CN114772871B

CN114772871B - Treatment method of polyoxymethylene production wastewater

Info

Publication number: CN114772871B
Application number: CN202210586365.1A
Authority: CN
Inventors: 刘霞; 卢毅明; 鲍磊; 朱核光; 徐祖武; 赵宁华
Original assignee: SHANGHAI ZHONGYAO ENVIRONMENTAL PROTECTION INDUSTRIAL CO LTD
Current assignee: SHANGHAI ZHONGYAO ENVIRONMENTAL PROTECTION INDUSTRIAL CO LTD
Priority date: 2022-05-27
Filing date: 2022-05-27
Publication date: 2023-07-25
Anticipated expiration: 2042-05-27
Also published as: CN114772871A

Abstract

The invention discloses a treatment method of wastewater from polyoxymethylene production, and relates to the technical field of polyoxymethylene wastewater treatment. The polyoxymethylene production wastewater sequentially passes through an adjusting tank, a polymerization reactor 1, a polymerization reactor 2, a pH callback tank, a cooling tower, a biological selector, an anaerobic hydrolysis composite reactor, an aerobic composite reactor, a radial flow sedimentation tank, a high-efficiency coagulation sedimentation tank and a heterogeneous Fenton oxidation reactor, and water and sludge are discharged. Adopts the formaldehyde-polysaccharide reaction principle to convert formaldehyde into three-carbon ketose or six-carbon hexose or derivatives thereof, eliminates the toxicity of the three-carbon ketose or six-carbon hexose to microorganisms, and improves the biodegradability of the wastewater. The formaldehyde-glycan reaction adopts a double-alkali method, namely, the pH is regulated, and the alkali metal alkali and the alkaline earth metal alkali are respectively adopted as the catalyst, so that the formaldehyde conversion rate is higher, the running cost is lower, and the scaling problem is avoided. The method is economical, efficient and stable, and the treated wastewater can be directly discharged.

Description

Treatment method of polyoxymethylene production wastewater

Technical Field

The invention relates to the technical field of polyoxymethylene wastewater treatment, in particular to a treatment method of polyoxymethylene production wastewater.

Background

Paraformaldehyde is an industrial raw material with wide application, and has many applications in synthesizing pesticides, synthetic resins and coatings and preparing fumigation disinfectants. The industrial synthesis method of paraformaldehyde is prepared by taking methanol as a raw material and adopting the steps of oxidation, catalytic polymerization and the like. The paraformaldehyde wastewater generated in the paraformaldehyde production process contains a large amount of formaldehyde, dimeric formaldehyde (DOX), trioxymethylene (TOX), methanol, sodium formate and other pollution components, and is typical high-concentration organic wastewater with poor biodegradability. Formaldehyde is a commonly used disinfectant, commonly known as formalin, which can cause protein denaturation, so that the formaldehyde has strong killing effect on bacteria and strong toxicity on human and animals. It is stated that the formaldehyde content of the secondary emission standard must not be higher than 2mg/L. If the concentration of formaldehyde in the wastewater is higher (more than or equal to 200 mg/L), the biodegradability of the wastewater can be seriously reduced, so that the wastewater containing formaldehyde, especially the organic wastewater containing high concentration formaldehyde, can be discharged only after the concentration of formaldehyde in the formaldehyde wastewater is reduced by adopting a targeted method and other components in the wastewater are removed by adopting an effective method.

At present, chemical, physical and chemical methods or a combination of several methods are generally adopted for treating formaldehyde-containing wastewater.

Chinese patent CN105819564 proposes a method for treating wastewater of paraformaldehyde, which uses a particulate carrier impregnated with noble metal (ruthenium, rhodium, or palladium) catalyst to treat the wastewater at about 200 ℃ and 2-4Mpa pressure, so that the organic matters in the wastewater are subjected to wet catalytic oxidation to be treated. The method is carried out at high temperature and high pressure, and has high requirements on a treatment device and high energy consumption.

Chinese patent CN105060553 discloses a method for treating formaldehyde wastewater, which comprises adding calcium hypochlorite into wastewater, stirring for 1-3 hours, and then adding hydrochloric acid or sulfuric acid to adjust the pH of the reacted liquid to 1-5. The invention does not disclose whether the wastewater after treatment needs to be subjected to neutralization treatment, but a large amount of calcium hypochlorite, acid and alkali are needed to be used in the reaction, and the corrosion protection requirement of the device is extremely high.

