Emulsified wastewater treatment and resource recovery method based on composite demulsifier

Abstract

The invention belongs to the technical field of industrial wastewater treatment, and particularly discloses an emulsified wastewater treatment and resource recovery method based on a composite demulsifier. The method comprises the following steps: adding a composite demulsifier composed of aluminum sulfate and polyaluminum chloride in a mass ratio of 1: 1 into the emulsified wastewater; after stirring and mixing, standing for 30 minutes to form oil-water-floc three-phase layering; filtering and separating by using 200-600-mesh filter cloth, and collecting clear liquid and floc; and heating the floc at 60 DEG C, cooling to 10 DEG C, crystallizing, and centrifugally recovering grease. By adopting the method provided by the invention, the removal rate of COD (Chemical Oxygen Demand) in the emulsified wastewater reaches 16.1%-27.3%, the recovery rate of grease is 26.90%, the turbidity of clear liquid after the emulsified wastewater is treated is 0NTU, and the crystal yield is 8.47%-9.54%. The method has the advantages of efficient demulsification, resource recovery and low cost, and is suitable for emulsified wastewater treatment in the industries of food, chemical engineering and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial wastewater treatment, and particularly relates to an emulsified wastewater treatment and resource recovery method based on a composite demulsifier. Background Art

[0002] Against the backdrop of accelerating industrialization, the production of emulsified wastewater is increasing, posing a growing threat to the ecological environment and human health. The oil and fat contained in this wastewater interact with substances such as proteins, colloids, and surfactants contained in the wastewater during processing, forming a highly stable emulsion system. This system is not only difficult to separate through natural sedimentation, but also difficult to separate in the natural waters where industrial wastewater is discharged. When emulsified wastewater flows into rivers and lakes, the oil and fat in the emulsified wastewater forms an oil film on the water surface, hindering the exchange of oxygen between the water surface and the air, leading to the death of aquatic organisms due to lack of oxygen. Harmful substances contained in the oil and fat may also be enriched through the food chain, ultimately causing damage to human health.

[0003] The treatment of industrial emulsified wastewater is a key issue in environmental engineering. Traditional physical separation techniques generally retain less than 60% of these fine emulsion particles. With advances in surfactant compounding technology, the zeta potential of wastewater systems often drops to -40 mV, forming a double-layer structure with strong electrostatic stability, posing a significant technical bottleneck for previous desolidification methods. Currently, most oil in emulsified wastewater is directly discharged due to a lack of effective extraction technology, resulting in significant resource waste. Establishing a method for extracting and recovering oil and other resources from emulsified wastewater would not only address environmental pollution issues but also enable resource reuse.

[0004] At present, the demulsification method for extracting oil from emulsified wastewater is the mainstream method. The demulsification methods commonly used in industry mainly include chemical methods, physical methods and biological methods, but all of them have significant limitations.

[0005] The main principle of the chemical demulsification method is to add demulsifiers with various functions to the emulsified wastewater, and use the charge neutralization, adsorption bridging and other effects of the demulsifier to destroy the stability of the emulsion and separate the oil and water. Commonly used demulsifiers include cationic, anionic and non-ionic surfactants, and inorganic salt demulsifiers. For example, in the treatment of emulsified wastewater generated by oil extraction, polyepichlorohydrin amine cationic demulsifiers are often used to neutralize the negative charge on the surface of the oil droplets and aggregate the oil droplets. However, the chemical demulsification method has obvious disadvantages. The use of a large amount of demulsifiers not only increases the treatment cost, but may also introduce harmful substances such as heavy metals, causing secondary pollution. It is not difficult to find that different types of emulsified wastewater require screening for suitable demulsifiers, which increases the difficulty of process debugging.

[0006] The physical demulsification methods mainly include heating demulsification, centrifugal demulsification, ultrasonic demulsification and membrane separation. The heating demulsification reduces the oil-water interfacial tension by increasing the temperature, promotes the aggregation of oil droplets, and the shortcoming is that the method consumes a large amount of energy, and high temperature may cause the denaturation of oil. The centrifugal demulsification realizes oil-water separation by centrifugal force generated by high-speed rotation, and the shortage is that the requirement for equipment is high, the processing capacity is limited, the ultrasonic demulsification destroys the emulsion structure by the cavitation effect of ultrasonic waves, and the great defect is that the equipment cost is high, and it is difficult to be applied on a large scale. The advantage of membrane separation technology is that it can realize high-precision oil-water separation, and the defect is that the membrane material is easy to block, and frequent cleaning and replacement are required, and the maintenance cost is high.

