Production of nopal-based biogas

Proceedings of the 2018 IISE Annual Conference Espinosa-Garza G., Loera-Hernández I., Antonyan N., eds.

Production of nopal-based biogas Abstract ID: 1508

Espinosa Garza G., Loera Hernández I., Antonyan N., Cárdenas Barrón L., Villanueva Vega V., Espino Barros M., Conde Rodríguez C., Díaz Meraz C., Ayora-Peón R., PérezSuazo A. Tecnologico de Monterrey, Escuela de Ingeniería y Ciencias, Eugenio Garza Sada 2501, Monterrey, N.L., Mexico, 64849, Mexico. Abstract This research work presents an analysis of the possibilities to increase cactus biodegrability in a mixture with other types of biodegradable substances that can be degraded in a biodigestor. Based on the results obtained, the optimal amounts of biomass of the cactus Opuntia ficus, cow manure and water to generate biogas in the most efficient manner were determined. The prototype of the biodigestor designed based on the results obtained was approved by a Mexican company of the agricultural sector. The materials used for the fabrication of the biodigestor have a duration of 15 years. The viability studies performed showed high performance of the mixture used in the biodigestor. The technology used and the low maintenance cost makes the project economic for its sustainable use and demonstrates its competiveness to be expanded for use in small and medium businesses. A comparative analysis of the production of biogas between the different types of entries that the biodigestor can have is presented. The biodigestor designed is capable of producing methane (CH4) in a cheap and optimum way, taking advantage of the waste. Because it is isolated and completely closed off, it allows the decomposition process to be faster and more efficient.

Keywords Biodigestor, decomposition process, nopal-based biogas, sustainable

1. Introduction Currently in Mexico, there are great amounts of nopal that are grown in a wild form. This plant is mostly consumed in a natural way, and it is also processed and transformed in products such as candies, sweets, snacks, etc. The nonconsumed nopal as well as the leftovers of the productive processes generate lots of waste that can be used for biogas generation. The molecular structure of the plant, the high performances of its biomass, the wide adaptation range, its rapid growth, its low nutrient requirements such as soil and water, converts it into an important bioenergetic source. The latter is through the nopal’s conversion to biogas through its anaerobic digestion [1]. Currently, 80% of the world´s overall energy supply of about 400 EJ per year is derived from fossil fuels. Nevertheless, roughly 10-15% of this demand is covered by biomass resources. Biomass combustion is responsible for over 90% of the current production of secondary energy carriers from biomass, making biomass by far the most important renewable energy source used to date [2]. Thanks to the development of new technologies, it has been discovered that the nopal biomass can become a renewable source with lots of potential. This one has the capacity to provide solid, liquid, and gas biofuels that can be used to produce heat, electricity, and fuel. The latter represents an excellent opportunity to diversify the productive activities of nopal producers. Through the energy auto-generation from nopal wastes, more rural employment can be generated, thus elevating the farmers´ quality of life [3]. Aerobic digestion of cow manure and organic waste for biogas treatment and production can be used as renewable energy. This process is commonly undertaken in a biodigester [4, 5]. Methane has a heat combustion approximately of 882 kJ/mol and can be mostly employed as domestic fuel. Currently estimates of different greenhouse gas emissions coming from cattle raising are being realized in diverse countries of the world. Although there are no up to date estimates of methane emissions coming from cattle raising in Mexico, we know that methane´s production represents between 7 and 15% of gross consumed energy by cattle raising. All actions directed to reduce these losses will contribute to a more efficient and friendlier cattle-raising activity with regards to the environment.

Espinosa-Garza G., Loera-Hernández I., Antonyan N., eds. The goal of this research consists in showing that with a mix of nopal and bovine manure, it is possible to generate biogas whose main component is methane with the goal to produce sustainable energy to be used in farms. As a final result, optimal amounts of nopal and manure will be obtained, which will generate biogas in a more efficient way. The separated production capacity of biogas production by nopal and manure will also be compared. To carry out this project, two completely sealed bioreactor prototypes were generated.