Chinese patent CN108246290 discloses an oxidation catalyst for removing formaldehyde from wastewater and a preparation method thereof. The new catalyst adopts manganese-based composite oxide as a carrier, and noble metal (ruthenium, rhodium, platinum or palladium) as a catalytic active component, so that formaldehyde can be adsorbed on the surface of a filter material at room temperature and converted into carbon dioxide and water. The method does not show whether the catalyst has a removal effect on other components in the wastewater.

Treatment of formaldehyde wastewater with hydrogen peroxide under alkaline conditions has been reported ("study on oxidation treatment of formaldehyde wastewater with basic hydrogen peroxide", yang Xiangyu, etc.), but hydrogen peroxide decomposes oxygen when it is heated or exposed to light, and oxygen is generated in large quantities to cause explosion of a closed container, so that potential safety hazard is caused in mass storage. Treatment of formaldehyde wastewater with ozone has also been reported ("research on photocatalytic degradation of formaldehyde in water by ozone", lu Jingxia, etc.), but ozone treatment requires the use of a catalyst or irradiation of ultraviolet light, and the effect of ozone alone is not ideal.

Chinese patent CN107879502 discloses a pretreatment method of formaldehyde wastewater, which comprises treating suspended solid SS of wastewater to less than 80mg/L by coagulating sedimentation, adjusting pH of wastewater to 2-6 with acid or alkali, adding Na at a certain molar ratio ₂ SO ₃ And reacted for 0.5 to 1 hour. The reaction reduces formaldehyde into alcohols, and the toxicity of the alcohols to organisms is smaller, so that the biodegradability of the wastewater can be improved, and the subsequent biochemical treatment is facilitated. The method needs to adopt coagulating sedimentation in advance, so that a part of organic matters are directly fed into the sediment sludge without biological treatment, and in addition, the pH is regulated to be acidic, so that the requirement on corrosion resistance of the device is high.

Chinese patent 201320863274.4 discloses a treatment method of formaldehyde-containing industrial wastewater, wherein wastewater, melamine and a catalyst enter a reaction kettle to carry out mixed reaction to generate crystals, then enter a multistage sedimentation tank to carry out sedimentation separation, supernatant and 40-70% raw formaldehyde are mixed to prepare 35-40% diluted formaldehyde, and the sediment is returned to the reaction kettle to be recycled. The method realizes zero emission, formaldehyde enters the subsequent products, but the reaction is only applicable to the situation that the formaldehyde waste liquid with high concentration is pure in components.

Chinese patent CN101830604 discloses a process for treating formaldehyde wastewater by using waste lye, wherein the wastewater enters a polymerization reaction tank after being uniformly mixed in a regulating tank, and industrial waste lye is added to adjust pH to 9 or higher, and steam is introduced to make the temperature reach 40 ℃ or higher. Under the condition, formaldehyde is polymerized to generate polysaccharide substances such as glucose and the like, and the residence time of the polysaccharide substances in a polymerization reaction tank is 0.1-80h. The method uses waste alkali, avoids Ca (OH) ₂ And calcium oxide is used as an alkaline agent for polymerization reaction, so that the treatment cost is reduced. However, the invention does not specifically mention the waste alkali composition, and the several examples of waste alkali listed are sodium-containing alkali, nor do they describe in detail the specific reactions that take place and the catalysts that are used, the residence time of the polymerization reaction that is specified being too wide to technically dictate the actual reaction time that is required for the polymerization reaction, equivalent to the fact that no specific technical regulations have been made.

Chinese patent CN112456716 discloses a pretreatment method of formaldehyde wastewater, wherein the formaldehyde wastewater enters a collecting tank, pH is regulated to 11-13 by alkali liquor such as NaOH, and the like, and the formaldehyde wastewater is preheated to 60-80 ℃, then enters a catalytic reaction tower, and a catalyst adopts solid CaCO ₃ And enabling formaldehyde to react for 3-5h, and finally, enabling the wastewater to enter a collecting tank to adjust the pH value to be neutral. The method introduces granular CaCO ₃ As a catalyst for the formose reaction, the cost is relatively low. But the patent does not disclose CaCO ₃ CaCO as a catalytic mechanism for the catalyst ₃ Solubility under alkaline conditions is extremely low, and a large amount of CaCO is required to allow the catalytic reaction to proceed thoroughly ₃ And requires the provision of a fixed bed reaction column, using a large amount of CaCO ₃ And can also cause fouling problems in the process equipment.

