Hydrolysis of Chlorella biomass for fermentable sugars in the presence of HCl and MgCl2

► HCl and MgCl2 as synergic catalyst. ► Synergic chemical hydrolysis of Chlorella biomass to produce more fermentable sugars. ► The sugar recovery with mixed HCl/MgCl2 catalyst was more than the sum of that with HCl or MgCl2 as single catalyst, respectively. ► Glucose in Chlorella biomass hydrolysate could be conversed into ethanol at high yield. When Chlorella biomass was hydrolyzed in the presence of 2% HCl and 2.5% MgCl2, a sugar concentration of nearly 12%, and a sugar recovery of about 83% was obtained. Fermentation experiments demonstrated that glucose in the Chlorella biomass hydrolysates was converted into ethanol by Saccharomyces cerevisiae with a yield of 0.47gg−1, which is 91% of the theoretical yield. This chemical hydrolysis approach is thus a novel route for the hydrolysis of biomass to generate fermentable sugars.