Biomass immobilization in hydrolyzed lignocellulosic material can enhance biohydrogen production from cassava residues?

This study evaluated cassava stems (CS) as support material and a potential co-substrate in dark fermentation. Pre-tests were carried out with cell immobilization in CS without hydrolysis and submitted to acid and steam hydrolysis. Subsequently, hydrogen production was evaluated in an anaerobic sequencing batch biofilm reactor inoculated with biomass immobilized in CS, using cassava starch wastewater as substrate (OLR of 11 and 15 gCarb L-1d-1). The reactor was run for 180 cycles with maximum volumetric hydrogen productivity and a yield of 1.48 LH2 L-1d-1 and 1.98 molH2 kg- 1Carb (OLR 15 gCarb L- 1d- 1). The carbohydrate conversion remained above 97% in both assays, with a predominance of the acetate-ethanol route. During the assays, the Food/Mi-croorganisms ratio remained between 0.8 and 1.0 gCarb gTVSd-1, promoting the biomass control in the reactor. The structural characterization of CS before and after fermentation indicates that the cellulose, hemicellulose, and lignin content in the stems were changed after hydrolysis and fermentation, confirming the material degradation. In addition, the hydrolysis increased the CS surface area and favored cell immobilization of hydrogen-producing microorganisms such as bacteria of the genus Clostridium and Hydrogenispora, demonstrating that CS can be an alternative support material and co-substrate to be explored in dark fermentation.