WO1994002418A1

WO1994002418A1 - A method of and an apparatus for purifying aqueous suspensions containing organic material and cations

Info

Publication number: WO1994002418A1
Application number: PCT/DK1993/000245
Authority: WO
Inventors: Jens Sønderberg FREDERIKSEN; Karsten Stig Henriksen
Original assignee: Flocco-Tec Aps
Priority date: 1992-07-22
Filing date: 1993-07-22
Publication date: 1994-02-03
Also published as: DK94292D0; AU4559493A

Abstract

Waste water containing suspended organic material is separated into a thick slurry phase and an aqueous phase by a method wherein coarse solid matter is removed in a first treatment step. The resulting primary aqueous phase is discharged as aqueous phase with a high content of contaminants, when desired, or passed to a second treatment step where it is mixed with an aqueous suspension of one or more flocculating smectitic clays, and flocculated and sedimented into a thick slurry phase, which is withdrawn as a product, and a secondary aqueous phase, which is discharged as aqueous phase with a moderate content of contaminants, when desired, or passed to a third treatment step where it is subjected to ion exchange with a cation exchanger and discharged as aqueous phase with a low content of contaminants.

Description

A method of and an apparatus for purifying aqueous suspensions containing organic material and cations

The present invention relates to a method of and an appa- ratus for purifying aqueous suspensions containing organic material and cations, e.g. ammonium ions, wherein the aqueous suspension of organic material is separated into a thick slurry phase with high dry matter content and an aqueous phase with a desired - high, moderate or low - content of contaminants.

The disposal of waste water, in particular aqueous sus¬ pensions containing organic material and cations, e.g. ammonium ions, constitutes a considerable problem.

In the present context "organic waste water" is defined as aqueous suspensions containing organic material and ca¬ tions, e.g. ammonium ions; and "content of contaminants" is defined as the total content of organic and inorganic contaminants in the form of suspended solids or contaminating cations.

Organic waste water is traditionally disposed of by dis¬ charge to artificial or natural recipients, e.g. municipal sewage systems, rivers and watercourses or fields.

Discharge of untreated organic waste water to natural re¬ cipients may lead to serious environmental problems. Direct discharge to municipal sewage systems is also pro- blematic because the untreated waste water may exhibit high BOD and COD values and a high ammonium content, which causes an undesired loading on the biological purification plants attached to the municipal sewage systems. In order to maintain acceptable operating conditions in such sys- terns it is highly desirable to operate with a biologically optimized C/N-ratio in the waste water to be treated.

A characteristic feature of the above-mentioned recipients consists in that the recipients can accept varying levels of impurities at different times. The acceptable level for aqueous phases irrigated over fields or discharged to na¬ tural recipients such as e.g. watercourses does thus vary with a periodicity of one year. The corresponding period for municipal sewage systems may typically be 24 h.

A variety of methods of treating waste waters is known by which the suspended organic nitrogen containing material is concentrated to a product which is suitable as nutrient for plants or animals.

Thus, DE OS 21 61 131 describes a method of purifying and clarifying waste water involving treatment thereof with a precipitation agent e.g. Ca(OH).-,, Al„( SO. )„, FeCl-, or bentonite, whereafter the precipitated material is sepa- rated from the aqueous phase which is subsequently treated first with a cation exchanger and then with an anion ex¬ changer. The precipitated material may be used as a plant nutrient.

Danish patent application no. 0773/75 describes a method for treating waste water. According to this specification a flocculating agent is added to the waste water contain¬ ing proteins, the flocculated material is collected and the essentially clear liquid is brought into contact with an ion exchanger material based upon regenerated cellu¬ lose, which is able to adsorb the remaining protein from the clear liquid.

DK patent application No. 7149/88 describes a method of treating liquid manure, which comprises clarification by flocculation and subsequent ion exchange. By this method liquid manure is first subjected to a mechanical separa¬ tion step, whereafter the mechanically separated liquid manure is mixed with an aqueous suspension of one or more flocculating clay minerals, e.g. bentonite, which has been activated by aging during a standing period of at least about 48 hours, the resulting mixture subsequently being introduced into a sedimentation tank for flocculation and sedimentation, whereafter clarified liquid and flocculated slurry are taken out separately from the sedimentation tank. The clarified liquid is then mixed with one or more ion exchange minerals, the resulting mixture subsequently being introduced into a sedimentation tank from which ion exchanged liquid and a slurry of spent ion exchanger are taken out separately. These slurries may be used as plant nutrients.

International patent application PCT/DK92/00020 (with priority from 23 January 1991) describes a method of se¬ parating liquid manure into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - N-content. This method is charac¬ terized in that liquid manure is subjected to sedimenta¬ tion in a sedimentation tank in a first treatment step with formation of a thick slurry phase having high dry matter content containing the coarse solid matter compo¬ nents of the liquid manure and a primary aqueous phase freed of the coarse solid matter content of the liquid manure, the latter phase after filtration being discharged as aqueous phase with high N-content, when this is de- sired, or, if not, passed to a second treatment step where the primary aqueous phase is mixed with an aqueous solu¬ tion or suspension of a flocculant, preferably with an aqueous suspension of one or more flocculating smectitic clays in a mixing ratio of 0.3-10, preferably 1-3 kg smectite/t liquid phase, whereafter the mixture is sub¬ jected to flocculation and sedimentation with formation of a secondary thick slurry phase with high dry matter con¬ tent containing sedimented flocculated material which is returned to the first treatment step and united with the thick slurry phase formed therein, and a secondary aqueous phase freed of the suspended solid matter content in the primary aqueous phase, the said secondary phase being dis¬ charged as aqueous phase with moderate N-content, when this is desired, or - if it is desired to take out an aqueous phase with low N-content - passed to a third treatment step where the secondary aqueous phase is sub¬ jected to ion exchange with a cation exchanger, preferably an inorganic cation exchanger, in particular selected from clays and/or zeolites with a high specific ion exchange capacity for ammonium, whereafter the thus treated secon- dary aqueous phase is discharged as aqueous phase with low N-content, and that the thick slurry phase is discharged from the sedimentation tank as thick slurry phase with high dry matter content. The thick slurry phase is suited for use as a plant nutrient.

