# The Potential of the Biodigester as a Useful Tool in Coffee Farms
## 4 Conclusions  
The anaerobic digestion process was proven to be an application useful for the care, growth, and obtaining of a product that is eco-sustainable on coffee farms. Additionally, by its nature, renewable biogas allows for the replacing of fuels such as firewood in a way that is more efficient and, likewise, to make the use of a biodgester for the treatment of honey waters more attractive. The use of biogas would also replace the propane gas usually employed. The composition of the biogas analyzed allows the delivery of sufficient energy for cooking and drying coffee in the on-farm process.  
The studies and analyzes performed regarding the co-digestion process in the biodigesters installed determined a reliance on substrates because these help to maintain stable conditions and avoid affecting the microbial diversity in charge of the transformation of matter to biogas. Consequently, it is considered important for the maintenance and engagement of farmers to achieve efficiency of the system. Due to this, the environment conditions can severely affect the physical condition of components (heat exchanger, solar tunnel dryer, biogas pipeline and biodigester) because these are submerged natural habitats. The proposed thermal system allows for the drying of coffee through the use of biogas, reducing process times and maintaining appropriate temperatures.  
On the other hand, biol has been considered as a beneficial subproduct, on account of its properties, as a natural fertilizer for the crops according to the literature studied. In addition, economic analysis infers that biol reduces the payback time due to savings in chemical fertilizer costs. However, the composition of biol and its effects on the soil require further study for coffee farms.  
Therefore, the cost analysis shows that the investment will only be profitable in the fourth year and that the investment cost of the bioreactor is quite high compared to the benefits. This is due to the high cost of the technology, and, mainly, transport costs. This fact may require government incentives to improve social and environmental conditions in the rural sector. Consequently, the thermal system proposed in this research highlights the use of biodigesters as a useful tool in rural coffee growing areas because of its environmental impact mitigation of the coffee post-harvesting process and the economic sustainability of agriculture.  
Future research should analyze the co-digestion process in coffee's honey waters, to comprehend the microbial dynamics and the stability of the anaerobic process. In addition, future research should evaluate the application to find an optimal dosage of biol and obtain a system that is more efficient in the soil to obtain eco-sustainable production.  
The authors are responsible for all the aspects of the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research has been financed by the project \"Innovacion de procesos a nivel de poscosecha para la incorporacion de valor agregado en la diferenciacion de cafes especiales del Tolima\". Special cooperation agreement N\({}^{\circ}\)1874-2018.  
Not applicable.  
All data are available after reasonable request to the corresponding author.  
The authors appreciate the support of Gobernacion del Tolima, in the financing of the project code BPIN 2016000100049, Innovacion de procesos a nivel de poscosecha para la incorporacion de valor agregado en la diferenciacion de cafes especiales del Tolima, special cooperation agreement N\({}^{\circ}\)1874-2018. In the same manner to the Universidad de Ibague by the financial support, technique, and administration of project code 18-487-ESP. Finally, to Cortolima for the support given in the visits made to the coffee farms in the department of Tolima.