Integrated cultivation and photohydrogen production of tetraselmis subcordiformis in a flat-plate photobioreactor system

This paper aimed to develop an integrated processes of microalgal cultivation and hydrogen photoproduction in a flat-plate photobioreactor system combined with alkaline fuel cell. The optimal high cell density of 8.5 × 10⁶ cell/mL was achieved on 9 d when the cultivation of Tetraselmis subcordiformis was supplemented with CO² of 2%-5% (volume fraction) in the flat-plate photobioreactor. When the bioreactor system was switched to the hydrogen production condition, hydrogen evolution was induced by the addition of carbonylcyanide (m-chlorophenylhydrazone, CCCP) and anaerobic condition, with a maximum hydrogen production rate of 1.1 mL/(h·L) for 60 h. The kinetics analysis of algal chlorophyll fluorescence was carried out to identify the limiting factors in both algal growth and hydrogen production at 2% CO² supplementation. At hydrogen production phase, algal PS II activity and relative electron transfer rate (rETR) decreased with the increase of time, which caused the decline and eventual stop in hydrogen production. To sustain the hydrogen production, PS II activity and rETR must be maintained. The results demonstrate the feasibility of process integration of algal cultivation and hydrogen production in one single system, which will significantly improve the process economics.