As mentioned above the acceptable level of impurities in a discharged waste water is often a function of time for a given recipient. However, the composition of the waste water itself does also often vary as a function of time, typically with a period of 24 h due to the change of work¬ ing routines in the factories, etc. which are sources of the waste water.

It is desired to provide a method of treating organic waste water by which the following is achieved:

reduction of storage capacity for the waste water to be treated; simple, efficient, flexible and economic purification allowing adaptation to the above-mentioned time varia¬ tions, in particular providing a process securing a cation level, e.g. an ammonium level, in the treated water below a desired level; reduction of supended solids in the treated water to a desired level; improved exploitation of the content of nutrients; reduction of environmental problems, most importantly reduced N-pollution and reduced odour nuisances; and provision of control of the C/N-ratio for water dis¬ charged to artificial or natural recipients.

It is further desired to provide a method of treating organic waste water which results in

an aqueous phase having properties ( low content of nutrients and suspended solids ) allowing it to be distributed directly to recipients at any time without restrictions;

and further in

a phase in the form of thick slurry with high dry matter content, which may be used as a nutrient for plants or animals, as starting material for biogas production or other (aerobic or anerobic) fer enta- tion processes or incinerated or deposited, e.g. as land fill.

It is the object of the present invention to provide such a method of and an apparatus for purifying organic waste water which meet the above demands.

According to the invention the object is achieved by a method of purifying aqueous suspensions containing organic material and cations, e.g. ammonium ions, wherein the aqueous suspension of organic material is separated into a thick slurry phase with high dry matter content and an aqueous phase with a desired - high, moderate or low - content of contaminants, which is characterized in that coarse solid material is removed from the aqueous suspen¬ sion of organic material in a first treatment step with formation of a primary aqueous phase freed of the coarse solid matter content of the aqueous suspension of organic material which is discharged as aqueous phase with a high content of contaminants, when this is desired, or, if not, passed to a second treatment step where the primary aqueous phase is mixed with an aqueous suspension of one or more flocculating s ectitic clays in a mixing ratio of 0.3-10, preferably 1-3 kg smectite/t liquid phase, which has been activated by aging, preferably during a standing period of 24-48 hours, whereafter the mixture is subjected to flocculation and sedimentation with formation of a thick slurry phase with high dry matter content containing sedimented flocculated material which is wihdrawn as a product, and a secondary aqueous phase freed of the sus¬ pended solid matter content in the primary aqueous phase, the said secondary phase being discharged as aqueous phase with a moderate content of contaminants, when this is de¬ sired, or - if" it is desired to take out an aqueous phase with a low content of contaminants - passed to a third treatment step where the secondary aqueous phase is sub- jected to ion exchange with a cation exchanger, preferably an inorganic cation exchanger, in particular selected from clays and/or zeolites exhibiting a high reaction velocity for the reaction with contaminating cations, e.g. ammonium, whereafter the thus treated secondary aqueous phase is discharged as aqueous phase with a low content of contaminants.

When carrying out the method according to the invention it is possible to remove a liquid phase which can be recycled or discharged directly to farm land or other recipients without risk of contamination, its BOD, COD, C/N-ratio value and its content of suspended solids and contaminating cations, e.g. ammonium, always being ad¬ justable to a desired, safe value, without performing more process steps than strictly necessary.

Hereby a particularly economic and environmentally accept¬ able treatment method is provided by which both initial and operational costs are kept at a minimum.

Due to the presence of the smectitic clay used as floccu¬ lating and precipitating agent, the thick slurry phase exhibits excellent properties as nutrient for plants or animals and during incineration and fermentation pro¬ cesses.

The present method is suited for purification of organic waste water including:

waste water from:

dairies, e.g. obtained by manufacturing of milk, cheese, and butter;

breweries, malting and fermentation;

manufacturing must and fruit juice;

canneries;

- marmalade and jam factories;

fermentation plants;

textile industry; sugar factories;

slaughterhouses;

fish industry;

abatoires;

oil mills;

food industry, including manufacture of deep-frozen products, e.g. animal and vegetable products; and

liquid manure, comprising excrements, urine and clean- ing from animal husbandry (including pigs, cows, horses and sheep) and poultry; and

purification of waste water in municipal sewage plants, in particular purification of "reject water", i.e. water (having a high content of NH. ions) removed from sludge withdrawn from anaerobic fermentation tanks.

According to a special embodiment the second treatment step is repeated at least once. The repetition of the second treatment step may be performed either before or after the third treatment step.

According to another preferred embodiment the third treatment step is repeated at least once.

As well the second as the third treatment step may be per¬ formed continuously or batch-wise.

The cation loaded ion exchanger may be discharged from the third treatment step and either stored as a separate pro¬ duct or united with the discharged thick slurry phase. The loaded ion exchanger may also be discharged from the third treatment step and regenerated with an aqueous so¬ lution of a regeneration agent, e.g. in the form of an aqueous solution of a calcium salt, such as CaCl,-,, providing a fresh regenerated cation exchanger and an aqueous cation containing eluate, which may be discharged as a separate product united with the discharged thick slurry phase.

