Method for treating wastewater

Abstract

The invention relates to the field of sewage treatment, and discloses a method for treating wastewater. The method comprises the following steps: carrying out contact reaction on wastewater, ferric salt and a betaine compound to obtain a turbid liquid; contacting the turbid liquid with a flocculating agent for reaction; wherein in the wastewater, the content of organic phosphorus in terms of phosphorus is 0.5-3 mg / L. The method provided by the invention can effectively improve the removal effect of organic phosphorus in the wastewater. Under the preferable condition, the method provided by the invention can synchronously, efficiently and economically remove phosphorus in the wastewater and reduce the hardness, the reaction pH is low, the phosphorus removal and hardness removal effects are good, the dosage of chemicals is small, and the cost is lower. Besides, the method is especially suitable for treating circulating water sewage, double-membrane backwashing water and the like containing the organic phosphorus scale inhibitor, has good phosphorus removal (especially organic phosphorus) and hardness removal effects, and can realize the technical effects of low agent dosage and low reaction pH.

Description

Technical Field

[0001] The invention relates to the field of sewage treatment, and in particular to a method for treating wastewater. Background Art

[0002] At present, the shortage of water resources has become one of the main bottlenecks restricting the sustainable development of the economy and society. Industry is one of the major water users, accounting for about 25% of the total water intake in the society. Among them, the water used by industrial circulating water systems accounts for 70%-80% of the total industrial water use. If the circulating water and sewage are treated and reused, water resources can be effectively utilized. Generally, reverse osmosis, electrodialysis and other technologies are used to deeply treat and reuse the circulating water. However, the circulating water and sewage contain high concentrations of salt, hardness, alkalinity and phosphorus (especially organic phosphorus). If it is not treated for phosphorus removal and hardness removal, it will cause scaling of the membrane and affect the normal operation of the membrane.

[0003] Phosphorus in circulating water wastewater includes inorganic phosphorus and organic phosphorus. Inorganic phosphorus can be removed by adding aluminum salts, iron salts or calcium salts to form phosphate precipitation. As for the removal of organic phosphorus, due to the large molecular volume of organic phosphorus molecules, the steric hindrance of the phosphorus-containing groups in the reaction with the phosphorus removal agent is large; on the other hand, most organic phosphorus molecules also contain carboxylic acid groups, which can also react with phosphorus removal agents to form soluble compounds, making it difficult for organic phosphorus molecules to form precipitation with phosphorus removal agents, resulting in the difficulty of combining with organic phosphorus molecules and then removing them.

[0004] For the removal of organic phosphorus, the commonly used method is Fenton oxidation reaction, which requires adjusting the pH to acidic and adding FeSO4 and H2O2 for Fenton oxidation treatment. However, this method is prone to produce a large amount of iron sludge, and the reaction process is highly corrosive, causing harm to the environment and equipment.

[0005] Therefore, it is of great practical significance to find a new low-cost process for treating organic phosphorus wastewater, especially a deep phosphorus removal method when the organic phosphorus content has been reduced to a lower level.

[0006] CN105668747A discloses a method for treating wastewater containing a plurality of mixed organic phosphorus scale and corrosion inhibitors, which first adds solid calcium hydroxide to the wastewater to adjust the pH of the wastewater to 11-12, then adds iron salt thereto, and finally adds flocculant anionic polyacrylamide for precipitation and separation. According to calculations, in this method, the mass concentration ratio of iron salt to phosphorus is 166-420:1, and the amount of dephosphorization agent used is too large.

[0007] The most commonly used methods for removing hardness from circulating water include lime softening, soda ash softening, and lime-gypsum softening. CN112079518A discloses a method for treating circulating water wastewater, which sequentially performs hardness removal filtration treatment, ozone oxidation treatment, etc. on the circulating water wastewater. In the hardness removal filtration treatment, the hardness remover includes sodium carbonate and / or sodium hydroxide. The pH of the water after the reaction is 10.5-11.5, and the resulting precipitate needs to be removed by membrane filtration. Since the circulating water wastewater contains scale inhibitors and dispersants, when the double alkali method is used to remove hardness, the scaling ions will not precipitate when their solubility exceeds their solubility, and more alkali needs to be consumed. At the same time, the resulting precipitate particles are small and difficult to remove.

[0008] CN114684930A discloses a wastewater de-hardening agent and a method for removing hardness from wastewater. The wastewater de-hardening agent includes, by mass percentage: 48wt%-68wt% calcium chloride, 20wt%-40wt% calcium sulfate, 5wt%-15wt% coal slag powder, 1wt%-3wt% waste biological filler powder, and is suitable for efficient and stable removal of hardness in external drainage containing scale inhibitors and corrosion inhibitors and scale inhibitors and dispersants. However, the reaction pH still needs to be adjusted to above 12; at the same time, hydrogen peroxide and oxidized scale inhibitors and dispersants need to be added to achieve better treatment effects.

