# Development of a Locally Sourced Miniature Facility
## Capable of Transforming Bio-Waste into Renewable
## Energy

Constance Obituo Nwankwo, Nkemakonam Chidiebube Igbokwe

► To cite this version:

Constance Obituo Nwankwo, Nkemakonam Chidiebube Igbokwe. Development of a Locally Sourced Miniature Facility Capable of Transforming Bio-Waste into Renewable Energy. INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING, MANAGEMENT & APPLIED SCIENCE, 2023, 12 (9), pp.56-65. 10.51583/IJLTEMAS.2023.12906. hal-04263012

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# Development of a Locally Sourced Miniature Facility Capable of Transforming Bio-Waste into Renewable Energy

Constance Obituo Nwankwo and Nkemakonam Chidiebube Igbokwe*

Department of Industrial/Production Engineering, Nnamdi Azikiwe University, Awka, Nigeria

*Corresponding Author

DOI: https://doi.org/10.51583/IJLTEMAS.2023.12906

Received: 24 July 2023; Revised: 12 September 2023; Accepted: 16 September 2023; Published: 01 October 2023

**Abstract:** The primary challenge facing the globe today is finding environmentally friendly, ecologically balanced ways to use bio-waste as a source of energy. Typically, the term “biogas” or “renewable energy” refers to a gas created when organic matter breaks down without oxygen. Thus, this study designed and developed a 200L miniature facility capable of transforming bio-waste into renewable energy using locally available materials and tested under the existing weather condition in Awka, Anambra State. The facility developed in this study was utilized to decompose cow manure anaerobically, producing 21.9L of cooking gas overall over the course of a 35-day retention period. Additionally, the water boiling test demonstrated that the purified cooking gas’ high methane gas content development of the digesting chamber using high-density polyethylene plastic (HDPE) allows a reduction in the overall cost of setting up a small-scale plant.

**Keywords:** Bio-waste; Renewable energy; Bio-gas; Cow dung; Anaerobic digestion.

## I. Introduction

Fossil fuels are the main source of energy on the planet(Benali, Hamad, and Hamad, 2019). This kind of energy source releases a significant amount of carbon dioxide gas, one of the main greenhouse gas contributors. According to recent findings, the atmospheric carbon dioxide concentration has dramatically increased over the past century, rising from about 275 to 387 ppm with an average annual increase of 3 ppm(Igboro, 2011). This has led to an increase in global temperatures, clearly indicating that global warming will continue(Hassan, Abdullahi, and Garba, 2022).

Fossil fuels have been used as the main source of energy, causing problems with the environment, the climate, and human health. One of the main issues facing every growth is improper garbage management. This is due to the rise in commercial, agricultural, industrial, and environmental activities, which has significantly increasing waste production(Hunt et al., 2020). These wastes contribute to unsanitary environmental conditions that encourage the growth of pathogenic bacteria when they are incorrectly treated. Wastes have adverse effects on health aside from making the environment unpleasant and unsightly. These wastes can, however, be appropriately managed by being transformed into biogases, which are valuable and more environmentally beneficial forms(Castro-Amoedo et al., 2021). It is important to note that for the production of biogas, any sort of biological waste could be utilized(Shaibur, Husain, and Arpon, 2021).

The term “biogas” often refers to a gas created when organic matter breaks down in the absence of oxygen. Like solar and wind energy, it is a renewable source of energy (Sambo, 2009). It is one of the most effective and efficient options for renewable energy (Halder et al., 2016).

Additionally, the need to create alternative energy sources, such as biogas generation, has been driven by the rising cost of petroleum goods, particularly in Nigeria.Most people live in rural areas of underdeveloped nations like Nigeria, where there is little to no access to gas or electricity(Kehinde et al., 2018). As a result, they rely primarily on firewood for lighting and cooking(Sambo 2009). However, one of the main factors contributing to erosion in the southern part of the country and desertification in the arid-zone states is the sourcing of fuel wood for residential and commercial purposes(Sambo, 2009). The annual rate of deforestation is roughly 350,000 hectares, or 3.6% of the total area of forests and woodlands(Sambo, 2009). In contrast, the annual rate of regeneration is only about 10% of the annual rate of deforestation(Sambo, 2009). Biogas-based alternative energy sources can expand rural energy availability and decrease reliance on fossil fuels(Sarker et al., 2020). When properly managed, it is a cost-effective means of managing bio-waste and the most affordable way to supply both rural and urban settlements with natural gas and affordable electricity (Amakom, Nnabuchi, and Abubuko, 2015).

