A pretreatment method for high-concentration slicing wastewater in a photovoltaic industry

Abstract

The application discloses a kind of photovoltaic industry high concentration slice wastewater pretreatment method, comprising the following working steps: step S1, in slice wastewater, add alkaline substance, react 30min;The alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and alkaline substance dosing concentration is 1000~5000mg / L;Step S2, the slice wastewater after processing in step S1 is heated to 38~45 ℃, so that polyether compound is converted from dissolved state to insoluble state and precipitates;Step S3, in the slice wastewater after processing in step S2, add high ferric acid salt, react 30min;The high ferric acid salt is sodium ferrite or potassium ferrite, and the high ferric acid salt dosing concentration is 50~400mg / L.The application can reduce the temperature required for polyether compound thermal destabilization in slice wastewater, save wastewater treatment operation energy consumption, also can avoid when slice wastewater temperature reduces again dissolved state polyether compound, increase the actual removal rate of polyether compound.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic slicing wastewater technology, and in particular to a pretreatment method for high-concentration photovoltaic slicing wastewater. Background Technology

[0002] The wastewater from the silicon rod cutting process in the upstream production of solar cells is generated. Its COD is as high as 20,000 to 30,000 mg / L. Because the wastewater contains a large number of recalcitrant polyether compounds, it is difficult to directly carry out biochemical treatment.

[0003] Chinese invention patent disclosure, "A Treatment Device and Method for High-Concentration Photovoltaic Chip Slicing Wastewater," patent number 2024109813985, proposes a method for removing polyether compounds from chip slicing wastewater using a "heating / destabilization-coagulation-flocculation-precipitation" process. Specifically, the wastewater is first treated using an organic separation membrane. Then, the membrane concentrate enriched with polyether compounds is heated to 50℃~80℃, causing the polyether compounds to change from a dissolved state to an insoluble state. Next, coagulant PAC and flocculant PAM are added sequentially for reaction and precipitation, ultimately removing the insoluble polyether compounds. This method mainly utilizes the property of polyether compounds destabilizing and precipitating at high temperatures, achieving a COD removal rate of 30%~50% for chip slicing wastewater.

[0004] Further research and application of the above-mentioned wastewater treatment methods for slicing revealed the following shortcomings:

[0005] (1) This method requires heating the wastewater to 50℃~80℃ to destabilize and precipitate the polyether compound. Although some heat can be recovered and utilized through overall process optimization, there is still a problem of high energy consumption in wastewater treatment.

[0006] (2) The COD removal rate of the chip wastewater by this method increases with the increase of reaction temperature, but even when the wastewater is heated to 70℃~80℃, the COD removal rate is only 45% at most, which is difficult to improve further.

[0007] (3) When the temperature of the heated destabilized sludge is reduced from 50℃~80℃ to room temperature, the polyether compounds precipitated at high temperature will dissolve again and be returned to the chip wastewater treatment system along with the sludge dewatering liquid. This will result in the actual removal rate of polyether compounds by the heated destabilization method being low.

[0008] Based on the above, we have designed a pretreatment method for high-concentration wafer slicing wastewater in the photovoltaic industry to solve the above problems. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by proposing a pretreatment method for high-concentration wafer slicing wastewater from the photovoltaic industry.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A pretreatment method for high-concentration photovoltaic wafer slicing wastewater includes the following steps:

[0012] Step S1: Add an alkaline substance to the slicing wastewater and react for 30 minutes; the alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and the concentration of the alkaline substance is 1000~5000 mg / L.

[0013] Step S2: Heat the slicing wastewater treated in step S1 to 38℃~45℃ to cause the polyether compound to precipitate out from a dissolved state to an insoluble state.

[0014] Step S3: Add ferrate to the sliced ​​wastewater after step S2 and react for 30 min; the ferrate is sodium ferrate or potassium ferrate, and the concentration of ferrate added is 50~400 mg / L;

[0015] Step S4: Add calcium hydroxide to the wastewater from the sliced ​​material treated in step S3 and react for 15 minutes; the concentration of calcium hydroxide added is 500~2000 mg / L.

[0016] Step S5: Add flocculant PAM to the sliced ​​wastewater after step S4, react for 15 minutes, and then let it stand to settle; the concentration of PAM added is 5 mg / L.

