2.6. Determination of immobilized yeast embedding rate
In the process of preparing immobilized yeast cells for bioethanol
fermentation, the embedding rate of calcium alginate gel
S.-Q. Tian et al. / Renewable Energy 86 (2016) 858e865 859
beads had a greater impact on yeast fermentation [25]. This
embedding rate could be influenced by a multiplicity of different
factors, including sodium alginate, CaCl2, and pretreated substrates.
The amount of the embedding rate (%) was calculated using the
following equation:
YI ¼ AI=AF (2)
where Y1 is the embedding rate (%), A1 is the volume of calcium
alginate gel beads, and AF is the total volume before
immobilization.
2.7. Microstructure analysis of manganese alginate beads
After cutting through the manganese alginate beads and wiping
the exposed surface of the beads across the center of a slide, a small
droplet of DDW was added to the dissected manganese alginate
beads and a coverslip was placed over them. The preparation was
examined under a 40 inverted microscope (IM) to observe the
manganese alginate beads. A picture was taken of the outline of a
few manganese alginate beads, as seen under photographic camera
CANON IXUS 245 HS (at least 5 cm in diameter). Photographs were
taken with various diaphragm apertures, levels of focus and
condenser lens settings.
Surface morphology of the manganese alginate beads was
observed using atomic force microscopy (AFM), a Scanning Probe
Microscopy (SPA-300HV), in tapping mode. For each microstructure
image was scanned on at least four different surface texture.
Usually two different areas of each manganese alginate bead were
investigated. Only one representative image per manganese alginate
bead is shown.
2.8. Experimental design and data analysis
Bioethanol production profiles were designed using a
BoxeBehnken design (BBD) of RSM to examine the relationship
Table 1
Experimental range and coded level of variables tested with BBD in RSM model.
Code Parameter name 1 0 þ1
X1 Corn stover concentration (%) 0.15 0.20 0.25
X2 Yeast concentration (%) 1.5 2.0 2.5
X3 pH 4.0 4.5 5.0
Table 2
BoxeBehnken design matrix for the predicted values and the experimental values
for the bioethanol yield.
Run Coded variable levels The yield of ethanol (%)
X1 (%) X2 (%) X3 Experimental values Predicted values
1 0.15 2.5 4.5 76.17 76.42
2 0.20 2.0 4.5 81.61 81.14
3 0.15 2.0 5.0 73.12 73.25
4 0.15 1.5 4.5 71.40 71.31
5 0.15 2.0 4.0 66.89 66.73
6 0.20 2.0 4.5 82.94 81.98
7 0.20 2.5 4.0 71.00 71.15
8 0.25 2.0 5.0 72.99 72.93
9 0.25 2.0 4.0 69.54 69.52
10 0.20 2.0 4.5 84.16 84.11
11 0.20 2.5 5.0 72.46 72.32
12 0.20 2.0 4.5 84.13 84.78
13 0.20 1.5 4.0 65.29 65.01
14 0.25 1.5 4.5 68.34 68.45
15 0.20 2.0 4.5 84.09 84.14
16 0.20 1.5 5.0 74.05 74.66
17 0.25 2.5 4.5 75.78 75.11
0123
55
60
65
70
75
The yield of ethanol(%)
Yeast concentration (%)
A
0.0 0.1 0.2 0.3
60
66
72
78
84
The yield of ethanol (%)
LPCS substrates (%)
B
456
50
55
60
65
70
75
80
85
The yield of ethanol(%)