Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 3~5~
In the treatment of sewage and other aqueous wastes,
(i.e. waste waters) generally two distinc-t areas of solid/
liquids separation are recognised.
The first of these concerns the removal of solid
constituents from the bulk liquid effluent with the ob~ect of -
producing a purified aqueous liquid effluent which may or may
not require further purification before dlscharge or re-use. ;~
Examples of this are primary or secondary sedimenta-tion
processes, filtration processes and flotation processes.
The solids removed in such processes usually are
associa-ted with an appreciable quantity of water but because of
their nature and consistency they are classified as sluclges.
The further dewatering of such sludges may also be by sedimen-
tation, filtration, flota-tion or centrifuga-tion but constitu-tes
a somewhat differen-t and often more difficult -teQhnology which
is commonly referred to as sludge dewatering.
Whilst it is true -to say that there are certain common
,
features between the two, for instance,in relation to the site
of operation, nevertheless in practice the overall technlques, ~ ;
handling methods, reagent dosages and reagent types are usually ~ `
quite different for the two areas.
There is often some confusion in the patent literature
concerning these two areas and accordingly it is to be stated
that the usage of the present invention is connected with
technology of the first area, i.e., bulk effluent treatment and
not at all with the second area i.e., sludge dewatering. This
will be readily apparent to those skilled in the art.
- 2 -
` ' '
~3t~511 . ~ ~
As a typical example of a conventional sewage treatment,
the raw sewage generally undergoes a preliminary treatment
for the removal of grit and coarse matter, followed by
primary sedimenta-tion, where finer solids are settled ou-t
by slow passage through large sedimentation tanks. This
primary treatment may be followed by a secondary stage where ~;-
~urther purification of the sewage is carried out biologically.
As the biological stage creates more insoluble solids, a
secondary sedimentation step follows. The sludges ~rom each
sedimentation step are then combined and de-watered while
the effluent from the Pinal sedimentation step is discharged.
The presence of phosphorus in sewage e~fluents has been
recognised as promoting the growth of algae and aquatic
plants in receiving waters by providing a source of nutrition.
Excessive plant growth can cause clogging of water courses,
and the growth and subsequent death of algae can be responsible
for the eutrophication of lakes and other receiving waters.
Wh~rea~ it is recognised that oth~r elements, such as
carbon and nitrogen, contribute towards the nu-tritive value
o~ effluents, recent attention has focussed mainly on the
remo~al of phosphorus as being -the simplest contributing
element to remove.
Phosphorus can be found in sewage in a number of forms,
for instance as both soluble and insoluble phosphates or
complex phosphates. Thus a typical raw sewage enterlng a
sewage treatment works migh-t contain two thirds of the i~
- 3 -
:; , . - : ,. , ~ : : . : i -
,,. , .,. , ~ ~ .................. .,. , : -
.. . . . . .
phosphorus as soluble orth ~Q ~ ~ and polyphosphates and
one third as insoluble phosphat~ Further, because part
of the insoluble phosph~e~ may be present in a colloidally
dispersed form) not all of the insoluble phospha~ can be
removed from the sewage by a sedimentatio~ process.
The objec-t of the presen-t invention is to provide ways
of reducing conveniently and satisfactori:Ly the phospha-te
content of bulk effluent aqueous wastes. The invention is
o~ particular value when utilised to reduce the phosphate
content of the effluent from a sewage bulk effluent process,
but is also applicable to the -treatment of a~y bulk effluent
aqueous waste containing soluble phosphate, for example
a chemical waste.
It is known to remove soluble phosphates from sewage
by chemical treatment that causes precipitation o~ -the
dissolved colloidal phosphates, followed by removal of the
precipitated phosphates generally by settlement. Inorga~ic
coagulants suitable for this purpose include certain soluble -~
: ~.
salts containing multivalent cations, such as aluminium
sulphate, ferrous sulphate, ferric sulphate, ferric chloride,
sodium aluminate and calcium hydroxide, the use of which
result in the phosphates becoming precipitated as the ~ `
corresponding insoluble me-tal phosphates.
