Page 407 - Industrial Wastewater Treatment, Recycling and Reuse

An Introduction to Biological Treatment and Membrane Filtration 379

1. Biological reactor
2. Membrane properties
3. MBR configuration.

9.5.1 Biological Reactor
Membrane is merely a filtration device in the entire process, thus the biological
process of the effluent needs is the first step of importance. With advancement
in understanding of bio-technology, the biological treatment section of
MBR is being improved, which makes the bioreactor sturdy and efficient.
However, dampening of hydraulic and organic load fluctuations is a key factor
to guarantee a consistent bio-treatment operation.
Biological processes are slow and invariably require close monitoring
because any change, if it happens, appears as an observation after a lapse of
time. There are specific parameters, such as DO, MLSS, SRT, HRT, inlet
wastewater quality, and quantity, that need to be checked and logged. The
sludge character varies with the variation in feed characteristics However, it
is very important to acclimate the MLSS properly so that the system can oper-
ate efficiently.The biologically treated wastewater is then fed to the MBR
membrane system. Because the membrane performs the filtration, oversized
sludge is retained in the feed side and is recirculated back to the aeration tank
to maintain the MLSS quantity in the reactors. Bleed (sludge wastage) is main-
tained from the reactor to remove the dead cells or to maintain MLSS. The
deposition of sludge over the membrane surface is bound to take place and so
periodic back flush/cleaning is recommend by individual suppliers.
9.5.2 Membrane Properties

Filtering properties depend on the type of membrane, its pore size, its hydro-
philic properties, and chemical properties (Judd, 2011). The membrane sup-
plier recommends a process wherein to operate at a defined minimum to
maximum flux under different conditions. This is to safeguard the membrane
against becoming fouled without notice to avoid reaching a non-recovery
point on the membrane and thus the system.

9.5.3 MBR Configuration
Available MBR technologies employed for wastewater treatment can be
classified according to membrane configuration: flat sheet (FS), hollow fiber,
and multi-tubes.
The FS base submerged MBR was piloted early in 1990 for wastewater
application (Judd, 2011). The membrane material used was chlorinated poly-
ethylene over a robust nonwoven support. The pore size of such membrane