Method for treating nitrile-containing wastewater by wet method

Abstract

The application discloses a treatment method of wet nitrile-containing sewage, which comprises the following steps: step 1, adding terephthalic acid sewage and ethylene glycol sewage into the nitrile-containing sewage to obtain first mixed sewage, and the concentration of acrylonitrile in the first mixed sewage is not more than 10 mg / L; step 2, adding calcium salt, nitrogen salt and phosphorus salt into the first mixed sewage, and adjusting the pH value to 6-8 to obtain second mixed sewage; step 3, making the second mixed sewage carry out anaerobic reaction in an anaerobic device inoculated with anaerobic sludge; step 4, monitoring the concentrations of acrylonitrile, terephthalic acid and COD in the effluent of the anaerobic device; if it is determined that the concentration of acrylonitrile is less than 5 mg / L, and the removal rates of terephthalic acid and COD are greater than 50%, then domesticating the anaerobic sludge, and repeating steps 1-4. The treatment method is economic, efficient, environment-friendly, low in carbon emission, and can effectively remove acrylonitrile in the nitrile-containing sewage.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of water treatment, and particularly relates to a treatment method of wet-process nitrile-containing wastewater. BACKGROUND

[0002] The wet-process nitrile-containing wastewater refers to the process wastewater produced by the one-step and two-step wet process of producing acrylic fiber, using acrylonitrile, methyl acrylate and sodium methallyl sulfonate as raw materials, and using NaSCN (sodium thiocyanate) as a spinning dope preparation solvent. The wastewater mainly includes one-step nitrile-containing wastewater, two-step nitrile-containing wastewater, and wastewater from the polymerization, dope, and bath adjustment processes in the acrylic fiber production process. The main components include acrylonitrile, methyl acrylate, butanedinitrile, 2-aminobenzene thiol, o-xylene, 3-methylthiopropionitrile, and sodium methallyl sulfonate. The wastewater mainly contains nitrile-containing wastewater and does not contain acid and alkali wastewater. The concentration of sodium thiocyanate is very low, the CODcr is about 1500 mg / L, the concentration of acrylonitrile fluctuates greatly, about 20-2000 mg / L, the average concentration is about 70 mg / L, and the water temperature is about 40℃.

[0003] The common treatment method for the wet-process nitrile-containing wastewater is to first flocculate and precipitate, and then hydrolyze and acidify and perform aerobic biochemical treatment, i.e. the AO biochemical method. Some wastewater is treated by Fenton or ozone catalytic oxidation. The disadvantages of these methods are that the actual effect of flocculation and precipitation is not ideal, and the residual acrylonitrile and other difficult-to-degrade and toxic organic substances greatly inhibit the subsequent biochemical microorganisms. The AO method has a certain effect, but still needs to provide dissolved oxygen by aeration, cannot produce biogas, instead produces a large amount of residual sludge and waste gas, the concentration of acrylonitrile in the waste gas is very high, it is very difficult to treat the waste gas to meet the standard, the carbon emission to the atmosphere is very high, the COD volume load is very low, the structure occupies a large area, a secondary sedimentation tank is needed, carbon source needs to be added, and the operation cost is high. The problems of the Fenton method and the ozone catalytic oxidation method are that the operation cost such as reagents and power consumption is very high, the use of hydrogen peroxide has safety hazards, and the use of ferrous sulfate produces a large amount of sludge. SUMMARY

[0004] The purpose of the present application is to provide a treatment method of wet-process nitrile-containing wastewater, which is economic, efficient, environmentally friendly, low in carbon emission, can effectively remove acrylonitrile in the nitrile-containing wastewater, does not affect the subsequent biochemical treatment, does not produce a large amount of waste gas with high concentration of acrylonitrile to cause subsequent difficulty in treatment, also has the removal of COD, is stable in operation, high in treatment load, low in reagent and energy consumption cost, low in residual sludge, and small in occupied area.