Unfortunately the settlement is much too slow and
ineffective to be accomplished satisfactorily in a normal
sewage sedimentation stage and it is already known to
improve the settlement by adding polyelectrolyte flocculants.
- 4 -
:- :
~ .
: .
;,, . ;. : . . . . ... .. .; ,.. ,.,. , ;.. ; ;,
Thus U.S. Patent ~,506,570 teaches the use of
trivalent aluminium ions and anionic polyelectrolyte
flocculants, being high molecular weigh copolymers of
from 80 to 50 weight percent acrylamide or methacrylamide
and from about 20 to 50 weight percent acrylic or
methacrylic acid or water-soluble salts thereof.
Likewise, U.S. Patent 3,617,569 discloses that
the separation of precipitated metal phosphates is facilitated
by the use of a water-soluble organic polyelectrolyte
flocculating agent such as a partially hydrolysed poly-
acrylamide. The use is described7 in U.S. Patent 3,171,802,
of metal salts and anionic or nonionic polyelectrolyte
flocculants followed by filtration -through coal, sand and
activated carbon, for sewage -treatment. U.S. Patent
3,655,552 teaches the removal of phosph~s by the synergistic
admixture of a water-soluble, high molecular weight nonionic
polymer, preferably polyacrylamide, and a water-soluble salt
containing ferric ions, preferably ferric chloride. Also,
U-50 Patent, 3,607,738 describes thë use of lime and ca-tionic
polyamines for phosphate removal during tertiary treatment
of sewage, and U.S. Patent 3,453,207 describes the use of
alum and a homogeneous latex emulsion comprising water,
polybutadiene and a cationic emulsifying agent. ~ ~
' ~ :
- 5 - ~` ~
. ..
.
10385 3L~L
Also of course it is well known to use a variety of
flocculants~ either by themselves or in combination with
other materials, to promote de-watering o~ sewage sludge.
For example one such process is described in U.S0 Patent
No. 3,472,767 in which specified cationic copolymers are
added to sewage sludge in the presence of polyvalent
metal ions to facilitate de-watering of the sludge. This
however,is not relevant to the problem of reducing the
phosphate content of the effluent from a sewage sedimentation
process.
A disadvantage of the processes described abo~e for the
reduction of phosphate in bulk e~fluent is that all the
described processes tend to be rather slow. For example
UOS. Specification No. 3,506,570 suggests that a time of at
least two minutes and preferably five minutes should elapse
between the addition of coagulent and flocculant while
U.S. Patent No. 3,453,207 suggests periods of five -to thirty ~ '~
minutes with agitation as being required. It would be i~
desirable to be able to obtain good results by-adding the
flocculant much more quickly after the coagulant and quickly
thereafter passing the mixture to the sedimentation stage. -;
Thus in many sewage works now there is a relatively high
speed of flow such that the time be-tween the raw sewage
entering the works and reaching the primary sedimentation
tank may be less than five minutes. Similarly after
biological treatment of the effluent from the first step
insufficient time may be available before the secondary
sedimentation step to allow adequate precipitation by
known processes. ~;`
.
- - 5a -
~ 385~
According to our invention we remove phosphate from an
aaueous waste bulk effluent con-taining phosphate by precipitating
soluble and colloidal phosphates in the medium by adding -to the
, .
medium an inorganic coagulant, and therea~ter we add to the
medium certain wa-ter soluble high molecular weight cationic
polyelectrolyte ~locculants, and then we subject the waste to
a liquids-solids separation process.
