Treatment methods and equipment for cold rolling wastewater

Abstract

The application provides a treatment method and device for cold rolling wastewater. The treatment method comprises the following steps: adding first oily wastewater into a demulsifier for first air flotation to obtain first floating oil and air flotation wastewater. The first floating oil is mixed with second oily wastewater, and then second air flotation is performed under the action of the demulsifier. Then, first pH adjustment, biochemical treatment and operation are sequentially performed to obtain first post-treatment water. The air flotation wastewater and acid-base wastewater are mixed, and then neutralization treatment is performed. Then, a flocculating agent is added for clarification. Then, second pH adjustment is performed, and oil removal and filtration are performed to obtain second post-treatment water. The oil and water in the first oily wastewater are relatively easy to separate. In the treatment method for the cold rolling wastewater, the treatment capacity of the acid-base wastewater is reasonably distributed according to the performance difference of the oily wastewater, and the treatment capacity of the acid-base wastewater is increased. Therefore, the treatment capacity of the total amount of the cold rolling wastewater is increased without expanding the capacity of the cold rolling wastewater station.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more particularly to a method and apparatus for treating cold rolling wastewater. Background Technology

[0002] Wastewater generated from cold rolling includes oily wastewater, acid and alkali wastewater, and heavy metal wastewater. The oily wastewater and acid and alkali wastewater are treated separately and then collected in the discharge pool before entering the centralized sewage treatment plant for final water reuse.

[0003] As the number of cold rolling mills continues to increase, the amount of wastewater generated also increases. The wastewater treatment capacity of cold rolling wastewater treatment plants is basically determined during the construction period. Expanding the capacity of cold rolling wastewater treatment plants to increase treatment capacity is costly and requires a lot of time. Summary of the Invention

[0004] The main objective of this invention is to provide a method and apparatus for treating cold rolling wastewater, in order to solve the technical problems of high cost and long time consumption in expanding cold rolling wastewater treatment plants.

[0005] To achieve the above objectives, the present invention provides a method for treating cold rolling wastewater, comprising the following steps:

[0006] The first oily wastewater is added to a demulsifier for first-stage air flotation, resulting in first-stage floating oil and air-flotated wastewater. The first oily wastewater includes at least one of the following: concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and winding machines, and wastewater from finishing and straightening processes.

[0007] The first floating oil is mixed with the second oily wastewater, and then subjected to a second air flotation under the action of a demulsifier. Following this, the mixture undergoes a first pH adjustment and a biochemical treatment process to obtain the first post-treated water. The second oily wastewater includes at least one of the following: oily wastewater from rolling mill emulsion, oily wastewater from leveling fluid, and oily wastewater from grinding fluid.

[0008] The air flotation wastewater and acid / alkali wastewater are mixed, neutralized, clarified by adding flocculant, and then subjected to a second pH adjustment and oil removal filtration to obtain the second post-treated water. The acid / alkali wastewater includes at least one of the following: dilute alkaline wastewater from galvanizing lines, acidic wastewater from pickling acid regeneration, and wastewater from a clean water circulation station.

[0009] According to an embodiment of this application, the first oily wastewater includes at least concentrated alkaline wastewater from galvanizing lines.

[0010] According to embodiments of this application, the flocculant includes at least one of polyferric sulfate, polyacrylamide, and silica monomer.

[0011] According to an embodiment of this application, the flocculant includes polyacrylamide, polyferric sulfate, and silicate monomer, wherein the amounts of polyacrylamide, polyferric sulfate, and silicate monomer added are 1.5-2.5 mg / L, 25-35 mg / L, and 0.8-1.2 mg / L, respectively.

[0012] According to an embodiment of this application, prior to the neutralization process, the first post-treated water, the flotation wastewater, and the acid-base wastewater are mixed.

[0013] According to the embodiments of this application, the first post-treated water is treated with sodium hypochlorite and then mixed with the flotation wastewater and the acid-base wastewater.

[0014] According to an embodiment of this application, the oil removal and filtration operation further includes the addition of clinoptilolite.

[0015] According to an embodiment of this application, the second air flotation includes a first-stage air flotation and a second-stage air flotation performed sequentially.

[0016] This application also provides a cold rolling wastewater treatment device, including an oily wastewater treatment system and an acid and alkali wastewater treatment system.

[0017] The oily wastewater treatment system includes a first air flotation unit, an oily wastewater conditioning tank, a second air flotation unit, a first pH conditioning tank, and a biological contact oxidation tank connected in sequence.

[0018] The acid-base wastewater treatment system includes an acid-base wastewater equalization tank, a neutralization tank, an acid-base precipitation tank, a second pH equalization tank, and an oil removal filter connected in sequence.

[0019] The first air flotation unit is used to add a demulsifier to the first oily wastewater for first air flotation to obtain first floating oil and air-flotated wastewater. The first oily wastewater includes at least one of the following: concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and winding machines, and wastewater from finishing and straightening processes.

[0020] An oily wastewater equalization tank is used to receive and mix the first floating oil and the second oily wastewater to obtain mixed oily wastewater. The mixed oily wastewater is then sequentially treated by a second air flotation mechanism under the action of a demulsifier, a first pH adjustment tank for first pH adjustment, and a biological contact oxidation tank for biochemical treatment to obtain first post-treated water. The second oily wastewater includes at least one of the following: oily wastewater from rolling mill emulsion, oily wastewater from leveling fluid, and oily wastewater from grinding fluid.

