Page 231 - Refining Biomass Residues for Sustainable Energy and Bioproducts

202 Refining Biomass Residues for Sustainable Energy and Bioproducts

converting glycerol to lipids with a lipid yield of 0.31 g/g substrate (Grady and
Morgan, 2011), or a lipid productivity of 3 g/L/day. Chen and Walker (2011)
observed that the biomass and lipid concentration was merely doubled in a fed-
batch operation when compared with batch operations on utilizing crude glycerol as
a carbon source by C. protothecoides. Liang et al. (2010a) showcased that the high-
est cellular lipid content of 73.3% was produced from Schizochytrium limacinum
SR21 a marine microalga on 35 g/L of crude glycerol derived from cooking oil.
Fed-batch system appears to be more advantageous over batch systems in terms of
substrate inhibition and increased accumulation of intracellular triacylglycerols
(TAGs) (Luo et al., 2016).

9.4.1.4 Hydrogen
The most serious environmental issue for the world is global warming and which
causes many deleterious issues. The alternate clean energy source is hydrogen
which can be produced by the broad spectrum of substrate and microorganisms.
The consumption of hydrogen reduces CO 2 ,NO x , particulate, and other emissions
that accompany the use of fossil fuels.
The energy content of crude glycerol (25.30 MJ/kg) is high when compared with
the pure glycerol (19.0 MJ/kg) due to the presence of methanol and other traces of
biodiesel components. The high-energy content of crude glycerol designates as a
potential substrate for hydrogen production glycerol can be converted into hydrogen
by a number of methods, such as biological, steam reforming, partial oxidation, and
auto-thermal reforming. Ito et al. (2005) demonstrated the combined production of
hydrogen and ethanol from glycerol by using Enterobacter aerogenes HU-101. As
the purity of glycerol increases the production of hydrogen increases and has
reported a maximum hydrogen yield rate of 80 mmol/L/h. Wu et al. (2011) reveal
that Klebsiella sp. HE1 can be employed for the production of hydrogen using glyc-
erol as a feedstock (Ken Jer et al., 2011).

9.4.1.5 Other generalities by biological route
1,3-PDO, a diol monomer, was well known for numerous applications in cosmetics,
solvents, adhesives, detergents, and resins. Various wild-type strains, such as
Klebsiella pneumoniae, Clostridium butyricum, Clostridium diolis, Citrobacter
freundii, Lactobacillus diolivorans, Lactobacillus brevis, Lactobacillus reuteri, and
genetically modified strains of K. pneumoniae, E. coli, and Clostridium pasteuria-
num were well reported anaerobic fermentation of glycerol for 1,3-propanediol pro-
duction (Zhong et al., 2014; Vivek et al., 2016; Vaidyanathan et al., 2011; Jensen
et al., 2012). In anaerobic fermentation with glycerol as the sole energy source, K.
pneumoniae strains were reported to produce 1,3-PDO titers between 60 and 90 g/L
(Zhao et al., 2009), and C. butyricum strains were observed to produce more than
60 g/L (Wilkens et al., 2012). 1,3-Propanediol production from crude glycerol using
K. pneumoniae ATCC 15380 was optimized, and yield, purity, and recovery were
56 g/L, 99.7%, and 34%, respectively (Hiremath et al., 2011).