Note: Descriptions are shown in the official language in which they were submitted.
~ go/l43l0 2 0 S 7 8 7 2 PCI/AV90/1)0213
,
EFFI,UENT TREATMENT
~:
This inventlon relates to a new ef~luent treatme~t
process. More specifically, the invention is concerned
with the separation of the organic material in aqueous
industrial effluents by flotation to leave a treated
liquid effluent, and a concentrated sludge COntaiRing ~he
unwanted contaminants.
Aqueous industrial effluents containing high ~,
concentrations o~ organlc compounds include sewage -.
effluents, paper and pulp mill effluents, leachates from
chemical waste land fills, wool scour effluents and
effluents from water clarifioation processes such as the
"Sirofloc" process whlch is described in Australian : :
Patent No. S12,553. The disposal of these e~fluents
usually involves direct discharge to a water course,
sewer or land. However, environmental considerations now
demand some form of additional treatment to remove the
poll~tants.
.
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WO90/14310 ~ 7 ~ 7 ~ PCT/AV90/00213
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,
The success of any effluent treatment process will
be based on concentration, that is, the extent ~o which
the contaminants are separated into a low volume phase
("sludge") thereby recovering as much of the water as
possible. The quality of`the recovered water should be
at least sufficient to recirculate this as feedwaterO
Disposal of the relatively small volume of sludge can
then be achieved more easily and cheaply.
A wide range of possible treatment methods are
conventionally considered. These include removal
techniques such as coagulation, precipitation, adsorpt.ion
and filtration, as well as destructive techniques such as
oxidation and biological processes. Commonly economic
evaluation of the most promising options determined ~hat
treatment with alum or ferric coagulants was likely to be
the cheapest method.
Foam separation techniques have been used for many
years to remove traces of heavy metal ions from
industrial effluents. Adsorbing colloid flotation has ~ow
been developed and involves the addition of a high
surface area solid onto which the heavy metal ions can
adsorb. The loaded substrate is then removed by addition
of a surfactant and the injection of a gas, usually air.
The substrate is usually aluminium or ferric hydroxid~
which is generated in-situ and the surfactant employed is
anionic. The technique has been applied to a wide range
of waters and wastewaters with a variety of metal ions.
The techniques of pressure flotation or dissolved
air flotation (DAF) is commonly used in water
purificatlon. The lack of industrial acceptance of this
technique is pro~ably due to economic factors related to
the high operating costs of the DAF plants. However, the
potential value of DAF for potable water treatment,
WO90/14310 2 0 ~ 7 ~ 7 2 PCT~AU~/00213
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particularly for raw waters with hi~h algal populations,
is now recognised and indications are that it is
competitive with conventional sedimentation processes.
For sewage effluents, the activated sludge process
is widely used to reduce biochemical oxygen demand (BOD),
but requires long residence times and large plants with
high capital and operating costs. Biological methods
such as the activated sludge process have long been
favoured over physico-chemical methods for economic
reasons. However, a variation of the "Sirofloc" process
for water clarification has been shown to satisfactorily
trea-t such effluents with the promise of smaller, cheaper
plants. This process which is described in Australian
Patent Specification No. 79700/87 uses magnetite to
rapidly clarify the sewage effluent with the production
of a sewage concentrate some 30 to 40 times more
concentrated than the original.
Despite interest in the use of flotation in the
treatment of sewage and sewage effluents, the technique
is primarily used in the thickening of excess activated
sludge as a means of assistin~ o~erloaded plants.
The use of metallurgical flotation techniques in the
recovery of wool grease from wool scour effluents has
also been described in L.F. Evans and W.E. Ewers,
Australian Journal of A~plied Science, Vol 4, 552-58
(1953)-
We have now found that the combination of a
coagulant and a mixture of a cationic polymer or
copolymer wlth an anionic surfactant, a non-ionic
surfactant or both can be used to concentrate and
separate the organic material present in effluents using
the technique of flotation. This process is economically
viable due to its fast rate of separation and small
, ~ ', ; '
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WO90/14310 2 ~ ~ 7 8 7 2 PCT/AU90/00213
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sludge volume, which reduces the capital, operating and
disposal costs.
