ORIGINAL ARTICLE

Dimensioning and Energy Potential of Biodigesters Installed in Productive Systems in the Department of Cundinamarca, Colombia

Yanoy Morejón Mesa^{I  *} 
http://orcid.org/0000-0002-1125-3105

Vilma Moreno Melo^II 
http://orcid.org/0000-0002-1982-3993

Andrés Mogollón Reina^II 
http://orcid.org/0000-0003-1354-5897

^IUniversidad Agraria de La Habana, Facultad de Ciencias Técnicas, San José de las Lajas, Mayabeque, Cuba.

^IIUniversidad de Cundinamarca, Facultad de Ciencias Agropecuarias, Sede Fusagasugá, Cundinamarca, Sumapaz, Colombia.

ABSTRACT

This research is oriented towards determining the size and energy potential of a system of biodigesters installed in six livestock production systems, which are in the provinces of Sumapaz and Ubaté, in Cundinamarca Department, Colombia. Thus, the existing animal species in the scenario are determined, since they will contribute organic waste to the biodigester; the number of animals is also determined, considering the herd movement, which would make it possible to determine the biomass generated daily with the purpose of establishing the sizing of the appropriate biodigester technology and to know the behavior of the energy parameters. Among the main results obtained, it was evidenced that the biomass generated daily was not considered for the dimensioning and establishment of the polyethylene tubular biodigesters. In addition, the biodigesters installed in the production systems at La Meseta and El Tibar are oversized by 4,8 and 1,6 times, respectively; aspect that evidences the need to increase the daily biomass generated, which is achievable by increasing of animals in the herd. The biodigesters installed in the production systems at Santa Bárbara, El Mirador, La Saucita and La Esperanza, demonstrate an under-sizing, with inferiority values of 2,9; 1,97; 1,49; 2,04 times. These results indicate that, in these scenarios, the total number of animals used for biomass production is greater than that required with respect to the installed biodigester or that the installed biodigesters cannot take advantage of the biomass generated daily.

Keywords:  Renewable Energy; Livestock Production; Anaerobic Digestion; Energy Feasibility; Environmental Impact

INTRODUCTION

Currently, it is necessary to take advantage of renewable energy sources based on the best use of local resources which, through the best use of appropriate technologies, contribute to save conventional fuel and serve to return the soil the nutrients it needs and preserve the environment from pollution (^{Santos et al., 2012}).

Anaerobic digestion is a good alternative to treat waste with high biodegradable organic matter (^{Flotats et al., 2001}; ^{Sosa, 2017}). Therefore, according to ^{Suárez et al. (2018)}, this treatment is indicated for agro-industrial wastewater, with a high load of biodegradable organic matter discharges from the production of sugar, alcohol, meat, paper, preserves and distilleries according to ^{Rahayu et al. (2015)}. Anaerobic digestion is also indicated to treat agricultural residues, such as slurry and manure according to ^{Bansal et al. (2017)}, and urban waste that includes both the organic fraction of solid waste according to ^{Biogas Association Ottawa (2015)} and urban wastewater treatment plant sludge (^{Frankiewicz, 2015}).

Precisely, the biodigester is an anthropogenically produced (produced by human activity) technology to highlight in the biotechnological process of anaerobic digestion of biomass to obtain biogas. It is a hermetic reactor with a side inlet for organic matter, an outlet at the top through which biogas flows, and an outlet to obtain effluents with biofertilizing properties, both products contribute to meeting the needs of producers and to promote organic agriculture, as an economically feasible and ecologically sustainable alternative (^{Zheng et al., 2012}).

To these aspects, it should be added the high prices of fuels and the high local rates of electricity, being factors to consider for the introduction of biodigesters or biogas plants at the national and regional level that produce energy from the use of waste of agricultural production (^{Parra et al., 2019}).

Considering the criteria described above, in different production systems located in the department of Cundinamarca, Colombia, a set of biodigesters were installed with the aim of producing biogas and biofertilizers, towards which the objective of the present investigation was oriented in determining the sizing and the energetic potentialities of the use of this technology for each productive system studied.

MATERIALS AND METHODS

Characterization of Experimental Areas

The research was carried out in six livestock production systems, four of them belonging to private producers and two to the University of Cundinamarca. Of these systems, five are located in the Sumapaz Province and one in the Ubaté Province. In all scenarios, Biodigesters with different capacities were installed with the aim of producing biogas and biofertilizers.

The diet of this pig herd was composed of concentrated flour feed, made with raw materials such as American corn, soybean cake, palm oil, wheat byproducts, molasses, calcium carbonate and Nuclei (commercial amino acids with vitamins) and in the case of cattle, their diet was basically made up of pastures and forages.

According to ^{Cardona (2012)}, the most common and used grasses in Colombia, in the low tropics, are angleton, pangola and bracharias grasses depending on soil fertility and acidity, while for the high tropics the most common are kikuyu, ryegrass, orchard grass and canary-grass. Pastures in the low tropics are rich in energy, therefore, the supplement that should be given to the animal must be rich in protein, while, in the high tropics, the forages contain more protein for which it is necessary to opt for products with high energy content.

Native grasses in general terms have low nutritional value and do not provide the amount of adequate nutrients to maintain sustained production in cattle farms. In this situation, the producer, in order to continue producing (milk), would have to complement the forage deficiencies with the use of feeds that provide protein to the cattle, such as soybean paste, flour, fish or alfalfa meal, which are products that have high prices in the market, but that are essential to obtain good production of meat and/or milk, so it is necessary to look for other alternative sources that allow maintaining production at a reasonable cost (^{Bonilla et al., 2014}).

The quality and quantity of forage during the summer season in the low and high tropics is drastically reduced, causing a decrease in milk production, hence, farmers have decided to implement strategies using supplements. In the case of the low tropics, they are choosing to use forage crops such as silage to reduce production costs of forage crops and increase milk production in the dry season by 15%, resulting in greater profitability and competitiveness of dual-purpose systems (^{Castro et al., 2016}). While in the high tropics, golden fodder oats are being used because they are ideal for farms located between 2,200 and 3,000 meters above sea level, offering cattle the energy they need to withstand the dry season (^{Villegas & Llanos, 2014}).

Another way managed by ranchers to increase the productivity of the cattle herd is to use the paddock rotation grazing system, which is based on adequately alternating the period of using with the rest time of the paddock, allowing the forage of each paddock has a recovery period and natural reseeding increasing forage production to facilitate weed control (^{Ruiz, 2013}).

Regarding the behavior of climatic variables, in the case of Sumapaz Province, the behavior of temperature and humidity varies depending on the time of year, obtaining the following values according to climate variability: in warm climate: 24 °C to 28 °C (9,21%), in temperate climate: 18 °C to 23 °C (54%), in cold climate: 12 °C to 18 °C (32,2%) and in the case of Ubaté Province, the warm season lasts 3,7 months (December - April), and the average daily high temperature is over 19°C. The warmest month of the year in Ubaté is May, with an average maximum temperature of 18 °C and a minimum of 10 °C. The cool season lasts 2.4 months, (June-September), and the average daily maximum temperature is less than 18 °C. The coldest month of the year in Ubaté is January, with an average minimum temperature of 7 °C and a maximum of 19 °C, the relative humidity ranges between 75…90% throughout the year.

TABLE 1 Agricultural systems selected for research 

Producer	Vereda (country road)	Production system	Municipality	Province	Productive goal
Alirio Herrera	Bermejal	La Meseta	Fusagasugá	Sumapaz	Dairy bovine
Álvaro Rodríguez	Jordán Bajo	Santa Bárbara	Fusagasugá	Sumapaz	Swine production
Avelino Godoy	Guayabal	El Mirador	Fusagasugá	Sumapaz	Swine production/crops
Naiceline Castro	Tierra Negra	La Saucita	Fusagasugá	Sumapaz	Swine production
Universidad de Cundinamarca	Guavio Bajo	La Esperanza	Fusagasugá	Sumapaz	Swine production / Dairy bovine
Universidad de Cundinamarca	Palogordo	El Tibar	Ubaté	Ubaté	Swine production

Methodology for Dimensioning and Installation of Polyethylene Tubular Biodigesters

To calculate the design parameters of a tubular polyethylene biodigester, it is necessary to know the input data, and those that must be determined (Table 2).

