Produção de biogás a partir da macrófita aquática Hydrilla verticillata

Abstract

Human activities generate polluting waste which, when improperly managed, can contaminate water bodies and contribute to the proliferation of photosynthetic organisms. Among these organisms is Hydrilla verticillata, an aquatic weed of significant global importance found in the Paraná River Basin. In this context, this study assessed the potential for the energy utilization of Hydrilla verticillata through anaerobic digestion, using digested swine slaughterhouse sludge as inoculum. To determine the potential for biogas production, assays were performed to characterize the inoculum, substrates, and digestates, evaluating the following parameters: total, fixed, and volatile solids, total and ammoniacal nitrogen, pH, intermediate and partial alkalinity. Biochemical methane potential (BMP) assays were carried out in batch reactors using sun-dried macrophytes with inoculum:substrate ratios (ISR) of 3:1, 2:1, and 1:1. Microcrystalline cellulose was used as a positive control (RIS 2:1), and the blanks contained only the inoculum. The biogas production in ISR was 1122.9 ± 42.4 mL, 1048.8 ± 32.7 mL, and 905.2 ± 19.9 mL, respectively, with no significant difference. The systems achieved stability within 42 days and showed satisfactory biogas production. Throughout the BMP test, pH values in the assays remained between 6.71 and 8.15, close to the optimal range for biogas production. A reduction of 18.3% ± 3.7% in partial alkalinity was observed in the blanks, while the cellulose assays exhibited increases of 34.9% ± 4.0%, and the ISR showed an increase of 138.5% ± 33.9%. Additionally, the assays showed reduced intermediate alkalinity ranging from 66.5% to 82.2%. Carbon content decreased by 26.9% ± 6.0% in the blanks, 27.1% ± 7.5% in the cellulose assays, and 24.1% ± 6.6% in the ISR. Despite the influents' carbon-to-nitrogen (C/N) ratio being below the ideal range for anaerobic digestion, biogas production was satisfactory, with a gradual increase in methane content throughout the process. On day 30, methane content reached 65.53% ± 3.87% in the ISR, 59.40% ± 4.50% in the cellulose assays, and 66.39% ± 2.64% in the blanks. This study demonstrated that Hydrilla verticillata could be a promising option for energy utilization through anaerobic digestion, contributing to biogas production. Moreover, employing digested slaughterhouse sludge as inoculum makes it possible to provide a more suitable destination for these wastes, thus avoiding negative environmental impacts. Given the growing demand for resources and the need for more sustainable alternatives, using aquatic macrophytes for biogas production emerges as a promising solution, combining environmental and energy benefits.