Note: Descriptions are shown in the official language in which they were submitted.
~ D~
The present invention relates to a process for removing
fatty substances or degradation products thereof or proteinaceous
substances or degradation products thereof from aqueous effluents
containing these materials and is particularly concerned with an
improvement in or modification of the process described and claimed
in our co-pending Canadian application No. 192,265 filed February
8th, 1974.
Our co-pending application No. 192,265 describes and
claims a method for recovering a stabilised fatty substance or
10 degradation product thereof or a proteinaceous substance or
degradation product thereof from effluent containing said sub-
tances or degradation products thereof wherein acid hydrolysing
metal salt is added to the effluent in an amount sufficient to
` comple~ the substances or degradation products thereof, mineral
acid being added at the same time or after said addition, if
necessary, to reduce the pH to 5 or below, the resulting complex
precipitated by raising the pH to 6 or more by addition of a base
and by addition of alkaline earth-metal ions.
The method of our àpplication NoO 192,265 produces a
stabilised fatty substance or degradation product thereof in the
form of an aqueous sludge. These aqueous sludges have a high
water content and consequently are of relatively large volume and
from the practical point of view, it is desirable to reduce the
volume of this fatty sludge by dehydration. The fatty sludge
contains, in addition to water, the chemicals that are used in
the precipitation process which produces the fatty sludge and it
is also desirable, from the practical point of view, to be able
to recover these precipitation chemicals from the sludge for
further use. We have now discovered how it is possible to
dehydrate -this fatty sludge easily and ~uickly to produce a con
centrated sludge of smaller volume and also, if desired, to recover
from this concentrated sludge the precipitation chemicals so that
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~r~ 3~3
they can be reused.
The present invention provides a method for dehydrating
a stabilised fatty sludge, obtained by adding an acid hydrolysing
metal salt to an aqueous effluent containing fatty substances or
degradation products thereo in an amount sufficient to complex
the fatty substances or degradation products thereof, mineral
acid being added at the same time or after said addition, if
necessary, to reduce the pH to 5 or below, and precipitating the
resulting complex as a stabilised fatty sludge by raising the pH
to 6 or more by addition oE a base and by the addition of alkaline
earth-metal ions, wherein the separated stabilised fatty sludge is
acidified preferably to a pH below 2 so that the acidified sludge
separates into an upper concentrated fatty sludge phase and a
lower aqueous phaseO
The acidification of the stabilised aqueous fatty sludge
may be brought about by addition of a mineral acid. One particu-
larly suitable mineral acid is the so-called "soap stock" which
is the highly acidic effluent obtained from the decomposition of
soap in the fat refining industry. Another mineral acid which can
be used with advantage is hydrochloric acid as when this acid is
used, the problem of calcium sulphate precipitation is avoided.
Phase separation occurs when the stabilised aqueous
fatty slud~e is acidified in accordance with the present invention.
The upper concentrated fatty sludge phase may then be separated
from the lower aqueous phase and it has been found, in accordance
with a further feature oE the invention, that if this concentrated
fatty sludge phase is heated, for example to its boiling point,
-urther phase separation occurs and an upper phase, containing
technical fatty acid, separates from a lower aqueous phase which
contains the precipitation chemicals that are used to precipitate
the original stabilised aqueous fatty sludge. Separation of these
two phases means that the precipitation chemicals can be recovered
~.a~
in a form in which they can be reutilised for the precipitation
of the -fatty materials in an a.queous effluentO
The following examples are given to illustrate the
invention:
EXAMPLE I
The sludge used was sludge from pilot plant experiments
for the stabilisation and recovery of fats and fatty substances
from process water in a combined fat refining~margarine factory
using FeC13, CaC12, and Ca(0~)2 as precipitating chemicals.
The following experiments were then carried out on the
precipitated sludge:
1.1 150 ml sludge was heated on a hotplate almost to
boiling point. This resulted only in slight non-
homogeneity in the sludge, which disappeared upon
stirring.
1 2 Concentrated sulphuric acial was added to 150 ml sludge
dropwise while stirring unt;il rapid separation into
two phases occurredO This was after the addition of
2 5 ml concentrated sulphuric acid when the pH was 1 D 5.
The $1Oating, concentrated sludge phase, which was
~o porous, was easily removed with a spoon and was col-
lected as a specimen marked "sludge conc D 1 D 2"; the
hydrous phase was fil~bered and collected as a specimen
marked "hydrous phase 1.2".
1.3 3 ml concentrated sulphuric acid was added to 150 ml
sludge dropwise while stirring. Rapid separation
into two phases occurred when the pH reached 1=2 D
The iloating concentrated sludge phase appeared more
compact and had a volume of only 25 ml. The hydrous
phase was slightly cloudy~ The whole mixture was
heated, whereupon the layer of sludge that had formed
turned darker and contracted to a volume of about
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3;~
10 ml. Large, light gypsum flocks formed in the
hydrous phase and sank to the bottom.