The high molecular weight cationic polyelectrolyte
flocculants used in the invention are water soluble salts or
quaternary ammonium salts of copolymers containing (a) units of
alkylaminoalkyl esters of methacrylic or, pre~erably, acrylic
acid and (b) acrylamide units. ~;
The addition of the cationic polyelectrolyte appears to
result in assisting and accelerating flocculation and
sedimentation of the precipitated phosphates. Whatever the
mechanism, by the invention it is possible to achieve
phosphate removal ~rom sewage very quickly and to a greater
degree than by previous methods. The method has the advantage
that a wide variety of metal salts can be used ~or precip-
itation o~ the phosphorus compound and it generally requires
no elaborate agitation means. This method usually also
results in good reductions in other pollution parame-ters,
such as suspended solids content and Biochemical Oxygen
Demand and generally can be applied at any par-t of a sewage
puri~ication process immediately prior to a sedimentation `
stage
As the inorganic coagulant, metal salts such as those
mentioned above can be used. In general the salt is a water
soluble compound, usually an acid salt, containing a multivalent ` `
metal cation and in particular is usually one of the
- 6 -
. ..... . ~.. " .. .-. .- - . ~ : .
. r~
~.Q385~
compo~mds that is of-ten used in was-te water treatment,
examples being compounds of A13 , Fe2~, Fe3 and Ca~
e.g. aluminium sulphate, sodium aluminate, ferrous
sulphate, ferric sulpha-te, ferric chloride and calcium
hydroxide. ` ;~
Preferred copolymers contain the following groups~
(a) R3 (b)
,, : ~ .
-CH2- R and -CH2-~H~
¦ R4 ~
00- ~ NH2
2 ;~
in which Rl and R2 may be the same or different and are
hydrogen or alkyl or, together with the nitrogen a-tom to
which they are attached, form a heterocyclic ring, R4 is
alkylene containing 1 to 8, usually 2 to 4, carbon atoms
and R is methyl or, preferably, hydrogen. If Rl and R2
form a heterocyclic radical they preferably represent an
alkylene chain of 4 to ~ carbon atoms. Alkyl groups
represented by Rl and R2 usually contain no more than 8
carbon atoms, preferably 1 to 4 carbon atoms, preferably
methyl or ethyl. R4 preferably contains 2 carbon atoms
(e-thylene).
Salts can be formed with an acid capable of forming
salts with the amino groups present in the copolymers, ~ ~-
2~ for example hydrogen bromide and hydrogen chloride.
- 7 -
Preferred copolymers are quaternary ammonium salts, and
especially such salts where Rl and R2 contain 1 or 2
carbon atoms each. Preferred quaternising reagents are
those that introduce the alkyl group, for example Cl 4
alkyl (especially methyl or e-thyl), onto the nitrogen
atom. Thus typical quaternising reagents are dimethyl
sulphate and methyl chloride.
The preferred copolymers have R4 represen-ting C2H4,
Rl and R2 being the same of different and representing
methyl or ethyl and which are quaternised with dimethyl
sulphate.
The copolymers must contain from 80 to 97 mole per
cent (b), (i.e. a molar ratio of (a) : (b) of approximately
of l:L~ to 1:33) and -the most preferred copolymers generally
contain from 85 to 97 mole per cent, especially 85 to 93
mole per cent, b (i.e. molar ratios of approximately 1:6 to
1:33 or 1:6 to 1:12). All mole percentages are based on a
- plus b.
Generally the copolymer consists solely of the two
specified types of groups bu-t of course smaller amounts
of other vinyl groups may be included in the copolymers.
As these other vinyl groups, there may be used any vinyl
monomers that can copolymerise with the other vinyl monomers-
that are specified and that do not interfere deleteriously
with the properties of the copolymer. Such vinyl monomers
may be selected from all the conventional vinyl monomers.
The amount is usually below 20 mole per
-- 8 --
:: . .. . :: ~ : . : : :: : .: ..................... -
: ," ' ' ~ , ' ' . ' .. .. ,~ : , . ,~ ;' . ' ; . .
`~
~ (~3~
cent preferably below lO mole per cent.
We prefer to specify the molecular weight o~ the
polyelec-troly-tes we use in this in~ention in terms o~
the viscosity of their solutions. The polymers are
pre~erably such that at 25C the viscosity in centipoise
of their aqueous solutions a-t pH 6.0~ containing 1% by
weight of -the polymer, and in the absence of added salts,
using a Brookfield Model RVT viscometer with spindle
No. 3 and at 20 rpm is greater than 2000. A ~iscosity
greater than 3000 is especially pre~erred.
