Method for treating oily wastewater in rail transit production and maintenance process

Abstract

The invention provides a method for treating oily wastewater in the production and maintenance process of rail transit, which comprises the following steps: carrying out cleaning, drying, cutting and microwave treatment on waste cotton-based textiles of rail transit to obtain a waste cotton-based textile material, and carrying out ball milling treatment to obtain a pretreated waste cotton-based textile material; carrying out pyrolysis carbonization treatment on the cotton fiber biochar under a high-temperature condition to obtain cotton fiber biochar; the cotton fiber biochar is added into the oily wastewater in the production and maintenance process of the rail transit, and adsorption and oil removal treatment are carried out. The method provided by the invention not only realizes resource utilization of a large amount of waste textiles in rail transit, but also provides a new solution for the environmental pollution problem caused by oil-containing wastewater in a rail transit system. The scheme of treating waste with waste has important value and significance on recycling of waste and treatment of pollutants in rail transit, sustainable development of rail transit is facilitated, and the method has wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of oily wastewater treatment, and relates to a method for treating oily wastewater in the process of rail transit production and maintenance, and specifically relates to a method for treating rail transit oily wastewater by utilizing waste textile fiber materials generated by rail transit. Background Art

[0002] Rail transit includes traditional railways (ordinary railways, intercity railways and urban railways), subways, light rails and trams, as well as new rail transit such as magnetic levitation rail systems and monorail systems. During the production and maintenance of these rail transit systems, a large amount of oily wastewater will be generated. These oily wastewaters have the problems of low oil pollutant concentration (50-500 mg / L), mainly small-particle emulsified oil (0.1-10 μm) and dissolved oil (<0.1 μm), and are difficult to treat and have high treatment costs.

[0003] Common treatment processes for oily wastewater generated by rail transit include regulated sedimentation, oil separation, and flotation processes. Among them, the grease trap method is based on the density difference between oil and water and the immiscibility of the two to separate heavier oil droplets from water. This method has the characteristics of a wide range of applications and the ability to remove oil and suspended solids at the same time, but the effluent usually contains more pollutants such as emulsified oil and dissolved oil. The centrifugal method can efficiently remove suspended oil, but the removal effect on dissolved oil and emulsified oil is poor. The oil displacement agent method is to add surfactants to dissolve the oil floating on the surface of the wastewater in the water. This method not only fails to effectively eliminate oil substances, but may also cause more serious subsequent pollution. In addition, these processes also have the disadvantages of large land occupation and high civil engineering and equipment investment.

[0004] In recent years, with the continuous upgrading and improvement of rail transit vehicle maintenance technology, the amount of wastewater discharged from production has gradually decreased, and the content of pollutants such as petroleum in wastewater has gradually decreased. The idleness of oily wastewater treatment facilities built according to traditional technology is relatively prominent. In the context of green construction and cost-saving and efficiency-enhancing requirements, the treatment technology of rail transit oily wastewater also needs to be constantly adapted and adjusted.

[0005] The tens of thousands of kilometers of rail transit system provides great convenience for the production and life of billions of people every year. At the same time, its operation process also generates a large amount of waste textile materials, including waste seat sets, waste train bedding such as sheets, quilt covers, pillowcases, pillow cores and other textiles, waste work clothes, waste cotton-based sound insulation materials, and waste filter cotton, waste gloves, waste cotton yarn and other materials. These waste textiles have the characteristics of large production volume, high processing cost, and difficulty in being reused in traditional textile production. At present, it is urgent to develop new technologies for the treatment, disposal and reuse of textile waste to alleviate the problems of environmental pollution and resource waste caused by improper disposal.

