A pretreatment method for chemical mechanical pulp wastewater from bamboo.

Abstract

This invention belongs to the field of wastewater treatment technology, and particularly relates to a pretreatment method for chemimechanical pulp wastewater from *Bambusa textilis*. Addressing the problem that existing technologies cannot easily and stably remove lignin from *Bambusa textilis* chemimechanical pulp wastewater, this invention provides a pretreatment method for such wastewater, including pH control and initial lignin precipitation steps, coagulation and deep lignin precipitation steps, enhanced flocculation and floc growth steps, and solid-liquid separation steps. This invention is the first to propose and realize a synergistic treatment system integrating HCl+PAC+CPAM, achieving the integration of three functions within the same process unit: precise pH control inducing lignin precipitation, charge neutralization and destabilization coagulation, and polymer adsorption bridging flocculation. The three reagents are functionally interconnected and complementary, forming a complete reaction chain from precipitation to destabilization to flocculation, with a significant synergistic effect.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and particularly relates to a pretreatment method for chemical mechanical pulp wastewater from bamboo. Background Technology

[0002] The production of chemimechanical pulp from bamboo requires the use of large amounts of NaOH for chemical impregnation to soften the fibers, resulting in wastewater with extremely unique pollution characteristics. The wastewater often has a COD concentration exceeding 10,000 mg / L, a pH value above 10, extremely deep color (often thousands of times greater), and is rich in recalcitrant soluble lignin. The BOD5 / COD ratio is often below 0.35, classifying it as typical recalcitrant organic wastewater, making direct biological treatment extremely inefficient.

[0003] Existing chemical pulp wastewater treatment technologies mainly have the following problems and shortcomings: (a) MVR evaporation and concentration treatment. The amount of NaOH used in the chemimechanical pulping process is much lower than that in chemical pulping, resulting in a low solids concentration in the concentrated black liquor. This leads to low MVR evaporation efficiency, high operating costs, low calorific value of the concentrated black liquor, difficulty in utilization, and poor economic efficiency.

[0004] (ii) Combined process of sedimentation-anaerobic-aerobic-advanced treatment. The biodegradability of the wastewater is poor (BOD5 / COD<0.35), which severely limits the efficiency of anaerobic treatment; aerobic treatment requires a large amount of aeration energy consumption, resulting in high operating costs; and advanced treatment (such as Fenton oxidation) has high reagent costs.

[0005] (iii) Acid precipitation method. The pH value of lignin is adjusted to near the isoelectric point by adding acid to alkaline wastewater, causing it to precipitate. However, the acid precipitation method consumes a large amount of acid, and the precipitated lignin particles are small, have poor settling performance, and are difficult to separate from solids.

[0006] (iv) Advanced oxidation methods. Advanced oxidation technologies such as Fenton oxidation and catalytic oxidation are expensive to operate, consume large amounts of reagents, and have harsh operating conditions, making them difficult to promote on a large scale in industrial applications.

[0007] To address this issue, people have conducted exploratory research in long-term production and daily life practices. For example, a Chinese invention patent application discloses a method for treating mechanical pulp with a purely plant-extracted bio-enzyme and paper products prepared from the treated mechanical pulp [Application No.: CN 202311238172.8]. The method of this invention application is completed according to any one of the following processing steps: Process (A): Using naturally extracted peroxidase, the mechanical pulp is treated at pH 5.0 and a temperature of 60°C for 2-6 hours. The amount of peroxidase added is 0.5-1.5 g / kg oven-dry pulp, and the reaction concentration of the mechanical pulp is 10%. The mechanical pulp is washed with deionized water to balance the moisture content, completing the treatment; Process (B): First, the mechanical pulp is treated with naturally extracted peroxidase at pH 5.0 and a temperature of 60°C for 2-6 hours. The amount of peroxidase added is 0. 5-1.5 g / kg oven-dry pulp, the reaction concentration of the mechanical pulp is 10%. The mechanical pulp is washed with deionized water and adjusted to a solid content of 10%, and set aside. 5 g / L ethylenediaminetetraacetic acid (EDTA) is added to the mechanical pulp treated with oxidase. The mechanical pulp to be treated with EDTA is placed in a polyethylene sealed bag, kneaded to mix the mechanical pulp and the solution evenly, and placed in a 60℃ constant temperature water bath for 60 min. After the bath, it is cooled to room temperature and washed with deionized water to adjust the solid content to 10%. The mechanical pulp treated with EDTA is then bleached with H2O2 under the following conditions: 40 g / L H2O2, 20 g / L NaOH, 5 g / L MgSO4, mechanical pulp concentration of 10%, and reaction at 80℃ for 120 min. During the reaction, the pulp is kneaded every 15 min to ensure uniform reaction. After bleaching, it is washed with deionized water until neutral to balance the moisture content. The treatment is then complete.

