FI20215496A1

FI20215496A1 - Method for recycling side products and/or waste for wastewater purification

Info

Publication number: FI20215496A1
Application number: FI20215496A
Authority: FI
Inventors: Pertti Koukkari; Martin Björnström; Otso Seppälä; Matti Kumpulainen; Markku Karlsson; Virpi Siipola
Original assignee: Aquaflow Oy
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2022-10-29
Also published as: WO2022229512A1; EP4330193A1

Abstract

Esitetään menetelmä metsätuotelaitoksessa tuotettujen sivutuotteiden ja/tai jätteiden käyttämiseksi uudelleen vedenpuhdistusprosessissa. Edelleen esitetään järjestelmä jäteveden puhdistamiseksi.

Description

METHOD FOR RECYCLING SIDE PRODUCTS AND/OR WASTE FOR

WASTEWATER PURIFICATION

TECHNICAL FIELD

The present disclosure relates to a method for reusing side products and/or waste produced in a forest product mill in a water purification process. The present disclosure further relates to a system for purification of wastewater.

BACKGROUND

In addition to other streams of waste or side products, many industrial processes produce large amounts of wastewater that must be purified before it is allowed to exit the process. Typical water purifica- tion processes that may be applicable to both industrial and municipal wastewaters may include several distinct processes intended to purify the water in a stepwise manner. Water purification processes commonly include methods such as flocculation, filtration, precipita- tion, clarification, biological treatment, and others.

SUMMARY

A method for reusing side products and/or waste originating in a forest product mill is disclosed. The

SN method may comprise carbonization of side products a and/or waste to form biochar and using the biochar in a x water purification process to form a used biochar co composition, wherein the used biochar composition can r 30 be burned, recycled, or regenerated.

E A system for purification of wastewater is also

O disclosed. The system may comprise a primary, a 5 secondary, and a tertiary purification. 3

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the embodiments and constitute a part of this specification, illustrates various embodiments. In the drawings:

Fig. 1 presents a flow chart of one embodiment of the water purification process utilizing activated carbon.

Fig. 2 presents a schematic view of a jar test as described in Example 3.

DETAILED DESCRIPTION

A method for reusing side products and/or waste produced in a forest product mill in purification of wastewater from said mill is disclosed. The method may comprise carbonization of side products and waste streams from the forest product mill to form biochar and using the biochar in a water purification process. In the water purification process, a used biochar composition is formed from the biochar. In one embodiment, the method comprises reusing side products and/or waste produced in a forest product mill including carbonization of side products and/or waste to form biochar and using the biochar in a water purification process to form a used biochar composition, wherein the used biochar composition can be burned, recycled, or

N regenerated.

N As used herein, the term "biochar” refers to x carbon or activated carbon produced from renewable 2 30 sources of raw material. Terms such as “activated

I biochar”, "biocarbon”, or "activated biocarbon” may be - used as synonyms to biochar.

S As used herein, the term "forest product mill” 2 refers to any factory or mill producing refined products

S 35 from a raw material or raw materials originating from forests or other plant-based raw material. Non-limiting examples of forest product mills are paper mills, sawmills, pulp mills, biorefineries, plywood mills, board mills, and paperboard mills. As used herein, the term "forest product mill” also serves as a collective term including all separate activities and production facilities located in one facility.

The biochar used in water purification may be formed by carbonization of side products and/or waste produced in a forest product mill. In one embodiment, the side products and/or waste comprise side products and waste streams of the forest product mill. As used herein, the term "side products” refers to any parts or components of the raw material that is not a part of and included in the main product of the forest product mill.

As used herein, the term "waste streams” refers to waste materials produced in the processes of a forest product mill. Non-limiting examples of side product and/or waste streams produced in forest product mills include sawdust, bark, knots, branches, lignin, sludge from water purification, black liquor residues, wood chips, or any combination thereof. In one embodiment, the sludge used for the production of biochar may be sludge formed in the purification of wastewater from a forest product mill.

In one embodiment, the sludge used for the production of biochar may be sludge recovered from — primary, secondary, tertiary water purification, or any

O combination thereof. In certain embodiments, the sludge <t used for the production of biochar may be sludge formed 2 30 in the purification of wastewater from a forest product

N mill, purification of municipal wastewater,

E purification of other industrial wastewater, side

O products from other industrial process, OT any 5 combination thereof.