[0021] An acid-base wastewater equalization tank is used to receive and mix the air flotation wastewater and the acid-base wastewater to obtain mixed acid-base wastewater. This mixed acid-base wastewater is then sequentially treated by a neutralization tank, clarified by adding flocculant in an acid-base sedimentation tank, adjusted to a second pH in a second pH adjustment tank, and filtered to remove oil from an oil filter to obtain second post-treated water. The acid-base wastewater includes at least one of the following: dilute alkaline wastewater from a galvanizing line, acidic wastewater from pickling acid regeneration, and wastewater from a clean water circulation station.

[0022] According to an embodiment of this application, the oily wastewater treatment system further includes a pit, which is connected to the biological contact oxidation tank and the acid-base wastewater equalization tank, and sodium hypochlorite is added to the pit.

[0023] In the aforementioned cold rolling wastewater treatment method, the oil and water in the first oily wastewater are relatively easy to separate. Therefore, the first oily wastewater undergoes a first-stage air flotation process. The flotated wastewater is then mixed with acidic and alkaline wastewater and treated according to the acidic and alkaline wastewater treatment method, thus reducing the treatment load on the oily wastewater. During the acidic and alkaline wastewater treatment process, flocculants are added for clarification, accelerating the clarification speed and increasing the treatment capacity of the acidic and alkaline wastewater, which can be adapted to the wastewater treatment volume after the addition of the flotation wastewater. In the aforementioned cold rolling wastewater treatment method, based on the performance differences in the oily wastewater, air flotation is used to rationally allocate the treatment volume of oily wastewater and acidic and alkaline wastewater, and the treatment capacity of acidic and alkaline wastewater is increased. This increases the total treatment capacity of cold rolling wastewater without expanding the cold rolling wastewater treatment plant. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a cold rolling wastewater treatment device based on related technologies;

[0026] Figure 2 This is a schematic diagram of a cold rolling wastewater treatment apparatus according to one embodiment of this application;

[0027] Figure 3 This is a schematic diagram of a cold rolling wastewater treatment apparatus according to another embodiment of this application.

[0028] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0029] 100. Oily wastewater treatment system; 200. Acid and alkali wastewater treatment system;

[0030] 110. First air flotation unit; 120. Oily wastewater equalization tank; 130. First-stage air flotation unit; 140. First pH adjustment tank; 150. Heat exchanger; 160. Biological contact oxidation tank; 170. Sump;

[0031] 131. First-stage air flotation mechanism; 132. Second-stage air flotation mechanism;

[0032] 210. Acid-base wastewater equalization tank; 220. Neutralization tank; 230. Acid-base sedimentation tank; 240. Second pH adjustment tank; 250. Oil removal filter;

[0033] 221. Primary neutralization tank; 222. Secondary neutralization tank;

[0034] 300. Drainage pool; 400. Centralized sewage treatment pool. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be noted that all directional indicators (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0037] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0038] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0039] This application discloses a method for treating cold rolling wastewater, see [link to relevant documentation]. Figure 2 and Figure 3 This includes the following steps:

[0040] S100: The first oily wastewater is added to a demulsifier for first air flotation to obtain first floating oil and air-flotated wastewater. The first oily wastewater includes at least one of the following: concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and winding machines, and wastewater from finishing and straightening processes.

[0041] Wastewater generated from cold rolling is classified into oily wastewater and acid / alkali wastewater based on its properties. Oily wastewater typically includes oily wastewater from rolling mill emulsions, oily wastewater from leveling solutions, oily wastewater from grinding solutions, concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and coiling machines, and wastewater from finishing and straightening processes.

[0042] In related technologies, see Figure 1 The above six types of oily wastewater are treated uniformly in the oily wastewater treatment system. For example, they are separately collected in an equalization tank, mixed, and then subjected to air flotation (e.g., vortex air flotation). After air flotation, the floating oil and the wastewater are initially separated. The floating oil enters a waste oil collection tank, while the wastewater after air flotation is usually treated through a pH adjustment tank, a heat exchanger, and a biological contact oxidation tank (e.g., a four-stage cascade biological contact oxidation tank) to complete the treatment. Specifically, in some embodiments, the effluent from the vortex air flotation unit, after pH and temperature adjustment, needs further treatment through contact biological oxidation to ensure that the oil and COD in the effluent are within acceptable limits. Cr It meets emission requirements.

[0043] COD may consist of oil in water, surfactants, rust inhibitors, and other organic substances. Cr The COD data is obtained by oxidizing water with potassium dichromate, hence the name COD. Cr .

[0044] Accordingly, in related technologies, acidic and alkaline wastewater such as dilute alkaline wastewater from galvanizing lines, acidic wastewater from pickling acid regeneration, and drainage from the wastewater treatment plant flows into an acidic and alkaline wastewater equalization tank (e.g., two acidic and alkaline wastewater equalization tanks). Aeration heads are evenly installed in the equalization tanks to oxidize ferrous iron (Fe2+) to ferric iron (Fe3+). In some embodiments, the effluent from the equalization tanks is pumped to a first-stage neutralization tank, and the effluent from the first-stage neutralization tank flows by gravity to a second-stage neutralization tank. Lime solution is added to both the first and second-stage neutralization tanks, and aeration is applied to reduce the Fe2+ concentration in the wastewater. 2+ The wastewater is converted into Fe(OH)3, which is more easily precipitated. The effluent from the secondary neutralization tank flows into the acid-base sedimentation tank (also known as the acid-base clarification tank) through a distribution channel. A high-molecular-weight flocculant is added to the acid-base sedimentation tank to further increase the size of the flocs and improve the sedimentation effect. The effluent from the acid-base sedimentation tank is discharged into the final pH adjustment tank. In the final pH adjustment tank, the wastewater is adjusted to pH by adding chemicals, and then pumped to a walnut shell filter for filtration. The effluent flows by gravity to the discharge tank. The sludge from the sedimentation tank is periodically transported to the sludge thickening tank by a sludge pump, and then from the sludge thickening tank to the filter press.