[0009] The removal of hardness and phosphorus affect each other. The literature (Rott E, Minke R, Steinmetz H. Removal of phosphorus from phosphonate-loaded industrial wastewaters via precipitation / flocculation [J]. Journal of Water Process Engineering, 2017, 17: 188-196.) discloses that the effect of aluminum salts and iron salts in removing organic phosphorus decreases with the increase of hardness in wastewater.

[0010] There are few reports on the simultaneous removal of hardness and phosphorus (especially organic phosphorus). The literature (Optimization of conditions for simultaneous removal of phosphorus and hardness from water by roasted starch hydrotalcite, Journal of Hunan City University (Natural Science Edition), 2022, 31(1), 72) discloses the effect of roasted starch hydrotalcite on simultaneous removal of phosphorus and hardness from water. Since the phosphate removal rate decreases with increasing pH value, and the hardness ion removal rate increases with increasing pH value, even under the optimal conditions (pH = 7.8), the phosphate and hardness removal rates are 98.36% and 53.96% respectively, and the hardness removal rate is still relatively low. Summary of the invention

[0011] The purpose of the present invention is to overcome the problem of poor removal effect of organic phosphorus in existing wastewater treatment methods.

[0012] In order to achieve the above object, the present invention provides a method for treating wastewater, the method comprising the following steps:

[0013] (1) contacting the wastewater with iron salt and betaine compounds to react and obtain a suspension;

[0014] (2) contacting the suspension with a flocculant to react;

[0015] Wherein, the content of organic phosphorus in terms of phosphorus in the wastewater is 0.5-3 mg / L.

[0016] Preferably, in step (1), the content of organic phosphorus in the wastewater is 1-2 mg / L in terms of phosphorus.

[0017] Preferably, in step (1), the iron salt is selected from inorganic metal iron salts and / or polymeric metal iron salts, preferably at least one of ferric chloride, ferric sulfate, polyferric chloride and polyferric sulfate.

[0018] Preferably, in step (1), the concentration of the iron salt added is 20-120 mg / L, preferably 60-110 mg / L.

[0019] Preferably, in step (1), the betaine compound is selected from at least one of dodecyl dimethyl betaine, tetradecyl dimethyl betaine, octadecyl dimethyl betaine, dodecyl dihydroxyethyl betaine and 3-sulfopropyl dodecyl dimethyl betaine, preferably at least one of 3-sulfopropyl dodecyl dimethyl betaine, octadecyl dimethyl betaine and dodecyl dihydroxyethyl betaine.

[0020] Preferably, in step (1), the betaine compound is added at a concentration of 2-10 mg / L, preferably 5-8 mg / L.

[0021] Preferably, in step (1), the contacting comprises a rapid stirring process and a slow stirring process performed sequentially.

[0022] Preferably, the conditions for the rapid stirring treatment include: a time of 2-5 min and a rotation speed of 200-300 rpm; the conditions for the slow stirring treatment include: a time of 5-15 min and a rotation speed of 20-100 rpm.

[0023] Preferably, in step (2), the flocculant is anionic polyacrylamide and / or cationic polyacrylamide, preferably anionic polyacrylamide.

[0024] Preferably, the flocculant is added at a concentration of 0.5-2 mg / L, preferably 1-1.5 mg / L.

[0025] Preferably, in step (2), the contacting is carried out under stirring conditions, and the stirring conditions include: time of 10-20 min, and rotation speed of 20-100 rpm.

[0026] Preferably, the wastewater further contains calcium salts and magnesium salts; the total hardness of the wastewater calculated as CaCO3 is 300-2500 mg / L, and the total alkalinity calculated as CaCO3 is 50-900 mg / L;

[0027] Preferably, the total phosphorus content of the wastewater is 2-4.5 mg / L in terms of phosphorus.

[0028] Preferably, in step (1), before the contacting, the method further comprises adjusting the pH value of the wastewater to 9.5-11.

[0029] Preferably, in step (1), the adjusting step comprises: contacting the wastewater with a base for reaction.

[0030] Preferably, the base is sodium hydroxide and / or sodium carbonate.

[0031] Preferably, in step (1), when the total alkalinity of the wastewater as CaCO3 is greater than 500 mg / L, the alkali is sodium hydroxide;

[0032] When the total alkalinity of the wastewater in terms of CaCO3 is not greater than 500 mg / L, the alkali is sodium carbonate or a combination of sodium carbonate and sodium hydroxide.

