Scale prevention and nutrition supplement cooperative treatment method and system for wastewater anaerobic treatment system

Abstract

The invention belongs to the technical field of industrial wastewater treatment, and relates to a wastewater anaerobic treatment system scale prevention and nutrition supplement cooperative treatment method and a wastewater anaerobic treatment system scale prevention and nutrition supplement cooperative treatment system. A long-chain structure of sodium hexametaphosphate can efficiently inhibit formation of calcium carbonate scale through a threshold effect and a lattice distortion effect, and meanwhile, the sodium hexametaphosphate can be slowly hydrolyzed in an anaerobic acid environment, orthophosphate ions are gradually released, and stable and continuous phosphorus source nutrition is provided for anaerobic microorganisms, so that in the anaerobic treatment process of the papermaking wastewater, the phosphorus source content of the papermaking wastewater is increased. And the dual goals of scale prevention and nutrition supplement are achieved.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, and relates to a method and system for the synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system. Background Technology

[0002] Papermaking wastewater is a typical high-concentration industrial wastewater generated during the papermaking process. It has complex water quality and high pollutant concentration, and is often pretreated using anaerobic biological technologies (such as UASB and IC anaerobic reactors).

[0003] Currently, there are two major problems with papermaking wastewater: (1) High calcium scaling problem: The wastewater contains a high concentration of calcium ions (Ca ions). 2+ Under anaerobic conditions, especially at the higher pH levels in the methanogenic stage, it readily reacts with carbonate (CO3-). 2- (2) Phosphorus nutrient deficiency problem: Papermaking raw materials and processes result in a lack of phosphorus (P) element necessary for microbial metabolism in raw water. Nutrient imbalance will inhibit the activity of anaerobic microorganisms (including acid-producing bacteria and methanogens), resulting in slow sludge proliferation and reduced treatment efficiency.

[0004] In existing technologies, separate treatment methods are typically used. For scaling, synthetic scale inhibitors (such as organophosphates and polycarboxylates) are often added at the inlet of the anaerobic reactor. However, this method increases operating costs, and microorganisms cannot directly utilize organophosphates for synthesis and metabolism; excessive addition may lead to excessive total phosphorus in the effluent. For phosphorus deficiency, phosphates (such as sodium dihydrogen phosphate) are directly added to supplement nutrients, but this does not solve the scaling problem. Furthermore, traditional phosphates have a low phosphorus content, resulting in relatively high cost per unit of phosphorus added.

[0005] Therefore, there is a need to develop a cost-effective method that can solve the two problems mentioned above simultaneously, which is of great significance to the technological progress in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method and system for the synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system. This invention offers a simple, effective, and low-cost synergistic method that achieves the dual objectives of scale prevention and nutrient supplementation in the anaerobic treatment of papermaking wastewater.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: This invention provides a method for the synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system, which involves adding sodium hexametaphosphate to the wastewater.

[0008] Furthermore, the sodium hexametaphosphate is added before the wastewater enters the anaerobic reactor.

[0009] Furthermore, sodium hexametaphosphate is added to the pre-acidification tank at the front end of the anaerobic reactor before the wastewater enters.

[0010] Furthermore, the dosage of sodium hexametaphosphate is the greater of the dosage required for scale inhibition and the dosage required for nutrient supplementation.

[0011] It should be understood that when the calculated scale inhibition dosage is greater than the nutrient supplementation dosage, the dosage of sodium hexametaphosphate is the scale inhibition dosage; when the calculated scale inhibition dosage is less than the nutrient supplementation dosage, the dosage of sodium hexametaphosphate is the nutrient supplementation dosage.

[0012] Furthermore, the required scale inhibitor dosage is calculated based on the calcium ion concentration in the influent.

[0013] Furthermore, the ratio of the required scale inhibitor dosage to the influent calcium ion concentration is 1:(20~50).

[0014] Furthermore, the required amount of nutrient supplementation is calculated based on the influent COD (chemical oxygen demand).

[0015] Furthermore, the formula for calculating the required amount of nutritional supplements is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage (mg / L); x is the influent COD (mg / L); y is a coefficient with a value of 300-500; and P is the influent total phosphorus concentration (mg / L).

[0016] The present invention also provides a wastewater anaerobic treatment system, based on the above-described synergistic treatment method for scale prevention and nutrient supplementation in the wastewater anaerobic treatment system, wherein the treatment system includes a pre-acidification tank and an anaerobic reactor connected in sequence.

[0017] Furthermore, it also includes a dosing device for adding the sodium hexametaphosphate into the pre-acidification tank.

[0018] Preferably, the dosing device includes a storage tank and a metering pump for storing sodium hexametaphosphate and / or an aqueous solution of sodium hexametaphosphate.

[0019] The above-mentioned anaerobic wastewater treatment system's synergistic treatment method for scale prevention and nutrient supplementation includes the following steps:

[0020] S1. Water quality analysis: Detect the concentration of calcium ions and total phosphorus in the influent of the anaerobic system; S2. Calculate the dosage: The dosage of sodium hexametaphosphate [(NaPO3)6] simultaneously meets the requirements for scale inhibition and nutrient supplementation; (1) Scale inhibition dosage: Based on the influent calcium ion concentration obtained in step S1, add scale according to (NaPO3)6 / Ca 2+ The mass ratio is calculated based on a ratio of 1:20 to 1:50. (2) Nutrient Supplementation Requirements: Based on the influent COD (Chemical Oxygen Demand) concentration, the formula for calculating the nutrient supplementation requirements is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage, mg / L; x is the influent COD, mg / L; y is a coefficient, with a value of 300-500; and P is the total phosphorus concentration in the influent, mg / L. Ultimately, the larger value between the scale inhibition dosage and the nutrient supplement dosage was selected to ensure that both requirements were met simultaneously. S3. Dosing: Weigh out sodium hexametaphosphate according to the dosage calculated in step S2, dissolve the sodium hexametaphosphate in water, and continuously add it to the pre-acidification tank through a metering pump. The retention time is ≥1h. After homogenization and mixing, the mixed wastewater is pumped to the anaerobic reactor.

[0021] The beneficial effects of this invention are: 1. This invention achieves two goals at once through the special molecular structure of sodium hexametaphosphate. The long-chain structure of sodium hexametaphosphate can effectively inhibit the formation of calcium carbonate scale through threshold effect and lattice distortion effect; at the same time, it can slowly hydrolyze in an anaerobic acidic environment, gradually releasing orthophosphate ions, providing a stable and continuous phosphorus source for anaerobic microorganisms; this invention solves two problems at the cost of one reagent, reduces reagent dosing equipment and storage space, simplifies the operation process, and significantly reduces the system's operating cost and maintenance complexity; 2. The sodium hexametaphosphate is added at the pre-acidification section, where the pH is relatively low, which helps the sodium hexametaphosphate molecules remain stable and give full play to its excellent scale inhibition function. Then it enters the main anaerobic reactor, where it is gradually hydrolyzed and phosphorus is released under the action of microorganisms. This avoids the problem of calcium phosphate precipitation that may be caused by the direct addition of orthophosphate, and realizes the slow release and efficient utilization of phosphorus. 3. The method of the present invention fundamentally curbs the calcification trend of anaerobic sludge, ensures the activity of granular sludge, and solves the problem of nutrient deficiency, thereby significantly improving the long-term operational stability and treatment efficiency of the entire anaerobic treatment system. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0023] The principles and features of the present invention are described below (in conjunction with the accompanying drawings). The examples given are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0025] As used in this article, "influent COD" refers to the COD (chemical oxygen demand) of the influent to the anaerobic system.

[0026] The sources of some of the experimental materials and instruments used in this invention are shown below: Sodium hexametaphosphate was purchased from Tianjin Dingshengxin Chemical Co., Ltd.

[0027] This invention provides a method for the synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system, which involves adding sodium hexametaphosphate to the wastewater.

[0028] In one alternative embodiment, the sodium hexametaphosphate is added before the wastewater enters the anaerobic reactor.

[0029] Furthermore, sodium hexametaphosphate is added to the pre-acidification tank at the front end of the anaerobic reactor before the wastewater enters.

[0030] In one alternative implementation, the amount of sodium hexametaphosphate added is the greater of the scale inhibition requirement and the nutrient supplementation requirement.