According to the present invention there is provided
an effluent treatment process which comprises the steps
of:-
(a) adding a coagulant to the effluent to concentratethe organic material therein;
(b) treating the thus concentrated organic material with
a mixture of a cationic polymer or copolymer in the
presence of an anionic surfactant, a nonionic
surfactant or both; and
(c) separating the organic material from the effluent by
flotation.
Coagulants suitable for use in the process of the
invention are inorganic coagulants such as alum, lime
magnesium salts or ferric salts, for example, ferric
chloride.
Process conditions, such as pH may need to be
adjusted to allow for generation of the flocs. It will
be understood that the process conditions will vary with
the composition of the effluent treated. Optimum
conditions will therefore need to be determined by
experiment.
Some effluents which may be treated in accordance
with the process of this invention may already contain a
sufficient quantity of a surfactant (anionic andJor non
ionic~ to fulfil the requirements of the process.
Otherwise, the required surfactant may be added to the
effluent undergoing treatment.
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WO90~l4310 2 ~ ~ 7 ~ 7 ~ PCT/AU90/0021~ '
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In one embodiment of the present invention, a
mixt~re of a cakionic polymer or copolymer and an anionic
surfac-tant may be added to the effl~ent. The cationic
polymer or copolymer functions to reverse the charge on
the floc and thereby allow the anionic surfactant to
adsorb onto the floc in a suitable configuration for
subsequent flotation.
Suitable cationic polymers or copolymers include
Poly(diallyl dimethylammonium chloride) (eg. Catfloc T),
polyethyleneimine, polyvinylamine, acrylamide co~
polymers, acrylic copolymers containing quaternary
ammonium groups, poly(vinyl 4~alkylpyridinium) salts,
poly(methylene-N,N-dimethylpiperidinium) salts,
poly(vinylbenzyltrimethylammonium) salts, polyalkylene
polyamines, (eg. polyethyleneamine), poly~hydroxyalkylene
polyamines) and cationic starch.
Suitable anionic surfactants may be selected from
carboxylates, sulphonates, sulphates or phosphates. More
preferably, the anionic surfactants include
polyalkoxycarboxylates, N-acylsarcosinates (eg. Sandopan
MS-40 Registered Trademark), acylated protrein
hydrolysates ~eg. Maypon K), sulphonates (eg. Hostapur ;
SAS 60), alkylbenzenesulphonates-(eg. SDS),
alkylarylenesulphonates, lignosulphonates, naphthalene
sulphonates (eg. Aerosol OS), a-olefin sulphonates (ey.
Boioterg AS40), petroleum sulphonates,
Dialkylsulphosucciantes (eg. Aerosol OT1,
amidosulphonates (eg Igepon TC42), alkyl sulphates, (eg.
Avirol SG100), ethoxylated and sulphated alcohols,
ethoxylated and sulphated alkylphenols (eg. ICI Al~anate
3SL3 or 3SN5), sulphated acids, amides or esters (eg.
Trlton X-301), sulphated natural oils or fats, phosphate
ssters (eg. decyl phosphate). It will be appreciated
that the ultimate choice of surfactant will be a
compromise between efficiency (as determined by froth
concentration, volume, ease of collapsing), toxicity and
cost.
WO90/l4310 2 0 ~ 7 ~ 7 2 PCT/AU90/00213
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In a fu~ther embodiment of the present inventlon, a
nonionic surfactant may be employed toyether with or
instead of the anionic surfactant. Preferred nonionic
S surfactants include ethoxylates, such as octyl phenol
ethoxylates, fo~ example Teric X11 (Registered
Trademark), nonyl phenol ethoxylates, or example Teric
N20 (Registered Trademark), fatty alcohol ethoxylates,
for example Teric 12A9 (Registered Trademark) and fatty
amine ethoxylates, for example ~eric 18M2 (Registered
Trademark).
