## 2 Materials and Methods
### Theoretical Assessment  
#### 2.2.1 Available Manure Generation  
The manure yield is calculated as 10%, 4%, and 3% of the body weight for large animals, small animals, and poultry, respectively [28]. In Bangladesh, the average weights of livestock are 190 kg for large animals, 20 kg for small animals, and 1.5 kg for poultry [29; 30]. Consequently, the projected daily manure output is 19 kg for large animals, 0.8 kg for small animals, and 0.045 kg for poultry. However, collecting all the generated manure is impractical; thus, the efficiency of available manure collection has been incorporated to quantify the overall potential for biogas and compost. It was assumed that the availability  
Figure 3: Research flowchart.  
coefficient is 50% for large animals, 13% for small animals, and 90% for poultry manure generation [12; 19]. The available manure was evaluated for each district and sub-district by considering the total numbers and specific livestock types across all districts and sub-districts of Bangladesh.  
Biogas, Electricity, and Biofertilizer Potential  
Total solids (TS) represent a critical factor for biogas generation from animal manure, with TS distribution in manure ranging from 10-30% for different types of livestock [30; 31]. Furthermore, biogas production based on TS varies among livestock types, with estimates of 0.6-0.8 m\({}^{3}\) kg\({}^{-1}\) TS for large animals, 0.3-0.4 m\({}^{3}\) kg\({}^{-1}\) TS for small animals, and 0.3-0.8 m\({}^{3}\) kg\({}^{-1}\) TS for poultry [13; 30; 31; 32]. However, the values of various factors employed in this study to estimate biogas potential are displayed in Table 1. Equations (1)-(3) were utilized to calculate the biogas production potential from manure [19; 21; 32; 33].  
Theoretical potential of biogas production (m\({}^{3}\)/year) = Total manure (kg/year) \(\times\)  
TS in manure \(\times\) availability coefficient \(\times\) Biogas yield (m\({}^{3}\)/kg TS)  
Electricity generation from biogas = Quantity of biogas produced  
\[\times\]  
Energy content in biogas  
\[\times\]  
\[\eta\]  
(2)  
Biofertilizer Potential = (DM \[-\] VS) + 40% of VS (3)  
Here, \(\eta\) denotes the coefficient factor (in %) for biogas to electricity transformation. The \(\eta\) value depends on energy generation systems, and it varies from 35 to 42% for large turbine structures and is around 25% for small dynamo plants [29; 34]. However, this study presumed the lowest values for this coefficient factor for electricity generation from biogas. Energy content in biogas was estimated by considering the calorific value (21.8 MJ/m\({}^{3}\)) of biogas. Thus, the computed energy content was 6 kWh m\({}^{-3}\), as 1 kWh is the equivalent of 3.6 MJ [35]. DM indicates the dry mass, while VS represents volatile solids in manure. VS in DM is responsible for the production of biogas. The values used in this study for DM and VS percentages for biogas generation [36] are also shown in Table 1. The CH\({}_{4}\) content in biogas varies with manure types, and this study classifies CH\({}_{4}\) concentrations as 60% for large animals and poultry manure and 45% for small animal manure [37; 38].