The conversion of formaldehyde into a carbohydrate by polymerization (known as the glycan reaction, i.e., the Formose process) is effected at a suitable temperature and with a suitable catalyst which is essentially complexed with formaldehyde or an intermediate of the reaction to alter the charge distribution of the formaldehyde or intermediate such thatThe polymerization of formaldehyde can take place. The formaldehyde polysaccharide reaction catalyst is various, and common catalysts include alkali metal, alkaline earth metal hydroxide and oxide, metal oxide or chloride, organic base (such as organic amine), thiazole salts and the like. The choice of catalyst and the conditions will lead to a different final product of the glycan reaction, for example if in Ca (OH) ₂ As a catalyst, formaldehyde polymerization involves multiple steps including aldol condensation, acyloin condensation, metathesis and cross-reaction to produce more than 30 products, including 2-carbon or 3-carbon methylaldehyde and ketose, and hexoses such as glucose, which are more selective if certain organic amine and thiazole salt catalysts are used, and the glycan reaction is more prone to ketose and hexose.

In summary, the existing formaldehyde wastewater treatment process generally adopts an oxidation method or a catalytic oxidation method to thoroughly oxidize and decompose formaldehyde into harmless CO ₂ And water, or formaldehyde is converted into saccharides and the like by polymerization of formaldehyde, and then treated by a biochemical method. The oxidation method is generally not specific to formaldehyde, other organic pollutants in the wastewater are oxidized, so that a large amount of oxidant is inevitably consumed, meanwhile, a catalyst is often needed in the complete oxidation reaction at normal temperature and normal pressure, the use of the catalyst not only increases the treatment cost, but also belongs to dangerous waste due to the fact that the catalyst generally contains rare earth or noble metal, and the final treatment cost of the dangerous waste is high. As formaldehyde wastewater, particularly high-concentration formaldehyde wastewater, the components and properties of the wastewater after polymerization reaction are special, the wastewater not only has high alkalinity and temperature, but also contains high-concentration saccharide substances and salt, the main organic matters treated by an activated sludge method in a common wastewater biological treatment process are proteins and low-molecular organic acids, and the post treatment process of the saccharide substances and the salt is not described.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for treating wastewater in polyoxymethylene production, which is economical, efficient and stable, and the treated wastewater can be directly discharged.

In order to achieve the above purpose, the present invention proposes the following technical scheme:

a method for treating wastewater from polyoxymethylene production comprises the following steps:

the polyoxymethylene production wastewater (wherein the concentration of formaldehyde can be up to more than 1000ppm and even thousands ppm) sequentially passes through an adjusting tank, a polymerization reactor 1, a polymerization reactor 2, a pH callback tank, a cooling tower, a biological selector, an anaerobic hydrolysis composite reactor, an aerobic composite reactor, a radial flow sedimentation tank, a high-efficiency coagulating sedimentation tank and a heterogeneous Fenton oxidation reactor, and water and sludge are discharged;

the polymerization reactor 1 is operated as follows: adding a catalyst into the wastewater produced by polyformaldehyde, adjusting the pH value by using alkali liquor, stirring, and carrying out polymerization reaction at 40-80 ℃. Preferably 50-60 ℃. The polymerization reactor 1 is provided with a stirring device, a pH probe and a temperature probe, the water temperature in the tank is increased by introducing water vapor or adopting electric heating, and when the temperature reaches a set value, the heating is stopped.

The molar ratio of the catalyst to formaldehyde in the wastewater from polyoxymethylene production is (0.1-1): 1. preferably (0.3-0.5): 1.

the catalyst is any alkaline earth metal hydroxide, preferably Ca (OH) ₂ Solutions or Mg (OH) ₂ The solution may be a waste liquid containing the component.

The alkali liquor is any alkali metal hydroxide, preferably NaOH solution or KOH solution, and can also be waste liquor containing alkali liquor. The pH is adjusted to be more than or equal to 9. Preferably 9-10.

