT: Due to recent developments in environmental legislation in Europe (e.g. European Union (EU) and Switzerland), many WWTPs will be equipped with ozonation. These new regulations will aim at controlling the discharge of Trace Organic Compounds (TOrCs) into the natural environment. Switzerland is the first country that enforced TrOC control at the point source on a national scale using five indicator compounds. The EU will soon establish a watch list with compounds (including 3 pharmaceuticals) for which monitoring data will have to be gathered on which further regulatory developments will be based. In the United States, some WWTPs were proactively equipped with ozonation (mainly to protect surface waters/water sources) but as in the EU, control at the point source is not enforced by law. Furthermore, the US focus is mainly on disinfection. Further data on the occurrence and fate of TOrCs is essential for the development of effective and accepted regulation. In parallel, on-line monitoring frameworks (e.g. based spectral measurements) have to be further established to continuously assess plant performance in terms of TOrC removal. These tools will also be useful for the control of those plants (i.e. optimal ozone dosing).
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    ABSTRACT: Background Persistence of ammonium nitrogen in landfill leachate still remains a challenge. Autotrophic Nitrogen Removal (ANR) system has been shown its promise and became one of the treatments for removing nitrogen from high strength wastewater. Less well known is the fact that the nitrifying-denitrifying inoculum can readily be grown in large quantities and can be used in the ANR system directly to treat real leachate without adaption. As such, a scale–up study from lab-scale to pilot-plant scale was performed using nitrifying-denitrifying sludge to analyse the feasibility.ResultsResults showed on average 72 mg N L−1 d−1 was effectively removed in the lab-scale bioreactor and up to 36.6 mg N L−1 d−1 could be removed in the pilot-scale reactors. When the leachate was treated in order to reduce considerably the ammonium content, it was also found to be possible to reach a COD removal of roughly 40% in both lab and pilot scale reactors. Operational costs were decreased by 37 % in operational costs while combining ANR and nitrification-denitrification compared to individual conventional nitrification-denitrification.Conclusions This study demonstrates high-rate ammonium nitrogen and organic matter removal from landfill leachate by ANR is possible and this will allow a significant decrease in operational costs without significant investment costs.
    Journal of Chemical Technology & Biotechnology 09/2014; 90. DOI:10.1002/jctb.4526 · 2.49 Impact Factor
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    ABSTRACT: Anammox has shown its promise and low cost for removing nitrogen from high strength wastewater such as landfill leachate. A reactor was inoculated with nitrification-denitrification sludge originating from a landfill leachate treating waste water treatment plant. During the operation, the sludge gradually converted into red Anammox granular sludge with high and stable Anammox activity. At a maximal nitrogen loading rate of 0.6 g N l(-1) d(-1), the reactor presented ammonium and nitrite removal efficiencies of above 90%. In addition, a modified Stover-Kincannon model was applied to simulate and assess the performance of the Anammox reactor. The Stover-Kincannon model was appropriate for the description of the nitrogen removal in the reactor with the high regression coefficient values (R2 = 0.946) and low Theil's inequality coefficient (TIC) values (TIC < 0.3). The model results showed that the maximal N loading rate of the reactor should be 3.69 g N l(-1) d(-).
    Environmental Technology 05/2014; 35(9-12):1226-33. DOI:10.1080/09593330.2013.865084 · 1.20 Impact Factor
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    ABSTRACT: More and more stringent requirements for pollution control and the implementation of the new discharge standard for landfill leachate make the development and application of landfill leachate treatment a research focus. The aim of the review is to determine appropriate technique for effective treatment of landfill leachate. In the paper, various leachate treatment technologies are presented and summarized, the key control parameters and some main problems are discussed from a technological point of view. It is proposed that the improvement of existing technical and the development and industrial application of a new treatment for landfill leachate are necessary. The development and application of integrated leachate treatment process of different physical, biological and chemical technologies could be a suitable option to reduce the contamination levels of leachate. Particularly, advanced oxidation technologies and an efficient integration between physical-chemical processes and biochemical processes are indicated as a significant research direction of new technology development.
    Reviews in Environmental Science and Bio/Technology 03/2014; 14(1):1-30. DOI:10.1007/s11157-014-9349-z · 2.26 Impact Factor
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    ABSTRACT: Ozonation was investigated as a potential post-treatment step for biologically treated landfill leachate to enhance the biodegradability and observe the influence of the initial organic matter concentration and pH. Changes in COD, UV absorption at 254 nm (UVA254) and BOD content were measured during and after ozonation, and the ozone utilisation efficiency at different conditions was calculated. The initial COD concentration was found to influence the absolute removal of UVA254 significantly, but especially changes in pH influenced the ozone reactions. Increased pH (pH 10) most probably increased the overall hydroxyl radical production leading to a higher COD removal and a much better ozone utilisation compared to lower pH. This in contrast to initial COD variations which had little influence on the determined ozone utilisation. Regardless of initial COD content or pH, on average 10% of the initial COD content was converted to BOD, next to 10% COD that was removed.
