Continuous production of 1-butanol via Synechocystis sp. PCC 6803: growth, product separation and industrial scale evaluation
File(s)
Author(s)
Wang, Zhixuan
Type
Thesis
Abstract
Cyanobacteria have great potential for biofuel production due to their fast growth rates, ability
to fix carbon dioxide gas, and genetic tractability. Biobutanol produced by genetically
engineered Synechocystis sp. PCC 6803 is considered as the fourth-generation biofuel with a
carbon negative impact. In this study, a genetically modified strain of Synechocystis sp. PCC
6803 is cultivated in a 2.7 L photobioreactor (PBR) and firstly achieves continuous cultivation
in both chemostat and turbidostat for 145 days. The light intensity, dilution rate, pH level, and
culture circulation rate are comprehensively and systematically varied to determine the optimal
growth condition for maximal biomass and 1-butanol production. During chemostat cultivation,
a light intensity of 45 µmol m-2
s
-1
, a dilution rate of 0.19 d
-1
, a culture circulation rate of 2500
mL min-1
and a pH of 7.6 yielded the maximal 1-butanol (2.353 g L
-1
) and biomass (1.232 g L
-
1
) concentrations. This equates to a 1-butanol productivity rate of 0.439 g L
-1
d
-1
and a biomass
productivity rate of 0.230 g L
-1
d
-1
. Upon switching to turbidostat cultivation, the optimal light
intensity increased to 50 µmol m-2
s
-1
, and the dilution rate increased to 0.35 d
-1
. Under these
conditions, 1-butanol and biomass concentrations increased to 3.293 and 2.186 g L
-1
,
respectively. This equates to a 1-butanol productivity rate of 0.731 g L
-1
d
-1
and a biomass
productivity rate of 0.485 g L
-1
d
-1
. Under chemostat and turbidostat cultivation, 1-butanol
productivity represented 66% and 60% of the total cyanobacterial productivity, respectively.
Hence, after a significantly long period of cultivation (> 4 months) with many cell generations,
the Synechocystis sp. PCC 6803 strain is still growing in a biocatalytic physiological state and
presented a potential for a further long term growth. Further scaling-up of this cultivation
reactor (> 1000 L) and applying equivalent culture conditions, could make this strain of
Synechocystis sp. PCC 6803 a promising candidate for the future biofuel production in industry.
Three different separation processes including distillation, pervaporation and adsorption are
3
designed and simulated for the purification of 1-butanol produced by the Synechocystis sp.
PCC 6803 under chemostat operation. Energy consumption and economic investment for the
industrialization are also initiated in this project for future scaleup.
to fix carbon dioxide gas, and genetic tractability. Biobutanol produced by genetically
engineered Synechocystis sp. PCC 6803 is considered as the fourth-generation biofuel with a
carbon negative impact. In this study, a genetically modified strain of Synechocystis sp. PCC
6803 is cultivated in a 2.7 L photobioreactor (PBR) and firstly achieves continuous cultivation
in both chemostat and turbidostat for 145 days. The light intensity, dilution rate, pH level, and
culture circulation rate are comprehensively and systematically varied to determine the optimal
growth condition for maximal biomass and 1-butanol production. During chemostat cultivation,
a light intensity of 45 µmol m-2
s
-1
, a dilution rate of 0.19 d
-1
, a culture circulation rate of 2500
mL min-1
and a pH of 7.6 yielded the maximal 1-butanol (2.353 g L
-1
) and biomass (1.232 g L
-
1
) concentrations. This equates to a 1-butanol productivity rate of 0.439 g L
-1
d
-1
and a biomass
productivity rate of 0.230 g L
-1
d
-1
. Upon switching to turbidostat cultivation, the optimal light
intensity increased to 50 µmol m-2
s
-1
, and the dilution rate increased to 0.35 d
-1
. Under these
conditions, 1-butanol and biomass concentrations increased to 3.293 and 2.186 g L
-1
,
respectively. This equates to a 1-butanol productivity rate of 0.731 g L
-1
d
-1
and a biomass
productivity rate of 0.485 g L
-1
d
-1
. Under chemostat and turbidostat cultivation, 1-butanol
productivity represented 66% and 60% of the total cyanobacterial productivity, respectively.
Hence, after a significantly long period of cultivation (> 4 months) with many cell generations,
the Synechocystis sp. PCC 6803 strain is still growing in a biocatalytic physiological state and
presented a potential for a further long term growth. Further scaling-up of this cultivation
reactor (> 1000 L) and applying equivalent culture conditions, could make this strain of
Synechocystis sp. PCC 6803 a promising candidate for the future biofuel production in industry.
Three different separation processes including distillation, pervaporation and adsorption are
3
designed and simulated for the purification of 1-butanol produced by the Synechocystis sp.
PCC 6803 under chemostat operation. Energy consumption and economic investment for the
industrialization are also initiated in this project for future scaleup.
Version
Open Access
Date Issued
2020-12
Date Awarded
2021-11
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Hellgardt, Klaus
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)