Environmental Engineering Reference
In-Depth Information
municipal waste can be dropped below 5.5 during acidogenic fermentation (Barlaz
et al. 2010 ), meanwhile optimal pH for acidogens is above 6.0 (Moosbrugger et al.
1993 ). To maintain optimal pH during acidogenic fermentation of organic wastes
the fine powder of limestone (CaCO 3 ) or dolomite (CaMgCO 3 ) can be added.
There will be two fractions at the end of the process: dissolved acetate salts of Ca
and Mg that could be used for biosynthesis of bioplastic, and semi-solid residuals
that can be used for biocementation (Ivanov and Chu 2008 ; Ivanov 2010 ) of sand
and gravel in road, pond, or channel construction or for soil erosion control. Using
this semi-solid residual all solid wastes from bioplastic production can be used as
the components of biocement (see below).
Batch biosynthesis of bioplastic is simpler but less productive than continuous
process, which productivity can be about 1 kg of PHAs/day/m 3 of bioreactor (Ben
Rebah et al. 2009 ). Production of PHAs can be done as semi-continuous culti-
vation of a mixed culture using a feast-famine cycle comprising a feast phase and a
famine phase in one bioreactor. This cycling process promotes not only accu-
mulation of PHAs in biomass but also selection of PHAs-producing microorgan-
isms (Beun et al. 2006 ; van Loosdrecht et al. 1997 , 2008 ).
All known methods of PHAs extraction suffer from a high cost or environmental
pollution and are difficult to be industrialized. Therefore, crude bioplastic, without
extraction of PHAs, could be used for construction applications. Major advantage
of PHAs for construction applications is biodegradability of bioplastic to carbon
dioxide and water for about 1.5 months in anaerobic sewage, 1.5 years in soil, and
6.5 years in seawater (Mergaert et al. 1992 ; Reddy et al. 2003 ; Castilhio et al.
2009 ). Dead bacterial biomass with PHAs contains also polysaccharides of cell
wall, proteins, polynucleotides, and phospholipids, which content is about 15, 50,
25, and 10 % of dry biomass without PHAs, respectively, and biodegradation rate is
higher than that of PHAs. Therefore, from the point of view of biodegradability of
bioplastic construction wastes there is no need to extract PHAs from biomass but to
use dry biomass with PHAs as a crude nanocomposite material. Such nanocom-
posites should be more flexible and better biodegradable than extracted PHAs.
Sustainability of this biodegradable construction materials is due to: (1) production
of bioplastic from renewable sources or even from organic wastes; (2) fast biode-
gradability of this material under the conditions of landfill or composting so neg-
ative effect of construction waste on environment will be minimized.
One area of applications of nanocomposite bioplastic from bacterial biomass
containing PHAs is the production and use of biodegradable construction materials,
which do not require removal and incineration after temporary application. Bio-
degradable bioplastic foam can be used for insulation walls and partitions, con-
struction of nonstructural (internal) elements such as separating walls and
partitions, and for the temporarily constructions that can be landfilled for fast
degradation. Other examples of potential application of crude nanocomposite from
bacterial biomass and PHAs are construction silts and dust fences that can be
landfilled for fast biodegradation or composted as biomass. Biodegradable plastics
could be also useful for vertical drains, geotextile, geomembranes, soil stabilization
mats. These materials are used temporarily for soft soil stabilization, filtration and
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