The daily amount of material (Bmd) is directly related to the amount of biomass that is generated, whether it is domestic, agricultural or animal waste. In addition, the maximum amount obtained, and the production increase plans must be considered.

TABLE 2 Input and output data required for the design of an anaerobic biodigester 

Parámeters	Unit
Imput data
Amount of daily biomass generated (Bmd)	kg day^-1
Excrets-water ratio (N)	L kg^-1
Biogas yield (Y)	m^3 kg^-1
Hydraulic retention time (HRT)	day
Output date
Daily volume of material (mixture of manure and water) (Vdm)	kg day^-1
Biodigester volume, (Vbiodig)	m^3
Daily volume of biogas produced (G)	m^3 day^-1
Biogas holding volume (V_2)	m^3
Surge Tank Volume (Vtc)	m^3

The amount of daily biomass generated (Bmd), is determined through the following expression:

$B{m}_d=Ca\times Ce\times Rp\times Rt,kg{day}^{-1}$

where: Ca- Number of animals; Ce-Amount of excreta per animal, kg/day; Rp- Ratio between the average live weight of the animal population and the tabulated equivalent live weight; Rt- Fraction between the stabling time with respect to the duration of the day, h/day

$B{m}_d=Ca\times Ce\times \left(\frac{PVp}{PVe}\right)\times \left(\frac{Te}{24h}\right),kg{·day}^{-1}$

where:

PVp-Average live weight of the animal population, kg; PVe- Tabulated live weight equivalent; Te-Hours of the day that the animal remains stabled, h/day

The daily volume of material (mixture of manure and water) (Vdm) is the sum of the residual and the dilution of the biomass (residual and water).

$\mathrm{V}\mathrm{d}\mathrm{m}=\left(1+N\right)\bullet Bmd,m^3·{day}^{-1}\mathrm{}\mathrm{}$

where:

N: Excreta-water ratio, L/ kg, it is required to know that the density of water is: 1000 kg/m³.

Meanwhile, the volume of the biodigester (Vbiodig) is calculated considering the value of the volume of material (mixture of manure and water) Vdm that enters the biodigester and the retention time TRH.

$V_{biodig}=\mathrm{V}\mathrm{d}\mathrm{m}\bullet TRH,m^3$

Subsequently, the daily volume of biogas (G) produced is calculated:

$G=Y\times B_{md},m^3·{day}^{-1}$

where:

Y- Biogas yield, m³· kg^-1

The biogas yield (Y), is determined by the expression:

$Y=\frac{X}{C_e},m^3·{kg}^{-1}$

where:

X- energy conversion coefficient of the excreta produced daily, that is, the daily production of biogas depending on the type of organic waste, m³/day.

For all types of biodigesters, the volume of the compensation tank (Vtc) is equivalent to the volume of gas produced, that is, it ranges between 25…30% of the volume of the biodigester.

RESULTS AND DISCUSSION

Dimensioning of the Biodigester

For the correct dimensioning of the biodigester, it is necessary to determine the following parameters:

• Amount of daily biomass generated (Bmd);

• Daily volume of material (mixture of manure and water) (Vdm);

• Volume of the biodigester (Vbiodig);

• Volume of the compensation tank (Vtc).

The obtained results from each of these parameters are represented in Table 2, these values are obtained from the herd movement conceived by the owner of the farm during the month of April 2022.

Potential Energy Input

In order to determine the potential energy supply to be obtained based on the number of animals available, the following parameters must be determined:

• Biogas productivity (Y);

• Daily volume of biogas (G).

To determine the energy contribution of the animal population in each production system, it is necessary to consider that for every 50 kg of swine, 2,25 kg of excreta are obtained, generating 0,10 m³ of biogas/day, and for every 350 kg of cattle (specifically dairy cows) 10 kg of excreta are obtained, generating 0,36 m³ of biogas/day, for the mixture a ratio of 1:1 excreta-water is established (for both species) and with a retention time recommended 40 days (Table 3).

