Modelling of slaughterhouse solid waste anaerobic digestion: Determination of parameters and continuous reactor simulation (original) (raw)
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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.
This paper deals with the assessment of daily methane yield from anaerobic digestion (AD) of slaughterhouse waste using mathematical modelling based on data obtained from 15 days long experimental period. The experiment is carried out in laboratory scale continuous stirred tank reactor (CSTR) operated under different temperature and mixing conditions. The waste mixture was composed of two input substrates: manure from cattle depots and vehicles for cattle transport (labelled as O1) and inedible offal, stomach contents, sludge from washing and cleaning, and the meat leftovers (labelled as O2). The ratio used was O1:O2=80:20. The results show that operating temperature of 35 o C and mixing speed of 20 o /min is the most promising modus of work that produces stable yield but with lower methane quantities.
A simple kinetic model applied to anaerobic digestion of cow manure
Environmental Technology, 2020
A simple model of anaerobic degradation in a continuous stirred digester is presented. The hydrolysis of cow manure was modelled as consisting of two fractions, one rapidly degradable and the other more slowly degradable, and both processes were represented by first-order kinetics in a two-substrate first-order (TSFO) model. The fractions were separated by water flushing. Biomethane potential (BMP) tests were performed to determine the hydrolysis constant and biodegradability of each fraction. The hydrolysis constants of the rapidly and slowly degradable fractions were 0.278 and 0.069 d −1 , respectively. Coupled with a simple anaerobic digestion model, the TSFO model was used to simulate the digester behaviour and predict methane production. Experiments in a 3.0 L digester were used to determine the decay constant and yield values and to validate the model. Two solid loads (2.9 and 4.4 gVS/L.d) were applied to the digester, and the dynamics of both biodegradable fractions, the non-biodegradable fraction and the microorganism concentration were reproduced by the model. These results approximate the actual biodegradable solids removal to within 85%. A parametric sensitivity study was performed, and the results show that the hydrolysis constant mainly influences the biodegradable fractions and that the decay and yield parameters mainly influence the microorganism concentration.
Design, Development and Evaluation of Slaughterhouse Anaerobic Digestion Plant Model
ABSTRACT: While extensive researches have been and are being carried out on biogas production from cow dung from abattoirs, the need to design, develop and evaluate a biogas plant specifically for the treatment of abattoir waste, production of biogas and compost materials has not received the attention of researchers. It was for this reason that this was explored in this study. An abattoir biogas plant model comprising of a 2.5 m3 equalization tank, 2.5m3 digester, 0.7m3 gasholder and 2.5 m3 digestate collection tank as well other appurtenances was developed and evaluated. The Modified gompertz model was used to describe the cumulative production. The total biogas produced was 0.61m3 while the maximum biogas potential was 0.771m3 . The maximum biogas production was 0.037 m3 /day while the lag phase was 10.53 days implying that it took the microorganisms more than 10 days to acclimatize and begin active digestion for biogas production. The parameters obtained would provide useful information for the eventual development of the prototype abattoir biogas plant
A review of simple to scientific models for anaerobic digestion
Renewable Energy, 2014
To fully model the anaerobic digestion process, biological and physico-chemical background, the kinetics of bacterial growth, substrate degradation and product formation have to be taken into account. The presented approaches differ depending on the requirements and the developer of the model. Important parameters affecting the process such as temperature, which can cause great inaccuracy, are rarely included in the models. Simple calculators are also available that estimate the applicability of the process to a specific farm and provide information to a farmer or a decision maker. Six simple calculators are presented in this study: AD decision support software, Anaerobic Digestion Economic Assessment Tool, BEAT 2 , BioGC, FarmWare and GasTheo. The simpler calculators mainly use the relation that exists between volatile solids and biogas production. A tested case of 100 dairy cows and 50 sows was applied to the simple calculators to compare the results.