In order to enable the reaction to be more thoroughly carried out, the waste water from the production of the polyoxymethylene enters the polymerization reactor 2 for further reaction, the polymerization reactor 2 is provided with a stirring device for mixing and stirring, and no reagent is added, so that the reaction conditions are more uniform, the residence time of the polymerization reactor 2 and the residence time of the polymerization reactor 1 can be equal to or longer than the former, but the total residence time of the two tanks is 3-14h. The choice of the total residence time is determined by the concentration of formaldehyde and the conversion to be achieved, the higher the concentration, the higher the conversion requirement and the longer the residence time required.

Further, acid liquor is added into the pH callback tank, the pH is adjusted to 7-8, and the addition amount is 1-4% of the COD mass in the polyoxymethylene production wastewater. The acid liquor is phosphoric acid, hydrochloric acid or sulfuric acid, or mixed acid or waste acid liquor containing the above acids, and the phosphoric acid is preferably added in the invention.

Further, the natural evaporation cooling tower is preferably selected as the cooling tower, water is cooled to 35-40 ℃, the circulating water quantity of the cooling tower and the air draft quantity of the axial flow fan are regulated according to the water temperature in the water collecting tank of the cooling tower, and the water temperature is ensured to be lower than 37 ℃ when the polyoxymethylene production wastewater enters the biological selector.

The cooled wastewater enters a biological selector. The biological selector further adjusts the nutrition ratio of the water quality, supplements necessary nitrogen sources (the adding amount of the nitrogen sources is determined by controlling the ratio of carbon, nitrogen and phosphorus), and adds nitrogen and phosphorus in the domestic sewage supplementary wastewater, so that the mass ratio of the biological oxygen demand (COD), the Total Nitrogen (TN) and the Total Phosphorus (TP) of the mixed wastewater is 100:5:1, such components are more beneficial to the growth metabolism of microorganisms; meanwhile, the reflux sludge discharged from the sedimentation tank also enters the biological selector, so that the reflux sludge and dissolved oxygen in raw water can be consumed as soon as possible under the action of microorganisms for aerobic respiration, and the anaerobic condition of a subsequent anaerobic hydrolysis reactor is formed. The traditional method is to reflux the sludge to the anaerobic tank, so that dissolved oxygen contained in the returned sludge can impact the operation of the anaerobic reaction tank to influence the operation effect of the anaerobic tank. Various autotrophic and heterotrophic microorganisms contained in the return sludge are used as inoculation flora to effectively grow and reproduce in a biological selector and a subsequent biochemical functional area, and various organic and inorganic nutrient components contained in the wastewater are effectively decomposed and utilized.

The wastewater from the biological selector automatically flows into the anaerobic hydrolysis composite reactor. The reactor adopts a hydraulic plug flow mixing reaction mode, a plurality of mixing reactors are arranged along the water flow direction, and power is provided to enable water to flow in a long and narrow channel in the reactor, so that the water levels of an inlet and an outlet are kept consistent. The arrangement ensures that the reaction device has enough transverse mixing effect to relieve the fluctuation of water quality and water quantity to the effluentImpact caused by water quality and reduction of oxygen mixed from air; meanwhile, due to the water quality change of different longitudinal positions, more kinds of microorganisms and hydrolytic enzymes can be enriched in the whole reactor, so that organic matters in the wastewater are hydrolyzed and acidified more thoroughly, more macromolecules are cut into small molecules, and the hydrolysis and acidification effects are ensured; and placing a filler in the anaerobic hydrolysis composite reactor. The filler has the function of providing an anchor carrier for microorganisms, so that more microorganisms (biofilms) in an anchor state can be accommodated in the reaction device, the concentration of microorganisms in the reactor is improved, the biological phases in the reactor are enriched, the volume load of the reactor is increased, and the load impact resistance of the reaction device is further improved. The sessile growth of hydrolytic acidification bacteria can also reduce the flow of the microorganisms into an aerobic reaction tank along with sewage, so that the biological phases of the microorganisms are more specific and stable, and the effect of the hydrolytic acidification process section is further ensured; the packing density is preferably such that at least 3-4 kg (dry solids) of equivalent microorganism sessile growth per cubic meter is provided. The filler used in the invention can be any wastewater treatment filler capable of providing microorganism fixation growth, and is preferably a ZYZX series lamination expansion microbial carrier produced by Shanghai Yao environmental protection and practice Co., ltd. The packing placement density when the microbial carrier is unfolded by using ZYZX lamination is 60/m ³ 。

