An analytical model to study the performance of an anaerobic digester (original) (raw)
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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 .
Design considerations and operational performance of anaerobic digester: A review
Cogent Engineering, 2016
Due to the decline in fossil fuel reservoirs, the researchers emphasized more on the production of biogas from organic waste. Producing the renewable energy from biodegradable waste helps to overcome the energy crisis and solid waste management, which is done by anaerobic digestion. Anaerobic digestion is the controlled breakdown of organic matter into methane gas (60%), carbon dioxide (40%), trace components along with digested used as soil conditioner. However, there is vast dearth of literature regarding the design considerations. The batch digestion system yields a cost-effective and economically viable means for conversion of the food waste to useful energy. It is therefore recommended that such process can be increasingly employed in order to get and simultaneously protect the environment. This paper aims to draw key analysis and concern about the design considerations, analysis of gas production, substrates and inoculua utilization, uses and impacts of biogas.
2006
An anaerobic digester of 10 dm 3 capacity has been operated in batch mode at an optimum temperature of 40 o C and pH 6.8 using vegetable market-waste as the feed material. The effect of slurry concentration and that of the concentration of carbohydrate, protein and fat in the slurry on the biogas production rate and methane concentration in the biogas have been studied. A maximum concentration of methane in the order of 80% has been obtained. The liquid medium of a running digester based on vegetable market waste has been used as seed culture. Both acidogenic and methanogenic bacterial strains have been isolated from the broth. Growth kinetics of acidogenic bacteria have been determined using carbohydrate, fat and protein individually as limiting substrates. Kinetics of exponential growth of methanogenic bacteria have been determined using different volatile fatty acids and long chain fatty acids as substrates. In all the cases, Monod type model has been observed to fit well with th...
Validation of a simple kinetic modelling approach for agro-industrial waste anaerobic digesters
Chemical Engineering Journal, 2015
Anaerobic co-digestion of agroindustrial wastes constitutes a promising option for the stabilisation of residues producing biogas. A mixture of bovine ruminal content, tannery carving fat and activated sludge purge was considered for this work. Biodegradability tests for individual wastes and for the mixture of wastes were performed in batch and also in continuous conditions in a completely mixed reactor. The continuous reactor was operated at 30-day average residence times with a load volume of 3.0 g VS/L.d, reaching a VS removal efficiency of 66%, and yielding 0.38 L CH4 /kg VS added and 0.58 L CH4 /kg VS removed. A first order kinetic model with time delay was used to describe the behaviour of the whole process. The determination of parameters was performed in both systems using direct search methods. Monte Carlo methods were used in order to determine the range of parameters. Ultimate methane yield of 90 ± 6% was obtained from batch tests and 88 ± 9% in the continuous reactor. The kinetic rate constant in the reactor (0.205 ± 0.013 d-1) was twice the value obtained in batch conditions (0.089 ± 0.010 d-1), showing that microbial adaptations occurred in the continuous mode.
Paper IGRC, 2008
The interest in biogas plants to produce the renewable energy source "biogas" is unbroken. The number of plants is increasing as well as the average plant size. A trend of the last years is the growing interest in substituting natural gas by treated biogas in natural gas networks. The option to convert biogas to (bio) natural gas quality is primarily relevant for large-scale biogas plants. Due to increasing investment and operating costs, the need for a fully developed design and optimised operation increases for profitable operation of large-scale plants. The development of an appropriate model for the complete process is an important step in this direction. Crucial elements of a complete process model are detailed models for the upgrading process and the anaerobic digestion.
Fuels
Anaerobic digestion is a promising method of organic waste valorisation, particularly for fish farm waste, which has experienced a high growth rate in recent years. The literature contains predictive mathematical models that have been developed by various authors, allowing the prediction of the composition of bio-gas production from organic waste. In general, Monod’s kinetic expression is the basis for describing the enzymatic reaction rates for anaerobic digestion. In this work, several parameters are taken into account, such as temperature, cell growth inhibition, and other operating parameters, and systems of differential equations coupling the kinetics and stoichiometry for bio-reactions are applied to better describe the dynamics. Because of the high number of initial parameters that need to be defined for the anaerobic digester, the use of this model requires significant resources and a long calculation time. For this reason, a global sensitivity analysis (GSA) is applied to t...
2017
In 21 st century, sustainable development has a colossal and crucial role to play in global environmental apprehensions such as GHG emission from fossil fuel combustion, damage to the environment by the haphazard disposal of waste. Under these current circumstances, biogas production technology has flourished and has proved to be a meritorious success story today. Biogas is produced by microbial anaerobic digestion of organic wastes such as animal waste, plant material, sewage crops etc. Biogas principally comprises of 50% -60% of methane and 25%-45% of CO2. In the recent past, research on this technology has been limited to some extent due to the complex phenomenon existed with various factors and parameters influencing it. Optimization of parameters like organic loading rate, pH, C/N ratio, total solids, volatile solids content hydraulic retention time and temperature of the digester will have a synergistic effect on the yield. Adopting the principle of co-digestion, for biogas pr...
Water science and technology : a journal of the International Association on Water Pollution Research, 2007
Different digestion technologies for various substrates are addressed by the generic process description of Anaerobic Digestion Model No. 1. In the case of manure or agricultural wastes a priori knowledge about the substrate in terms of ADM1 compounds is lacking and influent characterisation becomes a major issue. The actual project has been initiated for promotion of biogas technology in agriculture and for expansion of profitability also to rather small capacity systems. In order to avoid costly individual planning and installation of each facility a standardised design approach needs to be elaborated. This intention pleads for bio kinetic modelling as a systematic tool for process design and optimisation. Cofermentation under field conditions was observed, quality data and flow data were recorded and mass flow balances were calculated. In the laboratory different substrates have been digested separately in parallel under specified conditions. A configuration of four ADM1 model re...
Initial rates technique as a procedure to predict the anaerobic digester operation
Biochemical Engineering Journal, 2011
In this study a novel and practical procedure was developed, that involves: initial methane production rate measurement in batch tests, kinetic parameters determination and modeling application in a continuous digester. The procedure was evaluated with three experimental conditions: raw sludge as substrate incubated at 35 • C and 55 • C and thermal pretreated sludge incubated at 35 • C. The initial specific methane production rate was fitted with the Monod type equation in order to calculate the kinetic parameters. The values obtained for the maximum specific methane production rate were 0.043, 0.143 and 0.052 gCH 4 gVS I −1 d −1 for each experimental condition, aforementioned. The substantial increment of this parameter at thermophilic condition shows the differences in the specific maximum growth rate between thermophilic and mesophilic populations. The affinity constant values were 3.842, 4.790 and 4.623 g L −1 for each experimental condition; however, a significant uncertainty was obtained due to some identification problems. A preliminary validation of the procedure was applied for predicting the operation of a continuous digester treating raw sewage sludge. The overall behavior of the system was represented by the model, although it slightly underestimates the experimental values, by approximately 20%. The results achieved, indicate that the procedure may be used as a tool in a real scale operation; however, further research must be performed.