Kinetic study of biogas production from energy crops and animal waste slurry: Effect of organic loading rate and reactor size

Abstract

To cite this article: P. Mähnert & B. Linke (2009) Biogas production in agriculture is processed mostly continuously at mesophilic temperatures in completely stirred tank reactors. Therefore, reactor performance data were studied in long-term semi-continuous laboratory-scale experiments with maize silage, whole-crop rye silage and fodder beet silage as mono-substrate and cattle slurry at mesophilic temperatures. For calculation of biogas yield as function of the organic loading rate, a hyperbolic equation was developed on the base of a first-order reaction rate for substrate degradation. The biogas yield depends also on the maximum biogas yield, the concentration of volatile solids of the input, the density of the effluent, the density of the biogas and the reaction rate constant, which are all substrate-or process-specific. Values of the theoretical maximum biogas yield and the reaction rate constant were observed in the range 0.61-0.93 m 3 per kg volatile solids and 0.032 -0.316 d − 1 , respectively. By means of the hyperbolic equation, the proportion of the biogas yield from the maximum can be calculated for the first and a second reactor which also depends on the volume of each reactor. Keywords: biogas yield; modelling; organic loading rate IntroductionSince the amendment of the Renewable Energy Sources Act in Germany (Erneuerbare Energien Gesetz) the utilization of energy crops for biogas production has become more cost-effective. The treatment of animal waste slurry and energy crops in co-digestion is a proven technology and recently interest has grown in the potential of using anaerobic processes [1,2]. With respect to energy crops as a single substrate in mono-digestion pioneer work was performed with sorghum ( Sorghum bicolor ), napiergrass ( Pennisetum purpureum ), corn ( Zea mays ), and sorghum/alpha-cellulose in mix experiments about 15 years ago [3]. Further laboratory-, pilotand farm-scale experiments were conducted to obtain kinetic data for anaerobic digestion of energy crops and crop residues [4][5][6][7][8][9][10][11]. Numerous full-scale biogas plants are in operation and digest mainly maize silage, whole crop cereal silage and mixtures of other energy crops.The financial success of a biogas plant results from the quality and the biogas yield of the applied substrate and the process engineering. However, agricultural biogas plants in practice are mostly processed intuitively because the measurement engineering is not improved adequately. Additionally, for energy crops the experience is difficult to generalize because of the great diversity of substrates. Furthermore, high-energetic

Giant reed (Arundo donax L.) for biogas production: land use saving and nitrogen utilisation efficiency compared with arable crops

“…Grasses and other lignocellulosic feedstock have been extensively studied as interesting biomasses for biogas production (Lehtomäki et al, 2008;Nizami et al, 2009;Massé et al, 2010;Kandel et al, 2012). Although BMP is the most important parameter, anaerobic digestion kinetics is also relevant, since a higher methane production rate leads to better yields in real-scale plants (Mähnert and Linke, 2009;Grieder et al, 2012). Furthermore, it is important to note that chemical composition of crops influences their biomethane production.…”

Technologies and Varieties of Fodder Beet in Organic Farming

“…Besides the traditional use of fodder beet as the dietary food new ways of use appear. It is the use in bioenergetics, such as the production of bioethanol (Reed et al, 1986;Mähnert and Linke, 2009;Chochola, 2007;Pulkrábek et al 2007) and biogas (Scherer, et al, 2009;Klocke et al, 2007). Use of fodder beet as a source of renewable energy results from the fact that it provides more energy than cereals and fodder crops Hnilička et al, 2009;Martínez-Pérez et al, 2007).…”

Process Optimization and Modeling of Anaerobic Digestion of Cow Manure for Enhanced Biogas Yield in a Mixed Plug-flow Reactor using Response Surface Methodology

“…As shown in Table 4, the 'Prob > F' value for the models were <0.0001 (p-value < 0.05), which indicates that the models were statistically significant with a confidence interval of 99.99%. 14 ) imply that the models were significant and that there was only a 0.01% chance that a 'Model F-value' could occur because of noise. The actual and the predicted bio-gas and methane production are shown in Fig.…”

“…According to previous research, the performance of animal waste-fed anaerobic digesters is affected by important process parameters such as the temperature 12,13 , organic loading rate (OLR) 14 , and mixing regime 15 . In the past literature, The technique of RSM has been used to optimize, evaluate and analyze the interactive effects of autonomous agents in numerous biochemical, bioenvironmental processes and chemical , but its use to the modeling of anaerobic digestion processes and analysis has been presented only few studies 16,17 .…”