The effluent of the anaerobic hydrolysis composite reactor automatically flows into the aerobic composite reactor. An aeration device is laid in the aerobic composite reactor for oxygen supply, and the aeration device adopts a microporous aerator preferentially. In the reaction unit, a large amount of heterotrophic bacteria degrade BOD and other components in sewage under aerobic conditions, and simultaneously grow and reproduce themselves continuously to absorb nitrogen sources and phosphorus sources and synthesize own cells. And placing a filler in the aerobic reactor. The function of the filler is to provide an anchor carrier for the microorganisms, so that more microorganisms (biofilms) in an anchor state can be accommodated in the reaction device, which not only increases the concentration of microorganisms in the reactor, but also makes the biological phase in the reactor more abundantThe reactor is rich, the volume load of the reactor is increased, and the load impact resistance of the reaction device is further improved. The packing is preferably applied at a density of at least 2-3 kg (dry solids) of microorganism per cubic meter. The filler used in the invention can be any wastewater treatment filler capable of providing microorganism fixation growth, and is preferably a zyzx series lamination expansion microbial carrier manufactured by Yao environmental protection and practice Co., ltd. In the sea, and the throwing density is 60 pieces/m ³ 。

And the effluent of the aerobic composite reactor automatically flows into a sedimentation tank to carry out mud-water separation. The sedimentation tank is preferably in the form of radial sedimentation tank. And discharging the clear liquid obtained after precipitation to coagulating sedimentation to further remove suspended solids and the like, wherein part of the obtained precipitated sludge is returned to a biological selector to be used as population inoculation and regeneration, and enters the next circulation of hydrolytic acidification and heterotrophic growth, and part of the precipitated sludge is used as residual sludge to be sent to a sludge concentration tank to be concentrated, and discharged after sludge dehydration and drying, and a large amount of carbon, nitrogen and phosphorus contained in the residual sludge are permanently removed from the system.

And a high-efficiency coagulating sedimentation tank is arranged behind the sedimentation tank, suspended solids, total phosphorus, macromolecular nondegradable COD components and the like in the clear liquid are further removed, sediment sludge generated by the sedimentation tank and residual sludge of a previous stage sedimentation tank enter a sludge concentration tank together for sludge treatment, and the obtained clear liquid is discharged into a heterogeneous Fenton oxidation tank for further oxidation treatment.

The heterogeneous Fenton oxidation pond is filled with iron-carbon particle filter materials, the iron-carbon particle filter materials are filled in the whole filter bed space, the size of the filter bed space is such that the residence time of wastewater in an empty bed is 1-3h, hydrogen peroxide oxidant is added into an inlet, and the mass ratio of the addition to COD of the wastewater entering the oxidation pond is (1-2): 1. The iron-carbon particle filter material contains active carbon and reduced iron, the reduced iron and the active carbon form an electrochemical system, electrons can be released by the reduced iron to form ferrous salt, the ferrous salt is used as a hydrogen peroxide catalyst, so that hydrogen peroxide is cracked to generate hydroxyl free radicals, residual organic matters in water are oxidized, COD (chemical oxygen demand) of wastewater is further reduced, and water produced can be directly discharged to the external environment.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides an efficient, reliable and economic treatment process for treating the polyoxymethylene wastewater. The high concentration formaldehyde contained in the wastewater is effectively converted into three-carbon and six-carbon saccharides and aldol substances under relatively mild conditions in a polymerization reactor, so that the toxicity of the three-carbon and six-carbon saccharides and aldol substances to microorganisms is eliminated, and the three-carbon and six-carbon saccharides and aldol substances are removed together with other organic components by a biochemical method. The alkaline conditions required for the polymerization are regulated with alkali metal hydroxides, and the required catalysts are alkaline earth metal hydroxides Ca (OH) ₂ Or Mg (OH) ₂ The double-alkali process can not only reduce the dosage of the alkali agent for regulating the pH value, but also obtain better catalytic effect, obtain higher formaldehyde conversion efficiency, shorten the required reaction time and reduce the required reaction temperature.

