1,721,018 research outputs found
Surrogate based Global Sensitivity Analysis of ADM1-based Anaerobic Digestion Model
No full textIn order to calibrate the model parameters, Sensitivity Analysis routines are mandatory to rank the parameters by their relevance and fix to nominal values the least influential factors. Despite the high number of works based on ADM1, very few are related to sensitivity analysis. In this study Global Sensitivity Analysis (GSA) and Uncertainty Quantification (UQ) for an ADM1-based Anaerobic Digestion Model have been performed. The modified version of ADM-based model selected in this study was presented by Esposito and co-authors in 2013. Unlike the first version of ADM1, focused on sewage sludge degradation, the model of Esposito is focused on organic fraction of municipal solid waste digestion. It his recalled that in many applications the hydrolysis is considered the bottleneck of the overall anaerobic digestion process when the input substrate is constituted of complex organic matter. In Esposito's model a surfaced based kinetic approach for the disintegration of complex organic matter is introduced. This approach allows to better model the disintegration step taking into account the effect of particle size distribution on the digestion process. This model needs thus GSA and UQ to pave the way for further improvements and reach a deep understanding of the main processes and leading input factors. Due to the large number of parameters to be analyzed a first preliminary screening analysis, with the Morris' Method, has been conducted. Since two quantities of interest (QoI) have been considered, the initial screening has been performed twice, obtaining two set of parameters containing the most influential factors in determining the value of each QoI. A surrogate of ADM1 model has been defined making use of the two defined quantities of interest. The output results from the surrogate model have been analyzed with Sobol’ indices for the quantitative GSA. Finally, uncertainty quantification has been performed. By adopting kernel smoothing techniques, the Probability Density Functions of each quantity of interest have been defined
Modelling the ecology of phototrophic-heterotrophic biofilms
No full textA mathematical model describing the microbial interactions in phototrophic-heterotrophic biofilms is presented. The main phenomena and factors involved in the model include: biomass growth and decay, substrates production, diffusion and consumption, biological invasion of planktonic species and detachment. In particular, non linear hyperbolic PDEs describe the growth of the microbial species while quasi-linear parabolic PDEs govern the dynamics of substrates and invading species. The whole system of PDEs is considered in a free boundary domain. The following syntrophic interactions are also modelled: the exchange of dissolved oxygen, organic carbon and inorganic carbon produced and released by phototrophs and heterotrophs, respectively. The positive effect of heterotrophic pioneers on the phototrophic growth is modelled by introducing a phototrophic colonization rate depending on the EPS fraction in the biofilm. Numerical simulations are performed to test model accuracy. Simulation results reproduce the main symbiotic mechanisms between phototrophs and heterotrophs reported in literature, such as the positive effect of heterotrophic pioneers and their EPS production on phototrophic growth and the effects of phototrophic organic carbon release on the invasion and growth of heterotrophic bacteria. Furthermore, model results highlight the role played by heterotrophic species under photoinhibition conditions, which provide a positive shading contribution to phototrophic growth. Light is confirmed as the most significant factor in the ecology of phototrophic-heterotrophic biofilms. Such results confirm the accuracy of the model that correctly predicts the evolution of a phototrophic-heterotrophic biofilm and the main phenomena involved, and can be seen as an auxiliary tool in different industrial applications, such as wastewater treatment and bioenergy production
Qualitative analysis and simulations of the biological fouling problem on filtration membranes
No full textThe mitigation of fouling formation and development in filtration systems represents the most critical aspect for water treatment, as it naturally affects both the operational costs for management procedures, and the duration of filtration devices. As it constitutes an artificial physical barrier for solid particles retention, membrane systems are perfect environments for the adhesion and development of biological fouling layers, especially in wastewater treatment reactors. Based on recent results, the present work focuses on the qualitative analysis of a mono dimensional continuous model for biofouling dynamics in microfiltration systems. The free boundary problem accounting for the evolution of the biofouling layer during the filtration regimen has been discussed in terms of existence and uniqueness of the solution. The achieved results represent a consistent base for numerical studies related to the correct prediction of transmembrane pressure in membrane systems. Numerical examples related to the heterotrophic-autotrophic interaction occurring in wastewater treatment plants have been presented to highlight the effect of crucial biological aspects, such as extracellular polymeric substances (EPS) accumulation, usually neglected in the classical membrane filtration modeling. The description of biofouling dynamics and membrane performance during the filtration regimen highlight key aspects for microfiltration system management in all industrial applications
Modelling the comparative influence of conjugation and transformation on plasmid spread in biofilms
No full textIn this work, we propose a multidimensional continuum model for plasmid dissemination in biofilms via horizontal gene transfer. The model is formulated as a system of nonlocal partial differential equations derived from mass conservation laws and reaction kinetics principles. Biofilm is modelled as a homogeneous, viscous, incompressible fluid with a velocity given by Darcy's law. The model considers plasmid-carrying cells as distinct volume fractions and their vertical and horizontal gene transfer via conjugation and natural transformation. The model encompasses local detoxification of biofilm due to plasmid-borne resistance gene and its effect at the community scale. The equations are solved numerically and simulations are performed to investigate how transformation and conjugation regulate the dynamics and the ecology of plasmid spread in both a multidimensional and one-dimensional biofilm system. Model results are able to predict relevant experimentally observed results in plasmid spread, such as the respective intensity of different horizontal gene transfer mechanisms and the importance of selective pressure. Moreover, model results predict coexistence of plasmid-carrying and plasmid-free bacteria even in conditions when one should out-compete the other, offering a simple modelling explanation on global plasmid persistence in bacterial communities