[0008] This invention application utilizes bio-enzymes extracted from pure plants to remove lignin. However, the bio-enzymes themselves are relatively difficult to obtain, and their activity is affected by various environmental factors such as reaction temperature, pH value, and water hardness, resulting in a complex process and relatively poor stability of the process results. Summary of the Invention

[0009] The purpose of this invention is to address the above-mentioned problems by providing a pretreatment method for chemical mechanical pulp wastewater from bamboo.

[0010] To achieve the above objectives, the present invention adopts the following technical solutions: A pretreatment method for chemimechanical pulp wastewater from *Bambusa textilis* includes the following steps: Step 1: pH adjustment and initial precipitation of lignin. Hydrochloric acid is added to the chemimechanical pulp wastewater of bamboo under stirring conditions to adjust the pH value to 6.5±0.2, so that soluble lignin is initially precipitated, and primary treated wastewater is obtained. Step 2: Coagulation and deep precipitation of lignin. Polyaluminum chloride is added to the primary treated wastewater obtained in Step 1 under stirring conditions to adjust the pH value to 6.0±0.2, so that the soluble lignin can be further precipitated and the particles can be destabilized to obtain secondary treated wastewater. Step 3: Enhance flocculation and floc growth. Under stirring conditions, add cationic polyacrylamide aqueous solution to the secondary treated wastewater obtained in Step 2 to cause the precipitated lignin particles and colloids to aggregate into coarse flocs, thus obtaining flocculated wastewater. Step 4: Solid-liquid separation. The flocculated wastewater obtained in Step 3 is allowed to settle and the supernatant and sludge are separated to obtain pretreated wastewater.

[0011] In the above-mentioned pretreatment method for chemimechanical pulp wastewater from *Cymbidium goeringii*, the mass fraction of hydrochloric acid in step one is 31%, and the amount added is 1.0-3.0 kg of hydrochloric acid per cubic meter of chemimechanical pulp wastewater from *Cymbidium goeringii*.

[0012] In the above-mentioned pretreatment method for chemical mechanical pulp wastewater from Cizhu, the Al2O3 content of polyaluminum chloride in step two is above 10%, and the addition amount is 1.0-5.0 kg of polyaluminum chloride per cubic meter of primary treated wastewater.

[0013] In the above-mentioned pretreatment method for chemical mechanical pulp wastewater from *Cymbidium goeringii*, the stirring speed in both step one and step two is 200-500 rpm, and the stirring time is 2-5 min.

[0014] In the above-mentioned pretreatment method for chemical mechanical pulp wastewater from Cizhu, the mass fraction of cationic polyacrylamide in the cationic polyacrylamide aqueous solution in step three is 0.1%-0.3%.

[0015] In the above-mentioned pretreatment method for chemical mechanical pulp wastewater from Cizhu, the amount of cationic polyacrylamide aqueous solution added is 4.0-6.0 kg per cubic meter of secondary treated wastewater.

[0016] In the above-mentioned pretreatment method for chemical mechanical pulp wastewater from *Ciba oleifera*, the molecular weight of the cationic polyacrylamide is 8 million to 15 million.

[0017] In the above-mentioned pretreatment method for chemical mechanical pulp wastewater from *Cymbidium goeringii*, the stirring speed in step three is 40-80 rpm, and the stirring time is 1-3 min.

