07-07-2012, 04:18 PM
Removal of disperse dyes from textile wastewater using bio-sludge
Removal of disperse dyes.pdf (Size: 174.91 KB / Downloads: 61)
Abstract
Granular activated carbon (GAC) did not show any significant adsorption ability on the disperse dyes, while resting (living) biosludge
of a domestic wastewater treatment plant showed high adsorption abilities on both disperse dyes and organic matter. The dye
adsorption ability of bio-sludge increased by approximately 30% through acclimatization with disperse dyes, and it decreased by autoclaving.
The deteriorated bio-sludge could be reused after being washed with 0.1 N NaOH solution.
Introduction
Effluent from industries, such as dyeing, pulp and paper,
and textile industries, contain many coloring substances,
which are toxic (Benefield et al., 1982; Chu, 2001) and need
to be removed. Removal techniques for coloring substances
include adsorption, precipitation, coagulation, filtration,
and chemical oxidation (Benefield et al., 1982; El-Geundi,
1991; Janos et al., 2003; Meshko et al., 2001). Although
these physical and chemical treatment processes might be
effective for color removal, they use more energy and chemicals
than biological treatment processes. Chemical wastes
are also generated from these processes.
Chemical analysis
COD, BOD5, TKN, MLSS, pH of influent and effluent,
sludge settled volume test at 30 min (SV30), and sludge
volume index (SVI) of the SBR system were determined
using ‘‘Standard Methods for the Examination of Water
and Wastewater’’ (APHA, AWWA, WEF, 1998). The
color intensity of STWW and TWW was determined as
the absorbance at the optimum wavelength (see Table 1).
The SRT (solid retention time) was determined as the ratio
of total MLSS of the system to the amount of excess sludge
wasted in a day.
Stability of bio-sludge on dye adsorption capacity
The dye adsorption stability of bio-sludge after washing
with 0.1 N NaOH solution was also determined. The biosludge
type A, type B and type C could be reused for disperse
dye adsorption after being washed with 0.1 N NaOH
solution, as shown in Table 8, and unexpectedly, the dye
adsorption capacity of reused bio-sludge was 20–60%
higher than that of raw bio-sludge. For example, the Disperse
Blue 60 adsorption capacity of bio-sludge type C
upon the first reuse was 55.6% higher than that of raw
bio-sludge type C, and 51.1% and 48.7% higher adsorption
capacities were maintained on the second and third reuses
of bio-sludge type C.
Discussion
GAC type CGC-11 could not be used as the adsorbent
for disperse dyes or organic matter of STWW (the main
organic matter caused by glucose). This could be explained
because the surface of GAC consists mainly of negative
charges, while disperse dyes and organic matter (BOD5)
that are mainly generated from glucose are non-polar
(Metcalf & Eddy Inc., 1991; Cheremisinoff and Morresi,
1978; Perrich, 1981).
However, the resting bio-sludge of the domestic wastewater
treatment plant could be used as an adsorbent of
both organic matter and disperse dyes, and the adsorption
capacities decreased by autoclaving. Disperse Red 60 was
more easily adsorbed onto bio-sludge than Disperse Blue
60 because the molecular weight of Disperse Red 60 is less
than that of Disperse Blue 60 (Society of Dyes and
Colourists, 1987). The adsorption mechanisms of this
bio-sludge might be similar to that of the melanoidin
adsorption mechanism in Rhizoctonia sp.
Conclusion
From the results of this study, it could be suggested that
the resting bio-sludge of a domestic wastewater treatment
system could be used as an adsorbent of both organic matter
and disperse dye due to its high adsorption ability and
its ability to be reused after washing with a diluted alkali
solution. The biological treatment system, especially the
GAC–SBR system, was more suitable for treating raw
TWW due to the high removal efficiencies of disperse dyes,
as well as organic matter, under low excess sludge production
and low SVI. The advantage of using GAC in the
GAC–SBR system is that the GAC acts mainly as the
media for bio-film to attach to, but the GAC does not
absorb the disperse dyes directly onto its surface.