Method for treating chemimechanical pulping effluent

Abstract

The present invention relates to a method for treating a chemimechanical pulping effluent. The method comprises the following steps: a) mixing a coagulant and an adsorbent with a chemimechanical pulping effluent; and b) mixing a flocculant with the effluent from step a). Compared with a traditional method, the effluent treatment method in the present invention has a better removal effect on suspended solids, turbidity and COD, and can reduce toxicity, decrease foam and improve the dryness of sludge, thereby exhibiting significant application prospects.

Description

Chemical Mechanical Pulp Wastewater Treatment Method Technical Field

[0001] The present invention relates to the field of wastewater treatment in the papermaking industry, and in particular to a combination of different chemicals or materials and a method for treating chemical-mechanical pulping wastewater. Background Art

[0002] As the supply of papermaking materials becomes increasingly limited, chemical-mechanical pulp (CMP), as a high-yield pulp, has been increasingly widely used in China. However, the pulping process of CMP produces a large amount of wastewater with complex components, which may contain lignin, degraded cellulose, hemicellulose and other wood additives (such as resin, etc.). In addition, the wastewater also has extremely high chemical oxygen demand (COD), extremely high temperature and foaming tendency. The treatment of this highly polluted wastewater is very difficult, which poses a continuous challenge to the stable operation of the wastewater treatment plant (ETP). In particular, the wastewater also contains substances that are toxic to anaerobic organisms in the anaerobic biological treatment stage. Therefore, the treatment of highly polluted wastewater has always been a key issue in the papermaking industry.

[0003] Before the wastewater enters the biological treatment stage, it must first be treated. Traditional treatment methods utilize coagulation and flocculation to clarify the wastewater in sedimentation tanks or flotation tanks. However, the combination of coagulants and flocculants is ineffective, failing to effectively remove colloids and dissolved substances, and its effectiveness in removing turbidity and reducing COD is also very limited. Furthermore, the surfactants contained in the wastewater can also commonly cause foaming, which can potentially negatively impact the normal operation of subsequent processes. Furthermore, traditional treatment methods require that CMP wastewater be diluted to a certain percentage before treatment, especially when the wastewater volume is large. Consequently, such processes have gradually become incompatible with the requirements of the modern papermaking industry. Consequently, developing environmentally friendly and efficient wastewater treatment processes has long been a goal pursued by those skilled in the art. Summary of the Invention

[0004] The present invention provides a method for treating CMP wastewater. The present invention also provides a (chemical) combination that can be used to treat CMP wastewater. The (chemical) combination for treating CMP wastewater in the present invention comprises a coagulant, an adsorbent, and a flocculant. In addition, the applicant has unexpectedly discovered that, compared with conventional treatment methods, the method or combination of the present application has the following technical advantages: (1) Better solid-liquid separation is achieved, resulting in better removal of suspended solids (SS) and turbidity, and the ability to increase the removal rate of wood extractives in wastewater. (2) Better COD removal can reduce the COD load entering the subsequent biological stage. (3) The foaming tendency of the wastewater is reduced, which is beneficial to the oxygen transfer in the subsequent A / O stage. (4) The biological toxicity of the extractive components in the wastewater to anaerobic granular sludge is reduced. (5) The dewatering properties of the mixed sludge are significantly improved, and the dryness of the sludge is significantly increased, which is of great significance to the energy saving of sludge incineration. (6) The sludge treatment load of the wastewater system is reduced.

[0005] In one embodiment, the combination of the present invention comprises a coagulant, an adsorbent, and a flocculant.

[0006] In one embodiment, the coagulant comprises at least one selected from the group consisting of aluminum chloride, ferric chloride, polyaluminum chloride, polyaluminum ferric chloride, and polyferric chloride.

[0007] In one embodiment, the coagulant is polyaluminium chloride.

[0008] In one embodiment, the coagulant is polyaluminum chloride, preferably with a basicity of 60-90%, for example, 60.0, 60.5, 61.0, 61.5, 62.0, 62.5, 63.0, 63.5, 64.0, 64.5, 65.0, 65.5, 66.0, 66.5, 67.0, 67.5, 68.0, 68.5, 69.0, 69.5, 70.0, 70.5, 71.0, 71.5, 72.0, 72.5, 73.0, 73.5, 74.0 , 74.5, 75.0, 75.5, 76.0, 76.5, 77.0, 77.5, 78.0, 78.5, 79.0, 79.5, 80.0, 80.5, 81.0, 81.5, 82.0, 82.5, 83.0, 83.5, 84.0, 84.5, 85.0, 85.5, 86.0, 86.5, 87.0, 87.5, 88.0, 88.5, 89.0, 89.5, 90.0%, or sub-ranges consisting of any value within these ranges.

[0009] In one embodiment, the coagulant is polyaluminum chloride, and the content of Al2O3 is preferably greater than or equal to 5wt%, for example, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0 , 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12. 5, 12.6, 12.7, 12.8, 12.9, 13.0, 13.1, 13.2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 14.0, 14.1, 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.8, 14.9, 15 .0, 15.1, 15.2, 15.3, 15.4, 15.5, 15.6, 15.7, 15.8, 15.9, 16.0, 16.1, 16.2, 16.3, 16.4, 16.5, 16.6, 16.7, 16.8, 16.9, 17.0, 17.1, 17.2, 17.3, 17.4, 1 7.5, 17.6, 17.8, 17.9, 18.0, 18.1, 18.2, 18.3, 18.4, 18.5, 18.6, 18.7, 18.8, 18.9, 19.0, 19.1, 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8, 19.9, 20.0, 20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8, 20.9, 21.0, 21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7, 21.8, 21.9, 22.0, 22.1, 22.2, 22.3, 22.4, 22.5 , 22.6, 22.7, 22.8, 22.9, 23.0, 23.1, 23.2, 23.3, 23.4, 23.5, 23.6, 23.7, 23.8, 23.9, 24.0, 24.1, 24.2, 24.3, 24.4, 24.5, 24.6, 24.7, 24.8, 24.9, 25.0 wt%, or a sub-range consisting of any value within these ranges.