Upon boiling, the ~atty acid separated from the
sludge phase as dark drops on the surface, while
the separated hydrous phase was turned yellow by
the iron (III) ions. The fatty acid drops collected
into a coherent layer and were collected as a specimen
marked "fatty acid 1.3".
1.4 7 ml concentrated nitric acid was added to 150 ml
sludge. This avoids precipitation of gypsumO When
the pH dropped below 2, a spongy and coherent con-
centrated sludge phase separated and floated up to
the sur-faceO A specimen was taken from the concen-
trated sludge phase and marked "sludge conc. 1.4".
1.5 3 ml concentrated sulphuric acid was added quickly
to 150 ml sludge while sti]rring well. A coherent
sludge of 20 ml volume which floated well separated
rapidly when the pH dropped below 2. A specimen of
the concentrated sludge was taken and marked as
` 20 "sludge conc~ 1~5"o
The various specimens were analysed for their fat content
and the analysis results, volume of the sample and brief reference
to its method of preparation are set out belowO
33
RBSULTS, EXAMPLE I
Test Specimen Treatment Volume Fat % of
ml Content Total
grams Fat
_ .. ... .
1.1 Sludge None 150 1.~03100.0
1.2 Concentrated sludge H2S04
2.5 ml52 1,7469609
Hydrous phase H2S04
2.5 ml98 0.0482.7
_
1.3 Concentrated sludge 3.0 ml25
Hydrous phase H2S04
300 ml125 001075.9
Fatty acid Brief
_ Boil 12 1.68393.3
1.4 Concentrated sludge HN03
. 7.0 ml30 1.70294.4
1.5 Concentrated sludge H2S04 _
_ 3.0 ml 20 1~72395.7
The hydrous phases from tests 1.2 and 1.3 were dif~erent
to one another, as hydrous phase 1.3, which was removed after the
deacidised sludge specimen had been boiled, had a strong yellow
colour. When both specimens were neutralised by NH3~ sedimentation
from specimen 1.3 was heavy and brownish in colour, while sedimen-
tation from specimen 1.2 was sparse and almost white.
Rhodanide reaction of the dissolved sediments clearlyidentified a high Fe content in hydrous phase 1.3, while hydrous
phase 1.2 contained only an insignificant amount of Fe.
These results made it clear that it is possible to recover
the precipitation agent by heating the sludge which separates into
the free fatty acid which ~loats up and the precipitation agent
(cation) used remains in the lower hydrous phase.
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EXAMPLE II
The sludge used was a fatty sludge obtained by ~lotation
and recovered from process water from a margarine factory by
sedimentation and stabilisation using A12(SO4)3, CaC12, and NaOH
in accordance with the procedure claimed in application No.
Hydrochloric acid was added to the fatty sludge until
its pH was 1.6, when the sludge split into two phases, an upper
concentrated sludge phase and a lower aqueous phase. Fat analyses
of the two phases were carried out and the volume of the phases
was measured, the results are set out below.
ANALYSES
- Specimen Treatment Fat Volume
Content in ml
grams
. . .
Sludge None 2.648 250
Concentrated sludge Acid 2.622 14
Hydrous phase Acid 0.023 236
_
Sludge None 2.701 250
Concentrated sludge Acid 2,625 13
20 Hydrous phase ~cid 0.076 237
I
As the analyses show, only a very small portion of the
~` fat passes into the hydrous phase (about 100 - 300 ppm) and at
the same time a good concentration o~ the fatty sludge is ob-
tained i.e. from about 1000 ml to about 56 ml.
EXAMPLE III
-
The sludge used was a fatty sludge obtained by flotation
and recovered from condensate effluents as they occur from the
production of meat/bone meal (sterilising, boiling, drying) by
sedimentation and stabilisation using FeC13, H2SO4, and Ca(OH)2.
The sludge was acidified to pH 1.8 with hydrochloric
acid, and two phases separated, an upper concentrated sludge phase
and a lower aqueous phase. The concentrated sludge phase was
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, , ,, , . .... ~ .. . ..... .....
removed by skimming and was treated further by boiling for 10
minutes, During the boiling, dark drops of liquid fatty acid
separated and collected as a separate liquid phase. This liquid
fatty a~id phase was separated in a separating funnel and its
fat content determined. The following results were obtained
which show that substantially all of the fat in the original
250 ml sample is transferred to the 8 ml fatty acid phase.
ANALYSES
Specimen Treatment Fat Volume
Content in ml
grams
Sludge None 2,693 250
Concentrated sludge HCl to pH 1,8 _ 18
P'atty acid phase 2.532 _
I
,, . . .,, . ~ . . , , . ., , . " . ... ., ~ .. . .. .