Modeling heavy metal sorption and interaction in a multispecies biofilm
No full textA mathematical model able to simulate the physical, chemical and biological interactions prevailing in multispecies biofilms in the presence of a toxic heavy metal is presented. The free boundary value problem related to biofilm growth and evolution is governed by a nonlinear ordinary differential equation. The problem requires the integration of a system of nonlinear hyperbolic partial differential equations describing the biofilm components evolution, and a systems of semilinear parabolic partial differential equations accounting for substrates diffusion and reaction within the biofilm. In addition, a semilinear parabolic partial differential equation is introduced to describe heavy metal diffusion and sorption. The biosoption process modeling is completed by the definition and integration of other two systems of nonlinear hyperbolic partial differential equations describing the free and occupied binding sites evolution, respectively. Numerical simulations of the heterotrophic-autotrophic interaction occurring in biofilm reactors devoted to wastewater treatment are presented. The high biosorption ability of bacteria living in a mature biofilm is highlighted, as well as the toxicity effect of heavy metals on autotrophic bacteria, whose growth directly affects the nitrification performance of bioreactors
Enhanced bio-methane production from co-digestion of different organic wastes
No full textThis paper deals with an experimental study aimed at assessing the effect of mixing different organic wastes on the anaerobic digestion process. Livestock manure and organic solid wastes have been taken into account as substrates to verify if their mixing gives rise to higher methane production rates and lower risk of process failure. Bio-methane potential (BMP) tests have been conducted using the following substrates: buffalo manure (BM), poultry manure (PM), organic fraction of the municipal solid waste (OFMSW), greengrocery waste (GW) and two different mixtures composed of BM and OFMSW. Mixing BM with OFMSW resulted in 12% and 30% higher methane volumes after 30 and 15 days from the test start, respectively. Experimental data have been also used to calibrate and validate a mathematical model previously proposed by the authors, showing its capability to reproduce the synergistic effect on methane production promoted by co-digesting BM and OFSMW. © 2012 Taylor and Francis
Mathematical Modelling of Disintegration-Limited Co-Digestion of OFMSW and Sewage Sludge
No full textModelling Plasmid-Mediated Horizontal Gene Transfer in Biofilms
No full textIn this study, we present a mathematical model for plasmid spread in a growing biofilm, formulated as a nonlocal system of partial differential equations in a 1-D free boundary domain. Plasmids are mobile genetic elements able to transfer to different phylotypes, posing a global health problem when they carry antibiotic resistance factors. We model gene transfer regulation influenced by nearby potential receptors to account for recipient-sensing. We also introduce a promotion function to account for trace metal effects on conjugation, based on literature data. The model qualitatively matches experimental results, showing that contaminants like toxic metals and antibiotics promote plasmid persistence by favoring plasmid carriers and stimulating conjugation. Even at higher contaminant concentrations inhibiting conjugation, plasmid spread persists by strongly inhibiting plasmid-free cells. The model also replicates higher plasmid density in biofilm’s most active regions
Modelling the effect of the OLR and OFMSW particle size on the performances of an anaerobic co-digestion reactor
No full textA dynamic mathematical model capable to predict the methane production in an anaerobic completely stirred tank reactor (CSTR), performing the co-digestion of the organic fraction of municipal solid waste (OFMSW) and sewage sludge, is used to assess the effect of the organic loading rate (OLR) and OFMSW particle size on the reactor performances. The model is based on the approach proposed by the IWA Anaerobic Digestion Model no. 1 (ADM1), which has been modified to take into account the peculiarities of a co-digestion process. The main distinctiveness of the proposed model consists in considering two separate influent substrates (i.e. sewage sludge and OFMSW), which are modelled with different biodegradation kinetics. The sewage sludge degradation is modelled according to the ADM1 while a surface based kinetics is used to simulate the OFMSW disintegration process, which depends on particle size distribution (PSD) of the solid waste to be disintegrated. The methane production of a full scale municipal wastewater treatment plant (MWWTP) digester has been evaluated to assess the model capability to estimate the potential energy production under different process conditions. In particular, a sensitivity analysis on two key operational parameters of the CSTR co-digestion process, i.e. OLR and OFMSW particle size, has been carried out. This analysis shows the model suitability to assess the combined effect of such parameters on the digester performances, predicting the process failure occurrence. © 2010 Elsevier Ltd
Modeling biological systems with an improved fractional Gompertz law
No full textThe aim of this paper is to provide a fractional generalization of the Gompertz law via a Caputo-like definition of fractional derivative of a function with respect to another function. In particular, we observe that the model presented appears to be substantially different from the other attempt of fractional modifications of this model, since the fractional nature is carried along by the general solution even in its asymptotic behavior for long times. We then validate the presented model by employing it as a reference frame to model three biological systems of peculiar interest for biophysics and environmental engineering, namely: dark fermentation, photofermentation and microalgae biomass growth
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