[0010] In one embodiment, any of the coagulant, adsorbent and / or flocculant can be used in liquid or solid form. In one embodiment, the coagulant is liquid polyaluminium chloride.

[0011] In the present invention, the Al2O3 content and basicity in polyaluminium chloride are determined according to conventional methods in the art. The Al2O3 content in liquid polyaluminium chloride is the mass percentage of Al2O3 in the liquid polyaluminium chloride; the Al2O3 content in solid polyaluminium chloride is the mass percentage of Al2O3 in the solid polyaluminium chloride.

[0012] In one embodiment, the adsorbent comprises at least one selected from the group consisting of silica gel, activated carbon, bentonite, diatomaceous earth, molecular sieves, acidic alumina, neutral alumina, basic alumina, polyamide, zeolite, aluminum hydroxide gel, calcium phosphate gel, and kaolin.

[0013] In one embodiment, the adsorbent is bentonite, preferably sodium bentonite.

[0014] In one embodiment, the adsorbent is bentonite, preferably montmorillonite, with a content greater than or equal to 90 wt%, for example, 90.0, 90.1, 90.2, 90.3, 90.4, 90.5, 90.6, 90.7, 90.8, 90.9, 91.0, 91.1, 91.2, 91.3, 91.4, 91.5, 91.6, 91.7, 91.8, 91.9, 92.0, 92.1, 92.2, 92.3, 92.4, 92.5, 92.6, 92.7, 92.8, 92.9, 93.0, 93.1, 93.2, 93.3, 93.4, 93.5, 93.6, 93.7, 93.8, 93.9, 94.0, 94.1, 94.2, 94.3, 94.4, 94.5, 94.6, 94.7, 94.8, 94.9, 95.0, 95.1, 95.2, 95.3, 95.4, 95.5, 95.6, 95.7, 95.8, 95.9, 96.0, 96.1, 96.2, 96.3, 96.4, 96.5, 96.6, 96.7, 96.8, 96.9, 97.0, 97.1, 97.2, 97.3, 97.4, 97.5, %, or a subrange consisting of any value within these ranges.

[0015] In one embodiment, the adsorbent is bentonite, preferably with a whiteness greater than or equal to 45%, for example, 45.0, 45.5, 46.0, 46.5, 47.0, 47.5, 48.0, 48.5, 49.0, 49.5, 50.0, 50.5, 51.0, 51.5, 52.0, 52.5, 53.0, 53.5, 54.0, 54.5, 55.0, 55.5, 56.0, 57.5 6.5, 57.0, 57.5, 58.0, 58.5, 59.0, 59.5, 60.0, 60.5, 61.0, 61.5, 62.0, 62.5, 63.0, 63.5, 64.0, 64.5, 65.0, 65.5, 66.0, 66.5, 67.0, 67.5, 68.0, 68.5, 69.0, 69.5, 70.0, 70.5, 71.0, 71 .5, 72.0, 72.5, 73.0, 73.5, 74.0, 74.5, 75.0, 75.5, 76.0, 76.5, 77.0, 77.5, 78.0, 78.5, 79.0, 79.5, 80.0, 80.5, 81.0, 81.5, 82.0, 82.5, 83.0, 83.5, 84.0, 84.5, 85.0, 85.5, 86.0, 86. 5, 87.0, 87.5, 88.0, 88.5, 89.0, 89.5, 90.0, 90.5, 91.0, 91.5, 92.0, 92.5, 93.0, 93.5, 94.0, 94.5, 95.0, 95.5, 96.0, 96.5, 97.0, 97.5, 98.0, 98.5, 99.0, 99.5%, or a sub-range consisting of any value within these ranges.

[0016] In one embodiment, the adsorbent is bentonite, preferably having a sieve residue content of less than or equal to 1.00 wt % at 45 μm (325 mesh), for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.1 8, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0. 47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0 %, or a subrange consisting of any value within these ranges.

[0017] In one embodiment, the flocculant comprises at least one selected from the group consisting of polyallylamine, polyacrylamide, polyethyleneamine, a copolymer of vinylamine and acrylamide, polydiallyldimethylammonium chloride, polyvinylacetamide, polyvinylmethylformamide, polyvinylmethylacetamide, polydimethylaminopropyl methacrylamide, dimethylaminoethyl acrylate methyl chloride quaternary ammonium salt-acrylamide copolymer, sodium acrylate-acrylamide copolymer, polyethylene oxide, polyvinyl imidazoline, polyacrylic acid, sodium polyacrylate, and calcium polyacrylate.

[0018] In one embodiment, the flocculant is polyacrylamide, preferably anionic polyacrylamide.

[0019] In one embodiment, the anionic polyacrylamide has a degree of hydrolysis (also known as anionicity) of less than or equal to 25%, for example, less than or equal to 24%, less than or equal to 23%, less than or equal to 22%, less than or equal to 21%, less than or equal to 20%, less than or equal to 19%, less than or equal to 18%, less than or equal to 17%, less than or equal to 16%, less than or equal to 15%, less than or equal to 14%, less than or equal to 13%, less than or equal to 12%, less than or equal to 11%, less than or equal to 10%, less than or equal to 9%, less than or equal to 8%, less than or equal to 7%, less than or equal to 6%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or a sub-range consisting of any value in these ranges. For example, an anionic polyacrylamide with a degree of hydrolysis of 12%-17%, or 3%-12%, preferably, an anionic polyacrylamide with a degree of hydrolysis of 3%-12%. In one embodiment, the anionic polyacrylamide has a molecular weight greater than 5 million, such as greater than 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 20 million, preferably greater than 10 million. In a preferred embodiment, the anionic polyacrylamide is FennoPol A8931 or FennoPol A8842, both available from Kemira.

