The Investigation of Chemical Composition and the Specific Heat Capacity of Cow Dung and Water Mixture

Abstract

Energy is essential for the progress and development of nations. It must be reliable, affordable, and environmentally friendly. Among the most promising renewable energy sources, biogas technology has been developed to secure the existing energy supply. However, there is a need for more scientific research on the optimal use and performance of biogas plants for beneficiaries and installers. This study investigated the chemical composition of cow dung and its specific heat capacity. The results show that elements such as Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, SiO2, and TiO2 have different chemical compositions. Furthermore, the results show that cow dung’s composition and oxide content affect its specific heat capacity. Dzwerani had the highest concentrations of Al2O3, Fe2O3, and SiO2. Since the oxide composition of the dung samples from Tshino, Maila, and Gogogo differed, their specific heat capacities were also different. The results of this study encourage further investigations to determine a more accurate relationship between specific heat capacity and oxide composition.

1. Introduction

As nations strive to progress, they need energy to power their industries, fuel transportation, and provide electricity for homes and businesses. Additionally, access to energy also allows countries to pursue other goals, such as improving healthcare, education, and infrastructure. Without reliable access to energy, economic growth is severely limited, as many industries and businesses require energy to operate. Furthermore, access to energy can also provide a source of employment to citizens, creating jobs, and helping to lift people out of poverty. As a result, almost all developing countries have taken initiatives to introduce biogas technology in rural areas to improve energy supply and reduce poverty [1, 2, 3, 4, 5]. However, the beneficiaries and installers of these plants still need more scientific knowledge about biogas production. This means that they need help to make the best use of the technology available and optimize the performance of their plants. Due to its availability, cow dung is the most common feedstock used in household biogas digesters in rural areas. The investigation results of the study [6] showed that cow dung might be one of the feedstocks for efficient biogas production. Fresh cow dung is estimated to contain 28% water [7]. However, Refs. [8, 9] indicated that fresh cow dung contains approximately 80% water. For anaerobic digestion (AD) to generate biogas energy, fresh cow dung is mixed with water at a widely-used ratio of 1:1 [6]. Cow dung moisture is an important parameter that influences biogas production. In the absence of moisture, the anaerobic bacteria responsible for biogas production cannot function properly, and the process slows down. If moisture levels are too high, sludge may form, clogging the digester and reducing efficiency. Research shows that cow dung slurry comprises 1.8–2.4$\%$ N₂, 1.0–1.2$\%$ P₂O₅, 0.6–0.8$\%$ potassium, and 50–75$\%$ organic humus [10]. The main issue for biogas energy production lies in knowing several parameters in the mixture, building materials of the digester, insulation, and a heat source. Alfa et al. [11] indicated that biogas production depends on the physical and chemical properties of the feedstock type used. Cow dung’s physiochemical properties are important in operating a biogas digester system and maintaining digestion stability [12, 13].

Temperature is one of the most important parameters of AD system [14]. It was shown that the temperature of the AD system’s manure directly influences biogas production. They found that the higher the temperature, the higher the biogas production [15]. This indicates that thermal energy management is crucial for the efficiency of anaerobic digestion. Obot et al. [16] indicated that heat transfer problems are associated with thermal properties, one of which is specific heat capacity. Obot et al. [16] argued that specific heat capacity is critical for thermal analysis problems. Specific heat capacity is defined as the measure of the amount of heat energy required to raise the temperature of a slurry inside the digester by $1°\mathrm{C}$ [16]. The heat demand of AD systems depends on substrate characteristics, operating temperature, geographic region, and AD parameters such as digester type or size [17]. Thus, knowing the specific heat capacity of cow dung and the water mixture added to the digester is beneficial when determining the amount of heat required to raise the slurry temperature to the desired operating temperature. This information can help select the appropriate heating system and equipment for a biogas digester, leading to an efficient and effective biogas production process. As a result, the biogas production process is optimized, leading to a more cost-effective and reliable energy source. Methods for determining the specific heat capacity of material have been reported. However, few reported specific heat capacity of cow dung and water mixture. Gebremedhin et al. [18] assumed that the specific heat of cow dung is equal to the specific heat of water when modeling heat transfer problems in their study. Nayyeri et al. [19] conducted a study aiming to determine the thermal properties of cow dung. Only three physical quantities were determined: specific heat capacity, thermal conductivity, and thermal diffusivity. They reported that the specific heat capacity of cow dung increased linearly from $1.992$ to $3.606\mathrm{kJ}/\mathrm{kg}°\mathrm{C}$. Yerima et al. [20] reported the specific heat capacity of cow dung to be $2.0525\mathrm{kJ}/\mathrm{kg}°\mathrm{C}$. Ref. [21] reported the specific heat of cow dung to be 2.7992 $\mathrm{kJ}/\mathrm{kg}°\mathrm{C}$ and further showed that the specific heat capacity of the slurry mixture of water and cow dung is the sum of the specific heat of the water and that of cow dung $\left(3.490\mathrm{kJ}/\mathrm{kg}°\mathrm{C}\right)$. Das and Mondal [22] used the following expression for the specific heat capacity of the slurry of cow dung and water mixture added to the digester when determining the amount of heat required to raise the slurry temperature to the digester operating temperature of 35$°\mathrm{C}$

