Codigestão do caldo de capim elefante BRS-Capiaçu com efluente de suinocultura visando a produção de metano

Abstract

Waste generated in agricultural or farming activities are promising sources for the production of renewable energy. Currently, the demand for the production of biofuels is growing and analyzing the Brazilian agricultural and industrial market, we can observe the growing production of elephant grass and the consumption of pork. Elephant grass is an energetic biomass widely used for the production of briquettes and pellets, with the grass juice being a residue resulting from this production. The high levels of nitrogen present in swine effluent and the high carbon content in the elephant grass broth may represent a favorable combination for the anaerobic co-digestion process aiming at the production of biogas. The objective of this study was to carry out the co-digestion of elephant grass (BRS-Capiaçu) (CC) and swine effluent (ES) aiming at the production of methane. The research was carried out in batch-type reactors. In a first stage (E1) without the addition of alkalinizer, a Simplex Lattice mixture planning was carried out, where the COD apl was set at 4.0 g/L and the mixture compositions were varied (0:100, 20:80, 40:60, 60:40, 80:20, 100:0, CC:ES) to evaluate the fits to the linear and quadratic model. In the second stage (E2) with the addition of sodium bicarbonate, an experimental design 23 was used with conditions where it varied (4.0-8.0gDQOapl/L; 0.0- 0.20g/g CNaHCO3; 40: 60-20:80 CC:ES), to evaluate the linear model. In E1, the results showed carbohydrate removal efficiency between 42 and 72.48%, COD between 18.78 and 53.82% and SVT between 34.81 and 54.78%. The highest accumulated methane production was related to the monodigestion of swine effluent with 2,728.11 mLCH4 and secondly 2,235.49 mLCH4 in the 20:80 condition. Still under the same condition, maximum yield and volumetric production rate values of 3,921.90 mL-CH4/gDQOapl and 98.11 mLCH4/(gDQOapl.d) were obtained, respectively. The quadratic model had the best fit compared to the linear model and it was found that there was a synergistic interaction between them. It was found in E2 that the presence of sodium bicarbonate was essential for buffering the reaction medium, as the pH remained in the appropriate range under the experimental conditions in which the alkalinizer was added. The linear model obtained a better fit for the maximum potential and lag phase. In view of this, it is concluded that the anaerobic co-digestion technology was satisfactory since the digestibility of the residues involved, the swine effluent (rich in nitrogen) and the elephant grass broth (high carbon content), was positive for the treatment. of both and for the production of methane.