[0020] In one embodiment, the wastewater treatment method of the present invention comprises the following steps:

[0021] a) mixing the coagulant and adsorbent with the wastewater;

[0022] b) mixing a flocculant with the wastewater from step a).

[0023] In one embodiment, the treatment method is a pretreatment method.

[0024] In one embodiment, the wastewater of step a) is chemical mechanical pulp wastewater, including but not limited to bleached chemical thermomechanical pulp (BCTMP) wastewater, alkaline hydroperoxide mechanical pulp (APMP) wastewater, chemical thermomechanical pulp (CTMP) wastewater, thermomechanical pulp (TMP) wastewater or groundwood mechanical pulp (GMP) wastewater, etc.

[0025] In one embodiment, the mixing rate in step a) is greater than, equal to, or less than (preferably greater than) the mixing rate in step b).

[0026] In one embodiment, the mixing in step a) and / or step b) can be performed by stirring.

[0027] In one embodiment, the unit with a faster mixing rate is called a fast mixing unit (or fast mixing pool). In one embodiment, the number of the fast mixing units (or fast mixing pools) can be one or more, such as 1, 2, 3, or 4.

[0028] In one embodiment, the unit with a slower mixing rate is called a slow mixing unit (or slow mixing pool). In one embodiment, the number of the slow mixing units (or slow mixing pools) can be one or more, such as 1, 2, 3, or 4.

[0029] The terms "fast mixing" and "slow mixing" used herein refer only to the relative speed of mixing between any two units / pools, or between any two operations within the same unit / pool, and are not intended to have any other meaning. Depending on the object of comparison, a unit / pool may be referred to as either a fast-mixing unit / pool or a slow-mixing unit / pool.

[0030] In one embodiment, step a) and step b) may be performed in the same or different units / cells.

[0031] In one embodiment, the mixing of the coagulant and adsorbent with the wastewater in step a) can be performed in the same or different units / tanks. In one embodiment, the mixing of the coagulant and adsorbent with the wastewater in step a) can be performed simultaneously or sequentially. For example, the coagulant can be added to the wastewater first, followed by the adsorbent.

[0032] In one embodiment, after the coagulant and the adsorbent are mixed with the wastewater in step a), the wastewater mixed with the coagulant and the adsorbent is discharged to a slow mixing tank.

[0033] In one embodiment, both step a) and step b) are mixed by stirring.

[0034] In one embodiment, the stirring rate of step a) is greater than the stirring rate of step b).

[0035] In one embodiment, step b) is performed in a slow mixing tank, and step a) is performed in a fast mixing tank.

[0036] In one embodiment, in step b), after the wastewater from step a) is mixed with a flocculant, the treated wastewater is discharged into a primary sedimentation tank.

[0037] In one embodiment, in step a), the coagulant is added to the wastewater before the adsorbent.

[0038] In one embodiment, in step a), the mixing rate (eg, stirring rate) of the coagulant and the wastewater is the same as or different from the mixing rate (eg, stirring rate) of the adsorbent and the wastewater.

[0039] In one embodiment, in step a), the mixing rate (eg, stirring rate) of the coagulant and the wastewater is greater than, equal to, or less than (preferably greater than) the mixing rate (eg, stirring rate) of the adsorbent and the wastewater.

[0040] In one embodiment, in step a), the coagulant and the wastewater are mixed in a fast mixing tank, and the adsorbent and the wastewater are mixed in a slow mixing tank.

[0041] In one embodiment, in step a), after the coagulant is added, the concentration of the coagulant in the wastewater is 0.0001wt%-10wt%, for example, 0.0001wt%, 0.0002wt%, 0.0003wt%, 0.0004wt%, 0.0005wt%, 0.0006wt%, 0.0007wt%, 0.0008wt%, 0.0009wt%, 0.001wt%, 0.002wt%, 0.003wt%, 0.004wt%, 0.005wt%, 0.006wt%, 0.007wt%, 0.008wt% , 0.009wt%, 0.01wt%, 0.015wt%, 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt%, 0.04wt%, 0.0 %, 4wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, or a sub-range consisting of any value within these ranges. In another embodiment, the concentration of the coagulant in the wastewater is 1-100,000 ppm, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 2000, 3000 , 4000, 5000, 6000, 7000, 8000, 9000, 10000, 15000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, 55000, 60000, 65000, 70000, 75000, 80000, 85000, 90000, 95000, 100000 ppm, or a sub-range consisting of any value within these ranges.

[0042] In one embodiment, in step a), after the adsorbent is added, the concentration of the adsorbent in the wastewater is 0.0001wt%-10wt%, for example, 0.0001wt%, 0.0002wt%, 0.0003wt%, 0.0004wt%, 0.0005wt%, 0.0006wt%, 0.0007wt%, 0.0008wt%, 0.0009wt%, 0.001wt%, 0.002wt%, 0.003wt%, 0.004wt%, 0.005wt%, 0.006wt%, 0.007wt%, 0.008wt%, 0.009wt%, 0.01wt%, 0.015wt%, 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt%, 0.04wt%, 0.0 %, 4wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, or a sub-range consisting of any value within these ranges. In another embodiment, the concentration of the adsorbent in the wastewater is 1-100,000 ppm, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 2000, 3000 , 4000, 5000, 6000, 7000, 8000, 9000, 10000, 15000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, 55000, 60000, 65000, 70000, 75000, 80000, 85000, 90000, 95000, 100000 ppm, or a sub-range consisting of any value within these ranges.