The term "flotation" as used herein refers to the
technique in which air is passed through the effluent
mixture and air bubbles become attached to surfactant -
treated, flocculated organic material which then rises to
the surface of the effluent water.
This technique results in rapid transport of the
flocs to the effluent surface as a froth which, af~er
collapsiny, can be easily filtered to yield a filtrate
with a small volume of sludge for disposal. In general,
greater than 90%-concentration-of organics can be
achieved after 10 minutes of flotation.
The ultimate fractions from the process of the
invention expressed as a percentage of the effluen~
volume are a clear product water 97~, froth filtrate 2 to
3% and sludge less than 1%.
The clear product water is suitable for discharge or
reuse. The small volume of sludge produced may be
disposed of by land fill. Some of the coagulant and
surfactant may be retrieved from the sludge for reuse.
Examples of the use of the process of the invention
are given in the descriptions which follow. It will be
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WO90/14310 2 ~ ~ 7 ~ 7 2 Pcr/Augo/oo2l3
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understood, however, that the invention is not limited by
these examples.
The following abbreviations are used:-
s
TOC - total organic carbon
PCU - platinum-cobalt unlts
NTU - nephelometric turbidity units
CTAB - cetyl trimethylammonium bromide
c - colour
t - time
HLB - hydrophilic - lipophilic balance
The regeneration effluents used in Examples l to 5
were obtained from the Bell Bay water treatment plant,
Tasmania. The chemicals added as coa~ulants were AR
grade alum and ferric chloride with the exception that in
some experiments, a commercial product "Ferriclear" from
Tioxide Limited was used as a source of ferric sulphate.
The surfactants and coagulants were all of commercial
origin and will be described further in the examples.
The flotation vessel was a Hallimond tube with a
cell volume of approximately lOO ml, fashioned from a
mercury filter of high porosity. The air was controlled
to a rate of 250 ~l/min. The froth was allowed to
overflow a lip in the cell and collected for analysis.
In Examples 5 and 8 the ~xperiments were scaled up using
a Denver flotation cell of the type used in mineral
beneficiation.
Example l
A volume of effluent was placed in the Hallimond
tube apparatus with air flow, followed by the addition of
a coagulant, pH adjustment and then the addition of a
cationic polymer or copolymer and a surfactant. The
.
wo go/l431n 2 0 ~ ~ ~ 7 ~ PCT/AU90/00213
- 8 f
duration of the experiment was one of the variables
examined but rarely exceeded ten minutes, by which time
either little froth remained or what froth remained was
white in colour (in the earlier s-tages the froth was
5 discoloured). The froth generated was collected, allowed
to collapse (over 30 minutes), filtered and the filtrate , !
analysed for colour, TOC, metal ion concentration and
volume.
10 Example 2 - Cationic polymers or copolymers and
anionic surfactants.
The tests were carried out using a Bell Bay (2)
effluent sample of the following composition:-
Colour = 1250 PCU
Ph = 11.3
TOC = 106.1 mg/l.
20 together with the anionic surfactant sodium dodecyl
sulphate (SDS). The results are shown in Table 1. ~
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TABLE 1
XPEAIMENTAI, CONDI~IO~S PRODUCI ~AT~R OU,P.LI~Y.
30 ~o. p~ Ir~ [æL~ [SDS] COLOUR
~mg/l) (mg/l) ~mg/l) ~PCU)
4.50100 0 20.0196
2 ~) 4 56100~ . 0 20 . 0173
2 ~c) 4 53 100 q . 5 20 . 0 1~
2 (d) ~.51 100 5.0 20.0 19
2 ~ . 5050 5 . 0 20 . O~.7
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WO90/14310 2 0 ~ ~ ~, 7 2 PCT/AU90/00213 ~ I
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Further tests under similar conditions were carried
out with more comprehensive analyses of both the product
water quality and the froth fraction. The results are
shown in Table 2.