[0007] The biological demulsification method can utilize microorganisms or biological enzymes to decompose emulsifiers and reduce the stability of emulsions. The biological demulsification method has the advantages of green and environmental protection, and the shortcoming is that the growth of microorganisms has high requirements for environmental conditions, the treatment period is long, and it is difficult to handle high-concentration emulsified wastewater, which limits its actual application range. When these traditional demulsification methods are faced with complex component emulsified wastewater, it is often difficult to achieve ideal treatment effect, and it is urgent to develop more efficient, environmentally friendly and economic demulsification technology.

[0008] In recent years, scholars at home and abroad have begun to apply crystal growth kinetics to high-purity oil systems in the food industry, but the applicability research on industrial emulsified wastewater containing complex interfacial active substances (such as Tween80, sodium dodecyl benzene sulfonate, etc.) is obviously insufficient, especially when there are high-valence cations such as Ca 2+ , Mg 2+ in the wastewater, and the concentration is >50mg / L, the synergistic effect of metal ions and surfactants can make the oil-water interfacial film strength increase by 2-3 times, which puts forward a new scientific problem for the crystal growth to effectively destroy the interfacial structure. It is urgent to develop an industrial emulsified wastewater treatment technology suitable for complex interfacial active substances and a method for recycling oil resources in industrial emulsified wastewater. SUMMARY

[0009] The purpose of the present application is to realize the synchronous removal and resource of oil and salt by demulsification-crystallization synergy, to reveal the oil-salt co-crystallization mechanism, to provide a theoretical basis for high-salt oil-containing wastewater treatment, and to develop a low-cost composite demulsifier and improve the oil-water separation efficiency.

[0010] In one aspect, the present application provides an emulsified wastewater treatment and resource recovery method based on a composite demulsifier, comprising the following steps:

[0011] Step one, adding a composite demulsifier to the emulsified wastewater, the composite demulsifier is composed of aluminum sulfate and polyaluminum chloride at a mass ratio of 1:1, and the mass-volume ratio of the composite demulsifier to the emulsified wastewater is 4-5g / L;

[0012] Step two, after stirring and mixing, stand for 30 minutes to form oil-water-floc three-phase stratification;

[0013] Step three, filter separation by using 200-600 mesh filter cloth, collect the supernatant and floc;

[0014] Step four, after warming up at 60°C, cool down to 10°C for crystallization, and centrifugal recovery of oil and fat.

[0015] Further, in the method, the emulsified wastewater is coconut emulsified wastewater.

[0016] Further, in the method, the mass-volume ratio of the composite demulsifier to the emulsified wastewater is 4-5 g / L, and the turbidity after standing and stratifying is 0 NTU.

[0017] Further, in the method, in step three, 400-600 mesh filter cloth is used, and the crystal yield in step four is 8.47%-9.54%.

[0018] Further, in the method, when 600 mesh filter cloth is used, the crystal yield is 9.54%.

[0019] The second aspect also provides a composite demulsifier for implementing the method of the application, which is formed by mixing aluminum sulfate and polyaluminum chloride in a mass ratio of 1:1. When the composite demulsifier is used to treat emulsified wastewater, the COD removal rate of the emulsified wastewater is 16.1%-27.3% when the mass-volume ratio of the composite demulsifier to the emulsified wastewater is 4-5 g / L.

[0020] The third aspect of the application also provides an emulsified wastewater treatment and resource recovery system, which comprises:

[0021] A composite demulsifier dosing unit;

[0022] A standing and stratifying tank;

[0023] A 400-600 mesh filter cloth filtering device;

[0024] A temperature-controlled crystallization centrifuge.

[0025] Further, the system also comprises an oil and fat recovery module for purifying the oil and fat after centrifugation by n-hexane extraction and rotary evaporation.

[0026] The fourth aspect of the application also provides a method for recovering coconut oil from coconut emulsified wastewater. After treating the coconut emulsified wastewater by the method provided by the application, the recovery rate of coconut oil reaches 26.90%.

[0027] Finally, the application of the method of the application in industrial emulsified wastewater oil and fat recovery is also provided.