[0017] Step S6: The supernatant after sedimentation in step S5 is used as the pretreatment effluent. After the sedimented sludge is dewatered, the resulting sludge dewatering liquid and sedimentation supernatant are combined for subsequent treatment.

[0018] Preferably, the concentration of the alkaline substance added in step S1 is 2000~4000 mg / L.

[0019] Preferably, in step S2, the temperature is raised to 40°C~43°C.

[0020] Preferably, the concentration of ferrate added in step S3 is 100~300 mg / L.

[0021] Preferably, the concentration of calcium hydroxide added in step S4 is 800~1500 mg / L.

[0022] Preferably, the initial conductivity of the wastewater from the slicing process is 250~850 μS / cm, and the initial pH value is 3~4.5.

[0023] Preferably, the temperature of the pretreated effluent is 38℃~45℃, and it can be directly introduced into the anaerobic biological treatment system.

[0024] Preferably, the method can achieve a COD removal rate of 40% to 50% in the wastewater from the slicing process.

[0025] Preferably, the method can effectively remove recalcitrant polyether compounds from wastewater and improve the biodegradability of the wastewater.

[0026] Preferably, the method lowers the critical value of the thermal destabilization precipitation temperature of the polyether compound by using alkaline substances, breaks hydrogen bonds and generates adsorption by ferrate oxidation, and strengthens coagulation with calcium hydroxide to form dense sludge flocs.

[0027] Compared with the prior art, the beneficial effects of the present invention are: under the premise of similar COD removal rate of chipping wastewater, the technical solution of the present invention can reduce the temperature required for thermal destabilization of polyether compounds in chipping wastewater, save energy consumption for wastewater treatment operation, and also avoid the re-dissolution of insoluble polyether compounds when the temperature of chipping wastewater decreases, thereby increasing the actual removal rate of polyether compounds. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the pretreatment method for high-concentration photovoltaic wafer slicing wastewater proposed in this invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0030] Reference Figure 1 A pretreatment method for high-concentration photovoltaic wafer slicing wastewater includes the following steps:

[0031] Step S1: Add an alkaline substance to the slicing wastewater and react for 30 minutes; the alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and the concentration of the alkaline substance is 1000~5000 mg / L, wherein the concentration of the alkaline substance in step S1 is 2000~4000 mg / L.

[0032] Step S2: Heat the slicing wastewater treated in step S1 to a temperature preferably 40°C to 43°C, so that the polyether compound changes from a dissolved state to an insoluble state and precipitates out.

[0033] Step S3: Add ferrate to the sliced ​​wastewater after step S2 and react for 30 min; the ferrate is sodium ferrate or potassium ferrate, and the preferred concentration of ferrate is 100~300 mg / L.

[0034] Step S4: Add calcium hydroxide to the wastewater from the sliced ​​material treated in step S3 and react for 15 minutes; the preferred concentration of calcium hydroxide is 800~1500 mg / L.

[0035] Step S5: Add flocculant PAM to the sliced ​​wastewater after step S4, react for 15 minutes, and then let it stand to settle; the concentration of PAM added is 5 mg / L.

[0036] Step S6: The supernatant after sedimentation in step S5 is used as the pretreatment effluent. After the sedimented sludge is dewatered, the resulting sludge dewatering liquid and sedimentation supernatant are combined for subsequent treatment.

[0037] The initial conductivity of the wastewater from the slicing process is 250~850 μS / cm, and the initial pH value is 3~4.5. The pretreated effluent temperature is 38℃~45℃, and it can be directly introduced into the anaerobic biological treatment system. This method can achieve a COD removal rate of 40%~50% for the wastewater from the slicing process. This method can effectively remove recalcitrant polyether compounds from the wastewater and improve the biodegradability of the wastewater. This method uses alkaline substances to lower the critical value of the thermal destabilization and precipitation temperature of polyether compounds, uses ferrate oxidation to destroy hydrogen bonds and generate adsorption, and uses calcium hydroxide to strengthen coagulation to form dense sludge flocs.

[0038] In this invention, the fundamental principle of thermal destabilization of polyether compounds is as follows: the ether bonds in polyether compounds can form hydrogen bonds with water molecules, making the polyether compounds hydrophilic and thus soluble in the aqueous phase. When the solution is heated, the hydrogen bonding forces weaken and eventually disappear. Above a certain temperature, the polyether compounds no longer bind with water but instead aggregate and precipitate in an insoluble state. This temperature can be called the critical value for thermal destabilization precipitation.

