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

and 4, with decreasing observations of these micro-organisms in dispersed sludge of later
compartments. This implies that partial phase separation has occurred between the first and subsequent
compartments with hydrolysis and acidogenesis predominating in the first compartment and
establishment of acetoclastic methanogenesis thereafter.
These results confirm the hypotheses presented in Sections 5.6.1.4 and 5.6.2 that proposed that high
solids accumulation rates (normalised for OLR) in Phase III compared to those in Phase IV were due
to the establishment of a stable anaerobic population at the lower flow rate of Phase IV. As the
concentrations of soluble components in the pilot-scale ABR are relatively low during the treatment of
domestic sewage, the cause of the differences in population stability between the different flow rates
must be due to the higher upflow velocities employed in Phase III resulting in the washout of
anaerobic micro-organisms. Thus it may be concluded that the upflow velocity in each compartment is
a critical design factor that must be considered in conjunction with A-HRT and OLR when sizing a
baffled reactor for the treatment of domestic sewage.
5.8 SUMMARY OF OPERATION AT KINGSBURGH WASTEWATER TREATMENT PLANT
Table 5.5 and Table 5.6 (pages 117 and 127) are summaries of all inflow and outflow measurements
averaged for operation of the pilot-scale ABR at Kingsburgh WWTP for Phase II, III and IV. In the
sections that follow, the main conclusions drawn from the data presented in this chapter are
summarised.
5.8.1 Outflow characteristics
Substantial reductions in COD were observed in all operating periods, with lowest values (around
130 mgCOD/ℓ) measured in Phase IV. A number of factors contributed to the best performance being
observed in Phase IV:
• The ABR was operated at low flow rates, resulting in low upflow velocity and therefore good
solids retention characteristics and development of a balanced anaerobic population to
facilitate digestion.
• The low feed rate in Phase IV corresponded to a low OLR.
• Significant improvements in management and control of the pilot-scale ABR resulted in fewer
sludge loss incidents
Anaerobic treatment of domestic wastewater in the ABR caused a net increase in alkalinity and free
and saline ammonia concentrations, and a slight decrease in TKN. A small amount of sulphate in the
feed stream was removed by the ABR. Nitrate present in the wastewater was expected to be
completely removed within the first one or two compartments of the system. Phosphate in the inflow
stream was not expected to change as a result of treatment in the ABR. The ABR outlet stream
therefore contained increased concentrations of alkalinity and free and saline ammonia and similar
concentrations of phosphate compared to the influent wastewater. No sulphate or nitrate was detected
in the outlet stream.
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