Membrane and Desalination Technologies - TCE Moodle Website

494 P. Kajitvichyanukul et al.
3. Eight reactions that describe the rates of consumption or production of the different species, as
well as the stoichiometric linkages among the rates
4. Reaction with diffusion of all the soluble species in the biofilm
5. Growth, decay, detachment, and flux of each biomass type by location in the biofilm
6. Constant or periodic detachment of biofilm, both of which allow for protection of biomass deep
inside the biofilm.
A series of examples illustrates insights that the TSMSBM can provide the transient
development of multiple-species biofilms; the roles of soluble microbial products, and detachment
in controlling the distribution of biomass types and process performance; and how
backwashing affects the biofilm in drinking-water biofiltration.
4.2. Membrane Bioreactor
The MBR is usually referred to a bioreactor integrated to a membrane module system. This
technology has been developed over 30 years ago (79) and it is mostly applied to treat
industrial wastewater, domestic wastewater, and specific small municipal wastewater treatment
plants (80). In drinking water treatment, a promising area of MBR application is NO3 –
removal. Advantages of the MBR include better control of biological activity, effluent that is
free of bacteria and pathogens, smaller plant size, and higher organic loading rates (81).
In general, membrane bioreactors consist of two compartments, the biological unit and the
membrane module (82). The biodegradation of the compounds occur in the biological unit,
while the physical separation of the treated water from the mixed liquor takes place in the
membrane module. MBR systems can be classified into two groups: integrated or submerged
membrane bioreactors and external or recirculated membrane bioreactors (82). The first
group, integrated membrane bioreactors, involves outer skin membranes that are internal to
the bioreactor. The driving force across the membrane is achieved by pressurizing the
bioreactor or creating negative pressure on the permeate side (82–85). A diffuser is provided
for mixing and facilitating the filtration surface scouring. The second type, external or
recirculated membrane bioreactors, involves the recirculation of the mixed liquor through a
membrane module that is outside the bioreactor (85). The driving force is the pressure created
by high cross-flow velocity along the membrane surface (86, 87). For drinking water and
groundwater treatment, external membrane bioreactors are widely used for pesticide removal
and denitrification.
Types and configurations of membranes used in MBR applications include tubular, plate
and frame, rotary disk, hollow fiber, organic (polyethylene, polyethersulfone, polysulfone,
polyolefin, etc.), metallic and inorganic (ceramic) microfiltration, and ultra-filtration membranes
(88). The pore size of membranes ranges from 0.01 to 0.4 mm (82). The fluxes range
from 0.05 to 10 m/day (m 3 /m 2 /day), strongly depending on the configuration and membrane
material (82).
In drinking water treatment, major application of membrane bioreactors is denitrification.
This process has many advantages over traditional biological denitrification (22, 82). In
a typical biological denitrification system, post treatment processes are required to separate
microorganisms and DOM. By using a membrane bioreactor, the number of post treatment