[0028] Compared with the prior art, the technical scheme provided by the present application has at least the following beneficial effects or advantages:

[0029] (1) The present application discloses a composite demulsifier formed by mixing aluminum sulfate and polyaluminum chloride at a mass ratio of 1:1. The composite demulsifier significantly improves the demulsification efficiency through charge neutralization and flocculation synergistic effect. The COD removal rate is 26.8%, and the turbidity is reduced to 0 NTU, which is significantly better than the COD removal rate of 7.2% and the turbidity of 36 NTU when aluminum sulfate is used alone, and the COD removal rate of 5.7% and the turbidity of 218 NTU when polyaluminum chloride is used alone, indicating that aluminum sulfate and polyaluminum chloride have a synergistic effect.

[0030] (2) The method provided by the present application realizes efficient separation of oil and fat by adopting a demulsification method combined with a temperature control crystallization process, and the oil and fat recovery rate reaches 26.90%. The method realizes oil and fat recovery while treating emulsified wastewater, and reduces resource waste.

[0031] (3) The method uses a cheap inorganic demulsifier formed by mixing aluminum sulfate and polyaluminum chloride at a mass ratio of 1:1, and the dosage is only 4-5 g / L, which is lower than that of an organic demulsifier. The process does not require complex equipment and is suitable for industrial application. In addition, the method avoids secondary pollution caused by traditional incineration or landfill treatment, recovers oil and fat for reuse, and conforms to the concept of circular economy. The method has wide applicability and is suitable for high-concentration emulsified wastewater, especially for food industry wastewater such as coconut oil, and has the dual benefits of treatment and resource utilization. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The figure is the demulsification phenomenon of different types of demulsifiers for 0-30 min. From left to right, they are blank, aluminum sulfate, aluminum chloride, and composite demulsifier.

[0033] Figure 2 The figure is the COD value of emulsified wastewater treated by different types of demulsifiers.

[0034] Figure 3 The figure is the demulsification phenomenon of emulsified wastewater treated by adding different amounts of composite demulsifier for 0-30 min.

[0035] Figure 4 The figure is the COD value of emulsified wastewater treated by adding different amounts of composite demulsifier.

[0036] Figure 5 The figure is the COD value of emulsified wastewater filtered by different mesh filter cloths.

[0037] Figure 6 The figure is the crystal yield of emulsified wastewater filtered by different mesh filter cloths. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be described below in conjunction with embodiments, but the present application is not limited to the following embodiments.

[0039] In order for those skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific embodiments and drawings, but the embodiments are not limiting to the present application.

[0040] The experimental methods and detection methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0041] Example 1

[0042] This embodiment is to characterize the emulsified wastewater before treatment.

[0043] Before the emulsified wastewater is treated, the characteristics of the emulsified wastewater are characterized, the pH value of the emulsified wastewater before treatment is measured, the chemical oxygen demand (COD) is measured by the acid potassium permanganate method, and the oil content is measured.

[0044] Determination of chemical oxygen demand (COD):

[0045] Take 100 mL of the water sample to be tested, if the permanganate index is > 5 mg / L, take 1 mL and dilute to 100 mL, and take 0.1 mL and dilute to 100 mL, then add 5 mL of sulfuric acid (1+3) and shake well, after adding acid, add 5 mL of 0.1 mol / L silver nitrate solution, then add 10.00 mL of 0.02 mol / L potassium permanganate solution, shake well, the solution turns light purple, immediately put into a boiling water bath and heat for 30 min (counting from the reboiling of the water bath), it should be noted that the boiling water level should be higher than the reaction solution level to ensure sufficient reaction. After sufficient reaction, remove the conical flask, add 10.00 mL of 0.01 mol / L sodium oxalate standard solution while hot, shake well, and immediately titrate with 0.02 mol / L potassium permanganate solution until the solution turns slightly red, at which time record the consumption of potassium permanganate V1, in (mL)

[0046] Heat the titrated solution to 75℃, after heating, accurately add 10.00 mL of 0.01 mol / L sodium oxalate standard solution and shake well. Immediately afterwards, titrate with 0.02 mol / L potassium permanganate solution until the solution turns slightly red, at which time record the consumption of potassium permanganate V2, in (mL) and calculate the correction coefficient K of potassium permanganate solution:

[0047]

[0048] According to the following formula, the permanganate index O2 (mL / L) in the water sample is calculated:

[0049] Water sample not diluted:

[0050]

[0051] Water sample diluted:

[0052]

[0053] In the formula:

[0054] O2(mg / L) - the permanganate index of the water sample (mg / L)

[0055] V1(mL) - the consumption of potassium permanganate solution (mL) when titrating the water sample