Suitable copolymers are well known and are commercially
available. They can be made in~any convenient manner, for
example by well known vinyl type polymerisation methods
including, ~or example, free radical initia-ted solution
polymerisation.
The aqueous medium -to which the additions are made
may be, ~or example, a chemical e~luent but pre~erably ~ -
it is raw sewage or the e~luent from a primary or
secondary sedimentation stage. The sludge resulting ~rom
the process when the aqueous medium is raw sewage or a
sedimentation e~luent may be subjected to de-watering by
any suitable method.
The process is conveniently carried out by adding the
metal salt or other inorganic coagulant in an amount such
that the metal cation : phosphate molar ratio is at least
1:1, preferably about 2:1. Naturally it is necessary that
the metal cation becomes mixed rapidly through the aqueous
medium but this is conveniently achieved by adding the
metal cation to a ~lowing stream of the medium. The pH of
- _ 9 _
. .. .. ,, ~.. .. . . - ..
:, . . ., , .... . , .: , - . .
.: . ~, , . :. . . . , :......... ... . . , , . . . .,~ ,
1C~38Sl~
the stream is preferably such as to promote precipi-tation
of insoluble phosphate. It is important that the
polyelectrolyte is added a~-ter -the coagulant but it is
desirable that it should not be added too long after the
coagulant. Thus pre~erably it is added within five
minutes of adding the coagulan-t and generally wi-thin two
minutes. Mos-t preferably it is added less than a minute
after adding the coagulant~ There must be a de~inite -time
interval between adding the coagulant and the flocculan-t,
for example, at least five and preferably at least ten
seconds. A preferred interval is a quarter of a minute -to
one minute. Naturally it is necessary that the flocculant
shall mix rapidly through the aqueous medium: conveniently
this is achieved by adding it to a flowing stream of the
medium. The amount of polyelectroly-te added is generally
from 0.1 to 2 or perhaps 3 mg/l, preferably about 0.5 -to 1 mg/l. `
It is generally introduced in the form of a dilute a~ueous
solution having a concen-tra-tion of from 0.01 to 0.05 per
cent by weight. `
The invention is illustrated by the following examplesD ~
E~{amPle 1 ':
~,
To 200 ml aliquots of a raw sewage, obtained before
primary sedimentation, aluminium sulphate was added in various
amounts as a 5% weight by volume solution of A12(S04)3. 16H20,
with stirring at 160 rpm.
After 30 seconds, various polyelectrolyte flocculants
were added at a doseo`f 1 mg/l, with further stirring at
160 rpm for 30 seconds, folIowed by stirring at 40 rpm for
1 minute and stirring at 5 rpm for 3 minutes~
- 10 -
. . . .
. . . . ... . . ... . .. . . . , . . ~ - - . . ' .
' ` "' ' ' ', ` .' ` '. ' '', ` '` ' ` ' ' ' ' ' ' ', ~ ` ' ' ' , . ` ' '` ` '' '. ` ' .
i' ' ~ '.'. ' ' ., . . ' ' .' . ' ' , " .. . . , . ' ' ,~
The polyelectrolytes added were~
1. An anionic polyelec-trolyte, being a copolymer : ;
of about 60% by weight acrylamide and about 40/0 by
weight sodium acrylate, that iSJ about 66 mole percen-t
acrylamide and about 54 mole percent sodium acrylate.
2. An anionic polyelectroly-te as No. 1, but with
about 10% sodium acrylate, -that is, about 92 mole percent
acrylamide iand about 8 mole percent sodium acrylate.
-- 11 --
10385~
3. A cationic polyelectroly-te, being a copolymer
of about 90% by weight acrylamide and about 10% by weight
of dimethyl sulphate quaternised diethylamino ethyl acrylate,
that is about 97 mole percent acrylamide and about 3 mole
percent quaternised diethylaminoethylacrylate.
