The MBR Book: Principles and Applications of Membrane

240 The MBR Book
Table 5.14 Comparison of MBR plant at Rödingen and Kaarst
Parameter Rödingen Kaarst
Design
Capacity (p.e.) 3000 80 000
Bioreactor volume (m3 ) 400 9200
Membrane area (m2 ) 5280 84 480
Sludge concentration (g/L)
Operation
12–18 12
Sludge loading (kg BOD/(kg MLSS day)) 0.04 �0.05
HRT, h 3.6 4.6
Sludge retention time (day) 25 25
Flux (LMH) 28 25
Figure 5.27 Aerial view of the Kaarst site
chamber and the denitrification tanks, the two latter operations being open to the
atmosphere (Fig. 5.27). Water is pumped from the original WWTP 2.5 km east of
the site to 5 mm step screens, followed by an aerated grit chamber. It is then fed to
two Huber rotary drum 1 mm mesh-grid fine screens, changed from 0.5 mm fine
screens originally installed, each providing a capacity of 24 MLD. There is a standby
1 mm fine screen which comes on-line in case of a mechanical breakdown of the
former two. Screenings are discharged into a skip and subsequently disposed of by
incineration off-site. The screened water is transferred to the MBR.
Biotreatment comprises four tanks each fitted with two membrane trains with an
upstream denitrification zone of 3500 m 3 total capacity; the latter receives sludge
from the subsequent membrane aeration tank at a recycle ratio of 4:1. The membrane
trains are each fitted with 24 ZW500c membrane cassettes of 440 m 2 membrane
area, such that the total membrane area is 84 480 m 2 (20 m 2 /elements; 22
elements/cassette), and the aeration tanks receive supplementary mechanical agitation
from impeller blade stirrers to maintain biomass suspension. The total volume of
the tanks is 5800 m 3 , of which about one-third comprise the membrane aeration,
which together with the denitrification tanks provide a total HRT of �5 h at 48 MLD