[0006] Based on this, a method for treating oily wastewater in rail transit using waste textile fiber materials generated by rail transit as the main raw material is provided, which can not only realize the reuse of waste textile resources, but also provide a new low-cost and high-efficiency way to solve the oily wastewater in rail transit systems. It will have great application prospects and value, and is also a technical problem that needs to be solved urgently. Summary of the invention

[0007] The purpose of the present invention is to address the deficiencies of the prior art and provide a low-cost, high-efficiency method for treating oily wastewater in the production and maintenance process of rail transit using waste textile fiber materials generated by rail transit as the main raw material.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for treating oily wastewater in the process of rail transit production and maintenance is provided, comprising the following steps: S1. Waste cotton-based textiles from rail transit are washed, dried, cut and microwaved to obtain waste cotton-based textile materials; S2, ball milling the waste cotton-based textile material to obtain a pretreated waste cotton-based textile material; S3, subjecting the pretreated waste cotton-based textile material to pyrolysis carbonization treatment at 300-700° C. for 1-5 h to obtain cotton fiber biochar; S4. Adding the cotton fiber biochar into the oily wastewater produced during the production and maintenance of rail transit for adsorption and oil removal.

[0009] The general idea of ​​the present invention is as follows: The present invention aims at the high cost of processing a large amount of waste textile materials generated by rail transit, which are difficult to reuse, and the large land occupation, high civil engineering and equipment investment in the treatment of oily wastewater generated by rail transit by traditional processes. The present invention provides a method for preparing cotton fiber biochar using waste cotton-based textiles from rail transit as raw materials, and then using cotton fiber biochar to adsorb and deoil oil-containing wastewater in the production and maintenance process of rail transit. The method can reduce textile pollution while achieving low-cost and high-efficiency removal of petroleum substances in urban railway wastewater.

[0010] In the present invention, firstly, the waste cotton-based textiles of rail transit are pretreated, and microwave treatment is used to reduce their surface energy and increase the fiber void structure, and then ball milling is used to increase the surface roughness of the cotton-based textiles, so as to facilitate the agglomeration, adsorption and removal of oil substances on their surface. Secondly, the pre-treated waste cotton-based textile materials are placed under certain temperature conditions for pyrolysis and carbonization treatment. During the pyrolysis and carbonization process under inert gas atmosphere conditions, only a small part of the fibers in the waste cotton-based textile materials are carbonized, and the fiber structure of most cotton-based textiles is not destroyed. Its fiber skeleton structure is looser, the surface energy of the material is lower, and the hydrophobicity is stronger, which is more conducive to the agglomeration and removal of oil substances; finally, the cotton fiber biochar is added to the oily wastewater in the production and maintenance process of rail transit. Its strong hydrophobicity and strong lipophilicity make it easy to contact with the oil substances in the wastewater, carry out the adsorption process, and then achieve efficient adsorption and removal of oil pollutants in the oily wastewater.

[0011] Furthermore, in step S1, the waste cotton-based textiles of rail transit include one or more combinations of waste seat sets, waste train bedding (including textiles such as sheets, quilt covers, pillowcases, pillow cores, etc.), waste work clothes (also including gloves, hats, etc.), waste cotton-based sound insulation materials, waste filter cotton, and waste cotton threads.

[0012] Furthermore, in step S1, the thickness of the waste cotton-based textiles from rail transit is 0.5-3 cm, and the weight percentage of the cotton fibers contained therein is 80%-100%.

[0013] Further, in step S1, the power of the microwave treatment is 100-800 W, and the time of the microwave treatment is 3-30 min. Preferably, the power of the microwave treatment is 300-550 W, and the time is 10-20 min. By optimizing and adjusting the parameters in the microwave treatment process, the surface energy of the cotton-based textile material can be reduced and the fiber void structure can be increased.

[0014] Further, in step S2, the rotation speed of the ball milling treatment is 1000-5000 rpm, and the time of the ball milling treatment is 0.5-3 hours. Preferably, the rotation speed of the ball milling treatment is 1000-3000 rpm, and the time is 0.5-1 hour. By optimizing and adjusting the parameters in the ball milling process, it is beneficial to improve the roughness of the pretreated waste cotton-based textile material.

[0015] Furthermore, in step S3, the pyrolysis carbonization treatment is carried out under an inert atmosphere at a heating rate of 4-6°C / min.

[0016] Furthermore, in step S3, the product of the pyrolysis and carbonization treatment is cooled to room temperature and then taken out, and the cooled product is sieved to obtain cotton fiber biochar, which has a block-like three-dimensional structure and a particle size of 0.3-2 cm.

