Chemical Engineering September 2015 - 58

MBBR
isms that are free-floating attach
to the media and form biofilm. the
sludge that is free-floating passes
with the wastewater to a clarifier. a
portion of the sludge is removed and
sent back to the Potw.
the integrated fixed-film activated
Effluent
Aeration
Sludge
FiguRe 2. This schematic shows a moving bed biofilm reactor (MBBR) with water flowing from left to
right through media with aeration
vated membranes for solid and liquid
separation (microfiltration).
typical mixed-liquor suspendedsolids
concentrations in mbR systems
are 10,000-12,000 mg/l. the
two types of membranes available
for use in mbR include hollow-fiber
and flat-sheet membranes. the mbR
technology replaces clarification,
disk filtration or ultrafiltration required
in industrial plants. effluent is sent
to the service water tank, or plant
water system, and from there to the
demineralization systems and cooling
water system. with an mbR, the
effluent can attain nh3-n concentrations
less than 1 mg/l, bod of less
than 5 mg/l, and cod of less than
50 mg/l.
table 2 lists the advantages and
disadvantages of the mbR. effluent
water quality and ability to handle influent
variability are the major reasons
that many mbRs have been installed
over the past 50 years.
Moving bed biofilm reactor
(MBBR). a schematic of an mbbR
is shown in Figure 2. secondary
treated water flows from left to right,
through biofilm carrier elements or
media in an aerated bioreactor. the
biofilm is attached to the media. typical
carrier elements look like pretzels
with inner and outer grooves
and ridges: but the quantity, shapes
and sizes depend on the specific
application, based on water temperature,
ph, capacity, constituents
and required effluent quality.
activated sludge and microorganService
water
&
firewater
tank
H
10,000 gal/min
Secondary treated
wastewater
Media filter
8,500
gal/min
Service
water
users
MBBR
nitrification
clarifer
Oil-water
separator
Backwash waste
Cooling
tower
Blowdown
storage tanks
FiguRe 3. This is an example of a water balance for an MBBR and clarifier system
58
Discharge to wastewater
treatment plant (WWTP)
24.5% of total flow
2,450 gal/min
COC: cycles of concentration; CTG: combustion turbine generator;
HRSG: heat recovery steam generator; H: stream number
ChemiCal engineering www.Chemengonline.Com september 2015
Evap. & drift
75% @ 5 COC
Quench water
to HRSG blowdown
tank
300-600
gal/min
UF
1st pass
RO
1st pass RO
permeate tank
Evaporation
0.5% @ 5 COC
50 gal/min
CTG evap
cooler
Sample panel
Quench water from
service water &
firewater tank
H
HRSG
Flash stream
HRSG
blowdown
tank
(2)
Demineralized
water
users
2nd
pass
RO
sludge (iFas) variation of the mbbR
process takes its name from the integration
biofilm media technology
inside the conventional activated
sludge, where some of the sludge
is recycled back to the mbbR. the
iFas/mbbR requires return activated
sludge (Ras) pumps and piping. the
mbbR produces an effluent with
nh3-n levels of less than 1 to 3 mg/l,
no3-n less than 1 mg/l and total nitrogen
(tn) less than 3 mg/l. table 3
lists the advantages and disadvantages
of the mbbR.
an example of a power-plant
water balance using an mbbR/clarifier
system is shown in Figure 3. the
1,000-mw combined cycle plant has
three gas turbines with heat recovery
steam generators (hRsG), and one
steam turbine, one demineralization
system and one cooling system.
Biological aerated filter (BAF). the
baF shown in Figure 4 was introduced
in the early 1980s. this system
has lower operating and maintenance
costs and a smaller footprint
than the mbR and mmbR. the baF
Electrodeionization
(EDI)
system
Demineralized
water
tank

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Chemical Engineering September 2015

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