The regeneration of the ion exchanger may also be per¬ formed "in situ", i.e. without transfer of the ion ex¬ changer to a separate regeneration unit.

In this case the introduction of the secondary aqueous phase is cut off when about 2/3 of the capacity of the ion exchanger has been utilized and an aqueous solution of a regeneration agent, e.g. an aqueous solution of a calcium salt, such as CaCl„, is introduced continuously in an amount corresponding to at least about 2/3 of the capacity of the ion exchanger. Thereafter the introduction of the secondary aqueous phase is immediately resumed.

The introduced solution of the regeneration agent will move through a fixed ion exchange bed as a plug having a front end and a rear end. The arrival of the front end and rear end, respectively, at the exit end of the ion ex¬ change unit is detected by a monitor, e.g. a conductivity sensor, controlling a valve at the exit end of the ion exchange unit having two positions, a first position corresponding to withdrawal of aqueous phase with a low content of contaminating cations, and a second position corresponding to separate withdrawal of exhausted regeneration liquid.

According to a third preferred embodiment the cation ex¬ changer is added and discharged continuously in the third treatment step in counter-current to the secondary aqueous phase, and the cation regeneration step is also carried out continously and in counter-current.

According to a preferred embodiment the concentration of the aqueous suspension of smectitic clay is 1-40, prefer¬ ably 5-15 weight-%, in particular about 10 weight-%.

It is important that the aqueous suspension of smectitic clay is activated by aging, typically aged for up to 3 days, before use. The aging process of the clay suspension may be performed batch-wise or preferably continuously in an aging tank with a mean retention time, typically from 24 to 48 hours. By using a continuously aged clay suspen- sion increased sedimentation velocity, increased concen¬ tration of solid material in the precipitated thick slurry at any given time, and reduced clay consumption is obtained compared to the process using a clay suspension aged batch-wise for about 3 days. Aging by batch-wise or continuous operation can be further improved by inter¬ mittent stirring in a period of about 10 min. at intervals of about 2 h, whereby a particularly stable, aged suspen¬ sion can be obtained at a solids content of approx. 10 weight-%.

The invention also relates to an apparatus for purifying aqueous suspensions containing organic material and ca¬ tions, e.g. ammonium ions, wherein the aqueous suspensions of organic material is separated into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - content of contaminants, which is characterized in that it comprises

a separation unit (3) having an inlet for aqueous sus- pensions of organic material (2), an outlet for coarse solid material ( 4 ) and an outlet ( 5 ) for a primary aqueous phase, which via a change-over valve (6) is connected with an outlet ( 7 ) for aqueous phase with high content og contaminants and a transfer pipe (11' ) communicating with an inlet pipe ( 14 ) of a flocculation and sedimentation unit (15);

a tank (13) for an aqueous suspension of flocculating agent, which via a pipe (12) and the inlet pipe (14) is connected with the flocculation and sedimentation unit (15) having an outlet (16) for thick slurry phase, and an outlet (17) for secondary aqueous phase, which via a change-over valve ( 8 ) communicates with an outlet ( 9 ) for aqueous phase with a moderate content of contaminants and a transfer pipe ( 18 ) being connected with a liquid inlet in an ion exchanger unit (19) having an outlet for treated liquid phase being an outlet ( 21 ) for an aqueous phase with a low content of contaminants and optionally an inlet ( 20 ) for fresh ion exchanger and an outlet for spent ion exchanger ( 22 ) .

The flocculation and sedimentation unit (15) may be shaped as a tank, a channel or in other known manner.

The ion exchanger unit (19) may be shaped as a tank, a fixed bed column or in other known manner.

An apparatus according to the invention suited for conti¬ nuous operation of the second treatment step further com¬ prises a buffer tank for primary aqueous phase arranged between the outlet for filtered liquid and the inlet pipe of the flocculation and sedimentation unit and a mixing unit arranged between the. transfer pipes and said inlet pipe.

An apparatus according to the invention suited for batch- wise operation of the second treatment step further com- prises a buffer tank for the secondary aqueous phase arranged between the outlet for secondary aqueous phase and the transfer pipe connected with the liquid inlet in the ion exchanger unit.

In the following the invention is described in more detail by way of examples, reference being made to the drawing, wherein

Fig. 1 shows a continuously operating plant for carrying out the present method;

Fig. 2 shows a corresponding plant in which the floccu¬ lation and sedimentation step is performed batch- wise;

Figs. 3 and 4 show diagrams illustrating the efficiency index defined below for the second treatment step; and

Fig. 5 shows a batch-wise operating pilot plant for carrying out the present method.

Fig. 1 shows a continuously operating plant for carrying out the present method comprising a separation unit 3 having an inlet for organic waste water 2 coming from a source 1, an outlet for coarse solid material 4 and an outlet 5 for aqueous phase, which outlet is connected with a buffer tank 10 with an outlet 11 which via a change- over valve 6 is connected with an outlet 7 for aqueous phase with a high content of contaminants, e.g. a high N- content, and a transfer pipe 11' being connected with a mixing unit 115.

The apparatus further comprises a tank 13 for an aqueous suspension of flocculating smectite containing clay which via pipes 12 and 12' communicates with the mixing unit 115 and which via pipes 12 and 12' ' communicates with a second mixing unit 115'.

The mixing unit 115 is via a pipe 14 connected with a flocculation and sedimentation tank 15 having an outlet 16 for thick slurry phase.