Installing biogas plants in these rural areas would aid in mitigating these current issues and preserving the natural environment, as agricultural residues and large amounts of solid waste are abundant and, if not properly disposed, leads to environmental and public
health hazard. Transforming such waste into renewable energy can mitigate such effects. Therefore, this study aims to develop a
locally sourced miniature facility capable of transforming bio-waste into renewable energy.

II. Materials and Method

The miniature facility was made from high-density polyethylene (HDPE) plastic. It has the following parts: the inlet chamber (feed entrance), outlet chamber A (removal of raw gas), outlet chamber B (removal of digestate), filtration chamber (A, B and C) for filtering of hydrogen sulphide, carbon dioxide/trace of hydrogen sulphide, water vapour and the gas storage chamber (for storing pure cooking gas). The inlet and outlet chambers were both incorporated into the mini plant tank, making it a single system. The reason for choosing plastic as a digester tank in this study was based on the following properties: noncorrosive, a good insulator, cost-effective, and easy to maintain. The cylindrical shape was adopted to enhance better cow dung and water mixing. This is illustrated in Figure 1.

<figure><img src="image_2.png" /><figcaption>Fig 1: Bio-waste transforming facility</figcaption></figure>

The following were considered during the design procedure:

i. Operating Volume: This is simply the volume of the slurry in the digester. It can be calculated using part-per-volume method as follows:

Let, B₂₀ = 20 litres bucket as a part per volume tank

B₁₀₀ = 100 litres bucket as a mixing tank,

D₂₀₀ = 200 litres drum as a digester tank,

C_b = 150 litres calibrated bucket,

The mixing ratio of cow dung to water is 1:1

V₁₃₀ = required operating volume of the slurry = D₂₀₀ × 65% of the slurry = 200 litres × 0.65 of the slurry = 130 litres of the slurry.

1. A bucket full of fresh cow dung was measured with B₂₀ and poured into the B₁₀₀,

2. The bucket full of water with another B₂₀ was also measured and poured into the B₁₀₀, and stirred homogeneously.

3. The mix was poured into the C_b and its volume was calibrated.

4. Steps 1 & 2 were repeated until the required operating volume of the slurry, i.e., 130 Litres of the slurry were achieved.

5. Finally, the V₁₃₀ or 130 litres of the slurry was fed into the D₂₀₀.

ii. Total Volume: The total volume of the digester (VT) should be greater than the operating volume. This is to give room for the cooking gas produced and the rise of the slurry during fermentation. It can be calculated as follows;

$$
V_T = V_{130} / \text{Required fraction of the slurry}
$$
Therefore:

130 litres of the slurry/0.65 of the slurry = 200 L.

iii. Digester Dimensions: Having determined the total volume of the digester, a ratio for the dimensions can be adopted, depending on the chosen geometric shape of the digester. For a cylindrical digester, the chosen geometry for this work

$$V_T = \pi r_d^2 h_d \quad (1)$$

Were,

$V_T$ = Total volume of digester = 200 L or $0.2m^3$.

$r_d$ = Radius of digester = 0.27m or 270mm.

$h_d$ = Height of digester = $V_T r_d^2 = 0.2m^3/ \pi \times 0.272 = 873mm$.

<figure><img src="image_3.png" /><figcaption>Fig 2: Digester Tank 200 L Capacity</figcaption></figure>

iv. **Digester Temperature Detector (DTD):** This is simply a slurry temperature-detecting device. This digester was designed to operate within the mesospheric temperature range (20°C – 40°C).

