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ABSTRACT A pilot-scale anaerobic fluidized bed (AnFB)
reactor was operated to treat the purified terephthalic acid
(PTA) manufacturing wastewater. Due to high complexity of
aromatic constituents in the wastewater, it took a long time to
start up the anaerobic reactor with acclimating microbes.
Anaerobic process engineering and commercialization will be
dependent on the critical biotechnology. Therefore, the purpose
of this study was try to start-up the AnFB pilot rapidly, and to
promote the degradation of aromatic wastewater with process
control. By this way, we also tried to work out the optimum
strategy during the start-up duration. The major organic
components in the PTA wastewater were terephthalic acid (TA),
benzoic acid (BA), p-toluic acid (p-Tol) and acetic acid (HAc).
The results of batch isotherm tests showed that the adsorptive
characteristic of PTA wastewater in terms of COD was fitted with
Freundlich model. There was favorable adsorption of activated
carbon for removing the aromatic compounds in PTA wastewater.
The adsorptive capacity of major aromatic compounds was BA, p-
Tol, TA, in order. Only BA had the property of larger adsorptive
capacity at lower temperature. After the anaerobic bacteria
were cultivated in the batch system, the manure digested sludge
was seeded into a GAC fluidized bed reactor. An innovative
technology of rapid start-up was established in the AnFB pilot.
A large amount of the digested sludge was physically attached
onto the GAC media within several days of batch recirculation.
The strategy of the start-up was conducted to operate the
fluidized bed at lower organic loading (0.2~0.3 kgCOD/kgVSS-
day), the volumetric loading rate was controlled at 0.5~1.0
kgCOD/m3-day. After 49 days operation, HAc and BA removal were
achieved up to 100%, the TA removal was achieved with 41%, while
the CODs removal was achieved at 46%.With 6 months' operation of
continuous flow, the volumetric loading rate could be increased
up to 4.0~4.5 kgCOD/kgm3-day with 60~70% of COD removal
efficiency. HAc and BA removal were still complete, the TA
removal was promoted to 80~90%, while p-Tol removal still
maintained from 10% to 20%. It showed that p-Tol was difficult
to be biodegraded anaerobically. With biokinetic of
biochemical methane potential (BMP) test, two methods were
employed to describe the biokinetic models of the existed
anaerobic biofilm. The initial biogas production rate and the
maximum biogas production rate were represented the bioactivity
of the existed microbes degrading the individual component. Both
parameters showed that the anaerobic biofilm degrading HAc, BA
and TA were fitted with Monod model in BMP test. The result of
BMP test also showed that the rate-limiting step in anaerobic
conversion from aromatic compounds to methane was acidogensis
instead of methanogensis. Anaerobic toxicity assessment (ATA)
test on biodegradation showed that both HAc and BA had substrate
inhibition with TA degradation. The lag time of TA degradation
would be influenced by the high concentration of HAc or BA. As
to the maximum biogas production rate (mL.biogas/gVSS-day), TA
degradation would be influenced by HAc and BA, too, while HAc
was more serious than BA.According to microbial morphology of
electronic microscopy of the existed biofilm, anaerobic floc was
easily attached onto the GAC surface by the hydraulic control of
the granule fluidization. Biofilm was found out to grew
initially in the surface hole and cave of the GAC. With gradual
load increasing, microbial growth was observed in the fluidized
bed. The outer layer of the granular bioparticle was grown with
the predominant Methanothrix species, while the biofilm
interior was filled with syntrophic ecosystem of anaerobic
bacteria.Appropriate inoculation and loading increment provided
good biofilm attachment and microbial growth onto the fluidized
GAC particles. Meantime, process control with decreasing HAc and
BA inhibition could enhance the biodegradation of aromatic
constituents in the PTA manufacturing wastewater. The GAC
anaerobic fluidized process could achieve excellent performance.
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