Table 2 demonstrates that if sufficient cationic
polymer (Catfloc T) is added to reverse the charge then
an anionic surfactant at low concentration will suffice~
The process is still Ph sensitive but takes less than
three minutes and produces a much smaller volume of froth
which collapses immediately and can be rapidly filteredO
Calculations of mass balances show that the sludge
contains 80% of the colour, 25% of the TOC and 75% of the
iron which indicates that further improvements is
possible.
Example 3 - Cationic polymers or copolymers and
anionic surfactants.
In these tests the Bell Bay (2) effluent sample
described in Example 2 was used and the pH was kept
constant at appro~imately 4.5. The coagulant dose, the
type and dose of polymer or copolymer and the type and
dose of surfactant used were varied. The results are
shown in Table 3.
As a consequence of the results sho~n in Table 3,
the operating conditions were chosen to allow [Fe] = lOO
mg/l and [Catfloc T] = 5.0 mg/l. Higher coagulant doses
achieved greater clarification and froths of smaller
volume but at higher costs. The other cationic polymer
used was less effective, probably due to its
higher molecular weight. The anionic surfactant did not
function and too high a concentration of Catfloc T was
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WO90/14310 2 0 5 7 ~ 7 2 PCT/AU90/002t3
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also counterproductive with some flocs remaining in theproduct water unfloated.
Exam~le 4 - Flotation cell tests on a larger scale
:` "
More tests were carried out on a l litre scale using
the Denver flotation cell to treat a Bell Bay (3)
effluent of the following characteristics:
Colour = 940 PCU ~ :
TOC = 106.l mg/l
Turbidity = 28.5 NTU.
The flotation regimes of Examples 2 to 3 were used
i.e the cationic polymer Catfloc T and the anionic
surfac'cant SDS. The conditions for each test are shown
in Table 4 and the results are shown in Table 5.
In the final test of Table 4, a period of 30 minutes
was allowed between the addition of the coagulant and the
cationic polymer or copolymer.
From Table 5 it can be seen that the effect of
surfactant concentration (SDS) is readily apparent from
25 the trends in product water turbidity and froth volume. ;:
Excess SDS caused too much froth to be collected too
quickly, leaving many flocs and a lot of surfactant in
the cell. In contrast to the earlier tests
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WO 90/~14310 2 ~9 5 7 ~ 7 ~ P~/AU90/00213 .
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W~90/14310 ( ~ i
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only one tray was needed for froth collection emphasizing
that the foam does collapse more readily.
Again, the e~periment demonstrates that
extrapolation from the Hallimond tube tests to the larger
flotation cell is possible. Although the mechanical
parameters such as air flow rate, stirring speed and the
means of froth collection assume importance and have not
been optimized, the concentration factors are still
acceptable and the sludge volume and ease of handling
remain impressive.
Exam~le 5 - Use of other anionic surfactants
Flotation tests were carried out with anionic
surfactants other than SDS, under the conditions
described in Examples 3 and 4. The pH was maintained at
4.5, [Fe] at lO0 mg/l and a cationic polymer (Catfloc T)
dose of 5 mg/l. The range of surfactants was limited in
these tests to the following products of ICI Australia
Operations Pty. Ltd:-
Alkanate 3SL3, HLB = 38
Alkanate 3SN5, HLB = 38
Alkanate CS, HLB = ll, similar to SDS.
.
The HLB number refers to the ratio of hydrophilic to
lipophilic segments and could be used as a guide to
surfactant selection. The ultimate choice will be a
compromlse between efficiency (as determined by froth
concentration, volume and ease of collapsing), toxicity
and C05t. The results are shown in Table 6.