$$C_p=4.19-0.00275\left(\mathrm{TS}\right)$$E1

where 𝐶𝑝 is the specific heat capacity$\left(\frac{\mathrm{J}}{\mathrm{kg}}°\mathrm{C}\right)$ of the slurry, and ($\mathit{TS}$) is the total solid of cow dung expressed in ($\mathrm{kg}/{\mathrm{m}}^3$).

This research aims to investigate the chemical composition and specific heat capacity of cow manure-water mixtures, with a special focus on their suitability for biogas production. Anaerobic digestion can be optimized by investigating the thermal properties of cow manure-water mixtures, which increase the biogas production efficiency. Different cow manure-water mixtures will be tested under different conditions, including temperature and mixing ratio, to measure their specific heat capacities. Additionally, we will analyze the chemical composition of cow dung to identify the main components that contribute to biogas production. Research results from this study will contribute to a better understanding of cow dung’s potential as a biogas feedstock. To improve the efficiency and sustainability of biogas production from cow dung-water mixtures, we must understand the digester’s chemical composition and specific heat capacity.

2. Methods

2.1 Analytical methods of chemical composition

After arrival from the feedlot, the quantity of fresh cow dung samples was heated in an oven to 103°C for 24 hours to remove the moisture content. The procedure was carried out following the Standard Methods for the Examination of Water and Wastewater [23]. The samples were milled with the vibrating disc mill RS 200 until the final analytical fineness (< 40 μm) was reached. Each 10 g of milled powder was mixed with boric acid before palletization. The powder was then pressed onto a bed of 2.5 g boric acid in an aluminum cup (40 mm diameter), applying a pressure of 30 tonnes for 20 seconds. The chemical composition was measured using S2 Ranger (Bruker) X-ray fluorescence (XRF) in a vacuum with a 30 mm sample holding mask. The pellets were introduced into the XRF instrument after calibration. The measurement results were displayed as main oxides (%) or trace elements (ppm).

2.2 Determination of specific heat capacity

A recent study found that there is no universal method for determining specific heat capacity [24]. An experimental method is described for determining the specific heat capacity of cow dung mixed with water in the study. Researchers used the method of mixtures to determine the specific heat capacity of a mixture, which involves the combination of two substances with known properties. The method consists of the mixture of cow dung sample and water of known mass ($m_s=0.1\mathrm{kg}$) and temperature $T_i\left({}^{\mathrm{o}}\mathrm{C}\right)$ placed in an aluminum calorimeter mass,$m_{\mathit{Al}}=0.033\mathrm{kg}$specific heat capacity $C_{\mathrm{Al}}=0.900\mathrm{J}/\mathrm{g}°\mathrm{C}$ . A brass metal of mass $m_b=0.20\mathrm{kg}$ and specific heat capacity ($C_b=0.38\mathrm{J}/\mathrm{g}°\mathrm{C}$) was then heated to the desired temperature of 65$°\mathrm{C}$ using a water bath and immediately dropped into the mixture before wiping excess water. The equilibrium temperature was recorded as $T_e\left(°\mathrm{C}\right)$. The method determines the specific heat capacity by cooling the hot brass sample in cool cow dung and equating the heat losses of the brass metal with the heat gains of the cool cow dung slurry [19, 25]. Mathematically, the equation is written as:

$$C_s=\frac{m_b{C}_b\left(T_b-T_e\right)-m_{\mathit{Al}}{C}_{\mathit{Al}}\left(T_{\mathit{Al}}-T_e\right)}{m_s\left(T_e-T_i\right)}$$E2

As a result of this method, it is possible to determine the specific heat capacity of cow-dung-water mixtures by comparing the heat losses and gains during heat transfer.