[0045] The applicant found in actual process that the cold rolling wastewater station has a large capacity to treat acidic and alkaline wastewater, but a small capacity to treat oily wastewater due to the long treatment time. Therefore, its treatment capacity does not match the amount of wastewater generated in actual production.

[0046] The applicant discovered through extensive research that the three types of oily wastewater—rolling mill emulsion oily wastewater, leveling fluid oily wastewater, and grinding fluid oily wastewater—remain partially miscible with water and oil even after demulsification. Furthermore, these three types of oily wastewater contain high levels of water-soluble surfactants and rust inhibitors, resulting in high levels of COD and ammonia nitrogen.

[0047] The sources of ammonia nitrogen in cold rolling wastewater include: 1. Acid regeneration wastewater containing NH4. + 1. Because ammonia is added to adjust the pH in the acid regeneration desilication process, acidic wastewater containing ammonia nitrogen is produced; 2. The rust inhibitor in oily wastewater contains organic matter containing amino groups, such as leveling fluid wastewater, emulsion wastewater, and grinding fluid wastewater.

[0048] In the case of demulsification, the concentrated alkaline wastewater from galvanizing lines, the oily wastewater from uncoiling and winding machines, and the wastewater from finishing and straightening machines are basically completely separated from the oil. Moreover, the content of surfactants and rust inhibitors in these three types of wastewater is relatively low and they are relatively easy to remove. For example, they can be removed by subsequent aeration in acid and alkali wastewater equalization tanks, flocculant addition, and the action of walnut shell filters.

[0049] The first type of oily wastewater includes at least one of the following: concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and winding machines, and wastewater from finishing and straightening processes.

[0050] In this situation, the inventors classified and treated the oily wastewater. The first oily wastewater underwent a first air flotation process to obtain first floating oil and air flotation wastewater. Only the first floating oil was transferred to the oily wastewater treatment system for further treatment, reducing the treatment load on the oily wastewater treatment system. The air flotation wastewater was transferred to the acid and alkali wastewater treatment system for further treatment, making full use of the design margin of the treatment system.

[0051] In some embodiments, the demulsifier includes nitric acid, PAC, and PAM.

[0052] In some specific embodiments, the demulsification step involves first adding nitric acid with a concentration of 40%-45% to the first oily wastewater, at a concentration of 1-3‰ of the wastewater's volume. The specific amount is adjusted between 0.1% and 0.3% depending on the oil content of the wastewater. Then, PAC and PAM are added. The concentration of PAC added to the first oily wastewater is 30-50 g / m³, and the concentration of PAM added is 1-3 g / m³. PAC is polyaluminum chloride, and PAM is polyacrylamide (e.g., cationic polyacrylamide).

[0053] In some other specific embodiments, nitric acid, PAC, and PAM are simultaneously added to the first oily wastewater to demulsify it.

[0054] The following describes the oil-water separation of concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and winding machines, and wastewater from finishing and straightening machines, using vortex-type air flotation as an example.

[0055] The concentrated alkaline wastewater from galvanizing lines is generated from cleaning residual emulsion on the surface of steel strips using alkaline cleaning agents. It is highly alkaline but contains oil, surfactants, and iron-containing powdery sludge. However, after removing the upper layer of floating oil through vortex-induced air flotation demulsification and oil flocculation, the lower layer of iron-containing powdery sludge, due to its higher density, settles or remains suspended in the liquid. The middle layer of liquid is the air flotation wastewater.

[0056] Oily wastewater from unwinding and coiling machines is caused by the leakage of lubricating oil and hydraulic oil into the wastewater. In this type of wastewater, the oil and water are originally separated into layers due to the density difference. After the upper layer of floating oil is removed by vortex air flotation demulsification and oil flocculation, the clear water is the air flotation wastewater.

[0057] When the wastewater from the optical straightening process is left to settle, it separates into three layers: an oily layer, a clear water layer, and a zinc powder layer. After removing the upper layer of floating oil through vortex-induced flotation demulsification and oil flocculation, the lower layer of iron and zinc powder sludge, due to its higher density, settles or remains suspended in the liquid. The middle layer of liquid is the flotation wastewater.

[0058] S200: The first floating oil is mixed with the second oily wastewater, and then subjected to a second air flotation under the action of a demulsifier. The mixture is then subjected to a first pH adjustment and a biochemical treatment operation to obtain the first post-treated water. The second oily wastewater includes at least one of the following: oily wastewater from rolling mill emulsion, oily wastewater from leveling fluid, and oily wastewater from grinding fluid.

[0059] See Figure 2 and Figure 3In this step, the first floating oil is mixed with the second oily wastewater, such as in an oily wastewater equalization tank. The type and ratio of demulsifier can be referenced in step S100 and will not be repeated here. Overall, the addition of PAC and cationic PAM causes oil ions to accumulate and grow, floating on the liquid surface. The floating oil from the rolling mill emulsion, leveling fluid, and grinding fluid enters the waste oil collection tank. The wastewater, excluding the upper layer, then undergoes a first pH adjustment and biological treatment process to obtain the first post-treated water.

