Mathematical modelling of the anaerobic digestion includingthe syntrophic acetate oxidation (original) (raw)
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International Biodeterioration & Biodegradation, 2017
A system using a two-phase anaerobic configuration (mesophilic/thermophilic) was tested by feeding waste activated sludge (WAS). The first acidogenic stage presented a hydraulic retention time (HRT) of 3 days, while the second methanogenic stage had an HRT of 10 days. Both raw and ultrasonically pretreated WAS samples were utilized for the experiment. Previous Fluorescence in Situ Hybridization (FISH) observations, revealed that in the thermophilic phase, the acetoclastic methanogenesis was likely replaced by a nonacetoclastic pathway, namely, syntrophic acetate oxidation (SAO). A modified version of Anaerobic Digestion Model n 1 (ADM1), accounting for the SAO pathway, was implemented and calibrated. The proposed model addressed the relationship between the hydrogen concentration and Gibbs free energy and showed the thermodynamic feasibility of the SAO pathway, while simultaneously highlighting the role played by hydrogenotrophic methanogens in maintaining a sufficiently low hydrogen partial pressure so that the SAO was energetically feasible. The estimated energy loss was estimated to be approximately 20% due to the switch of the microbial pathway from acetoclastic methanogenesis to SAO.
Mathematical modelling of anaerobic digestion of biomass and waste: Power and limitations
Progress in Energy and Combustion Science, 2013
Anaerobic digestion is an excellent technique for the energetic valorisation of various types of biomass including waste forms. Because of its complex nature, the optimisation and further process development of this technology go hand in hand with the availability of mathematical models for both simulation and control purposes. Over the years, the variety of mathematical models developed has increased as have their complexity. This paper reviews the trends in anaerobic digestion modelling, with the main focus on the current state of the art. The most significant simulation and control models are highlighted, and their effectiveness critically discussed. The importance of the availability of models that are less complex, which can be used for control purposes, is assessed. The paper concludes with a discussion on the inclusion of microbial community data in mathematical models, an innovative approach which could drastically improve model performance 2 wastewater sludge, the organic fraction of municipal solid waste and some types of industrial wastes (e.g. fats, oils and grease (FOG), manure, crop waste from agriculture and dedicated energy crops). Anaerobic digestion comprises a myriad of reactions, most of which are biochemical in nature. A simplified reaction scheme is depicted in .
Modelling and Simulation of Anaerobic Digestion of Wastewater Sludge using Mathematica
The increasing demand of energy has led to a chaos among the existing energy sources and the tremendous amount of solid waste generation on a daily basis is making the country a dumping ground. Hence, it becomes an urgent need to address the problem of waste management and energy crisis. Municipal solid waste (MSW) thus serves as an efficient and reliable option for the conversion of waste to energy. The anaerobic digestion of solid waste to produce biogas is gaining importance. The growing need of the process involves increased efforts in reducing biogas plant design cost and optimizing process operation. This could be possibly done through mathematical modelling of the process. This paper particularly highlights the deviation of theoretical method with that obtained during experimentation through simulation results. Simulation is done in Mathematica and the concentration profiles of the substrate, anaerobic microorganisms and methane generation are plotted against various dilution rates and specific growth rate. The results reveal that at lower value of specific growth rate and dilution rate the experimental results fit best with the simulation result. This study can contribute in solving the complex unsteady state modelling equations of anaerobic digestion using Mathematica and pre-simulation of the experimentation results.
Folia Microbiologica, 1986
Anaerobic process modelling is a mature and well-established field, largely guided by a mechanistic model structure that is defined by our understanding of underlying processes. This led to publication of the IWA ADM1, and strong supporting, analytical, and extension research in the 15 years since its publication. However, the field is rapidly expanding, in terms of new technology, new processes, and the need to consider anaerobic processes in a much broader context of the wastewater cycle as a whole. Within the area of technologies, new processes are emerging (including high-solids and domestic wastewater treatment). Challenges relating to these new processes, as well as the need to intensify and better operate existing processes have increased the need to consider spatial variance, and improve characterisation of inputs. Emerging microbial processes are challenging our understanding of the role of the central carbon catabolic metabolism in anaerobic digestion, with an increased importance of phosphorous, sulfur, and metals as electron source and sink, and consideration of hydrogen and methane as potential electron sources. The paradigm of anaerobic digestion is challenged by anoxygenic phototrophism, where energy is relatively cheap, but electron transfer is expensive. These new processes are commonly not compatible with the existing structure of anaerobic digestion models. These core issues extend to application of anaerobic digestion in domestic plant-wide modelling, with the need for improved characterisation, new technologies having an increased impact, and a key role for the linked phosphorous-sulfur-iron processes across the cycle. The review overall finds that anaerobic modelling is increasing in complexity and demands on the modeller, but the core principles of biochemical and physicochemical processes, metabolic conservation, and mechanistic understanding will serve well to address the new challenges.
