Rice Husk to Produce Both Bio-H 2 via Dark Fermentation and Photocatalytic Hydrochar

In this work, Bio-H 2 was produced through a dark fermentation (DF) process from granulated anaerobic sludge (GAS) using rice husk (RH) as substrate, and to reuse the solid residue generated in this step, a hydrochar capable of degrading the dye rhodamine B (RhB) and the herbicide dicamba were produced. The RH was characterized, prepared, and submitted to an acid hydrolysis process and evaluated from the total sugar (TS) content and concentration of inhibitors. The highest recovery of TS was 19.97 g L −1 and the inhibitors concentrations were lower than the limit of quantification of 0.005 g L −1 for furfural and 0.0005 g L −1 for 5-(hydroxymethyl)furfural. The maximum production and yield of Bio-H 2 were 5.37 mL g RH −1 and 0.179 ml H 2 h −1 g RH −1 , respectively, obtained when using the acid hydrolyzate (1% v/v H 2 SO 4 ) as substrate and GAS as inoculum in the DF process. The solid residue produced in the acid hydrolysis was used to produce hydrochar. Hydrochar: ZnO and hydrochar: TiO 2 proportions were added and the increase in their photocatalytic efficiency was evaluated, as well as different granulometries. Three granulometries of hydrochar and composites were also evaluated. Photocatalytic assays showed that the hydrochar was able to degrade 100% of the herbicide at a concentration of 4.8 g L −1 at a dosage of 10 g L −1 in 60 min under UV irradiation. The composite of hidrochar: ZnO was the most efficient in the degradation of RhB dye (100%) with a concentration of 10 mg L −1 and a dosage of 2 g L −1 in 60 min. Graphical Abstract