[0060] In some embodiments, heat exchange is also included between the first pH adjustment and the biochemical treatment operation. The microorganisms in the biological contact oxidation tank have an optimal survival temperature at which their reactivity is highest. For example, the optimal survival temperature for the microorganisms in the biological contact oxidation tank is in the range of 30-36°C. Therefore, adjusting the temperature of the wastewater after the first pH adjustment to the optimal survival temperature for the microorganisms before performing the biochemical treatment operation allows the microorganisms to more efficiently degrade COD.

[0061] S300: The air flotation wastewater and acid / alkali wastewater are mixed, neutralized, clarified by adding flocculant, and then subjected to a second pH adjustment and oil removal filtration to obtain the second post-treated water. The acid / alkali wastewater includes at least one of the following: dilute alkaline wastewater from galvanizing lines, acidic wastewater from pickling acid regeneration, and wastewater from a clean water circulation station.

[0062] See Figure 2 and Figure 3 In this step, the flotation wastewater and acid / alkali wastewater are mixed, such as in an acid / alkali wastewater equalization tank. Aeration is also performed in the acid / alkali wastewater equalization tank, which oxidizes ferrous iron to ferric iron and also degrades some COD and ammonia nitrogen.

[0063] The neutralization process involves adding slaked lime powder to neutralize the acid in the acidic or alkaline wastewater. The neutralized wastewater becomes weakly alkaline, facilitating subsequent clarification. In some embodiments, slaked lime powder is added to a solution prepared in water to neutralize the acid in the wastewater.

[0064] In some embodiments, a two-stage neutralization process is performed, exemplarily in a primary neutralization tank and a secondary neutralization tank. The primary neutralization tank is for coarse pH adjustment, and the secondary neutralization tank is for fine pH adjustment, so that after aeration, ferric iron, along with oil, silicon, organic matter, and other metal ions, precipitates in the ferric hydroxide flocs entering the acid-base precipitation tank. To accelerate the mixing and reaction of quicklime powder with the acidic and alkaline wastewater, in some embodiments, aeration is performed during the neutralization process.

[0065] After neutralization, flocculant is added for clarification. Due to the introduction of flotation wastewater, the amount of flocculant added should be appropriately increased to remove additional substances brought in by the flotation wastewater. A second pH adjustment is then performed to bring the wastewater, which was originally weakly alkaline after neutralization, to neutral or near-neutral.

[0066] The oil removal and filtration process may be the same as or different from the conventional processes for treating acidic and alkaline wastewater in related technologies.

[0067] Adding flocculants for clarification accelerates the clarification process, increasing the treatment capacity of acid and alkaline wastewater and making it compatible with the wastewater volume after adding flotation wastewater. The main rate-limiting step in an acid and alkaline wastewater treatment system is the flocculant clarification step; therefore, increasing the treatment rate of this step will significantly improve the system's overall treatment capacity.

[0068] In contrast, the main rate-limiting step in oily wastewater treatment systems is the treatment rate of the biological contact oxidation tank, which is difficult to increase. Due to the low efficiency of the biological treatment process in removing COD and ammonia nitrogen, oily wastewater requires a long residence time during biological treatment, and the longer the residence time, the better the effect. Therefore, to achieve good treatment results, the residence time often needs to exceed 8 hours or even longer.

[0069] In this embodiment, a flocculant is added for clarification, which accelerates the clarification process and shortens the sedimentation time (2-4 hours). This solves the problem of balancing treatment capacity and reduces the load on the oily wastewater treatment system.

[0070] Therefore, the inventors chose to improve the treatment capacity of the acid and alkali wastewater treatment system, thereby enhancing the overall treatment capacity of the cold rolling wastewater station and adapting to the increased demand for cold rolling wastewater treatment.

[0071] Overall, the above-mentioned methods for treating cold rolling wastewater separate oily wastewater from rolling mill emulsion, oily wastewater from leveling solution, oily wastewater from grinding solution, concentrated alkaline wastewater from galvanizing line, oily wastewater from uncoiling and coiling machine, and wastewater from finishing and straightening, based on the different characteristics of the wastewater.

[0072] Faced with the problem of a large wastewater treatment load, the load on the oily wastewater treatment system was reduced by rationally allocating the wastewater's destination without reducing the total wastewater treatment load.

[0073] In the aforementioned cold rolling wastewater treatment method, the oil and water in the first oily wastewater are relatively easy to separate. Therefore, the first oily wastewater undergoes a first-stage air flotation process. The flotated wastewater is then mixed with acidic and alkaline wastewater and treated according to the acidic and alkaline wastewater treatment method, thus reducing the treatment load on the oily wastewater. During the acidic and alkaline wastewater treatment process, flocculants are added for clarification, accelerating the clarification speed and increasing the treatment capacity of the acidic and alkaline wastewater, which can be adapted to the wastewater treatment volume after the addition of the flotation wastewater. In the aforementioned cold rolling wastewater treatment method, based on the performance differences in the oily wastewater, air flotation is used to rationally allocate the treatment volume of oily wastewater and acidic and alkaline wastewater, and the treatment capacity of acidic and alkaline wastewater is increased. This increases the total treatment capacity of cold rolling wastewater without expanding the cold rolling wastewater treatment plant.

[0074] In some embodiments, see Figure 2 and Figure 3 The first oily wastewater includes at least concentrated alkaline wastewater from the galvanizing line.

[0075] The inventors also discovered that the cost of treating cold rolling wastewater accounts for a large portion of the overall cost. In particular, acidic wastewater constitutes a significant portion of the treatment cost, while oily wastewater is alkaline. Therefore, in conventional treatment processes, large amounts of alkaline substances such as lime are often added to acidic wastewater to neutralize the acidity, while oily wastewater, being alkaline, requires the addition of acidic substances such as nitric acid to neutralize the alkali.

