Flat sheet membranes

Fig. 1 shows the modules from Kubota. Over the past decade, it has evolved to become taller to utilize scouring air more efficiently.

 Table 1. Types of Kubota membrane unit and their dimension
Flat s2

Fig. 1. Various types of submerged membrane unit (SMU) aka cassette (Kubota, 2010).

More recently, Kubota introduced SP-400 SMU (submerged membrane unit) in 2010. This SMU includes 40 membrane sub-cassettes with 40 0.25 m2 panels (Fig. 2a) are stacked in a large cassette (Fig. 2b). One SMU contains 1,600 small membrane panels total. According to manufacturer’s spec, specific air demand per surface area (SADm) is 0.30 m3 air/m2 membrane/hr as discussed here. However, the actual field data is not available yet in public domain to the author’s best knowledge.

Fig. 2. Kubota’s SP-400 module and submerged membrane unit (SMU), where each module contains  (Codianne, 2012)


There are many other flat sheet membrane suppliers, but Pure-Envitech is one of the early starters in late 1990. Envis® flat sheet membranes are based on similar concept with Kubota. Fig. 3 shows the membrane frame (also known as cassette). Pure Envitech introduced the stacked cassette design earlier than Kubota as shown in Fig. 4. Pure Envitech’s SBM®(submerged block membrane) cassette holds SBM blocks with 13 0.3 m3 membrane panels.

Fig. 3. Envis® flat sheet membranes (Pure Envitech, 2011).

Fig. 4. SBM® flat sheet membranes module and cassette (Pure Envitech, 2011).


Mycrodyn-Nadir‘s BIO-CEL® membrane and modules are unique from the perspective of membrane plate design. Two flat sheet UF membranes made of polyether sulfone (PES) with 0.04 micron pore size are fused on non-woven polyester support. This module is backwashable at up to 15 kPa (or 2.2 psi). Membranes have finger-type structure as shown in Fig. 5a. Each membrane panel is 2 mm thick and the permeate outlet is in the middle of the panel (Fig. 5b) to minimize the localized filtration due to the pressure loss in the thin polyester support.

Flat s4    Flat s5
a) Membrane cross-section                                  b) Panel structure
Fig. 5.  Membrane cross-section and panel structure (Microdyne, 2011).

Fig. 6 shows the structure of membrane frame/cassette, where membrane panels are fixed in a rectangular module that is in turn fixed in a cassette. Due to the thin panel structure, irregular panel spacing is inevitable as shown in Fig. 6c.

Flat s6      Flat s7
a) Module                                                 b) Membrane panel corners fixed by a skewer pipe/bar

Flat s9    Flat s10
c) Membrane panels in a module                                                       d) Two modules in a cassette
Fig. 6. Structure of BIO-CEL module and cassette (Microdyne, 2011)

© Seong Hoon Yoon