[0033] Through the above technical scheme, the method provided by the present invention first contacts the wastewater with iron salts and betaine compounds for reaction, and then adds a flocculant for reaction. The addition of a small amount of betaine compounds can effectively improve the removal effect of organic phosphorus in the wastewater. In a preferred case, the method provided by the present invention can also synchronously, efficiently and economically remove phosphorus and reduce hardness in the wastewater, with a low reaction pH, good phosphorus removal and hardness removal effects, and a small amount of reagents, and lower costs. In addition, the inventors of the present invention found during the research process that the method is particularly suitable for treating circulating water wastewater, double membrane backwash water, etc. containing organic phosphorus scale inhibitors, with good phosphorus removal (especially organic phosphorus) and hardness removal effects, and can achieve the technical effects of low reagent usage and low reaction pH. DETAILED DESCRIPTION

[0034] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0035] Technical terms in the present invention shall be understood according to their general meanings in the art unless otherwise stated, if they are defined.

[0036] In the present invention, "at least one" means one or two or more.

[0037] In the present invention, the addition concentration of the raw material is ab mg / L, where ab is a numerical range, that is, relative to 1L of wastewater, the addition amount of the raw material is ab mg. For example, the addition concentration of the iron salt is 20-120 mg / L, that is, relative to 1L of wastewater, the addition amount of the iron salt is 20-120 mg. The addition concentrations of the other raw materials are understood with reference to the above, and will not be repeated here.

[0038] As mentioned above, the present invention provides a method for treating wastewater, the method comprising the following steps:

[0039] (1) contacting the wastewater with an iron salt and a betaine compound to react to obtain a suspension I;

[0040] (2) contacting the suspension I with a flocculant to react;

[0041] Wherein, the content of organic phosphorus in terms of phosphorus in the wastewater is 0.5-3 mg / L.

[0042] The inventors of the present invention found during the research process that first contacting the wastewater with iron salts and betaine compounds for reaction and then adding a flocculant for reaction can improve the removal effect of organic phosphorus in the wastewater, and the addition of a small amount of betaine compounds can effectively improve the removal effect of organic phosphorus.

[0043] According to some embodiments of the present invention, the content of organic phosphorus in terms of phosphorus in the wastewater is 0.5-3 mg / L, for example, it can be 0.5 mg / L, 1 mg / L, 1.5 mg / L, 2 mg / L, 2.5 mg / L, 3 mg / L and any value in the range formed by any two of these values, preferably 1-2 mg / L. The wastewater can be, for example, circulating water wastewater, double membrane backwash water, etc. whose organic phosphorus content meets the above requirements. The method is particularly suitable for treating circulating water wastewater, double membrane backwash water, etc. containing organic phosphorus scale inhibitors that meet the above requirements to remove the organic phosphorus contained therein. In a preferred case, the method can also achieve the technical effects of low dosage of reagents and low reaction pH, and has good phosphorus removal and hardness removal effects.

[0044] According to some embodiments of the present invention, in step (1), the iron salt has a wide range of selectable types, and can be various trivalent iron salts conventionally used in the art. Preferably, the iron salt is selected from inorganic metal iron salts and / or polymeric metal iron salts, preferably a combination of inorganic metal iron salts and polymeric metal iron salts. Wherein, the inorganic metal iron salt (such as trivalent iron salts, aluminum salts, etc.) can form a chelate with organic phosphorus; the adsorption effect of the flocs and the bridging effect of the polymeric metal salt during the hydrolysis process can promote the detachment of the chelate from the water. In the combination, there is no particular restriction on the amount of the inorganic metal iron salt and the polymeric metal iron salt, and they can achieve the purpose of the invention to a certain extent. Preferably, in the combination, the mass ratio of the inorganic metal iron salt to the polymeric metal iron salt is (1.5-4): 1, and the inorganic metal iron salt and the polymeric metal iron salt can play a better synergistic role at the above-mentioned specific mass ratio.

[0045] According to some embodiments of the present invention, preferably, the iron salt is at least one of ferric chloride, ferric sulfate, polyferric chloride and polyferric sulfate.

[0046] According to some embodiments of the present invention, preferably, in step (1), the concentration of the iron salt added is 20-120 mg / L, for example, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L, 110 mg / L, 120 mg / L and any value in the range formed by any two of these values, preferably 60-110 mg / L. By adopting the above preferred embodiment, the organic phosphorus removal effect, phosphorus removal effect and hardness removal effect of wastewater are better.

[0047] According to some embodiments of the present invention, in step (1), the betaine compounds have a wide range of selectable types, and can be various betaine compounds conventionally used in the art, which can achieve the purpose of the present invention to a certain extent. Betaine compounds are amphoteric, and on the one hand, they can adsorb organic phosphorus anions through their own cations and calcium carbonate particles through their own anions; more importantly, on the other hand, the long chains they carry can be inserted into the micelles of the flocs, increasing the hydrophobicity of the micelles, thereby promoting the destabilization of the flocs and the collision and aggregation between the flocs through van der Waals interactions, thereby achieving the purpose of phosphorus removal and hardness removal of wastewater. Preferably, the betaine compound is selected from at least one of dodecyl dimethyl betaine, tetradecyl dimethyl betaine, octadecyl dimethyl betaine, dodecyl dihydroxyethyl betaine and 3-sulfopropyl dodecyl dimethyl betaine, preferably at least one of 3-sulfopropyl dodecyl dimethyl betaine, octadecyl dimethyl betaine and dodecyl dihydroxyethyl betaine. By adopting the above preferred embodiment, the method has better effects on removing organic phosphorus, phosphorus and hardness from wastewater.

