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Modelling the energy balance of an anaerobic digester fed with cattle manure and renewable energy crops. Water Res

Institute of Water Quality Control, Technische Universität München, Am Coulombwall, 85748 Garching, Germany.
Water Research (Impact Factor: 5.32). 11/2007; 41(18):4085-96. DOI: 10.1016/j.watres.2007.05.061
Source: PubMed

ABSTRACT Knowledge of the net energy production of anaerobic fermenters is important for reliable modelling of the efficiency of anaerobic digestion processes. By using the Anaerobic Digestion Model No. 1 (ADM1) the simulation of biogas production and composition is possible. This paper shows the application and modification of ADM1 to simulate energy production of the digestion of cattle manure and renewable energy crops. The paper additionally presents an energy balance model, which enables the dynamic calculation of the net energy production. The model was applied to a pilot-scale biogas reactor. It was found in a simulation study that a continuous feeding and splitting of the reactor feed into smaller heaps do not generally have a positive effect on the net energy yield. The simulation study showed that the ratio of co-substrate to liquid manure in the inflow determines the net energy production when the inflow load is split into smaller heaps. Mathematical equations are presented to calculate the increase of biogas and methane yield for the digestion of liquid manure and lipids for different feeding intervals. Calculations of different kinds of energy losses for the pilot-scale digester showed high dynamic variations, demonstrating the significance of using a dynamic energy balance model.

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    • "Substrate composition in terms of particulate carbohydrates, proteins and lipids was defined within the input stream, and a similar influent characterization approach as described in [27] was performed. The conversion of the analytical fractions, which are analyzed on a volatile solids (VS) basis, into COD units was performed using COD conversion factors for carbohydrates (1.19 g COD g VS "
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    Applied Energy 03/2015; 142:352-360. DOI:10.1016/j.apenergy.2015.01.014 · 5.61 Impact Factor
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    • ". b Calculated based on Ref. [25]. c Calculated based on Ref. [27]. "
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    • "). This value is similar to the value used by Lübken et al. [21] for the modeling of anaerobic digestion of cattle manure (7 d À1 ). Silva et al. [29] used a value of 13.2 d À1 for the modeling of anaerobic digestion of evaporator condensate. "
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    ABSTRACT: In this study it is demonstrated that a correct description of the mixing behavior of an anaerobic digester is necessary to accurately model and predict the reactor performance, especially at a larger scale operation. A lab-scale (3.78 l) and a pilot-scale (120 l) anaerobic digester were operated at both mixing and non-mixing conditions. At lab-scale no significant difference in performance was found between these conditions. In each case about 0.25 lCH4/lreactor/d of biogas was produced. The model predictions were in close agreement with measured values. At pilot-scale, however, the influence of mixing became important. A reduction of about 10% of methane production occurred during unmixed conditions. Furthermore also a build-up of volatile fatty acids (up to 3 gCOD/l) prevailed. This behavior could not be predicted by using a CSTR approach. In contrast, it was accurately predicted with the proposed model, which includes a more rigorous mixing next to common reaction kinetics. Prediction of the daily biogas production assuming a perfectly mixed reactor revealed an overestimation of the biogas production by 10%. It is therefore recommended to use more accurate mixing models in order to predict biogas production from anaerobic digesters.
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