    Communications in agricultural and applied biological sciences 01/2014; 79(1):97-101.
  • Michael Chys · Wesley Declerck · Wim T.M. Audenaert · Stijn W.H. Van Hulle
    3rd IWA BeNeLux Regional Young Water Professionals Conference; 10/2013
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    W.T.M. Audenaert · M. Vandevelde · S. W. H. Van Hulle · I. Nopens
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    ABSTRACT: Ozone decomposition in real water is often empirically modelled due to the system complexity. Mechanistic models, however, can be of great value in view of engineering applications. The high number of model parameters often restricts their applicability. In this study, sensitivity analyses were used to determine the most important elementary reactions from a kinetic model and to understand the reaction mechanism. Only seven of the twenty-eight rate constants showed to impact ozone and hydroxyl radical concentrations. Mass-transfer related parameters were of major importance. Ozone decomposition was extremely sensitive to parameters involving dissolved organic matter (DOM) at very low scavenger levels implying that even in “ultrapure” water systems impurities should be considered. To increase the applicability of mechanistic ozonation models, simplification of the elementary radical scheme combined with a more detailed description of reactions involving DOM is needed.
    Ozone: Science and Engineering 05/2013; 35:338–349. DOI:10.1080/01919512.2013.797884 · 0.95 Impact Factor
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    W T M Audenaert · D Vandierendonck · S W H Van Hulle · I Nopens
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    ABSTRACT: This study experimentally examined the impact of oxidation on the properties of effluent organic matter (EfOM) using two different oxidation techniques: ozonation and UV/H2O2 treatment. Multiple surrogates for EfOM related to its spectral properties, molecular size, concentration, polarity and biodegradability were used to study the oxidant induced conversions. Spectral calculations as differential absorbance spectra (DAS) and absorbance slope index (ASI) were applied for the first time to describe EfOM oxidation and proved to be useful to unravel differences in working mechanism between ozone and hydroxyl radical (HO) induced transformation of EfOM. Effluent ozonation inherently led to significant HO production as a result of electron transfers between ozone and electron rich moieties of EfOM. HO production increased as function of ozone dose and was strongly correlated to UV absorption at 254 nm (UV254). During the UV moderated process, pseudo steady-state behaviour of the HO concentration was observed. Ozone decomposition was extremely sensitive to EfOM reactivity. Most likely, the degree of dissociation of EfOM controlled its reactivity towards ozone. The pH effect was quantified by calculating the pseudo-first order decay constant for ozone as function of reaction time and pH. Treatment with both processes led to more oxygen rich, less hydrophobic and more biodegradable EfOM.
    Water Research 02/2013; 47(7):2387-2398. DOI:10.1016/j.watres.2013.02.003 · 5.32 Impact Factor
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    ABSTRACT: The autotrophic nitrogen removal process (partial nitritation combined with the Anammox process) is a sustainable nitrogen removal technique for nitrogen-rich streams. A modelling and experimental study was performed to define optimal process conditions for the autotrophic nitrogen removal process. Special attention was given to the influence of feeding characteristics on the performance of both the partial nitritation reactor and the Anammox reactor. It was revealed that the feeding regime is an important factor in the successful start-up of the Anammox process. Nitrite concentration peaks at the beginning of a feeding period will lead to an unsuccessful start-up, while a slow input of nitrogen speeds up the process. Feeding regimes are less important in partial nitritation reactors since laboratory results show that slow or fast supply of influent does not influence the growth of ammonium oxidisers.
    Water S.A 07/2011; 37(3):289-294. DOI:10.4314/wsa.v37i3.68479 · 0.81 Impact Factor
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    ABSTRACT: Numerous mechanistic models describing the UV/H2O2 process have been proposed in literature. In this study, one of them was used to predict the behaviour of a full-scale reactor. The model was calibrated and validated with non-synthetic influent using different operational conditions. A local sensitivity analysis was conducted to determine the most important operational and chemical model parameters. Based on the latter, the incident UV irradiation intensity and two kinetic rate constants were selected for mathematical estimation. In order to investigate changes of the NOM content over time, some time delay was considered between calibration and validation data collection. Hydrogen peroxide concentration, the decadic absorption coefficient at 310 nm (UVA310, as a surrogate for natural organic matter) and pH could be satisfactorily predicted during model validation using an independent data set. It was demonstrated that quick real-time calibration is an option at less controllable full-scale conditions. The reactivity of UVA310 towards hydroxyl radicals did not show significant variations over time suggesting no need for frequent recalibration. Parameters that determine the initiation step, i.e. photolysis of hydrogen peroxide, have a large impact on most of the variables. Some reaction rate constants were also of importance, but nine kinetic constants did show absolutely no influence to one of the variables. Parameters related to UV shielding by NOM were of main importance. At the conditions used in this study, i.e. H2O2 concentrations between 0.5 and 4 mM, hydraulic residence times between 90 and 200 s and alkalinity concentrations between 2.5 and 6 mM, competitive radiation absorption by NOM was more detrimental to the micro pollutant removal efficiency than hydroxyl radical scavenging. Hydrogen peroxide concentration was classified as a non-sensitive variable, in contrast to the concentration of a micro pollutant which showed to be very to extremely influential to many of the parameters. UV absorption as a NOM surrogate is a promising variable to be included in future models. Model extension by splitting up the UVA310 into a soluble and a particulate fraction seemed to be a good approach to model AOP treatment of real (waste)waters containing both dissolved and particulate (suspended) material.