[0039] The purpose of adding an alkaline substance in step S1 of the technical solution of this invention is to reduce the critical value of the thermal destabilization precipitation temperature of polyether compounds.

[0040] This invention, through experiments, reveals that the critical temperature for the thermal destabilization and precipitation of polyether compounds is significantly related to the solution's conductivity and pH value. As the solution's conductivity and pH value increase, the critical temperature for the thermal destabilization and precipitation of polyether compounds decreases. Photovoltaic wafer slicing wastewater is characterized by low electrolyte concentration and a slightly acidic nature. The wastewater's conductivity ranges from 250 to 850 μS / cm, and its pH value ranges from 3 to 4.5. Under these conductivity and pH conditions, to induce the thermal destabilization and precipitation of polyether compounds in the water, the wastewater needs to be heated to a relatively high temperature (e.g., 50°C to 80°C).

[0041] This invention increases the electrolyte concentration and pH value of the chipping wastewater by adding alkaline substances such as sodium hydroxide or sodium carbonate. Since the electrolyte's affinity for water is greater than water's hydrogen bonding affinity for polyethers, it promotes the dehydration of the polyether compound macromolecules. Therefore, the polyether compound can be converted into a solid phase and precipitated at a relatively low temperature of 38℃~45℃ (step S2 of this invention). Furthermore, the high concentration of hydroxide ions added to the chipping wastewater can also disrupt hydrogen bonds, thereby promoting the precipitation of the polyether compound at a lower temperature.

[0042] The addition of ferrate in step S3 of this invention serves two main purposes: first, the strong oxidizing properties of ferrate further disrupt the hydrogen bonds formed between the ether and water molecules, promoting the precipitation of polyether compounds at lower temperatures. Second, the nascent nano-iron oxide particles generated by the ferrate reduction reaction possess excellent adsorption properties and a strong affinity for the destabilized and precipitated insoluble polyether compounds. Through the adsorption and coagulation effects of the nano-iron oxides, the amount of insoluble polyether compounds redissolved after the temperature of the chipping wastewater decreases can be reduced.

[0043] The calcium hydroxide added in step S4 of this invention mainly serves to enhance coagulation. The added calcium hydroxide combines with carbonate ions in the chip wastewater to form calcium carbonate. The insoluble calcium hydroxide and calcium carbonate can adsorb and encapsulate the nano-iron oxide particles and the precipitated polyether compounds, forming dense sludge flocs. This not only accelerates the settling speed of the flocs but also slows down the redissolution rate of the insoluble polyether compounds when the temperature of the chip wastewater decreases.

[0044] Under the coagulant effect of adding PAM in step S5 of the technical solution of the present invention, the sludge flocs formed by the reaction of calcium hydroxide, ferrate and polyether compound will precipitate and be separated from the wastewater, thereby achieving the purpose of removing polyether from the pretreatment of chip wastewater.

[0045] The treatment effect of the device and method of the present invention is illustrated by using the wafer slicing wastewater discharged from a photovoltaic silicon wafer manufacturing plant as the treatment target. The water quality data of the high-concentration wafer slicing wastewater to be treated are shown in Table 1.

[0046] Table 1 Typical water quality of high-concentration wafer slicing wastewater from the photovoltaic industry

[0047] Water quality projects unit numerical values COD mg / L 17360~29220 pH / 2.9~4.3 electrical conductivity μS / cm 264~856 <![CDATA[SO4 2- ]]> mg / L 34~41 <![CDATA[Cl - ]]> mg / L 177~248

[0048] The wastewater from the slice was treated according to the steps in the embodiment, and the COD removal rate at different reagent concentrations in each step is listed in Table 2.

