H-2 production from marine and freshwater species of green algae during sulfur deprivation and considerations for bioreactor design

Summary

Twenty-one species of green algae isolated from marine, freshwater and terrestrial environments were screened for the ability to produce H-2 under anaerobic conditions. Seven strains found positive for H-2 production under anaerobic conditions were also screened for the ability to produce H-2 under sulfur (S) deprivation. In addition to the traditional model species Chlamydomonas reinhardtii, C. noctigama (freshwater) and C. euryale (brackish water) were able to produce significant amounts of H-2 under S-deprivation. These species were also able to utilize acetate as a substrate for growth in light. The S-deprivation experiments were performed under photoheterotrophic conditions in a purpose-specific designed bioreactor, and it was shown that an automated pH adjustment feature was essential to maintain a stable pH in the cultures. Several materials commonly used in bioreactors, such as rubber materials, plastics and steel alloys, had a negative effect on the survival of S-deprived algae cultures. Unexpectedly, traces of H-2 were produced under S-deprivation during O-2 saturation in the cultures, possibly derived from local anaerobic environments formed in algal biofilms on the membranes covering the O-2 electrodes.