N 35 In one embodiment, the side products and/or

N waste used for the production of biochar may be a mixture of sludge and other side products and/or waste or side streams. A non-limiting example of such a mixture is a mixture of sludge with bark, knots, sawdust, or any combination thereof.

In certain embodiments, it will be necessary to decrease the moisture content of the side products and/or waste before production of the biochar. The moisture content of the side products and/or waste may be reduced using any suitable method known to a person skilled in the art. The final moisture content will differ depending on the carbonization method. In one embodiment, the water content of the side products and/or waste is reduced to 60 weight-% or less before production of the biochar.

The biochar used in the method according to the present disclosure may be produced by carbonization of side products and/or waste produced in a forest product mill. In certain embodiments, the carbonization may be performed using any carbonization method known to a person skilled in the art. Examples of suitable carbonization methods include, but are not limited to, pyrolysis, slow pyrolysis, hydrothermal carbonization (HTC), torrefaction, or any combination thereof.

The biochar used for water purification may be activated biochar or activated carbon, which are used synonymously in the present disclosure. Activation of — the biochar formed from the side products and/or waste

O may be done using any method for carbon activation known <t to a skilled person such as chemical or physical 2 30 activation.

N In one embodiment, the method comprises reusing = side products and/or waste produced in a forest product

O mill comprising carbonization of side products and/or 5 waste to form activated biochar and using the activated 3 35 biochar in a water purification process to form a used biochar composition, wherein the used biochar composition can be burned, recycled, or regenerated.

The water purification that utilizes the activated biochar may be any water purification process 5 known to a person skilled in the art, including, but not limited to, purification of wastewater from a forest product mill, municipal wastewater, or any other wastewater in need of purification. In one embodiment, the water purification step includes removal of soluble material, colloidal material, microplastics, or any combination thereof. The use of biochar or activated carbon in a water purification treatment may enable elimination of one or more chemicals commonly used in the water purification process.

In one embodiment, the efficiency of the water purification according to the method of the present disclosure may be measured using any conventional measurement known to a skilled person. A non-limiting example of a measurement used to determine the efficiency of the water purification is chemical oxygen demand (COD).

In one embodiment, the used hbiochar is separated from the water and recovered. In one embodiment, the used biochar is separated from the water and recovered after the use in a water purification process. Separation of the used biochar from the water — following the water purification may be performed using

O any suitable method or methods known to a person skilled < in the art. Non-limiting examples of methods for 2 30 separating biochar from water include filtration, - centrifugation, and filter pressing. a In one embodiment, the used biochar is burned,

O regenerated, or recycled after the use in water > purification. In one embodiment, the used biochar is

N 35 separated from the water, recovered, and recycled after

N the use in water purification.

Once the used biochar has been recovered, it may be recycled by any method known to a person skilled in the art. In certain embodiments, the used biochar may be burned, regenerated, or recycled. In certain embodiments, the used biochar may be recycled as raw material for concrete, as filler material, as a metallurgical reducing agent, for soil amendment, or any combination thereof. In one embodiment, the regenerated used biochar may be reused in water purification.

A system for purification of wastewater is also disclosed. In one embodiment, the system for purification of wastewater comprises a primary, a secondary, and a tertiary purification. In one embodiment, the system comprises a quaternary purification.

In one embodiment, the quaternary purification comprises purification using biochar produced from side products and/or waste produced in a forest product mill.

In one embodiment, the primary purification is a physical purification, the secondary purification is a biological purification, and the tertiary purification is a chemical treatment. In one embodiment, the chemical treatment is a coagulation and/or flocculation.

In one embodiment, the quaternary purification is a purification using biochar or activated carbon.

