joris roels - Academia.edu (original) (raw)

Papers by joris roels

Doboku Gakkai Ronbunshu, 2002

Proceedings of the Water Environment Federation, 2011

ABSTRACT At the WWTP of Oostende, operated by Aquafin, an advanced aeration control is installed,... more ABSTRACT At the WWTP of Oostende, operated by Aquafin, an advanced aeration control is installed, based on online measurement of oxygen in the carrousel and of both nitrate and ammonium at the effluent of the activated sludge tanks. As the plant meets the discharge limits at all times, a model was set up to evaluate the possibilities to reduce the energy consumption of the plant. Based on data from the years 2006 and 2007, the model was calibrated and resulted in good agreement with the available data of daily aeration energy consumption. Monthly averages agree with differences around 5% and never more than 10%. The same conclusion could also be made for total energy.A scenario analysis on the aeration controller settings (based on DO, NH4 and NO3 on-line sensors) revealed that an energy saving up to 5.5% can be obtained. Total nitrogen would slightly deteriorate (effluent NH4 increases but NO3 decreases). So, it is clear that – as the plant already has an advanced aeration controller – no gain in energy consumption can be achieved without giving up on effluent quality, and that an optimum combination of set-points can be selected whether energy or effluent consents are the target.

Water Science & Technology, 2012

This study analyzes the effect of inoculating membrane bioreactor (MBR) sludge in a parallel-oper... more This study analyzes the effect of inoculating membrane bioreactor (MBR) sludge in a parallel-operated overloaded conventional activated sludge (CAS) system. Modelling studies that showed the beneficial effect of this inoculation were confirmed though full scale tests. Total nitrogen (TN) removal in the CAS increased and higher nitrate formation rates were achieved. During MBR sludge inoculation, the TN removal in the CAS was proven to be dependent on MBR sludge loading. Special attention was given to the effect of inoculation on sludge quality. The MBR flocs, grown without selection pressure, were clearly distinct from the more compact flocs in the CAS system and also contained more filamentous bacteria. After inoculation the MBR flocs did not evolve into good-settling compact flocs, resulting in a decreasing sludge quality. During high flow conditions the effluent CAS contained more suspended solids. Sludge volume index, however, did not increase. Laboratory tests were held to dete...

Science of The Total Environment, 2005

There is still a lot of controversy in literature concerning the question whether a biochemical s... more There is still a lot of controversy in literature concerning the question whether a biochemical system exists enabling micro-organisms to reduce phosphate to phosphine gas. The search for so-called 'de novo synthesised' phosphine is complicated by the fact that soils, slurries, sludges, etc., which are often used as inocula, usually contain matrix bound phosphine (MBP). Matrix bound phosphine is a general term used to indicate non-gaseous reduced phosphorus compounds that are transformed into phosphine gas upon reaction with bases or acids. A study was carried out to compare the different digestion methods, used to transform matrix bound phosphine into phosphine gas. It was demonstrated that caustic and acidic digestion methods should be used to measure the matrix bound phosphine of the inoculum prior to inoculation to avoid false positive results concerning de novo synthesis. This is especially true if anthropogenically influenced inocula possibly containing minute steel or aluminium particles are used. The comparative study on different digestion methods also revealed that the fraction of phosphorus in mild steel, converted to phosphine during acid corrosion depended on the temperature. Following these preliminary studies, anaerobic growth experiments were set up using different inocula and media to study the emission of phosphine gas. Phosphine was detected in the headspace gases and its quantity and timeframe of emission depended on the medium composition, suggesting microbially mediated formation of the gas. The amount of phosphine emitted during the growth experiments never exceeded the bound phosphine present in inocula, prior to inoculation. Hence, de novo synthesis of phosphine from phosphate could not be demonstrated. Yet, microbially mediated conversion to phosphine of hitherto unknown reduced phosphorus compounds in the inoculum was evidenced.