[0048] According to some embodiments of the present invention, the inventors of the present invention have found in the course of research that a small amount of betaine compounds can effectively improve the phosphorus removal and hardness removal effects of wastewater. Preferably, in step (1), the addition concentration of the betaine compounds is 2-10 mg / L, for example, it can be 2 mg / L, 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L and any value in the range formed by any two of these values, preferably 5-8 mg / L. By adopting the above preferred embodiments, the method can achieve better organic phosphorus removal effect and improvement of wastewater phosphorus removal and hardness removal effect while using less reagents, and the cost is lower.

[0049] According to some embodiments of the present invention, the total phosphorus content of the wastewater in terms of phosphorus is 2-4.5 mg / L, for example, it can be 2 mg / L, 2.5 mg / L, 3 mg / L, 3.5 mg / L, 4 mg / L, 4.5 mg / L and any value in the range formed by any two of these values.

[0050] According to some embodiments of the present invention, preferably, in step (1), the mass ratio of the total amount of the iron salt and the betaine compound added to the total phosphorus contained in the wastewater is 35-55:1, and the total phosphorus is calculated as phosphorus, for example, 35:1, 40:1, 45:1, 50:1, 55:1 and any value in the range formed by any two of these values. The method can significantly reduce the amount of iron salt used while achieving a better organic phosphorus removal effect by combining the iron salt with the betaine compound.

[0051] According to some embodiments of the present invention, preferably, in step (1), the contacting comprises a rapid stirring process and a slow stirring process performed sequentially.

[0052] Preferably, the conditions for the rapid stirring treatment include: time of 2-5 minutes, rotation speed of 200-300 rpm; the conditions for the slow stirring treatment include: time of 5-15 minutes, rotation speed of 20-100 rpm. With the above preferred implementation, the organic phosphorus removal effect, phosphorus removal effect and hardness removal effect of wastewater are better.

[0053] According to some embodiments of the present invention, in step (2), the range of selectable types of the flocculant is relatively wide, and various flocculants conventionally used in the art can be used. Preferably, the flocculant is anionic polyacrylamide and / or cationic polyacrylamide, preferably anionic polyacrylamide. By adopting the above preferred embodiments, the organic phosphorus removal effect, phosphorus removal effect, and hardness removal effect of the wastewater are better.

[0054] According to some embodiments of the present invention, preferably, in step (2), the concentration of the flocculant added is 0.5-2 mg / L, for example, 0.5 mg / L, 1 mg / L, 1.5 mg / L, 2 mg / L and any value in the range formed by any two of these values, preferably 1-1.5 mg / L. By adopting the above preferred embodiment, the organic phosphorus removal effect, phosphorus removal effect and hardness removal effect of wastewater are better.

[0055] According to some embodiments of the present invention, preferably, in step (2), the contact is carried out under stirring conditions, and the stirring conditions include: a time of 10-20 minutes and a rotation speed of 20-100 rpm. By adopting the above preferred embodiment, the organic phosphorus removal effect, phosphorus removal effect and hardness removal effect of wastewater are better.

[0056] According to some embodiments of the present invention, the wastewater further contains calcium salts and magnesium salts; the total hardness of the wastewater calculated as CaCO3 is 300-2500 mg / L, and the total alkalinity calculated as CaCO3 is 50-900 mg / L.

[0057] According to some embodiments of the present invention, in step (1), before the contacting, the step further includes adjusting the pH value of the wastewater to 9.5-11, and the pH value may be, for example, 9.5, 10, 10.5, 11, and any value in the range formed by any two of these values. The method first adjusts the pH value of the wastewater to the above-mentioned specific range, and then adds iron salt and betaine compounds, which can promote the reaction of iron salt and alkali to generate iron oxyhydroxide in situ, flocculate and adsorb phosphorus and calcium carbonate microcrystals, and improve their sedimentation performance.

[0058] According to some embodiments of the present invention, in step (1), there is no particular limitation on the method of adjustment, as long as the pH value of the wastewater can be adjusted to the above range. Preferably, the adjustment step comprises: contacting the wastewater with a base for reaction;

[0059] Preferably, the contacting of the wastewater with the alkali for reaction is carried out under stirring conditions, and the contacting conditions include: a rotation speed of 300 rpm and a reaction time of 2-10 min. The contacting can be carried out using equipment such as a rapid mixer to achieve rapid and thorough mixing of the alkali and the wastewater.

