Biorefinery of cassava pulp: Biohydrogen production through high-solids simultaneous saccharification and dark fermentation, and poly(3-hydroxybutyrate) production from lactic acid-rich hydrogenic effluent

Cassava ( Manihot esculenta Crantz) pulp (CP) is a solid residue generated in large quantities as a by-product of the cassava starch industry. Owing to its ready availability, low cost, and high carbohydrate content, it is used in the present study as a feedstock for biohydrogen production under a high-solids simultaneous saccharification and dark fermentation (SSDF) process. The hydrogenic effluent containing lactic acid, acetic acid, and butyric acid, was subsequently fermented by Paracoccus sp. KKU01 to produce poly(3-hydroxybutyrate) (PHB), a bioplastic recognized as a viable alternative to the synthetic ones. Using a CP concentration of 150 g/L, the high-solids SSDF process yielded 3168 ± 85 mL of biohydrogen, equivalent to a yield of 21.1 ± 0.6 mL-H 2 /g-CP. The hydrogenic effluent contained lactic acid as the major component (44.1 ± 0.1 g/L), with small amounts of acetic acid (3.7 ± 0.1 g/L) and butyric acid (12.5 ± 0.1 g/L). Using a fed-batch fermentation process, with four feedings of undiluted hydrogenic effluent, Paracoccus sp. KKU01 consumed approximately 96 % of the acids, producing 19.7 ± 0.3 g/L of biomass, and 5.8 ± 0.4 g/L of PHB, which was equivalent to a PHB content of 29.7 ± 1.8 %. Based on the results, a sequential process of high-solids SSDF and fed-batch fermentation, with mass balance, is proposed for valorization of CP to address both the energy and environmental challenges. • Sequential process for efficiently valorizing cassava pulp (CP) into biofuel and bioplastic. • High-solid SSDF process was developed for biohydrogen production from CP. • Up to 21.1 mL/g-CP of hydrogen was obtained through the high-solid SSDF process. • Utilization of lactic acid-rich hydrogenic effluent for PHB production. • Efficient conversion of acids, including lactic acid, into PHB at high yield (0.12 g/g-acids).