Enhanced biohydrogen production from tofu residue by acid/base pretreatment and sewage sludge addition

摘要

Anaerobic dark fermentation is considered a promising technology for clean energy production and waste reduction. In the present work, tofu residue and sewage sludge were utilized as substrates for fermentative hydrogen production. To increase the biodegrad-ability, tofu residue was pretreated for 30 min in the presence of HC1 and NaOH at various concentrations (0, 0.5,1.0, and 2.0%), and then fermented by a thermophilic (60 °C) mixed culture. The solubility (SCOD/TCOD ratio) of the tofu residue increased from 4 to 30-40% after pretreatment, and the increased soluble constituents were mainly protein rather than carbohydrate compounds. However, in spite of a slight increase of carbohydrate solubility, the H_2 production performance was significantly enhanced by pretreatment, owing to the degradability of thermophilic cultures used on insoluble tofu residues. The limited H_2 yield of 0.30 mol H_2/mol hexose_added achieved in the raw tofu residue was increased 1.6- to 4-fold with the highest H_2 yield of 1.25 mol H_2/mol hexose_added at 1.0% HC1 concentration. Carbohydrate degradation and the H_2 production rate also increased from 39 to 50—65% and 27 to 50—120 mL H_2/L/h, respectively. The role of pretreatment was not only to increase the biodegradability but also to suppress the activity of indigenous non H_2-producers such as lactic acid bacteria and propionic acid bacteria. When sewage sludge was added to acid pretreated (1.0% HC1) tofu residue as a co-substrate, the H_2 yield and H_2 production rate increased to 1.48 mol H_2/mol hexose_added and 161 mL H_2/L/h, respectively, which was attributed to the abundant minerals, vitamins, and metals contained in sewage sludge.