Mark van Loosdrecht

Multidimensional modelling to investigate interspecies hydrogen transfer in anaerobic biofilms

Publisher: Elsevier BV

Date: 09-2006

DOI: 10.1016/J.WATRES.2006.06.014

Abstract: Anaerobic digestion is a multistep process, mediated by a functionally and phylogenetically erse microbial population. One of the crucial steps is oxidation of organic acids, with electron transfer via hydrogen or formate from acetogenic bacteria to methanogens. This syntrophic microbiological process is strongly restricted by a thermodynamic limitation on the allowable hydrogen or formate concentration. In order to study this process in more detail, we developed an in idual-based biofilm model which enables to describe the processes at a microbial resolution. The biochemical model is the ADM1, implemented in a multidimensional domain. With this model, we evaluated three important issues for the syntrophic relationship: (i) Is there a fundamental difference in using hydrogen or formate as electron carrier? (ii) Does a thermodynamic-based inhibition function produced substantially different results from an empirical function? and (iii) Does the physical co-location of acetogens and methanogens follow directly from a general model. Hydrogen or formate as electron carrier had no substantial impact on model results. Standard inhibition functions or thermodynamic inhibition function gave similar results at larger substrate field grid sizes (> 10 microm), but at smaller grid sizes, the thermodynamic-based function reduced the number of cells with long interspecies distances (> 2.5 microm). Therefore, a very fine grid resolution is needed to reflect differences between the thermodynamic function, and a more generic inhibition form. The co-location of syntrophic bacteria was well predicted without a need to assume a microbiological based mechanism (e.g., through chemotaxis) of biofilm formation.

Incorporating microbial ecology into the metabolic modelling of polyphosphate accumulating organisms and glycogen accumulating organisms

Publisher: Elsevier BV

Date: 09-2010

DOI: 10.1016/J.WATRES.2010.06.071

Abstract: In the enhanced biological phosphorus removal (EBPR) process, the competition between polyphosphate accumulating organisms (PAO) and glycogen accumulating organisms (GAO) has been studied intensively in recent years by both microbiologists and engineers, due to its important effects on phosphorus removal performance and efficiency. This study addresses the impact of microbial ecology on assessing the PAO-GAO competition through metabolic modelling, focussing on reviewing recent developments, discussion of how the results from molecular studies can impact the way we model the process, and offering perspectives for future research opportunities based on unanswered questions concerning PAO and GAO metabolism. Indeed, numerous findings that are seemingly contradictory could in fact be explained by the metabolic behaviour of different sub-groups of PAOs and/or GAOs exposed to different environmental and operational conditions. Some ex les include the glycolysis pathway (i.e. Embden-Meyerhof-Parnas (EMP) vs. Entner-Doudoroff (ED)), denitrification capacity, anaerobic tricarboxylic acid (TCA) cycle activity and PAOs' ability to adjust their metabolism to e.g. a GAO-like metabolism. Metabolic modelling may further yield far-reaching influences on practical applications as well, and serves as a bridge between molecular/biochemical research studies and the optimisation of wastewater treatment plant operation.

Wastewater-based epidemiology predicts COVID-19-induced weekly new hospital admissions in over 150 USA counties

Publisher: Springer Science and Business Media LLC

Date: 28-07-2023

DOI: 10.1038/S41467-023-40305-X

Abstract: Although the coronavirus disease (COVID-19) emergency status is easing, the COVID-19 pandemic continues to affect healthcare systems globally. It is crucial to have a reliable and population-wide prediction tool for estimating COVID-19-induced hospital admissions. We evaluated the feasibility of using wastewater-based epidemiology (WBE) to predict COVID-19-induced weekly new hospitalizations in 159 counties across 45 states in the United States of America (USA), covering a population of nearly 100 million. Using county-level weekly wastewater surveillance data (over 20 months), WBE-based models were established through the random forest algorithm. WBE-based models accurately predicted the county-level weekly new admissions, allowing a preparation window of 1-4 weeks. In real applications, periodically updated WBE-based models showed good accuracy and transferability, with mean absolute error within 4-6 patients/100k population for upcoming weekly new hospitalization numbers. Our study demonstrated the potential of using WBE as an effective method to provide early warnings for healthcare systems.

