Modelagem matemática da co-digestão anaeróbia de dejetos de suínos e bagaço de mandioca para produção de metano

Abstract

Anaerobic digestion (AD) is considered a promising approach for waste treatment, since it combines the most suitable destination of large generation biomass with the production of renewable energy from biogas. In this context, in search of an efficient energy conversion process, which reuses different substrates simultaneously, anaerobic co-digestion (AcoD) stands out as a viable biotechnology to improve the performance of methane production. Therefore, the development of this work was guided by the methane production from AcoD of swine manure (SM) with different concentrations of cassava bagasse (CB). For this, a preliminary AcoD test was carried out, in which was possible to evaluate that, given the high rapidly degradable organic matter of the CB, an accumulation of volatile fatty acids (VFA) occurred at the beginning of the AD. This condition was visualized by final pH reduction of the reactors containing the co-substrate, which inhibited the production of methane. Thereby, it was implemented for the next two experimental batch, exposed by the main article of this work, the AcoD of DS with increasing additions of CB and adjustment of the initial pH with a buffering solution of Na2CO3. At experimental batch 1, the characterizations at the end of AD pointed high removals of Total Solids (TS), Volatile Solids (VS), Chemical Oxygen Demand (COD) and Soluble Chemical Oxygen Demand (CODS) in all experimental groups. Moreover, relevant results of methane production were observed particularly for the group R4 (16.87 g/L TS) containing the highest concentration of CB with accumulated volume of 41129 ± 1783,6 mL CH4/L reactor. In addition, this group showed the highest removal of TS, VS and COD, of 62.5%, 58.6% and 77.3%, respectively, and a methane production that exceeded the control group by 46.8% (containing SM only). At experimental batch 2, methane production was severely inhibited in the reactors with the addition of 21.39 to 33.79 g/L of TS of cassava bagasse, due to the possible accumulation of large amounts of VFA during AcoD. Thus, it was observed that the buffering solution added was not sufficient to avoid pH reducing in very high amounts of CB. Finally, to describe the kinetics of methane production of AcoD of swine manure and cassava bagasse, in relation to the buffering capacity of the system, the solution of three mathematical models from two structures developed for this work was proposed. The simulation results indicated that the model that adequately represented the experimental data, with determination coefficients close to the unit (𝑅 2 𝐶𝐻4,𝑡𝑜𝑡𝑎𝑙 = 0.9811; 𝑅 2 𝐶𝑂𝐷 = 0.9636; 𝑅 2 𝑝𝐻 = 0.9912), succeeded for proposed structure 1 (limiting step model), with a specific first order growth rate and with the hypothesis of buffering capacity is linearly dependent on the BM substrate. Therefore, it can be verified that the model of structure 1 described in a potential and simplified way the buffering capacity of the system, based on the cell growth step and the concentration of the added cosubstrate in the system.