Science of The Total Environment, 2004

A landfill (Hooge Maey, Flanders, Belgium) was subjected to an in-depth study in order to explain... more A landfill (Hooge Maey, Flanders, Belgium) was subjected to an in-depth study in order to explain the origin of phosphine detected in high amounts in landfill gas, in comparison with biogas from other sources, during a previous study. The spatial and temporal variability of the phosphine concentration in landfill gas was assessed. Twenty-four wells were monitored and differences in phosphine concentration up to one log unit were observed (3.2-32.4 microg/m(3)). The phosphine concentration in each well was constant in time over a period of 4 months. No correlation was found between the phosphine concentration and methane, carbon dioxide, hydrogen sulfide, ethene or ethane concentration. In a series of laboratory tests, it was shown that phosphine was emitted during batch fermentation tests inoculated with landfill leachate when Fe(0) or Al(0) specimens were added. Conditions favouring corrosion of iron gave rise to higher emissions of phosphine. The phosphine concentration in the headspace of a batch test rose to 1.43 mg/m(3) after 27 days of incubation. Weight loss of corroding steel coupons correlated with phosphine emission. Calculations showed that all phosphine emitted from the 0.005 km(3) landfill (160 g/year) could be attributed to corrosion of metals. No evidence of de novo synthesis could be established.

Journal of Microbiological Methods, 2014

is one of the most common filamentous bacteria reported to be involved in bulking and foaming pro... more is one of the most common filamentous bacteria reported to be involved in bulking and foaming problems in activated sludge plants worldwide. In order to detect and quantify both M. parvicella and Microthrix calida by quantitative PCR (qPCR), primers targeting 16S rDNA genes were designed. The qPCR reaction was optimized by using the TaqMan technology and an internal positive control was included to ensure the absence of PCR inhibitors. A total of 29 samples originating from different wastewater treatment plants were analyzed and the results were compared by using conventional microscopy, fluorescent in situ hybridization and an existing SYBR Green-based assay. Our assay showed a 100% specificity for both M. parvicella and M. calida, a sensitivity of 2.93 × 10 9 to 29 copy numbers/reaction, an amplification efficiency of 93% and no PCR inhibition. By performing a spiking experiment including different Microthrix concentrations, recovery rates ranging from 65 to 98% were obtained. A positive correlation with the SYBR Green assay (R 2 = 0.85) was found and most of the samples were in accordance with the microscopical observation. In comparison with SYBR Green assay, the probe-based TaqMan assay had a much lower detection limit. Compared with microscopy, some samples had a lower or higher enumeration when using qPCR. In conclusion, a qPCR method is forwarded here that could be useful as an early warning tool for fast and reliable detection of Microthrix in for instance sludge bulking events.

Environmental Engineering Science, 2008

Page 1. ENVIRONMENTAL ENGINEERING SCIENCE Volume 25, Number 6, 2008 © Mary Ann Liebert, Inc. DOI:... more Page 1. ENVIRONMENTAL ENGINEERING SCIENCE Volume 25, Number 6, 2008 © Mary Ann Liebert, Inc. DOI: 10.1089/ees.2007.0143 Distribution of Sulphur Compounds in Sewage Sludge Treatment Raf Dewil,1,* Jan Baeyens ...

Environmental Engineering Science, 2009

Abstract The present research studies the evolution of sulphur concentrations during wastewater t... more Abstract The present research studies the evolution of sulphur concentrations during wastewater treatment for various full-scale treatment plants and reveals that a significant amount of S is released as highly soluble sulphates with the sludge water during sludge thickening when sludge is still in aerobic conditions. During digestion, sulphur concentrations in the sludge (expressed as mg S/kg of dry solids) generally increased due to destruction of organic material, and relatively low release of H2S. During sludge dewatering following anaerobic digestion, only a minor fraction of sulphur is found in sludge water, because sulphates have already been reduced into insoluble sulphides. To limit the sulphur concentration in the waste sludge, it is beneficial to extensively dewater the sludge when still under aerobic conditions, that is, before long-term sludge storage. If anaerobic digestion is used, the formation of sulphides is inevitable, as insoluble sulphides, and to a lesser extent H2S.

Bioresource Technology, 2001

Journal of Chromatography A, 2002

A gas chromatographic (GC) system to measure free phosphine in biogas and matrix bound phosphine ... more A gas chromatographic (GC) system to measure free phosphine in biogas and matrix bound phosphine in manure and sludge is presented. The system consists of a sample preconcentration trap filled with glass beads, connected with a capillary GC equipped with a thermionic specific detector. With a trap temperature as low as -155 degrees C, a sampling flow of 20 ml/min and a typical total sample volume of 100 ml, free phosphine concentrations in the low ng/m3 range and matrix bound phosphine in the low ng/kg dry matter range, can be accurately and reproducibly determined.