[0017] In the present invention, waste cotton-based textiles with a high cotton content are used as raw materials for biochar, which is low in cost compared with synthetic high molecular polymers; at the same time, since it does not require petroleum as a raw material, it can save energy consumption. In addition, the main components of waste cotton-based textiles are cellulose substances, and the main elements are carbon, hydrogen, and oxygen. When these natural products are burned in an incinerator after absorbing petroleum substances, they rarely produce air pollutants such as nitrogen oxides or sulfur oxides. However, when high molecular adsorption materials with polyurethane, polyamide, etc. as the main components are burned, they will produce air pollutants such as nitrogen oxides, which are easy to cause secondary pollution.

[0018] Further, in step S4, the amount of cotton fiber biochar added to the oily wastewater is 0.1-10 g / L. Preferably, the amount of cotton fiber biochar added to the oily wastewater is 0.3-5 g / L.

[0019] Furthermore, in step S4, the time for adsorption and oil removal treatment is 1-72 hours, preferably 1-24 hours, and more preferably 1-3 hours. Specifically, it can be flexibly adjusted according to the oil concentration in the oily wastewater and the amount of cotton fiber biochar added.

[0020] Furthermore, in step S4, the oily wastewater includes oily wastewater generated during the production and maintenance of urban rail, urban subway and national railway.

[0021] Furthermore, in step S4, the concentration of oil pollutants in the oily wastewater is 50-500 mg / L, and the oil pollutants include petroleum and diesel pollutants. At present, with the continuous upgrading and improvement of rail transit vehicle maintenance technology, the content of pollutants such as petroleum in wastewater has gradually decreased, basically maintaining in the range of 50-500 mg / L. The method provided by the present invention has a very good treatment effect for wastewater with a low concentration of oil pollutants. At the same time, compared with traditional treatment processes, it has the advantages of small site occupation, no reliance on and use of complex equipment, and low treatment cost.

[0022] In some special cases, when the concentration of oil pollutants in the oily wastewater during rail transit production and maintenance reaches 500 mg / L or above, the method provided by the invention can be combined with traditional methods such as the grease trap method or the centrifugal method to achieve effective treatment of the oily wastewater.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for treating oily wastewater in the process of rail transit production and maintenance. The waste textile fiber materials generated by the rail transit system are used as the main raw materials to prepare cotton fiber biochar. Compared with synthetic materials, it has the advantages of low cost and reduced environmental pollution. Compared with other natural products, cotton fiber biochar retains the skeleton structure of cotton fiber. The inside of the cotton fiber skeleton is porous and has a larger specific surface area, providing enough adsorption sites and thus having a larger adsorption capacity and special adsorption characteristics. In addition, on a macro scale, cotton fiber biochar also retains the spatial network structure of cotton fibers interwoven together. After pyrolysis and carbonization treatment, there are relatively large gaps between the fiber skeletons, and water can flow freely between the fiber skeletons almost without hindrance. The polluted water can fully and quickly exchange substances with the fibers, and quickly transfer the petroleum pollutants in the wastewater to the tiny holes in each fiber. The petroleum pollutants with a certain viscosity will also adhere between the fiber skeletons, thereby generating additional adsorption and increasing their adsorption capacity.

[0024] (2) The present invention provides a method for treating oily wastewater generated during the production and maintenance of rail transit. In view of the problems that the oily wastewater generated during the production and maintenance of rail transit at this stage has a low concentration of oil pollutants (50-500 mg / L), the oil form is mainly small-particle emulsified oil (0.1-10 μm) and dissolved oil (<0.1 μm), and it is difficult to treat and has a high treatment cost, the present invention optimizes and improves the conventional oil removal process in combination with water quality characteristics, improves the oil removal efficiency of the core process, and makes the oily wastewater treatment process smoother, simpler, less space-consuming, less investment, lower operating costs, and more convenient to manage.