[0076] Therefore, the inventors fully utilized the alkalinity of oily wastewater to reduce wastewater treatment costs. The middle layer of the concentrated alkaline wastewater from galvanizing lines contains alkali and a small amount of iron powder. The alkali and the small amount of iron powder can neutralize the acidic wastewater, reducing the amount of lime that needs to be added.

[0077] In oily wastewater, since the alkali and iron powder carried by the concentrated alkaline wastewater that originally entered the oily wastewater no longer enter the mixing process, the acid consumed in this part does not need to be added, such as reducing the amount of nitric acid that needs to be added.

[0078] Therefore, in the above embodiments, wastewater resources are effectively utilized to treat waste, while reducing the dosage of acidic and alkaline substances and lowering the cost of wastewater treatment.

[0079] In some embodiments, the flocculant includes at least one of polyferric sulfate, polyacrylamide, and silicate monomer.

[0080] (1) Polyferric sulfate (PFS)

[0081] Polymerized flocculation (PFS) is an intermediate product in the hydrolysis of Fe2(SO4)3, which is gradually converted into Fe(OH)3. It polymerizes into an inorganic polymer through a hydroxyl-bridged reaction. PFS has two performance indicators: basicity and degree of polymerization. Basicity B = [OH] / 3 [Fe], representing the equivalent ratio of hydroxyl groups to iron in the compound. Generally, higher basicity indicates a greater number of low-charge, high-polymerization polynuclear complexes, resulting in better flocculation and bonding properties. Conversely, lower basicity leads to a predominance of high-charge, low-polymerization inorganic polymers, which compress the electric double layer and neutralize charges, thus achieving better colloidal destabilization. The basicity range of PFS is typically around 9%–16%. Using PFS alone cannot achieve optimal coagulation and flocculation results.

[0082] (2) Polyacrylamide (PAM)

[0083] PAM is a high molecular weight coagulant that disperses into a large number of linear chain polymers after dissolving in water. These large chain molecules can act as adhesives and bridges, while the charged groups on the molecules can compress the electric double layer and neutralize charges. Currently, anionic PAM is used, but the colloidal particles in wastewater are generally negatively charged. In such wastewater, anionic coagulants can only perform flocculation. PAM has a relatively narrow application range; excessive dosage can lead to colloidal protection, which increases the stability of the colloids and worsens the coagulation effect.

[0084] (3) Silicate monomers

[0085] The condensation polymerization of silica monomers in solution is a result of hydroxyl and oxygen bridging. The inorganic polymers formed by condensation polymerization have tetrahedral anions that can develop into filamentous, branched chain, or spherical particles. It only acts as a flocculator for negatively charged colloidal particles in water. Therefore, it is often used as a coagulant aid in combination with aluminum and iron salts. Even at very low dosages, it can significantly enhance the flocculation process, reduce the amount of coagulant needed, and improve coagulation performance under low temperature and low alkalinity conditions.

[0086] The main rate-limiting step in an acid and alkali wastewater treatment system is the clarification step by adding flocculants. Therefore, if the treatment rate of this step is increased, the treatment capacity of the acid and alkali wastewater treatment system will be greatly improved.

[0087] The inventors conducted a series of experiments, using combinations of different types and amounts of flocculants in the clarification step to clarify neutralized acidic and alkaline wastewater, and then tested the COD in the clarified liquid. Cr Oil content, calculate COD Cr The removal rates and oil removal rates are shown in Tables 1 and 2.

[0088] Table 1. Dosage and type of flocculant added (mg / L)

[0089]

[0090] Table 2 COD and petroleum hydrocarbon removal rates

[0091]

[0092] Among them, COD Cr Removal rate = (1 - COD in the supernatant) Cr COD of neutralized acidic and alkaline wastewater Cr ) 100%, oil removal rate = (1 - oil content in the clarified liquid / oil content in the neutralized acidic / alkaline wastewater) 100%.

[0093] It is evident that using any of the aforementioned flocculants can improve flocculation efficiency, thereby enhancing the treatment capacity of acid and alkaline wastewater treatment systems without requiring expansion.

[0094] Taking into account the properties of the wastewater, treatment effect, and cost, a mixture of PAM, PFS, and activated silica can be selected for addition. In some embodiments, the flocculant includes polyacrylamide, polyferric sulfate, and silica monomer, with the addition amounts of polyacrylamide, polyferric sulfate, and silica monomer being 1.5-2.5 mg / L, 25-35 mg / L, and 0.8-1.2 mg / L, respectively. Under these conditions, the flocculation effect is better, and the treatment capacity of the acid and alkaline wastewater treatment system is further improved. Specifically, the order of addition of PAM, PFS, and activated silica is not limited; however, if the three are mixed and added to the neutralized acid and alkaline wastewater, the expected treatment effect can be fully achieved.

[0095] In some embodiments, prior to the neutralization process, see Figure 3 It also includes mixing the first post-treated water, the flotation wastewater, and the acid-base wastewater.

[0096] In some embodiments, the first post-treated water is treated with sodium hypochlorite and then mixed with the flotation wastewater and the acid-base wastewater.

