# The Potential of the Biodigester as a Useful Tool in Coffee Farms
## 3 Results and Discussion
### Economic Analysis  
The implemented study provides an approach to the economic analysis of the biodgester on the coffee farms studied. We analyzed different economic indicators taking into account the investment, costs, and benefits of the application of biodgester on farms. The major cost components of the biodigester included the investment cost incurred to acquire the digester, and the operational and maintenance costs. The key part of the operational cost is the household labor time on various activities such as collecting substrate, mixing feedstock, and feeding the digester. The benefits gained include biogas for cooking, use of biol as a fertilizer, improvement in health, and reduction in negative environmental impacts. Nevertheless, sometimes social and environmental benefits are difficult to quantify (not measured). Biogas benefits are due to: (1) the substitution of fuelwood and LPG for biogas, (2) reduction in labor for fuelwood collection, and (3) the cost of LPG saved. On average the investment of the biodigester was approximately USD 1424, which included a flexible balloon, pipe connections, biogas filter, tanks for feeding and leaving the substrate, stove, transportation and installation, labor cost, civil work, and protection cover. The operational costs were obtained by asking the farmers how much time they spent on carrying out the activities each time they fed the digester. As a result, the time operational was estimated at 1/5, which would translate into a price of one fifth of the current legal minimum wage. However, it is possible that the costs associated with the labor for fuelwood collection are offset by the biodigester activities. The benefits were mainly divided into two: savings in the LPG cost and saving in fertilizer consumption. According to the information collected, each household consumed at least one LPG cylinder per month. This is the cost saved by using biogas for cooking. Regarding the replacement of fertilizer by biol, a saving of one third is expected. On average, a coffee farm uses 35 bags of fertilizer per hectare annually. So, for a two-hectare farm, USD 2554 per year would be paid. This could translate into savings of USD 851 annually for the first year. Table 4 shows the cash flow for a period of five years with a fixed annual variation of 3.5% (corresponds to an average annual inflation). Equipment depreciation and maintenance costs are included, which corresponds to 2% of the investment. In this analysis, a 12.5% discount rate was chosen based on the average interest rate charged by a bank in Colombia. As a result of cash flow, NPV was positive and IRR (21%) was higher than the discount rate. The positive response is attributed to taking into account the use of biogas and biol for farm activities. Therefore, BCR is greater than 1.0 and PBP was estimated at 3.9 years. In contrast, [PERSON] estimated a negative NPV and PBP of 5.2 years for biodigester implementation in Africa, attributed mainly to the high investment cost of the technology [49]. According to [PERSON], the design of a biodigester to fulfill cooking gas sourced from one cow's manure is optimal and profitable in Indonesia, [50]. This produces 2.247 m\({}^{3}\) gas/day and results in a positive NPV, 32.3% of IRR, 2.7 years of PBP, and 1.78 times of BCR based on price and cost reference. Moreover, we simulated a scenario without using the biol as fertilizer, and the results showed a negative NPV and IRR, BCR minor to 1.0, and PBP of 12.5 years. Although the PBP was less than the useful life of the biodigester (20 years), in this scenario the technology loses viability, and it would be necessary to adopt government incentives to encourage