The MBR Book: Principles and Applications of Membrane

176 The MBR Book
called Skyland Baseball Park, in New Jersey in June 1994, and the product subsequently
sold in several small land development MBRs, such as Thetis Lake
Campground and Trailer Park, BC (1995) – which, as of July 2005, was still operating
with its original membranes. ZeeWeed ® modules were also used for the first time
in potable and industrial pure water treatment applications from 1995 onwards.
The early experiences in continuous aeration also led to the development in
1998–1999 (and later patenting) of two-phase aerator flushing to prevent aerator
plugging.
Zenon introduced the ZeeWeed ® 500a for wastewater treatment and the
ZeeWeed ® 500b for drinking water treatment in 1997. The new membrane modules
had significantly higher surface area per plant footprint than the ZeeWeed ® 150,
with the drinking water modules constructed with more fibres, and hence a greater
surface area (650 ft 2 , 60.4 m 2 ), than those for wastewater (500 ft 2 , 46.5 m 2 ). These
modules not only provided a greater membrane area through employing a higher,
wider and slightly more densely packed fibre bundle, but could also be housed within
a single, standardised cassette of eight modules (Fig. 4.15a). The membrane material
was also made more selective than those used previously, with these membranes,
the nominal pore size being reduced to 0.04 �m.
Two further vertical HF modules, the ZeeWeed ® 500c (23.2 m 2 membrane area)
and the ZeeWeed ® 500d (340 ft 2 , 31.6 m 2 ) were introduced in 2001 and 2002 respectively.
These modules (Fig. 4.15b–c) provided further improvements in clogging
amelioration and ease of element removal and refitting over the earlier modules. In
addition to further increasing the membrane surface area per module footprint, the
ZeeWeed ® 500c is more flexible, being no longer self-supporting but designed to be
applied to either drinking water or wastewater simply by varying the number of
modules within the same, standard-size cassette. Aerators are incorporated into the
bottom of each cassette, and permeation is no longer from both ends, but from the
top only. This design capitalises on the fact that the highest shear from the air scour
occurs at the top section of the membrane fibre in an MBR. When permeation is
from the top only, the top section of the membrane is also the point of the greatest
flux. The configuration allows the effectiveness of the scouring to match the flux
magnitude across the length of the membrane fibre, maximising the treatment
capacity of the MBR system. The ZeeWeed ® 500c module includes a top permeate
header (complete with o-ring seals) that interlocks with other modules to form an
integrated permeate collection header at the top of each cassette. Since permeation
does not occur at the bottom header, a more streamlined design results with better
airflow into the membrane fibre bundle.
The ZeeWeed ® 500d, commercially released in 2002, is geared towards even larger
scale potable water and wastewater treatment plants. Modules are wider and higher
than the ZeeWeed ® 500c and can be easily isolated and removed from the cassette. Like
the ZeeWeed ® 500c, the cassette incorporates aerators and a central permeate header.
ZeeWeed ® 500d modules are arranged in two parallel rows within the cassette, with
central permeate collector pipes between them. To simplify manufacturing, the
top and bottom headers are identical, and because these membranes are more
frequently used in potable water projects, permeation occurs through both headers.
This product is employed in the world’s largest MBR plants, currently at the planning