[0056] V0(mL) - the consumption of potassium permanganate solution (mL) in the blank test

[0057] V2(mL) - the volume of potassium permanganate solution consumed when calibrating the potassium permanganate solution (mL)

[0058] M(mol / L) - the concentration of the potassium permanganate solution (mol / L), in this experiment M = 0.02 mol / L

[0059] V s (mL) - the volume of the water sample actually taken

[0060] C - the ratio of water in the diluted water sample

[0061] K - the correction coefficient of the potassium permanganate solution

[0062] Determination of oil content:

[0063] Take 50 mL of coconut emulsified wastewater and add it to a 100 mL beaker to preheat the sample. Heat the sample in a 50°C water bath for 10 minutes to reduce the oil viscosity and improve demulsification efficiency. Then, add 10 mL of 1 mol / L dilute sulfuric acid and stir thoroughly. Place the mixed sample in an 80°C water bath and heat for 30-40 minutes, stirring continuously, and observe the separation. If the emulsification is not completely broken, add another 5 mL of H₂SO₄ and continue heating for 10 minutes. If salting out occurs to promote separation, add 10 mL of 6% NaCl solution, stir thoroughly, and let it stand for 10-15 minutes. Observe the oil-water separation. If separation is not obvious, increase the salt concentration to 10% NaCl to enhance separation. After separation, transfer the organic phase to a centrifuge tube and centrifuge at 4°C, 4000 rpm, and centrifuge for 30 minutes. After centrifugation, the upper solid was removed and melted in a 50 ° C water bath, 20-30 mL of n-hexane was added, and the mixture was shaken for 5-10 minutes to ensure that the oil was effectively dissolved in the organic solvent. The mixture was centrifuged again at 30 ° C, 10000 rpm, and 30 minutes. After the second centrifugation, the solvent was evaporated and the oil content was determined. The organic phase (n-hexane) was transferred to the evaporating dish of the rotary evaporator (or evaporated in a water bath). The evaporation temperature was set below 50 ° C to ensure complete evaporation of n-hexane and avoid excessive temperature causing solvent volatilization loss (if evaporating in a water bath, the water bath temperature should be controlled below 50 ° C). Evaporation was performed until the solvent was completely removed, and the dry oil was obtained and the evaporating dish was weighed using an electronic balance to calculate the oil content. The results are shown in Table 1. The untreated emulsified wastewater had a weak alkaline pH value ranging from 7.28 to 7.41, a COD value of 353.76 mg / L, and an oil content of 22.60 g / L.

[0064] Table 1 pH value, COD value and oil content of raw water samples

[0065] Original water sample pH COD value (mg / L) Oil content (g / L) 1% milky wastewater 7.28～7.41 353.76 22.60

[0066] Example 2

[0067] This embodiment is for screening demulsifiers.

[0068] Take 100 mL emulsified wastewater sample 4 times, respectively in 220 mL specimen bottle, do well mark, carry out emulsified wastewater treatment, divide into 4 experimental groups, experimental group 1~3 add 0.5g aluminum sulfate, 0.5g polyaluminum chloride, 0.5g aluminum sulfate-polyaluminum chloride composite emulsifier (wherein aluminum sulfate and polyaluminum chloride each is 0.25g), control group 4 is not to add any emulsifier emulsified wastewater sample treatment group.After the addition of emulsifier, appropriate stirring, make emulsified wastewater and emulsifier fully mixed.Observe the delamination phenomenon after 30min (every 10min take a photo record), after the end of standing, with 400 mesh nylon filter cloth filtration, take 50mL filtrate, determine pH value, turbidity and COD value to select the best demulsifier.

[0069] The delamination time is a direct index to measure the demulsification effect.The shorter the delamination time, the better the demulsification effect;otherwise, the longer the delamination time, the worse the demulsification effect.The delamination phenomenon during the standing process is shown in Figure 1 and Table 2.

[0070] Table 2 delamination phenomenon observation results after different demulsifier treatment

[0071]

[0072]

[0073] Combined Figure 3 and Table 2, after 30min standing, the blank group and the aluminum chloride treatment group are consistent with the initial state, no obvious change occurs;the aluminum sulfate treatment group delaminates more clearly, the upper and lower limits are obvious, but the lower layer is still slightly turbid, the separation effect is general;the composite demulsifier treatment group has good delamination effect, the upper and lower limits are distinct, the lower layer is basically clear, and the separation effect is best.