4. A cationic polyelectrolyte as Nro. 3, but wi-th
about 70% acrylamide 9 that is, about 90 mole percent
acrylamide and about 10 mole percent quaternised diethyl~
aminoethylacrylate.
5. A nonionic polyelectrolyte, being a homopolymer
of acrylamide.
Polyelectrolytes Nos. 3 and 4 had viscosities as
previously described o~ 2140 cp and 3370 cp respectively.
Analyses were made to determine the total phosphorus
contents of the superna~nk liquors produced after treatment
of the sewage with aluminium sulphate and the above polymers,
resulting in the following data. Results are given as mg/l
phosphorus and the initial total phosphorus content of the ~;
sewage was 14 mg/l. Aluminium sulphate doses are given as
mg/l A12(S0~)3 16H20. ~;
:
'
- 12 - ~
: '
.
Supernatant total phosphorus content (mg/l) ~or
aluminium sulphate doses of
Polymer
_ _ ~ . ~
lO0 mg/l 200 mg/l 300 mg/l 400 mg/l ~
. . .. _ .~
None 9.8 7.6 5.9 2.2
No. l 7.2 4.5 203 l.l
No. 2 7.5 4.9 2.6 1.3 ~ ;
No. 3 6.0 2.4 0.6 0.5 ;
No. 4 5.2 2.0 0.4 0.3
No. 5 9.8 7.2 4.9 _
,
The results show that whileincrea9ed phosphate removal
results ~rom the use of the anionic polyelec-trolytes compared
with the aluminium sulphate alone, much better resul-ts are
possible with the cationic polymers, particularly No. 4. The
nonionic polyelectrolyte, No. 5, gave almost no improvement
over aluminium sulphate alone.
Similarly, good results can also be obtained i~ other
quatenary or other salts of polymer 4 are used or i~ polymers
similar to poly~er 4 are used but in which either or both R
and R2 are replaced by methyl.
Example II ~;
A similar series o~ tests was carried out with a sample of
sewage obtained just before secondary settlement, that is, a~ter
the raw sewage had undergone primary sedimentation and biological
puri~ication in bacteria filters, but before settlement for
removal of solids produced by the biological purification.
- 13 -
1038Sll
A 10% slurry of calcium hydroxide was added at :;~
various doses ~or the precipitation o~ the phosphates and
the polyelectrolytes of Example 1 were added at a dose of
1 mg/l. ~ :
The total phosphorus content of the sample was
ini-tially 7.4 mg/l and the ~ollowing results were obtained. ~-
..... ~ ~
Supernatan-t to-tal phosphorus content (mg/l) :~:
Polymer ~or calcium hydroxide dose of
,,_ , . _ ._ .... .. . _
. 100 mg/l 200 mg/l300 mg/l :
._ .~ ~ I ' ' ~:
None 5 5 1.8 0.4
No. 1 4.1 0.9 0.3
No. 2 3.6 0~8 0.3
No. 3 2.4 0.6 0~1
No. 4 1.9 0.3 0.07
_ _ __ _~ 4-6 _ _ _ -1`
As with Example 1, -the results show that, whlle the
nonionic polymer, No. 5, gives only slight improvement and
the anionic polymers Nos. 1 and 2 give fairly good improvements ;~
in phosphate removal, very superior results are obtained with
the cationic polymers, Nos. 3 and 4, again particularly No. 4.
: - 14 ~
' ~
,. :
' ' .
ExamPle III ~03~
This example illus-trates processes in which the coagulant
and flocculant are added to the effluent going to a tertiary
sedimentation process involving settlement or fil-tration. ~
Such processes are desirable where it is necessary to remove ~ `
residual suspended solid in the effluent from a secondary ~;~
sedimentation stage or where it is considered advan-tageous to
remove nutrients after the conventional sedimentation process
is complete.
For this example, a series of jar tests was carried out
by the procedure described above for Examples I and II on
effluent following a secondary sedimentation process.
