Basics of Construction Microbial Biotechnology - Biotechnologies and Biomimetics for Civil Engineering - page 45

4Fe 2 O 3 þ CH 3 COOH þ 16 H þ ! 8Fe 2 þ þ 2CO 2 þ 10 H 2 O, ð 2 : 24 Þ

8Fe 2 þ þ 16 CH 3 COOH ! 8Fe CH 3 COOH Þ 2 þ 16 H þ ;

ð ð 2 : 25 Þ

4Fe 2 O 3 þ 17 CH 3 COOH ! 8Fe CH 3 COOH ð Þ 2 þ 2CO 2 þ 10 H 2 O :

ð 2 : 26 Þ

• oxidation and bioprecipitation of ferrous chelates (Stabnikov and Ivanov 2006 ;
Ivanov et al. 2012a):

Fe 2 þ þ 1 : 5NH 2 ð Þ 2 CO þ 0 : 25 O 2 þ 5 : 5H 2 O þ UPB ! Fe O ð 3 #

þ 1 : 5 ð NH 4 Þ 2 CO 3 þ 2H þ :
ð 2 : 27 Þ

Urease-producing bacteria and urea are used to maintain the pH to be above the
neutral value because oxidation of ferrous ions and hydrolysis of ferric ions is
accompanied with acidification of solution. The advantages of using iron
hydroxide as the clogging compound are that the soil treated by iron minerals is
more ductile and able to resist low pH conditions. The soil treated using iron based
biocement is not as strong as that treated using calcium based biocement (Ivanov
et al. 2012a) but the clogging effect of precipitated iron hydroxide is higher than
that of calcium carbonate (Fig. 2.8 ).
Precipitation of ferric and manganese hydroxide from chelates of Fe 2+ and
Mn 2+ for soil bioclogging can be done using neutrophilic iron-oxidizing bacteria.
For example, precipitation of iron/manganese minerals by iron-oxidizing bacteria
Leptothrix discophora is a promising technology for modifying engineering soil
properties and mitigating geologic hazards (Weaver et al. 2011 ).

2.5.8 Eco-Efficient Biocement

By the analogy with eco-efficient concrete (Pacheco-Torgal and Jalali 2011 ;
Pacheco-Torgal et al. 2012; Pacheco-Torgal and Jalali, 2013 ), eco-efficient bio-
cement can be produced using mining tails/residuals of limestone, dolomite, iron
ore and organic agricultural, food-processing, or municipal wastes using acido-
genic fermentation and bioreduction of iron with production of dissolved salts of
calcium, magnesium, and iron.
The problem with the brittleness of biocementation could be solved using
biomimetic approach (Sarikaya 1994 ; Mayer and Sarikaya 2002 ) using composite
strengthening through combination of mineral and organic nano- and micro-par-
ticles. By the analogy with nanomaterials in cement (Pacheco-Torgal and Jalali