[0074] COD (Chemical Oxygen Demand) as an important index to evaluate and measure the concentration of organic pollutants in water, has the treatment effect of evaluating demulsifier during the experiment.Emulsified oil wastewater contains a large amount of emulsified oil, surfactant and various refractory organic matter, resulting in high COD value.If the demulsifier has good effect, the oil and water can be completely separated, and the organic matter can be effectively removed, and the COD value will also decrease significantly.The decrease of COD value is the proof of the removal efficiency of oil and organic pollutants in the demulsification process, which directly reflects the performance of demulsifier.The COD value of emulsified wastewater treated by different demulsifiers is shown in Figure 2As shown in the results, the COD values of the supernatant after treatment with aluminum sulfate, polyaluminum chloride, and the composite demulsifier were 328.43 mg / L, 333.69 mg / L, and 259.11 mg / L, respectively; and the COD removal rates were 7.2%, 5.7%, and 26.8%, respectively. In combination with statistical significance analysis, the results showed that there was a significant difference (P < 0.05) between the COD value obtained after using the composite demulsifier (aluminum sulfate and aluminum chloride mixed at a mass ratio of 1:1) and the COD values obtained after using aluminum sulfate or aluminum chloride alone. It can be clearly observed from Table 2 that the COD value of the composite demulsifier showed a continuous decreasing trend during the treatment of the wastewater, which was significantly better than the treatment results of using aluminum sulfate or aluminum chloride alone. This trend indicates that the composite demulsifier has stronger stability and higher efficiency in demulsification. Based on the above, it is determined that the composite demulsifier is the best demulsifier for subsequent experiments. Figure 1

[0075] The turbidity of the supernatant is also an important indicator for measuring the demulsification effect. As shown in Table 3, the turbidity of the supernatant of the emulsified wastewater treated with aluminum sulfate, polyaluminum chloride, and the composite demulsifier was 36 NTU, 218 NTU, and 0 NTU, respectively. The results show that the turbidity of the composite demulsifier is the smallest, and there is a significant difference between the treatment results of the composite demulsifier and aluminum sulfate or polyaluminum chloride. In addition, the pH value of the supernatant is also lower than the initial pH value.

[0076] Table 3 Detection results of emulsified wastewater treated with different demulsifiers

[0077]

[0078] In summary, the COD value and turbidity of the supernatant after treatment of the emulsified wastewater with the composite demulsifier prepared by mixing aluminum sulfate and polyaluminum chloride at a mass ratio of 1:1 are significantly better than the treatment results of using aluminum sulfate or aluminum chloride alone, indicating that the composite demulsifier has stronger stability and higher efficiency in demulsification. In addition, the mixing of aluminum sulfate and polyaluminum chloride at a mass ratio of 1:1 has a synergistic effect, and the effect of the composite demulsifier prepared by mixing aluminum sulfate and polyaluminum chloride at a mass ratio of 1:1 is significantly better than the effect of using aluminum sulfate or polyaluminum chloride alone. The composite demulsifier is the best demulsifier in this example.

[0079] Example 3

[0080] This example is to screen the concentration of the demulsifier.

[0081] ​Take 100 mL emulsified wastewater sample 11, respectively, in 220 mL specimen bottle, do well mark. Experimental group 1~10 compound emulsifying agent (aluminum sulfate and polyaluminum chloride with mass ratio 1:1 mixed) adding amount respectively 0.1g, 0.2g, 0.3g, 0.4g, 0.5g, 0.6g, 0.7g, 0.8g, 0.9g, 1.0g, control group 11 is not to add any emulsifier emulsified wastewater sample processing group. After adding emulsifier, appropriate stirring, make emulsified wastewater and emulsifier fully mixed. Stand 30 min, (every 5 min take a picture record) observation of demulsification phenomenon, record solution clarity, flocculation, degree of stratification and other key phenomena, evaluate the demulsification performance difference under different dosage. After standing, with 400 mesh nylon filter cloth filtration, take 50 mL filtrate, determine turbidity and COD value, to select the best demulsifier concentration.

[0082] The effect of different amounts of composite demulsifier on the demulsification of emulsified wastewater is shown in Figure 3 and Table 4.