Doboku Gakkai Ronbunshu, 2002

Proceedings of the Water Environment Federation, 2011

ABSTRACT At the WWTP of Oostende, operated by Aquafin, an advanced aeration control is installed,... more ABSTRACT At the WWTP of Oostende, operated by Aquafin, an advanced aeration control is installed, based on online measurement of oxygen in the carrousel and of both nitrate and ammonium at the effluent of the activated sludge tanks. As the plant meets the discharge limits at all times, a model was set up to evaluate the possibilities to reduce the energy consumption of the plant. Based on data from the years 2006 and 2007, the model was calibrated and resulted in good agreement with the available data of daily aeration energy consumption. Monthly averages agree with differences around 5% and never more than 10%. The same conclusion could also be made for total energy.A scenario analysis on the aeration controller settings (based on DO, NH4 and NO3 on-line sensors) revealed that an energy saving up to 5.5% can be obtained. Total nitrogen would slightly deteriorate (effluent NH4 increases but NO3 decreases). So, it is clear that – as the plant already has an advanced aeration controller – no gain in energy consumption can be achieved without giving up on effluent quality, and that an optimum combination of set-points can be selected whether energy or effluent consents are the target.

Water Science & Technology, 2012

This study analyzes the effect of inoculating membrane bioreactor (MBR) sludge in a parallel-oper... more This study analyzes the effect of inoculating membrane bioreactor (MBR) sludge in a parallel-operated overloaded conventional activated sludge (CAS) system. Modelling studies that showed the beneficial effect of this inoculation were confirmed though full scale tests. Total nitrogen (TN) removal in the CAS increased and higher nitrate formation rates were achieved. During MBR sludge inoculation, the TN removal in the CAS was proven to be dependent on MBR sludge loading. Special attention was given to the effect of inoculation on sludge quality. The MBR flocs, grown without selection pressure, were clearly distinct from the more compact flocs in the CAS system and also contained more filamentous bacteria. After inoculation the MBR flocs did not evolve into good-settling compact flocs, resulting in a decreasing sludge quality. During high flow conditions the effluent CAS contained more suspended solids. Sludge volume index, however, did not increase. Laboratory tests were held to dete...

Science of The Total Environment, 2005

There is still a lot of controversy in literature concerning the question whether a biochemical s... more There is still a lot of controversy in literature concerning the question whether a biochemical system exists enabling micro-organisms to reduce phosphate to phosphine gas. The search for so-called 'de novo synthesised' phosphine is complicated by the fact that soils, slurries, sludges, etc., which are often used as inocula, usually contain matrix bound phosphine (MBP). Matrix bound phosphine is a general term used to indicate non-gaseous reduced phosphorus compounds that are transformed into phosphine gas upon reaction with bases or acids. A study was carried out to compare the different digestion methods, used to transform matrix bound phosphine into phosphine gas. It was demonstrated that caustic and acidic digestion methods should be used to measure the matrix bound phosphine of the inoculum prior to inoculation to avoid false positive results concerning de novo synthesis. This is especially true if anthropogenically influenced inocula possibly containing minute steel or aluminium particles are used. The comparative study on different digestion methods also revealed that the fraction of phosphorus in mild steel, converted to phosphine during acid corrosion depended on the temperature. Following these preliminary studies, anaerobic growth experiments were set up using different inocula and media to study the emission of phosphine gas. Phosphine was detected in the headspace gases and its quantity and timeframe of emission depended on the medium composition, suggesting microbially mediated formation of the gas. The amount of phosphine emitted during the growth experiments never exceeded the bound phosphine present in inocula, prior to inoculation. Hence, de novo synthesis of phosphine from phosphate could not be demonstrated. Yet, microbially mediated conversion to phosphine of hitherto unknown reduced phosphorus compounds in the inoculum was evidenced.