New framework for standardized notation in wastewater treatment modelling

Publisher: IWA Publishing

Date: 02-2010

DOI: 10.2166/WST.2010.912

Abstract: Many unit process models are available in the field of wastewater treatment. All of these models use their own notation, causing problems for documentation, implementation and connection of different models (using different sets of state variables). The main goal of this paper is to propose a new notational framework which allows unique and systematic naming of state variables and parameters of biokinetic models in the wastewater treatment field. The symbols are based on one main letter that gives a general description of the state variable or parameter and several subscript levels that provide greater specification. Only those levels that make the name unique within the model context are needed in creating the symbol. The paper describes specific problems encountered with the currently used notation, presents the proposed framework and provides additional practical ex les. The overall result is a framework that can be used in whole plant modelling, which consists of different fields such as activated sludge, anaerobic digestion, sidestream treatment, membrane bioreactors, metabolic approaches, fate of micropollutants and biofilm processes. The main objective of this consensus building paper is to establish a consistent set of rules that can be applied to existing and most importantly, future models. Applying the proposed notation should make it easier for everyone active in the wastewater treatment field to read, write and review documents describing modelling projects.

Variable stoichiometry with thermodynamic control in ADM1

Publisher: IWA Publishing

Date: 08-2006

DOI: 10.2166/WST.2006.531

Abstract: The effect of a variable stoichiometry of the carbohydrate fermentation process in the IWA Anaerobic Digestion Model No.1 (ADM1) is investigated. Most existing anaerobic digestion models including ADM1 consider a fixed-stoichiometry for their conversion processes. The ADM1 model was first transformed into an only mol based model to remove some errors derived from the mixed COD-mol based standard model and to allow for implementation of the variable stoichiometry. Consequently, the values of the butyrate and acetate catabolic yields of carbohydrate fermentation are made dependent on the hydrogen concentration and the reactor pH according to the predictions of a recently developed mixed culture fermentation model based on thermodynamic considerations. The simulation results obtained showed no significantly different responses in terms of effluent quality and system robustness between the standard and the variable stoichiometry ADM1 under overload conditions, and for both single- and two-step anaerobic digestion configurations. This behaviour is explained by the non-limiting acetogenic activity that compensated for the changes in the acidogenic products, typical behaviour for serial processes close to equilibrium. Based on the results obtained, thermodynamic rather than kinetic control for these conversions is suggested. Depending on the objectives to be met, lumping of carbohydrate fermenters and oxidative acetogens into a single biomass group with a variable stoichiometry is proposed for further consideration.

Three-Dimensional Simulations of Biofilm Growth in Porous Media

Publisher: Wiley

Date: 29-12-2009

DOI: 10.1002/AIC.11674

Response to the comment on “Modelling the PAO-GAO competition: Effects of carbon source, pH and temperature” by Dwight Houweling et al.

Publisher: Elsevier BV

Date: 06-2009

DOI: 10.1016/J.WATRES.2009.03.043

Aggregation and surface hydrophobicity of selected microorganism due to the effect of substrate, pH and temperature

Publisher: Elsevier BV

Date: 09-2014

DOI: 10.1016/J.IBIOD.2014.05.023

Modelling anaerobic, aerobic and partial nitritation-anammox granular sludge reactors - A review

Publisher: Elsevier BV

Date: 02-2019

DOI: 10.1016/J.WATRES.2018.11.026

Abstract: Wastewater treatment processes with granular sludge are compact and are becoming increasingly popular. Interest has been accompanied by the development of mathematical models. This contribution simultaneously reviews available models in the scientific literature for anaerobic, aerobic and partial nitritation-anammox granular sludge reactors because they comprise common phenomena (e.g. liquid, gas and granule transport) and thus pose similar challenges. Many of the publications were found to have no clearly defined goal. The importance of a goal is stressed because it determines the appropriate model complexity and helps other potential users to find a suitable model in the vast amount of literature. Secondly, a wide variety was found in the model features. This review explains the chosen modelling assumptions based on the different reactor types and goals wherever possible, but some assumptions appeared to be habitual within fields of research, without clear reason. We therefore suggest further research to more clearly define the range of operational conditions and goals for which certain simplifying assumptions can be made, e.g. when intragranule solute transport can be lumped in apparent kinetics and when biofilm models are needed, which explicitly calculate substrate concentration gradients inside granules. Furthermore, research is needed to better mechanistically understand detachment, removal of influent particulate matter and changes in the mixing behaviour inside anaerobic systems, before these phenomena can be adequately incorporated in models. Finally, it is suggested to perform full-scale model validation studies for aerobic and anammox reactors. A spreadsheet in the supplementary information provides an overview of the features in the 167 reviewed models.