[0043] In one embodiment, in step b), after the flocculant is added, the concentration of the flocculant in the wastewater is 0.0001wt%-5wt%, for example, 0.0001wt%, 0.0002wt%, 0.0003wt%, 0.0004wt%, 0.0005wt%, 0.0006wt%, 0.0007wt%, 0.0008wt%, 0.0009wt%, 0.001wt%, 0.0011wt%, 0.0012wt%, 0.0013wt%, 0.0014wt%, 0.0015wt%, 0.0016wt%, 0.0017wt%, 0.0018wt%, 0.0019wt%, 0.002wt%, 0.0021wt%, 0.0022wt%, 0 .0023wt%, 0.0024wt%, 0.0025wt%, 0.0026wt%, 0.0027wt%, 0.0028wt%, 0.0029wt%, 0.003wt%, 0.0031wt%, 0.0 032wt%, 0.0033wt%, 0.0034wt%, 0.0035wt%, 0.0036wt%, 0.0037wt%, 0.0038wt%, 0.0039wt%, 0.004wt%, 0.00 41wt%, 0.0042wt%, 0.0043wt%, 0.0044wt%, 0.0045wt%, 0.0046wt%, 0.0047wt%, 0.004wt8%, 0.0049wt%, 0.005 wt%, 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, or a sub-range consisting of any value within these ranges.In another embodiment, the concentration of the flocculant in the wastewater is 1-50,000 ppm, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43 ppm, or a sub-range consisting of any value within these ranges.

[0044] In one embodiment, the wastewater before treatment is acidic, neutral or alkaline, preferably acidic.

[0045] In one embodiment, the pH of the wastewater is lowered prior to treatment.

[0046] In one embodiment, the pH of the wastewater is lowered to 3.5-6.9, e.g., 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, or a sub-range consisting of any value within these ranges, prior to adding the coagulant and adsorbent.

[0047] Unless otherwise specified, the percentages, proportions, ratios, contents, or parts of the present invention are by mass or volume fraction. In one embodiment, the percentages, proportions, ratios, contents, or parts of the agents described herein are calculated based on the added commercial product form of the agent. In another embodiment, the percentages, proportions, ratios, contents, or parts of the agents described herein are calculated based on the active ingredient in the added agent. Those skilled in the art will be able to determine the specific meaning based on practice in this field.

[0048] Chemicals as used herein refer to pure substances and / or mixtures of various elements, whether natural or artificial. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG1 depicts that the technical solution of the present application can significantly reduce the turbidity and COD of BCTMP wastewater.

[0050] FIG2 illustrates that the technical solution of the present application can significantly reduce the turbidity and COD of BCTMP wastewater.

[0051] Figure 3 depicts the changes in foam and solid-liquid separation of wastewater in an on-site experiment (Example 6) conducted at a wastewater treatment plant of a pulp and paper joint enterprise: (a) Before adopting the wastewater treatment method of the present application, a large amount of foam existed in slow mixing tanks 1 and 2 (slow mixing tank 1 is not shown); (b) Two hours after adopting the wastewater treatment method of the present application, the foam in slow mixing tanks 1 and 2 almost disappeared (slow mixing tank 1 is not shown); (c) Before adopting the wastewater treatment method of the present application, there was no obvious solid-liquid separation in the influent of the primary sedimentation tank; (d) After adopting the wastewater treatment method of the present application, the influent of the primary sedimentation tank showed significantly better solid-liquid separation.

[0052] Figure 4 depicts the changes in sludge dewatering during an on-site experiment (Example 7) conducted at a wastewater treatment plant of a pulp and paper joint venture. After adopting the wastewater treatment method of the present application, the moisture content of the sludge cake after compression was significantly reduced.

[0053] Figure 5 depicts the changes in the amount of biological sludge floating on the surface of the secondary sedimentation tank in an on-site experiment (Example 8) conducted at a wastewater treatment plant of a pulp and paper joint enterprise: (a) Before the wastewater treatment method of the present application was adopted, the amount of biological sludge floating on the surface of the secondary sedimentation tank was relatively high; (b) On the 14th day after the wastewater treatment method of the present application was adopted, the amount of biological sludge floating on the surface of the secondary sedimentation tank was significantly reduced; (c) On the 16th day after the wastewater treatment method of the present application was adopted, the amount of biological sludge floating on the surface of the secondary sedimentation tank was further significantly reduced. DETAILED DESCRIPTION

[0054] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples. The experimental procedures described in the following examples are all conventional procedures unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0055] Materials and methods

[0056] Various reagents and materials described herein include commercially available components and, unless otherwise noted, were used without further purification.

[0057] coagulants

[0058] Liquid polyaluminium chloride PAC: from Kemira, with an aluminium oxide content of 8% and a basicity of 80%.

[0059] Polyferric chloride: from domestic suppliers, iron content greater than 8%, basicity 25%.

[0060] Ferric sulfate: from Kemira, with an iron content of 10%.

[0061] adsorbent

[0062] Bentonite FennoLite CC-R: from Kemira; whiteness 50%, sodium bentonite, sieve residue content under 45 μm (325 mesh) less than 0.1%.

[0063] Bentonite Fennolite CC-W: from Kemira; whiteness 45%, sodium bentonite, sieve residue content under 45 μm (325 mesh) less than 0.1%.

[0064] Talc: laboratory product, analytical grade AR.

[0065] flocculants

[0066] Anionic polyacrylamide FennoPol A8931: from Kemira, molecular weight ~15 million, degree of hydrolysis 5%.

[0067] Anionic polyacrylamide FennoPol A8842: from Kemira, molecular weight ~15 million, degree of hydrolysis 10%.

[0068] Cationic polyacrylamide FennoPol K9952: from Kemira, molecular weight ~12 million, cationic degree 5%.

