Biohydrogen and methane production via a two-step process using an acid pretreated native microalgae consortium

•A native microalgae consortium was pretreated using thermal-acidic hydrolysis.•Hydrogen and methane were produced sequentially with the acidic hydrolysates.•The lower acid concentration gave the highest H2 and CH4 production.•H2 and CH4 yields were up to 45.4 and 432 mL g VS−1, respectively.

A native microalgae consortium treated under thermal-acidic hydrolysis was used to produce hydrogen and methane in a two-step sequential process. Different acid concentrations were tested, generating hydrogen and methane yields of up to 45 mL H2 g VS−1 and 432 mL CH4 g VS−1, respectively. The hydrogen production step solubilized the particulate COD (chemical oxygen demand) up to 30%, creating considerable amounts of volatile fatty acids (up to 10 g COD L−1). It was observed that lower acid concentration presented higher hydrogen and methane production potential. The results revealed that thermal acid hydrolysis of a native microalgae consortium is a simple but effective strategy for producing hydrogen and methane in the sequential process. In addition to COD removal (50-70%), this method resulted in an energy recovery of up to 15.9 kJ per g of volatile solids of microalgae biomass, one of the highest reported.