Further, the tank 15 has an outlet 17 for liquid phase which is connected with the mixing unit 115' which via a pipe 14 ' is connected with a second flocculation and sedimentation tank 15' having an outlet 16' for thick slurry phase, which is connected with the pipe 16.

The tank 15' is further provided with an outlet for liquid phase 17' which via a change-over valve 8 is connected with an outlet 9 for aqueous phase with a moderate content of contaminants, e.g. a moderate N-content, and a transfer pipe 18, which is connected with a liquid inlet in an ion exchanger tank 19 having an inlet 20 for fresh ion exchanger, an outlet 22 for spent ion exchanger and an outlet 21 for treated liquid phase for taking out an aqueous phase with a low content of contaminants, e.g. a low N-content.

The apparatus furthermore comprises a tank 23 for regene¬ ration of spent ion exchanger being introduced via the pipe 22. The apparatus also comprises a tank 29 for aqueous regeneration liquid which is connected with the tank 23 via a pipe 24. The tank has further outlets 26 and 27 for regenerated ion exchanger and a concentrated aqueous salt solution containing the contaminating cations, e.g. ammonium, respectively.

Fig. 2 shows a plant for carrying out the present method in which the flocculation and sedimentation step is per- formed batch-wise. This plant comprises a separating unit 3 having an inlet for organic waste water 2 coming from a source 1, an outlet for coarse solid material 4 and an outlet 5 for aqueous phase, which outlet via a change-over valve 6 is connected to an outlet 7 for aqueous phase with a high content of contaminants, e.g. a high N-content, and a transfer pipe 11 being connected with a combined mixing and sedimentation tank 15.

The apparatus further comprises a tank 13 for an aqueous suspension of flocculating smectite containing clay mine¬ ral which via pipes 12, 12' and 14 communicates with the combined mixing and sedimentation tank 15 and which via pipes 12, 12' ' and 14' communicates with a second combined mixing and sedimentation tank 15'.

The tank 15 has an outlet 16 for thick slurry phase.

Further, the tank 15 has an outlet 17 for liquid phase which is connected with the pipe 14' which is connected with a second flocculation and sedimentation tank 15' having an outlet 16' for thick slurry phase, which is connected with the pipe 16.

The tank 15' is further provided with an outlet 17' for liquid phase which via a change-over valve 8 is connected with an outlet 9 for aqueous phase with a moderate content of contaminants, e.g a moderate N-content, and a transfer pipe 30, which is connected to a buffer tank 31 with an outlet 32 which via a transfer pipe 18, which is connected with a liquid inlet in an ion exchanger tank 19 having an inlet 20 for fresh ion exchanger, an outlet 22 for spent ion exchanger and an outlet 21 for treated liquid phase for taking out an aqueous phase with a low content of contaminants, e.g. a low N-content. The apparatus shown furthermore comprises a tank 23 for regeneration of spent ion exchanger being introduced via the pipe 22. The apparatus comprises also a tank 29 for aqueous regeneration liquid which is connected with the tank 23 via a pipe 24. The tank has further outlets 26 and 27 for regenerated ion exchanger and a concentrated aqueous salt solution containing the contaminating cations, e.g. ammonium, respectively.

In operation of the plant shown in fig. 1 the coarse solid material is removed from the organic waste water in the separation unit 3, and the resulting primary aqueous phase is transferred into the buffer tank 10. This liquid is easily pumpable and may be irrigated using standard agricultural irrigation equipment or transferred to a biological purification plant when such irrigation or transfer is acceptable. In such case the liquid is with¬ drawn via the outlet 7 for aqueous phase with a high con¬ tent of contaminants, e.g. a high N-content. This aqueous phase is a colloidal solution of organic material in an aqueous solution of organic and inorganic salts, including salts of ammonia and other contaminating cations.

In periods where this liquid is not an acceptable effluent the liquid is subjected to further treatment. First, a flocculant is added and it has been found that the smectitic clay type bentonite is not only suited but also the best out of a number of substances investigated. The bentonite is added as an aqueous suspension of bentonite (activated by aging in about 48 h) having a bentonite concentration about 10 weight-%. The amount of added bentonite is about 0.2 weight-%, corresponding to about 2 kg bentonite per 1 t of liquid phase per treatment. By this process colloidal particles and clay particles gather in lumps (flocks) and sink to the bottom in the sedimenta¬ tion and flocculation tanks 15 and 15'. These lumps will only sink very slowly, as the sedimentation velocity is approx. 1 cm per min. Therefore, the liquid phase admixed with bentonite must be passed to the tanks 15 and 15' at a velocity which ensures that the upward movement in the tanks is less than 1 cm per min. If the velocity is higher the flocculated material will be entrained in the upwardly moving flow and discharged via the outlet pipes 17 and 17'. By these two treatments with bentonite, the second treatment being performed essentially for security reasons and in order to absorb peak loads, it is possible to remove the organic dry matter from the liquid. This ends the ammonium production, but there are still ammonium and inorganic salts dissolved in the liquid referred to above as the secondary aqueous phase.

In periods when this liquid is acceptable as effluent the liquid is withdrawn via the outlet 9 for aqueous phase with a moderate content of contaminants, e.g. a moderate N-content.

In case the secondary aqueous phase is not acceptable the liquid is subjected to further treatment in the next step in which the contaminating cations, e.g. ammonium, are removed by ion exchange, preferably exchanged with calcium ions.

