Environmental Engineering Reference
In-Depth Information
(2)
Isolation, identification, and testing of wild strains from natural sites with
environmental conditions close to the conditions that are needed for the
biotreatment, for example, with high salinity, high or low temperature, aer-
obic or anaerobic conditions, alkaline, or acid pH. However, many bacteria
are pathogenic (causing diseases) for human, animal, and plants. Therefore,
biosafety of biotechnological process is always an important issue and only
nonpathogenic isolated strains of bacteria can be used for civil engineering
applications.
(3)
Autoselection in continuous culture (Cheng and Cord-Ruwisch 2013 ),
screening of the mutants (Li et al. 2011 ), and construction of the recombinant
microbial strains from wild strains for the biotreatment. However, there are
many restrictions on the applications of recombinant microbial strains so they
can be used mainly for industrial production of such construction materials as
polysaccharides or bioplastic.
(4)
Selection and testing of suspended enrichment cultures using such selective
conditions (selection pressure) as source of energy, carbon, nitrogen and
phosphorus, temperature, pH, salinity (osmotic pressure), concentration of
heavy metals, concentration of dissolved oxygen, spectrum and intensity of
light (for photosynthetic microorganisms). Some autoselected features of the
enrichment culture can be genetically unstable and could disappear after
several generations when the selection pressure will be absent (Ivanov et al.
2012b ).
(5)
Selection and testing of aggregated enrichment cultures, such as flocs, biofilms,
granules using such selective pressure as settling rate of microbial aggregates
and adhesion of cells to solid surface. An example is formation of bacterial
cells aggregates that cannot penetrate inside sand, settled onto the surface of
sand and formed calcite crust (Stabnikov et al. 2011 ; Chu et al. 2012b ).
In some cases, when soil is rich with indigenous microorganisms able to per-
form needed biogeochemical reaction, for example urease activity, soil biotreat-
ment can be performed by indigenous microorganisms, without preparation and
supply of microbial inoculum (Burbank et al. 2011 , 2012a , b ). To enhance the
needed biogeochemical function of indigenous microorganisms, soil can be
amended with the related reagent. For example, to enhance urease activity of
indigenous microorganisms before the biotreatment, urea can be added to soil
(Burbank et al. 2011 ). However, if microorganisms used in geotechnical bio-
process are indigenous it does not mean that they are safe for human, animals, and
plants because nonselective conditions of the soil bioprocess, especially applica-
tion of nutrients-rich medium, can enhance the proliferation of pathogens or
opportunistic pathogens in soil.
Core process in the production of construction material, i.e., cultivation of
microorganisms is performed in batch, semi-continuous (sequencing batch),
complete mixing continuous, or plug-flow continuous mode in the bioreactor,
where the components are mixing using stirring, upflow of liquid or gas through
the reactor, or horizontal rotation of the bioreactor.
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