Page 406 - Industrial Wastewater Treatment, Recycling and Reuse

378 Industrial Wastewater Treatment, Recycling, and Reuse

reuse possible. Membranes have been used more recently in suspended
growth reactors for wastewater treatment (Sarin, 2013). The membrane bio-
reactor (MBR) is the latest technology for biological degradation of soluble
organic impurities. MBR technology has been in extensive usage for treat-
ment of domestic sewage, but for industrial waste treatment applications, its
use has been somewhat limited or selective. The MBR process is very similar
to the conventional ASP in that both have mixed liquor solids in suspension
in an aeration tank. The difference in the two processes lies in the method of
separation of bio-solids. In the MBR process, the bio-solids are separated by
means of a polymeric membrane based on a microfiltration or UF unit, as
compared to the gravity settling process in the secondary clarifier in the con-
ventional ASP (Mittal, 2011). Therefore, the advantages of an MBR system
over a conventional activated sludge system are obvious:
• Membrane filtration provides a positive barrier to suspended bio-solids
so that they cannot escape the system, unlike gravity settling in the
ASP, where the bio-solids continuously escape the system along with
clarified effluent. Sometimes a total loss of solids is also encountered
due to process upsets causing sludge-bulking in the clarifier. As a result,
the bio-solid concentration measured as MLSS/MLVSS can be maintained
at three to four times greater in an MBR process ( 10,000 mg/L) in com-
parison to the ASP ( 2500 mg/L).
• Due to the above aspect of MBR, aeration tank size in the MBR system
can be one-third to one-fourth the size of the aeration tank in an acti-
vated sludge system. Further, instead of a gravity settling-based clarifier,
a much more compact tank is needed to house the membrane cassettes
in the case of submerged MBR along with skid-mounted membrane
modules in the case of a non-submerged, external MBR system.
• Thus, an MBR system requires only 40–60% of the space required for an
activated sludge system, therefore significantly reducing the construction
work/cost and overall footprint.
• Due to membrane filtration (micro/UF), the treated effluent quality in
the case of the MBR system is far superior compared to conventional
activated sludge, so the treated effluent can be directly reused as cooling
tower make-up or for gardening or other uses. Typical treated water
quality from the MBR system is:
BOD 5 <5 mg/L
Turbidity<0.2 NTU
The MBR system has three important parts that play an important role in
overall performance; the development at each has been moving fast since
1990 for its commercial usage (Frenkel, 2013).