    Chemical Engineering Journal 06/2011; 171(1):113-126. DOI:10.1016/j.cej.2011.03.071 · 4.32 Impact Factor
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    W Audenaert · Y Vermeersch · S Van Hulle · I Nopens
    Communications in agricultural and applied biological sciences 01/2011; 76(1):181-4.
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    ABSTRACT: The autotrophic nitrogen removal process (partial nitritation combined with the Anammox process) is a new and sustainable nitrogen removal technique for nitrogen rich streams. A modeling study was performed to define optimal process conditions on two reactor configurations: a single oxygen limited partial nitritation reactor and a single Anammox reactor and to investigate the influence of feeding characteristics on the performance of the Anammox reactor. The simulations revealed that the feeding regime is an important factor in the successful startup of Anammox reactors. Nitrite concentration peaks in the beginning of a feeding period will lead to an unsuccessful start-up while a slow input of nitrogen fastens up the process. Feeding regimes are less important in partial nitritation reactors since lab results show that slow or fast supply of influent does not influence the growth of partial nitrifiers.
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    ABSTRACT: The autotrophic nitrogen removal process (partial nitritation combined with the Anammox process) is a new and sustainable nitrogen removal technique for nitrogen-rich streams. A modelling study has been performed to define optimal process conditions (temperature, oxygen supply, pH and biomass retention) and to investigate the influence of chemical oxygen demand, nitrogen loading rate and hydraulic retention time on three alternative reactor configurations: a single oxygen-limited partial nitritation reactor, a single Anammox reactor, and a combination of partial nitritation and Anammox in a single reactor. The model applied was compared to experimental data from the literature and gave good agreement for all three reactor configurations. The simulations revealed that a system with separated partial nitritation and Anammox offered a wider range of optimal process conditions than a one-reactor system. The key factors in the successful operation of partial nitritation were found to be control of aeration, ammonium loading rate and temperature. Heterotrophs remained present in all three reactor systems and it was confirmed that interaction between heterotrophs and Anammox and between heterotrophs and ammonium oxidizers was possible.
    Environmental Technology 11/2010; 31(12):1311-24. DOI:10.1080/09593331003713685 · 1.20 Impact Factor
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    ABSTRACT: In 2003, the Flemish Water Supply Company (VMW) extended its drinking water production site in Kluizen (near Ghent, Belgium) with a combined ozonation and biological granular activated carbon (BGAC) filtration process. Due to this upgrade, biostability increased, less chlorination was needed and drinking water quality improved significantly. The aim of this study was to describe the full-scale reactor with a limited set of equations. In order to describe the ozonation process, a model including key processes such as ozone decomposition, organic carbon removal, disinfection and bromate formation was developed. Kinetics were implemented in WEST® and simulation results were compared to real data. The predicting performance was verified with a goodness-of-fit test and key parameters were determined through a local sensitivity analysis. Parameters involving optical density (both rate constants and stoichiometric coefficients) strongly affect model output. Some parameters with respect to bromate and bacteria showed to be only, but to a large extent, sensitive to their associated concentrations. A scenario analysis was performed to study the system's behavior at different operational conditions. It was demonstrated that the model is able to describe the operation of the full-scale ozone reactor, however, further data collection for model validation is necessary.
    Chemical Engineering Journal 03/2010; 157(2-3):551-557. DOI:10.1016/j.cej.2009.12.051 · 4.32 Impact Factor
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    ABSTRACT: The aim of this study was to evaluate the use of nanofibre microfiltration membranes, spun by an innovative electrospinning technique, in water filtration applications. As such, this study bridges the gap between developments in electrospinning techniques for the production of flat-sheet membranes and the application of these membranes in water filtration. Three different applications were examined. Firstly, the use of the membrane (functionalised or non-functionalised) for the removal of pathogens was investigated. Secondly, the electrospun flat-sheet membranes were applied for wastewater treatment in a laboratory-scale submerged membrane bioreactor (MBR). In addition to these applications, physical properties such as clean water permeability (CWP) and strength were also examined. The tests showed that the electrospun membranes can be used for water filtration applications, but that further improvements are necessary before these membranes can be practically employed. In particular, the level of functionality and the properties of irreversible fouling require further research.
    Water S.A 02/2010; 36(1):151-156. DOI:10.4314/wsa.v36i1.50924 · 0.81 Impact Factor

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