[0025] (3) The present invention provides a method for treating oily wastewater in the process of rail transit production and maintenance. The waste textile fiber materials generated by the rail transit system are used as the main raw materials to prepare cotton fiber biochar, and then the cotton fiber biochar is used as a high-efficiency oil removal material for the adsorption and treatment of oily wastewater in the process of rail transit production and maintenance. This method not only realizes the resource utilization of a large amount of waste textile resources in rail transit, but also provides a new solution to the environmental pollution problem caused by oily wastewater in the rail transit system. This "waste treatment" solution has important value and significance for the recycling of waste and the treatment of pollutants in rail transit, is conducive to the sustainable development of rail transit, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1The SEM images of the cotton fiber biochar prepared in Example 1 of the present invention are as follows; wherein, (a) is an image of the cotton fiber biochar under the condition of a scale of 50 microns, (b) is an image of the cotton fiber biochar under the condition of a scale of 20 microns, (c) is an image of the cotton fiber biochar under the condition of a scale of 10 microns, (d) is an image of the cotton fiber biochar under the condition of a scale of 5 microns, (e) is an image of the cotton fiber biochar under the condition of a scale of 2 microns, and (f) is an image of the cotton fiber biochar under the condition of a scale of 0.5 microns; Figure 2 The XRD patterns of cotton fiber biochar and coconut shell biochar prepared in Example 1 of the present invention; wherein (a) is cotton fiber biochar, and (b) is coconut shell biochar; Figure 3 FTIR images of cotton fiber biochar and coconut shell biochar prepared in Example 1 of the present invention; Figure 4 The characteristic diagram of the contact angle of cotton fiber biochar on the water surface prepared in Example 1 of the present invention; wherein (a)-(c) are angle tests during the contact between the cotton fiber biochar surface and water droplets; (d) is the average contact angle test result of cotton fiber biochar on the water surface; Figure 5 This is a characteristic diagram of the contact angle of the cotton fiber biochar prepared in Example 1 of the present invention on the oil surface within 0-200 ms; Figure 6 This is the XPS graph of the cotton fiber biochar prepared in Example 1 of the present invention; Figure 7 This is a diagram showing the treatment effect of the cotton fiber biochar prepared in Example 1 of the present invention at dosages of 1.5 g / L, 2.5 g / L, 3 g / L, and 4 g / L on simulated oily wastewater with an oil concentration of 50 mg / L. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0029] The embodiment of the present invention provides a method for treating oily wastewater in a rail transit production and maintenance process, comprising the following steps: Step 1: Wash the waste cotton-based textiles from rail transit with ultrapure water for 3-5 times, dry at 70-80° C., cut into suitable specifications, and treat with a 100-800 W microwave for 3-30 min to obtain a waste cotton-based textile material; Step 2: placing the waste cotton-based textile material in a ball mill, and ball milling the material at 1000-5000 rpm for 0.5-3 hours to obtain a pretreated waste cotton-based textile material; Step 3: placing the pretreated waste cotton-based textile material under the condition of 300-700°C for pyrolysis carbonization treatment for 1-5 h to obtain cotton fiber biochar; the pyrolysis carbonization treatment is carried out in a tubular furnace under a nitrogen atmosphere, and the heating rate is controlled to be 4-6°C / min; Step 4: Add the cotton fiber biochar at a dosage of 0.1-10 g / L into the oily wastewater (oil concentration of 50-500 mg / L) produced during rail transit production and maintenance, and perform adsorption treatment for 1-72 hours to complete the oil removal operation.

[0030] In each embodiment of the present invention, 0# diesel is dissolved with a surfactant (the amount of surfactant added is 2 g / L), and then dissolved in water by ultrasound, rapid stirring, etc. to prepare emulsified oil-containing wastewater with an oil concentration of 50-500 mg / L, which is used to simulate the oil-containing wastewater in the production and maintenance process of rail transit.

[0031] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0032] Example 1 This embodiment provides a method for treating oil pollutants in oily wastewater using waste cotton-based textiles, comprising the following steps: Step 1: The waste cotton-based sound insulation material (cotton content 98%) of rail transit was washed with ultrapure water for 5 times, dried at 75°C, and then cut into 2 cm × 2 cm specifications, and subjected to 500 W microwave treatment for 20 min to obtain the waste cotton-based textile material; Step 2: placing the waste cotton-based textile material in a ball mill and ball milling the material at 3000 rpm for 0.5 h to obtain a pretreated waste cotton-based textile material; Step 3: Place the pretreated waste cotton-based textile material in a tubular furnace, and heat it to 500 °C at a heating rate of 5 °C min-1 in a nitrogen atmosphere. Continue heating at 500 °C for 3 h. After cooling to room temperature, take it out and grind it to obtain cotton fiber biochar.

