Pyrolysis and anaerobic digestion of the Egeria Densa biomass in different pretreatment conditions for potential use as a substrate in the generation of bioproducts

Abstract In recent years, the interest in clean and sustainable energy technologies has grown significantly. As an alternative to fossil fuels, organic raw materials can reduce the emission of pollutants and greenhouse gases, positively impacting the environment. Submerged aquatic plants, such as Egeria densa, have become an interesting alternative. Due to the high capacity for proliferation and its physicochemical characteristics, E. densa has potential in the generation of bio-oil and biogas for thermochemical and biological processes, respectively. Here, the authors study the pyrolysis of lignocellulosic biomass and the feasibility of methane gas production through anaerobic digestion, after different pretreatments. The design of experiments (DOE) was used to investigate mass loss, biogas yield, and extractives content. Changes in surface morphology (coloration, roughness, and porosity), during pretreatment steps, were evaluated by colorimetric assays and scanning electronic microscopy. The kinetics of biogas production was modeled through a first-order equation. According to DOE results, the degradation of lignocellulose and the efficiency of methane production were favored by the alkaline pretreatment. The maximum yield of methane at 35 °C was 231.82 mL of CH4 g−1 (VS). Changes in the chemical constitution of biomass pretreated with acid, via thermochemical strategy, were observed in colorimetric and microstructural tests, justified by the increase in the concentration of extracts. The maximum mass loss was 80 % (pyrolysis) after biomass was submitted to an acid catalyst. The results showed that the physically-chemically pre-treated aquatic macrophyte E. densa is a renewable source in bio-oil and methane production.