[0005] The method for treating wet nitrile-containing wastewater of the present application comprises: step 1: adding terephthalic acid wastewater and ethylene glycol wastewater into the nitrile-containing wastewater to obtain first mixed wastewater, and the concentration of acrylonitrile in the first mixed wastewater is not more than 10 mg / L; step 2: adding calcium salt, nitrogen salt and phosphorus salt into the first mixed wastewater, and adjusting the pH value to 6-8 to obtain second mixed wastewater; step 3: allowing the second mixed wastewater to undergo anaerobic reaction in an anaerobic device inoculated with anaerobic sludge; step 4: monitoring the concentrations of acrylonitrile, terephthalic acid and COD in the effluent of the anaerobic device; if it is determined that the concentration of acrylonitrile is less than 5 mg / L, and the removal rates of terephthalic acid and COD are greater than 50%, then domesticating the anaerobic sludge, and repeating steps 1 to 4, and increasing the concentration of acrylonitrile each time step 1 is repeated, until the concentration of acrylonitrile in step 1 is increased to 35-50 mg / L.

[0006] In some embodiments, the concentration of acrylonitrile each time step 1 is repeated is 1.45-1.55 times the concentration of acrylonitrile in the previous step 1.

[0007] In some embodiments, in the initial step 1, the ratio of the total volume of the terephthalic acid wastewater and the ethylene glycol wastewater to the volume of the nitrile-containing wastewater is 9:1; steps 1 to 4 are repeated until the ratio of the total volume of the terephthalic acid wastewater and the ethylene glycol wastewater to the volume of the nitrile-containing wastewater in step 1 is 1:1.

[0008] In some embodiments, if it is determined that the concentration of acrylonitrile is not less than 5 mg / L, and the removal rates of terephthalic acid and COD are not more than 50%, then the concentration of acrylonitrile in the first mixed wastewater is reduced and / or the mass of the anaerobic sludge is increased and / or the reflux ratio of the anaerobic device is increased.

[0009] In some embodiments, the COD concentration of the wet nitrile-containing wastewater is 1000-2000 mg / L, and the concentration of acrylonitrile is 20-2000 mg / L; the COD concentration of the terephthalic acid wastewater is 4000-10000 mg / L, and the concentration of terephthalic acid is 500-2000 mg / L; the COD concentration of the ethylene glycol wastewater is 1000-3500 mg / L; in the initial step 1, the COD concentration when the terephthalic acid wastewater and the ethylene glycol wastewater are mixed is 4000-6000 mg / L.

[0010] In some embodiments, in the initial step 1, the volume ratio of the terephthalic acid wastewater to the ethylene glycol wastewater is 2:1.

[0011] In some embodiments, in the second mixed sewage, the molar ratio of carbon element, nitrogen element and phosphorus element is (400-1000):(4-5):1, the concentration of calcium ions is 70-100 mg / L, the calcium salt includes calcium chloride, the nitrogen salt includes urea, and the phosphorus salt includes disodium hydrogen phosphate.

[0012] In some embodiments, during the anaerobic reaction, the temperature of the second mixed sewage is controlled at 33°C to 39°C, the rising velocity of the second mixed sewage is 3.5 to 10 m / h, the hydraulic retention time is 5 to 10 hours, the COD volumetric load is 5 to 9 g / L·d, and the sludge load is 0.2 to 0.6 COD / gVSS·d. The hydraulic retention time is the average residence time of the second mixed sewage in the anaerobic reactor, which is numerically equal to the effective volume of the anaerobic reactor divided by the influent flow rate of the second mixed sewage.

[0013] In some embodiments, the anaerobic device is a combined reactor, including: a regulating tank, which mixes the nitrile-containing wastewater, purified terephthalic acid wastewater and ethylene glycol wastewater to obtain a uniform first mixed wastewater and output it; a circulation tank, which inputs the first mixed wastewater and converts it into the second mixed wastewater and outputs it; an anaerobic reactor, which is inoculated with anaerobic sludge and inputs the second mixed wastewater to allow the second mixed wastewater to undergo anaerobic reaction, output biogas and waste gas, and discharge water.