[0060] Preferably, the base is sodium hydroxide and / or sodium carbonate.

[0061] Preferably, when the total alkalinity of the wastewater calculated as CaCO3 is greater than 500 mg / L, the alkali is sodium hydroxide; when the total alkalinity of the wastewater calculated as CaCO3 is not greater than 500 mg / L, the alkali is sodium carbonate or a combination of sodium carbonate and sodium hydroxide.

[0062] The inventors of the present invention found during the research process that when the total alkalinity of the wastewater in terms of CaCO3 is greater than 500 mg / L, the effect of phosphorus removal will be greatly reduced when the pH value is adjusted using sodium carbonate.

[0063] There is no particular restriction on the dosage of the alkali, as long as the pH value of the wastewater can be adjusted to the above range.

[0064] The inventors of the present invention found during the research process that when the wastewater also contains calcium salts and magnesium salts; the total hardness calculated as CaCO3 is 300-2500 mg / L, and the total alkalinity calculated as CaCO3 is 50-900 mg / L, by first adjusting the pH value of the wastewater to 9.5-11, and then adding iron salts and betaine compounds to react, and then adding flocculants to react, the removal effect of organic phosphorus can be effectively improved, and phosphorus in the wastewater can be removed and hardness can be reduced simultaneously, efficiently and economically, the reaction pH is low, and the phosphorus and hardness removal effects are good; at the same time, the amount of reagents used is small and the cost is lower.

[0065] According to a particularly preferred embodiment of the present invention, the method comprises:

[0066] (S1) adjusting the pH value of the wastewater to 9.5-11 to obtain adjusted wastewater; wherein:

[0067] The organic phosphorus content in the wastewater is 0.5-3 mg / L in terms of phosphorus; the total hardness of the wastewater in terms of CaCO3 is 300-2500 mg / L, the total alkalinity in terms of CaCO3 is 50-900 mg / L; the total phosphorus content in terms of phosphorus is 2-4.5 mg / L;

[0068] The adjustment step comprises: contacting the wastewater with an alkali for reaction; the alkali is sodium hydroxide and / or sodium carbonate; when the total alkalinity of the wastewater calculated as CaCO3 is greater than 500 mg / L, the alkali is sodium hydroxide; when the total alkalinity of the wastewater calculated as CaCO3 is not greater than 500 mg / L, the alkali is sodium carbonate or a combination of sodium carbonate and sodium hydroxide;

[0069] (S2) contacting the regulated wastewater with an iron salt and a betaine compound to react to obtain a suspension I; wherein:

[0070] The iron salt is at least one of ferric chloride, ferric sulfate, polyferric chloride and polyferric sulfate; the concentration of the iron salt is 20-120 mg / L;

[0071] The betaine compound is at least one of 3-sulfopropyl dodecyl dimethyl betaine, octadecyl dimethyl betaine and dodecyl dihydroxyethyl betaine; the addition concentration of the betaine compound is 2-10 mg / L;

[0072] The contacting includes a rapid stirring process and a slow stirring process performed sequentially; the conditions of the rapid stirring process include: a time of 2-5 minutes and a rotation speed of 200-300 rpm; the conditions of the slow stirring process include: a time of 5-15 minutes and a rotation speed of 20-100 rpm;

[0073] (S3) contacting the suspension I with a flocculant to react; wherein:

[0074] The flocculant is anionic polyacrylamide; the addition concentration of the flocculant is 0.5-2 mg / L;

[0075] The contact is carried out under stirring conditions, and the stirring conditions include: a time of 10-20 minutes and a rotation speed of 20-100 rpm.

[0076] The above particularly preferred embodiment is particularly beneficial for removing organic phosphorus from wastewater, and has good effects in removing phosphorus and hardness, and has low dosage of reagents and low reaction pH.

[0077] According to some embodiments of the present invention, the product obtained after wastewater is treated by the method can meet the requirements of subsequent double membrane treatment on hardness and phosphorus content.

[0078] The present invention will be described in detail below through examples.

[0079] In the following examples and comparative examples, unless otherwise specified, the raw materials used are all commercially available products.

[0080] in:

[0081] Phosphorus-containing wastewater A is wastewater from a refinery's circulating water system: its circulating water system adds orthophosphorus, organic phosphorus scale inhibitor HPAA and other agents; the total phosphorus mass concentration (content) of the wastewater in terms of phosphorus is 2.2 mg / L, of which the mass concentration of organic phosphorus in terms of phosphorus is 1.86 mg / L; the total hardness in terms of CaCO3 is 489 mg / L, the calcium hardness in terms of CaCO3 is 330 mg / L; the total alkalinity in terms of CaCO3 is 385 mg / L;