The method for reusing side products and/or — waste produced in a forest product mill described in the

O current specification has the added utility of being + suitable for the reusing or recycling of side products 2 30 and/or waste produced in a forest product mill at the

N mill. This provides the advantage that the waste sludges z and side products instead of their separate treatments

O are processed in a single processing unit within the > mill, which may produce both energy and the added value

N 35 biochar, leading to higher utilization degree of the

N acguired raw material. In certain embodiments, the single processing unit may be a carbonization unit,

wherein the carbonization is performed by pyrolysis. In addition, due to the pyrolysis process, the inorganic elements contained in the side streams and waste sludges will remain immobilised within the biochar, thus reducing their impact as undesired non-process elements in the mill.

An additional advantage provided by the method of the present disclosure is a reduction in the amount of material needed to be purchased for the water purification process, leading to a reduction in costs.

EXAMPLES

Reference will now be made in detail to various embodiments.

The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the embodiments based on the disclosure. Not all steps or features of the embodiments are discussed in detail, as many of the steps or features will be obvious for the person skilled in the art based on this specification.

Example 1 - Production of activated carbon using hydrothermal carbonization and steam activation

Dried wood bark (with a dry matter content of

N approximately 90 %) and excess sludge from secondary

N treatment from the same softwood pulp mill as described

S 30 in example 3 was thoroughly mixed in a ratio of 1:1

S relative to dry matter content. The dry matter content =E of the mixture was adjusted by adding water. 2.1 kg of * bark:sludge mixture with a dry matter content of 18.1 3

S was mixed with 3.9 kg water to yield 6.0 kg of a = 35 bark:sludge mixture with a dry matter content of 6.7 %.

S The pH of the diluted mixture was adjusted to approximately 4 by the addition of 6.0 g concentrated sulphuric acid using mechanical stirring.

The formed mixture was treated in a Hastelloy

C276 high-temperature autoclave at 260 °C for 2 h with constant stirring (300 rpm). After 3 h, the mixture was weighed (5.79 kg) and the pH was measured (4.7). The mixture was filtered using a Biichner funnel to collect the formed biochar. The collected biochar was dried at 105 °C to yield 200.2 g biochar with a dry matter content of 95.3 % (52.9 % yield). 45 g of the dried biochar was weighed on a steel dish and placed in a batch carbonization reactor.

The reactor was sealed and purged with nitrogen to remove all air inside the reactor.

The reactor was heated to 800 °C at a rate of 5 °C/min under a nitrogen flow of 5 l/min. Once the target temperature was reached, water was pumped into the oven to generate steam. The water flow rate was 4,5 ml/min and nitrogen flow 5 1/min.

The process was allowed to proceed for 3.5. h after which the flow of water was stopped, and the reactor allowed to cool before opening. Once the reactor had cooled, the obtained activated biochar was collected and weighed (10.1 g, yield 26.4 %).

Example 2 - Producing activated carbon using slow pyrolysis and steam activation

N

N Dried wood bark (with a dry matter content of

S 30 approximately 90 %) and sludge from the same softwood e pulp mill as described in example 3 was thoroughly

Ek mixed in a ratio of 1:1 relative to dry matter content * and the mixture dried to a total dry matter content of

S approximately 90 %. 200 g of the dried bark:sludge = 35 mixture was weighed and placed inside a batch

S carbonization reactor which was thoroughly sealed and purged with nitrogen to remove any air inside the reactor.

The reactor was slowly heated using a ramped heating program with temperature holding steps at 280 °C (heating rate 8 °C/min, hold time 3 h), 330 °C (heating rate 1 °C/ min, hold time 20 min) and 475 °C (heating rate 5 °C/ min, hold time 3 h). Nitrogen flow during entire program was 5 1/min. After carbonization at 475 °C, the reactor was allowed to cool before opening. Once the reactor had cooled, the obtained activated biochar was collected and weighed (66 g, yield 33 %).

Example 3 - Jar tests with different doses of activated biochar

A wastewater sample was taken from a softwood pulp mill secondary clarifier overflow. The pulp mill has modern low-water consuming debarking and it produces 330 000 t/a bleached chemi-thermomechanical pulp. There is no other industry that produces wastewater to the wastewater treatment plant. The wastewater treatment plant has a first primary clarification and an activated sludge plant, from where the treated water is discharged into a lake.

