Additional Lactose Recovery from Reduced Lactose
Permeate (DPL).
Base Assumption: If ~50% of the ash is removed from DPL by
electrodialysis (ED), a 2nd crystallization step will recover ~50%
of the contained lactose.
Advantage: This process
will increase lactose yield for a lactose-from-permeate operation by 15-20%
while reducing DPL disposal costs by ~50%.
Example Case
Feed: 50,000 kg/d of
reduced lactose permeate solids. The
feed is the mother liquor remaining following crystallization of lactose from
the permeate from a UF operation producing WPC from sweet whey.
Typical Feed composition: Total solids = 25%
Lactose = 16%
Protein = 2.125%
Ash = 5.125%
Other = 1.750%
ED Operation: Continuous,
feed & bleed @ 9 m3/h, 85-90 ºF, 20 hrs/d operation with 4 hrs/d available
for CIP.
Pretreatment: Suspended solids must be removed prior to
ED. When processing whole whey, WPC and
de-lactosed whey, sock filters (if SS load is light) or centrifuges are
commonly used. Precipitated calcium
phosphate might present a particular problem in DPL. Membrane filtration using ceramic UF elements
might be considered for this application, if conventional separation methods
have difficulty handling the calcium phosphate.
ED Product: The composition of the ED product is quite
similar to composition of the original UF permeate except the protein content
(mostly NPN) is higher and lactose content lower. Solids yield across ED will be 80%.
Total solids = 24.2%
Lactose = 18.5%
Protein = 1.8%
Ash = 2.4%
Other
= 1.5%
ED Mass
Balance: kg/d
|
|
Feed to ED
|
ED product
|
ED effluent
(1)
|
2nd
DPL (2)
|
|
total weight
|
200,000
|
165,000
|
510,000
|
?
|
|
total solids
|
50,000
|
40,000
|
10,900
|
24,750
|
|
lactose
|
32,000
|
30,500
|
1,500
|
15,250
|
|
protein
|
4,250
|
3,000
|
1,250
|
3,000
|
|
ash
|
10,250
|
4,000
|
7,150
|
4,000
|
|
other
|
3,500
|
2,500
|
1,000
|
2,500
|
(1) Includes ~500 m3 of make-up water + 900 kgs
of HCl added for brine pH control.
(2) Mother Liquor from the 2nd
crystallization.
ED Effluent: The
ED brine blow down stream contains the ash removed from the DPL along with
~1,500 kg/d of lactose and 1,250 kg/d of NPN that pass through the ED membranes
during demineralization. BOD (5 day) is
estimated at 2,500 kg/d. This effluent
stream, with its BOD and salt content, is the main drawback of the ED
process. However, it should be compared
to the larger effluent problem (in many situations) created by DPL itself.
In situations
where there are strict limits on BOD or PO4 discharge, an NF/RO system can be
supplied with the ED system. The NF system will
remove and concentrate ~90% of the BOD-creating organics (NPN, lactose,
organic acids) along with most of the Ca, Mg and PO4 present in the ED
effluent, producing a byproduct that can be sold as ingredient for animal
feeding. The RO system polishes the NF permeate, producing water that is
clean enough for recycle back to the ED system. The combined benefit of
the NF/RO system is to reduce BOD by at least 90%, effluent volume by ~75% and
make-up water requirement by ~75%.
In situations
where effluent volume or water supply are the main concern, the RO system alone
can recover ~70% of the water from ED effluent.
DPL#2
Disposal: The Mother Liquor (DPL#2) from the 2nd crystallization
step is fairly similar in composition to the original DPL feed, although lower
ash and higher protein:
Lactose = 61.6% of solids
Protein = 12.1%
Ash = 16.2%
Other = 10.1%
It should be
possible to dispose of DPL#2 in the same manner that DPL is currently handled.,
whether field spread, given away for animal feed and sent to WWPT. The DPL disposal problem is reduced to ~50%
of what it was (24,759 kg/d solids vs. 50,000 kg/d solids).
Additional
Lactose Recovery: 15,250 kg/d. This
is based on the assumption that 50% of the lactose contained in the ED product
can be recovered by a 2nd crystallization step.
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