J. Chem. Chem. Eng. 8 (2014) 834-840
Apparatus Prototype for Purpos of Teaching in
Bio-digesters
Martin Trinidad Martinez Garcia*, José Luis Magaña Ramírez and Rodrigo Mauricio Rodriguez Cuellar Department of Chemical Engineering, University of Guanajuato, Guanajuato 36000, México
Abstract: A mathematical model is developed bad on a simplified mechanism of anaerobic digestion. The main objective is to quantitatively analyze the digestion process to optimize operating conditions and maintenance of this equipment, which could be ud to test different materials and be able to apply the results to the possible scaling to bio-digesters installed in the field. The experiments were carried out in a hybrid system bio-digester photovoltaic cells. The bio-digester is made of stainless steel with dimensions to treat an average of 10 kg of raw material and produce biogas from different organic materials. The reactor has been conditioned with temperature nsors, pressure and methane gas that allow monitoring the concentration of the gas and the conditions of operation during the time of digestion. The system has a photovoltaic array to provide the energy required to keep the temperature constant. The experiment was conducted using materials such as goat manure mixed with
houhold waste, and various formulations of the materials were prepared. The experimental results were ud to test the mathematical model.
Key words: Biodigester, anaerobic digestion, methane production, biomass treatment.
1. Introduction
cj是什么In recent years, it has carried out the design and implementation of many types of bio-digester to produce biogas from organic waste in different areas. The most well-known type is the large-scale communal type, which fixed dome or floating [1]. In China, one of the first countries to systematically develop biogas technology for rural communities, it was obrved that the bio-digesters in scale often had certain disadvantages on their operation and implementation in rural communities, such as maintenance problems and high costs. The work reported in Refs. [1-3] above low-cost bio-digesters are dominated in general by the implementation and results obtained primarily in field tests, its result motivates them to perform the more systematic study of this phenomenon to improve the efficiency of the equipment and determine the performance in the production of methane in the stationary state. The anaerobic treatment process are microbiological *Corresponding author:Martin Trinidad Martinez Garcia, Dr., rearch fields: renewable energies and heat transfer. E-mail:****************.pr
ocess, which involve veral steps of biological made by specific groups of bacteria that work only in the abnce of air. Such procedures are often ud to remove waste, while promoting the generation of gas with some utility or application. The applications are becoming increasingly popular, for example, in the water treatment industry, which already have considerable advantages on aerobic process, including the low sludge production, the production of a uful fuel (methane, commonly called biogas), relatively high-performance and finally the generation of electricity.
All organic compounds convertible to biogas are known as volatile solid (S). Volatile solids reprent a portion of the power to form methane. The first stage of the process of biogas production is the conversion of the organic compounds in the simple carboxylic acids, as the result of hydrolytic activities of microorganisms. The cond pha is the formation of biogas, which is an anaerobic process due to methanogen bacteria [4]. The conversion of the carboxylic acids has two possibilities. The first is the desired conversion to CH4. However, in the
cond
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Apparatus Prototype for Purpos of Teaching in Bio-digesters 835
possibility, a part always inevitably becomes CO2 as a condary product of the metabolism of the organism. The anaerobic digestion is often identified three main steps:
(1) the hydrolysis of the complex organic matter;
(2) acidogenic pha, due to the production of volatile acids;
(3) methanogenic pha where the methanogen bacteria convert the volatile acids in the final product, CO2 and CH4 [1].
Between the volatile acids, acetic acid is the most important precursor of methanogenesis. Since the methanogen bacteria are the most nsitive, with the lowest growth rates, methanogenesis is often considered the step that controls the speed in the various work of modeling for this process [1, 5-7]. The u of a realistic and accurate model allows the study of performance of the anaerobic digester in transient conditions and measured quantitatively the stability of the process at different operating conditions. Andrews [1] prents a dynamic model for the study of the process of anaerobic digestio
n, considering only the reactions concerning the biological methanogenic pha of the process. Most of the mathematical models which are currently ud for the description of the biological diversity of the process are models of steady state and therefore cannot be ud to process of predicting performance during the start-up operations or in transient conditions resulting from changes in the loading process. Most models of steady state current of the process of anaerobic digestion are bad on the relationship between the limitation of the concentration of substrate and the rate of growth as propod by Yu [3, 5]. Especially, the development of dynamic models for biological process had been limited in the past, due to the analytical solutions of systems of nonlinear differential equations that reprent the process are not very simple to resolve. At prent, however, there are tools such as computers and various software analog simulations that facilitate the solution of such systems of differential equations.
The lectivity in the process of biogas production is given by the ratio between CH4formed to the unwanted CO2. The purpo of optimizing the production of biogas is not only to get the highest conversion of solid, but also to achieve the greatest possible lectivity of CH4. Scheme 1 show the reaction stoichiometry for the gasification is given by Yu [3]:
cancellingFor this reaction, it is ud the model of Monod kinetics [1] that considers the inhibition of the substra
功夫熊猫感恩节特辑te, i.e.:
μ=μmax
1 + Ks
S
+ I
Ki
(1) where, µis the specific growth rate, µmax is the maximum rate of growth, Ks is the constant of average speed, S is the concentration of substrate limiting growth, Ki is the inhibition constant and finally, I is the concentration of inhibitor material. The no dissociated acetic acid is considered as the limiting of the substrate S, and also as the inhibitor. Its concentration is determined bad on the assumption of equilibrium of the reaction of disassociation from the acetic acid. For the liquid pha in the reactor, it will have the following equations [3-5]:
For the mass balance:
d X短裙英文
dt
=F
V
X0−[X]+μX−K T T(2) For the balance of substrate:
d S
dt
=F
艾滋病英文简称
V
S0−[S]−μ
Y X
S
X(3) where, the rate of change in the substrate concentration is a function of X the concentration of total bacteria, F substrate addition rate, of V the volume of reactor and finally Y X/S is mol organism/mol substrate ratio.
