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.