Promotion of H2 production by microwave-assisted treatment of water hyacinth with dilute H2SO4 through combined dark fermentation and photofermentation

• Water hyacinth is microwaved with dilute H2SO4 to improve enzymatic hydrolysis.
• Hydrolyzed hyacinth is fermented by hydrogenogens to improve dark H2 yield.
• Nearly 100% glucose and most arabinose in hydrolysate are used in dark fermentation.
• H2 yield from hyacinth via combined fermentation is 75.2% of theoretical H2 yield.

Water hyacinth was treated with microwave-assisted dilute H2SO4 to improve saccharification before enzymatic hydrolysis and H2 production during dark fermentation. A maximum reducing sugar (RS) yield of 64.4 g/100 g total volatile solid (TVS) (96.1% of the theoretical RS yield) was achieved when water hyacinth was treated through microwave heating with 1% dilute H2SO4 for 15 min at 140 °C and then enzymatically hydrolyzed for 72 h. During enzymatic hydrolysis, glucose was efficiently produced from the hydrolysis of cellulose that resulted from the disruption of the lignocellulosic structure of water hyacinth after microwave-assisted H2SO4 treatment. When the hydrolyzed water hyacinth was inoculated with H2-producing bacteria to produce H2 during dark fermentation, a maximum H2 yield of 112.3 ml/g TVS was obtained. The major sugar compositions in the residual solution from dark fermentation were xylose and cellobiose (total RS utilization efficiency: 88.5%). Through a combination of dark fermentation and photofermentation, the maximum H2 yield from water hyacinth was significantly increased from 112.3 ml/g TVS to 751.5 ml/g TVS, which is 75.2% of the theoretical H2 yield.