Environmental Engineering Reference
In-Depth Information
2.1 Introduction
The discipline of Microbial Biotechnology includes a scientific and practical
knowledge of using microorganisms and their products. We differentiate by the
area of biotechnological applications such subdisciplines as Medical, Pharma-
ceutical, Industrial, Agricultural, and Environmental Biotechnology. Currently, a
new subdiscipline of Microbial Biotechnology, Construction Microbial Biotech-
nology, can be differentiated. There are two major directions in Construction
Microbial Biotechnology: (1) the microbial production of construction materials
and (2) the applications of microorganisms in construction process. Many different
biotechnological products and biotechnologies for civil engineering are developing
within these directions (Fig.
2.1
).
Production of cement, which is a major construction material, is energy-con-
suming and environmentally-unfriendly. Energy represents 20-40 % of the total
cost of cement production because temperature above 950 C is needed for
transformation of limestone to cement clinker. New construction materials,
microbial biocements, can be produced from limestone, dolomite, or iron ore at
temperature 20-60 C with less than 10 % of energy used for the manufacturing of
conventional cement. Therefore, cost of biocements can be lower than that of
conventional cement. There are also a lot of other advantages of microbially-based
biocementing or bioclogging materials over conventional cements and grouts, for
example sustainability due to production from organic matter, low viscosity, and
low risk of negative environmental consequences. It is important that biocement
can be produced from the same raw materials that are using for cement production.
Another type of biomaterials, which are used in construction industry are
industrially produced or in situ synthesized microbial polysaccharides. Such
industrially produced polysaccharides as xanthan, welan, succinoglucan, curdlan,
chitosan are used in dry-mix mortars, wall plasters, self-leveling underlayers,
injection grouts to improve viscosity, water retention, set retarding, flowability
(Plank
2004
). Other biopolymers for example, proteins or their hydrolysates as
biosurfactant, can also be used for if the cost is acceptable. Sewage sludge of
municipal wastewater treatment plants, which is a waste microbial biomass pro-
ducing in quantities of several million tons a year, could be used also as a source of
cheap microbial polymers.
Production of bacterial polysaccharides in soil after addition of bacterial cells
and necessary nutrients in situ is used to modify soil properties. This approach
could be used for such geotechnical applications as dam control, wind soil erosion
control, earthquake liquefaction mitigation, construction of reactive barrier, and
long-term stabilization of contaminated soils. Different kinds of organic wastes can
be used as a source of organic matter for polysaccharide-producing microorgan-
isms in large-scale geotechnical applications to diminish the cost of soil clogging.
Initiated growth of exopolysaccharide-producing photosynthetic bacteria or algae
on the surface of sand can be used for the wind erosion control. Surface growth of
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