[0033] Figure 1 This is a SEM image of the cotton fiber biochar prepared in Example 1 of the present invention. Figure 1It can be seen that although the cotton-based fiber biochar material presents a three-dimensional multilayer structure as a whole, the length of some fiber skeletons is mainly around 10-40 μm ( Figure 1 ), has a certain specific surface area, and the surface of the material presents a corrugated shape with typical fiber characteristics. This three-dimensional multi-layer network structure is conducive to the adsorption, aggregation and efficient removal of oil substances on its surface.

[0034] Figure 2 XRD patterns of cotton fiber biochar and coconut shell biochar prepared in Example 1 of the present invention; Figure 2 It can be seen that for the XRD spectra of fiber biochar and coconut shell biochar, these two materials basically have no characteristic peaks and both are typical amorphous carbon material structures.

[0035] Figure 3 FTIR images of cotton fiber biochar and coconut shell biochar prepared in Example 1 of the present invention; Figure 3 The FTIR spectrum of cotton fiber biochar material shows that -1 、2831 cm -1 、1692 cm -1 and 1565 cm -1 It has strong characteristic absorption peaks, corresponding to the -CH2, C=O and C=C functional groups in the fibrous biochar material.

[0036] Figure 4 and Figure 5 The contact angle characteristic diagrams of the cotton fiber biochar prepared in Example 1 of the present invention on the water and oil surfaces are shown respectively. Figure 4 and Figure 5 It can be seen that the average contact angle between the cotton fiber biochar material and water reaches 145.2°; while the contact angle of the oil droplets on its surface is smaller, and the oil droplets can be quickly adsorbed by the fiber biochar material within 200ms. This fully demonstrates that the cotton fiber biochar material prepared by the present invention has strong hydrophobicity and lipophilicity, and is easy to contact with oil substances in wastewater, and then carry out the adsorption process.

[0037] Figure 6 This is the XPS graph of the cotton fiber biochar prepared in Example 1 of the present invention; Figure 6 From the XPS spectrum, it can be seen that the main components of the fiber biochar material are C, O, N, S and other elements. The main chemical components of cotton fiber biochar and coconut shell biochar are shown in Table 1.

[0038] Table 1 Comparison of main components of cotton fiber biochar and coconut shell biochar

[0039] It can be seen from Table 1 that the C element content of cotton fiber biochar is slightly lower than that of coconut shell biochar, and its H / C and N / C ratios are slightly higher than those of coconut shell biochar, indicating that the carbonization degree of cotton fiber biochar is higher and it has stronger hydrophobicity. Therefore, it has stronger affinity for non-polar oil pollutants and higher oil removal efficiency.

[0040] Step 4: The cotton fiber biochar was added to the simulated oily wastewater (oil concentration was 50 mg / L) at dosages of 1.5 g / L, 2.5 g / L, 3 g / L, and 4 g / L, respectively, and stirred and mixed, and adsorbed for 3 hours, and then the oil removal operation was performed, and the residual oil content in the simulated oily wastewater was reduced to 4.6 mg / L, 4.3 mg / L, 4.2 mg / L, and 3.4 mg / L, respectively, and the removal rates were 90.8%, 91.4%, 91.6%, and 93.2%, respectively. It can be seen that the cotton fiber biochar prepared by the present invention has a good oil removal effect, and a small dosage can achieve a good oil removal effect.

[0041] Example 2 This embodiment provides a method for treating oil pollutants in oily wastewater using waste cotton-based textiles, comprising the following steps: Step 1: The waste train bedding cotton sheets (100% cotton content) of rail transit were washed with ultrapure water for 4 times, dried at 80°C, and then cut into 2 cm × 2 cm specifications, and subjected to 300 W microwave treatment for 20 min to obtain waste cotton-based textile materials; Step 2: placing the waste cotton-based textile material in a ball mill and subjecting the material to ball milling treatment at 2000 rpm for 1 h to obtain a pretreated waste cotton-based textile material; Step 3: Place the pretreated waste cotton-based textile material in a tubular furnace, heat it to 300 °C at a heating rate of 4 °C min-1 in a nitrogen atmosphere, and continue heating at 300 °C for 5 h. After cooling to room temperature, take it out and grind it to obtain cotton fiber biochar.