It was designed as follows;

* DTD was purchased with a maximum temperature of 260°C and minimum temperature of 10°C,

* 50mL of slurry was collected from the outlet chamber with a beaker every week.

* Slurry temperature was measured and recorded with DTD.

v. **Filter ‘A’ Design:** This simple filter filters hydrogen sulphide H2S. The following materials and specifications were used to design it;
<table><caption>Table 1: Filter ‘A’ Design Materials/Specifications</caption><thead><tr><td>S/N</td><td>MATERIALS</td><td>SPECIFICATIONS</td></tr></thead><tbody><tr><td>1</td><td>Thread socket</td><td>(25mmx1/2'')</td></tr><tr><td>2</td><td>Reducer bush</td><td>(25mmx25mm)</td></tr><tr><td>3</td><td>Reducer socket</td><td>(32mmx25mm)</td></tr><tr><td>4</td><td>PVC pipe</td><td>(215mmx25mm)</td></tr><tr><td>5</td><td>Nozzle</td><td>(1/2''x 10mm)</td></tr><tr><td>6</td><td>Steel wool</td><td>(1 strand)</td></tr><tr><td>7</td><td>Gum</td><td>------</td></tr></tbody></table>

iv. Filter ‘B’ Design: This simple filter filters carbon dioxide, CO2 and some trace of hydrogen sulphide, H2S. The following materials and specifications were used to design it as follows:

<table><caption>Table 2: Filter ‘B’ Design Materials/Specifications</caption><thead><tr><td>S/N</td><td>MATERIALS</td><td>SPECIFICATIONS</td></tr></thead><tbody><tr><td>1</td><td>Reducer socket</td><td>(20mmx1/2'')</td></tr><tr><td>2</td><td>PVC pipe</td><td>(300mmx20mm), (120mmx20mm)</td></tr><tr><td>3</td><td>Filter tank</td><td>(20L capacity)</td></tr><tr><td>4</td><td>Water</td><td>(15L)</td></tr><tr><td>5</td><td>Sodium Bicarbonate</td><td>(30g)</td></tr><tr><td>6</td><td>Gum</td><td>-----</td></tr><tr><td>7</td><td>Tap</td><td>-----</td></tr></tbody></table>

v. Filter ‘C’ Design: This simple filter filters water vapours. The following materials and specifications were used to design it as follows:

<table><caption>Table 3: Filter ‘C’ Design Materials/Specifications</caption><thead><tr><td>S/N</td><td>MATERIALS</td><td>SPECIFICATIONS</td></tr></thead><tbody><tr><td>1</td><td>Thread socket</td><td>(25mmx1/2'')</td></tr><tr><td>2</td><td>Reducer bush</td><td>(25mmx25mm)</td></tr><tr><td>3</td><td>Reducer socket</td><td>(32mmx25mm)</td></tr><tr><td>4</td><td>PVC pipe</td><td>(130mmx25mm)</td></tr><tr><td>5</td><td>Nozzle</td><td>(1/2''x 10mm)</td></tr><tr><td>6</td><td>Foam</td><td>(25mmx20mm)</td></tr><tr><td>7</td><td>Silica gel</td><td>(30g)</td></tr><tr><td>8</td><td>Gum</td><td>-----</td></tr></tbody></table>
## 2.1 Gas Storage Tank Design

The gas tank volumedepends on the relative rates of gas generation and gas consumption. The motor tire tube shown in Figure 3 was selected as the gas storage tank due to the following properties:

* Chemical inertness of the tube, i.e., hydrogen sulphide present in the raw gas which when in contact with metals, causes pitting corrosion butdoes not attack tube materials.

* Expansion and contraction ability, i.e., the tube material allows expansion and contraction of the gasses without bursting.

* Low-pressure flow rate of the gas, i.e., the gas flows at self-pressure, and as a result of this self-pressure, the tube takes in the gas gradually without bursting.