3. Results and discussion

3.1 Chemical composition and specific heat of cow dung

According to the present results in Table 1, four different sites (Dzwerani, Tshino, Maila, and Gogogo) have different chemical compositions based on various elements such as Al₂O₃, CaO, Fe₂O₃, K₂O, MgO, MnO, Na₂O, P₂O₅, SiO₂, and TiO₂. It has been demonstrated that these results are relevant to biogas production using organic materials found at these sites. Several factors, including the chemical composition of the organic material, temperature, pH, and the presence of inhibitors influence biogas production efficiency. Biogas production is highly dependent on the chemical composition of the organic material. It is imperative to note that organic materials’ chemical compositions can vary from place to place. Consequently, determining the feasibility of biogas production requires knowing the chemical composition of organic materials at different locations. According to the results, site A has a high SiO₂ and Al₂O₃ content, which could affect biogas production efficiency. The inert substances SiO₂ and Al₂O₃ might reduce nutrient availability for microorganisms engaged in anaerobic digestion. Alternatively, site B has low levels of SiO₂ and Al₂O₃, making it a desirable location for biogas production. In site B, CaO could act as a buffer and maintain digester pH because of its high content. It is possible to produce biogas from Site C because it contains a high level of CaO and P₂O₅. CaO could act as a buffer, and P₂O₅ could provide important nutrients for microorganisms’ growth in anaerobic digestion. As MgO is well known for influencing microbial activity in the anaerobic digestion process, Site D has a high content of MgO, which might be advantageous for biogas production. The chemical composition of organic materials at different sites can significantly affect biogas production efficiency. Based on the results presented, it is important to understand the chemical composition of organic matter at different sites to determine whether biogas production is feasible. Data from the table can be used to analyze the relationship between cow dung’s specific heat and the oxides present at each site. In the last column, the specific heat values are expressed in (J/g°C) and represent the specific heat of cow dung. Specifically, specific heat measures how much heat energy is required to raise a substance’s temperature by a certain amount. Other factors affecting cow dung’s specific heat are the organic matter’s composition and the oxides it contains. Although the table does not directly provide specific heat values for individual oxides, we can still make some observations and discuss the potential effects of oxide composition on specific heat cow dung.

Location	Dzwerani	Tshino	Maila	Gogogo
Al2O3 (%)	2.2	<0.1	<0.1	<0.1
CaO (%)	2.9	2.95	7.49	3.19
Fe2O3 (%)	5.52	1.94	1.52	1.96
K2O (%)	4.74	1.92	1.93	1.39
MgO (%)	1.44	0.96	1.12	1.079
MnO (%)	0.105	0.082	0.094	0.17
Na2O (%)	<0.1	<0.1	<0.1	1.502
P2O5 (%)	0.958	1.67	3.86	1.21
SiO2 (%)	41.6	28.3	16.34	24.93
TiO2 (%)	0.427	0.247	0.141	0.143
pH	6.95	6.79	6.99	7.01
C (J/g°C)	2.97	2.79	2.21	2.49

Table 1.

Chemical compositions and specific heat capacity of cow dung.

Dzwerani:

Dzwerani has relatively high proportions of Al₂O₃, Fe₂O₃, and SiO₂ compared to other sites. There is a possibility that these oxides contribute to the cow dung’s overall specific heat. Dzwerani dung likely has a higher heat capacity because of its higher specific heat value (2.97 J/g°C); in other words, it requires more energy to warm up than other dung samples.

Tshino:

Compared to other sites, Tshino has a lower oxide content overall. Compared to Dzwerani cow dung, Tshino cow dung has a lower specific heat value (2.79 J/g°C).

Maila:

Maila has lower oxide content than Dzwerani. The cow dung from Maila appears to have a lower heat capacity based on its specific heat value of 2.21 J/g°C.

Gogogo:

There are slightly higher proportions of oxides such as CaO and MgO at the Gogogo site than at Maila. The specific heat of the cow dung from Gogogo (2.49 J/g°C) is slightly higher than the heat capacity of the cow dung from Maila. These observations can be made considering the given data and assumptions. A detailed analysis and measurement of the specific heat of each oxide present in cow dung would be required to establish a more accurate relationship between the specific heat of cow dung and its oxides. Other factors, such as moisture content, density, and impurities, may also impact cow dung-specific heat. Therefore, further experimental data and analysis are needed to determine the relationship between specific heat and oxide composition.

4. Conclusions

Based on the results of this study, it can be concluded that cow dung is characterized by its composition. Higher proportions of Al₂O₃, Fe₂O₃, and SiO₂ increase specific heat capacity. Specific heat capacity can be used to determine how much heat is required to raise a slurry’s temperature to a desired operating temperature. Since anaerobic digestion is determined by cow dung and water heat and capacity, biogas production can be optimized using information about cow dung’s chemical composition and specific heat capacity. Through experimentation, it was found that cow dung’s chemical composition influences biogas production efficiency. Certain elements and oxides stop microorganisms from digesting cow dung.

This study could help increase agricultural production, as biogas can be used for more efficient irrigation and fertilization. This would lead to more efficient resource management and increased sustainability in rural communities.

It can be concluded that cow dung’chemical composition affects the specific heat capacity at different sites. Based on the specific heat values of cow dung at various sites, it appears to have a varying heat capacity, possibly due to the oxide composition. To assess the feasibility of biogas production, it is crucial to understand the chemical composition of organic matter at different locations. Further research and analysis are necessary for a more comprehensive understanding of the relationship between specific heat capacity and oxide composition in cow dung. This includes measurements of specific heat for individual oxides.

Acknowledgments

I would like to thank all participants who collected samples for investigation.

Conflict of interest

No conflict of interest to declare.