Evaluating sludge minimization caused by predation and viral infection based on the extended activated sludge model No. 2d.

Publisher: Elsevier BV

Date: 10-2011

DOI: 10.1016/J.WATRES.2011.07.013

Abstract: The Activated Sludge Model No. 2d (ASM2d) was extended to incorporate the processes of both predation and viral infection. The extended model was used to evaluate the contributions of predation and viral infection to sludge minimization in a sequencing batch reactor (SBR) system enriching polyphosphate-accumulating organisms (PAOs). Three in idual decay processes formulated according to the general model rules were used in the extended model. The model was firstly calibrated and validated by different experimental results. It was used to evaluate the potential extent of predation and viral infection on sludge minimization. Simulations indicate that predation contributes roughly two times more to sludge minimization than viral infection in the SBR system enriching PAOs. The sensitivity analyses of the selected key parameters reveal that there are thresholds on both predation and viral infection rates, if they are too large a minimal sludge retention time is obtained and the effluent quality is deteriorating. Due to the thresholds, the contributions of predation and viral infection to sludge minimization are limited to a maximal extent of about 21% and 9%, respectively. However, it should be noted that the parameters concerning predation and viral infection were not calibrated separately by independent experiment in our study due to the lack of an effective method, especially for the parameters regarding viral infection. Therefore, it is essential to better evaluate these parameters in the future.

Experimental evaluation of decrease in bacterial activity due to cell death and activity decay in activated sludge.

Publisher: Elsevier BV

Date: 08-2009

DOI: 10.1016/J.WATRES.2009.05.019

Abstract: Decrease in bacterial activity (cell decay) in activated sludge can be attributed to cell death (reduction in the amount of active bacteria) and activity decay (reduction in the specific activity of active bacteria). The aim of this study was to experimentally differentiate between cell death and activity decay as a source of decrease in microbial activity. By means of measuring maximal oxygen uptake rates, verifying membrane integrity by live/dead staining and verifying presence of 16S rRNA with fluorescence in-situ hybridization, the decay rates and the death rates of ammonium oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and ordinary heterotrophic organisms (OHOs) were determined respectively in a nitrifying sequencing batch reactor (SBR) and a heterotrophic SBR. The experiments revealed that in the nitrifying system activity decay contributed 47% and 82% to the decreased activities of AOB and NOB and that cell death was responsible for 53% and 18% of decreases in their respective activities. In the heterotrophic system, activity decay took a share of 78% in the decreased activity of OHOs, and cell death was only responsible for 22% of decrease in their activity. The difference between the importance of cell death on the decreased activities of AOB and OHOs might be caused by the mechanisms of substrate storage and/or cryptic growth/death-regeneration of OHOs. The different nutrient sources for AOB and NOB might be the reason for a relatively smaller fraction of cell death in NOB.

Modeling the PAO–GAO competition: Effects of carbon source, pH and temperature

Publisher: Elsevier BV

Date: 02-2009

DOI: 10.1016/J.WATRES.2008.10.032

Abstract: The influence of different carbon sources (acetate to propionate ratios), temperature and pH levels on the competition between polyphosphate- and glycogen-accumulating organisms (PAO and GAO, respectively) was evaluated using a metabolic model that incorporated the carbon source, temperature and pH dependences of these microorganisms. The model satisfactorily described the bacterial activity of PAO (Accumulibacter) and GAO (Competibacter and Alphaproteobacteria-GAO) laboratory-enriched cultures cultivated on propionate (HPr) and acetate (HAc) at standard conditions (20 degrees C and pH 7.0). Using the calibrated model, the effects of different influent HAc to HPr ratios (100-0, 75-25, 50-50 and 0-100%), temperatures (10, 20 and 30 degrees C) and pH levels (6.0, 7.0 and 7.5) on the competition among Accumulibacter, Competibacter and Alphaproteobacteria-GAO were evaluated. The main aim was to assess which conditions were favorable for the existence of PAO and, therefore, beneficial for the biological phosphorus removal process in sewage treatment plants. At low temperature (10 degrees C), PAO were the dominant microorganisms regardless of the used influent carbon source or pH. At moderate temperature (20 degrees C), PAO dominated the competition when HAc and HPr were simultaneously supplied (75-25 and 50-50% HAc to HPr ratios). However, the use of either HAc or HPr as sole carbon source at 20 degrees C was not favorable for PAO unless a high pH was used (7.5). Meanwhile, at higher temperature (30 degrees C), GAO tended to be the dominant microorganisms. Nevertheless, the combined presence of acetate and propionate in the influent (75-25 and 50-50% HAc to HPr ratios) as well as a high pH (7.5) appear to be potential factors to favor the metabolism of PAO over GAO at higher sewage temperature (30 degrees C).

