Environmental Engineering Reference
In-Depth Information
In an earlier study, two types of bacteria in monoculture and two consortia have
been isolated and found to decolorize Congo red under fermentative, nitrate
reducing and denitrifying condition (Decena and Barraquio
2004
; Jalandoni-Buan
et al.
2010
). Samples used for isolation included sediment from polluted canal
receiving the ef
uents containing Congo red and other dyes, soil from non-polluted
source, rhizospheric soil and roots of Imperata cylindrica growing in the vicinity of
the Congo red-polluted canal. For the enrichment of the Congo Red Decolorizing
Bacteria (CRDB), minimal salts medium with glucose, ammonium sulfate, potas-
sium nitrate and Congo red were used in both aerobic and anaerobic conditions.
Putatively decolorizing cultures were further enriched by transferring aliquots of the
enriched cultures into fresh media. The
nal enriched culture medium was analyzed
for Congo red and nitrate colorimetrically.
Potentially decolorizing cultures were plated onto same medium for monoculture
isolation. Pure cultures and consortia were con
rmed for decolorization activities.
Our study showed that in the presence of oxygen as electron acceptor, no decol-
orization of the dye occurred. The rate of decolorization of the monocultures after
puri
cation was observed to be slower than that of the consortia. The monocultures
decolorized Congo red after 2 weeks of incubation (SB13B, SB12D and IRRI-1C)
and after 1 month of incubation in the case of S22B. However, the consortia, on the
other hand, decolorized Congo red after only a week of incubation. Blackening of
the rubber stopper was observed in consortium S22 together with rotten egg odor
which indicated the possible presence of a sulfate reducing organism in the mixed
bacterial culture. The presence of sulfate reducing bacteria in the consortium could
have hastened the rate of decolorization of the dye. Van der Zee et al. (
2003
)
reported that the sulphide produced by a sulfate reducing bacteria can reduce azo
bonds.
The monocultures, SB13B and S22B decolorized Congo red concurrently with
nitrate reduction. The 16S rRNA sequencing identi
ed SB13B as E. coli, SB12D as
Enterobacter dissolvens and S22B as Pseudomonas citronellolis. API 20E identi-
ed IRRI-1C as Klebsiella oxytoca.
3 Factors Affecting Degradation Process
We conducted a microcosm experiment wherein both polluted and unpolluted
waters were inoculated with the monocultures and consortia and incubated with
Congo red statically at room temperature and at 28
C (Jalandoni-Buan et al.
2009
). Polluted water was collected from a portion of the Laguna de Bay near a
duck farm in Victoria, Laguna (Fig.
1
). That part of the bay was polluted with waste
products coming from the ducks as well as other waste products coming from
different sites. The pH of the water was found to be 7.37. The water appeared brown
to black with odor of manure. Clean water was collected near the middle of Lake
Caliraya also in Laguna (Fig.
2
). The water appeared clear with a pH of 7.16. Both
the monocultures and consortia were able to decolorize the polluted water with the
-
30
°
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