Orthogonal optimization of Carboxydothermus hydrogenoformans culture medium for hydrogen production from carbon monoxide by biological water-gas shift reaction

The objective of the present study was to investigate the optimal nutritional requirements for hydrogen production from carbon monoxide by biological water-gas shift (WGS) reaction with Carboxydothermus hydrogenoformans using orthogonal layout methods. Cultures of C. hydrogenoformans on the medium as formulated by the strain supplier (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH) unexpectedly showed a large content in inorganic material. This was confirmed by the rather elevated levels of calcium and phosphorus contained in the grown biomass. As an excessive production of those minerals may interfere with the growth and catabolism rates as well as clog up biofilm-based reactors, it was desirable to minimize the mineral accumulation during growth, while keeping at maximal levels both the H2 yield and the specific H2 production rate (SHPR). PO43−, HCO3−, Ca2+ and Mg2+ were considered as potentially the major factors of the mineral accumulation. The experiments were designed according to the Taguchi’s orthogonal method, using the above factors at three levels, and considering the culture mineral content, the H2 yield and the SHPR as optimization criteria. Optimal concentrations of PO43−, HCO3−, Ca2+ and Mg2+ were determined as (mM): 1.0, 5.0, 0.1 and 0.5, respectively. Under those culture conditions, Ca + P content decreased from 55.6 ± 1.8 to 9.5 ± 3% while the highest H2 yield at 90.9 ± 1.2% and SHPR at 0.85 ± 0.06 mol H2 g−1 VSS d−1 were achieved in bottle batch tests at 100% CO headspace atmosphere, neutral pH, a temperature of 70 °C, and an agitation of 100 rpm.

► Carboxydothermus hydrogenoformans   can accumulate up to 94% of minerals during growth.
► Medium content was optimized using Taguchi’s orthogonal method.
► Optima for PO43−, HCO3−, Ca2+ and Mg2+ were 1.0, 5.0, 0.1 and 0.5 mM, respectively.
► Ca + P content of cells grown on optimal medium decreased from 56 to 10%.
► Meanwhile H2 yield kept at 91% and specific activity, at 0.85 mol H2 g−1 VSS d−1.