[0014] In some embodiments, the anaerobic reaction tank includes a first-layer three-phase separator and a second-layer three-phase separator, wherein: the first-layer three-phase separator includes a primary three-phase separator and a secondary three-phase separator provided with external circulation, and the effluent of the first-layer three-phase separator is returned to the bottom inlet of the anaerobic reactor, and the reflux ratio is 5 to 8 times; the effluent of the second-layer three-phase separator is returned to the circulation tank and then enters the anaerobic reactor, and the reflux ratio is 2 to 3 times.

[0015] In some embodiments, the anaerobic reactor has a height-to-diameter ratio greater than 3.

[0016] In some embodiments, the anaerobic device further comprises: a biogas desulfurization tower for receiving the biogas output from the anaerobic reactor and performing desulfurization; and a biogas burner for burning the desulfurized biogas.

[0017] In some embodiments, the regulating tank, circulation tank, anaerobic reactor, biogas desulfurization tower and biogas burner are all fully enclosed, the biogas generated by the anaerobic reactor is subjected to gas-liquid separation, collection and recovery, and the waste gas volatilized from the top of the anaerobic reactor is collected and disposed of, and the waste gas volume is 5 to 10 m 3 / h, the concentration of acrylonitrile in the exhaust gas is 0.4~1mg / m 3 .

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] (1) The wet process nitrile-containing wastewater is mixed with PTA wastewater and ethylene glycol wastewater for treatment. The concentration of toxic organic matter such as acrylonitrile is controlled by using PTA and ethylene glycol wastewater, anaerobic microorganisms are gradually domesticated, and the influence of acrylonitrile polymers is eliminated, ultimately achieving a more ideal treatment effect on acrylonitrile and terephthalic acid.

[0020] (2) Through the direct degradation of anaerobic sludge, acrylonitrile in nitrile-containing wastewater is removed, so that a large amount of waste gas with high acrylonitrile concentration is not produced, which greatly reduces the difficulty of subsequent waste gas treatment to meet standards, significantly improves the on-site air environment, reduces carbon emissions, and also produces biogas to achieve energy recovery.

[0021] (3) Utilize a large height-to-diameter ratio, device-based, and enclosed anaerobic sludge reactor to directly treat wet nitrile-containing wastewater without the need for aeration and resulting in a small amount of waste gas; the treatment load is high and the residence time is short; there is no residual sludge, no need for a sedimentation tank or sludge return, and the footprint is small; no external carbon source or flocculant is required, resulting in low operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figure is a flow chart of a method for treating nitrile-containing wastewater by a wet method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solutions in this application, the present invention will be further described below in conjunction with the following embodiments. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of this application.

[0024] The present invention is further described below through some specific examples.

[0025] The removal rate described in the embodiment of the present invention is defined as follows: Removal rate = (influent concentration - effluent concentration) / influent concentration.

[0026] The inlet water quality of the wet process nitrile-containing wastewater, PTA wastewater (purified terephthalic acid wastewater) and ethylene glycol wastewater used in the examples of this application is:

[0027] Wet nitrile-containing wastewater: COD is 1000-2000 mg / L; acrylonitrile concentration is 20-2000 mg / L; pH is 6-7; temperature is 30℃-50℃.

[0028] PTA wastewater: COD is 4000-6000 mg / L; the concentration of terephthalic acid is 500-2000 mg / L; pH is 5-6; temperature is 45℃-60℃.

[0029] Ethylene glycol wastewater: COD is 1000-3500 mg / L; pH is 7-11; temperature is 25-38°C.

[0030] Example 1

[0031] refer to Figure 1 Wet-process nitrile-containing wastewater, PTA wastewater, and ethylene glycol wastewater are separately placed in three ton barrels. A pump is used to distribute the first mixed wastewater, with the volume of the nitrile-containing wastewater to the total volume of the terephthalic acid wastewater and the ethylene glycol wastewater being 1:9. This mixed wastewater is then fed into a regulating tank 1, mechanically agitated and homogenized, and then pumped into a circulation tank 2 at an inflow rate of 400 L / d. Urea, disodium hydrogen phosphate, and calcium salt are added to circulation tank 2 to achieve a molar ratio of carbon, nitrogen, and phosphorus of (400-1000):(4-5):1, and a calcium ion concentration of 70-100 mg / L. 30% by mass of sodium hydroxide is added to adjust the pH to 6-8. The wastewater is then pumped into an anaerobic reactor 3 for anaerobic reaction. The effective volume of the anaerobic reactor 3 is 170 liters, the diameter is 0.3m, and the height is 2.4m. It is pre-inoculated with about 40 liters of granular sludge. The effluent from the first three-phase separator is partially returned to the bottom inlet of the reactor, with a reflux ratio of 5 to 8 times; the effluent from the second three-phase separator is partially returned to the circulation tank, with a reflux ratio of 2 to 3 times.

