Fermentative biohydrogen production from molasses wastewater—Experiences of substrate storage and concentration indicator

Sugarcane processing would generate large volume of wastewater rich-in organic matters that could be used as a substrate for biohydrogen production via dark fermentation. This work reports on the experiences of using real wastewater, generated by a company that used molasses as raw-material to produce brown sugar, molasses-syrup, and ginger-brown sugar tea, for biohydrogen production with a continuously stirred tank reactor fermenter. The wastewater had variable characteristics of chemical oxygen demand (COD) concentration 104–180 g/L, total sugars 59–181 g/L, and ethanol 6.4–11.8 g/L. The continuous fermentation resulted in average values of hydrogen production rate 2.43 L/L-d, total sugar degradation rate 91%, and hydrogen yield 0.56 mol H 2 /mol hexose. Main findings were that a long wastewater retention would generate a high ethanol concentration that might inhibit biohydrogen production, and total sugar concentration was a more practical feeding-load indicator than COD, and they are less be reported in fermentative biohydrogen technology studies. Strategies for reducing ethanol inhibition and increasing bioenergy recovery were discussed. The significance of this study is to provide useful information for molasses-related industries having existing wastewater treatment infrastructure about how to effectively use its organic-rich wastewater for producing biohydrogen as green fuel. • Biohydrogen production from molasses-based wastewater. • Hydrogen production rate 3.28 L/L-d and yield 0.46 mol/mol hexose were obtained. • Total sugar is more suitable than chemical oxygen demand as a feeding concentration indicator. • Wastewater management and increasing bioenergy recovery strategies were discussed.