[0049] Operating conditions The first step involves adding alkaline substances at a certain concentration. The second step is to heat the wastewater to the desired temperature. The third step involves adding ferrate concentration. Step 4: Add calcium hydroxide concentration Step 5: Add PAM concentration COD of raw water Treating effluent COD COD removal rate COD of supernatant when mud-water mixture is cooled to 25°C 1 <![CDATA[Na2CO3=5000mg / L]]> 45℃ <![CDATA[Na2FeO4=400mg / L]]> 2000mg / L 5 24640 12024 51.2% 12500 2 <![CDATA[Na2CO3=5000mg / L]]> 42℃ <![CDATA[Na2FeO4=400mg / L]]> 2000mg / L 5 24640 13108 46.8% 13642 3 <![CDATA[Na2CO3=5000mg / L]]> 38℃ <![CDATA[Na2FeO4=400mg / L]]> 2000mg / L 5 24640 14660 40.5% 15240 4 <![CDATA[Na2CO3=2500mg / L]]> 42℃ <![CDATA[Na2FeO4=400mg / L]]> 1000mg / L 5 24640 12221 50.4% 12893 5 <![CDATA[Na2CO3=2500mg / L]]> 42℃ <![CDATA[Na2FeO4=400mg / L]]> 1000mg / L 5 24640 13724 44.3% 14520 6 <![CDATA[Na2CO3=1000mg / L]]> 42℃ <![CDATA[Na2FeO4=400mg / L]]> 500mg / L 5 24640 13256 46.2% 14290 7 <![CDATA[Na2CO3=1000mg / L]]> 42℃ <![CDATA[Na2FeO4=400mg / L]]> 500mg / L 5 24640 14587 40.8% 15783 8 <![CDATA[Na2CO3=2500mg / L]]> 42℃ <![CDATA[Na2FeO4=250mg / L]]> 1000mg / L 5 24640 14414 41.5% 15800 9 <![CDATA[Na2CO3=2500mg / L]]> 42℃ <![CDATA[Na2FeO4=100mg / L]]> 1000mg / L 5 24640 14980 39.2% 16778 10 <![CDATA[Na2CO3=2500mg / L]]> 42℃ <![CDATA[Na2FeO4=50mg / L]]> 1000mg / L 5 24640 15178 38.4% 18660 11 <![CDATA[Na2CO3=2500mg / L]]> 42℃ <![CDATA[Na2FeO4=0mg / L]]> 1000mg / L 5 24640 15572 36.8% 21855 12 NaOH = 5000 mg / L 42℃ <![CDATA[Na2FeO4=400mg / L]]> 500mg / L 5 24640 12960 47.4% 13600

[0050] In addition, as a comparison, the same water sample was treated using the method described in the existing (comparative) technology. The reaction conditions were as follows: the wastewater was first heated to 70°C, and then 300 mg / L PAC and 5 mg / L PAM were added sequentially for reaction. The COD concentration of the supernatant after precipitation was measured to be 14050 mg / L, and the COD removal rate was 43%. The mud-water mixture was then allowed to cool naturally to 25°C, and the COD concentration of the supernatant was measured to be 21760 mg / L.

[0051] Based on the data from operating conditions 1, 2, and 3 in Table 2, it can be concluded that when the concentrations of sodium carbonate, sodium ferrate, and calcium hydroxide are the same, heating the chip wastewater to 38℃, 42℃, and 45℃ respectively can achieve good COD removal effects, with COD removal rates greater than 40%.

[0052] As shown in Table 2, under operating condition 4, sodium hydroxide achieves a similar COD removal effect compared to sodium carbonate, which is used as the alkaline substance in the first step. Furthermore, data from operating conditions 4-7 indicate that adding both sodium carbonate and sodium hydroxide simultaneously to the chipping wastewater to increase its pH and conductivity has little impact on the COD removal rate.

[0053] From the data of working conditions 5, 8, 9, 10 and 11 in Table 2, it can be concluded that when the concentrations of sodium carbonate, sodium hydroxide and calcium hydroxide are the same and the reaction temperature is 42℃, the COD removal rate of the chip wastewater increases with the increase of sodium ferrate concentration, indicating that the addition of sodium ferrate during the reaction can promote the precipitation of polyether compounds.

[0054] Furthermore, data from operating condition 11 in Table 2 shows that when no sodium ferrate is added during the reaction, the COD of the supernatant after coagulation and sedimentation is 15572 mg / L. However, when the water temperature drops to 25°C, the COD of the supernatant increases to 21855 mg / L, an increase of 40.3%. In the treatment effect of the existing (comparative) technology mentioned above, when the treated mud-water mixture is cooled to 25°C, the COD of the supernatant increases by 54.9%. In contrast, under the operating condition of sodium ferrate addition concentration of 250~400 mg / L in the technical solution of this invention, the increase in COD of the supernatant after the water temperature drops to 25°C is less than 10%; under the operating condition of sodium ferrate addition concentration of 50~100 mg / L, the increase in COD of the supernatant after the water temperature drops to 25°C is less than 25%. This indicates that sodium ferrate can effectively prevent the redissolution of precipitated polyether compounds after cooling.