[0031] It should be understood that when the calculated scale inhibition dosage is greater than the nutrient supplementation dosage, the dosage of sodium hexametaphosphate is the scale inhibition dosage; when the calculated scale inhibition dosage is less than the nutrient supplementation dosage, the dosage of sodium hexametaphosphate is the nutrient supplementation dosage.

[0032] In one alternative implementation, the required scale inhibitor dosage is calculated based on the calcium ion concentration in the influent.

[0033] Furthermore, the ratio of the required scale inhibitor dosage to the influent calcium ion concentration is 1:(20~50).

[0034] In one alternative implementation, the required nutrient supplementation dosage is calculated based on the influent COD (chemical oxygen demand).

[0035] Furthermore, the formula for calculating the required amount of nutritional supplements is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage (mg / L); x is the influent COD (mg / L); y is a coefficient with a value of 300-500; and P is the influent total phosphorus concentration (mg / L).

[0036] The present invention also provides a wastewater anaerobic treatment system, based on the above-described synergistic treatment method for scale prevention and nutrient supplementation in the wastewater anaerobic treatment system, wherein the anaerobic treatment system includes a pre-acidification tank and an anaerobic reactor connected in sequence.

[0037] In an alternative embodiment, a dosing device is also included for adding the sodium hexametaphosphate into the pre-acidification tank.

[0038] Preferably, the dosing device includes a storage tank for storing an aqueous solution of sodium hexametaphosphate and a metering pump.

[0039] In this invention, the sodium hexametaphosphate is continuously added in solution form to the pre-acidification tank, the effluent pipe of the pre-acidification tank, or the influent pipe of the anaerobic reactor.

[0040] More preferably, the sodium hexametaphosphate is prepared as a 10-30% aqueous solution.

[0041] Furthermore, the sodium hexametaphosphate is prepared as a 10% aqueous solution.

[0042] The above-mentioned anaerobic wastewater treatment system's synergistic treatment method for scale prevention and nutrient supplementation includes the following steps: S1. Water quality analysis: Detect the concentration of calcium ions and total phosphorus in the influent of the anaerobic system; S2. Calculate the dosage: The dosage of sodium hexametaphosphate [(NaPO3)6] simultaneously meets the requirements for scale inhibition and nutrient supplementation; (1) Scale inhibition dosage: Based on the influent calcium ion concentration obtained in step S1, add scale according to (NaPO3)6 / Ca 2+ The mass ratio is calculated based on a ratio of 1:20 to 1:50. (2) Nutrient supplementation requirement: The nutrient supplementation requirement is calculated based on the influent COD (chemical oxygen demand) concentration. The formula for calculating the nutrient supplementation requirement is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage, mg / L; x is the influent COD, mg / L; y is a coefficient, with a value of 300-500; and P is the total phosphorus concentration in the influent, mg / L. Ultimately, the larger value between the scale inhibition dosage and the nutrient supplement dosage was selected to ensure that both requirements were met simultaneously. S3. Dosing: Weigh out sodium hexametaphosphate according to the dosage calculated in step S2, dissolve the sodium hexametaphosphate in water, and continuously add it to the pre-acidification tank through the metering pump of the dosing device. The residence time is ≥1h, and the mixture is homogenized. The mixed wastewater is then pumped to the anaerobic reactor.

[0043] In this invention, the wastewater after pretreatment enters the anaerobic treatment system (pre-acidification tank + anaerobic reactor), and the wastewater treated by the anaerobic treatment system is discharged and then undergoes a downstream treatment process to meet discharge standards. It is understood that the specific processes for pretreatment and downstream treatment can be selected based on actual treatment conditions and requirements; no specific limitations are imposed here.

[0044] The present invention will now be described in detail with reference to embodiments and experimental data.

[0045] In the following examples, the calcium ion concentration was determined by EDTA titration (GB / T 7476-1987); the total phosphorus was determined by ammonium molybdate spectrophotometry (GB 11893-89); and the COD was determined by dichromate method for chemical oxygen demand (COD) in water (HJ 828—2017).