2. Problem Definition It must be recalled that a biodigestor is a simple and practical alternative that allows biogas production through the decomposition of organic wastes. A biodigestor usually consist of a totally hermetic container where wastes are introduced and thanks to an anaerobic digestion process, biogas mainly consisting of methane is produced. This will create a cheaper and more environmentally friendly energy remedy. As mentioned above during the project realization, various alternatives were analyzed to contemplate their advantages and disadvantages for their development in the region of the state of Nuevo Leon, Mexico, and its surroundings. Finally, it was decided to develop the fabrication of biodigestors using nopal and manure as a base, taking into account different factors that are considered feasible of the biodigestor itself:  Innovation: unlike the existing biodigestors in the market, in the present project, suitable percentages of two organic matters are determined to produce a higher amount of methane.  Sustainability: by capturing the methane emissions generated by manure inside the biodigestor, it is possible to reduce their atmospheric emissions. Additionally, the user would be taking advantage of the nopal, a resource that was before considered as waste, which results in savings and increased productivity.  Economic Surroundings of the Region: the state of Nuevo Leon and its surroundings are known for having great economic activity. In this zone, a great amount of money is circulated and a bioenergy generation will generate new opportunities for small and medium enterprises.  Weather Conditions: the weather conditions of the region allow the easy obtainment of sunlight and heat so that the masses inside the biodigestor can react and generate methane in an optimal way. During the project development, different factors were considered to be taken care of at the moment of producing the biodigestor:  The temperature inside the biodigestor has to be constant most of the time.  Air entry must be avoided inside the biodigestor to avoid outside microorganisms from stopping the anaerobic fermentation process.  Manure or animal urine treated with antibiotics, as well as residuals from fungicides or insecticides must not be used. The former with the goal to not hinder the biodigestor’s operation.  Humidity in the biodigestor may depend of the amount of water present in the raw matter.  The decrease of the biodigestor efficiency must be avoided. The latter is achieved by ensuring that no more than 25% of vegetable waste is added at a time. The production of biogas is done in 4 stages of waste decomposition:  Hydrolysis: the organic material is transformed in liquid monomers and polymers due to bacteria presence. In this stage, protein amino acids, carbohydrate monosaccharides and fatty acids from fats are produced.  Acid genesis: the products of this first stage are transformed into volatile acids, ketones, alcohol, carbon dioxide and hydrogen due to the acidogenic bacteria in the mixture. Procionid acid (𝐶𝐻3 𝐶𝐻2 𝐶𝑂𝑂𝐻 ) , acetic acid (𝐶𝐻3 𝐶𝑂𝑂𝐻), butyric acid (𝐶𝐻3 𝐶𝐻2 𝐶𝐻2 𝐶𝑂𝑂𝐻) , formic acid (𝐻𝐶𝑂𝑂𝐻), ethanol (𝐶2 𝐻5 𝑂𝐻 ) and lactic acid (𝐶3 𝐻6 𝑂3 ) are produced.  Acetogenesis: hydrogen, carbon dioxide, and acetic acid from the second stage products are obtained. The hydrogen is the main component of this stage since it allows acid conversion at a low pressure.  Methanogenesis: hydrogen and acetic acid are obtained due to the activity of the microorganisms in the mixture. The microorganisms of this stage are completely anaerobic. Once the stages are finalized, biogas is obtained. 2.1 Chemical Reactions: Hydrolysis: the equation shown represents the step where the organic matter gets decomposed into simple sugar, in this case, glucose: 𝐶6 𝐻10 𝑂5 + 2𝐻2 𝑂 → 𝐶6 𝐻12 𝑂6 + 𝐻2 (1)

Espinosa-Garza G., Loera-Hernández I., Antonyan N., eds. Acid Genesis: the equations below shows how glucose is converted into ethanol (2), into propionic acid (3) and into acetic acid (4): 𝐶6 𝐻12 𝑂6 → 2𝐶𝐻3 𝐶𝐻2 𝑂𝐻 + 2𝐶𝑂2 𝐶6 𝐻12 𝑂6 + 2𝐻2 → 2𝐶𝐻3 𝐶𝐻2 𝐶𝑂𝑂𝐻 + 2𝐻2 𝑂 𝐶6 𝐻12 𝑂6 → 3𝐶𝐻3 𝐶𝑂𝑂𝐻