[0082] Phosphorus-containing wastewater B is wastewater from a refinery's circulating water system: its circulating water system adds various agents such as organic phosphorus scale inhibitor HEDP; the total phosphorus mass concentration of the wastewater in this system is 1.2 mg / L in terms of phosphorus, of which the mass concentration of organic phosphorus in terms of phosphorus is 1.2 mg / L; the total hardness in terms of CaCO3 is 417 mg / L, the calcium hardness in terms of CaCO3 is 250 mg / L; the total alkalinity in terms of CaCO3 is 821 mg / L;

[0083] Phosphorus-containing wastewater C is wastewater from a refinery's circulating water system: its circulating water system adds orthophosphorus, organic phosphorus scale inhibitor PBTCA and other agents; the total phosphorus mass concentration of the wastewater in terms of phosphorus is 2.93 mg / L, of which the mass concentration of organic phosphorus in terms of phosphorus is 1.93 mg / L; the total hardness in terms of CaCO3 is 2152 mg / L, the calcium hardness in terms of CaCO3 is 1534 mg / L; the total alkalinity in terms of CaCO3 is 110 mg / L;

[0084] Polyaluminium chloride (PAC) was purchased from Henan Haiyun Environmental Protection Technology Co., Ltd., and its basicity was 88 wt %.

[0085] In the following examples and comparative examples, unless otherwise specified, the methods used are conventional methods in the art.

[0086] The mass concentration (i.e. content, measured in P) of total phosphorus and orthophosphorus is determined according to the ammonium molybdate spectrophotometric method specified in GB / T 6913-2008; the mass concentration (i.e. content, measured in P) of organic phosphorus is the mass concentration of total phosphorus minus the mass concentration of orthophosphorus;

[0087] Total hardness (calculated as CaCO3): Determined by EDTA titration method specified in GB / T 15452-2009;

[0088] Turbidity was measured using a turbidity meter in accordance with HJ 1075-2019.

[0089] The following examples are used to illustrate the method for treating wastewater provided by the present invention.

[0090] Example 1

[0091] (S1) adjusting the pH value of the wastewater to 10.5 to obtain adjusted wastewater; wherein:

[0092] The wastewater is phosphorus-containing wastewater A;

[0093] The adjustment steps are: contacting the wastewater with a base to react under stirring;

[0094] The alkali is NaOH (dosage concentration is 240 mg / L) and Na2CO3 (dosage concentration is 300 mg / L);

[0095] The contact conditions were: rotation speed of 300 rpm, reaction time of 5 min;

[0096] (S2) contacting the regulated wastewater with an iron salt and a betaine compound to react to obtain a suspension; wherein:

[0097] The iron salt is FeCl3; the concentration of the iron salt added is 80 mg / L;

[0098] The betaine compound is 3-sulfopropyl dodecyl dimethyl betaine; the addition concentration of the betaine compound is 8 mg / L;

[0099] The contacting is a rapid stirring process and a slow stirring process performed sequentially; the conditions for the rapid stirring process are: time for 3 minutes, rotation speed for 300 rpm; the conditions for the slow stirring process are: time for 15 minutes, rotation speed for 50 rpm;

[0100] (S3) contacting the suspension with a flocculant to react; wherein:

[0101] The flocculant is anionic polyacrylamide; the concentration of the flocculant added is 1 mg / L;

[0102] The contact was carried out under stirring conditions, and the stirring conditions were: time 15 min, rotation speed 50 rpm;

[0103] (S4) The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness thereof are measured. The results are shown in Table 1.

[0104] Example 2

[0105] (S1) adjusting the pH value of the wastewater to 11 to obtain adjusted wastewater; wherein:

[0106] The wastewater is phosphorus-containing wastewater B;

[0107] The adjustment steps are: contacting the wastewater with a base to react under stirring;

[0108] The base is NaOH (dosage concentration is 120 mg / L);

[0109] The contact conditions were: rotation speed of 300 rpm, reaction time of 5 min;

[0110] (S2) contacting the regulated wastewater with an iron salt and a betaine compound to react to obtain a suspension; wherein:

[0111] The iron salt is FeCl3; the concentration of the iron salt added is 60 mg / L;

[0112] The betaine compound is octadecyl dimethyl betaine; the addition concentration of the betaine compound is 5 mg / L;

[0113] The contacting is a rapid stirring process and a slow stirring process performed sequentially; the conditions for the rapid stirring process are: time for 3 minutes, rotation speed for 240 rpm; the conditions for the slow stirring process are: time for 15 minutes, rotation speed for 20 rpm;

[0114] (S3) contacting the suspension with a flocculant to react; wherein:

[0115] The flocculant is anionic polyacrylamide; the concentration of the flocculant added is 1 mg / L;

[0116] The contact was carried out under stirring conditions, and the stirring conditions were: time 15 min, rotation speed 20 rpm;

[0117] (S4) The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness thereof are measured. The results are shown in Table 1.

