| Green seaweed Enteromorpha prolifera(E. prolifera), a huge amount of biomass resource, is one of the dominant seaweeds in the littoral zone of China. It distributes in a wide variety of coastal waters, such as brackish-waters of inner bays and estuaries. Green tide, frequently induced by large-scale proliferation of algae due to seawater eutrophication, has become a global ecological phenomenon, resulting in the destruction of ocean ecology, pollution, economic loss. E. prolifera bloom appeared for years in coastal cities such as Qingdao and Shanghai. Most of E. prolifera were abandoned without treatment. So, it is urgent to find a feasible method to utilize this waste effectively.In order to solve these problems, hydrothermal treatment was used to hydrolyze and saccharify fresh E. prolifera in this study. And the effect of operating conditions during hydrothermal treatment on hydrolysis and saccharification process was also analyzed to optimize the reaction parameters. Hydrolysates were used for fermentation and anaerobic digestion to assess the potency for bioethanol and SCFAs production, respectively, which could provide a meaningful reference for further large-scale utilization. Finally, characterization of residual solids was conducted to investigate the effect on compositions and properties to discuss the subsequent use of residual solids.E. prolifera contains plenty of polysaccharides, which could be hydrolyzed effectively after hydrothermal treatment to obtain biodegradable reducing sugar. The results shown that harsher hydrothermal treatment (higher catalyst concentration and temperature, longer residence time) led to greater hydrolysis. However, excessive conditions intensify the decompose of liquid products and decrease reducing sugar yield. Reducing sugar yield reached the maximum of 33.8% under the optimal condition (11% of biomass concentration,0.5% H2SO4,130? and 30 min), and the concentrations of glucose, rhamnose and xylose were 5.55 g/L,4.90 g/L and 3.65 g/L, respectively.Hydrothermal condition had a significant influence on the ethanol fermentation process. Growth and activity of yeast in the hydrolysate obtained at 110? were the best. And the highest bioethanol yield was obtained after 48 h in the hydrolysate obtained at 130 ?. The results shown that the hydrolysate of E. prolifera after hydrothermal treatment could be a feasible feedstock for bioethanol production.SCFAs yields of hydrolysates obtained at different reaction temperatures were different during the anaerobic digestion process. The highest total SCFAs yield of 26.1% was obtained after 6 days in the hydrolysate obtained at 130?. Three principal components of SCFAs were acetate (3.1 g/L), propionate (2.0 g/L) and n-butyrate (0.4 g/L).Compositions and physicochemical characteristics of E. prolifera changed dramatically after hydrothermal treatment. With the increasing of reaction temperature from 90? to 150?, volatile component of residual solids decreased from 60.8% to 45.8%, and higher heating value (HHV) increased from 11.2 kJ/g to 15.3 kJ/g. The results shown that hydrothermal treatment process was a devolatilization and energy concentration process. The amount of oxygenated functional groups, such as OH and C=O groups increased gradually after hydrothermal treatment. And oxygenated functional groups could greatly enhance the adsorption capacity to adsorb heavy metals, which provided an ideal property for the utilization of residual solids as adsorbent for heavy metals removal. |
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