[0018] In the above-mentioned pretreatment method for chemical mechanical pulp wastewater from *Cymbidium goeringii*, the settling time in step four is 1.0-3.0 h.

[0019] In the above-mentioned pretreatment method for chemimechanical pulp wastewater from *Bambusa textilis*, the COD of the chemimechanical pulp wastewater is 10000-15000 mg / L, the pH value is 9.5-10.5, the temperature is 25-35℃, and the BOD5 / COD ratio is below 0.3. The COD of the pretreated wastewater is below 6000 mg / L, and the BOD5 / COD ratio is above 0.45.

[0020] Compared with existing technologies, the advantages of this invention are: 1. This invention proposes and realizes for the first time a three-in-one synergistic treatment system of HCl+PAC+CPAM. It integrates the three functions of pH precise control to induce lignin precipitation, charge neutralization destabilization and coagulation, and polymer adsorption bridging flocculation within the same process unit. The three reagents are interconnected and complementary in function, forming a complete reaction chain from precipitation to destabilization to flocculation, with a significant synergistic effect.

[0021] 2. Under preferred conditions, the present invention can achieve a COD removal rate of 40%-50%, a color removal rate of 90%-97%, and a BOD5 / COD ratio that increases from about 0.30 to over 0.45, which signifies that the wastewater has been transformed from being difficult to biodegrade to being biodegradable, creating extremely favorable conditions for subsequent biological treatment.

[0022] 3. This invention avoids inefficient MVR evaporation, reduces the cost of subsequent biochemical treatment (improved anaerobic efficiency and reduced aerobic aeration energy consumption), and reduces the consumption of deep treatment reagents. HCl, PAC, and CPAM are all commercially available conventional water treatment reagents, widely available and with stable prices. The unit water treatment reagent cost is reduced by 20%-30% compared to traditional treatment methods.

[0023] 4. The main control parameters of this invention are pH value and reagent dosage, both of which are easy to monitor and control online and automatically. The floc settling performance is excellent, the solid-liquid separation efficiency is high, the system has strong tolerance to fluctuations in influent water quality (COD 10000~15000 mg / L, pH 9.5~10.5), and the continuous operation stability is good.

[0024] 5. Through experiments, this invention has found that when the HCl dosage increases from 1.0 kg / m³, the effect is more effective. 3 Increased to 2.0 kg / m 3 At that time, the COD removal rate increased significantly from 16.9% to 51.4%, and the color removal rate increased from 52.3% to 97.7%. (Exceeding 2.0 kg / m³) 3The rate of increase then slowed down. Taking all factors into account, the recommended HCl dosage is 2.0 kg / m³. 3 The optimal pH level for cost-effectiveness is 6.0-6.5, which falls within the range of efficient lignin precipitation. When the PAC dosage increases from 1.0 kg / m³... 3 Increased to 3.0 kg / m 3 At that time, the COD removal rate increased from 25.4% to 51.4%, and the color removal rate increased from 68.9% to 97.7%, exceeding 3.0 kg / m³. 3 The rate of increase then slowed down, with a PAC dosage of 3.0 kg / m³. 3 This offers the best value for money. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to specific embodiments.

[0026] Example 1

[0027] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0028] Treatment steps: (1) Add 2.0 g of HCl (31%) (i.e., 2.0 kg / m³) 3 (1) Stir rapidly (400 rpm) for 2 minutes until the pH drops to 6.52; (2) Add 3.0 g of PAC (Al2O3 content ≥10%) (i.e., 3.0 kg / m³). 3 (2) Stir rapidly (400 rpm) for 2 minutes until the pH drops to 5.98; (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0029] Treatment results: effluent COD=5756 mg / L, COD removal rate 51.4%; effluent color approximately 180 times, color removal rate 97.7%; effluent pH=6.0; effluent BOD5=2680 mg / L, BOD5 / COD=0.466, an improvement of 60.7% compared to before treatment (0.29).