[0069] Polyamine: Supplier from China, solid content 50%, pH 3.5-5.5, molecular weight 500,000-1,000,000.

[0070] Sewage on-site anionic flocculant Ref APAM: from domestic suppliers, the composition is anionic polyacrylamide. After testing, the hydrolysis degree is 30%, the molecular weight

[0071] ~12 million.

[0072] Mechanical pulp wastewater

[0073] Bleached chemithermomechanical pulp (BCTMP) wastewater.

[0074] Alkaline Peroxide Mechanical Pulping (APMP) Wastewater.

[0075] Wastewater pH adjustment method: Slowly add dilute hydrochloric acid to the experimental wastewater to slowly adjust to the required pH value.

[0076] Turbidity measurement: The turbidity value of the treated wastewater was measured using a Hach portable turbidity meter. The turbidity value was expressed in NTU. The test method was based on the Hach portable turbidity meter operating manual.

[0077] COD value determination: Take an appropriate amount of the supernatant of the treated wastewater, stir it evenly, and then use a COD tester to measure the COD value of the supernatant. The COD value result is expressed in mg / L. The COD test method is based on the national standard GB11914.

[0078] Example 1

[0079] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent bentonite FennoLite CC-R was added to a concentration of 500 ppm and stirred for one minute. Finally, the flocculant FennoPol A8931, anionic polyacrylamide, was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute, then stopped and the wastewater was allowed to stand for 10 minutes. After standing, the supernatant was measured.

[0080] Example 2

[0081] The pH of the BCTMP wastewater was lowered to 6.0 and stirred using a six-axle agitator at 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was then added to the BCTMP wastewater to a concentration of 1000 ppm, maintaining the same stirring rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent bentonite FennoLite CC-R was added to a concentration of 500 ppm and stirred for one minute. Finally, the flocculant FennoPol A8931, anionic polyacrylamide, was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute, then stopped and the wastewater allowed to stand for 10 minutes. After this standing period, the supernatant was measured.

[0082] Example 3

[0083] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 300 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent FennoLite CC-R bentonite was added to a concentration of 500 ppm and stirred for one minute. Finally, the flocculant FennoPol A8931 anionic polyacrylamide was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute, then stopped and the wastewater was allowed to stand for 10 minutes. After standing, the supernatant was measured.

[0084] Example 4

[0085] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 300 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent bentonite FennoLite CC-R was added to a concentration of 1000 ppm and stirred for one minute. Finally, the flocculant FennoPol A8931, anionic polyacrylamide, was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute, then stopped and the wastewater was allowed to stand for 10 minutes. After standing, the supernatant was measured.

[0086] Example 5

[0087] After the BCTMP wastewater and paper machine wastewater are mixed in a ratio of 1:2, the mixed wastewater is injected into the fast mixing tank. Subsequently, the coagulant liquid polyaluminium chloride (PAC) is directly added to the fast mixing tank (stirring rate: 120 rpm). The concentration of the coagulant in the wastewater is 300 ppm (measured as commercial liquid PAC). The residence time of the wastewater in the fast mixing tank is 5 minutes. The mixed wastewater then enters the slow mixing tank 1. A screw pump is used to add the adsorbent bentonite FennoLite CC-W with a concentration of 4wt% prepared in advance using the factory's dissolution unit to the slow mixing tank 1 and mix it with the wastewater (stirring rate: 60 rpm). The concentration of the adsorbent bentonite in the wastewater is 500 ppm (measured as commercial solid bentonite). The residence time of the wastewater in the slow mixing tank 1 is 10 minutes. The wastewater then entered slow mixing tank 2, where a screw pump was used to add 0.1 wt% of the anionic polyacrylamide FennoPol A8842, prepared in advance using a factory production unit, to fully achieve flocculation (stirring rate: 60 rpm). The flocculant concentration in the wastewater was 5 ppm (based on commercial solid flocculant). The wastewater was retained in slow mixing tank 2 for 10 minutes. Finally, the wastewater was injected into the primary settling tank, and subsequent experimental phenomena were observed.

[0088] Example 6

[0089] After the BCTMP wastewater and paper machine wastewater are mixed in a ratio of 1:2, the mixed wastewater is injected into a fast mixing tank. Subsequently, the coagulant liquid polyaluminium chloride (PAC) is directly added to the fast mixing tank (stirring rate: 120 rpm). The concentration of the coagulant in the wastewater is 300 ppm (measured as commercial liquid PAC). The residence time of the wastewater in the fast mixing tank is 5 minutes. The mixed wastewater then enters the slow mixing tank 1. A screw pump is used to add the adsorbent bentonite FennoLite CC-R with a concentration of 4wt% prepared in advance using the factory's dissolution unit to the slow mixing tank 1 and mix it with the wastewater (stirring rate: 60 rpm). The concentration of the adsorbent bentonite in the wastewater is 500 ppm (measured as commercial solid bentonite). The residence time of the wastewater in the slow mixing tank 1 is 10 minutes. The wastewater then entered slow mixing tank 2, where a screw pump was used to add 0.1 wt% of the anionic polyacrylamide FennoPol A8931 flocculant, prepared in advance using a factory production unit, to achieve full flocculation (agitation rate: 60 rpm). The flocculant concentration in the wastewater was 5 ppm (based on commercial solid flocculant). The wastewater remained in slow mixing tank 2 for 10 minutes. After treatment, the foam changes in slow mixing tanks 1 and 2, as well as the changes in the solid-liquid separation of the water sample entering the primary sedimentation tank, were observed.

[0090] Example 7

[0091] The same operation as in Example 6 was used to study changes in sludge dehydration. Sludge was concentrated and dehydrated using a drum concentrator and a screw press, and the average moisture content of the sludge was calculated. The sludge consisted primarily of primary sludge and a small amount of biological sludge.