Aluminium sulphate was added a-t two doses for the
precipitation of the phosphate a~d the polyelectrolytes of
Example I were added subsequently a-t 0.5 mg/1. ,
l . . . - ' -----'I : ~' '
Supernatant total phosphorous
content (mg/1) for Aluminium Sulphate
Polymer Dosage ¦~
. - .. _._ ..... ._., I ;
120 mg/l 150 mg/l
_ -
None 1.02 0.61
No. 1 0.64 0.55
No~ 2 0.64 0.54 ;~
No. 3 0.52 0.35
No. 4 0.40 0.20
No. 5 0.71 ~ O.70
~' , -
-- - 15 - ~
~0~51~
These results show that while all polyelectrolyte
treatments give better results than aluminium sulphate ~ ~
alone the best results are obtained in accor~ance with ~ :
the invention, using copolymers 3 and 4, especially 4.
~:,
` .~ '
:
- 16 - ;
Exam~le IV ~0
A series of tests was carried out by a similar
procedure to tha-t of Examples I and II, to investigate
the e~fect of varying the time between acldi-tion of the
metal salt and addi-tion of the polyelectrolyte, which we
call the intervening mixing time. A sample of raw sewage
was used, with a total phosphorus content of 12.0 mg/l.
The metal sal-ts used was aluminium sulphate, and a constant ;
amount of 150 mg/l A12(S04)3. 16H20 was added in each
case~
The polyelectrolyte flocculants, No. 1 and No. 4 ;~
from Example I were added at a dose of 0.5 mg/l, producing ~;~
the following results. ,
__ . ................................. ~ _ _ ~.,,
Supernatant phosphorus con-tent
Intervening Mixing Time (minutes) (mg/l)
, ~ -~ , _ ,, :
Flocculant Flocculant `
No.l No.4 ~;~
. ~ . . .
0 10.4 6.
0.25 9.0 0.43 ;
0.5 4.1 0.43
1 0.96 0.45
2 0.74
3 0.75
4 0.83 0059
1.0 0.73 ; ~
~ ' . :, . . .. ~.:,. 'i:,,. ,,':
- 17 ~
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. . - . . . . . . . ~ . .. , . . . ;~ .,. ,,; " . , .,. - ,. . .
:,. . . "~ .,: , : .. -, ., ......... , . ! :: , ., :: . ` . ` 1 :
' '' :' ' , :' ': . , ' ~ . : ' ' . ' ' ' '. ' ' ' : : ;'
' i .. ' ' ' ' " ' ' ' ~`' ', .. ' ' : ' ` ~ , . , .. . ,~ .
.. . . .
L038S~3L
The resul-ts illustrate an important bene~it of our
invention, namely that a very short intervening mixing time,
o~ten a minute or even half a minute or lesæ, is su~ficient
and that in fact the degree of suspended solids increases
if mixing is conducted for as long as has often been
necessary in the past.
This benefit means that the process of our inven-tion
can be readily applied to existing sewage works where longer
intervening mixing times are not possible without substantial
alterations involving high capital outlay. Such a situation
would occur where phosphate removal was -to be carried out
be~ore the primary sedimentation stage and, due to the speed
of flow of the sewage, only a short time would elapse between
entry of the raw sewage to the works and its entry to the
primary sedimentation tanks. Also, where a new works is
planned to incorporate phosphate removal by chemical treatment,
this ~eature o~ our invention means that extra land need not
be taken up in order to ensure long periods o~ ~low of sewage
between addition of metal salt and polyelectrolyte.
ExamPle V
The data presented in this example are obtained from
results on the plant scale at a sewage treatment works. At
this works, the raw sewage stream is divided into -two parts
which then pass separately through dif~erent primary
sedimentation tanks.
,~
:
- 18 - ~ ~
,
'
.. .. . . ... . .. . . . .
,.,: ; :, : , . .... . .: . . . .. . . .
, , ,. ... ... " . , . . . :- .. ..
