Environmental Engineering Reference
In-Depth Information
However, the cost of bioplastics produced aseptically in fermenters is usually
several times higher than the cost of petrochemical-based plastics, so the reduction
of the bioplastic production costs using cheap raw materials and technological
innovations is still essential for the bioplastic industry and applications. Most
available types of bioplastics for construction industry are polyhydroxyalkanoates
(PHAs), which are polyesters accumulated up to 80 % of dry bacterial biomass as
a storage compound. Most important PHAs are poly-3-hydroxybutyrate (PHB)
with monomer formula (-OCH(CH
3
)-CH
2
-C(O)-) and polyhydroxyvalerate (PHV)
with monomer formula (-OCH(CH
2
CH
3
)-CH
2
-C(O)-). Accumulated PHAs can be
extracted from bacterial biomass and used in practice as bioplastic with melting
temperature 160-180 C, tensile strength 24-40 MPa, and elongation at break
3-142 %. Chemical and physical properties of PHAs can be found in numerous
reviews (Lowell and Rohwedder
1974
; Braunegg et al.
1998
; Castilho et al.
2009
;
Sudesh et al.
2000
; Sudesh and Abe
2010
; Volova
2004
; DeMarco
2005
; Khanna
and Srivastava
2005
; Lenz and Marchessault
2005
).
The following options for raw materials, biotechnology of production, and
applications of bioplastic can help to diminish the cost of the bioplastic PHAs:
1. Use of cheap raw materials (Serafim et al.
2008
): organic fraction of municipal
solid wastes, liquid wastes of municipal wastewater treatment plants, food-
processing waste, or agricultural wastes such as unbaled straw; corn cobs,
stalks, and leaves (corn stover); silage effluent; horticulture residuals; farm yard
manure; coconut fronds, husks, and shells; coffee hulls and husks; cotton
(stalks), nut shells; rice hull, husk, straw, and stalks, sugarcane bagasse.
Globally, 140 billion metric tons of biomass is generated every year from
agriculture, which is equivalent to approximately 50 billion tons of oil. So,
biomass wastes have attractive potentials for large-scale industries and com-
munity-level enterprises (UNEP
2009
).
2. Batch or continuous nonaseptic cultivation for biosynthesis of bioplastic by
mixed bacterial culture (Yu et al.
1999
;Lu
2007
);
3. Production of crude bioplastic for construction industry and agriculture
avoiding its concentration and extraction of bioplastic using chemical treat-
ment, filtration, centrifugation, or flotation.
For the biosynthesis of PHAs under nonaseptic conditions, organic wastes can
be converted to organic acids through acidogenic fermentation of organics, then
organic acids can be converted to PHAs (Yu
2006
). Most typical material balance
of acidogenic fermentation is as follows (Madigan et al.
2012
):
C
6
H
12
O
6
þ
0
:
82 H
2
O
!
1
:
13 CH
3
COOH
þ
0
:
35 C
2
H
5
COOH
þ
0
:
26 C
3
H
7
COOH
þ
1
:
67 CO
2
þ
2
:
47 H
2
;
ð
2
:
1
Þ
where C
6
H
12
O
6
is a monomer of cellulose, CH
3
COOH, C
2
H
5
COOH, C
3
H
7
COOH
are acetic, propionic and butyric acids, respectively. The pH of organic fraction of
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