[0046] Example 1

[0047] A method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system includes the following steps: S1. Detect the calcium ion concentration, total phosphorus concentration, and COD in the influent of the anaerobic treatment system; S2. Calculate the dosage: The dosage of sodium hexametaphosphate [(NaPO3)6] simultaneously meets the requirements for scale inhibition and nutrient supplementation; (1) Scale inhibition dosage: Based on the influent calcium ion concentration obtained in step S1, add scale according to (NaPO3)6 / Ca 2+ The mass ratio is calculated to be 1:40. (2) Nutrient supplementation requirement: The nutrient supplementation requirement is calculated based on the influent COD (chemical oxygen demand) concentration. The formula for calculating the nutrient supplementation requirement is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage (mg / L); x is the influent COD (mg / L); y is a coefficient with a value of 400; and P is the influent total phosphorus concentration (mg / L). Ultimately, the larger value between the scale inhibition dosage and the nutrient supplement dosage was selected to ensure that both requirements were met simultaneously. S3. Dosing: Weigh out sodium hexametaphosphate according to the dosage calculated in step S2, dissolve the sodium hexametaphosphate in water to prepare a 10% aqueous solution, and continuously add it to the pre-acidification tank through the metering pump of the dosing device. The residence time is ≥1h, and the mixture is homogenized. The mixed wastewater is then pumped to the anaerobic reactor.

[0048] In this embodiment, the wastewater anaerobic treatment system includes a pre-acidification tank and an anaerobic reactor connected in sequence, as well as a dosing device for adding sodium hexametaphosphate solution.

[0049] Example 2

[0050] A method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system includes the following steps: S1. Detect the calcium ion concentration, total phosphorus concentration, and COD in the influent of the anaerobic treatment system; S2. Calculate the dosage: The dosage of sodium hexametaphosphate [(NaPO3)6] simultaneously meets the requirements for scale inhibition and nutrient supplementation; (1) Scale inhibition dosage: Based on the influent calcium ion concentration obtained in step S1, add scale according to (NaPO3)6 / Ca 2+ The mass ratio is calculated to be 1:50. (2) Nutrient Supplementation Requirements: Based on the influent COD (Chemical Oxygen Demand) concentration, the formula for calculating the nutrient supplementation requirements is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage, mg / L; x is the influent COD, mg / L; y is a coefficient, with a value of 500; and P is the influent total phosphorus concentration, mg / L. Ultimately, the larger value between the scale inhibition dosage and the nutrient supplement dosage was selected to ensure that both requirements were met simultaneously. S3. Dosing: Weigh out sodium hexametaphosphate according to the dosage calculated in step S2, dissolve the sodium hexametaphosphate in water to prepare a 10% aqueous solution, and continuously add it to the pre-acidification tank through the metering pump of the dosing device. The residence time is ≥1h, and the mixture is homogenized. The mixed wastewater is then pumped to the anaerobic reactor.

[0051] In this embodiment, the wastewater anaerobic treatment system includes a pre-acidification tank and an anaerobic reactor connected in sequence, as well as a dosing device for adding sodium hexametaphosphate solution.

[0052] Example 3

[0053] A method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system includes the following steps: S1. Detect the calcium ion concentration, total phosphorus (TP) concentration, and COD in the influent of the anaerobic treatment system; S2. Calculate the dosage: The dosage of sodium hexametaphosphate [(NaPO3)6] simultaneously meets the requirements for scale inhibition and nutrient supplementation; (1) Scale inhibition dosage: Based on the influent calcium ion concentration obtained in step S1, add scale according to (NaPO3)6 / Ca 2+ The mass ratio is calculated as 1:20. (2) Nutrient supplementation requirement: The nutrient supplementation requirement is calculated based on the influent COD (chemical oxygen demand) concentration. The formula for calculating the nutrient supplementation requirement is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage (mg / L); x is the influent COD (mg / L); y is a coefficient with a value of 300; and P is the influent total phosphorus concentration (mg / L). Ultimately, the larger value between the scale inhibition dosage and the nutrient supplement dosage was selected to ensure that both requirements were met simultaneously. S3. Dosing: Weigh out sodium hexametaphosphate according to the dosage calculated in step S2, dissolve the sodium hexametaphosphate in water to prepare a 10% aqueous solution, and continuously add it to the pre-acidification tank through the metering pump of the dosing device. The residence time is ≥1h, and the mixture is homogenized. The mixed wastewater is then pumped to the anaerobic reactor.