Modelling using rRNA-structured biomass models

Publisher: IWA Publishing

Date: 02-2009

DOI: 10.2166/WST.2009.592

Abstract: Models currently used have been developed to describe the storage response in the activated sludge process. In these models the distribution of the substrate flux between growth and storage is an empirical function. rRNA-structured biomass models are proposed to describe the metabolic status of cells in view of predicting the growth response (dμ/dt) of cells in activated sludge process. The autocatalytic reaction rate of the synthesis of the PSS component (rRNA) can provide a mechanistic explanation for the growth response and the growth lag phase. The proposed models were able to describe and predict properly the growth response of the biomass in various types of reactor. Such models could be more widely applicable by using intrinsic model parameters. This would be a key improvement for as it would lead to improved models for design.

A mathematical model for electrochemically active filamentous sulfide-oxidising bacteria

Publisher: Elsevier BV

Date: 04-2015

DOI: 10.1016/J.BIOELECHEM.2014.11.002

Abstract: Oxygen and sulfide in ocean sediments can be consumed biologically over long spatial distances by way of filamentous bacteria in electron-conducting sheaths. To analyse observations, a mathematical model of these filamentous sulfur-oxidising bacteria was developed, including electrical conduction between reactive zones. Mechanisms include Nernst-Planck diffusion and migration of ions coupled with Ohm's law for conduction along filaments, and metabolic activity throughout the filaments. Simulations predict outward biomass growth toward the boundaries of the sediment floor and top surface, resulting in two distinct zones with anode (sulfide consumption) and cathode (oxygen consumption) reactions enabled by electron conduction. Results show inward fluxes of 4.6 mmol O2/m(2)/d and 2.5 mmol S/m(2)/d, with consumption increasing with growth to final fluxes of 8.2 mmol O2/m(2)/d and 4.34 mmol S/m(2)/d. Qualitatively, the effect of varying cell conductivity and substrate affinity is evaluated. Controlling mechanisms are identified to shift from biomass limitation, to substrate limitation, and to conductivity limitations as the lengths of the filaments increase. While most observed data are reflected in the simulation results, a key discrepancy is the lower growth rates, which are largely fixed by thermodynamics, indicating that microbes may utilise secondary substrates or an alternative metabolism.

Microbiological endogenous processes in biological wastewater treatment systems

Publisher: Informa UK Limited

Date: 26-02-2010

DOI: 10.1080/10643380802278901

Corrigendum to “Modeling biofilm and floc diffusion processes based on analytical solution of reaction–diffusion equations”

Publisher: Elsevier BV

Date: 08-2006

DOI: 10.1016/J.WATRES.2006.06.007

Nuclear magnetic resonance microscopy studies of membrane biofouling

Publisher: Elsevier BV

Date: 10-2008

DOI: 10.1016/J.MEMSCI.2008.06.012

Chemical cleaning of biofouling in reverse osmosis membranes evaluated using magnetic resonance imaging

Publisher: Elsevier BV

Date: 10-2010

DOI: 10.1016/J.MEMSCI.2010.06.052

Modeling mixed culture fermentations; the role of different electron carriers

Publisher: IWA Publishing

Date: 03-2008

DOI: 10.2166/WST.2008.094

Abstract: A recently established mixed culture fermentation (MCF) model has been modified to account for the role of different electron carriers in the process. The MCF-model predicts the product spectrum as a function of the actual environmental conditions using a thermodynamic optimization criterion while satisfying a number of constraints. Other improvements made to the original model are the inclusion of formate as fermentation end-product, and gas-liquid mass transfer. The model is adequately capable of reproducing experimental results in terms of butyrate and formate versus hydrogen/carbon dioxide production. The model is not capable of predicting the production of an ethanol/acetate mixture as measured at higher pH-values, suggesting specific biochemical control. Catabolic acetate production can potentially be explained by anabolic requirements for a specific electron donor like NADH.