Science of The Total Environment, 2004

A landfill (Hooge Maey, Flanders, Belgium) was subjected to an in-depth study in order to explain... more A landfill (Hooge Maey, Flanders, Belgium) was subjected to an in-depth study in order to explain the origin of phosphine detected in high amounts in landfill gas, in comparison with biogas from other sources, during a previous study. The spatial and temporal variability of the phosphine concentration in landfill gas was assessed. Twenty-four wells were monitored and differences in phosphine concentration up to one log unit were observed (3.2-32.4 microg/m(3)). The phosphine concentration in each well was constant in time over a period of 4 months. No correlation was found between the phosphine concentration and methane, carbon dioxide, hydrogen sulfide, ethene or ethane concentration. In a series of laboratory tests, it was shown that phosphine was emitted during batch fermentation tests inoculated with landfill leachate when Fe(0) or Al(0) specimens were added. Conditions favouring corrosion of iron gave rise to higher emissions of phosphine. The phosphine concentration in the headspace of a batch test rose to 1.43 mg/m(3) after 27 days of incubation. Weight loss of corroding steel coupons correlated with phosphine emission. Calculations showed that all phosphine emitted from the 0.005 km(3) landfill (160 g/year) could be attributed to corrosion of metals. No evidence of de novo synthesis could be established.

Journal of Microbiological Methods, 2014

is one of the most common filamentous bacteria reported to be involved in bulking and foaming pro... more is one of the most common filamentous bacteria reported to be involved in bulking and foaming problems in activated sludge plants worldwide. In order to detect and quantify both M. parvicella and Microthrix calida by quantitative PCR (qPCR), primers targeting 16S rDNA genes were designed. The qPCR reaction was optimized by using the TaqMan technology and an internal positive control was included to ensure the absence of PCR inhibitors. A total of 29 samples originating from different wastewater treatment plants were analyzed and the results were compared by using conventional microscopy, fluorescent in situ hybridization and an existing SYBR Green-based assay. Our assay showed a 100% specificity for both M. parvicella and M. calida, a sensitivity of 2.93 × 10 9 to 29 copy numbers/reaction, an amplification efficiency of 93% and no PCR inhibition. By performing a spiking experiment including different Microthrix concentrations, recovery rates ranging from 65 to 98% were obtained. A positive correlation with the SYBR Green assay (R 2 = 0.85) was found and most of the samples were in accordance with the microscopical observation. In comparison with SYBR Green assay, the probe-based TaqMan assay had a much lower detection limit. Compared with microscopy, some samples had a lower or higher enumeration when using qPCR. In conclusion, a qPCR method is forwarded here that could be useful as an early warning tool for fast and reliable detection of Microthrix in for instance sludge bulking events.

Environmental Engineering Science, 2008

Page 1. ENVIRONMENTAL ENGINEERING SCIENCE Volume 25, Number 6, 2008 © Mary Ann Liebert, Inc. DOI:... more Page 1. ENVIRONMENTAL ENGINEERING SCIENCE Volume 25, Number 6, 2008 © Mary Ann Liebert, Inc. DOI: 10.1089/ees.2007.0143 Distribution of Sulphur Compounds in Sewage Sludge Treatment Raf Dewil,1,* Jan Baeyens ...

Environmental Engineering Science, 2009

Abstract The present research studies the evolution of sulphur concentrations during wastewater t... more Abstract The present research studies the evolution of sulphur concentrations during wastewater treatment for various full-scale treatment plants and reveals that a significant amount of S is released as highly soluble sulphates with the sludge water during sludge thickening when sludge is still in aerobic conditions. During digestion, sulphur concentrations in the sludge (expressed as mg S/kg of dry solids) generally increased due to destruction of organic material, and relatively low release of H2S. During sludge dewatering following anaerobic digestion, only a minor fraction of sulphur is found in sludge water, because sulphates have already been reduced into insoluble sulphides. To limit the sulphur concentration in the waste sludge, it is beneficial to extensively dewater the sludge when still under aerobic conditions, that is, before long-term sludge storage. If anaerobic digestion is used, the formation of sulphides is inevitable, as insoluble sulphides, and to a lesser extent H2S.

Bioresource Technology, 2001

Journal of Chromatography A, 2002

A gas chromatographic (GC) system to measure free phosphine in biogas and matrix bound phosphine ... more A gas chromatographic (GC) system to measure free phosphine in biogas and matrix bound phosphine in manure and sludge is presented. The system consists of a sample preconcentration trap filled with glass beads, connected with a capillary GC equipped with a thermionic specific detector. With a trap temperature as low as -155 degrees C, a sampling flow of 20 ml/min and a typical total sample volume of 100 ml, free phosphine concentrations in the low ng/m3 range and matrix bound phosphine in the low ng/kg dry matter range, can be accurately and reproducibly determined.