<figure><img src="image_4.png" /><figcaption>Fig 3: Gas storage tank</figcaption></figure>

## 2.2 Gas Valve Design

A 2-way ball returnable valve shown in Figure 4 was used to control the gas flow direction from the digester tank to the motor tire tube and through the filter ‘A’. Again, it was used to prevent pressure drop of the gas and maintain its self-pressurewhile flowing into the gas storage tank.

<figure><img src="image_5.png" /><figcaption>Fig 4: A 2-way ball returnable valve</figcaption></figure>

A tee fitting with a female threaded connection shown in Figure 5, was used to distribute the raw gases produced into the motor tire tube and through the filter ‘A’.

<figure><img src="image_6.png" /><figcaption>Fig 5: Tee fitting with female threaded connection</figcaption></figure>
Figure 6 shows the raw gas storage tank assembly incorporating tee fitting with a female threaded connection and a 2-way ball returnable valve

<figure><img src="image_7.png" /><figcaption>Fig 6: Raw gas storage tank assembly</figcaption></figure>

## 2.3 Gas Hose Design and Digester Tank Design

Factors considered during the selection of the appropriate hose for the inlet and outlet hose are as follows:

I. Material type and size

II. Thermal expansion and temperature effect

III. Maintenance ease and installation

IV. Safety, in terms of the design factor, and adequate support.

The inlet hose and tank are cylindrical, and the bursting pressure of the inlet hose was calculated using the following equation:

$$Pb = \frac{2 \times ST \times MT}{Dm} \quad (2)$$

Where

Pb= Bursting pressure of the inlet hose in psi.

ST = Tensile strength of the pipe = P105 or 724Mpa

MT = Minimum wall thickness of the pipe = 2.5mm,

Dm = Mean diameter = 10mm.

Thus the Bursting pressure of the inlet hose is 362psi.

The bursting pressure of the tank was calculated using the formula in Equation 2,

Where

Pb= Bursting pressure of the tank in psi.

ST = Tensile strength of the pipe = 22.1Mpa

MT = Minimum wall thickness of the pipe = 10mm,

Dm = Mean diameter = 540mm.

Thus the Bursting pressure of the tank is 0.82psi.
## 2.4 Sample Collection and Preparation Procedure

The cow dung for the present study was collected from Garki, Amansea Junction, Awka, Anambra State. It was dissolved with water at a ratio of 1:1 (waste/water) to obtain the slurry. This was done to ensure that the percentage of the total solids was less than 10% before being fed to the facility. The facility was fed with 130 L of slurry and allowed to undergo retention time of 7 days, 14 days, 21 days, 28 days and 35 days to evaluate the amount of cooking gas produced. The digester tank was covered with polyethylene material that could withstand harsh environmental conditions and maintain anaerobic conditions. The slurry temperatures were monitored using a Digester Temperature Detector (DTD) inserted into the slurry measured out of the outlet chamber. During the purification stage shown in Figure 7, steel wool, water and silica gel were used. The steel wool was used to react with the hydrogen sulphide, and the water was used to reduce the percentage of carbon dioxide and the silica gel was used to reduce the presence of water vapor in the purified cooking gas. The experiment took the raw cooking gas with pressure built up in the tank head and forced it through the steel wool to remove hydrogen sulphide from the cooking gas filtering unit. After steel wool removed the hydrogen sulphide, the raw cooking gas was passed into the water filtering unit for further purification.

<figure><img src="image_8.png" /><figcaption>Fig 7: Cooking Gas Filtering and Purification System</figcaption></figure>

The liquid leaving the filtering unit will thus contain an increased concentration of carbon dioxide, while the gas leaving the filtering unit will have an increased methane concentration. The purified cooking gas collected at the top of the filter unit contains some amount of water vapours. Since water vapor is the leading causes of corrosion, silica gel was used in this experimental set-up to absorb it.

## III. Results and Discussion

Details of the results obtained during the experiments are tabulated below. Volumes of cooking gas produced, the temperature of the environment, and the temperature of the slurry at a retention time of 7, 14, 21, 28, and 35 days are presented in Tables 4 and 5. The values of heating efficiency before and after filtering of impurities from the produced gas are also presented in Table 6.