[0054] In this embodiment, the wastewater anaerobic treatment system includes a pre-acidification tank and an anaerobic reactor connected in sequence, as well as a dosing device for adding sodium hexametaphosphate solution.

[0055] It should be understood that existing equipment such as pre-acidification tanks, anaerobic reactors, and dosing devices can be selected according to actual needs, and there are no restrictions here.

[0056] Figure 1 This is a schematic diagram of the wastewater treatment process of the present invention. The wastewater after the front-end treatment enters the anaerobic treatment system (pre-acidification tank + anaerobic reactor). The wastewater after the anaerobic treatment system is discharged and then undergoes a back-end treatment process to meet the discharge standards.

[0057] The following experimental examples illustrate the beneficial effects of the present invention. Experimental methods not specifying particular conditions in the following examples are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, standard conditions, or conditions recommended by the manufacturer shall be followed.

[0058] Experiment Example 1: Hydrolysis Kinetics Experiment

[0059] Sodium hexametaphosphate (20 mg / L) was added to water, and the hydrolysis rate of sodium hexametaphosphate was measured under simulated pre-acidification tank conditions (pH 5.5, reaction time 120 min) and pH 7.5 conditions, respectively. The content of orthophosphate in the water was measured every 20 min. The experimental results are shown in Table 1 below: Table 1. Results of Hydrolysis Kinetics Experiment

[0060] As shown in Table 1, under pH 5.5 conditions, the orthophosphate release rate (orthophosphate release rate = orthophosphate concentration / sodium hexametaphosphate dosage concentration) within 2 hours was only 8.2%, while under pH 7.5 conditions, the orthophosphate release rate within 2 hours was 11.8%. This indicates that sodium hexametaphosphate only undergoes a small amount of hydrolysis under the pre-acidification tank conditions, with most of it still existing in a polymerized state, suggesting that sodium hexametaphosphate has a slow-release effect in a weakly acidic environment.

[0061] Experiment Example 2: Comparison Experiment on Scale Inhibition Efficiency

[0062] The bubbling method was used in the experiment: a test solution was prepared by mixing water containing calcium bicarbonate and a water treatment agent (scale inhibitor). The test solution was heated and a certain flow rate of air was blown in to simulate the heating and aeration of water under actual conditions. The air carried away the carbon dioxide, shifting the reaction equilibrium towards the formation of calcium carbonate and accelerating the decomposition of calcium bicarbonate. When the test solution quickly reached its natural equilibrium pH, the concentration of calcium ions in the test solution was measured. Calcium ions are stable; the higher the concentration, the less calcium carbonate scale is formed, indicating better scale inhibition performance of the water treatment agent.

[0063] Sodium hexametaphosphate was used as the experimental group, and HEDP, ATMP, polyacrylic acid, and polymaleic anhydride were used as control groups to simulate the actual wastewater quality of papermaking. The bubbling method (reaction temperature 60℃, reaction time 24h) was used to compare the effects of different scale inhibitors on high-calcium wastewater (Ca... 2+ The scale inhibition effect is 600 mg / L.

[0064] Wherein, scale inhibition rate = (1 - scale amount of the system after adding scale inhibitor / scale amount of the system without scale inhibitor) × 100%.

[0065] SEM was used to observe the morphology of scale. The process of observing the morphology of scale by SEM mainly includes three steps. First, sample preparation: the precipitates generated in each group are collected, gently rinsed with ultrapure water to remove soluble salts, dried, and then their surfaces are treated with conductive treatments such as gold sputtering. Second, observation: the samples are placed in the electron microscope chamber and vacuumed. The field of view is searched from low to high magnification, and parameters such as focus, astigmatism, and voltage are finely adjusted before images are acquired. Finally, image analysis: the micro-area elements are analyzed by energy dispersive spectroscopy to comprehensively interpret the microstructural information of scale, such as crystal shape, size, and distribution.

