Membrane and Desalination Technologies - TCE Moodle Website

206 L.K. Wang and R. Menon
1.5. Membrane Bioreactors Research and Engineering Applications
In this section, various MBRs will be reviewed and discussed, although the remaining
sections of this chapter will introduce and discuss only the most common MBRs, which are
well-established and practically applied to the environmental engineering field for pollution
control.
MBRs consisting of an aerobic or anaerobic reactor with suspended biomass and membranes
for liquid–solid separation are now the mainstream environmental engineering processes
for water treatment and WWT. MBRs have been used for treatment of municipal and
industrial wastewater (13) and for reclamation of water for potential reuse in public water
supplies (14).
With respect to treatment efficiency and system stability, MBRs have several advantages
over conventional processes:
1. With complete solids–liquid separation by the membrane, high biomass concentrations and
relatively short reaction times are possible (13–21).
2. MBRs can produce a clear final effluent regardless of hydraulic retention time (HRT) and without
concerns of biomass settleability characteristics (15).
3. Biological nitrogen removal is also possible in an intermittently aerated single-stage MBR (16).
An MBR with powdered activated carbon (PAC) addition was applied for drinking water
treatment to remove nitrate, natural organic matter, and pesticides and to disinfect the water
(22). Also, the addition of PAC to the activated-sludge process with attached microbial
growth on the PAC enhanced membrane permeability. The flux enhancement could be
attributed to the development of dense floc particles around the PAC (23, 52).
Brindle and Stephenson (13) studied three generic membrane processes within bioreactors
for WWT, solids separation and recycling, bubble-less aeration, and priority organic pollutants
extraction. Commercial aerobic and anaerobic MBRs are already in use, producing a
high-quality effluent at high organic loading rates. However, bubble-less aeration and
extractive MBRs are still in development.
Dollorer and Wilderer (24) compared oxygenation by bubbling and via a silicone rubber,
bubble-free membrane system in sequencing batch biofilm reactors (SBBRs). The claypacked
SBBRs achieved 68% dissolved organic compounds removal from hazardous waste
with a 12-h cycle. The bubble-free SBBR emitted less biodegradable volatile organics than
the bubbled system.
Livingston et al. (25) used an extractive membrane bioreactor (EMBR) to remove a range
of toxic organic compounds from the chemical industry, achieving more than 99% removal
with a wastewater reactor contact time of fewer than 30 min. The removal efficiency was
modeled and a new EMBR configuration was discussed. Data on the effect of biofilms on
membrane mass transfer were shown. In an additional work, this group demonstrated that
the addition of sodium chloride to the biomedium increases the maintenance energy
requirement of the degradative organisms and resulted, in a carbon-limited situation, in
reduction of biofilm growth. Organic substrate flux remained high under reduced biofilm
growth conditions (26).