[0097] During their research, the inventors also discovered that conventional oily wastewater treatment systems, even after biochemical treatment, still retain certain levels of COD and ammonia nitrogen, failing to meet national standards. Direct discharge could still have a certain impact on the ecological environment. For example, the ammonia nitrogen in the water after contact with biological oxidation (i.e., the first post-treatment water) entering the station's pit still reached 20-40 mg / L. Therefore, by way of example, calcium hypochlorite powder or sodium hypochlorite powder was added to the pit to oxidize and remove the COD and ammonia nitrogen from the first post-treatment water (especially the leveling liquid wastewater).

[0098] After the first post-treatment water is treated with sodium hypochlorite or calcium hypochlorite, it is mixed with the flotation wastewater and the acid and alkali wastewater, and then treated again in the acid and alkali wastewater treatment system according to the acid and alkali wastewater treatment process.

[0099] For example, the biochemical effluent from the wastewater treatment plant is introduced into the plant's underground pit and then into an acid-base wastewater equalization tank. This embodiment extends the oily wastewater treatment process, aiming to reduce the COD and ammonia nitrogen levels in the wastewater through subsequent aeration, flocculation sedimentation, and oil removal filtration of the acid-base wastewater.

[0100] In some embodiments, see Figure 3 The oil removal and filtration operation also includes the addition of clinoptilolite.

[0101] Oil removal filtration can be achieved using a walnut shell filter, as its large surface area is effective for oil filtration. Taking a walnut shell filter as an example, clinoptilolite can be added. Zeolite is an aluminosilicate, and clinoptilolite is primarily used for removing ammonia nitrogen. Clinoptilolite has a sieving effect on ions in wastewater, as well as exchange adsorption effects, and is effective against NH4+. + It exhibits strong selectivity and can be used in exchange adsorption processes to remove ammonia nitrogen from water. It serves as the final step in removing ammonia nitrogen from cold rolling wastewater before it enters a centralized wastewater treatment plant.

[0102] In some embodiments, see Figure 2 and Figure 3 The second air flotation includes a first-stage air flotation and a second-stage air flotation performed sequentially.

[0103] Since oil-containing wastewater from rolling mill emulsions, leveling fluids, and grinding fluids is difficult to separate from water after demulsification, the existing two-stage vortex air flotation system is used for demulsification and oil flocculation. In addition, the load on the oil-containing wastewater treatment system is reduced. Therefore, the oil-containing wastewater from rolling mill emulsions, leveling fluids, and grinding fluids can be treated slowly and efficiently through two-stage vortex air flotation and biochemical treatment to achieve good treatment results.

[0104] This application also provides a treatment device for cold rolling wastewater, see [link to relevant documentation]. Figure 2 and Figure 3 This includes oily wastewater treatment systems and acid / alkali wastewater treatment systems.

[0105] The oily wastewater treatment system includes a first air flotation unit 110, an oily wastewater equalization tank 120, a second air flotation unit, a first pH equalization tank 140, and a biological contact oxidation tank 160 connected in sequence.

[0106] The acid-base wastewater treatment system includes an acid-base wastewater equalization tank 210, a neutralization tank 220 (also called a neutralization vessel), an acid-base sedimentation tank 230, a second pH adjustment tank 240, and an oil removal filter 250, all connected in sequence. For example, the neutralization tank 220 includes a primary neutralization tank 221 and a secondary neutralization tank 222, both connected in sequence. The primary neutralization tank 221 is connected to the acid-base wastewater equalization tank 210, and the secondary neutralization tank 222 is connected to the acid-base sedimentation tank 230.

[0107] The first air flotation unit 110 is used to add a demulsifier to the first oily wastewater for first air flotation to obtain first floating oil and air-flotated wastewater. The first oily wastewater includes at least one of the following: concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and winding machines, and wastewater from finishing and straightening processes.

[0108] An oily wastewater equalization tank 120 is used to receive and mix the first floating oil and the second oily wastewater to obtain mixed oily wastewater. The mixed oily wastewater is then sequentially treated by a second air flotation mechanism under the action of a demulsifier, followed by a first pH adjustment tank 140 for first pH adjustment, and a first biological contact oxidation tank 160 for biochemical treatment to obtain first post-treated water. The second oily wastewater includes at least one of rolling mill emulsion oily wastewater, leveling fluid oily wastewater, and grinding fluid oily wastewater. The second air flotation mechanism includes a first-stage air flotation mechanism 131 and a second-stage air flotation mechanism 132 connected in sequence. The first-stage air flotation mechanism 131 is connected to the oily wastewater equalization tank 120, and the second-stage air flotation mechanism 132 is connected to the first pH adjustment tank 140.

[0109] Acid-base wastewater equalization tank 210 is used to receive and mix the air flotation wastewater and the acid-base wastewater to obtain mixed acid-base wastewater. The mixed acid-base wastewater is then subjected to neutralization treatment in a neutralization tank 220, clarification by adding flocculant in an acid-base sedimentation tank 230, second pH adjustment in a second pH adjustment tank 240, and oil removal filtration in an oil removal filter 250 to obtain second post-treated water. The acid-base wastewater includes at least one of the following: dilute alkaline wastewater from galvanizing lines, acidic wastewater from pickling acid regeneration, and wastewater from a clean water circulation station.

[0110] The cold rolling wastewater treatment apparatus corresponds to the aforementioned cold rolling wastewater treatment method and is used to implement the above-described treatment method. When selecting the treatment method of different embodiments, the cold rolling wastewater treatment apparatus can be appropriately adjusted. The cold rolling wastewater treatment apparatus corresponds to the cold rolling wastewater treatment method and has the corresponding beneficial effects, which will not be elaborated further.

[0111] In some embodiments, see Figure 3 The oily wastewater treatment system also includes a pit 170, which is connected to the biological contact oxidation tank 160 and the acid-base wastewater equalization tank 210 respectively, and sodium hypochlorite is added to the pit 170.

