Biodigestor anaeróbico na agricultura familiar: produção de biogás e biofertilizante a partir de resíduos pecuários e implantação de cultivo de microalgas

Abstract

Researches on renewable energies has grown significantly over the years, as they generate clean and sustainable energy, seeking to reduce or replace fossil fuels. Because they are largely responsible for the emission of greenhouse gases and other environmental problems. Another problem that influences these environmental impacts is the inadequate discard of agricultural residues in the soil and water bodies, such as swine and poultry manure. Given this scenario, the production of biogas using these wastes, which are abundant and have great energy potential, emerges as a viable solution for rural family farmers, promoting an alternative energy source, reducing fossil fuel consumption and environmental damage generating biofertilizer that can be used in agriculture or in the cultivation of microalgae. In this sense, three homemade anaerobic digesters were developed, which were fed with swine and poultry manure and a binary mixture (swine and poultry manure). Biogas production and composition of CH4, CO2, H2S and NH3 gases, temperature and pH parameters were determined, as well as analysis of total solids, fixed and volatiles. The largest production of biogas was generated by the BS of 3.747 m3 in a period of 38 days, followed by the BB of 3.726 m3 in 56 days, and the lowest production was for BA with 0.650 m3 in 35 days. The biodigesters had a maximum temperature of 33.33 °C and a minimum of 26.59 °C, with an average temperature of 30.76 °C. The pH ranged from 7 to 7.5, from 7 to 8 and 6.8 to 6, for BS, BB and BA, respectively. The BS had CH4 concentrations ranging from 65% to 81%. The BA showed concentrations of CH4 that ranged from 60% to 43%. And BB had CH4 concentrations ranging from 68% to 80%. The BS showed the highest production of biogas and methane in relation to the reduced SV of the total volume of the biodigesters, which was 804.8 L/kg SV of biogas and 572.2 L/kg SV of methane. Followed by BB with 626.0 L/kg SV of biogas and 457.6 L/kg SV of methane, and the lowest values were reported in BA with 522.8 L/kg SV of biogas and 259.4 L/kg SV of methane. Another test was carried out with the poultry manure to correct the pH, the BAC produced 2.196m3 of biogas, that is, 3.3 times more than the uncorrected BA, and the pH ranged from 6.8 to 7.2. BAC obtained biogas production of 1102.4 and methane 628.5 L/kg of SVr. The media synthesized with the biofertilizers generated by the biodigesters showed efficiency for the cultivation of the microalgae Monoraphidium contortum, Golenkinia radiata and Chlorella sp. The purification of biogas in the cultivation of the microalgae Chlorella sp. showed removal efficiency from 20.5±1.6 to 53.8±3.3% depending on the concentration of CO2 in the biogas, and the calorific value ranged from 24702 to 32578 kJ m-3. Being close to the value of pure methane, which is 35800 kJ m-3, showing that the process of purification of CO2 through the cultivation of Chlorella sp. it is feasible to increase the purity of the biogas. The cultivation of Chlorella sp. with addition of biogas increased the concentration of algal biomass and the content of PT, CT and LT compared to the control trial and the alternative medium without addition of biogas. Showing the great potential of biogas generation by biodigesters using agricultural waste, and alternative means synthesized from biofertilizers and the addition of biogas for the production of microalgae, which can be implemented in family farming.