For the rate of appearance of CH4:
Scheme 1 Chemical reaction for methane production.
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Apparatus Prototype for Purpos of Teaching in Bio-digesters 836
R CH
4=Y CH
4/X
μX(4)
The formation of CO2involves both the biochemical reaction and association of bicarbonates. The rate of appearance of CO2 is:
R COlor of the year
2=Y CO
2/X
μX(5)
A anaerobic digester can be defined as esntially as a system of three pha current. The propod model assumes a gaous pha in contact but not in
equilibrium with the liquid pha. In the gaous pha, it is assumed that the gas obeys the ideal gas law. The methane is suppod to be insoluble in water and directly transferable to the gas pha, while part of CO2 generated dissolves in the liquid pha producing carbonic acid which, depending on the pH dissociates into bicarbonate ions and carbonate, and another part of CO2 escapes into the gas pha at a given speed by the equation:
T G=K L K H P CO
2
−CO2D(6) where, T G is the transfer speed of CO2 in the gas pha to a liquid, K L is the mass transfer coefficient, K H is constant, the P CO2of Henry is the partial pressure of CO2 and [CO2]D is the concentration of CO2 dissolved.
2. Experiments
2.1 Experimental Setup
有道2.1.1 The Mounting and Asmbly of the Equipment
Initially, the equipment is cleaned and verified that the measuring instruments and auxiliary are in good condition and working well. The cond step is to weigh the amount of material required, which in this ca is 2 kg, the properties of the goat manure ud in the experimentation are show in Table 1, and then the material is added to the bioreactor, and then add 4 L of water. The third step is to clo and al the equipment(Fig. 1), which has a rubber gasket, clos with 6 bolts of 0.5 in and is aled with silicon. The nsors connected to a computer for the control and registration of temperat
ures, and a gas nsor to Fig. 1 A general diagram of the experiment.
Fig. 2 Experimental hybrid system of the biodigester showing components.
Fig. 3 Biodigester with storage and methane gas nsor. quantify the production of methane (Fig. 2). In addition, a sample is taken to determine the pH and the percentage of moisture.
2.1.2 Photovoltaic Cell
There are a couple of photovoltaic cells with an output voltage of 22 V which have been connected in ries to provide energy to the batteries of support ud (Fig. 3). The cells have the option to vary
its
cream是什么意思All Rights Rerved.
Apparatus Prototype for Purpos of Teaching in Bio-digesters 837
inclination, and the most appropriate is 21° for the city of Guanajuato. The Fig. 4 shows the data acquisition process on the computer during experimentation time.
2.2 Experimental Methodologygo agent
The operation parameters in the biodigester are show in Table 2, and the steady-state operation is obtained by integration of the system of differential equations considering a time interval of large operation to bring the resulting to zero and solve the non-linear resulting from system of simultaneous equations [5, 8]. Fig. 5 shows modeling results for total concentration of substrate along the experimentation. The measurement data are ud to validate the mathematical model predict the biogas production rate (Fig. 6) and lectivity of methane production during the formation of carbon dioxide. The results obtained with the experimentation (Fig. 7) and contrasted with the mathematical model prented Table 1 Some properties of the goat manure ud in the experimentation.
Property Weight of sample (kg/kg)
skipalongWet droppings 0.036
Total of solids 0.0107
Moisture content 70%
Volatile solids 0.091
Total nitrogen 0.04
Fig. 4 Data acquisition software for the concentration of gas with the gas nsor CH4. Table 2 Operation parameters in the biodigester. Parameter Value Manure (%) 15
Total volumen of liquids (m3) 9.1 Retention time (Day) 30
Total solids (%) 4
Start of biogas production (Day) 15
Daily production of biogas (m3) 1.5
Room temperature (ºC) 21.5
Digester temperature (ºC) 37
Acidic level (PH) 7
here were reasonably good. What makes it possible to propo a systematic methodology and improve the operation of the bio-digester with other materials. Finally the mean temperature for CH4
production was 35 o C during the experimentation time as shown in Fig. 8.
3. Results and Discussion
The development of the model suggests the following:
(1) Methanogenesis is the rate limiting step in speed in the process;
(2) The substrate under consideration is the acetic acid.
The anaerobic digestion offers interesting alternatives for resolving problems of environmental pollution, either for the conventional treatment of waste or for the specific u of some of them. The u of a function of inhibition to the substrate and the microorganisms in the mass balance is esntial to develop an appropriate model for anaerobic process due to the inhibition of the biological growth. This inhibit function is important becau it implies a clo relationship between the concentration of acid and the speed of growth for the methanogen bacteria.
In general, the experimental production of biogas was obtained from the fourth day of anaerobic digestion. When the pressure reached values clo to 1.3 psi, some samples are taken for quantify the methane by chromatographic analysis. As en in Fig. 7 dotted line, the solid line reprents the
results with the theoretical
model. The model prented a is for All Rights Rerved.
Apparatus Prototype for Purpos of Teaching in Bio-digesters
838
Time (day)
Time (day)
S r e n t r a t i o n
V o l u m e M e t h a n e C H 4m L u s t r a t e c o n c e r t r a t i o n (g /L ) V o l u m e m e t h a n e C H 4 (m
L )
