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

• Information about the volume of accumulated sludge is important for planning of desludging
operations. With the current reactor design, desludging would only take place from the upflow
side of the reactor; hence volume of sludge calculated only from the upflow compartments
provides sufficient indication of the desludging requirements for the system.
Table 5.3: Results of regression analysis on solids accumulation in the pilot-scale ABR during
operation at Kingsburgh WWTP
Phase Calculated
quantity
II Sludge volume m 3 settled
sludge/year
III Sludge volume m 3 settled
sludge/ year
IV Sludge volume m 3 settled
sludge/ year
IV
III/IV
Mass of total
solids (dry)
Ratio of sludge
volume slopes:
Phase III/Phase IV
Units Average slope of
regression [Confidence
interval on slope]
kg dry
solids/year
The volume of sludge was calculated as follows:
107
Significance of
regression (P)
2.49 [-1.13, 6.12] 0.128
(not significant)
3.46 [2.28, 4.64] 0.00125
(significant)
0.901 [0.602, 1.20] 5.87 × 10 -6
(highly significant)
60.7 [33.5,87.8] 2.54× 10 -4
(highly significant)
No. of observations
used
in regression
- 3.84 [2.55, 6.06] - -
Vt
,
settled sludge =
⎛
y
⎞ ( ) ⎛
y
⎞
⎜∑
( w l)
i ⎟ ⋅ c/s area of up - flow compartment
= ⎜∑
i ⎟ ⋅ ⋅
⎝ i ⎠
⎝ i ⎠
Eq. 5-3
where y i is the height of settled sludge in compartment i and w and l are the width and length
respectively of the upflow side of each compartment.
There is a clear difference in the height of the beds between the different operating periods, with Phase
II (Figure 5.15) characterised by significantly lower sludge beds than in Phase III and Phase IV.
5.6.1.1 Phase II: Solids levels
There were many sludge washout incidents during Phase II. In these instances, high flow through the
reactor (due to poor control of feed rate, or sudden emptying following blockage of the outlet) caused
high internal flows with high upflow velocities, and carryover of sludge. Greatest settled sludge bed
height was usually found in compartment 2, although the difference between compartments was
generally not great. Figure 5.15(b) seemed to show a slight increase in volume of sludge with time
during Phase II. However, a regression analysis showed that there was no significant increase in
accumulated sludge volume with time, due to the small number of observations and the significant
scatter in the data (Table 5.3). Furthermore, such a correlation would not provide any indication of
sludge volume accumulation rates under stable operation due to the many sludge washout events in
this phase.
5.6.1.2 Phase III: Solids levels
A gradual increase in the overall sludge bed height with time is observed in Phase III.
Figure 5.16(b) shows a consistent increase in sludge bed volume from day 53 onwards. (In the period
5
6
20
17