[0083] Table 4: Phenomenon during standing after treating emulsified wastewater with different amounts of composite demulsifier

[0084]

[0085]

[0086] COD (Chemical Oxygen Demand) is an important indicator to measure the content of organic pollutants in water body, which can effectively reflect the removal efficiency of organic matter in the demulsification process. The COD determination results of emulsified wastewater treated with different amounts of composite demulsifier are as follows: Figure 4As shown, the results show that after 0.1-1.0 g of the composite demulsifier treatment, the COD values of the supernatant are 293.75 mg / L, 476.61 mg / L, 336.06 mg / L, 297.12 mg / L, 257.16 mg / L, 414.77 mg / L, 345.86 mg / L, 302.46 mg / L, 471.60 mg / L, and 279.04 mg / L, respectively; the COD removal rates are 17.0%, -34.7%, 5.0%, 16.0%, 27.3%, -17.2%, 2.2%, 14.5%, -33.3%, and 21.1%, respectively. In combination with statistical significance analysis, when the dosage is 0.5 g, the COD value of the composite demulsifier after demulsification is the lowest, and there is a significant difference between 0.5 g and other dosages (0.1-0.4 g and 0.6-1.0 g) (P<0.05), indicating that the treatment effect at a dosage of 0.5 g is the most superior in statistics. At the same time, the COD changes with the dosage in a "first decrease and then increase" trend, indicating that there is an optimal dosage window. As can be seen from the figure, the COD at a dosage of 1.0 g is also at a relatively low level, and further analysis shows that, under the condition of similar demulsification effects, selecting 0.5 g has higher economic benefits and resource utilization efficiency. After all, in industrial applications, the dosage of the reagent directly affects the operation cost and operation load, and 0.5 g as the minimum effective dosage not only ensures the treatment effect, but also realizes cost control and process optimization, and has good industrial adaptability. In summary, the optimal concentration of the demulsifier in the subsequent experiment is 0.5 g in this experiment.

[0087] The turbidity of the supernatant is an important indicator for measuring the influence degree of the suspended particulate matter in the water body on the light transmittance, and is usually expressed in NTU (turbidity unit). As shown in Table 5, the turbidity of the supernatant treated by the composite demulsifier with different concentrations is 1 NTU, 0 NTU, 0 NTU, 0 NTU, 0 NTU, 0 NTU, 0 NTU, 1 NTU, 0 NTU, and 0 NTU, respectively. The higher the turbidity value, the more suspended matter or colloidal particles in the water, and the less transparent the liquid. In the treatment of emulsified wastewater, turbidity can be used as one of the important evaluation parameters for the effect of the demulsification process. A large number of dispersed small particles, emulsified oil droplets, and surfactants in the emulsified wastewater cause a high initial turbidity. If the demulsifier used has good performance, it can promote the aggregation and sedimentation or floating of the particles, thereby greatly reducing the number of suspended solids in the liquid, resulting in a significant decrease in turbidity. The decrease in turbidity not only reflects the destruction and separation effect of the demulsifier on the dispersed phase, but also verifies the improvement degree of the water quality from the side, and is one of the intuitive bases for judging the performance of the demulsifier.

[0088] Table 5 Treatment effect of emulsified wastewater with different amounts of demulsifier

[0089]

[0090] The effect of different amounts of composite demulsifier was analyzed systematically. It was found that the demulsification effect was the most ideal when the dosage was 0.5 g. At this concentration, the treated system had the lowest supernatant turbidity, the largest COD value decrease, a clear layering boundary, and dense and stable settling flocs.

[0091] Example 4

[0092] In this example, the filter cloth mesh number was selected.

[0093] 100 mL of emulsified wastewater sample was taken into three 220 mL specimen bottles, and 0.5 g of composite emulsifier made by mixing aluminum sulfate and polyaluminum chloride in a mass ratio of 1:1 was added to each specimen bottle. The specimen bottles were labeled. After adding the demulsifier, the emulsified wastewater and the demulsifier were stirred to mix thoroughly. After standing for 30 min (photographs were taken every 5 min), the phenomenon was observed.

[0094] After standing, the layered solution was gently stirred to distribute evenly. The entire solution was poured into the temperature controller cylinder, and the program was set to increase the temperature to 60°C at room temperature for 60 min, maintain 60°C for 25 min, decrease the temperature to 10°C for 70 min, and then maintain 10°C for 720 min.

[0095] The weight of the nylon filter cloth was weighed in advance, and then the total weight of the crystals and the filter cloth was weighed to determine the crystal yield. 50 mL of filtrate was taken to measure the pH value, turbidity, and COD value to select the best filter cloth mesh number.

