Ethanol production from kelp slag hydrolysates using genetically engineered Escherichia coli KO11

Abstract

Kelp slag refers to industrial waste produced during sodium alginate extraction from kelp. The chemical components of kelp slag were analyzed in this study. The kelp slag contained large amounts of cellulose (25.88 %) and hemicellulose (12.52 %) with minimal acid-insoluble lignin content, making it an ideal raw material for ethanol fuel production. The saccharification and ethanol transformation of kelp slag by Escherichia coli KO11 were evaluated. When glucose or xylose was used as the fermentation substrate, theoretical ethanol yields of 82.35 % (glucose) and 84.78 % (xylose) were obtained. Xylose was not used until the glucose content was below 1 % when mixed sugars were fermented. Sulfuric acid pretreatment at 121 °C for 1 h was performed before enzymatic hydrolysis. The maximum rate of enzymatic hydrolysis was 93.32 % after dilute sulfuric acid (0.2 M) pretreatment and enzymatic hydrolysis by cellulase (50 °C, pH 4.8, 16 h). Separate hydrolysis and co-fermentation (SHCF), simultaneous saccharification and co-fermentation (SSCF), and non-isothermal simultaneous saccharification and co-fermentation (NSSCF) were also performed in this study. NSSCF (co-fermentation began after enzymatic hydrolysis for 6 h) was the most effective process for kelp slag fermentation where ethanol yield reached 0.45 g g−1.