[0066] The experimental results are shown in Table 2 below: Table 2. Experimental Results of Scale Inhibition Effect

[0067] As shown in Table 2, the results indicate that sodium hexametaphosphate exhibits superior scale inhibition performance compared to mainstream scale inhibitors, with an excellent unit dosage cost. In contrast, the phosphorus in HEDP and ATMP is organic phosphorus, which cannot be directly utilized by microorganisms and has a low system decomposition rate, easily leading to excessive total phosphorus levels in the effluent. The scale layer formed by the sodium hexametaphosphate group has the highest porosity and the most pores, meaning that the scale formed is soft and easily washed away by water flow, making it less prone to hard adhesion and clogging.

[0068] Experimental Example 3: Comparative Experiment of Long-Term Anaerobic Reactors

[0069] The IC anaerobic reactor (10L volume, HRT=24h) was operated for 60 days.

[0070] Experimental group: Sodium hexametaphosphate (15 mg / L) was added to the pre-acidification tank;

[0071] Control group A: Scale inhibitor HEDP (15 mg / L) and phosphorus nutrient NaH2PO4 (14 mg / L) were added to the pre-acidification tank;

[0072] Control group B: Only phosphorus nutrient salt NaH2PO4 (14 mg / L) was added to the pre-acidification tank;

[0073] Control group C: The only difference from the experimental group is that sodium hexametaphosphate was added to the IC anaerobic reactor.

[0074] Experimental Procedure: The IC anaerobic reactor simulates the high-calcium characteristics (Ca) of real papermaking wastewater. 2+ =600mg / L), after 60 days of operation, the sludge calcium content, COD removal rate, and sludge activity (characterized by specific methanogenic activity) were measured using the following methods: Calcium ions: EDTA titration method (GB / T 7476-1987). Under alkaline conditions with pH ≥ 12, water samples are titrated with EDTA standard solution using calcium carboxylic acid as an indicator. EDTA preferentially binds to calcium ions, and the solution changes from red to bright blue at the endpoint. The calcium content is calculated based on the amount of EDTA consumed. COD: Chemical Oxygen Demand in Water - Dichromate Method (HJ 828—2017). Under the action of a strong acid and catalyst, water samples are refluxed with excess potassium dichromate for 2 hours at high temperature. After the potassium dichromate oxidizes the organic matter, the remaining potassium dichromate is titrated with ferrous ammonium sulfate, and the equivalent chemical oxygen demand is calculated based on the amount of oxygen consumed. Specific methanogenic activity: Anaerobic sludge and excess substrate are incubated at a constant temperature in an anaerobic serum bottle, and the volume of methane gas produced is measured precisely at regular intervals. The specific methanogenic activity value, which measures sludge activity, is obtained by dividing the maximum methanogenic rate by the sludge concentration (VSS).

[0075] The experimental results are shown in the table below: Table 3. Comparative Experiment Results of IC Anaerobic Reactor Simulated Operation for 60 Days

[0076] As shown in the table above, the experimental group with appropriate sodium hexametaphosphate exhibited superior performance in preventing sludge calcification, maintaining COD removal stability, and preserving sludge activity. Control group C, where sodium hexametaphosphate was directly added to the IC anaerobic reactor, performed worse than the experimental group in preventing sludge calcification, maintaining COD removal stability, and preserving sludge activity. This indicates that placing the sodium hexametaphosphate in the pre-acidification section, where the pH is relatively low, is beneficial for maintaining the stability of sodium hexametaphosphate molecules and allowing it to exert its excellent scale inhibition function.

[0077] Experiment Example 4 Application Case

[0078] Case 1: Using the method in Example 1, a wastewater treatment system for a medium-sized paper mill (daily treatment capacity of 5000 m³ / h) was implemented. 3 The anaerobic stage process consists of a pre-acidification tank + IC anaerobic reactor. After pretreatment at the front end, the influent COD of the anaerobic stage is 3000 mg / L, and the Ca... 2+ =600mg / L, TP (total phosphorus) =2.0mg / L.

[0079] 1. Calculate scale inhibition requirements: based on (NaPO3)6 / Ca 2+ Based on a ratio of 1:40, the required sodium hexametaphosphate dosage is 600 / 40 = 15.0 mg / L. 2. Calculate nutritional requirements: Based on a C:P ratio of 400:1, the ideal P concentration is 3000 / 400 = 7.5 mg / L. The required P supplement is 7.5 - 2.0 = 5.5 mg / L. Sodium hexametaphosphate contains approximately 31.6% P, therefore the required sodium hexametaphosphate concentration is 5.5 / 0.316 = 17.4 mg / L. 3. Determine the dosage: Take the larger value, that is, control according to nutritional needs, and the final dosage is determined to be 17.4 mg / L.