[0092] Example 8

[0093] The same operation method as Example 6 was used. After the wastewater was treated, it entered the primary sedimentation tank, then the heat exchanger, IC tower, aeration tank, and finally the secondary sedimentation tank. The changes in the amount of biological sludge floating on the surface of the secondary sedimentation tank were observed.

[0094] Example 9

[0095] The pH of the APMP wastewater was lowered to 6.0 and stirred using a six-axle agitator at 150 rpm. A coagulant, liquid polyaluminium chloride (PAC), was added to the APMP wastewater to a concentration of 1000 ppm and stirred at the same rate for 1 minute. The stirring rate was then reduced to 50 rpm, and the adsorbent, bentonite FennoLite CC-R, was added to a concentration of 500 ppm and stirred for 1 minute. Finally, the flocculant, anionic polyacrylamide FennoPol A8931, was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for 1 minute, then stopped and the wastewater allowed to stand for 10 minutes. After this period, the supernatant was measured.

[0096] Example 10

[0097] The pH of the BCTMP wastewater was lowered to 6.0. The BCTMP wastewater was stirred using a six-axle agitator at 150 rpm. Liquid polyferric chloride (PFC) was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same rate for 1 minute. The stirring rate was then reduced to 50 rpm, and the adsorbent FennoLite CC-R bentonite was added to a concentration of 500 ppm and stirred for 1 minute. Finally, FennoPol A8931, an anionic polyacrylamide flocculant, was added to the wastewater to a concentration of 5 ppm. The mixture was stirred at 50 rpm for 1 minute, then stopped and allowed to stand for 10 minutes. After this period, the supernatant was measured.

[0098] Example 11

[0099] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same stirring rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent bentonite FennoLite CC-W was added to the BCTMP wastewater to a concentration of 500 ppm and stirred at the same stirring rate for one minute. Furthermore, the flocculant anionic polyacrylamide FennoPol A8842 was added to the wastewater to a concentration of 5 ppm and stirred at 50 rpm for one minute before stopping stirring and allowing the wastewater to stand for 10 minutes. After standing, the supernatant was measured.

[0100] Example 12

[0101] The pH of the BCTMP wastewater was lowered to 6.0 and stirred using a six-axle agitator at 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same rate for 1 minute. The stirring rate was then reduced to 50 rpm, followed by the addition of FennoLite CC-W, an adsorbent, to a concentration of 500 ppm and stirring at the same rate for 1 minute. Furthermore, the flocculant, anionic polyacrylamide FennoPol A8842, was added to the wastewater to a concentration of 5 ppm and stirred at 50 rpm for 1 minute before stopping stirring and allowing the wastewater to stand for 10 minutes. After standing, the supernatant was measured.

[0102] Comparative Example 1

[0103] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and Ref APAM, an anionic flocculant used in the wastewater treatment process, was added to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute before stopping and allowing the wastewater to settle for 10 minutes. The supernatant was then measured.

[0104] Comparative Example 2

[0105] The pH of the BCTMP wastewater was lowered to 6.0. The BCTMP wastewater was stirred using a six-axle agitator at 150 rpm. A coagulant, liquid polyaluminium chloride (PAC), was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent, bentonite FennoLite CC-R, was added to a concentration of 500 ppm and stirred for one minute. Finally, a flocculant, polyamine, was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute, then stopped and the wastewater allowed to stand for 10 minutes. After this period, the supernatant was measured.

[0106] Comparative Example 3

[0107] The pH of the BCTMP wastewater was lowered to 6.0 and stirred using a six-axle agitator at 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same rate for 1 minute. The stirring rate was then reduced to 50 rpm. The adsorbent bentonite FennoLite CC-R was then added to the BCTMP wastewater to a concentration of 500 ppm and stirred at the same rate for 1 minute. The flocculant cationic polyacrylamide FennoPol K9952 was then added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for 1 minute, then stopped and the wastewater allowed to stand for 10 minutes. After this standing period, the supernatant was measured.

[0108] Comparative Example 4

[0109] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 300 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent talc (Talc) was added to a concentration of 500 ppm and stirred for one minute. Finally, the flocculant FennoPol A8931, an anionic polyacrylamide, was added to the wastewater to a concentration of 5 ppm and stirred at 50 rpm for one minute before stopping stirring and allowing the wastewater to stand for 10 minutes. After standing, the supernatant was measured.

[0110] Comparative Example 5

[0111] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid polyaluminium chloride (PAC), a coagulant, was added to the BCTMP wastewater to a concentration of 1000 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent bentonite FennoLite CC-R was added to a concentration of 500 ppm and stirred for one minute. Finally, an in-situ anionic flocculant Ref APAM was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute, then stopped and the wastewater was allowed to stand for 10 minutes. After standing, the supernatant was measured.

[0112] Comparative Example 6

[0113] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 150 rpm. Liquid ferric sulfate, a coagulant, was added to the BCTMP wastewater to a concentration of 300 ppm and stirred at the same rate for one minute. The stirring rate was then reduced to 50 rpm, and the adsorbent FennoLite CC-R bentonite was added to a concentration of 500 ppm and stirred for one minute. Finally, FennoPol A8931, an anionic polyacrylamide flocculant, was added to the wastewater to a concentration of 5 ppm. The mixture was stirred at 50 rpm for one minute, then stopped and allowed to stand for 10 minutes. After this standing period, the supernatant was measured.

