Biological hydrogen production via self-immobilized bacteria
by Bo Hu, Ph.D.
Washington State University
Chair: Shulin Chen
This dissertation explored a creative bacteria immobilization method for hydrogen
fermentation. The low growth rate of hydrogen producing bacteria limits the productivity
of a suspended-growth reactor due to the requirement for long hydraulic resident time
(HRT) to maintain adequate bacteria population. Microbial immobilization is an effective
way for bacteria retention, however, traditional calcium alginate entrapment has many
limitations for applications in hydrogen fermentation. Anaerobic granular sludge was
proposed as the immobilized hydrogen producing bacteria to be used in hydrogen
fermentation after methanogenic activity of the granules was eliminated in the
pretreatment process. Chloroform treatment of methanogenic granules was compared
against acid and heat treatments for the effectiveness to eliminate methanogenic activity.
The results showed that chloroform treatment was the most effective among the three
methods tested. Chloroform caused elimination of methanogenic activity while allowing
normal hydrogen production. Chloroform treated anaerobic granular sludge was proposed
as immobilized hydrogen producing bacteria to be used in the hydrogen fermentation.
Chloroform treated granules could be re-used for over four fed-batch cultures with pH
adjustment, and could be repeatedly cultured for eight times without noticeable damage.
Continuous culture with chloroform treated granules showed that the granule structure
could be kept for over 15 days and new granules started to form after 10 days of
operation. The hydrogen productivity reached 11.6 L/L/day at HRT of 5.3 hours. The
optimum initial pH of the culture medium was neutral and the optimum glucose
concentration was below 20 g COD/L.
This study also investigated the possibility of integrating both the immobilized
hydrogen fermentation with chloroform treated granules and the immobilized methane
production with untreated granular sludge. The results showed that the integrated batch
cultures provided 1.01 mol hydrogen and 2 mol methane per mol glucose.
16s rRNA microbial analysis was used to investigate the community change
during the chloroform treatment. Most of the Methanogenic sp. was eliminated by
chloroform treatment, explaining the switching of methane production system to
hydrogen production system. However, Methanosaeta concilii, the key organism in
anaerobic granulation, was not eliminated from the hydrogen producing system,
unexpectedly, which might help explain the granulation of hydrogen producing granules.
School:Washington State University
School Location:USA - Washington
Source Type:Master's Thesis
Keywords:immobilized microorganisms hydrogen bacteria
Date of Publication: