Page 435 - Industrial Wastewater Treatment, Recycling and Reuse

Application of Anaerobic Membrane Bioreactor 407

technology should also afford sustainability and present minimal operational
difficulties. The anaerobic MBR (AnMBR) offers such advantages for the
treatment of domestic wastewater.

10.3 INTRODUCTION TO THE AnMBR

Relative to aerobic MBRs, little research has been carried out in using mem-
branes to retain the biomass in anaerobic systems. Anaerobic digesters with
membrane separation units facilitate retention of microorganisms and allow
operation with high biomass concentration. Thus, AnMBRs are expected to
provide more efficient digestion, higher methane production, better effluent
quality, and smaller size than conventional anaerobic digesters. Various stud-
ies have indicated that the main challenge with AnMBR has been fouling of
membrane units (Choo et al., 2000; He et al., 2005).
According to how the membrane is integrated with the bioreactor, two
AnMBR process configurations can be identified, mainly side stream and sub-
merged. In side stream AnMBRs, membrane modules are placed outside the
reactor, and the reactor mixed liquor circulates over a recirculation loop that
contains the membrane. The cross flow velocity of the liquid across the surface
of the membrane serves as the principal mechanism to disrupt cake formation
on the membrane. Due to the higher operating costs involved in side stream
MBRs, submerged MBRs, introduced by Yamamoto in 1989, have been the
preferred choice in MBR plant installations from the mid-1990s. In sub-
merged AnMBRs, the membranes are placed inside the reactor, submerged
in the mixed liquor. In this configuration, a pump or gravity flow due to ele-
vation difference is used to withdraw permeate through the membrane.
Because the velocity of the liquid across the membrane cannot be controlled,
cake formation can be disrupted by vigorously bubbling gas across the mem-
brane surface. In the case of aerobic MBR, air scouring used also provides aer-
ation in the bioreactor, while for AnMBRs biogas must be used.
Submerged AnMBRs consume much less power than external side
stream AnMBRs because of the absence of a high flow recirculation pump.
Side stream AnMBRs have a much higher energy requirement because of
higher operational transmembrane pressures (TMP) and the elevated volu-
metric flow required to achieve the desired cross-flow velocity. However,
side stream reactors have the advantage that the cleaning operation of mem-
brane modules can be performed more easily in comparison with submerged
technology, because membrane decoupling can be done effectively from the
bioreactor during membrane cleaning. Submerged AnMBR demands lower