[0055] It should be noted that the existing (comparative) technologies disclosed in the present invention and the background art both utilize the property that polyether compounds in chip wastewater will change from a dissolved state to an insoluble state at a certain temperature to remove polyether compounds. However, the reaction conditions and chemical agents used in the two schemes are different.

[0056] Existing (comparative) technologies require heating the wastewater from the slicing process to 50°C~80°C to precipitate polyether compounds. Then, coagulant PAC and flocculant PAM are added to react and convert the precipitated polyether compounds into sludge for removal.

[0057] This technical solution increases the pH and electrolyte concentration of the slicing wastewater by adding alkaline substances, thereby lowering the temperature threshold for the precipitation of polyether compounds. The polyether compounds can be precipitated simply by heating the wastewater to 38℃~45℃. Furthermore, by adding ferrate for oxidation and adsorption-coagulation reactions, and by adding lime for enhanced coagulation, not only can the precipitated polyether compounds be converted into sludge for removal, but the redissolution of insoluble polyether compounds can also be slowed down or even prevented when the temperature of the slicing wastewater decreases.

[0058] Therefore, compared with the prior art, under the premise of similar COD removal rate of chipping wastewater, the technical solution of the present invention can reduce the temperature required for thermal destabilization of polyether compounds in chipping wastewater, save energy consumption in wastewater treatment operation, and also prevent insoluble polyether compounds from redissolving when the temperature of chipping wastewater decreases.

[0059] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention, all of which fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A pretreatment method for high-concentration photovoltaic wafer slicing wastewater, characterized in that, The work includes the following steps: Step S1: Add an alkaline substance to the slicing wastewater and react for 30 minutes; the alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and the concentration of the alkaline substance is 1000~5000 mg / L. Step S2: Heat the slicing wastewater treated in step S1 to 38℃~45℃ to cause the polyether compound to precipitate out from a dissolved state to an insoluble state. Step S3: Add ferrate to the sliced ​​wastewater after step S2 and react for 30 min; the ferrate is sodium ferrate or potassium ferrate, and the concentration of ferrate added is 50~400 mg / L; Step S4: Add calcium hydroxide to the wastewater from the sliced ​​material treated in step S3 and react for 15 minutes; the concentration of calcium hydroxide added is 500~2000 mg / L. Step S5: Add flocculant PAM to the sliced ​​wastewater after step S4, react for 15 minutes, and then let it stand to settle; the concentration of PAM added is 5 mg / L. Step S6: The supernatant after sedimentation in step S5 is used as the pretreatment effluent. After the sedimented sludge is dewatered, the resulting sludge dewatering liquid and sedimentation supernatant are combined for subsequent treatment.

2. The pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, In step S1, the concentration of alkaline substance added is 2000~4000 mg / L.

3. The pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, In step S2, the temperature is raised to 40℃~43℃.

4. The pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, In step S3, the concentration of ferrate added is 100~300 mg / L.

5. The pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, In step S4, the concentration of calcium hydroxide added is 800~1500 mg / L.

6. The pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, The initial conductivity of the wastewater from the sliced ​​material is 250~850 μS / cm, and the initial pH value is 3~4.

5.

7. A pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, The pretreated effluent temperature is 38℃~45℃, and it can be directly introduced into the anaerobic biological treatment system.

8. The pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, The method can achieve a COD removal rate of 40% to 50% in the wastewater from the slicing process.

9. A pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, The method can effectively remove recalcitrant polyether compounds from wastewater and improve the biodegradability of wastewater.

10. A pretreatment method for high-concentration photovoltaic wafer slicing wastewater according to claim 1, characterized in that, The method lowers the critical value of thermal destabilization and precipitation temperature of polyether compounds by using alkaline substances, breaks hydrogen bonds and generates adsorption by ferrate oxidation, and strengthens coagulation with calcium hydroxide to form dense sludge flocs.

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