Developing pretreatment methods to promote the production of biopolymer and bioethanol from residual algal biomass (RAB)

Abstract

This study investigates the effect of acidic pretreatment (HT-ACPT), enzymatic pretreatment (ENZ-PT), and microwave laser-hydrogen peroxide-Fe-nanoparticle pretreatment (Mv-H2O2-Fe-PT) on the production of bioethanol (bio-eth.) and biopolymer (bio-p) from residual algal biomass (RAB). The effectiveness of these pretreatments is based on using the entire RAB and maximizing sugar liberation to produces bio-p and bio-eth under optimized conditions. The Mv-H2O2-Fe-PT yielded the maximum total and soluble sugar liberation of 0.988 ± 0.08 and 0.6888 ± 0.08 g/gDCW compared with HT-ACPT (0.588 ± 0.02 and 0.488 ± 0.02 g/gDCW) and ENZ-PT (0.528 ± 0.06 and 0.428 ± 0.06 g/gDCW). All pretreatment methods split the β-1, 4-glycosidic bonds into cellulose and liberate sugars that were later used to produce bio-p and bio-eth. The algal strains treated by Mv-H2O2-Fe-PT produced the highest bio-p of 0.740 ± 0.004 gpolyemer/gDCW, which is 1.3 folds higher than the productivity of HT-ACPT and ENZ-PT. The HT-ACPT and ENZ-PT produced 67 to 72 % and 59 to 63 % lower biopolymer yield. The maximum bioethanol production (Mbio−ethP) of 0.950 ± 0.005 mL/gRAB was achieved using microalgae pretreated with Mv-H2O2-Fe-PT and incubated at pH = 5.5 and 37 °C. The Mbio−ethP was negatively affect by increasing the pH or decreasing the temperature. The Mbio−ethP decreased to 0.853 ± 0.002 mL/gRAB by increasing the pH to 6 and to 0.761 ± 0.002 mL/g when the temperature decreased to 33 °C. The Mbio−ethP as a fraction of theoretical yield (%ThY) were in the ranges of 21 to 33 %, 33.3 to 51.1 % and 59.52 to 91.2 % for RAB pretreated with HT-ACPT, ENZ-PT and Mv-H2O2-Fe-PT, respectively. The produced bio-p exhibited excellent properties and can be used in a variety of applications including soil additives, biofuel production, regenerative medicine, and other medical applications. The Mv-H2O2-Fe-PT pretreatment offers complete use of RAB to produce different bio-products.