(2) (3) (4)

Acetogenesis: the equations below show the conversion of propionic acid into acetate (5), while equations (6) and (7) show how glucose and ethanol are covered into acetate. 𝐶𝐻3 𝐶𝐻2 𝐶𝑂𝑂𝐻 + 2𝐻2 𝑂 → 𝐶𝐻3 𝐶𝑂𝑂𝐻 + 6𝐻 + 𝐶𝑂2 (5) 𝐶6 𝐻12 𝑂6 + 2𝐻2 𝑂 → 2𝐶𝐻3 𝐶𝑂𝑂𝐻 + 2𝐶𝑂2 + 4𝐻2 (6) 𝐶𝐻3 𝐶𝐻2 𝑂𝐻 + 𝐻2 𝑂 ↔ 𝐶𝐻3 𝐶𝑂𝑂𝐻 + 2𝐻2 (7) Methanogenesis: microorganisms called methanogens convert hydrogen and acetic acid into methane and carbon dioxide, as shown in equations 8, 9 and 10: 𝐶𝑂2 + 4𝐻2 → 𝐶𝐻4 + 2𝐻2 𝑂 (8) 2𝐶2 𝐻5 𝑂𝐻 + 𝐶𝑂2 → 𝐶𝐻4 + 2𝐶𝐻3 𝐶𝑂𝑂𝐻 (9) 𝐶𝐻3 𝐶𝑂𝑂𝐻 → 𝐶𝐻4 + 𝐶𝑂2 (10) 2.2 Prototype 1 In the first prototype, four tests were done according to Figure 1, with each one of them with different proportions of nopal, manure, and water. The purpose was to detect which test would give the expected result: methane production. In the 20-liter capacity jug nozzle a universal package was placed to introduce PVC material. To ensure the hermeticity and null movement of this part, a clamp was placed and squeezed to the point of preventing the package from having movement. Then a 25-cm PVC tube was introduced for the gas exit. All made connections were sealed with special glue for PVC, so that no leakage from the prototype would exist. However, to ensure the leakage factor, hermeticity proofs were done. An extra installation done was to add a standard size balloon in the exit, which acts as a flexible storage for the introduced gas and helps to level up pressure.

Figure 1: Design of Container. Prototype 1 A mixture with a different amount of nopal, manure, and water was added to the jug, with the goal of verifying the proportions the nopal functions with or in which of the 4 jugs the greatest amount of methane gas is produced: Tabla 1: Prototype 1 Entries Nopal Manure Water Void

2.3 Prototype 2

Jug 1 1.5 liters 7.5 liters 5 liters 6 liters

Jug 2 2.5 liters 6 liters 5.5 liters 6 liters

Jug 3 4 liters 5 liters 5 liters 6 liters

Jug 4 6 liters 4 liters 4 liters 6 liters

Espinosa-Garza G., Loera-Hernández I., Antonyan N., eds. The second prototype consisted in comparing the amount of produced methane with the manure mixture and with the outcoming mixture of water and nopal: Table 2: Prototype 2 Entries Manure Container 41 liters of manure 41 liters of water

Nopal Container 75 kg de nopal 75 kg of water

Two containers with a capacity of 200 liters were used as biodigestors. The design consisted in the installation of two exits in the superior part: one was used for the organic material entry and the other of the gas exit. Once the organic material was introduced, the tube was covered and locked with a PVC lid. The gas exit part was screwed in with a spherical stopcock, which allowed to control the gas outlet while the fermentation process was taking place. All the unions were locked with glue for PVC. The reasons for choosing a plastic container are its economic price and its good gas insulation properties due to its high-density composition and high molecular weight.

