2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P02 REMOVAL OF 2-MERCAPTObENZOThIAZOLE
FROM SyNThETIC
wASTEwATER
BEáTA ALMáSIOVá, Ján DERCO, AnGELIKA
KASSAI and eVA HáSOVá
Slovak University of Technology, Faculty of Chemical and
Food Technology, Institute of Chemical and Environmental
Engineering, Radlinského 9, 812 37 Bratislava 1, Slovak
Republic,
beata.almasiova@stuba.sk
Introduction
2-Mercaptobenzothiazole (MBT) is the most important
member of the benzothiazole group of heterocyclic aromatic
compounds. It is a pale yellow, crystalline substance with an
unpleasant odor and a bitter taste . This xenobiotic compound
is used mainly in the manufacture of rubber additive chemicals
but also has other uses, notably as a corrosion inhibitor,
antifreeze for automobiles. It is known as a toxic and poorly
biodegradable pollutant. It is able to pass conventional treatment
systems, widespread with surface and underground
waters and enters into organisms 1 . Data concerning biodegradation
of MBT are inconclusive. Some authors 2 have suggested
it is recalcitrant to biodegradation.
Genotoxicity investigations in bacterial and mammalian
test systems provide some evidence indicating that MBT has
the potential to induce mutations and chromosomal aberrations.
Toxicity studies in rats and mice chronically exposed
to MBT identified increases in various tumors 3 . Epidemiological
investigations indicate that workers occupationally
exposed to MBT have an increased risk of death from bladder
cancer. MBT interfered with the nitrification processes and
exhibited biocidal effects. MBT inhibits the degradation of
easily degradable organics 4 .
This work was aimed at study biodegradation of MBT
and effect of this compound on activated sludge. Degradation
of MBT by ozone was also studied.
Experimental
B i o d e g r a d a b i l i t y o f M B T
Adaptation of activated sludge to MBT was carried out
in semicontinuos bioreactor. We were adapted MBT with
maximal concentration 25 and 50 mg dm –3 on the activated
sludge. Time of adaptation was 3 weeks. During the adaptation
Table I
Specific sorptive capacity of activated sludge
c MBT MTB decrease MTB decrease
at solution by adsorption by adsorption
[mg dm –3 ] [mg dm –3 ] [mg g –1 ]
10 4.2 42
20 5.9 59
60 6.8 68
s336
we measured inhibition effect of MBT on the activated sludge
by respirometric measurements.
Adsorption tests were performed both with adapted and
nonadapted activated sludge to MBT. Adsorption of MBT on
activated sludge was studied at various concentration values
of MBT. We were measured the specific sorptive capacity of
sludge at low (10, 20 and 60 mg dm –3 ) and high concentration
of MBT (100, 200 and 500 mg dm –3 ).
O z o n a t i o n o f M B T
The feasibility of utilisation of ozone for degradation
of MBT was investigated in laboratory scale equipment. The
experiments were performed in bubble ozonation column.
The ozonation equipment consists of two glass columns,
0.04 m diameter and 1.70 m height. The first column was
filled with synthetic water with MBT, and the other one was
filled with solution of potassium iodide to destroy residual
ozone in the outlet of the first ozonation column. The system
was operated in batch mode. Synthetic wastewater containing
MBT was added into ozonation reactor at the beginning of
trials. Continuous flow of oxygen 30 dm 3 h –1 was applied for
generation of ozone. The Lifetech ozone generator with the
maximum ozone production 5 g h -1 and Lifetech ozone UV
detector were used. Ozonation trials were carried out at 70 %
of the power maximum of ozone generator. Initial concentration
of MBT in synthetic water was 50 mg dm –3 .
Results
MBT is not consumed by non adapted activated sludge.
Decrease of respiration rate of non adapted activated sludge
was observed with the increase of 2-MBTconcentration.
Rapid decrease of respiration activity was observed for activated
sludge after adaptation. The endogenous respirometric
rate decreased by 6 % at concentration 25 mg dm –3 MBT in
comparison with reference model. The endogenous respirometric
rate decreased by 39 % at concentration 50 mg.dm –3
MBT in comparison with reference model.
The decrease of dissolved MBT concentration was
observed at the low concentration levels. The value of COD
and TOC increased after 10 days, which is caused by increase
of concentration of MBT in solution.
Table I shows the results of adsorption test carried out at
lower concentration values of MBT. negligible adsorption of
MBT on activated sludge was observed at MBT concentration
higher than 100 mg dm –3 .
According to results shown in the Fig. 1. the highest COD
removal was observed during the first 20 minutes of ozonation.
The initial COD value conversion achieved about 98 %
after 50 minutes. The efficiency of TOC removal was 54 %
after 50 minutes of ozonation. Almost total removal (96 %)
of 2-MBT from the sample was achieved after 5 minutes of
ozonation. Simultaneously the presence of benzothiazole was
identified as ozonation intermediate. The presence of benzothiazole
(BT) was identified in the sample after 50 minutes
of ozonation. Fien et al. 5 show, that MBT and its breakdown
products had a high affinity towards ozone as indicated by the