Phosphoric acid is used in pH neutralization callback of the reaction liquid after the polymerization reaction, and the phosphorus source required by subsequent biological treatment of the wastewater is supplemented while the neutralization effect is achieved. The cooling tower and the pH neutralization callback are combined together, so that the construction cost can be saved; the outlet temperature of the cooling liquid is controlled through the variable frequency adjustment of the cooling liquid circulating pump and the axial flow fan of the cooling tower, and the cooling energy consumption can be reduced on the premise of ensuring the cooling effect.

The pretreatment method (the regulating tank, the polymerization reactor 1 and the polymerization reactor 2) adopted by the invention can prevent the organic matters in the wastewater from being influenced by pretreatment, and the biological method is utilized for purification, so that the treatment cost is lower than that of the existing oxidation process. The biological treatment process adopts anaerobic hydrolysis acidification and aerobic biological treatment, can ensure that high concentration organic matters in the wastewater, especially macromolecular components, can be effectively removed, and has stable treatment effect. By arranging the biological selector, adopting a plug flow mixed reaction mode and corresponding power machinery and filling special biological filler in the anaerobic hydrolysis composite reactor and the aerobic reactor, the process can be optimized in the efficiency of removing suspended solids and organic matters, and meanwhile, the system can be kept stable and reliable in operation.

After passing through the pH callback tank and the cooling tower, the pretreated wastewater is mixed with factory waste water such as domestic sewage and the like for biological treatment, and the water quality reaches the discharge standard of the first-stage A after the wastewater sequentially enters into the treatment units such as a biological selector, an anaerobic hydrolysis composite reactor, an aerobic composite reactor, a radial flow sedimentation tank, a high-efficiency coagulation sedimentation tank, a heterogeneous Fenton oxidation reactor and the like. And special filler is placed in the reaction unit of the anaerobic hydrolysis composite reactor and the aerobic composite reactor to ensure the treatment effect of the system.

The polymerization reactor 1 uses the lye NaOH and the catalyst Ca (OH) ₂ The two kinds of alkali are carried out, so that the consumption of alkali can be greatly reduced. The alkali metal hydroxide has stronger capability of providing hydroxide ions, is advantageous in terms of improving the pH value of a reaction system, but is more advantageous as a ligand of formaldehyde and ions of alkaline earth metals with catalytic function, and the two bases are used together, so that the use amount of each base can be reduced, and in particular Ca (OH) is reduced ₂ The amount of the wastewater can be used to ensure that the wastewater is not easy to scale in a subsequent treatment device.

The radius of the sodium ion is different from that of the calcium ion, the electric potential of the outer charges is different, so that the intensity of the coordination ions formed by the sodium ion and the calcium ion is different, the sodium ion is easier to hydrate the ions, the sodium ion mainly exists in the form of hydrated ions in the solution, the calcium ion can form a firmer ligand with formaldehyde to promote the polymerization reaction between formaldehyde and other organic matters, naOH can provide more hydroxide radicals for the solution, and the pH is regulated to be higher than Ca (OH) ₂ More efficient.

After formaldehyde polymerization reaction, the concentration of formaldehyde in the wastewater can be lower than 200mg/L or even within 100mg/L, formaldehyde is mainly converted into three-carbon ketose, three-carbon aldol and hexose, the biodegradability of the wastewater is improved, and the components are converted into low-molecular organic acid after being acidified through anaerobic hydrolysis, so that the low-molecular organic acid can be well utilized by aerobic microorganisms. In addition, nitrogen and phosphorus required by the growth of microorganisms are further supplemented by adding domestic sewage and supplementing nitrogen and phosphorus.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings for a person having ordinary skill in the art.

FIG. 1 is a process flow diagram of an embodiment of the present invention;

fig. 2 is a schematic diagram of a cooling system coupled with pH adjustment and temperature control.

Detailed Description

Reference will now be made in detail to exemplary embodiments of the invention, which should not be construed as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.

The filler used in the following examples was a ZYZX series laminated expanded microorganism support manufactured by Shanghai Yao environmental protection industries, inc.

Chemical oxygen demand: COD;

suspension: an SS;

total nitrogen: TN;

total phosphorus: TP;

total dissolved solids: TDS;

biochemical oxygen demand: BOD;

ammonia nitrogen: NH (NH) ₃ -N。

Example 1

The process flow is shown in figure 1.