[0030] Example 2

[0031] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0032] Treatment steps: (1) Add 1.0 g of HCl (31%) (i.e., 1.0 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 3.0 g of PAC (Al2O3 content ≥10%) (i.e., 3.0 kg / m³). 3 (2) Stir rapidly (400 rpm) for 2 minutes until the pH drops to 8.41; (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0033] Treatment results: effluent COD = 9842 mg / L, COD removal rate 16.9%; effluent color approximately 3720 times, color removal rate 52.3%; effluent pH = 8.4.

[0034] Example 3

[0035] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0036] Treatment steps: (1) Add 1.5 g of HCl (31%) (i.e., 1.5 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 3.0 g of PAC (Al2O3 content ≥10%) (i.e., 3.0 kg / m³). 3 Stir rapidly (400 rpm) for 2 minutes until the pH drops to 7.28. (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0037] Treatment results: effluent COD = 7745 mg / L, COD removal rate 34.6%; effluent color approximately 1669 times, color removal rate 78.6%; effluent pH = 7.3.

[0038] Example 4

[0039] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0040] Treatment steps: (1) Add 2.5 g of HCl (31%) (i.e., 2.5 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 3.0 g of PAC (Al2O3 content ≥10%) (i.e., 3.0 kg / m³). 3 ), stir rapidly (400 rpm) for 2 minutes, and the pH drops to 5.60 (3) add 5.0 g (i.e. 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0041] Treatment results: effluent COD = 5679 mg / L, COD removal rate 52.1%; effluent color approximately 164 times, color removal rate 97.9%; effluent pH = 5.6.

[0042] Example 5

[0043] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0044] Treatment steps: (1) Add 3.0 g of HCl (31%) (i.e., 3.0 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 3.0 g of PAC (Al2O3 content ≥10%) (i.e., 3.0 kg / m³). 3 Stir rapidly (400 rpm) for 2 minutes until the pH drops to 5.31. (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0045] Treatment results: effluent COD = 5586 mg / L, COD removal rate 52.9%; effluent color approximately 140 times, color removal rate 98.2%; effluent pH = 5.3.

[0046] Example 6

[0047] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0048] Treatment steps: (1) Add 2.0 g of HCl (31%) (i.e., 2.0 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 1.0 g of PAC (Al2O3 content ≥10%) (i.e., 1.0 kg / m³) 3 (2) Stir rapidly (400 rpm) for 2 minutes until the pH drops to 8.11; (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0049] Treatment results: effluent COD = 8842 mg / L, COD removal rate 25.4%; effluent color approximately 2426 times, color removal rate 68.9%; effluent pH = 8.1.

[0050] Example 7

[0051] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0052] Treatment steps: (1) Add 2.0 g of HCl (31%) (i.e., 2.0 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 2.0 g of PAC (Al2O3 content ≥10%) (i.e., 2.0 kg / m³) 3 (2) Stir rapidly (400 rpm) for 2 minutes until the pH drops to 6.50; (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%).3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0053] Treatment results: effluent COD = 6745 mg / L, COD removal rate 43.1%; effluent color approximately 842 times, color removal rate 89.2%; effluent pH = 6.5.

[0054] Example 8

[0055] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0056] Treatment steps: (1) Add 2.0 g of HCl (31%) (i.e., 2.0 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 4.0 g of PAC (Al2O3 content ≥10%) (i.e., 4.0 kg / m³) 3 (2) Stir rapidly (400 rpm) for 2 minutes until the pH drops to 5.77; (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0057] Treatment results: effluent COD = 5671 mg / L, COD removal rate 52.1%; effluent color approximately 156 times, color removal rate 98.0%; effluent pH = 5.8.

[0058] Example 9

[0059] This embodiment provides a pretreatment method for chemical mechanical pulp wastewater from bamboo, including the following steps: Take 1.0 L of raw water from the chemical pulp of Cizhu bamboo. The water quality parameters are: COD=11850 mg / L, pH=10.22, color 7800 times, BOD5=3420 mg / L (BOD5 / COD=0.29), and temperature 28℃.