[0096] Take 50 mL of treated coconut emulsion wastewater, add to 100 mL beaker, preheat the sample, heat the sample in a 50°C water bath for 10 min to reduce the viscosity of the oil and fat to improve the demulsification efficiency, then add 10 mL of 1 mol / L dilute sulfuric acid and stir evenly. Put the mixed sample into a 80°C water bath and heat for 40 min, continue to stir, and observe the layering. If the emulsion is not completely destroyed, you can also add 5 mL of H2SO4 and continue to heat for 10 min. When salt precipitation promotes layering, add 10% NaCl solution 10 mL and stir evenly and stand for 10-15 min, observe the oil-water layering. After layering, transfer the organic phase to a centrifuge tube and centrifuge, set the centrifuge temperature to 4°C, the centrifuge speed to 4000 rpm, and centrifuge for 30 min. After centrifugation, melt the upper solid at 50°C water bath, add 30 mL of n-hexane, shake for 10 min to ensure that the oil is effectively dissolved into the organic solvent, and then centrifuge at 30°C, 10000 rpm for 30 min. After the second centrifugation, perform solvent evaporation and oil content determination. Transfer the organic phase (n-hexane) to the evaporation dish of the rotary evaporator, set the evaporation temperature below 50°C to ensure complete evaporation of n-hexane and avoid loss of solvent due to high temperature (400 mesh filter cloth and 600 mesh filter cloth); this step can also use water bath evaporation, the water bath temperature should be controlled below 50°C to evaporate the solvent completely (200 mesh filter cloth). After the solvent evaporation is completed, the dry oil obtained is weighed using an electronic balance to calculate the oil content.

[0097] Because the mixed liquid after demulsification still contains fine suspended flocs and impurities that have not completely settled, further physical means are needed to achieve solid-liquid separation, so the filtration link is particularly critical. To improve the separation efficiency and ensure the quality of the clear liquid, the filtration effects of 200 mesh, 400 mesh and 600 mesh filter cloths are tested, with the COD value and turbidity of the clear liquid after filtration as the main evaluation indexes to select the best filter cloth with the best mesh size.

[0098] The COD values of the treated clear liquids under the same demulsification conditions with different filter cloth mesh sizes are compared, and the results are shown in Table 5 and Table 6. Figure 5 The results show that the COD values of the clear liquids filtered by 200 mesh, 400 mesh and 600 mesh filter cloths are 332.22 mg / L, 219.76 mg / L and 192.33 mg / L, respectively, and the COD removal rates are 6.1%, 37.9% and 45.6%, respectively. The lower the COD value, the less organic matter remains in the clear liquid after filtration, and the better the overall treatment effect. When using 600 mesh filter cloth, the COD value of the water sample after demulsification is the lowest, which is significantly lower than that when using 200 mesh and 400 mesh (P<0.05), and 600 mesh filter cloth is the best filter cloth.

[0099] Turbidity was used as one of the key parameters to evaluate the demulsification and filtration effect. From Table 7, the turbidity of the filtrate after 200 mesh, 400 mesh, 600 mesh filter cloth filtration was 165 NTU, 0 NTU, 0 NTU. The lower the turbidity value, the clearer the liquid, the better the treatment effect.

[0100] Table 6 Filtration results of different mesh filter cloths

[0101] Filter cloth mesh number Clear liquid COD (mg / L) COD removal rate (%) Turbidity (NTU) 200 332.22±9.29 6.1 165±9.42 400 219.76±6.96 37.9 0±0.00 600 192.33±7.02 45.6 0±0.00

[0102] The crystal yield is an important indicator to measure the solid precipitation effect, which reflects the efficiency of target substance recovery from waste liquid. By calculating the ratio of the dry mass of the crystal obtained under different treatment conditions to the initial mass of the substance, the recovery ability of the demulsification-filtration system for the target substance was evaluated. From Figure 6 and Table 7, after filtration by filter cloths of different mesh, the crystal yield obtained was 5.22%, 8.47%, 9.54% respectively. The high and low of the crystal yield obtained not only reflects the pros and cons of the emulsified wastewater treatment effect, but also has guiding significance for the economy of subsequent resource recovery and reuse. The higher the yield, the more effective the flocculation and separation process under this condition.