[0042] Step 4: Add the cotton fiber biochar at a dosage of 3 g / L into the simulated oily wastewater (oil concentration is 50 mg / L), stir and mix, and adsorb for 3 hours to remove oil. According to the test, after 3 hours of adsorption and oil removal, the remaining oil content in the simulated oily wastewater was reduced to 4.8 mg / L, and the removal rate was 90.4%.

[0043] Example 3 This embodiment provides a method for treating oil pollutants in oily wastewater using waste cotton-based textiles, comprising the following steps: Step 1: The discarded work clothes (containing 95% cotton) from rail transit were washed with ultrapure water for three times, dried at 70°C, and then cut into 2 cm × 2 cm specifications, and subjected to 400 W microwave treatment for 15 min to obtain discarded cotton-based textile materials; Step 2: placing the waste cotton-based textile material in a ball mill and subjecting the material to ball milling treatment at 1000 rpm for 2 h to obtain a pretreated waste cotton-based textile material; Step 3: Place the pretreated waste cotton-based textile material in a tube furnace, heat it to 700 °C at a heating rate of 6 °C min-1 in a nitrogen atmosphere, and continue heating at 700 °C for 1 h. After cooling to room temperature, take it out and grind it to obtain cotton fiber biochar; Step 4: Add the cotton fiber biochar at a dosage of 3 g / L into the simulated oily wastewater (oil concentration is 50 mg / L), stir and mix, and adsorb for 3 hours to remove oil. According to the test, after 3 hours of adsorption and oil removal, the remaining oil content in the simulated oily wastewater was reduced to 4.4 mg / L, and the removal rate was 91.2%.

[0044] Example 4 The difference between this embodiment and embodiment 1 is that in step 4, the cotton fiber biochar is added to the simulated oily wastewater with an oil concentration of 50 mg / L in dosages of 0.1 g / L, 0.2 g / L, 0.3 g / L ... 3 g / L, respectively, the water temperature is controlled at 25°C, the wastewater pH is 6-8, and the adsorption reaction time is 3 hours.

[0045] After testing, when the dosage of cotton fiber biochar was 0.1g / L, the oil removal rate was 68.3%. With the increase of the dosage, the oil removal rate increased accordingly. When the dosage was 0.2 g / L, the oil removal rate increased to 76.5%. When the dosage was 3g / L, the oil removal rate reached 91.6%.

[0046] Example 5 The difference between this embodiment and embodiment 1 is that in step 4, the cotton fiber biochar is added at a dosage of 3 g / L to the simulated oily wastewater with an oil concentration of 250 mg / L, the water temperature is controlled at 25°C, the wastewater pH is 6-8, and the adsorption reaction time is 48h.

[0047] According to the test, when the dosage of cotton fiber biochar is 3 g / L, after 48 hours of long-term adsorption treatment, the oil removal rate can reach 91.4% for the simulated oily wastewater with an oil concentration of 250 mg / L.

[0048] Comparative Example 1 For simulated oily wastewater with an oil concentration of 50 mg / L, coal-based biochar, coconut shell biochar and commercial biochar were used for adsorption and oil removal, respectively, with an addition amount of 3 g / L and a treatment time of 3 h. The residual oil concentrations were 26.2 mg / L, 25.5 mg / L and 27.3 mg / L, respectively, and the removal rates were 47.6%, 49.0% and 45.5%, respectively. In contrast, the addition amount of cotton fiber biochar prepared by the present invention was 3 g / L, and the residual oil content in the simulated oily wastewater after treatment was reduced to 4.2 mg / L, and the removal rate reached 91.6%.

[0049] By comparison, it is found that the cotton fiber biochar prepared by the present invention has a significantly better removal effect on oil pollutants in simulated oily wastewater than the other three biochar materials. The removal rates of oil pollutants in simulated oily wastewater by different materials are shown in Table 2.

[0050] Table 2 Comparison of degreasing effects of different materials in Comparative Example 1

[0051] Comparative Example 2 For the simulated oily wastewater with an oil concentration of 50 mg / L, sponge material, bacterial cellulose, loofah and loofah biochar were used for adsorption and oil removal treatment, with the dosage of 3 g / L and the treatment time of 3 h.