Wastewater-based epidemiology predicts COVID-19-induced hospital and ICU admission numbers in over 100 USA counties

Publisher: Research Square Platform LLC

Date: 15-12-2022

DOI: 10.21203/RS.3.RS-2368434/V1

Abstract: With the ease of coronavirus disease (COVID-19) emergency status globally, a population-wide low-cost prediction for COVID-19-induced hospitalization and intensive care unit (ICU) admission numbers is essential for healthcare systems. For the first time, we evaluated the feasibility of using wastewater-based epidemiology (WBE) to predict COVID-19-induced hospitalization and ICU admission numbers in 102 counties across 42 states in the United States of America (USA), covering a population of nearly 60 million, through random forest models using the county-level weekly wastewater surveillance data (over 15 months). WBE-based models accurately predicted the admission numbers, allowing a preparation window of 5-28 days. In real applications, periodically updated WBE-based models showed good accuracy and transferability, with mean absolute error within 20 and 2 patients/100k population for upcoming hospitalization and ICU admission numbers in 28 days, respectively. Our study demonstrated the potential of using WBE as a cost-effective method to provide early warnings for healthcare systems.

Metabolic Model for Glycogen-Accumulating Organisms in Anaerobic/Aerobic Activated Sludge Systems

Publisher: Wiley

Date: 13-11-2003

DOI: 10.1002/BIT.10455

Abstract: Glycogen-accumulating organisms (GAO) have the potential to directly compete with polyphosphate-accumulating organisms (PAO) in EBPR systems as both are able to take up VFA anaerobically and grow on the intracellular storage products aerobically. Under anaerobic conditions GAO hydrolyse glycogen to gain energy and reducing equivalents to take up VFA and to synthesise polyhydroxyalkanoate (PHA). In the subsequent aerobic stage, PHA is being oxidised to gain energy for glycogen replenishment (from PHA) and for cell growth. This article describes a complete anaerobic and aerobic model for GAO based on the understanding of their metabolic pathways. The anaerobic model has been developed and reported previously, while the aerobic metabolic model was developed in this study. It is based on the assumption that acetyl-CoA and propionyl-CoA go through the catabolic and anabolic processes independently. Experimental validation shows that the integrated model can predict the anaerobic and aerobic results very well. It was found in this study that at pH 7 the maximum acetate uptake rate of GAO was slower than that reported for PAO in the anaerobic stage. On the other hand, the net biomass production per C-mol acetate added is about 9% higher for GAO than for PAO. This would indicate that PAO and GAO each have certain competitive advantages during different parts of the anaerobic/aerobic process cycle.

The effect of biofilm permeability on bio-clogging of porous media

Publisher: Wiley

Date: 12-12-2012

DOI: 10.1002/BIT.24381

Abstract: A 3D Biofilm model, appropriate for complex porous media support structures, is successfully modified such that non-zero permeability of biofilms structures is enabled. A systematic study is then conducted into the influence of biofilm permeability on overall biomass growth rate. This reveals a significant influence at large biofilm concentrations even when the permeability of the biomass is 1.25% of that of the free pore space, biomass accumulation increased by a factor of ∼3 over 40 h. The effect is shown to be retained when allowing for biomass detachment or erosion as a consequence of adjacent velocity shear. We conclude that biofilm permeability should be included in biofilm models and that further experimental work is required to better describe the link between biofilm permeability and local microstructure.

Toward a Universal Unit for Quantification of Antibiotic Resistance Genes in Environmental Samples

Publisher: American Chemical Society (ACS)

Date: 13-06-2023

DOI: 10.1021/ACS.EST.3C00159

New approaches to characterizing and understanding biofouling of spiral wound membrane systems

Publisher: IWA Publishing

Date: 07-2012

DOI: 10.2166/WST.2012.096

Abstract: Historically, biofouling research on spiral wound membrane systems is typically problem solving oriented. Membrane modules are studied as black box systems, investigated by autopsies. Biofouling is not a simple process. Many factors influence each other in a non-linear fashion. These features make biofouling a subject which is not easy to study using a fundamental scientific approach. Nevertheless to solve or minimize the negative impacts of biofouling, a clear understanding of the interacting basic principles is needed. Recent research into microbiological characterizing of biofouling, small scale test units, application of in situ visualization methods, and model approaches allow such an integrated study of biofouling.