TABLE 3 Energy supply from animal population in each production system 

Production System	Raw material source	Animal / day	Average Mass , kg	Bmd, kg/day	Y, m^3/kg	G, m^3/day
La Meseta	Bovine	20	400	25,71	0,036	0,92
Santa Bárbara	Swine	992	99	4 360,84	0,044	191,87
El Mirador	Swine	73	75	246,37	0,044	10,84
La Saucita	Swine	50	83	186,75	0,044	8,21
La Esperanza	Swine/Bovine	15/50	92/415	358,52	0,080	28,68
El Tibar	Swine	21	85	80,32	0,044	3,53

FIGURE 1 Biodigesters installed in the selected farms: a) Santa Bárbara, b) El Mirador, c) La Saucita, d) La Esperanza, e) El Tibar, f) La Meseta. 

TABLE 4 Energy potential depending on the biodigester installed in each production system 

Dimensioning of installed biodigesters	Premises (Selected production systems)
	La Meseta	Santa Bárbara	El Mirador	La Saucita	La Esperanza	El Tibar
Vbiodig, m^3	10	120	10	10	14	10
Vtc, m^3	3,3	39,2	3,3	3,3	4,6	3,3
Vgas, m^3	3,3	39,2	3,3	3,3	4,6	3,3
Energetic parameters
Y, m^3/kg	0,036	0,044	0,044	0,044	0,080	0,044
G, m^3/día	0,92	71,2	10,84	8,21	28,68	3,53
Potential energy savings
Electricity, kWh	1,6	128,6	19,5	14,7	51,6	6,3
Natural gas, m^3	0,5	42,7	6,5	4,9	17,2	2,1
Wood charcoal, kg	0,3	21,4	3,2	2,5	8,6	1,0
Wood, kg	2,5	192,2	29,2	22,2	77,4	9,5
Fuel, L	0,7	56,9	8,6	6,6	22,9	2,8
Alcohol fuel, L	1,1	85,4	12,9	9,8	34,4	4,2
Fuel oil, L	0,6	49,8	7,5	5,7	20	2,5

As evidenced in Table 4, the installation of biodigesters in agricultural production units constitutes an energetically viable option, to which the contribution to the conservation and care of the environment should be added.

It is valid to point out that the correct dimensioning of this type of technology favors the maximum use of the waste obtained in the productive scenarios, this criterion is based on the differences represented in the aforementioned table, evidencing that in the farms: La Meseta, el Tibar and Santa Bárbara, the volume of the installed biodigester is not used to the maximum, in the case of the first two farms the number of animals does not cover the potential of the installed biodigester and in the case of the third, the installed digester only uses approximately 35 % of the energy potential to be obtained. In La Esperanza Agro-Environmental Unit, it can be seen that the installed biodigester is also not capable of assimilating the amount of biomass generated daily, so it could be considered to reduce the amount of bovine excreta supplied or to install a biodigester with greater capacity.

Based on the results obtained and shown in Table 4, the design of the appropriate biodigester for each production system was carried out, these results can be seen in Table 5.

TABLE 5 Biodigester sizing suitable for each production system 

Dimensioning of installed biodigesters	Premises (Selected production systems)
	La Meseta	Santa Bárbara	El Mirador	La Saucita	La Esperanza	El Tibar
Vbiodig, m^3	2,05	348,8	19,7	14,9	28,6	6,4
Vtc, m^3	0,6	115,1	5,9	4,4	8,6	1,9
Vgas, m^3	0,6	115,1	5,9	4,4	8,6	1,9
Energetic parameters
Y, m^3/kg	0,036	0,044	0,044	0,044	0,080	0,044
G, m^3/día	0,92	191,8	10,84	8,21	28,68	3,53
Potential energy savings
Electricity, kWh	1,6	345,2	19,5	14,7	51,6	6,3
Natural gas, m^3	0,5	115	6,5	4,9	17,2	2,1
Wood charcoal, kg	0,3	57,5	3,2	2,5	8,6	1,0
Wood, kg	2,5	517,8	29,2	22,2	77,4	9,5
Fuel, L	0,7	153,4	8,6	6,6	22,9	2,8
Alcohol fuel, L	1,1	230,2	12,9	9,8	34,4	4,2
Fuel oil, L	0,6	134,3	7,5	5,7	20	2,5

