Biomedical Engineering Reference
In-Depth Information
Table 3. The percentage of oxygen utilization rate (OUR) compared to the control [7]
compound
Vanco-
mycin
Quina-
crine
Congo
red
Chlorpro-
mazine
Erythro-
mycin
2,4
DNP
Rote-
none
Trypan
blue
Dose (mg L
-1
)
1.0
800
0.008
1000
0.04
4
4
18
Time (h)
1
54
77
54
100
160
-
-
15
12
100
100
100
100
100
-
-
100
24
65
54
49
42
131
190
131
168
36
78
97
68
53
149
199
216
132
45
101
163
90
69
-
215
311
156
48
85
145
76
-
-
100
144
113
3,3',4',5-tetrachlorosalicylanilide (TCS) which is a component in the formulation of
soaps, rinses and shampoos [72] has attracted many researchers to study its effects on the
minimization of excess sludge in recent years because of its less toxicity. Chen et al. [73]
applied TCS as a metabolic uncoupler to reduce the sludge growth in activated sludge
cultures. The results revealed that TCS was an effective chemical agent in limiting the sludge
growth and the 0.4 mg L
-1
concentration was the threshold of inducing a reduction in sludge
growth which was associated with the enhancement in microbial activity and the percentage
of active cells over the total cell number. It was demonstrated that TCS was able to reduce
sludge growth rate by around 40% at a concentration of 0.8 mg L
-1
. Chen et al. [74] also
investigated the effect of TCS on the reduction of sludge production in the activated sludge
cultures operated in both batch and continuous modes through energy spilling stimulation,
and confirmed that TCS has more significant effect on the reduction of sludge growth, but
less influence on COD removal in the continuous culture than in the batch culture. The
reduction of the sludge growth yield is correlated with the release of energy, and it was found
that addition of TCS did not change the cell storage. Pure culture studies of
E. coli
AB1175
suggested that TCS would not cause the change in cell viability. Meanwhile, Chen et al. [75]
in another research group also used TCS as a metabolic uncoupler to investigate its effect on
the activated sludge cultures. Batch tests showed that TCS was an effective chemical
uncoupler in reducing the sludge yield by approximately 50% when the concentration was
greater than 1.0 mg L
-1
. Moreover, it did not affect substrate removal capability and effluent
nitrogen concentration adversely when dosed every other day in a range of 2.0-3.6 mg L
-1
during the 40-day operation period of the activated sludge batch cultures. However, TCS
would cause a shift in the predominant microbial population, e.g. in the reactors with TCS,
few filamentous microorganisms were observed, resulting in forming less dense sludge flocs.
Yang et al. [76] tested four metabolic uncouplers (p-chlorophenol, m-chlorophenol, m-
nitrophenol and o-nitrophenol) and compared their effectiveness in reducing excess sludge
production in the activated sludge process. Different concentrations of individual metabolic
uncouplers were added into a series of batch experiments with constant initial biomass and
glucose concentrations. Results showed that metabolic uncouplers are very effective in
reducing sludge production. Among the four tested metabolic uncouplers, m-chlorophenol
was found to be the most effective in reducing sludge production with less effect on the
process performance. The acidity constant (pK
a
) of a metabolic uncoupler highly influences
its effectiveness in sludge reduction, that is to say, stronger lipophilic weak acids may have
higher potentials to lower sludge production.