The ion exchanger is regenerated continuously, preferably with calcium chloride or another water soluble calcium salt, and is reused. Hereby the cations, e.g. ammonium, are liberated in a concentrated form as compared with the form it previously had in the organic waste water and withdrawn as the above-mentioned concentrated aqueous salt solution.

In operation of the plant shown in fig. 2 the liquid phase is filtered batch-wise in the separation unit 3 and transferred directly to the sedimentation and flocculation tank 15 with addition of about 0.2 weight-% bentonite as an aqueous bentonite suspension corresponding to that mentioned above. The two suspensions may be homogenized in the tank 15 for a few minutes, e.g. by repu ping, and then flocculation and sedimentation are allowed to take place.

Then the thick slurry of flocculated precipitated solid material is discharged via the outlet 16, and the aqueous phase is transferred to the second flocculation and sedi¬ mentation tank 15' with addition of a corresponding amount of aqueous bentonite slurry. The flocculation and sedimen¬ tation process in the tank 15' is carried out as described above for the process in the tank 15.

The thick slurry precipitated in the sedimentation tank 15' is discharged via outlets 16' and 16 and the aqueous phase is transferred to the buffer tank 31 which func¬ tions as a reservoir for aqueous phase which may be sub- jected to continuous ion exchange as described above.

Fig. 5 shows a pilot plant for carrying out the present method in which the flocculation and sedimentation step is performed batch-wise. This plant comprises a pipe Pi 9 having an inlet for primary aqueous phase coming from a not shown apparatus wherein the solid coarse matter has been removed. Close to the inlet end the pipe Pi 9 has a valve V 9, the other end of the pipe Pi 9 is via pump Pu 1 connected to an inlet of a valve V 10 with an outlet which is connected to a first end of a pipe Pi 20 having a valve V 20 arranged close to a second (outlet ) end of the pipe Pi 20.

The apparatus further comprises a storage tank Tl for primary aqueous phase connected to the pipe Pi 9 via a pipe Pi 1 provided with a valve

V 1 and connected to the pipe Pi 20 via a pipe Pi 14 provided with a valve V 14;

two flocculation and sedimentation tanks T 2 and T 3 each connected to the pipe Pi 9 via two pipes Pi 2, Pi 3 and Pi 4, Pi 5, respectively, said pipes Pi 2 - Pi 5 being provided with valves V 2 - V 5, respectively, the tanks T 2 and T 3 are connected to the pipe Pi 20 via pipes Pi 15 and Pi 16, respectively, said pipes being provided with valves V 15 and V 16, respectively;

two storage tanks T 4 and T 5 for the sludge precipi- tated in the tanks T 2 and T 3 connected to the pipe Pi 9 via pipes Pi 6 and Pi 7 provided with valves V 6 and

V 7, respectively, and connected to the pipe Pi 20 via pipes Pi 17 and Pi 18 provided with valves V 17 and V 18;

a storage tank T 6 for the secondary aqueous phase connected to the pipe Pi 9 via a pipe Pi 8 provided with a valve V 8 and connected to the pipe Pi 20 via a pipe Pi 19 provided with a valve V 19;

a tank T 7 for an aqueous suspension of flocculating smectite containing clay provided with a stirrer and having an exit pipe Pi 0 which via a pump Pu 3 is con¬ nected to a mixing circuit wherein the primary aqueous phase may be mixed with the above-mentioned aqueous suspension.

The mixing circuit comprises a pipe Pi 11. The first end of this pipe is connected to the pipe Pi 9 downstream the pump Pu 1 and the other end of the pipe Pi 11 is connected to an inlet of a pump Pu 4. The pipe Pi 11 is provided with a valve V 11 arranged close to its first end and connected to the exit end of the pipe Pi 0 downstream the valve V 11. The exit of the pump Pu 4 is connected to the pipe Pi 20 via a pipe Pi 12 which is provided with a valve V 12.

The mixing circuit further comprises a recirculation loop comprising a pipe Pi 13 provided with a valve V 13. The first end of the pipe Pi 13 is connected to the pipe Pi 12 and the second end is connected to the pipe Pi 11.

The apparatus further comprises an ion exchanger subunit comprising

- an ion exchanger unit I 1, a tank T 8 for aqueous re¬ generation liquid, a tank T 9 for ion exchanged secon¬ dary aqeuous phase, and a tank T 10 for eluate from the ion exchanger unit I 1;

- a pipe Pi 21 provided with a valve V 21 having a first end connected to the pipe Pi 8 between the valve V 8 and the tank T 6 and a second end connected to the first end of two pipes Pi 23 and Pi 25 provided with valves V 23 and V 25, respectively;

the pipe Pi 21 is further provided with a pump Pu 2 arranged between the valve V 21 and the second end of the pipe Pi 21;

- the second end of the pipes Pi 23 and Pi 25 are con¬ nected to the ion exchanger unit I 1 via pipes Pi 29 and Pi 30, respectively, and to inlets o.f the tanks T 10 and T 9 via pipes Pi 24 and Pi 26 provided with valves V 24 and V 26, respectively; the tanks T 9 and T 10 have outlets connected to pipes Pi 27 and Pi 28 provided with valves V 27 and V 28, respectively; and

a pipe Pi 22 provided with a valve V 22 having a first end connected to an exit of the tank T 8 and a second end connected to the pipe Pi 21 between the valve V 21 and the pump Pu 2.

In operation of the pilot plant shown in fig. 5 the coarse solid material, i.e. the material having a particle size greater than about 1 mm, is removed from the organic waste water in an apparatus (not shown), e.g. a wire mesh, a centrifuge, a cyclone, or a similar apparatus, and the resulting primary aqueous phase is discharged via pipes Pi 9 and Pi 20 if such discharge is acceptable. If not, the primary aqueous phase is transferred into the storage tank T 1.