[0112] Adding calcium hypochlorite powder to the pit 170 will oxidize and remove the COD and ammonia nitrogen values ​​in the first post-treatment water (especially the leveling liquid wastewater).

[0113] For example, in the wastewater treatment plant, the biochemical effluent enters the plant's pit 170 and is then introduced into the acid-base wastewater equalization tank 210. This embodiment extends the oily wastewater treatment process.

[0114] To better illustrate the technical solution of this application, a more detailed embodiment will be used to describe the technical solution of this application.

[0115] Example 1

[0116] This application also provides a treatment device for cold rolling wastewater, see [link to relevant documentation]. Figure 3 This includes oily wastewater treatment systems and acid / alkali wastewater treatment systems.

[0117] The oily wastewater treatment system includes a first air flotation unit 110, an oily wastewater regulating tank 120, a first-stage air flotation unit 131, a second-stage air flotation unit 132, a first pH regulating tank 140, a biological contact oxidation tank 160, and a pit 170 connected in sequence.

[0118] The acid and alkali wastewater treatment system includes an acid and alkali wastewater equalization tank 210, a primary neutralization tank 221, a secondary neutralization tank 222, an acid and alkali sedimentation tank 230, a second pH adjustment tank 240, and an oil removal filter 250, which are connected in sequence.

[0119] The first air flotation unit 110 adds a demulsifier to the first oily wastewater to perform a first air flotation, obtaining first floating oil and air-flotated wastewater. The first oily wastewater includes at least one of the following: concentrated alkaline wastewater from galvanizing lines, oily wastewater from uncoiling and winding machines, and wastewater from finishing and straightening processes.

[0120] One outlet pipe of the first air flotation unit 110 is connected to the oily wastewater equalization tank 120, and the first floating oil is transported to the oily wastewater equalization tank 120. The other outlet pipe of the first air flotation unit 110 is connected to the acid-base wastewater equalization tank 210, and the air flotation wastewater is transported to the acid-base wastewater equalization tank 210.

[0121] Oily wastewater equalization tank 120 receives and mixes the first floating oil and the second oily wastewater to obtain mixed oily wastewater.

[0122] The mixed oily wastewater is sequentially treated by a first-stage air flotation unit 131, a second-stage air flotation unit 132 under the action of a demulsifier for second air flotation, a first pH adjustment tank 140 for first pH adjustment, a heat exchanger 150 for temperature adjustment, and a first biological contact oxidation tank 160 for biochemical treatment to obtain first post-treated water. The second oily wastewater includes at least one of the following: oily wastewater from rolling mill emulsion, oily wastewater from leveling fluid, and oily wastewater from grinding fluid.

[0123] The first post-treatment water is treated with sodium hypochlorite in pit 170 and then enters acid-base wastewater equalization tank 210.

[0124] Acid-base wastewater equalization tank 210 receives and mixes the dissolved air flotation wastewater, acid-base wastewater, and the treated first post-treatment water to obtain mixed acid-base wastewater. The mixed acid-base wastewater is then sequentially neutralized in a primary neutralization tank 221 and a secondary neutralization tank 222, clarified by adding flocculant in an acid-base sedimentation tank 230, adjusted to a second pH in a second pH adjustment tank 240, and filtered for oil removal in an oil removal filter 250 to obtain second post-treatment water. The acid-base wastewater includes at least one of the following: dilute alkali wastewater from galvanizing lines, acidic wastewater from pickling acid regeneration, and wastewater from a clean water circulation station.

[0125] The second post-treatment water can be stored in the discharge pool 300, and after being treated by the centralized sewage treatment station, it can be reused or discharged.

[0126] Example 2

[0127] The comprehensive treatment method for cold rolling wastewater was implemented using the cold rolling wastewater treatment device described in Example 1. The specific treatment process will not be repeated here. The COD value, ammonia nitrogen and oil content of the wastewater before and after treatment were measured in some parts.

[0128] The oily wastewater (COD 4000-8000 mg / L; ammonia nitrogen 60-100 mg / L; oil 50-500 mg / L) in the oily wastewater equalization tank, after being treated by two-stage cascade air flotation (i.e., by the first-stage air flotation unit 131 and the second-stage air flotation unit 132), has the following parameters: COD 1800-2000 mg / L; ammonia nitrogen 60-100 mg / L; oil 7-10 mg / L.

[0129] After air flotation and further treatment in a biological contact oxidation tank, the oily wastewater (i.e., the first post-treatment water) has the following parameters: COD 100-120 mg / L; ammonia nitrogen 20-40 mg / L; oil 3-5 mg / L. This oily wastewater does not meet the new national standard GB 13456-2012 "Emission Standard of Water Pollutants for Iron and Steel Industry" (COD ≤50 mg / L; ammonia nitrogen ≤5 mg / L; oil ≤3 mg / L).

[0130] After the oily wastewater is treated in the biological contact oxidation tank, sodium hypochlorite is added to make it the first post-treatment water after chlorination. The indicators of the first post-treatment water after chlorination are as follows: COD 80-100 mg / L; ammonia nitrogen 10-20 mg / L; oil 3-5 mg / L.

[0131] The wastewater from finishing and straightening (oil 8-10 mg / L), the oily wastewater from unwinding and coiling machines (oil 10-200 mg / L), and the concentrated alkaline wastewater (COD 1500-2000 mg / L; oil 10-50 mg / L) is called flotation wastewater after the first-stage flotation (i.e., first flotation). The indicators of the flotation wastewater are: COD 400-600 mg / L; oil 8-20 mg / L.