A trial was carried ou-t to assess the process of our
invention by trea-tin~ one part of the flow and making a
comparison with the other~ untrea-ted part.
To one part of the ~low, ferric sulphate was added
as a 62.5% weight by volume solution7 foLlowed by addition
of a high molecular weight cationic polyelectrolyte of type
No. ~ of the previous examples. The time taken for the
sewage to flow between the two addition points was
approximately 20 seconds. Mixing of the chemicals with the
sewage was simply effected by placing a wooden baffle across
the channel at each addition point to provide the necessary
turbulence. ~ ;
: ~ :
Samples were taken of the sewage at various s-tages and ` ;
-the total phosphorous content was measured. In -the table ;
below Sample A denotes raw sewage en-tering the plant. Sample B
denotes the sewage effluent leaving the sedimenta-tion tanks when
no coagulant or flocculant is added. Sample C denotes -the
sewage effluent leaving the sedimentation tanks when ferric
sulphate and polyelectrolyte were added to the sewage leading ;
to the sedimen-tation tanks in the manner described abo~e.
Addition o~ ferric sulphate and polyelec-troiyte was~;
carried out only during the period of maximum flow, which was
for about 8 hours per day, but analyses were made on composite -~
samples obtained over 24 hour periods. As these composite
samples will therefore con-~ain some sewage which had not been
chemically treated and as the performance of -the sedimentation
tanks is subject to adverse effects from the build-up of
sludge, a further series of samples was taken. These samples,
D, were obtained from the chemically treated sewage before
-~ - 19-
... : ,~- ... ~ . ,. . , , : , ....................... . : .- , . .:: .
,. ; , . ....... , - -. - , . . . .
:. - ::: . . , . . .. . . . : -
entry to the sedimentation tanks to assess the performance
of the invention under optimum condi-tions. The samples
were allowed to settle for 5 minu-tes, and analysis was
made o~ the total phosphorus conten-t o~ the supernatan-t
liquid.
The average results and the range of results obtained
over a period of 6 months are shown below.
A~erage ferric sulpha-te dose = 23~ mg/l Fe2 (S04)3. -~
Average polyelectrolyte dose = 0.5-mg/1.
. ,, _ . , _ _ ., ~
Average Average
Total Phosphorus
10Sample PhosphorusRange Removal Range
content
(mg/l) (mg/l) (%) (%)
A 5.2 3.7 - 7.9 , _ _
B 3.8 2.5 - 5.1 29.8 17.2 - 51.5
C 0.57 o.oL~_ 2.0 90.0 72.1 - 99.0
¦ D ¦ 0 09 ¦ ~ 00- I 26 L 99 ~ 9Y~9 ¦
,
Comparison of the results o~ samples B and C illustrates
the e~fectiveness of the process o~ our invention on a plant ;`
scale. Although -the composite samples C contain some sewage to
which the chemical additions had not been made, a high average
removal o~ phosphates resulted. The results of samples D show
that, under optimum conditions, virtually complete removal of `; ~
~ phosphates is possible. - -
.
Further analysis of the above samples showed that compared
with the untreatad part o~ the sewage after sedimentation,
- 20 -
... .. , ., ~ . , ., , , ~ . " . . . . . . . .. . . .. . . .. .... .
r. . . . .. . .. ... . ... .. .. . ,
, ' ' ' - ' '.. ~ ' . , ' i :. ~" ' :
., , ' . . .' ' , ' ' ': ' :
~, , : . ` ~ ' ;;'' . ' '`' ' : ` :
` ` . .: ~ : ::: : . ' ' ` i" ' " ' ' ' ' '
~38511 ~` :
i.e. samples B, the treated par-t of -the sewa~e a~ter ~;
sedimentation, samples C, had a suspended solids content lower
by 66% and a Biochemical Oxygen Demand lower by 55%. :
: ' ' ~' '
. ~
: ' ~ ''`, ~`
:' :
, . '~ ` ~~ :~
:
. ~
: ':
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21
: : :
