The MBR Book: Principles and Applications of Membrane

Aeration tank 1
FBDA
FBDA
32 x J200 panel units per tanks
Denitrification/
recycle tank
FBDA
Aeration tank tan k 2
Aeration tank 4
Influent from
lamellar separators
Aeration tank 3
FBDA
Figure 5.6 Schematic layout of the Daldowie sludge liquor treatment plant
Case studies 217
280 mgN/L as NH 3 and 1500 mg/L as BOD, and mean COD levels are in the region
of 2600 mg/L; corresponding permeate levels are around 100–400 mg/L COD
(hence �90% removal) with ammonia levels of 1–2 mg/L (�95% denitrification). The
maximum design flow is 12.8 MLD (yielding a minimum hydraulic retention time
(HRT) of 15 h), obtained with six dryers running without a standby, with an average
of �9 MLD being sustainable according to information from site operations. Flows
pass through lamellar separators and a 3 mm screen into a central denitrification/
recycle tank. From there, flows are distributed into four combined membrane and aeration
tanks, each of 2000 m 3 volume (Fig. 5.6), and a sludge recycle stream returned
from the tanks to the denitrification section. In each of the aeration tanks there are 1378
diffusers and 32 � 200-panel membrane units, giving a combined 25 600 panels in
the plant (20 480 m 2 ). The flows thus equate to a mean design flux of 18 LMH and a
maximum of 26 LMH.
A great deal of time, effort and money has been spent on identifying the most appropriate
polymer and its dose for chemical conditioning to be effective in the belt press
and centrifugation dewatering operations without detriment to membrane permeability
in the downstream MBR. Despite the problems associated with optimising the polymer
dosing, the plant has maintained reasonable performance in terms of COD and
ammonia removal. Moreover, the membranes have proven very robust; no more than
40 of the 25 600 panels were replaced in the first 3 years of operation, despite there
being no ex situ chemical clean instigated over that period for permeability recovery.
Routine cleaning in place (CIP) with hypochlorite takes place every 6 weeks or so.
One unusual operational problem that was encountered during an early period of
operation was an abrupt increase in differential pressures accompanied by sudden
foaming. The foam on the top of the tanks was green-grey in colour, whereas the
sludge remained brown. Samples of the foam revealed it to consist almost entirely of
non-settling discrete chlorella algae of about 15 �m diameter. The algae were neutrally
buoyant and non-flocculating and appeared to pass through the centrifuge as
a result. The incident appeared to be due to the sludge plant processing waterworks
sludge from a site where an algal bloom had been experienced. Whilst differential