Modeling of Anaerobic Digestion of Sludge
Critical Reviews in Environmental Science and Technology, 2009
A.n. Li Ch Pr WAS X A X M FIGURE 4. Schematic representation of the Shimizu et al. (1993) model. Abbreviations: WAS = waste activated sludge, Pr = proteins, A.n. = nucleic acids, Li = lipids, Ch = carbohydrates, HAc = acetic acid, HPr = propionic acid, Hbu = butyric acid, HVa = valeric acid, HCa = caproic acid, X A = acidogenic biomass, X M = methanogenic biomass.
Anaerobic digestion models: A comparative study
7th Vienna International Conference on Mathematical Modelling, 2012
Based on the adoption of object-oriented modelling and simulation tools, in this paper a comparison between the ADM1 and the AMOCO models is investigated, mainly in order to assess the performance of AMOCO for control design. The ADM1 model has been calibrated with reference to the degradation of waste activated sludge, based on literature data, and assumed as reference model. Then, in order to compare the outputs of the two models, some variables of ADM1 have been lumped to match the relevant aggregated AMOCO variables. Since AMOCO failed in predicting the steady state values relevant to the inorganic carbon species and alkalinity, a new version of it has been developed, accounting for the dynamics of the inorganic nitrogen concentration. Steady-state and dynamic simulations based on this new version showed an improvement with reference to simulations obtained with ADM1.
Chemical Engineering Journal, 2013
In this study, the interactions between the microbial populations in an anaerobic digester leading to the acidification of the fermentation medium were investigated using numerical simulation in the Anaerobic Digestion Model No. 1 (ADM1). The anaerobic digestion of cattle manure at 10 g volatile solids (VS)/L and 35ºC was used as the case study. The numerical runs were performed using a factorial experimental approach with 2 levels. The minimum pH reached in the digestion was considered the response variable, whereas the initial concentrations of the main microbial groups included in the ADM1 were considered the factors. The statistical analysis demonstrated that the initial concentration of acetoclastic bacteria was the most critical variable in the acidification of the medium. It was estimated that permanent acidification occurred when the initial concentration of this group of microorganisms was less than or equal to 0.0838 g chemical oxygen demand (COD)/L, regardless of the population density of the other microbial groups.
A Formal Modeling Framework for Anaerobic Digestion Systems
2015 17th UKSim-AMSS International Conference on Modelling and Simulation (UKSim), 2015
The complexity of modeling the anaerobic digestion process meets the difficulty to describe and analyze them mathematically. In this paper, a simplified mathematical model for anaerobic digestion process of organic matter, in a continuous stirred tank reactor is proposed. With the aim of upgrading the produced biogas and integrate biogas plants in a virtual power plant, new control inputs reflecting addition of stimulating substrates (acetate and bicarbonate) are added. Based on two step (acedogenesis-methanogenesis) mass balance non linear model, a step-by-step model parameter's identification procedure is presented in the first step, then in the second step, the yield coefficients and the microbial growth rates are estimated when the later is assumed to be unknown a priori.
MODELLING AND SIMULATION OF METHANOGENIC PHASE OF AN ANAEROBIC DIGESTER
Journal of Engineering Research, 2009
A biological dynamic model for the methanogenic phase of an anaerobic digester with and without wall growth factor is developed for the substrate and microorganisms concentration. The model assumes a continuous feed of acetic acid to the continuously stirred anaerobic reactor. The model was numerically solved, without pH restriction, by the semi-implicit Runge-Kutta method combined with step-size adjustment strategy. The model was used for simulations on transient conditions namely the effects of initial conditions on the start-up of a digester and of changing the feed characteristics via a step increase in the influent substrate concentration for both cases of excluding and taking cognisance of microoganism growth on the digester wall. Inclusion of the wall growth factor in the model improves the stability of an anaerobic digester under drastic changes of its operational conditions. Simulated results obtained herein agree exceedingly well with the general observations in the literature.