Microbiology and application of the anaerobic ammonium oxidation (‘anammox’) process

Publisher: Elsevier BV

Date: 06-2001

DOI: 10.1016/S0958-1669(00)00211-1

Abstract: Ten years ago, an anaerobic ammonium oxidation ('anammox') process was discovered in a denitrifying pilot plant reactor. From this system, a highly enriched microbial community was obtained, dominated by a single deep-branching planctomycete, Candidatus Brocadia anammoxidans. Phylogenetic inventories of different wastewater treatment plants with anammox activity have suggested that at least two genera in Planctomycetales can catalyse the anammox process. Electron microscopy of the ultrastructure of B. anammoxidans has shown that several membrane-bounded compartments are present inside the cytoplasm. Hydroxylamine oxidoreductase, a key anammox enzyme, is found exclusively inside one of these compartments, tentatively named the 'anammoxosome'.

Measuring the activities of higher organisms in activated sludge by means of mechanical shearing pretreatment and oxygen uptake rate.

Publisher: Elsevier BV

Date: 07-2010

DOI: 10.1016/J.WATRES.2010.05.013

Abstract: A pretreatment method was developed to assess the activities of higher organisms. The method is based on mechanical shearing to damage the large cells of the protozoan and metazoan community in activated sludge. The procedure was confirmed through experimentation to be effective in determining the activities of higher organisms by comparing oxygen uptake rates (OURs) before and after the higher organisms were eradicated. Shearing led to disintegration of flocs, which could be effectively reconstituted by centrifugation. The reconstitution of the sludge flocs was essential since otherwise the activity of the floc mass would be too high due to lack of diffusion limitation. Mechanical shearing had no influence on the morphology, quantity and specific activity of yeasts, and it was inferred that bacteria smaller than yeasts in size would also not be influenced by the applied shearing procedure. Moreover, the effect of filamentous organisms on the measured activities of higher organisms was experimentally demonstrated and analyzed, and determined to be so weak that it could be ignored. Based on these tests, five typical activated sludge processes were selected to measure the contribution of higher organisms to the original OUR. The measured activities of higher organisms ranged from 9.4 to 25.0% of the original OURs.

Critical review of activated sludge modeling: State of process knowledge, modeling concepts, and limitations

Publisher: Wiley

Date: 05-09-2012

DOI: 10.1002/BIT.24624

Abstract: This work critically reviews modeling concepts for standard activated sludge wastewater treatment processes (e.g., hydrolysis, growth and decay of organisms, etc.) for some of the most commonly used models. Based on a short overview on the theoretical biochemistry knowledge this review should help model users to better understand (i) the model concepts used (ii) the differences between models, and (iii) the limits of the models. The seven analyzed models are: (1) ASM1 (2) ASM2d (3) ASM3 (4) ASM3 + BioP (5) ASM2d + TUD (6) Barker & Dold model and (7) UCTPHO+. Nine standard processes are distinguished and discussed in the present work: hydrolysis fermentation ordinary heterotrophic organisms (OHO) growth autotrophic nitrifying organisms (ANO) growth OHO & ANO decay poly-hydroxyalkanoates (PHA) storage polyphosphate (polyP) storage phosphorus accumulating organisms PAO) growth and PAO decay. For a structured comparison, a new schematic representation of these processes is proposed. Each process is represented as a reaction with consumed components on the left of the figure and produced components on the right. Standardized icons, based on shapes and color codes, enable the representation of the stoichiometric modeling concepts and kinetics. This representation allows highlighting the conceptual differences of the models, and the level of simplification between the concepts and the theoretical knowledge. The model selection depending on their theoretical limitations and the main research needs to increase the model quality are finally discussed.

Extracting DNA from ocean microplastics: a method comparison study

Publisher: Royal Society of Chemistry (RSC)

Date: 2017

DOI: 10.1039/C6AY03119F

Abstract: Molecular characterization of ocean plastic biofilms can shed light on the ecological implications of plastic pollution here we provide detailed protocols and compare different DNA extraction methods applied to marine microplastics.

