Chemical Engineering September 2020 - 42

to equalize and homogenize the
varying concentrations of different
wastewaters originating from the different
chemical plants, an equalization
tank is used at the beginning of
the overall treatment process. after
the equalization stage, two identical
dnF treatment units (dnF train a
and dnF train B) were designed to
add redundancy to the wastewater
treatment system and mitigate risks
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each unit is designed for an average
flow of 600 gal/min, a maximum flow
of 750 gal/min, and incorporates its
own in-line coagulation, flocculation
tank, flotation tank and pressurization
system. Both pressurization
systems include a pressurization
vessel and two dnF recycle pumps
(one duty and one spare) that recycle
recovered sludge from each dnF unit to a respective sludge tank
for storage.
circular dnF units were adopted
for the project to achieve better distribution
through one single-inlet
distribution chamber, which ensures
even distribution of the floating material
across the entire surface area.
use of a single mixing chamber allows
gas bubbles to attach to the
incoming flocs.
the dnF sludge tanks were
equipped with a vertical mixer to
ensure adequate sludge homogenization.
From the sludge tank, the
sludge is pumped to a three-phase
vertical centrifuge, which separates
water, oil and solids. the dnF design
parameters are summarized in
table 1.
Table 3. biologiCal sysTem DesigN
Biological trains
2
Aerobic tank volume per bio train
Total aerobic volume (excluding
membranes)
Membrane tank aerobic volume
MLSS design
Minimum water depth
196,500 gal
393,000 gal
38,800 gal
8,000 mg/L
18 ft
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42
Following dnF treatment, the effluent
is then conveyed onward to the
mBr package for aerobic biological
treatment of an average flow of 352
gal/min in a 2 x 100% configuration
and a cod of 1,275 mg/l, as shown
in table 2.
like the dnF units, the mBr package
also incorporates two treatment
train lines. at the beginning of
each treatment train, effluent from
the dnF units enters a large concrete
basin where air bubbles are
introduced into the water from diffusers
mounted on the bottom of the
basin. the water flows via gravity to
the membrane tank, which houses
the membrane cassettes. a portion
of the wastewater is sent back
to the bioreactor by return activated
sludge (ras).
the biological system consists of
two trains, each designed for a capacity
of 196,500 gal and mlss
concentration of 8,000 mg/l, as
shown in table 3. the bioreactor
is designed with a sludge retention
time (srt) of 31 days, an oxygen uptake
rate (our) of 44 mg/l/h, and a
ChemiCal engineering www.Chemengonline.Com September 2020
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Chemical Engineering September 2020

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