[0132] The flotation wastewater, the first post-treatment water after chlorination, and the acid and alkaline wastewater (including dilute alkaline wastewater, with COD of 200-300 mg / L and oil of 8-10 mg / L) are mixed in the acid and alkaline wastewater equalization tank to obtain the effluent from the acid and alkaline wastewater equalization tank (COD of 100-200 mg / L, oil of 3-7 mg / L, and ammonia nitrogen of 5-10 mg / L). This effluent undergoes primary neutralization to pH 8-9 and secondary neutralization to pH 9.5-10.5. After passing through the acid and alkaline clarification tank, the effluent (COD of 40-60 mg / L, oil of 2-4 mg / L, and ammonia nitrogen of 5-8 mg / L) is filtered through walnut shells (filled with clinoptilolite) and the water quality in the discharge tank (COD of 30-50 mg / L, oil of 1-2 mg / L, and ammonia nitrogen of 1-4 mg / L) meets the discharge standards.

[0133] Comparative Example

[0134] by Figure 1 The existing cold rolling wastewater treatment device shown is used to implement the cold rolling wastewater treatment method. The specific treatment process will not be described in detail. The COD value, ammonia nitrogen and oil content of the wastewater before and after treatment are detected by some of the components.

[0135] Oily wastewater in the oily wastewater equalization tank (including oily wastewater from rolling mill emulsion, leveling solution, grinding solution, concentrated alkaline wastewater from galvanizing line, oily wastewater from uncoiling and coiling machines, and finishing and straightening wastewater, with an overall COD of 2000-5000 mg / L, ammonia nitrogen of 50-80 mg / L, and oil of 50-500 mg / L) is treated with air emulsification. After treatment, the oily wastewater (COD of 1200-2500 mg / L, ammonia nitrogen of 50-80 mg / L, and oil of 10-20 mg / L) is treated with a four-stage cascade biological contact oxidation tank. After treatment, the oily wastewater (COD of 80-120 mg / L, ammonia nitrogen of 20-40 mg / L, and oil of 5-8 mg / L) is treated with air emulsification. According to the new national standard GB 13456-2012 "Water Pollutant Discharge Standard for Iron and Steel Industry" (COD ≤50mg / L; ammonia nitrogen ≤5mg / L; oil ≤3mg / L), it does not meet the standards.

[0136] Dilute alkaline wastewater (COD 200-300 mg / L; oil 8-10 mg / L). Effluent from the acid-base wastewater equalization tank (COD 100-150 mg / L; oil 3-5 mg / L; ammonia nitrogen 5-10 mg / L) undergoes primary neutralization to pH 8-9, followed by secondary neutralization to pH 9.5-10.5. After passing through the acid-base clarification tank, the effluent (COD 30-50 mg / L; oil 1-3 mg / L; ammonia nitrogen 5-10 mg / L) is filtered through walnut shells before being discharged into the effluent tank. The effluent quality thereafter is (COD 30-40 mg / L; oil 1-2 mg / L; ammonia nitrogen 5-10 mg / L; ammonia nitrogen still exceeds the standard).

[0137] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for treating cold rolling wastewater, characterized by, The method comprises the following steps: adding the first oily wastewater into a demulsifier for first air flotation to obtain first floating oil and air flotation wastewater; the first oily wastewater comprises at least one of galvanizing line concentrated alkali wastewater, uncoiler and recoiler oily wastewater and finishing mill oily wastewater; mixing the first floating oil with second oily wastewater, and then performing second air flotation under the action of a demulsifier, and then performing first pH adjustment and biochemical treatment to obtain first post-treatment water; the second oily wastewater comprises at least one of rolling mill emulsion oily wastewater, skin pass mill oily wastewater and grinding fluid oily wastewater; the biochemical treatment comprises placing the wastewater after the first pH adjustment in a biological contact oxidation tank for treatment; mixing the air flotation wastewater and acid-alkali wastewater, and then performing neutralization treatment, adding a flocculant for clarification, and then performing second pH adjustment and oil removal filtration to obtain second post-treatment water; the acid-alkali wastewater comprises at least one of galvanizing line dilute alkali wastewater, pickling acid regeneration acid-containing wastewater and drainage of a clean water station; before the neutralization treatment, the method further comprises mixing the first post-treatment water, the air flotation wastewater and the acid-alkali wastewater; after the first post-treatment water is treated by sodium hypochlorite, the first post-treatment water is mixed with the air flotation wastewater and the acid-alkali wastewater.

2. The treatment method of the cold rolling wastewater according to claim 1, characterized by, The first oily wastewater at least comprises galvanizing line concentrated alkali wastewater.

3. The treatment method of the cold rolling wastewater according to claim 1, characterized by, The flocculant comprises at least one of polymeric ferric sulfate, polyacrylamide and silicic acid monomer.

4. The treatment method of the cold rolling wastewater according to claim 3, characterized by, The flocculant comprises polyacrylamide, polymeric ferric sulfate and silicic acid monomer, and the adding amount of the polyacrylamide, the polymeric ferric sulfate and the silicic acid monomer is 1.5-2.5 mg / L, 25-35 mg / L and 0.8-1.2 mg / L respectively.

5. The treatment method of the cold rolling wastewater according to claim 1, characterized by, In the oil removal filtration, clinoptilolite is further added.

6. The treatment method of cold rolling wastewater according to claim 1, characterized by, The second air flotation comprises first-stage air flotation and second-stage air flotation performed in sequence.

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