Biofouling of spiral-wound nanofiltration and reverse osmosis membranes: A feed spacer problem

Publisher: Elsevier BV

Date: 02-2009

DOI: 10.1016/J.WATRES.2008.11.019

Abstract: Biofouling was studied in full-scale and pilot-scale installations, test-rigs and membrane fouling monitors by conventional methods as well as Magnetic Resonance Imaging (MRI). Independent of permeate production, the feed spacer channel pressure drop and biomass concentration increased similarly in a nanofiltration pilot installation. In the presence of a feed spacer the absolute feed channel pressure drop increase caused by biomass accumulation was much higher than when a feed spacer was absent: in both spiral-wound nanofiltration and reverse osmosis systems biofouling is dominantly a feed spacer problem. This conclusion is based on (i) in-situ visual observations of the fouling accumulation, (ii) in-situ non-destructive observations of the fouling accumulation and velocity distribution profiles using MRI, and (iii) differences in pressure drop and biomass development in monitors with and without feed spacer. MRI studies showed that even a restricted biofilm accumulation on the feed channel spacer influenced the velocity distribution profile strongly. Biofouling control should be focused on the development of low fouling feed spacers and hydrodynamic conditions to restrict the impact of biomass accumulation on the feed channel pressure drop increase.

Modeling product formation in anaerobic mixed culture fermentations

Publisher: Wiley

Date: 2006

DOI: 10.1002/BIT.20765

Abstract: The anaerobic conversion of organic matter to fermentation products is an important biotechnological process. The prediction of the fermentation products is until now a complicated issue for mixed cultures. A modeling approach is presented here as an effort to develop a methodology for modeling fermentative mixed culture systems. To illustrate this methodology, a steady-state metabolic model was developed for prediction of product formation in mixed culture fermentations as a function of the environmental conditions. The model predicts product formation from glucose as a function of the hydrogen partial pressure (P(H2)), reactor pH, and substrate concentration. The model treats the mixed culture as a single virtual microorganism catalyzing the most common fermentative pathways, producing ethanol, acetate, propionate, butyrate, lactate, hydrogen, carbon dioxide, and biomass. The product spectrum is obtained by maximizing the biomass growth yield which is limited by catabolic energy production. The optimization is constrained by mass balances and thermodynamics of the bioreactions involved. Energetic implications of concentration gradients across the cytoplasmic membrane are considered and transport processes are associated with metabolic energy exchange to model the pH effect. Preliminary results confirmed qualitatively the anticipated behavior of the system at variable pH and P(H2) values. A shift from acetate to butyrate as main product when either P(H2) increases and/or pH decreases is predicted as well as ethanol formation at lower pH values. Future work aims at extension of the model and structural validation with experimental data.

Aerobic sludge granulation: A tale of two polysaccharides?

Publisher: Elsevier BV

Date: 10-2012

DOI: 10.1016/J.WATRES.2012.06.018

Abstract: Aerobic sludge granules are suspended biofilms with the potential to reduce the cost and footprint of secondary wastewater treatment. Attempts to answer how and why they form leads to a consideration of the role of their extracellular polymeric substances (EPS) in determining their physical and microbiological properties. The exopolysaccharide components of this matrix, in particular, have received attention as putative structural, gel-forming agents. Two quite different exopolysaccharides have been proposed as the gel-forming constituents, with their gel properties clearly different from those of activated sludge EPS. This review aims to address the question of whether more than one gel-forming exopolysaccharide exist in granules. Based on the available structural data, it seems likely that they are different gel-forming polymers and their differences are not artifacts of the analytical methods used. Nonetheless, both proposed structural gel polymers are extracted and purified based on procedures selecting for anionic polar polysaccharides soluble at high pH, and both contain hexuronic acids. Granulation does not result from EPS synthesis by any single microbial population, nor from production of a single exopolysaccharide. Future studies using solvents suitable for recalcitrant polysaccharides are likely to reveal important structural roles for other polysaccharides. It is hoped that this article will serve as a guide for subsequent studies into understanding the roles of exopolysaccharides in aerobic granular sludge.

