analysis of a pilot-scale anaerobic baffled reactor treating domestic ...

that may be undertaken in a number of different ways (e.g. through flocculation and settling,
free settling, filtration or centrifugation) resulting in widely varying results.
There were also significant differences between suspended solids concentrations in the
different phases of operation at Kingsburgh (P < 0.02 for all combinations) with the highest
suspended solids values associated with Phase II. These results support the observation that
higher COD values were obtained in Phase II and indicate that the wastewater was generally
of a higher strength during this period.
All of the differences between Umbilo and Kingsburgh wastewaters can be explained by the different
sources of the wastewater: it is expected that the textile effluent component of the Umbilo wastewater
would have low alkalinity and low free and saline ammonia / organically bound nitrogen compared to
domestic wastewater, but could have high total solids due to the use of salts for dye fixing and the
presence of textile fibres in the effluent.
These data indicate that the feed characteristics may have been fundamentally different between Phase
I (Umbilo WWTP) and Phases II-IV (Kingsburgh WWTP), and that this may have affected the sludge
dynamics and outflow stream characteristics of the reactor at the different locations.
5.3.3 Hydraulic and organic loading rates: Phase II – IV
During Phase II and Phase III, the intention was to reproduce the hydraulic loading conditions that
were obtained in Phase I. Thus the A-HRT was between 20 and 24 h.
In Phase II, flow rate data were not recorded regularly. However, the average flow rate was inferred
from the total flow treated (350 kℓ) and the number of days of operation (excluding down-time: 99
days):
• Towards the end of operation of the pilot-scale ABR at Umbilo WWTP, the previous project
manager had caused the siphon breaker on the outlet line to be raised to the height of the first
baffle. This increased the internal volume of the ABR to (1 m × 3 m × 1.14 m =) 3.420 m 3
• The average flow rate through the reactor was 350 000 ℓ / 99 d = 3 500 ℓ/d
• The average A-HRT was thus 3 420 ℓ / 3 500 ℓ/d × 24 h/d = 23 h
In Phase III the pilot-scale ABR was operated with a T-HRT of between 20 and 24 h, with an average
of 22 h being achieved.
In Phase IV the loading rate was reduced to counteract some perceived instabilities in the system.
During this phase, three continuous operating periods were achieved with mean A-HRT of 41 h, 44 h
and 42 h.
The average OLRs exerted in each of the phases were calculated using average A-HRT and inflow
COD data and are presented in Table 5.2. The values of OLR presented in Table 5.2 are generally
lower than loading rates used in the treatment of domestic wastewater at ambient temperature reported
in literature (Table 2.5).
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