The aim of the investigation was to compare the performance of an anaerobic baffled reactor (ABR)
with a completely mixed anaerobic reactor (CMAR). The ABR was operated with a hydraulic retention
time (HRT) of 20 h while the CMAR was operated at 20 d. A control experiment was conducted with a
CMAR operated at a constant hydraulic retention time and substrate feed concentration. During the
first phase, the start-up performance of the ABR and CMAR were compared. In the second phase of the
study the steady state COD removals were compared.
The laboratory completely mixed anaerobic reactor was a 20L glass vessel with a stirrer coming in
through the neck. A second type of reactor, anaerobic baffled reactor (ABR) was also operated. The
ABR was a rectangular perspex box with internal vertical baffles alternately hanging and standing. The
baffles divide the reactor into eight compartments with a total working volume of 7.5 L. Each baffle is
angled at about 45Q to distribute the flow towards the centre of the upcomer. The reactors were seeded
with raw sewage and allowed to stand for 3 days after which a continous feed of sucrose and basal salts
was commenced. The initial HRT for the ABR and the CMAR were 60 h and 30 days respectively.
When the reactors reached steady state (pH, gas production, gas composition and alkalinity), the HRT
was reduced in a stepwise fashion (ABR 60 h to 35 h to 20 h and CMAR 35 d to 30 d to 20 d). At the
final HRT the COD removals were similar (67 %). The ABR took 120 d to attain final steady state
while the CMAR took 200 d.
The organic loading tests were undertaken with a stepwise increase (doubling) in the influent substrate
concentration. The feeding commenced at an organic loading rate (OLR) of 4.8 kg/m(3).d for the ABR.
The flow rate (HRT) into both reactors and other parameters were kept constant (HRT of 20 h and 20 d
for ABR and CMAR respectively). The substrate concentration was increased from 4 gCOD/L (4.8
kg/m(3).d) to 64 gCOD/L (76.8 kg/m(3).d) for the ABR. For the CMAR it was increased from 4 gCOD/L
(0.25 kg/m(3).d) to 32 gCOD/L (2 kg/m(3).d). The method used was to increase the organic loading rate
until the reactors failed. Since the two reactors had different operating HRTs, the tests began when both
had the same COD removal rate of about 60 % COD reduction. The same parameters as in the start-up
period were monitored for both reactors. The CMAR had a COD removal efficiency ca. 70 %, which
did not fluctuate when OLR was increased. The ABR reached a maximum COD removal of 80 %. An
increase in the OLR led to an initial decrease in the COD removal until the biomass recovered and the
high COD (80 %) removal rates resumed. The ABR reached a maximum OLR of 76.8 kg/m(3).d whilst
the CMAR reached a maximum OLR of 2.0 kg/m(3).d. The investigations showed that the ABR could be
operated at higher organic loads than the CMAR and give the same organic removal rate. This verified
the importance of increasing the SRT/HRT ratio in anaerobic reactors. The CMAR, however, proved to
be stable to changes in the influent feed strength, as there was no immediate noticeable changes in the
gas production. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5584 |
| Date | January 2000 |
| Creators | Mudunge, Reginald. |
| Contributors | Buckley, Christopher A. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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