Environmental Engineering Reference
In-Depth Information
at peak C-region during the second phase (10-20 days). The result is a decrease in
both the fluorescence intensities and the ratios of fluorescence intensities of peak
A- and peak C-regions. Thirdly, microbial processes may slowly alter the fluoro-
phores bound at both peak A- and C-regions during the third phase (20-70 days),
and much more slowly during the fourth phase (80-180 days). The gradual increase
in the fluorescence intensities of both peaks A and C suggest that a gradual con-
version could be operational of autochthonous fulvic acid (C-like) into compounds
highly recalcitrant or refractory to microbial degradation. These modifications are
in agreement with earlier studies, which suggest that microbial processes induce
rapid decomposition of the 'labile' fraction such as monosaccharides (e.g. glucose),
amino acids and fatty acids, which are the monometric molecules that make up car-
bohydrates, proteins and lipids. In contrast, the 'refractory' fraction is decomposed
more slowly (Zhang et al.
2009a
; Hama
1991
; Hama et al.
2004
; Wakeham and Lee
1993
; Wakeham et al.
1997
; Harvey and Macko
1997
; Hanamachi et al.
2008
).
Microbial Degradation of FWAs (DAS1 and DSBP)
FWAs-like fluorescence (peak W) is often increased, by 6-14 % in rivers, by 8 % in
drain samples, by 14 % for commercial detergents in Milli-Q water, and by 21 % in
river waters plus commercial detergents after 6-10 days dark incubation (Table
4
)
(Mostofa et al.
2011
). In rivers, commercial detergents or FWAs-like components
typically undergo an increase in fluorescence after microbial degradation. Such
a behavior is similar to that of fulvic acid under dark incubation in natural waters.
Upon microbial processing, the fluorescence of standard DSBP does not change sig-
nificantly upon 10 h of dark incubation (Table
4
). Commercial detergent (component
2) that shows fluorescence peak at Ex/Em
=
225-230/287-296 nm (peak T
UV
-
region), can be microbially decomposed by approximately 84 % in river plus deter-
gent samples, 90 % in sewerage drain samples, and 15 % in commercial detergents
samples dissolved in Milli-Q waters, within 10 days of dark incubation (Table
4
)
(Mostofa et al.
2010
). These results suggest that highly polluted waters can rapidly
decompose fluorophores at peak T
UV
-region, i.e., partly the commercial detergents.
In contrast, detergent components or FWAs (C-like) are unaltered microbially in
natural waters. Microbes are primarily unable to decompose the FWAs (DSBP and
DAS1) because of their complex molecular structure composed of a number of aro-
matic rings with several functional groups (Fig.
3
y, a′) (Mostofa et al.
2010
)).
Microbial Degradation of Aromatic Amino Acids
The fluorescence of tryptophan-like components under dark incubation is typi-
cally decreased, by approximately 13-24 % in unfiltered river waters, by 67 % in
unfiltered sewerage drain samples, and by 11 % in filtered river samples (Table
4
)
(Mostofa et al.
2010
). On the other hand, an increase in tryptophan-like fluo-
rescence is often observed in filtered river waters (4-6 %), in lake water in the