Biochemical Engineering Journal, 2013
The anaerobic co-digestion of cow manure and waste paper at ambient temperature condition was observed to be optimized at a mix proportion of 75:25 respectively. The development and testing of a set of simplified anaerobic digestion models (SADM's) for this mixture revealed that the Hill's based biogas yield rate model was most appropriate in describing the kinetics of biogas production. Parameter estimation using non-linear regression revealed that the half saturation constants expressed as acidified substrate and volatile solids equivalents were 0.228 g/L and 5.340 g VS/L respectively, and the maximum specific biogas yield rate and biodegradability were 2.2 mL/g VS/day and 0.313 respectively. The coefficients "n" and "m" indicative of acidogenic bacterial adaptation for degradation and acetogenic/methanogenic bacterial cooperativity were estimated to be 1.360 and 2.738 respectively, while hydrolysis/acidogenesis was considered the rate limiting step. The need of bacterial adaptation may be an important factor to consider during anaerobic modeling of complex biomass.
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 .
MATHEMATICAL MODELLING FOR THE CONVERSION OF ANIMAL WASTE TO METHANE IN BATCH BIOREACTOR
An investigation was conducted to predict the behaviour of microbial processes leading to the production of biogas from animal waste. Mathematical model were developed for the prediction of the behaviour of microbial processes. The development of the models was based upon a material balance analysis of the digester operation, substrate utilization, cell growth and product formation. The model was solved using Runge kutta numerical technique embedded in polymath software. The digesters' operations simulated with a starting valve of 300g/dm 3 as the concentration of the substrate and 1.5g/dm 3 as the concentration of the cell, within a period of 13days. The results of the simulation show that the substrate concentration shows exponential decline from (300g/dm 3 to 6.88g/dm 3 ), the cells growth shows exponential trend from (1.5g/dm 3 to 39g/dm 3 ) The rate of growth of cell was increased from (0.5g/dm 3 -2.53g/dm 3 ), death increased from (0.015g/dm 3 to 0.161g/dm 3 ) over the 13days and the biogas production which is the product also follow the exponential trend from (zero concentration to 219g/dm 3 ). In all the model does the prediction well on all the parameters simulated, so it was can be used to predict the product formation rate as well as the design of reactor or digester.
Process Simulation Model for Anaerobic Digestion
In this study, a novel process simulation model (PSM) was developed for anaerobic digestion using Aspen Plus ® (version 7.3.2). PSM has two parts, one for hydrolysis working based on extent of reaction and the other on kinetics of reactions. A total of 53 reactions were used in the model including inhibitions, rate kinetics, pH, ammonia, volume and HRT. Each reaction set in the kinetic reactor has a FORTRAN program to calculate the kinetics of biogas production. PSM was validated with earlier research studies and industrial experiments in Aspen Plus ® . The P-value after statistical analysis was found to be 0.324, which showed there was no significant difference between different validations, even after a change in process conditions, loading rate, HRT and substrate. The sensitivity analysis with a ±10% change in composition and extent of reaction would result in average 4.56% higher value than the experimental value.
Kinetic model for anaerobic digestion of livestock manure
Enzyme and microbial …, 1999
Two unstructured segregated kinetic models to describe the anaerobic digestion of livestock manure are developed and experimental batch data obtained from beef cattle in a 2.0-l work volume digestor fitted to both proposed kinetic models to obtain the values of the parameters. The results obtained by fitting show that the second model proposed has both statistical and physical meaning in the parameter values obtained. The model takes into account a simplified reaction scheme formed by six reactions. Several simplifications have been made (lumping, pseudo-steady state for one compound, first order kinetics, etc.) yielding four key compounds to be analysed and fitted to the model as production-rates expressions (total biomass, chemical oxygen demand (COD), volatile acids, and methane). The model considers three main stages in the process: enzymatic hydrolysis of the waste, growth of 'acetogenic' microorganisms (production of acids nongrowth associated), and growth of 'methanogenic' microorganisms associated with methane production; the two last processes are accompanied by substrate consumption for maintenance. A non-linear multiple-response regression technique coupled to a fourth-order Runge-Kutta algorithm has been employed to obtain the values of the ten parameters. The model is able to reproduce the experimental data obtained for beef manure anaerobic digestion with more accuracy than experimental error.