[0080] 4. Prepare a 10% aqueous solution of sodium hexametaphosphate and continuously add it to the pre-acidification tank through a metering pump. After being fully mixed with the wastewater, the solution enters the IC anaerobic reactor.

[0081] Results: After three months of continuous operation, sampling analysis and inspection of the IC anaerobic reactor revealed no significant calcium carbonate scale, good granular sludge activity, and a stable COD removal rate of over 85% in the effluent. Compared to previous methods that involved adding scale inhibitors and phosphates separately, the chemical costs were reduced by 40%.

[0082] In this case, the ratio of scale inhibition requirement to nutrient requirement was selected to be at the middle or lower value, which saved on chemical costs while ensuring the effect.

[0083] Case 2: Using the method in Example 2, a wastewater treatment system for a medium-sized paper mill (daily treatment capacity of 8000 m³ / h) was implemented. 3 The anaerobic stage process consists of a pre-acidification tank + IC anaerobic reactor, and the wastewater originally had a high concentration of calcium ions. After pretreatment, the influent COD of the anaerobic stage is 4000 mg / L, and the calcium content is... 2+ =1200mg / L, TP=1.0mg / L. The effluent discharge standard requires TP≤1.0mg / L.

[0084] 1. Calculate scale inhibition requirements: based on (NaPO3)6 / Ca 2+ Based on a ratio of 1:50, the required sodium hexametaphosphate dosage is 1200 / 50 = 24.0 mg / L.

[0085] 2. Calculate nutritional requirements: Based on a C:P ratio of 500:1, the ideal P concentration is 4000 / 500 = 8.0 mg / L. The required P supplement is 8.0 - 1.0 = 7.0 mg / L. Since sodium hexametaphosphate contains approximately 31.6% P, the required sodium hexametaphosphate concentration is 7 / 0.316 = 22.2 mg / L.

[0086] 3. Determine the dosage: Take the larger value, that is, control it according to the scale inhibition requirements. The final dosage is determined to be 24.0 mg / L.

[0087] 4. Implementation: Prepare a 10% aqueous solution of sodium hexametaphosphate and continuously add it to the pre-acidification tank through a metering pump. After being fully mixed with the wastewater, the solution enters the IC anaerobic reactor.

[0088] Results: After six months of continuous commissioning and operation of the papermaking wastewater treatment system, sampling analysis showed that the granular sludge in the IC anaerobic reactor exhibited good activity and no obvious calcification. According to the online effluent system, the COD removal rate remained stable above 82%, and the total phosphorus content consistently met the standard (TP≤1.0mg / L). This verifies that the addition of sodium hexametaphosphate has a dual synergistic effect of scale prevention and nutrient supplementation in this high-calcium wastewater treatment system for papermaking.

[0089] In this case, there are strict requirements for total phosphorus in the effluent (total phosphorus TP ≤ 1.0 mg / L). To avoid adding too much phosphorus and causing the total phosphorus in the effluent to exceed the standard, the addition ratios for scale inhibition and nutrient requirements are both set to low values.

[0090] Case 3: Using the method in Example 3, a wastewater treatment system (treatment capacity 18,000 m³) in a paper mill industrial park was implemented. 3 The anaerobic stage process consists of a pre-acidification tank + IC anaerobic reactor. The wastewater treatment system is designed primarily for automated operation to reduce manual workload; therefore, the system has higher requirements for scale prevention to minimize manual cleaning of scale-laden equipment. After pretreatment, the influent to the anaerobic stage has a COD of 2500 mg / L and a Ca... 2+ =500mg / L, TP=0.5mg / L.

[0091] 1. Calculate scale inhibition requirements: based on (NaPO3)6 / Ca 2+ Based on a ratio of 1:20 (higher value for scale prevention), the required sodium hexametaphosphate concentration is 500 / 20 = 25.0 mg / L.