[0118] Example 3

[0119] (S1) adjusting the pH value of the wastewater to 9.7 to obtain adjusted wastewater; wherein:

[0120] The wastewater is phosphorus-containing wastewater C;

[0121] The adjustment steps are: contacting the wastewater with a base to react under stirring;

[0122] The alkali is Na2CO3 (dosage concentration is 1300 mg / L);

[0123] The contact conditions were: rotation speed of 300 rpm, reaction time of 5 min;

[0124] (S2) contacting the regulated wastewater with an iron salt and a betaine compound to react to obtain a suspension; wherein:

[0125] The iron salt is FeCl3; the concentration of the iron salt is 110 mg / L;

[0126] The betaine compound is dodecyl dihydroxyethyl betaine; the addition concentration of the betaine compound is 5 mg / L;

[0127] The contacting is a rapid stirring process and a slow stirring process performed sequentially; the conditions for the rapid stirring process are: time for 3 minutes, rotation speed for 240 rpm; the conditions for the slow stirring process are: time for 15 minutes, rotation speed for 20 rpm;

[0128] (S3) contacting the suspension with a flocculant to react; wherein:

[0129] The flocculant is anionic polyacrylamide; the concentration of the flocculant added is 1 mg / L;

[0130] The contact was carried out under stirring conditions, and the stirring conditions were: time 15 min, rotation speed 20 rpm;

[0131] (S4) The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness thereof are measured. The results are shown in Table 1.

[0132] Example 4

[0133] The method of Example 1 is followed, except that in step (S2), the concentration of betaine compounds added is 2 mg / L, and the rest are the same. The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness, and total hardness thereof are measured. The results are shown in Table 1.

[0134] Example 5

[0135] The method of Example 1 is followed, except that the pH value of the wastewater is not adjusted, and the wastewater is directly contacted with the iron salt and betaine compounds for reaction. The rest is the same. The reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness, and total hardness are measured. The results are shown in Table 1.

[0136] Example 6

[0137] The method of Example 1 is followed, except that in step (S1), the pH value of the wastewater is adjusted to 8.5. The rest is the same. The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness are measured. The results are shown in Table 1.

[0138] Example 7

[0139] The method of Example 5 is followed, except that in step (S2), the iron salt is replaced by a combination of FeCl3 and polyaluminium chloride (PAC), wherein the mass ratio of FeCl3 to PAC is 7:3, and the rest are the same. The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness thereof are determined. The results are shown in Table 1.

[0140] Comparative Example 1

[0141] The method of Example 1 is followed, except that no iron salt and betaine compound are added in step (S2), and the rest are the same, as follows:

[0142] (S1) adjusting the pH value of the wastewater to 10.5 to obtain adjusted wastewater; wherein:

[0143] The wastewater is phosphorus-containing wastewater A;

[0144] The adjustment steps are: contacting the wastewater with a base to react under stirring;

[0145] The alkali is NaOH (dosage concentration is 240 mg / L) and Na2CO3 (dosage concentration is 300 mg / L);

[0146] The contact conditions were: rotation speed of 300 rpm, reaction time of 5 min;

[0147] (S2) stirring the adjusted wastewater to obtain a suspension; wherein:

[0148] The stirring process is a rapid stirring process and a slow stirring process performed sequentially;

[0149] The conditions for rapid stirring treatment were: time 3 min, rotation speed 300 rpm;

[0150] The conditions for slow stirring treatment were: time 15 min, speed 50 rpm;

[0151] (S3) contacting the suspension with a flocculant to react; wherein:

[0152] The flocculant is anionic polyacrylamide; the concentration of the flocculant added is 1 mg / L;

[0153] The contact was carried out under stirring conditions, and the stirring conditions were: time 15 min, rotation speed 50 rpm;

[0154] (S4) The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness thereof are measured. The results are shown in Table 1.

[0155] Comparative Example 2

[0156] The method of Example 1 is followed, except that no betaine compound is added in step (S2). The rest is the same. The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness thereof are measured. The results are shown in Table 1.

[0157] Comparative Example 3

[0158] The method of Example 1 is different from that of Example 1:

[0159] (S1) contacting the wastewater with an iron salt and a betaine compound to react and obtain a suspension;

[0160] The contact is carried out under stirring conditions; the contact conditions are: time is 3 minutes, rotation speed is 300 rpm;

[0161] (S2) adjusting the pH value of the suspension to 10.5 to obtain an adjusted suspension; wherein:

[0162] The adjusting step comprises: contacting the suspension with a base to react under stirring;

[0163] The alkali is NaOH (dosage concentration is 240 mg / L) and Na2CO3 (dosage concentration is 300 mg / L);

[0164] The contacting is a rapid stirring process and a slow stirring process performed sequentially; the conditions for the rapid stirring process are: time for 5 minutes and a rotation speed of 300 rpm; the conditions for the slow stirring process are: time for 15 minutes and a rotation speed of 50 rpm;

[0165] (S3) contacting the adjusted suspension with a flocculant to react; wherein:

[0166] The flocculant is anionic polyacrylamide; the concentration of the flocculant added is 1 mg / L;

[0167] The contact was carried out under stirring conditions, and the stirring conditions were: time 15 min, rotation speed 50 rpm;

[0168] (S4) The obtained reaction product is allowed to stand, and the total phosphorus content, organic phosphorus content, calcium hardness and total hardness thereof are measured. The results are shown in Table 1.