[0032] The circulation tank uses mechanical stirring to mix the influent and the return water from the anaerobic reactor. The operation time is 1 to 2 months.

[0033] Example 2

[0034] When it is determined that the concentration of acrylonitrile in the effluent of the anaerobic device is less than 5 mg / L and the removal rates of terephthalic acid and COD are greater than 50%, the concentration of acrylonitrile is increased so that the ratio of the volume of the acrylonitrile-containing wastewater to the total volume of the PTA wastewater and the ethylene glycol wastewater is 1:6. The process is operated for 1 to 2 months according to the method of Example 1, and the disintegrated fine mud is continuously discharged to retain the acclimated sludge.

[0035] Example 3

[0036] When it is determined that the concentration of acrylonitrile in the effluent of the anaerobic device is less than 5 mg / L and the removal rates of terephthalic acid and COD are greater than 50%, the concentration of acrylonitrile is continued to be increased so that the ratio of the volume of nitrile-containing wastewater to the total volume of PTA wastewater and ethylene glycol wastewater is 1:3, and the process is operated for 1 to 2 months according to the method of Example 1.

[0037] Example 4

[0038] When it is determined that the concentration of acrylonitrile in the effluent of the anaerobic device is less than 5 mg / L and the removal rates of terephthalic acid and COD are greater than 50%, the concentration of acrylonitrile is continued to be increased so that the ratio of the volume of nitrile-containing wastewater to the total volume of PTA wastewater and ethylene glycol wastewater is 1:2, and the process is operated for 1 to 2 months according to the method of Example 1.

[0039] Example 5

[0040] When it is determined that the concentration of acrylonitrile in the effluent of the anaerobic device is less than 5 mg / L and the removal rates of terephthalic acid and COD are greater than 50%, the concentration of acrylonitrile is continued to be increased until the ratio of the volume of the acrylonitrile-containing wastewater to the total volume of the PTA wastewater and the ethylene glycol wastewater is 1:1, and the process is operated for 1 to 2 months according to the method of Example 1.

[0041] The influent conditions and anaerobic reaction process conditions of Examples 1 to 5 are shown in Tables 1 and 2. The treatment effects of organic pollutants are shown in Table 3.

[0042] Table 1 Water inlet conditions

[0043]

[0044] Table 2 Anaerobic reaction process conditions

[0045]

[0046] Table 3 Treatment results of organic pollutants

[0047] Example Acrylonitrile removal rate TA removal rate COD removal rate 1 98.05％ 51.59％ 53.69％ 2 98.89％ 53.28％ 50.64％ 3 90.34％ 49.51％ 51.14％ 4 94.80％ 49.45％ 45.95％ 5 99.05％ 62.59％ 50.83％

[0048] Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for treating wet-process nitrile-containing sewage, characterized in that, include: Step 1: adding terephthalic acid wastewater and ethylene glycol wastewater to nitrile-containing wastewater to obtain first mixed wastewater, wherein the concentration of acrylonitrile in the first mixed wastewater does not exceed 10 mg / L; Step 2: adding calcium salt, nitrogen salt and phosphate salt to the first mixed sewage, and adjusting the pH value to 6-8 to obtain second mixed sewage; Step 3: subjecting the second mixed sewage to an anaerobic reaction in an anaerobic device inoculated with anaerobic sludge; Step 4: monitoring the concentrations of acrylonitrile, terephthalic acid, and COD in the effluent of the anaerobic device; If it is determined that the concentration of acrylonitrile is less than 5 mg / L and the removal rates of terephthalic acid and COD are greater than 50%, the anaerobic sludge is acclimated and steps 1 to 4 are repeated, and the concentration of acrylonitrile is increased each time step 1 is repeated until the concentration of acrylonitrile in step 1 increases to 35-50 mg / L.