[0092] 2. Calculate nutrient requirements: Based on a C:P ratio of 300:1 (using a higher value due to severe phosphorus deficiency in the raw water), the ideal phosphorus concentration is 2500 / 300 = 8.3 mg / L. The required phosphorus supplement is 8.3 - 0.5 = 7.8 mg / L. Since sodium hexametaphosphate contains approximately 31.6% phosphorus, the required sodium hexametaphosphate concentration is 7.8 / 0.316 = 24.7 mg / L.

[0093] 3. Determine the dosage: Take the larger value, that is, control it according to the scale inhibition requirements. The final dosage is determined to be 25.0 mg / L.

[0094] 4. Implementation: Prepare a 10% aqueous solution of sodium hexametaphosphate and continuously add it to the pre-acidification tank through a metering pump. After being fully mixed with the wastewater, the solution enters the IC anaerobic reactor.

[0095] Results: After two years of continuous operation, the wastewater treatment system in this paper mill industrial park, through the addition of sodium hexametaphosphate, not only meets the nutritional needs of microorganisms but also exhibits excellent scale prevention. The frequency of offline cleaning due to scaling of easily scaled components in the anaerobic section is only 0.5 times per year, which is 80% lower than the scaling cleaning frequency of traditional paper mill wastewater anaerobic section equipment, achieving a double reduction in both chemical dosage and labor maintenance costs.

[0096] In this case, the raw water has high requirements for scale inhibition and is severely deficient in phosphorus, so the dosage ratio for scale inhibition and nutrient requirements should be high.

[0097] In summary, this invention utilizes the long-chain structure of sodium hexametaphosphate, which can effectively inhibit the formation of calcium carbonate scale through threshold effect and lattice distortion effect. Simultaneously, it can slowly hydrolyze under anaerobic acidic conditions, gradually releasing orthophosphate ions, providing a stable and continuous phosphorus source for anaerobic microorganisms. This invention solves two problems at the cost of a single reagent, reducing reagent dosing equipment and storage space, simplifying the operation process, and significantly reducing system operating costs and maintenance complexity. This invention sets the sodium hexametaphosphate dosing point in the pre-acidification section, where the pH is relatively low, which is conducive to the stability of sodium hexametaphosphate molecules and allows it to preferentially exert its excellent scale inhibition function. Subsequently, it enters the main anaerobic reactor, where it is gradually hydrolyzed and phosphorus released under the action of microorganisms, avoiding the calcium phosphate precipitation problem that may be caused by direct addition of orthophosphate, thus achieving slow release and efficient utilization of phosphorus.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system, characterized in that, Sodium hexametaphosphate was added to the wastewater.

2. The method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system according to claim 1, characterized in that, The sodium hexametaphosphate is added before the wastewater enters the anaerobic reactor.

3. The method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system according to claim 2, characterized in that, Sodium hexametaphosphate was added to the pre-acidification tank at the front end of the anaerobic reactor.

4. The method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system according to claim 1, characterized in that, The dosage of sodium hexametaphosphate is the greater of the scale inhibition dosage and the nutrient supplementation dosage.

5. The method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system according to claim 4, characterized in that, The required dosage for scale inhibition is calculated based on the calcium ion concentration in the influent.

6. The method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system according to claim 5, characterized in that, The ratio of the required scale inhibitor dosage to the influent calcium ion concentration is 1:(20~50).

7. The method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system according to claim 4, characterized in that, The required amount of nutrient supplementation is calculated based on the COD (chemical oxygen demand) of the influent.

8. The method for synergistic treatment of scale prevention and nutrient supplementation in an anaerobic wastewater treatment system according to claim 7, characterized in that, The formula for calculating the required amount of nutritional supplementation is as follows: a = (x / yp) / 0.316 Where a is the required nutrient supplement dosage (mg / L); x is the influent COD (mg / L); y is a coefficient with a value of 300-500; and P is the influent total phosphorus concentration (mg / L).

9. A wastewater anaerobic treatment system, based on the synergistic treatment method for scale prevention and nutrient supplementation in the wastewater anaerobic treatment system according to any one of claims 1 to 7, characterized in that, The treatment system includes a pre-acidification tank and an anaerobic reactor connected in sequence.

10. The anaerobic wastewater treatment system according to claim 9, characterized in that, It also includes a dosing device for adding the sodium hexametaphosphate into the pre-acidification tank.

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