As shown in Table 5, the biodigesters installed in the production systems: La Meseta and El Tibar, are oversized by 4,8 and 1,6 times, respectively; this element evidences the need to increase the daily biomass generated, which is achievable with the increase of animals in the herds, whether they are pigs or cattle. On the other hand, in the case of the biodigesters installed in the production systems: Santa Bárbara, El Mirador, La Saucita and La Esperanza, a sub-dimensioning is observed, showing that the biodigesters installed in these production systems have dimensions smaller than those that could potentially be installed, finding inferiority values ​​of 2,9; 1,97; 1,49; 2,04 times; these results indicate that in these scenarios, the number of animals used for biomass production is greater than that required with respect to the installed biodigester or that the installed biodigesters cannot take advantage of the biomass generated daily due to their capacity. In the specific case of the Santa Bárbara farm, it is evident that the volume of the biodigester installed is well below what should be installed, based on the number of existing animals and the amount of matter generated daily; this element considerably limits the energy potential, only in this specific case, the daily volume of biogas increases considerably and therefore, the potential energy savings would increase.

CONCLUSIONS

• It is evident that in none of the production systems the daily biomass generated was considered for the establishment of the polyethylene tubular biodigesters based on their dimensioning.

• The biodigesters installed in the production systems: La Meseta and El Tibar, are oversized by 4,8 and 1,6 times, respectively; aspect that shows the need to increase the daily biomass generated, which is achievable with the increase of animals in the herds.

• The biodigesters installed in the production systems: Santa Bárbara, El Mirador, La Saucita and La Esperanza, show an under-sizing, with inferiority values of 2,9; 1,97; 1,49; 2,04 times. These results indicate that, in these scenarios, the number of animals used for biomass production is greater than that required with respect to the installed biodigester or that the installed biodigesters cannot take advantage of the biomass generated daily.

• The proper dimensioning of the anaerobic digestion technology is closely related to the biomass generated daily and therefore, to the number of animals in the production system.

• The implementation of these alternative technologies contributes to energy savings and the conservation and preservation of the environment, which is reflected in the values of potential energy savings obtained.

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Recebido: 26 de Abril de 2022; Aceito: 14 de Setembro de 2022

^*Author for correspondence: Yanoy Morejón Mesa, e-mail: [e-mail] o [e-mail]

Yanoy Morejón Mesa, Profesor Titular. Facultad de Ciencias Técnicas, Universidad Agraria de La Habana, Cuba. Correo: [e-mail] o [e-mail].

Vilma Moreno Melo, Profesora, Universidad de Cundinamarca, Facultad de Ciencias Agropecuarias, Sede Fusagasugá, Cundinamarca, Sumapaz Colombia, e-mail: [e-mail].

Andrés Mogollón Reina, Profesor, Universidad de Cundinamarca, Facultad de Ciencias Agropecuarias, Sede Fusagasugá, Cundinamarca, Sumapaz Colombia, e-mail: [e-mail] .

The authors of this work declare no conflict of interests.

AUTHOR CONTRIBUTIONS: Conceptualization: Y. Morejón, V. Moreno. Data curation: Y. Morejón, V. Moreno. Formal Analysis: Y. Morejón, V. Moreno, A. Mogollón. Investigation: Y. Morejón, V. Moreno, A. Mogollón. Methodology: Y. Morejón. Project administration: V. Moreno, A. Mogollón . Validation: Y. Morejón, V. Moreno, A. Mogollón. Visualization: Y. Morejón, V. Moreno, A. Mogollón. Writing - original draft: Y. Morejón, V. Moreno. Writing - review & editing: Y. Morejón, V. Moreno, A. Mogollón.