Lignocellulosics biomass biodegradation of water hyacinth and water lettuce by white rot fungi for bioethanol production

Abstract

Nowadays, renewable energy has become alternative energy to reduce the consumption of fossil fuels. Therefore, lignocellulosic materials such as crop residues, grass and wood, and aquatic plants that are inedible has become potential sources for bioethanol production. In this study, water hyacinth (WH) and water lettuce (WL) were selected as potential resources of their abundance in nature and can be easily propagated and cultivated. Although these floating aquatic plants are considered as the most problematic plants due to their uncontrollable growth in water bodies worldwide, their ability to remove pollutants from wastewater has created a sustainable approach for their use in phytoremediation and further use as biomass substrates for bioethanol production. The use of phytoremediation by implementing invasive floating aquatic plants can support the sustainable management of wastewater treatment in the future. This study aims to determine the potential of WH and WL as bioindicators for phytoremediation and at same time to produce a high amount of sugar consumption for bioethanol production. In addition, this study emphasizes the biodegradation of WH and WL by white-rot fungi collected from decayed wood and soil. White-rot fungi have the ability to degrade lignin, hydrolyze cellulose, and hemicellulose, and ferment alcohols for bioethanol production. Trichoderma citrinoviride M3, Schizophyllum commune M8, and Pestalotiopsis sp. M12 were selected from twelve fungal species on the basis of rapid growth rate after five days of incubation and further use for degradation of lignocellulosic materials from water hyacinth and water lettuce and for bioethanol production. These fungal species were identified by morphological characterization and 18S rRNA sequence analysis. To date, the use of biological pretreatment using T. citrinoviride M3, S. commune M8, and Pestalotiopsis sp. M12 with regard to water hyacinth and water lettuce substrates as well as its further use for the fermentation process to produce bioethanol has not been explored before. The parameters involved are sugar content by the dinitrosalicylic acid (DNS) Method, the determination of lignin by the Klason Method, the determination of cellulose and hemicellulose by the Chesson Method, and the determination of bioethanol by Gas Chromatography (GC). The results showed that both WH and WL indicated the same correlation trend between biomass growth and sugar content, as the sugar content increased when the plants reached the highest growth. However, WH has more extractable sugar than WL, which is more significant because fermentable sugar is needed for the fermentation process to produce bioethanol. The results also showed that T. citrinoviride M3 has the highest rate of degradation of lignocellulosic materials compared to S. commune M8 and Pestalotiopsis sp. M12. Therefore, T. citrinoviride M3 was selected for further investigation to evaluate the simultaneous saccharification and fermentation process for bioethanol production. The results showed that WH and WL produced 8.6 g/L and 7.4 g/L yield of ethanol, respectively, proportional to the fermentation time, with an increasing time of up to 96 hours. Overall, it can be concluded that WH is a promising biomass when the simultaneous co-cultivation of T. citrinoviride M3 with S. cerevisiae is used for bioethanol production and the fermentation process is fully optimized. The findings of this study would be beneficial for future investigation, especially in exploring the potential production of bioethanol from phytoremediation technology systems.