Thesis - faculty.ait.ac.th - Asian Institute of Technology

influent reached 200 mg/L. For the wastewater polluted with phenol, phenol concentration
range of 1,000-1,500 mg/L could inhibit the respiration of the sludge by 37%.
Kim, et al. (1994) investigated the toxicity by using respiration meter, the data
evaluation show that the respiration rate decreased about 20% at Cobalt (Co) concentration
of 28 mg/L. It was reported that the growth microorganisms was inhibited even at a
concentration lower than 0.08 mg/L. In addition, the toxicity test was conducted in high
and low pH conditions and it was found that respiration rate decreased in both.
Madoni, et al. (1996, 1999) investigated the effect of lead toxicity on activated
sludge process. The respiration rate was inhibited 67% at the soluble lead concentration of
16.9 mg/L after one hour exposure. The acute toxicity of lead to organisms has been
reported at concentration ranging from 2 to 6 mg/L.
The concentrations of various toxicants and their inhibitory on bacterial respiration
are summarized in Table 2.17.
Table 2.17 Inhibitory Effect of Various Toxicants
Toxicants Concentration Inhibition of Respiration Reference
(mg/L)
(%)
Co 28 20 Kim, et al., 1994
Cu 50 30 Temmink, et al., 1993
Cd 40 50 Talinli and Tokta, 1994
Ni 9 50 Talinli and Tokta, 1994
Pb 16.9 67 Madoni, et al., 1999
Phenol 1,000-1,500
37
Temmink, et al., 1993
1,600
50
Talinli and Tokta, 1994
2.11 Membrane Bioreactors
Bioreactors are reactors that convert or produce materials using functions naturally
endowed to living creatures. Reactors using immobilized enzymes, microorganisms,
animal, or plant cells and those applying new methodologies such as genetic manipulation
or cell fusion are typical bioreactors (Belfort, 1989). Therefore, bioreactors are reactors
used to produce material with new or advanced technology by the application of biological
functions.
The combination of membranes to biological processes for treatment has led to the
emergence of membrane bioreactors (MBR) for separation and retention of solids; for
bubble-less aeration within the bioreactor; and for extraction of priority organic pollutants
from industrial contaminated water (Stephenson, et al., 2000). The membrane unit can be
configured external to or immersed in the bioreactor (Figure 2.10).
In an external circuit, the membranes can be either internally or externally skinned
whilst submerged membrane reactors should contain membranes that are externally
skinned. The incorporating of membranes into the biological reactor has eliminated the
sedimentation tank from biological treatment step associated with conventional wastewater
treatment practices.
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