An aged aqueous suspension of flocculating smectitic clays is prepared in the tank T 7. Thereafter, the primary aqeous phase is discharged from the tank T 1 via the pipes Pi 1 and Pi 9 and continuously mixed with the aqueous suspension of smectitic clays in the mixing circuit. The mixture is withdrawn from the mixing circuit via the valve V 12 and via the pipe Pi 20 transferred into the tank T 2. When the material transferred into the tank T 2 has floc¬ culated and sedimentated the resulting secondary aqueous phase is removed via the pipe Pi 2. If it is desirable to subject this liquid to a second flocculation and sedimen¬ tation the liquid is mixed with the aqueous suspension of smectitic clays in the mixing circuit as described above and transferred into the tank T 3.

The aqueous phase withdrawn from the tank T 2 via the pipe Pi 2 or from the tank T 3 via the pipe Pi 4 is discharged via the pipes Pi 9 and Pi 20 if such discharge is accept¬ able. If not, the aqueous phase is transferred into the tank T 6 via the pipes Pi 9 and Pi 20.

Thereafter the secondary aqeuous phase contained in the tank T 6 is subjected to ion exchange in the ion exchanger unit I 1. The tranfer of the liquid is performed via the pipes Pi 21, Pi 23 and Pi 29. The ion exchanged liquid is withdrawn from the ion exchanger unit I 1 via the pipes Pi 30 and Pi 26 and transferred to the tank T 9 from which it may be withdrawn via the pipe Pi 27.

When necessary the ion exchanger is recuperated by intro¬ duction of the aqueous regeneration liquid which is trans- ferred from the tank T 8 via the pipes Pi 22, Pi 25 and Pi 30. The eluate from this treatment is transferred into the tank T 10 via the pipes Pi 29 and Pi 24.

The thick slurry phase precipitated in the tanks T 2 (and 3) is transferred to the tanks T 4 (and T 5) via the pipes Pi 3 (and Pi 4) , Pi 9, Pi 20 and Pi 17 (and Pi 18).

The following examples illustrate the functioning of the present invention.

Test Procedure 1 (second treatment step)

An aqueous suspension containing 10% by weight GEKO ben¬ tonite, i.e. calcium bentonite ion exchanged with sodium carbonate, was activated batch-wise during an aging period of 48 hours.

Organic waste water from a slaughterhouse and from fish industry was subjected to flocculation with the above- mentioned aqueous clay suspension. The addition of clay was 1, 2 and 4 g solid clay material per litre waste water .

Samples were collected after 0.5, 1, 2 and 24 hours and analyzed.

The analysis comprised measurement of:

volume of sedimented material; residual solid material after evaporation (at about 105 °C) (RM) of the liquid phase and of the sedimented phase; organic residual matter ( ORG RM) determined as the weight loss after ignition to about 600 °C of RM;

BOD (biological oxygen demand) of liquid phase; - COD (chemical oxygen demand) of liquid phase;

NH.-N in liquid phase and in the sedimented phase;

N0--N in liquid phase;

N total in liquid phase and in the sedimented phase;

Preac. (reactive P) in liquid phase and in the sedi- mented phase;

P total in liquid phase and in the sedimented phase;

K in liquid phase and in the sedimented phase;

Cl in liquid phase; and

Fe in liquid phase.

EXAMPLE 1 : Waste water from a slaughterhouse

The results are displayed in Table 1:

* Oxygen totally reacted ** No clay added TABLE 1

Comments

1

2

25 The content of K, Fe and Cl was not reduced in the aqueous phase.

% volume of purified liquid calculated on volume of treated liquid.

Efficiency index of the tests are shown in Fig. 3.

For waste water from a slaughterhouse it appears from Fig. 3 that the purification increases steadily as a function of the treatment time. Addition of 2 o/oo bentonite seems to be better than addition of 1 and 4 o/oo. The optimal treatment will probably be 2 x 2 o/oo bentonite.

Conclusion of the laboratory test ( slaughterhouse waste water)

According to the test it can be concluded that it is pos¬ sible to flocculate and precipitate organic solid matter from slaughterhouse waste water with bentonite.

Waste water containing blood (pale pink color) gets clear after one single treatment with 2 o/oo bentonite.

The BOD and COD values are reduced very significantly by the flocculation, while phosphor and total nitrogen are reduced significantly. The content of these compounds are connected to the organic particles and colloids which are removed by the flocculation.

EXAMPLE 2: Waste water from fish industry

The results are displayed in Table 2:

* Comparison sample not completely clear ** No clay added TABLE 2

Comments

1

2

25 The content of K in the aqueous phase was not reduced.

For waste water from a slaughterhouse it appears from Fig. 4 that the purification increases steadily as a function of the treatment time. Addition of 4 o/oo bentonite seems to be better than addition of 1 and 2 o/oo. The optimal treatment will probably be 2 x 2 o/oo bentonite.

The waste water does not get completely transparent after treatment with 2 o/oo bentonite, but it is possible to see through a 50 mm glass tube filled with the treated water. After treatment with 4 o/oo the aqueous phase is totally transparent.

According to the test it can be concluded that it is pos¬ sible to flocculate and precipitate organic solid matter from fish industry waste water with bentonite.

Test Procedure 2 (comprising first, second and third treatment step)

I the apparatus shown in fig. 5 an aqueous suspension containing 10% by weight LECA L5 bentonite, i.e. a natural calcium bentonite, was activated batch-wise in the tank T 7 during an aging period of 48 hours.

