Environmental Engineering Reference
In-Depth Information
carbonates as a binder material, i.e., biocementation, have been added to concrete
for the improvement of compressive strength and the remediation of concrete
surface cracks (Sect. 7.4 ). The chapter suggests potential applications of biode-
position as an eco-novel alternative to traditional techniques in remediation of
defects in concrete structures and accordingly enhancement in their service life.
15.2 Bacterial Induced Deposition
15.2.1 Bacterial Induced/Mediated Deposition
Bacterial induced carbonate deposition is a widespread natural process, occurring
by most soil bacterial isolates on a solid medium with added calcium and con-
cluded that under suitable conditions (Boquet et al. 1973 ), biodeposition as a
process which bacteria conduct both in bacterially induced (active) and/or in
bacterially influenced or mediated (passive) way (Dupraz et al. 2009 ). Different
bacterial strains can induce deposition of different amounts, shapes, and types of
carbonate crystals from exactly the same synthetic medium, with an apparent
occurring of environment- and species-specific biodeposition (Hammes and
Verstraete 2002 ). Some authors emphasize that carbonate deposition by bacteria is
an unwanted byproduct of bacterial physiological activities under special envi-
ronmental conditions, a simple physiological accident. Bacteria would not pre-
cipitate carbonate particles by a specific mechanism and the supply of a structure
by bacteria would not be necessary (von Knorre and Krumbein 2000 ). Other
authors emphasize that the role of bacteria in carbonate deposition can be specific
with ecological benefits for the precipitating organisms (McConnaughey and
Whelan 1997 ; Castanier et al. 1999 ; Barabesi et al. 2007 ). Castanier et al. ( 1999 )
distinguish between passive and active deposition mechanisms which may occur,
often concurrently, in heterotrophic bacteria. Passive deposition (or passive car-
bonatogenesis) operates by producing carbonate and bicarbonate ions and inducing
chemical modifications in the medium through metabolic pathways (e.g., linked to
nitrogen and sulfur cycles). In active deposition (or active carbonatogenesis), the
carbonate particles would be produced by ionic exchanges through the cell
membrane by activation of calcium and/or magnesium ionic pumps or channels,
probably coupled with carbonate ion production. Active deposition would be
independent of specific metabolic pathways (von Knorre and Krumbein 2000 ).
Accordingly, the role of bacteria in CaCO 3 deposition and different mechanisms of
biodeposition were proposed by different author (Ehrlich 1996), but the key role
played by bacteria in the processes is still debated and worthy of further dis-
cussing. They include calcium concentration of the medium by microbial binding,
metabolic alteration of the medium that results in changes in bicarbonate con-
centration and pH, and bacterial bodies acting as crystal nucleation sites (Little
et al. 1997 ). It seems that different bacteria as well as abiotic factors seem to
contribute
in
a
different
ways
to
carbonate
deposition
in
a
wide
range
of
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