Pretreatments On Lignocellulosic Substrates Of Water-Remediated Plants For Anaerobic Fermentation Conversion Into BioH₂

Biohydrogen (BioH2) conversion from lignocellulosic biomass substrates of waterbody remediated plants in constructed wetland is one of the promising alternatives to fossil fuels. In this study, wetland plants(Phragmites (sp.), Thalia dealbata) and aquatic emergent plants (Hydrocotyle verticillata, Myriophyllum aquaticum) were used as lignocellulosic substrates, to develop different pretreatments with steam explosion (SE) and/or ionic liquid ([Bmim]Cl) for enhancing bioH2conversion from substrates with different lignocellulosic structures.Both Phragmites (sp.) and Thalia dealbata are holocelluloses-rich and lignin-rich wetland plants for biomass (58-76%), and Phragmites (sp-) stalks enrich more holocelluloses than Thalia dealbata. Scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR) demonstrated alteration of lignocellulosic structures due to hemicelluloses removal and slightly lignin increase by steam explosion (SE) pretreatment, and further disruption of cellulose crystallinity after treatment with SE followed by [Bmim]Cl (SE-[Bmim]Cl). Thermogravimetry/differential thermogravimetry (TG/DTG) displayed increase in amorphous cellulose and partially delignification in lignocellulosic structures as a consequence of SE-[Bmim]Cl. The pretreatment of both SE and SE-[Bmim]Cl led to lignocellulosic substrates with improved properties in terms of their conversion into glucose and bioH2. Five-to-ten folds (by SE) and ten-to-twenty folds (by SE-[Bmim]Cl) glucose were released from the lignocellulosic substrates of both plants than those of contrast samples. Compared to Phragmites (sp.), the greater destruction in lignocellulosic structure of Thalia dealbata as consequences of SE and SE-[Bmim]Cl, increased the accessible surface area and disrupted the cellulose crystallinity much more thus efficient for bioH2conversion. The bioH2of1.97±0.14mmol H2/g dry weight (DW) yielded after sludge anaerobic fermentation of Thalia dealbata treated with SE, and it increased to4.79±0.86mmol H2/g DW after SE-[Bmim]Cl treatment; while for Phragmites (sp.) it was1.45±0.42and2.75±0.76mmol H2/g DW after SE and SE-[Bmim]Cl pretreatment, respectively. Therefore, SE-[Bmim]Cl pretreatment can be developed for efficiently enhancing bioH2conversion from wetland plant Thalia dealbata.Compared to cellulosic biomass of Phragmites (sp.) and Thalia dealbata, both Hydrocotyle verticillata and Myriophyllum aquaticum contain low levels of cellulose, hemicellulose and lignin (35%) but enrich high levels of crude protein, crude fiber and starch (63%). Observations from SEM, FTIR and TG/DTG demonstrated hemicelluloses degradation in lignocellulosic structure of both plants and decrease of cellulose crystallinity in Myriophyllum aquaticum lignocelluloses as a consequence of SE pretreatment. Two-to-three-fold (by SE) enhancement appeared in the enzymatic hydrolysis rate and glucose release from the lignocellulosic substrates of both plants than those of contrast samples. The structure of Myriophyllum aquaticum was greatly destroyed by SE compared to Hydrocotyle verticillata, which increasing the accessible surface area and pores volume of cellulose. The raw Myriophyllum aquaticum and Hydrocotyle verticillata exhibit high bioHb yield of2.9-8.1mmol H2/g DW after sludge anaerobic fermentation. SE pretreatment caused crude protein, crude fiber and starch degraded and released into liquid fraction and then producing cellulose-rich lignocelluloses in solid fraction. BioH2of0.7-3.0mmol H2/g DW yielded from the SE-pretreated lignocellulosic substrate for both plants. Therefore, the raw Hydrocotyle verticillata and Myriophyllum aquaticum can be efficiently converted into bioH2and the enhanced glucose were released by SE pretreatment from both plants biomass.