Data for LECA L5 are given in the following table:

LOI at 1000 °C 8-9% pH 9.3-9.8 Expansion index 48 h 10-20 ml

Sedimentation index 72 h 20-30 ml

Plasticity index 300-400%

Methyl blue index 45-55 ml/g

Smectite content about 80% Chem. Analysis

Organic waste water from a slaughterhouse, from a fish industry and from a municipal sewage plant (reject water) was subjected to the first treatment step, and the result¬ ing primary aqueous phases were subjected to flocculation and sedimentation ( repeated once) and subsequently to ion exchange as described above.

Samples were collected and analysed.

The analysis comprised measurement of:

volume of sedimented material; residual dry matter from liquid phase, determined by evaporation at about 105 °C; suspended solid material (SS) in liquid phase;

COD (chemical oxygen demand) of liquid phase; pH of treated liquids; total N in liquid phase;

NH. :N in liquid phase and in the sedimented phase;

NO- in liquid phase;

K in the liquid phase; and total P in liquid phase. EXAMPLE 3: Waste water from a slaughterhouse

The results are displayed in Tables 3 and 4 for two types of waste water from a slaughterhouse.

Comments

The COD values were reduced significantly, even before the ion exchange step. The content of total N, NH. :N, N0„, K and P was also reduced significantly.

EXAMPLE 4: Waste water from fish industry

The results are displayed in Tables 5 and 6 for a waste water from fish industry operating with a 2 o/oo and a 3 o/oo aqueous bentonite suspension, respectively.

Comments

It appears from Tables 5 and 6 that the concentration levels of the contaminants in the clear phase obtained in the second sedimentation step are practically identical.

The COD values were reduced significantly, even before the ion exchange step. The content of total N, NH. :N and P was also reduced significantly.

EXAMPLE 5: Reject water from municipal sewage system

The results are displayed in Tables 7 and 8 for a reject water from a municipal sewage system operating with a 2.9 o/oo and a 4.3 o/oo aqueous bentonite suspension, respec¬ tively. Comments

It appears from Tables 7 and 8 that the concentration levels of the contaminants in the clear phase obtained in the second sedimentation step are practically identical.

The COD values and the content of NH. :N and total P were all reduced significantly.

TABLE 3 (Slaughterhouse)

Dry

% of initial matter, SS, COD, Total N, NH. N. NO K, Total P,

Description volume % mg/1 mg/1 pH, g/1 g/1 mg/1 mg/1 mg/1

Raw sample 100 0.73 1240 4100 6.9 0.21 0.09 1.6 100 18.1

Raw sample, clear phase after 24 h 0.59 89 3300 6.8 0.12 0.14

First sedimentation 2.4 o/oo bentonite

Clear phase 99 0.58 248 1800 6.8 0.04 0.03 Slurry phase 1 2.39

Second sedimentation 3 o/oo bentonite

Clear phase 98 0.52 158 1100 6.9 0.07 0.07 0.9 155 1.9 Slurry phase 2 1.99

Purified liquid after ion exchange 98 0.47 24 260 4.9 0.00 0.4 0 0.3

Total treated volume: 18 1

% of initial m

Description volume

Raw sample 100 0.72 2730 10000 6.7 0.29 0.07 1.8 85 36.5

Raw sample, clear phase after 24 h 0.39 152 11000 6.5 0.20 0.05

First sedimentation

50 2160 6.7 0.12 0.08

212 1800 6.9 0.12 0.02 1.4 155 21.8

Purified liquid after ion exchange 98 0.21 50 500 5.4 0.00 0.00 0.6 <5 0.4

Total treated volume: 18 1 *)suspended clay particles

% of initial m

Description volume

Raw sample 100 0.14 259 1500 7.1 0.13 137 1.1 100 25.7

First sedimentation 2 o/oo bentonite

Clear phase 99 0.17 224 650 7.1 0.13 85

Slurry phase 1 1.20

Second sedimentation 2 o/oo bentonite

Clear phase 99 0.12 44 380 7.2 0.06 59 0.6 175 26.8

Slurry phase 1 1.64

Purified liquid after ion exchange 99 - 4 150 5.4 6 0.6 140 0.5

Total treated volume: 18 1

TABLE 6 (Fish industry)

Dry

% of initial matter, SS, COD, Total N, NH₄ :N, NO-,, K, Total P,

Description volume % mg/1 mg/1 pH, g/1 mg/1 mg/l mg/1 mg/1

Raw sample 100 0.14 259 1500 7.1 0.13 137 1.1 100 25.7

First sedimentation 3 o/oo bentonite

Clear phase 99 0.13 200 530 7.1 0.05 77 Slurry phase 1 1.87

Second sedimentation 3 o/oo bentonite

Clear phase 99 0.10 62 380 7.2 0.08 70 0.5 170 27.9 Slurry phase 1 1.53

Purified liquid after ion exchange nm nm nm nm nm nm nm nm nm nm

Total treated volume: 18 1 nm = not measured

TABLE 7 (Re ect water)