[0114] Comparative Example 7

[0115] The BCTMP wastewater used in the experiment was stirred using a six-axle agitator at a stirring rate of 50 rpm. The adsorbent FennoLite CC-R bentonite was added to the BCTMP wastewater to a concentration of 500 ppm and stirred at the same stirring rate for one minute. The stirring rate was then increased to 150 rpm, and the coagulant liquid polyaluminium chloride (PAC) was added to a concentration of 300 ppm and stirred for one minute. The stirring rate was then reduced to 50 rpm, and the flocculant FennoPol A8931 anionic polyacrylamide was added to the wastewater to a concentration of 5 ppm. Stirring was continued at 50 rpm for one minute, then stopped and the wastewater was allowed to stand for 10 minutes. After standing, the supernatant was measured.

[0116] Comparative Example 8

[0117] After mixing BCTMP wastewater and paper machine wastewater in a ratio of 1:2, the mixed wastewater was injected into a fast mixing tank. Subsequently, the coagulant liquid polyaluminum chloride (PAC) was directly added to the fast mixing tank (stirring rate: 120 rpm). The concentration of the coagulant in the wastewater was 300 ppm (calculated as commercial liquid PAC). The wastewater residence time in the fast mixing tank was 5 minutes. The mixed wastewater then entered the slow mixing tank, and a screw pump was used to add a 0.1wt% concentration of sewage on-site anionic flocculant Ref APAM, which was previously prepared using the factory's production unit, to fully achieve flocculation (stirring rate: 60 rpm). The concentration of the flocculant in the wastewater was 5 ppm (calculated as commercial solids). The wastewater residence time in the slow mixing tank was 10 minutes. Finally, the wastewater was injected into the primary sedimentation tank to observe subsequent experimental phenomena.

[0118] The above examples and comparative examples were subjected to various tests to characterize their treatment effects on wastewater. Specific results are shown in the following test examples.

[0119] Test Example 1

[0120] The turbidity and COD values ​​of the treated BCTMP wastewater in Examples 1 and 2 and Comparative Example 1 were measured, and the obtained values ​​were compared with the blank sample of untreated BCTMP wastewater. The results are shown in FIG1 .

[0121] Figure 1 shows that compared to existing wastewater treatment technology (Comparative Example 1), the technical solution of Example 1 of the present application can reduce the turbidity of BCTMP wastewater effluent by 67% and the COD by 11%. When the pH of the wastewater is pre-lowered to 6.0 (Example 2), the technical solution of the present application further significantly improves the turbidity and COD removal efficiency, with the COD of the treated wastewater decreasing by approximately 22% and the turbidity by approximately 87% compared to the blank sample.

[0122] Test Example 2

[0123] The turbidity and COD values ​​of the treated BCTMP wastewater in Comparative Example 1, Example 11, and Example 12 were measured, and the obtained values ​​were compared with the blank sample of untreated BCTMP wastewater. The results are shown in FIG2 .

[0124] Figure 2 shows that compared to existing wastewater treatment techniques (Comparative Example 1), the treatment method of Example 11 can reduce the turbidity of BCTMP wastewater effluent by 47% and the COD by 5.8%. When the pH of the wastewater is pre-lowered to 6.0 (Example 12), the technical solution of the present application further significantly improves the turbidity and COD removal efficiency, with the COD of the treated wastewater decreasing by approximately 13% and the turbidity by approximately 58% compared to the blank sample.

[0125] Test Example 3

[0126] The turbidity and COD values ​​of the treated BCTMP wastewater in Examples 3 and 4 and Comparative Example 4 were measured, and the obtained values ​​were compared with the blank sample of untreated BCTMP wastewater. The results are shown in Table 1.

[0127] Table 1 Effect of adsorbent type and dosage on wastewater treatment effect

[0128] Table 1 shows that compared to talc, a 500 ppm bentonite content provides significantly better adsorption when using a combination of PAC and the flocculant anionic polyacrylamide FennoPol A8931. The effluent turbidity and COD values ​​of BCTMP wastewater treated with 500 ppm bentonite are lower. However, increasing the adsorbent (bentonite) dosage to 1000 ppm further improves the treatment effect of BCTMP wastewater.

[0129] Test Example 4

[0130] The turbidity and COD values ​​of the treated BCTMP wastewater in Example 3 and Comparative Example 6 were measured, and the obtained values ​​were compared with the blank samples of untreated BCTMP wastewater. The results are shown in Table 2.

[0131] Table 2 Effect of coagulant types on wastewater treatment effects

[0132] Table 2 shows that when the same amount of bentonite and flocculant is used, PAC is more effective in treating wastewater than ferric sulfate. This is manifested in the fact that the flocs formed by PAC are larger in size and the effluent turbidity and COD values ​​are lower.

[0133] Test Example 5

[0134] The turbidity and COD values ​​of the treated BCTMP wastewater in Example 3 and Comparative Example 7 were measured, and the obtained values ​​were compared with the blank samples of untreated BCTMP wastewater. The results are shown in Table 3.

[0135] Table 3 Effect of the addition order of PAC and bentonite on wastewater treatment effect

[0136] Table 3 shows that compared with the technical solution of adding bentonite first and then adding PAC, the technical solution of adding PAC first and then adding bentonite will bring about significantly better wastewater treatment effects, as manifested in lower effluent turbidity and COD.

[0137] Test Example 6

[0138] The COD at the inlet and outlet of the primary sedimentation tank and the content of suspended solids at the inlet and outlet of Example 5 and Comparative Example 8 were measured, and the COD removal rate and suspended solids removal rate were calculated and compared. The results are shown in Table 4 below.

[0139] Table 4 Comparison of the wastewater treatment method of this application and the traditional treatment method in terms of suspended solids and COD removal

[0140] Table 4 shows that compared with Comparative Example 8, Example 5 exhibits higher COD removal rate and suspended solids removal rate, proving that the treatment method of the present application is more effective in removing COD and suspended solids than the traditional method, and can achieve a better wastewater treatment effect.

