The MBR Book: Principles and Applications of Membrane

(a) (b) (c)
Commercial technologies 177
Figure 4.15 Zenon MBR membrane elements and stacks: (a) ZeeWeed ® 500a, (b) ZeeWeed ® 500c and
(c) ZeeWeed ® 500d (see also Table 4.2)
or construction stage. These include plants such as John’s Creek Environmental
Campus in Georgia, USA (41 MLD average day flow; 94 MLD peak hourly flow) and
Brightwater, Washington, USA (117 MLD average day flow; 144 MLD peak hourly
flow). The Zenon cassettes (Fig. 4.15 and Table 4.2) are readily placed trains in trains
(Fig. 4.16) to attain the desired capacity.
A further innovative feature of the Zenon system is the use of cyclic aeration,
which was commercially introduced in 2000 following the introduction of the
ZeeWeed ® 500 series. In this aeration mode, the blowers are operated continuously
at a fixed speed and cyclic aeration is achieved by cycling the airflow from one air
header to the other using pneumatically actuated valves. Since one half of each cassette
is connected to one air header, this permits the air to be cycled. This was preferred
over continuous aeration primarily for technical and commercial reasons.
Technically, continuous aeration often resulted in air channelling through the module
and could only thoroughly clean portions of the module. Introducing shear and