Uso de biodigestor como proposta de tecnologia social de convivência com o semiárido

Abstract

Inflation in Brazil reached the highest rate for the month of August (0.87%) in the last 21 years. Causing successive increases in the price of cooking gas, currently sold in Ceará for R$110.00 (One hundred and ten reais). Biogas is a source of clean and renewable energy, which can be converted into thermal and electrical energy, and therefore can be a viable alternative in replacing firewood and LPG (Liquefied Petroleum Gas), commonly used for cooking food in the rural areas of the Global South. The majority of the inhabitants of the Brazilian semi-arid region, especially in the state of Ceara, are in a situation of socioeconomic vulnerability. Energy security, especially when it comes to the availability of thermal energy for cooking food, also interferes with the food security of this population. Therefore, it is believed that proposing alternative sources of thermal energy, viable and efficient, such as the use of biodigesters for the production of biogas, is a way to improve the quality of life of people living in rural areas in the countryside. The aim of this research was to propose the use of biodigesters for the production of biogas, through a technological adaptation, in order to replace cooking gas, firewood and/or coal as a source of thermal energy for cooking food in homes of family farmers in the semi-arid region of Ceará, in order to mitigate socioeconomic vulnerability, improving the energy and food security of these families. In this sense, we used a prototype of a small biodigester, in batch mode, using as biomass fresh bovine manure, under 30 days of hydraulic retention. For this purpose, the biogas production was characterized by investigating the main factors capable of inhibiting the production of biogas, namely: pH, temperature, total solids, fixed solids, volatile solids, volatile fatty acids (VFA), C/N ratio, volume of biogas generated and methane concentration. As a result of this investigation a prototype biodigester capable of producing biogas in a satisfactory manner was built. The characterization of the biogas production was also performed. The initial pH was 6.86, during the cycle it presented a mode of 5.8 and at the end it stabilized at 7.20. The initial temperature was 30°C, during the cycle it presented an average of 28.9°C, and at the end 28°C. The bovine manure used as biomass had 8.1% of total solids, 2.2% of fixed solids and 5.8% of volatile solids. The digested biomass presented 6.5% of total solids, 1.6% of fixed solids and 4.9% of volatile solids. The initial VFA concentration was 58.32 mg HAc.L-1 and the final concentration was 32.05 mg HAc.L-1. The biomass presented a C/N ratio of 13.28. The volume of biogas generated was 1.56 L.L-1. d-1, with 65% methane concentration. The proposed conceptual project was represented in a computational drawing, budgeted at R$3,670.37 (Three thousand, six hundred and seventy reais and thirty-seven cents), with a payback period of 33 months, considering the monthly consumption of 1 bottled of cooking gas (LPG). It was also performed a financing simulation for the project in 36 installments, of decreasing values, being the first R$125.02 (One hundred and twenty-five reais and two cents), and the last R$98.64 (Ninety-eight reais and sixty-four cents). And so, it proved to be an economically viable project.