Combining enzymatic hydrolysis and dark–photo fermentation processes for hydrogen production from starch feedstock: A feasibility study

In this work, an integrated enzymatic hydrolysis and dark–photo fermentation were employed to enhance the performance of H2 production from starch feedstock. The starch feedstock was first hydrolyzed in sequencing batch reactor containing indigenous starch hydrolytic bacterium Caldimonas taiwanensis On1, producing reducing sugar at a yield and rate of 0.5 g reducing sugar/g starch and 1.17 g reducing sugar/h/L, respectively, under the optimal condition of pH 7.0, 55 °C and 1.0 vvm (air volume per reactor volume per minute) aeration rate. The hydrolyzed starch was continuously introduced to dark fermentation bioreactor, where the hydrolysate was converted to H2 at a rate of 0.22 L/h/L by Clostridium butyricum CGS2 at pH 5.8–6.0, 37 °C and 12 h HRT. The resulting effluent from dark fermentation became the influent of continuous photo H2 production process inoculated with Rhodopseudomonas palustris WP3-5 under the condition of 35 °C, 100 W/m2 irradiation, pH 7.0 and 48 h HRT. Combining enzymatic hydrolysis, dark fermentation and photo fermentation led to a marked improvement of overall H2 yield (up to 16.1 mmol H2/g COD or 3.09 mol H2/mol glucose) and COD removal efficiency (ca. 54.3%), suggesting the potential of using the proposed integrated process for efficient and high-yield bioH2 production from starch feedstock.