Polyoxymethylene wastewater from a workshop (including 55m total of sewage discharged from a production plant and sewage from a polymerization area) ³ And/h), each index concentration is as follows: COD concentration is 5900mg/L, TP concentration is 10mg/L, SS concentration is 385mg/L, TN (NH) ₃ -N) concentration 25mg/L, formaldehyde concentration 1300mg/L, pH 4.18, temperature 25 ℃.

1. The polyoxymethylene wastewater enters a regulating tank (in wastewater treatment, regulation means homogenization, since the concentration of the inflow water generally changes with time, the water quality in the regulating tank is homogenized by staying in the regulating tank for a period of time, the change is not so severe, the water quantity is regulated and controlled by the regulating tank), and after staying for 24 hours, the mixture enters a polymerization reactor 1, and the polymerization reactor 1 is operated as follows: adding a catalyst Ca (OH) into the wastewater of polyoxymethylene production ₂ Solution, ca (OH) ₂ The molar ratio of the solution to formaldehyde in the wastewater from polyoxymethylene production is 0.3:1, naOH is used as alkali liquor to adjust the pH to 10, and the polymerization reaction is carried out at 55 ℃. The polymerization reactor 1 is provided with a stirring device, a pH probe and a temperature probe, and the water temperature in the tankThe increase is obtained by heating with steam, and when the temperature reaches the set value, the heating is stopped. The wastewater remained in the reaction tank for 7h.

Then the wastewater enters a polymerization reactor 2, a stirring device is arranged in the reaction tank for mixing and stirring, no reagent is added, and the wastewater stays in the reaction tank for 7 hours.

2. In the embodiment, the pH callback tank uses a water collecting tank of the cooling tower, so that the reaction liquid treated in the previous step enters the cooling tower by using a lifting pump to be cooled and pH callback, the adding amount of phosphoric acid is determined to be 10kg/h according to the phosphorus content and COD value in the wastewater, hydrochloric acid is automatically added according to the required pH, and the pH is controlled to be 8; the circulating water quantity of the cooling tower and the air draft quantity of the axial flow fan are regulated according to the water temperature in the water collecting tank of the cooling tower, and the water temperature is ensured to be lower than 37 ℃ when the polyoxymethylene production wastewater enters the biological selector.

3. The wastewater after pH neutralization and cooling enters a biological selector, the temperature of the wastewater is kept below 37 ℃, domestic sewage and initial rainwater in a factory area are introduced into the biological selector, the urea addition amount is determined to be 40kg/h according to the nitrogen concentration and COD value in the wastewater, and the water amount of the domestic wastewater is 10m ³ /h, initial rainwater of 10m ³ And (3) h, finally keeping the weight ratio of COD to TN in the wastewater to be 20:1, a step of;

the return sludge of the radial flow sedimentation tank also enters the biological selector, and the sludge return ratio is 0.5. The wastewater was left in the bioselect er for about 1.5 hours.

4. The wastewater enters an anaerobic hydrolysis composite reactor, and the reactor is internally provided with fillers, wherein the fillers adopt ZYZX biological carrier fillers, the total number of the fillers is 6 ten thousand, and the density is 60/m ³ The residence time was 19h.

Then the mixture enters an aerobic composite reactor, an aeration device is laid in the reactor for oxygen supply, the aeration device adopts a microporous aerator, the oxygen supply ensures that an aeration tank is in an aerobic condition, and the reactor is internally provided with 10 ten thousand fillers, and the density is 60 fillers/m ³ The residence time is 32h;

then the mixture enters a radial sedimentation tank for staying for 0.5h;

then the mixture enters a high-efficiency coagulating sedimentation tank for sedimentation, and the mixture stays for 3.6 hours at the stage;

finally, the mixture enters a heterogeneous Fenton oxidizer, an iron-carbon particle filter material is filled in the non-uniform Fenton oxidizer, a hydrogen peroxide oxidant is added into an inlet, and the addition amount of the iron-carbon particle filter material is 75m ³ The hydrogen peroxide addition was 13kg/h and the wastewater remained at this stage for 1.0h.

The effluent quality of each reaction unit is shown in Table 1.