Magnetic resonance imaging and 3D simulation studies of biofilm accumulation and cleaning on reverse osmosis membranes

Publisher: Elsevier BV

Date: 12-2010

DOI: 10.1016/J.FBP.2010.08.010

Experimental evaluation of decrease in the activities of polyphosphate/glycogen-accumulating organisms due to cell death and activity decay in activated sludge

Publisher: Wiley

Date: 30-03-2010

DOI: 10.1002/BIT.22703

Abstract: Decrease in bacterial activity (biomass decay) in activated sludge can result from cell death (reduction in the amount of active bacteria) and activity decay (reduction in the specific activity of active bacteria). The goal of this study was to experimentally differentiate between cell death and activity decay as the cause of decrease in bacterial activity. By means of measuring maximal anaerobic phosphate release rates, verifying membrane integrity by live/dead staining and verifying presence of 16S rRNA with fluorescence in situ hybridization (FISH), the decay rates and death rates of polyphosphate-accumulating organisms (PAOs) in a biological nutrient removal (BNR) system and a laboratory phosphate removing sequencing batch reactor (SBR) system were determined, respectively, under famine conditions. In addition, the decay rate and death rate of glycogen-accumulating organisms (GAOs) in a SBR system with an enrichment culture of GAOs were also measured under famine conditions. Hereto the maximal anaerobic volatile fatty acid uptake rates, live/dead staining, and FISH were used. The experiments revealed that in the BNR and enriched PAO-SBR systems, activity decay contributed 58% and 80% to the decreased activities of PAOs, and that cell death was responsible for 42% and 20% of decreases in their respective activities. In the enriched GAOs system, activity decay constituted a proportion of 74% of the decreased activity of GAOs, and cell death only accounted for 26% of the decrease of their activity.

Modelling the population dynamics and metabolic diversity of organisms relevant in anaerobic/anoxic/aerobic enhanced biological phosphorus removal processes

Publisher: Elsevier BV

Date: 08-2010

DOI: 10.1016/J.WATRES.2010.06.017

Abstract: In this study, enhanced biological phosphorus removal (EBPR) metabolic models are expanded in order to incorporate the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) under sequential anaerobic/anoxic/aerobic conditions, which are representative of most full-scale EBPR plants. Since PAOs and GAOs display different denitrification tendencies, which is dependent on the phylogenetic identity of the organism, the model was separated into six distinct biomass groups, constituting Accumulibacter Types I and II, as well as denitrifying and non-denitrifying Competibacter and Defluviicoccus GAOs. Denitrification was modelled as a multi-step process, with nitrate (NO(3)), nitrite (NO(2)), nitrous oxide (N(2)O) and di-nitrogen gas (N(2)) being the primary components. The model was calibrated and validated using literature data from enriched cultures of PAOs and GAOs, obtaining a good description of the observed biochemical transformations. A strong correlation was observed between Accumulibacter Types I and II, and nitrate-reducing and non-nitrate-reducing PAOs, respectively, where the abundance of each PAO subgroup was well predicted by the model during an acclimatization period from anaerobic-aerobic to anaerobic-anoxic conditions. Interestingly, a strong interdependency was observed between the anaerobic, anoxic and aerobic kinetic parameters of PAOs and GAOs. This could be exploited when metabolic models are calibrated, since all of these parameters should be changed by an identical factor from their default value. Factors that influence these kinetic parameters include the fraction of active biomass, relative aerobic/anoxic fraction and the ratio of acetyl-CoA to propionyl-CoA. Employing a metabolic approach was found to be advantageous in describing the performance and population dynamics in such complex microbial ecosystems.

Proposed modifications to metabolic model for glycogen-accumulating organisms under anaerobic conditions

Publisher: Wiley

Date: 11-09-2002

DOI: 10.1002/BIT.10370

Abstract: Filipe et al. (2001) proposed an anaerobic metabolic model for glycogen-accumulating organisms (GAO) in which the succinate-propionate pathway was used to describe the production of propionyl-CoA. However, propionyl-CoA is only an intermediate product in the above pathway. Stopping at propionyl-CoA instead of propionate (the end product of the pathway) results in the consumption of one ATP from succinate to succinyl-CoA, which was not accounted for in the model of Filipe et al. (2001). This resulted in significant errors in the stoichiometric coefficients in the final metabolic model. A modified model is presented in this communication and is shown to fit the experimental data significantly better than the original model.

Discovery Projects - Grant ID: DP190102979

Start Date: 02-2019

End Date: 12-2023

Amount: $408,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0342658

Start Date: 2003

End Date: 05-2006

Amount: $199,000.00

Funder: Australian Research Council