Microalgae Chlorella as a Sustainable Feedstock …
93
99.995% purity was used as the carrier gas and its flow rate was set at 0.7 ml/min.
The initial temperature of the oven is 40 °C and was increased at a rate of 10 °C/min
up to 100 °C (Mansa et al. 2013).
Prior to the analysis, the sample was distilled and sodium sulphate anhydrous
(NaSO 4 .H 2 O) was added to the resulting distillate to remove the water in it. The
addition of NaSO 4 .H 2 O was conducted slowly until there is no formation of solid
upon further addition. The sample was diluted with HPLC grade dichloromethane
buffer. The sample was then syringed through a 0.45 µm Durapore (PVDF) syringedriven filter unit into 1.5 ml vials. The vials were sealed with a crimp cap and stored
at 5–8 °C prior to analysis (Mansa et al. 2013). Ethanol solutions with different
concentrations were prepared and used to plot the calibration curve in order to obtain
the bioethanol concentration of the sample.
5.1 Effect of Yeast Inoculum Concentration on Bioethanol
Production
Fermentation was carried out with different yeast inoculum concentrations and
the fermentation samples were analysed after 24 h to determine their respective
bioethanol content. Figure 1.7 shows the relationship between the inoculum concentration and the bioethanol production. From the inoculum concentration of 5.0–15.0%
v/v, both the ethanol concentration and ethanol yield were in an increasing trend. Nevertheless, from 15.0 to 25.0% v/v, the bioethanol production showed a decreasing
trend for both the ethanol concentration and ethanol yield. According to Fig. 1.7,
the maximum bioethanol production was achieved with the inoculum concentration
of 15.0% v/v. The ethanol concentration of 1.126 g/l was achieved and the ethanol
yield obtained was 0.209 g/g glucose.
In this study, up to 15% v/v, increasing the concentration of yeast inoculum
resulted in an increase of bioethanol production from microalgal hydrolysate. At
higher concentration of yeast inoculum, both the concentration of bioethanol and
the ethanol yield were decreasing. Optimum inoculum concentration of 15% v/v
produced an ethanol yield of 0.209 g/g glucose with 1.126 g/l of bioethanol concentration.
A similar trend was observed in previous studies where lower bioethanol concentration or yield was obtained at yeast inoculum concentration that was higher than
optimal. Minh and Dao (2013) reported that fermentation with yeast ratio of 11%
v/v showed lower ethanol concentration than that of 9% v/v. In their study, 0.43%
v/v of ethanol was produced with 11% v/v yeast ratio while 1.43% v/v of ethanol
was obtained with 9% v/v yeast ratio. Besides, Thenmozhi and Victoria (2013) stated
the similar bioethanol production trend when they were working with cauliflower
and cabbage waste samples. In their study, 20% v/v yeast inoculum was proven
to be optimal. However, at higher yeast inoculum concentration, the ethanol yield
decreased. This trend might be related to the inhibitory effect of the oversaturation of
93
99.995% purity was used as the carrier gas and its flow rate was set at 0.7 ml/min.
The initial temperature of the oven is 40 °C and was increased at a rate of 10 °C/min
up to 100 °C (Mansa et al. 2013).
Prior to the analysis, the sample was distilled and sodium sulphate anhydrous
(NaSO 4 .H 2 O) was added to the resulting distillate to remove the water in it. The
addition of NaSO 4 .H 2 O was conducted slowly until there is no formation of solid
upon further addition. The sample was diluted with HPLC grade dichloromethane
buffer. The sample was then syringed through a 0.45 µm Durapore (PVDF) syringedriven filter unit into 1.5 ml vials. The vials were sealed with a crimp cap and stored
at 5–8 °C prior to analysis (Mansa et al. 2013). Ethanol solutions with different
concentrations were prepared and used to plot the calibration curve in order to obtain
the bioethanol concentration of the sample.
5.1 Effect of Yeast Inoculum Concentration on Bioethanol
Production
Fermentation was carried out with different yeast inoculum concentrations and
the fermentation samples were analysed after 24 h to determine their respective
bioethanol content. Figure 1.7 shows the relationship between the inoculum concentration and the bioethanol production. From the inoculum concentration of 5.0–15.0%
v/v, both the ethanol concentration and ethanol yield were in an increasing trend. Nevertheless, from 15.0 to 25.0% v/v, the bioethanol production showed a decreasing
trend for both the ethanol concentration and ethanol yield. According to Fig. 1.7,
the maximum bioethanol production was achieved with the inoculum concentration
of 15.0% v/v. The ethanol concentration of 1.126 g/l was achieved and the ethanol
yield obtained was 0.209 g/g glucose.
In this study, up to 15% v/v, increasing the concentration of yeast inoculum
resulted in an increase of bioethanol production from microalgal hydrolysate. At
higher concentration of yeast inoculum, both the concentration of bioethanol and
the ethanol yield were decreasing. Optimum inoculum concentration of 15% v/v
produced an ethanol yield of 0.209 g/g glucose with 1.126 g/l of bioethanol concentration.
A similar trend was observed in previous studies where lower bioethanol concentration or yield was obtained at yeast inoculum concentration that was higher than
optimal. Minh and Dao (2013) reported that fermentation with yeast ratio of 11%
v/v showed lower ethanol concentration than that of 9% v/v. In their study, 0.43%
v/v of ethanol was produced with 11% v/v yeast ratio while 1.43% v/v of ethanol
was obtained with 9% v/v yeast ratio. Besides, Thenmozhi and Victoria (2013) stated
the similar bioethanol production trend when they were working with cauliflower
and cabbage waste samples. In their study, 20% v/v yeast inoculum was proven
to be optimal. However, at higher yeast inoculum concentration, the ethanol yield
decreased. This trend might be related to the inhibitory effect of the oversaturation of