Table 1 main index of inlet and outlet water quality in biochemical treatment design of sewage treatment device

Note that: the "-" portion indicates that the detection at this stage is not performed.

As can be seen from Table 1, the treatment method of the wastewater from polyoxymethylene production provided by the invention can effectively remove formaldehyde content, the formaldehyde removal rate in the pretreatment section (to the cooling tower) reaches 96%, the formaldehyde removal rate in the whole process flow reaches 99.99%, and the pollutant content is effectively removed.

Comparative example 1

As in example 1, ca (OH) was used ₂ Substitution of solution with Mg (OH) ₂ A solution. The formaldehyde removal rate in the pretreatment section (to the cooling tower) was 94%.

Comparative example 2

The difference is that the NaOH solution is replaced with KOH solution as in example 1. The formaldehyde removal rate in the pretreatment section (to the cooling tower) was 96%.

The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims

1. The method for treating the wastewater generated in the production of the polyoxymethylene is characterized by comprising the following steps:

the polyoxymethylene production wastewater sequentially passes through an adjusting tank, a polymerization reactor 1, a polymerization reactor 2, a pH callback tank, a cooling tower, a biological selector, an anaerobic hydrolysis composite reactor, an aerobic composite reactor, a radial flow sedimentation tank, a high-efficiency coagulation sedimentation tank and a heterogeneous Fenton oxidation reactor, and water and sludge are discharged;

the polymerization reactor 1 is operated as follows: adding a catalyst into the wastewater produced by polyformaldehyde, adjusting the pH value by using alkali liquor, stirring, and carrying out polymerization reaction at 40-80 ℃;

adding acid liquor into the pH callback tank, wherein the acid liquor is phosphoric acid, hydrochloric acid or sulfuric acid;

adding a nitrogen source into the wastewater in the biological selector, so that the mass ratio of the biological oxygen demand, the total nitrogen and the total phosphorus of the mixed wastewater is 100:5:1;

placing a filler in the anaerobic hydrolysis composite reactor and the aerobic composite reactor; the filler is a ZYZX series lamination unfolding microbial carrier produced by Shanghai Yao environmental protection and practice limited company;

the concentration of formaldehyde in the polyoxymethylene production wastewater is 1300mg/L;

the molar ratio of the catalyst to formaldehyde in the wastewater of polyoxymethylene production is (0.1-1) to 1; the catalyst is alkaline earth metal hydroxide;

the alkali liquor is alkali metal hydroxide alkali liquor; the pH is adjusted to be more than or equal to 9.

2. The method for treating wastewater from polyoxymethylene production according to claim 1, wherein a stirring device is provided in the polymerization reactor 2, the sum of stirring time and stirring time of the polymerization reactor 1 is 3-14 hours, and the stirring time of the polymerization reactor 2 is equal to or longer than the stirring time of the polymerization reactor 1.

3. The method for treating wastewater from polyoxymethylene production according to claim 1, wherein an acid solution is added to the pH-adjusting tank to adjust pH to 7-8 in an amount of 1-4% by mass of COD in wastewater from polyoxymethylene production.

4. The method for treating wastewater from polyoxymethylene production according to claim 1, wherein the cooling temperature of the cooling tower is set to 35-40 ℃ and the water temperature at which wastewater from polyoxymethylene production enters the bioselection is ensured to be lower than 37 ℃.

5. The method for treating wastewater from polyoxymethylene production according to claim 1, wherein nitrogen source, waste water and domestic sewage are added to the bioselect er, and the discharged return sludge is back-filled to the bioselect er.

6. The method for treating wastewater from polyoxymethylene production according to claim 1, wherein the anaerobic hydrolysis composite reactor adopts a hydraulic plug flow mixing reaction mode, a plurality of mixing reactors are arranged along the water flow direction, and power is provided to enable water to flow in a long and narrow channel in the reactors, the water level of an inlet and an outlet is kept consistent, and meanwhile, a filler is built in;

an aeration device is laid in the aerobic composite reactor, and a filler is arranged in the aeration device.

7. The method for treating wastewater from polyoxymethylene production according to claim 1, wherein the heterogeneous Fenton oxidation reactor is filled with iron-carbon particle filter material, and hydrogen peroxide oxidizer is added at the inlet.