[0141] Test Example 7

[0142] The changes in the foam in the slow mixing tank and the solid-liquid separation of the wastewater in the primary settling tank in Example 6 were observed, and the results are shown in Figure 3. Figure 3 shows that after adopting the wastewater treatment method of the present application, the foam in the slow mixing tank almost disappeared, and at the same time, the influent of the primary settling tank showed significantly better solid-liquid separation.

[0143] Test Example 8

[0144] The sludge moisture content after and before the wastewater treatment method of the present application was compared (Example 7). The results are shown in Figure 4.

[0145] Figure 4 shows that before the wastewater treatment method of the present application was adopted, the average sludge moisture content was 79%. After the wastewater treatment method of the present application was adopted, the sludge moisture content was significantly reduced to an average of 65%, and the sludge dryness was significantly improved, indicating that the wastewater treatment method of the present application can effectively improve the dehydration properties, reduce the sludge moisture content, increase the daily sludge output of the filter press, save energy for subsequent sludge incineration, and also avoid the circulation of a large amount of suspended matter in the water system.

[0146] Test Example 9

[0147] The change in the amount of biological sludge floating on the surface of the secondary sedimentation tank in Example 8 was observed, and the results are shown in Figure 5. Figure 5 shows that after adopting the wastewater treatment method of the present application, the amount of biological sludge floating on the surface of the secondary sedimentation tank was significantly reduced.

[0148] Test Example 10

[0149] The turbidity and COD values ​​of the treated APMP wastewater in Example 9 were measured, and the obtained values ​​were compared with the blank sample of untreated APMP wastewater. The results are shown in Table 5.

[0150] Table 5 Application of the treatment method of this application in APMP wastewater

[0151] Test Example 11

[0152] The turbidity and COD values ​​of the treated BCTMP wastewater in Example 10 and Comparative Examples 2 and 3 were measured, and the obtained values ​​were compared with the blank samples of untreated BCTMP wastewater. The results are shown in Table 6.

[0153] Table 6 Treatment effect of BCTMP wastewater using other reagents in this application

[0154] Test Example 12

[0155] The turbidity and COD values ​​of the treated BCTMP wastewater in Example 1 and Comparative Example 5 were measured, and the obtained values ​​were compared with the blank samples of untreated BCTMP wastewater. The results are shown in Table 7.

[0156] Table 7 Effect of flocculant types on wastewater treatment effects

[0157] Table 7 shows that when the same amount of PAC and bentonite combination was used, the anionic polyacrylamide FennoPol A8931 achieved lower effluent turbidity and COD values ​​compared to the sewage on-site anionic flocculant Ref APAM.

Claims

1. A method for treating chemical mechanical pulp wastewater, characterized in that The following steps are involved: a) mixing a coagulant and an adsorbent with the chemical mechanical pulping wastewater; b) mixing a flocculant with the wastewater from step a).

2. The method according to claim 1, wherein In step a), the coagulant is mixed with the chemical mechanical pulping wastewater before the adsorbent.

3. A method according to any one of the preceding claims, wherein In step a), the concentration of the coagulant in the wastewater is 0.0001 wt%-10 wt%, preferably 0.025 wt%-1 wt%, more preferably 0.05 wt%-0.1 wt%.

4. A method according to any one of the preceding claims, wherein In step a), the concentration of the adsorbent in the wastewater is 0.0001 wt%-10 wt%, preferably 0.01 wt%-0.08 wt%, more preferably 0.03 wt%-0.08 wt%.

5. A method according to any one of the preceding claims, wherein In step b), the concentration of the flocculant in the wastewater is 0.0001 wt%-5 wt%, preferably 0.0001 wt%-0.003 wt%, more preferably 0.0001 wt%-0.001 wt%.

6. A method according to any one of the preceding claims, wherein Prior to step a), the pH value of the wastewater is lowered to 3.5-6.9, preferably 4.5-6.9, more preferably 5.5-6.

9.

7. A (chemical) combination for the treatment of chemimechanical pulp wastewater, comprising a coagulant, an adsorbent and a flocculant.

8. The method or combination according to any one of the preceding claims, wherein the coagulant comprises at least one selected from the group consisting of aluminum chloride, ferric chloride, polyaluminum chloride, polyaluminum ferric chloride, and polyferric chloride.

9. The method or combination according to any one of the preceding claims, wherein the coagulant is polyaluminium chloride, preferably having a basicity of 60-90%.

10. The method or combination according to any one of the preceding claims, wherein the coagulant is polyaluminium chloride, preferably containing greater than or equal to 5 wt% Al2O3.

11. The method or combination according to any one of the preceding claims, wherein the adsorbent comprises at least one selected from the group consisting of silica gel, activated carbon, bentonite, diatomaceous earth, molecular sieves, acidic alumina, neutral alumina, basic alumina, polyamide, zeolite, aluminum hydroxide gel, calcium phosphate gel, kaolin, preferably bentonite.

12. The method or combination according to any one of the preceding claims, wherein the flocculant comprises at least one selected from the group consisting of polyallylamine, polyacrylamide, polyethyleneamine, copolymers of vinylamine and acrylamide, polydiallyldimethylammonium chloride, polyvinylacetamide, polyvinylmethylformamide, polyvinylmethylacetamide, polydimethylaminopropyl methacrylamide, dimethylaminoethyl acrylate methyl chloride quaternary ammonium salt-acrylamide copolymer, sodium acrylate-acrylamide copolymer, polyethylene oxide, polyvinyl imidazoline, polyacrylic acid, sodium polyacrylate, and calcium polyacrylate; preferably anionic polyacrylamide; further preferably, the anionic polyacrylamide has a degree of hydrolysis of 3% to 12% and / or a molecular weight greater than 10 million.

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