Figure 2: Design of Container. Prototype 2

3. Results As it can be observed in the data presented in Table 3, methane can be generated with the mixture of nopal and manure. In addition, from the first mixture with 7.5 liters of manure, 1.5 liters generated its optimal amount: 0.162 cubic meters. Table 3: Outcome of Prototype 1

#1 #2 #3 #4

Entries Manure Nopal Manure Nopal Manure Nopal Manure Nopal

7.5 1.5 6 2.5 5 4 4 6

Biogas 0.27 0.0015 0.23 0.025 0.198 0.004 0.158 0.006

Methane 0.162 0.000975 0.138 0.01625 0.118 0.0026 0.0948 0.0039

Even though the outcome of the second prototype (Table 4) showed that manure is a better methane generator than nopal, the use of nopal to generate methane is an alternative that satisfies aspects of environmental improvement and is economically rentable. Table 4: Outcome of Prototype 2

Espinosa-Garza G., Loera-Hernández I., Antonyan N., eds. Content Manure Nopal

Manure amount (L) 41 68

Biogas amount (m3) 1.625 0.0068

Methane amount (m3) 0.975 0.00442

It is also woth mentioning that the materials that were used for the biodigestor fabrication of this project have a duration of 15 years. The low costs of their maintenance show the project rentability. The investment can be recovered in the first year (the investment with other alternatives can take up to 10 years of recovery). Once installed inside the biodigestor, the only client concern would be the maintenance of its content. Past the first 40 days of biodigestor feeding, it is no longer necessary to wait for climatic conditions for energy production. The biodigestor has the possibility to produce 2 types of energy: electric and thermic. The electric energy can help clients who have a problem to reach the electricity commission, while the thermic energy can generate heat for the cold populations in the north of the country.

4. Conclusion In the current market, there are several substitutes for fossil fuels. Among them, there is the solar, eolic, hydraulic, and geothermic energies. However, the production of these energies results in an initial elevated investment for the market so that the project succeeds. Nevertheless, there are 11 thousand nopal producers in Mexico, as well as a maintenance of 3.5 million tons of bovine cattle annually, whose wastes have can be used for energy creation. During the current research, a technical study of the market and economy of Nuevo Leon, Mexico and its greater area were done. The technical study covered all the necessary information for the construction and functionality of the nopal and manure based biodigestor. The market coverage gave visibility about the biodigestor’s demand and current supply. The economic and financial parts gave the necessary information to prove the project viability and at the same time indicate different financial sources to carry it on. The presented project has the ability to create a great ecologic and monetary impact for the state of Nuevo Leon, its greater area, and Mexico in general. The demand for energy solutions is not only monetary, but also ecologic.

References 1. 2. 3.

4.

5.

Arvizu Fernandez, J.L. “Produccion de biogás con nopal”, Boletin IIE 2015, avalible in: https://www.ineel.mx//boletin022015/tenden01.pdf https://www.ineel.mx//boletin022015/tenden01.pdf Murphy, J,, Braun, R., Weiland, P., Wellinger, A., 2011, “Biogas from crop digestión”, IEA Bioenergy, Task in 2010-2012 Work Programme. Méndez-Gallegos S., Rössel D., Amante-Orozco A., Gómez-González A., García-Herrera J., 2010, “ El nopal en la producción de biocombustibles “, RESPYN Revista Salud Pública y Nutrición, Edición Especial No. 5‐2010, ISSN 1870‐0160, avalible in: file:///C:/Users/HP640G2W10/Downloads/EL_NOPAL_EN_LA_PRODUCCION_DE_BIOCOMBUSTIB LES.pdf Sulistyo H. ; Syamsiah S.; Herawati D. ; Wibawa A., 2012, “Biogas production from traditional market waste to generat renewable energy”, Strategic Technology (IFOST), IEEE Conference Publication, DOI: 10.1109/IFOST.2012.6357507 Kaparaju P1, Ellegaard L, Angelidaki I., 2008, Optimisation of biogas production from manure through serial digestion: lab-scale and pilot-scale studies, Bioresour Technol. 2009 Jan;100(2):701-9. doi: 10.1016/j.biortech.2008.07.023. Epub 2008.