2. the treatment method of wet process nitrile-containing sewage as claimed in claim 1, is characterized in that, If it is determined that the concentration of acrylonitrile is not less than 5 mg / L and the removal rates of terephthalic acid and COD do not exceed 50%, the concentration of acrylonitrile in the first mixed sewage is reduced and / or the quality of the anaerobic sludge is increased and / or the reflow ratio of the anaerobic device is increased.

3. the treatment method of wet process nitrile-containing sewage as claimed in claim 1, is characterized in that, The COD concentration of the wet nitrile-containing wastewater is 1000-2000 mg / L, and the concentration of acrylonitrile is 20-2000 mg / L; the COD concentration of the terephthalic acid wastewater is 4000-10000 mg / L, and the concentration of terephthalic acid is 500-2000 mg / L; the COD concentration of the ethylene glycol wastewater is 1000-3500 mg / L; in the starting step 1, the COD concentration of the terephthalic acid wastewater and the ethylene glycol wastewater when mixed is 4000-6000 mg / L.

4. the treatment method of wet process nitrile-containing sewage as claimed in claim 1, is characterized in that, In the second mixed sewage, the molar ratio of carbon element, nitrogen element and phosphorus element is (400-1000):(4-5):1, the concentration of calcium ions is 70-100 mg / L, the calcium salt includes calcium chloride, the nitrogen salt includes urea, and the phosphorus salt includes disodium hydrogen phosphate.

5. the treatment method of wet process nitrile-containing sewage as claimed in claim 1, is characterized in that, During the anaerobic reaction, the temperature of the second mixed sewage is controlled at 33°C to 39°C, the rising flow rate of the second mixed sewage is 3.5 to 10 m / h, the hydraulic retention time is 5 to 10 hours, the COD volume load is 5 to 9 g / L·d, and the sludge load is 0.2 to 0.6 COD / gVSS·d.

6. The method for treating wet-process nitrile-containing sewage as claimed in claim 1, wherein The anaerobic device is a combined reactor, comprising: A regulating tank is used to mix the nitrile-containing wastewater, purified terephthalic acid wastewater and ethylene glycol wastewater to obtain a uniform first mixed wastewater and output the mixed wastewater; a circulation tank, inputting the first mixed sewage and converting it into the second mixed sewage for output; The anaerobic reactor is inoculated with anaerobic sludge and inputs the second mixed sewage to make the second mixed sewage undergo anaerobic reaction, output biogas and waste gas and discharge water.

7. The method for treating wet-process nitrile-containing sewage as claimed in claim 6, wherein: The anaerobic reaction tank includes a first-layer three-phase separator and a second-layer three-phase separator, wherein: The first three-phase separator includes a primary three-phase separator and a secondary three-phase separator provided with external circulation, and the effluent of the first three-phase separator is returned to the bottom inlet of the anaerobic reactor, and the reflux ratio is 5 to 8 times; The effluent from the second three-phase separator is returned to the circulation tank and then enters the anaerobic reactor, with a reflux ratio of 2 to 3 times.

8. The method for treating wet-process nitrile-containing sewage as claimed in claim 6, wherein: The anaerobic reactor has a height-to-diameter ratio greater than 3.

9. The method for treating wet-process nitrile-containing sewage as claimed in claim 6, wherein: The anaerobic device also includes: A biogas desulfurization tower, used for receiving the biogas output from the anaerobic reactor and performing desulfurization; Biogas burner, used to burn desulfurized biogas.

10. The method for treating wet nitrile-containing sewage according to claim 9, wherein: The regulating tank, circulation tank, anaerobic reactor, biogas desulfurization tower and biogas burner are all fully enclosed, and the biogas is collected and recycled by gas-liquid separation. The waste gas volatilized from the top of the anaerobic reactor is collected and disposed of, and the waste gas volume is 5 to 10 m 3 / h, the concentration of acrylonitrile in the exhaust gas is 0.4~1mg / m 3 .

Images