Enhancing hydrogen production of Clostridium butyricum using a column reactor with square-structured ceramic fittings

A new approach in bioreactor development for fermentative hydrogen production was undertaken using monoliths (square-structured ceramic fittings) as seeds to enhance bubble formation in the fermentation broth. Clostridium butyricum CGS2 was used throughout the batch and continuous experiments on sucrose substrate. In a batchwise column reactor with a COD of 20 g/L, the hydrogen-production performance increased and caused a shift in the metabolism when the ceramic fittings were installed. Compared to the stirred tank the H₂ yield and the volumetric production rate were lower, but the specific production rate turned out to be maximized using three monoliths. Continuous runs with and without monoliths were carried out with various sucrose concentrations leading to a COD loading of 10-40 g/L at an HRT of 5.5 h. Compared to the standard column reactor (SCR), the novel monolith column reactor (MCR) showed a 35% increase in hydrogen-production rate to 305 mL/L/h and a 30% increase in hydrogen yield to 0.92 mol per mol hexose consumed. Most interestingly, the specific hydrogen-production rate increased by about 60% to 292 mL/h/g CDW at a COD of 20 g/L. It is concluded that ceramic fittings in fermentative biohydrogen production offer a great potential for further improvements without the drawbacks of traditional methods to increase hydrogen-production performance.