[0060] Treatment steps: (1) Add 2.0 g of HCl (31%) (i.e., 2.0 kg / m³) 3 (1) Stir quickly (400 rpm) for 2 minutes; (2) Add 5.0 g of PAC (Al2O3 content ≥10%) (i.e., 5.0 kg / m³) 3(2) Stir rapidly (400 rpm) for 2 minutes until the pH drops to 5.63; (3) Add 5.0 g (i.e., 5.0 kg / m³) of CPAM solution (molecular weight 12 million, concentration 0.2%). 3 (3) Stir slowly (60 rpm) for 1 minute; (4) Let stand for 30 minutes and then take the supernatant for testing.

[0061] Treatment results: effluent COD = 5603 mg / L, COD removal rate 52.7%; effluent color approximately 133 times, color removal rate 98.3%; effluent pH = 5.6.

[0062] Application Example 1 Using fixed conditions (HCl 2.0 kg / m³) 3 PAC 3.0 kg / m 3 CPAM 5.0 kg / m 3 A solution with a molecular weight of 12 million and a concentration of 0.2% was used to treat different batches of raw water from Cizhu Chemical pulp (COD 10500-14500 mg / L, pH 9.6-10.4) for 20 consecutive batches. The COD removal rate remained stable at 47.9%-52.0%, and the effluent pH remained stable within the range of 5.8-6.1. The results indicate that the process of this invention has strong tolerance to fluctuations in influent water quality and excellent operational stability.

[0063] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A pretreatment method for chemimechanical pulp wastewater from *Bambusa textilis*, characterized in that, Includes the following steps: Step 1: pH adjustment and initial precipitation of lignin. Hydrochloric acid is added to the chemimechanical pulp wastewater of bamboo under stirring conditions to adjust the pH value to 6.5±0.2, so that soluble lignin is initially precipitated, and primary treated wastewater is obtained. Step 2: Coagulation and deep precipitation of lignin. Polyaluminum chloride is added to the primary treated wastewater obtained in Step 1 under stirring conditions to adjust the pH value to 6.0±0.2, so that the soluble lignin can be further precipitated and the particles can be destabilized to obtain secondary treated wastewater. Step 3: Enhance flocculation and floc growth. Under stirring conditions, add cationic polyacrylamide aqueous solution to the secondary treated wastewater obtained in Step 2 to cause the precipitated lignin particles and colloids to aggregate into coarse flocs, thus obtaining flocculated wastewater. Step 4: Solid-liquid separation. The flocculated wastewater obtained in Step 3 is allowed to settle and the supernatant and sludge are separated to obtain pretreated wastewater.

2. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 1, characterized in that: In step one, the hydrochloric acid has a mass fraction of 31%, and the amount added is 1.0-3.0 kg of hydrochloric acid per cubic meter of bamboo chemimechanical pulp wastewater.

3. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 1, characterized in that: In step two, the Al2O3 content of polyaluminum chloride is above 10%, and the addition amount is 1.0-5.0 kg of polyaluminum chloride per cubic meter of primary wastewater.

4. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 1, characterized in that: The stirring speed in both steps one and two is 200-500 rpm, and the stirring time is 2-5 min.

5. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 1, characterized in that: In step three, the mass fraction of cationic polyacrylamide in the cationic polyacrylamide aqueous solution is 0.1%-0.3%.

6. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 5, characterized in that: The cationic polyacrylamide aqueous solution is added at a rate of 4.0-6.0 kg per cubic meter of secondary treated wastewater.

7. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 5, characterized in that: The cationic polyacrylamide has a molecular weight of 8 million to 15 million.

8. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 1, characterized in that: The stirring speed in step three is 40-80 rpm, and the stirring time is 1-3 min.

9. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 1, characterized in that: The settling time in step four is 1.0-3.0 hours.

10. The pretreatment method for chemimechanical pulp wastewater of *Cymbidium goeringii* as described in claim 1, characterized in that: The COD of the chemimechanical pulp wastewater from Cizhu bamboo is 10,000-15,000 mg / L, the pH value is 9.5-10.5, the temperature is 25-35℃, and the BOD5 / COD ratio is below 0.

3. The COD of the pretreated wastewater is below 6000 mg / L, and the BOD5 / COD ratio is above 0.45.