Total N, NH :N, NO K, Total P,

Description 9/1 g/i mg/1 mg/1 mg/1

Raw sample 0.31 1.2 370 19.6

Raw sample, clear phase after 24 h

0.32 1.1 390 17.2

First sedimentation 4.3 o/oo bentonite

Clear phase 95 0.21 126 8.0 0.24 Slurry phase 5 1.44

Second sedimentation 4.3 o/oo bentonite

Clear phase 94 0.21 70 460 8.0 0.27 0.9 345 8.2 Slurry phase 6 1.06

Purified liquid after ion exchange 94 43 7.3 0.00 0.8 260

Total treated volume: 18 1

TABLE 8 (Reject water

Dry

% of initial matter, SS, COD, Total N,

Description volume % mg/1 mg/1 pH, g/1

Raw sample 100 0.24 551 800 8.0

Raw sample, clear phase after 24 h 320 670 8.0

First sedimenta ion 2.9 o/oo bentonite

Clear phase 95 0. 19 80 8.0 0.26 Slurry phase 5 1.19

Second sedimentation 2.9 o/oo bentonite

Clear phase 94 0.19 39 310 8.1 0.26 1.0 320 5.8 Slurry phase 6 0.94

Total treated volume: 18 1

Claims

P a t e n t C l a i m s :

1. A method of purifying aqueous suspensions containing organic material and cations, e.g. ammonium ions, wherein the aqueous suspension of organic material is separated into a thick slurry phase with high dry matter content and an aqueous phase with a desired - high, moderate or low - content of contaminants, c h a r a c t e r i z e d in that coarse solid material is removed from the aqueous suspension of organic material in a first treatment step with formation of a primary aqueous phase freed of the coarse solid matter content of the aqueous suspension of organic material which is discharged as aqueous phase with a high content of contaminants, when this is desired, or, if not, passed to a second treatment step where the primary aqueous phase is mixed with an aqueous suspension of one or more flocculating smectitic clays in a mixing ratio of 0.3-10, preferably 1-3 kg smectite/t liquid phase, which has been activated by aging, preferably during a standing period of 24-48 hours, whereafter the mixture is subjected to flocculation and sedimentation with formation of a thick slurry phase with high dry matter content containing sedimented flocculated material which is wihdrawn as a product, and a secondary aqueous phase freed of the suspended solid matter content in the primary aqueous phase, the said secondary phase being discharged as aqueous phase with a moderate content of contaminants, when this is desired, or - if it is desired to take out an aqueous phase with a low content of contaminants - passed to a third treatment step where the secondary aqueous phase is subjected to ion exchange with a cation exchanger, preferably an inorganic cation exchanger, in particular selected from clays and/or zeolites exhibiting a high reaction velocity for the reaction with contaminating cations, e.g. ammonium, whereafter the thus treated secondary aqueous phase is discharged as aqueous phase with a low content of contaminants.

2. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the second treatment step is repeated at least once.

3. A method according to claims 1-2, c h a r a c t e r - i z e d in that the third treatment step is repeated at least once.

4. A method according to claims 1-3, c h a r a c t e r ¬ i z e d in that the cation loaded ion exchanger is dis- charged from the third treatment step and either stored as a separate product or united with the discharged thick slurry phase.

5. A method according to claims 1-3, c h a r a c t e r - i z e d in that the cation loaded ion exchanger is rege¬ nerated with an aqueous solution of a regeneration agent, preferably in the form of an aqueous solution of a calcium salt, e.g. CaCl-, providing a fresh regenerated cation exchanger and an aqueous cation containing eluate, which is discharged as a separate product.

6. A method according to claims 1-5, c h a r a c t e r ¬ i z e d in that cation exchanger is added and discharged continuously in the third treatment step in counter- current to the secondary aqueous phase, and that the cation regeneration step is carried out continuously and in counter-current.

7. A method according to claims 1-6, c h a r a c t e r - i z e d in that the concentration of the aqueous suspen¬ sion of smectitic clay is 1-40, preferably 5-15 weight-%, in particular about 10 weight-%.

8. Apparatus for purifying aqueous suspensions contain¬ ing organic material and cations, e.g. ammonium ions, wherein the aqueous suspension of organic material is separated into a thick slurry phase with high dry matter content and an aqueous phase with desired - high, moderate or low - content of contaminants, c h a r a c t e r ¬ i z e d in that it comprises

a separation unit ( 3 ) having an inlet for aqueous sus¬ pensions of organic material ( 2 ) , an outlet for coarse solid material ( 4 ) and an outlet ( 5 ) for a primary aqueous phase, which via a change-over valve (6) is connected with an outlet (7) for aqueous phase with high content of contaminants and a transfer pipe (11' ) communicating with an inlet pipe ( 14 ) of a flocculation and sedimentation unit (15);

a tank ( 13 ) for an aqueous suspension of flocculating agent, which via a pipe (12) and the inlet pipe (14) is connected with the flocculation and sedimentation unit (15) having an outlet (16) for thick slurry phase, and an outlet (17) for secondary aqueous phase, which via a change-over valve ( 8 ) communicates with an outlet ( 9 ) for aqueous phase with a moderate content of contaminants and a transfer pipe (18) being connected with a liquid inlet in an ion exchanger unit (19) having an outlet for treated liquid phase being an outlet ( 21 ) for an aqueous phase with a low content of contaminants and optionally an inlet ( 20) for fresh ion exchanger and an outlet for spent ion exchanger (22 ) .

9. Apparatus according to claim 8, c h a r a c t e r - i z e d in that it has a buffer tank (10) for primary aqueous phase arranged between the outlet ( 5 ) for primary aqueous phase and the inlet pipe ( 14 ) and a mixing unit (115) arranged between the transfer pipes (11, 12) and the inlet pipe ( 14) .

10. Apparatus according to claim 9, c h a r a c t e r ¬ i z e d in that it has a buffer tank (31) for the secon¬ dary aqueous phase arranged between the outlet (17) for secondary aqueous phase and the transfer pipe (18) con¬ nected with the liquid inlet in the ion exchanger tank.