Uso do capim-elefante para produção de energia: tendências de pesquisas mundiais e potencial para geração de biogás no estado de Alagoas

Abstract

The growing demand for energy and the consequent threat to energy security have made the use of renewable sources a necessity worldwide. In this context, the use of energy crops is a promising alternative. Elephant grass (Pennisetum purpureum) is a grass with high biomass production, high adaptability and it grows in a wide variety of soils, including degraded soils, thus not competing with food crops. These characteristics have made elephant grass attractive to the energy market in several scenarios, such as biogas production. This study aimed to systematically analyze scientific research on anaerobic digestion from elephant grass for biogas production and evaluate the theoretical feasibility of energy production from codigestion of grass silage with waste from cattle, pig and poultry farming in the state of Alagoas. In order to understand the trends of scientific researches, a bibliometric analysis was performed using the Scopus database. To evaluate the theoretical potential for energy production from biogas in Alagoas, data on dairy cattle, pig and chicken herds in the microregions of Alagoas were collected. At first, only the herd numbers were considered and the quantitative of elephant grass was calculated from the C/N ratio of the mixture. Later, assuming that the planting of the grass is not feasible in the whole state, available hectares for grass cultivation were surveyed considering sugarcane harvest data provided by IBGE. The information about required area and available area were compared. The resulting areas were used to estimate the energy production. The results showed that 143 papers were published over 36 years. However, most of the papers had a subject matter different from the interest of this study. The remaining publications are mainly focused on the evaluation of the optimal age for harvesting elephant grass for biogas production, the application of pre-treatments in order to overcome the slow hydrolysis and the use of the grass as a second substrate in anaerobic co-digestion processes. Regarding the energy potential in Alagoas, the scenario where there was co-digestion of elephant grass silage and poultry waste showed better performance. As for the micro-region, the micro-region of Arapiraca stood out, especially the city of São Sebastião. At the end of the work, it was possible to conclude that, based on the number of publications observed, the production of biogas from elephant grass is still poorly disseminated in the scientific community. In Alagoas, Arapiraca presents itself as a potential pole of alternative energy production, thus contributing to the diversification of the energy matrix of the state.