Conventional tertiary treatment to remove dis- solved organic material was done with a laboratory scale

N batch-flotation unit. The unit consisted of a tank with

N a mixer and a dispersion water system. The tank was

S 30 filled with 5 1 of wastewater sample and its pH was e adjusted with HSO, to 5.5. 400 mg/l of alum solution

Ek containing 100 g alum/1 was dosed to the sample and * mixed well. Then, 3 mg/l of flocculant solution of 1 g/l

S cationic polyacrylamide was dosed. The water was mixed = 35 for 2 minutes at 120 rpm to achieve good flocs. Finally,

S flocs were separated with dispersion water and the treated water was collected for activated biochar treatment. Dispersion water pressure was 6 bar and dose 1 litre. Dispersion water was prepared from the same wastewater sample using the above tertiary treatment method, so it did not change the composition of the wastewater. 6 plastic jars were each filled with 500 ml of tertiary treated wastewater and put in a laboratory scale flocculator (jar test bench, Fig. 2). Doses of 100 and 200 mg/1 of different activated biochars were dosed.

The activated biochars were prepared according to exam- ples 1 or 2. One commercially available activated carbon was also tested. The tested commercial product was a powdered high-grade coal-based activated carbon de- signed for water treatment that had a BET number of 1150 m?/g. After activated biochar dosing, water was mixed for 15 minutes at 200 rpm. 3 mg/l of the same flocculant as in the tertiary treatment and approximately 5 ml of microsand (quartz, 60 — 180 pm particle size) were added and mixed at 120 rpm for 3 minutes. Mixing was stopped and after the flocculated solids had settled on the bottom of the jars, water samples for analysis were collected. Microsand was dosed only to help solids set- tle faster.

The jar tests proved that activated biochars can achieve the same COD reduction of 35 - 45 % with a dose of 100 mg/l as commercially available activated carbon. A dose of 200 mg/l activated biochar increased

N COD reduction compared to 100 mg/1, but the reduction

N was only 5 - 10 % higher. COD reduction depends on

S 30 wastewater composition, biochar raw material and

S carbonization and activation method. It was also

Ek possible to flocculate activated biochar with polymer * and microsand and settle on the bottom as easily as the

S commercial activated carbon. = 35

S It is obvious to a person skilled in the art that with the advancement of technology, the basic idea may be implemented in various ways. The embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A method or system disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items. The term “comprising” is used in this specification to mean including the feature(s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.

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Claims

1. Method for reusing side products and/or waste produced in a forest product mill comprising carbonization of side products and/or waste to form biochar and using the biochar in a water purification process to form a used biochar composition, wherein the used biochar composition can be burned, recycled, or regenerated.

2. The method of claim 1, wherein the biochar is activated biochar or activated carbon.

3. The method of any of the preceding claims, wherein the side products may be sludge, bark, knots, saw dust, wood chips, or any combination thereof.

4. The method of any of the preceding claims, wherein the biochar is produced by pyrolysis, slow pyrolysis, hydrothermal carbonization (HTC), torrefaction, or any combination thereof.

5. The method of any of the preceding claim, wherein the sludge used for biochar production is sludge formed in the purification of wastewater from a forest product mill.

6. The method of any of the preceding claims, wherein the used hbiochar composition is burned, regenerated, or recycled after the use in water = 25 purification.

N

7. The method of claim 6, wherein recycling is S burning, as raw material for concrete, as filler 2 material, as a metallurgical reducing agent, for soil E amendment, or any combination thereof. O 30

8. The method of any of the preceding claims, > wherein the water purification step includes removal of N soluble material, colloidal material, microplastics, or N any combination thereof.

9. The method of any the preceding claims, wherein the used biochar is separated from the water and recovered.

10. System for purification of wastewater comprising a primary, a secondary, and a tertiary purification.

11. The system of claim 10, wherein the system comprises a quaternary purification.

12. The system of any of claims 10 - 11, wherein the quaternary purification comprises purification using biochar produced side products and/or waste produced in a forest product mill.

13. The system of any of claims 10 - 12, wherein the primary purification is a physical purification, the secondary purification is a biological purification, and the tertiary purification is a chemical treatment.

14. The system of any one of claims 10 - 13, wherein the quaternary purification is a purification using biochar or activated carbon. N O N <+ <Q 00 N I jami a © O + LO N O N