WO 90tl4310 2 ~ ~3 7 ~ ~ - 16 - PCI/AU90/00213 ~ I
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The more hydrophobic surfactants formed more froth,
and transferred the particulate material rom the product
water. At lower concentrations the froth volumes were
reduced but the product water was not as clear indicating
that further optimization is possible. The other more
hydrophilic surfactant behaved similarly to SDS,
requiring a dose of 20 mg/l to be effective.
ExamPle 6 - Paper and pulp mill effluent
In another series of experiments the effluent
treated was of colour 1490 PCV, turbidity 76 NTU and TOC,
241 mg/l. The inorganic coagulant used was ferric
chloride, the cationic polymer was a relatively low
molecular weight cationic polymer of the DADMAC type,
Catfloc T, and the anionic surfactant was Sodium Dodecyl
Sulphate ~S~S). The results are presented in Table 7
TABLE 7
~XPERI~ENTAL .PkODUCT W~TER
COH~TION5 WQLITY
H~E~e~ . tPE~ t5DS~COLOUR TUF~. tOC
~mg/l ) ~ ) (mq/l ) ` ~CU) ~N~U) ~9~1
.8300 ~ 80 3 ~7 2~
The results demonstrate the ability of the flotation
process to treat another paper and pulp mill effluent,
this time with a combination of a cationic polymer or
copolymer and an anionic surfactant.
ExamDle 7 - Paper and pulp mill effluent
Treatment of a different mill effluent with colour
294 PCU, turbidity 141 NTU and TOC 1395 mg/l, required a
: . :
WO90/14310 2 0 ~ 7 ~ 1 2 PCT/AU90/00~13
- 18 -
different set of experimental conditions using a lime
slurry at a high pH to concentrate the organics. The
data is shown in Table 8.
TA~LE 8
;~PE~ IMENTAL ~f~ODUCT WQTEfi
COI`ID I T ~ ONS OU~ I T`1
P~'~COAGlJ~NT ~ F~E ~ t S~S ] CO~OUF~ TUf:~ . TCI~
S~RR~ lmg/l ~ (m9~l ) (F~CU) (NTU~ tl )
~2 2 LI11E ~ 1CJC' 85 2~3
12 4 L~ 17~i
12.~ L1~E 20 7O~ 1~2 4a
The results demonstrate the versatility of the
process in coping wlth different effluents of vastly
different character, but also illustrate the need for
preliminary testing to determine the optimum mode or
operation. In all of the above experiments the froth
volumes were small and the amount of filtered residue
from the froth even smaller.
Exam~le 8 - Flotation of Paper Mill Effluents.
The method described in Example l was employed and
lOO ml of effluent was used in eac~ experiment. The pH
~5 was adjusted as required, and air was bubbled through the
liquid for lO minutes. Fe indicates that Ferriclear was
the coagulant and lime indicates the addition of a lime
slurry as coagulant. The cationic polymer used was LT31
and the surfactant was sodium dodecyl sulphate (SDS).
The results are shown in Table 9.
. : :
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WO 90/14310 ~ PCI'/AU90/00213
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Example 9 Flotation of WOG1 Scour Effluents
The method described in Example 1 was employed and
lOOml of effluent was used in each experiment. The pH
was ad~usted as required and air was bubbled through the
liquid for 10 minutes. Fe indicates Ferriclear was the
coagulant. The catlonic polymer was LT22. Wool scour
effluents contain signlficant quantities of anionic
surfactants of synthetic or natural origin so that
further addition of surfactant was unnecessary. The
results are shown in Table 10.
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WO90/l4310 2 0 ~ ~ 8 7 2 PCT/~U90/00~13
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Exam~le lO - Flotation of Cosmetic Manufacturing -
Effluents.
The method described in Example 1 was employed and
lOOml of effluent was used in each experiment. The pH
was ad;usted as required and air was bubbled through the
liquid for lO minutes. Fe indicates Ferriclear was the
coagulant and lime indicates the addition of a lime
slurry as coagulant. The cationic polymer used was
CATFLOC T and the surfactant was sodium dodecyl sulphate
SDS. The results are shown in Table 11.
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