<table><caption>Table 4: Cooking gas produced against retention time</caption><thead><tr><td>Retention time (day)</td><td>Cooking gas produced (L)</td></tr></thead><tbody><tr><td>7</td><td>1.8</td></tr><tr><td>14</td><td>2.5</td></tr><tr><td>21</td><td>3.4</td></tr><tr><td>28</td><td>4.2</td></tr><tr><td>35</td><td>10.7</td></tr></tbody></table>
<table><caption>Table 5: Temperature of environment and slurry against retention time</caption><thead><tr><td>Retention (day)</td><td>Environment Temperature °c</td><td>Slurry Temperature °c</td></tr></thead><tbody><tr><td>0</td><td>20</td><td>20</td></tr><tr><td>7</td><td>25</td><td>30</td></tr><tr><td>14</td><td>26.5</td><td>32</td></tr><tr><td>21</td><td>28</td><td>34</td></tr><tr><td>28</td><td>24</td><td>29.5</td></tr><tr><td>35</td><td>30</td><td>38</td></tr></tbody></table>

<table><caption>Table 6: Time for boiling 200ml of water</caption><thead><tr><td>Days</td><td>Heating efficiency before filtering (mins)</td><td>Heating efficiency after filtering (mins)</td></tr></thead><tbody><tr><td>7</td><td>0</td><td>0</td></tr><tr><td>14</td><td>35</td><td>31.5</td></tr><tr><td>21</td><td>20.33</td><td>16.53</td></tr><tr><td>28</td><td>8.20</td><td>12.50</td></tr><tr><td>35</td><td>6.31</td><td>2.46</td></tr></tbody></table>

The designed and constructed 200 L facility was installed at the Faculty of Engineering foundry shop, Nnamdi Azikiwe University, Awka. Cooking gas yield was made possible by the action of anaerobic bacteria in the presence of moisture and the absence of oxygen. The mini plant's cooking gas performance over the 35 day' retention period and is presented in Figure 7. The facility was fed with cow dung at a mixing ratio 1:1 for slurry and water. Figure 7 shows that cooking gas production was initiated from day 7 with gradual increase in the volume of gas produced. The production of higher amount of cooking gas from day 7 to day 35 further proved that the three stages of anaerobic digestion were occurring simultaneously within the mini plant.

COOKING GAS PRODUCED AGAINST RETENTION TIME

<figure><img src="image_9.png" /><figcaption>Fig 7: Cooking Gas produced as against Retention Time</figcaption></figure>

The effect of environmental temperature was noticed in the digestion of the cow dung slurry. In Figure 8, it was observed that temperature affects the digestion of the slurry. This was observed from day 7 to day 21 and day 28 to day 35, where there was an increase in temperature. As a result of the variation in temperature of the environment, the digestion of the slurry was quickening, which led to a higher yield of cooking gas. From day 21 to day 28, the temperature of the environment reduces which also lowers
the slurry temperature and yieldslittle increase in the amount of cooking gas produced. Thus showing that the mini plant operated within the mesophilic temperature range.

<figure><img src="image_10.png" /><figcaption>Fig 8: Effect of Environmental Temperature</figcaption></figure>

## IV. Conclusion

The study designed and developed a 200 L miniature facility capable of transforming bio-waste into renewable energy using locally available materials and tested under the existing weather conditions in Awka, Anambra State. The facility developed in this study was utilized to decompose cow manure anaerobically, producing 21.9 L of cooking gas overall over the course of a 35-day retention period. Additionally, it was discovered that the environment's temperature was mesophilic and strictly related to the slurry's temperature. Additionally, the water boiling test demonstrated that the purified cooking gas' high methane gas content development of the digesting chamber using high-density polyethylene plastic (HDPE) allows a reduction in the overall cost of setting up a small-scale plant.

## V. Recommendation

Future research should consider, whether adding alkaline materials like limestone, sodium hydroxide, and potassium hydroxide to the water used to mix cow dung could raise the pH level to the ideal range for anaerobic digestion.

## References

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