[0052] The experimental results show that the concentration of oily wastewater in the sponge group and bacterial cellulose group was reduced to 9.4 mg / L and 4.6 mg / L, respectively, and the oil removal rates were 81.1% and 90.8%, respectively; in addition, the oil removal rates of loofah and loofah biochar were 90.7% and 90.1%, respectively. In contrast, when the dosage of cotton fiber biochar was 3 g / L and the treatment time was 3h, the residual oil content in the simulated oily wastewater after treatment was reduced to 4.2 mg / L, and the removal rate reached 91.6%. By comparison, under the same dosage conditions, cotton fiber biochar had a better removal effect on oil pollutants in simulated oily wastewater than the other four materials, and had a better application prospect. The removal rates of oil pollutants in simulated oily wastewater by different materials are shown in Table 3.

[0053] Table 3 Comparison of oil removal effects of different materials

[0054] In summary, The present invention uses waste textile fiber materials generated by the rail transit system as the main raw material to prepare cotton fiber biochar, which is then applied to the treatment of oily wastewater, and has the advantages of high oil removal efficiency and good oil removal effect. For simulated oily wastewater with an oil concentration of 50 mg / L, when the textile biochar dosage is 3 g / L, the oil removal rate reaches more than 90% after 3 hours of treatment time; for simulated oily wastewater with an oil concentration of 250 mg / L, by extending the treatment time, an oil removal rate of nearly 92% can also be achieved. Compared with conventional process methods for treating rail transit oily wastewater, the present invention has the advantages of convenient operation and management, low infrastructure investment, and low operating costs.

[0055] The present invention not only realizes the resource utilization of a large amount of waste textile resources in rail transit, but also provides a new treatment method for solving the environmental pollution problem caused by oily wastewater in rail transit systems. This "waste treatment with waste" solution has important value and significance for the recycling of waste and the control of pollutants in rail transit, is beneficial to the sustainable development of rail transit, and has broad application prospects.

[0056] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating oily wastewater in the process of rail transit production and maintenance, characterized in that: The following steps are involved: S1. Waste cotton-based textiles from rail transit are washed, dried, cut and microwaved to obtain waste cotton-based textile materials; S2, ball milling the waste cotton-based textile material to obtain a pretreated waste cotton-based textile material; S3, subjecting the pretreated waste cotton-based textile material to pyrolysis carbonization treatment at 300-700° C. for 1-5 h to obtain cotton fiber biochar; S4. Adding the cotton fiber biochar into the oily wastewater produced during the production and maintenance of rail transit for adsorption and oil removal.

2. The method according to claim 1, characterized in that In step S1, the waste cotton-based textiles of rail transit include one or more combinations of waste seat sets, waste train bedding, waste work clothes, waste cotton-based sound insulation materials, waste filter cotton, and waste cotton threads.

3. The method according to claim 1, characterized in that In step S1, the thickness of the waste cotton-based textiles from rail transit is 0.5-3 cm, and the weight percentage of the cotton fibers contained therein is 80%-100%.

4. The method according to claim 1, characterized in that In step S1, the power of the microwave treatment is 100-800 W, and the time of the microwave treatment is 3-30 min.

5. The method according to claim 1, characterized in that In step S2, the rotation speed of the ball milling treatment is 1000-5000 rpm, and the time of the ball milling treatment is 0.5-3 h.

6. The method according to claim 1, characterized in that In step S3, the pyrolysis carbonization treatment is carried out under an inert atmosphere at a heating rate of 4-6°C / min.

7. The method according to claim 1, characterized in that In step S4, the dosage of cotton fiber biochar in the oily wastewater is 0.1-10 g / L.

8. The method according to claim 1, characterized in that In step S4, the time for adsorption and oil removal treatment is 1-72 hours.

9. The method according to claim 1, characterized in that: In step S4, the oily wastewater includes oily wastewater generated during the production and maintenance of urban rail, urban subway and national railway.

10. The method according to claim 1, characterized in that In step S4, the concentration of oil pollutants in the oily wastewater is 50-500 mg / L.

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