[0169] Table 1

[0170] project Total phosphorus content Organic phosphorus content Calcium hardness Total hardness Turbidity unit mg / L mg / L mg / L mg / L NTU Example 1 0.20 0.20 48 77 3.2 Example 2 0.18 0.18 14 39 2.9 Example 3 0.23 0.23 61 143 3.1 Example 4 0.40 0.40 57 90 9.1 Example 5 0.15 0.15 1534 2152 1.5 Example 6 0.86 0.66 330 489 15 Example 7 0.10 0.10 1534 2152 1.0 Comparative Example 1 2.2 1.86 178 337 26 Comparative Example 2 0.72 0.59 63 107 14 Comparative Example 3 0.67 0.59 123 257 7.2

[0171] It can be seen from the above results that the method provided by the present invention can effectively improve the removal effect of organic phosphorus in wastewater by treating wastewater. In a preferred case, the method provided by the present invention can also simultaneously, efficiently and economically remove phosphorus and reduce hardness in wastewater, with low reaction pH, good phosphorus removal and hardness removal effects, and less dosage of reagents, resulting in lower cost.

[0172] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for treating wastewater, characterized in that: The method comprises the following steps: (1) contacting the wastewater with iron salt and betaine compounds to react and obtain a suspension; (2) contacting the suspension with a flocculant to react; Wherein, the content of organic phosphorus in terms of phosphorus in the wastewater is 0.5-3 mg / L.

2. The method according to claim 1, wherein: In step (1), the organic phosphorus content in the wastewater is 1-2 mg / L in terms of phosphorus; Preferably, in step (1), the iron salt is selected from inorganic metal iron salts and / or polymeric metal iron salts, preferably at least one of ferric chloride, ferric sulfate, polyferric chloride and polyferric sulfate; Preferably, in step (1), the concentration of the iron salt added is 20-120 mg / L, preferably 60-110 mg / L.

3. The method according to claim 1 or 2, wherein: In step (1), the betaine compound is selected from at least one of dodecyl dimethyl betaine, tetradecyl dimethyl betaine, octadecyl dimethyl betaine, dodecyl dihydroxyethyl betaine and 3-sulfopropyl dodecyl dimethyl betaine, preferably at least one of 3-sulfopropyl dodecyl dimethyl betaine, octadecyl dimethyl betaine and dodecyl dihydroxyethyl betaine; Preferably, in step (1), the betaine compound is added at a concentration of 2-10 mg / L, preferably 5-8 mg / L.

4. The method according to any one of claims 1 to 3, wherein: In step (1), the contacting includes a rapid stirring process and a slow stirring process performed sequentially; Preferably, the conditions for the rapid stirring treatment include: a time of 2-5 min and a rotation speed of 200-300 rpm; the conditions for the slow stirring treatment include: a time of 5-15 min and a rotation speed of 20-100 rpm.

5. The method according to any one of claims 1 to 4, wherein: In step (2), the flocculant is anionic polyacrylamide and / or cationic polyacrylamide, preferably anionic polyacrylamide; Preferably, the flocculant is added at a concentration of 0.5-2 mg / L, preferably 1-1.5 mg / L.

6. The method according to any one of claims 1 to 5, wherein: In step (2), the contact is carried out under stirring conditions, and the stirring conditions include: time is 10-20 minutes, and rotation speed is 20-100 rpm.

7. The method according to any one of claims 1 to 6, wherein: The wastewater also contains calcium salts and magnesium salts; the total hardness of the wastewater in terms of CaCO3 is 300-2500 mg / L, and the total alkalinity in terms of CaCO3 is 50-900 mg / L; Preferably, the total phosphorus content of the wastewater is 2-4.5 mg / L in terms of phosphorus.

8. The method according to any one of claims 1 to 7, wherein: In step (1), before the contacting, the method further comprises adjusting the pH value of the wastewater to 9.5-11.

9. The method according to claim 8, wherein: In step (1), the adjusting step comprises: contacting the wastewater with a base for reaction; Preferably, the base is sodium hydroxide and / or sodium carbonate.

10. The method according to claim 9, wherein: In step (1), when the total alkalinity of the wastewater in terms of CaCO3 is greater than 500 mg / L, the alkali is sodium hydroxide; When the total alkalinity of the wastewater in terms of CaCO3 is not greater than 500 mg / L, the alkali is sodium carbonate or a combination of sodium carbonate and sodium hydroxide.