[0103] Table 7 Crystal yield of samples treated by filter cloths of different mesh

[0104] Filter cloth mesh number Crystal weight (g) Water sample volume (ml) Crystal yield (%) 200 5.22 100 5.22 400 8.47 100 8.47 600 9.54 100 9.54

[0105] By comparing and analyzing the COD value and turbidity of the clear liquid obtained after treating emulsified wastewater by filter cloths of different mesh, and the crystal yield, the crystal yield obtained by using 400-600 mesh filter cloth was 8.47%-9.54%, the COD value of the clear liquid was 192.33-219.76, and the turbidity was all 0, indicating that the effect of 400-600 mesh filter cloth was better, and the clear liquid obtained by 600 mesh filter cloth under the same demulsification condition was the best, with lower COD value and higher crystal yield, which was the best filter cloth mesh.

[0106] Example 5

[0107] This example is to test the oil recovery rate of emulsified wastewater.

[0108] The oil recovery rate is an important parameter to evaluate the removal ability of the treatment system for oil substances in emulsified wastewater. Its calculation is based on the change of oil content before and after treatment, which reflects the adsorption and removal effect of emulsified oil in the demulsification-separation process. The higher the oil recovery rate, the more effective the demulsifier pretreatment condition, which promotes the destabilization, aggregation and separation of oil substances from water, and reflects the better oil-water separation efficiency. minitial(g) is the oil content in the emulsified wastewater before treatment in Example 1, mfinal(g) is the average mass of coconut oil after treatment by filter cloths of different mesh in Example 4, the oil recovery rate is calculated, and the calculation results are shown in Table 8.

[0109] Table 8 sample oil and fat recovery rate

[0110] m 初 (g / mL) <![CDATA[m 终 (g / mL)]]> Grease recovery rate (%) 0.022 0.006 26.90

[0111] As shown in Table 8, the calculated oil and fat recovery rate is 26.90%, which indicates that the oil and fat treated away in the prior art can be effectively recovered by using the method provided by the present application, and the oil and fat can be recycled.

[0112] As described above, the basic principles, main features and advantages of the present application are better described. The above examples and descriptions are only for describing the preferred embodiments of the present application, and the present application is not limited by the above examples. Without departing from the spirit and scope of the present application, various changes and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the scope of protection of the present application.

Claims

1. A method for treating emulsified wastewater and recovering resources based on a composite demulsifier, characterized in that: The following steps are involved: Step 1: adding a composite demulsifier to the emulsified wastewater, wherein the composite demulsifier is composed of aluminum sulfate and polyaluminum chloride in a mass ratio of 1:1, and the mass volume ratio of the composite demulsifier to the emulsified wastewater is 4-5 g / L; Step 2: After stirring and mixing, let it stand for 30 minutes to form oil-water-flocculation three-phase separation; Step 3: Filter and separate using 200-600 mesh filter cloth to collect the clear liquid and flocs; Step 4: Heat the flocs at 60°C and then cool them to 10°C for crystallization, and recover the oil by centrifugation.

2. The method according to claim 1, characterized in that The emulsified wastewater is coconut emulsified wastewater.

3. The method according to claim 2, characterized in that The mass volume ratio of the composite demulsifier to the emulsified wastewater is 4-5 g / L, and the turbidity after standing and stratification is 0 NTU.

4. The method according to claim 1, wherein In the step 3, a 400-600 mesh filter cloth is used, and the crystal yield of the crystallization in the step 4 is 8.47%-9.54%.

5. The method according to claim 4, characterized in that When a 600-mesh filter cloth was used, the crystal yield was 9.54%.

6. A composite demulsifier for implementing the method according to claim 1, characterized in that: The composite demulsifier is prepared by mixing aluminum sulfate and polyaluminum chloride in a mass ratio of 1:

1. When the composite demulsifier is used to treat emulsified wastewater, when the mass volume ratio of the composite demulsifier to the emulsified wastewater is 4-5g / L, the COD removal rate in the emulsified wastewater is 16.1%-27.3%.

7. An emulsified wastewater treatment and resource recovery system, characterized in that: include: Composite demulsifier dosing unit; Static stratification tank; 400~600 mesh filter cloth filter device; Temperature controlled crystallization centrifuge.

8. The system according to claim 7, characterized in that It also includes an oil recovery module for purifying the oil after centrifugation through n-hexane extraction and rotary evaporation.

9. A method for recovering coconut oil from coconut emulsified wastewater, characterized in that: After being treated by the method according to any one of claims 2 to 3, the recovery rate of coconut oil is higher than 26.90%.

10. Use of the method according to claim 1 in the recovery of grease from industrial emulsified wastewater.

Images