Experimental workflow for developing a feed forward strategy to control biomass growth and exploit maximum specific methane productivity of Methanothermobacter marburgensis in a biological methane production process (BMPP)

Recently, interests for new biofuel generations allowing conversion of gaseous substrate(s) to gaseous product(s) arose for power to gas and waste to value applications. An example is biological methane production process (BMPP) with Methanothermobacter marburgensis. The latter, can convert carbon dioxide (CO 2 ) and hydrogen (H 2 ), having different origins and purities, to methane (CH 4 ), water and biomass. However, these gas converting bioprocesses are tendentiously gas limited processes and the specific methane productivity per biomass amount (qCH 4 ) tends to be low. Therefore, this contribution proposes a workflow for the development of a feed forward strategy to control biomass, growth (r x ) and q CH4 in a continuous gas limited BMPP. The proposed workflow starts with a design of experiment (DoE) to optimize media composition and search for a liquid based limitation to control selectively growth. From the DoE it came out that controlling biomass growth was possible independently of the dilution and gassing rate applied while not affecting methane evolution rates (MERs). This was done by shifting the process from a natural gas limited state to a controlled liquid limited growth. The latter allowed exploiting the maximum biocatalytic activity for methane formation of Methanothermobacter marburgensis . An increase of q CH4 from 42 to 129 mmol CH4 g −1 h −1 was achieved by applying a liquid limitation compare with the reference state. Finally, a verification experiment was done to verify the feeding strategy transferability to a different process configuration. This evidenced the ratio of the fed KH 2 PO 4 to r x (R(F KH2PO4 /r x )) has an appropriate parameter for scaling feeds in a continuous gas limited BMPP. In the verification experiment CH 4 was produced in a single bioreactor step at a methane evolution rate (MER) of   132 mmol CH4 *L −1 *h −1 at a CH 4 purity of 93 [Vol.%].