Water treatment method for high-algae, high-plankton and iron-manganese composite micro-pollution source in middle Yunnan region

Abstract

The invention discloses a water treatment method for high-algae, high-plankton and iron-manganese composite micro-pollution sources in the middle Yunnan region, and relates to the technical field of tap water treatment. According to the technical scheme, the method comprises the following steps: diluting 10-13% sodium hypochlorite stock solution to about 5%, and storing for later use; sodium hypochlorite is detected in the storage process through a portable chlorate detector; when the manganese content of the source water is lower than 0.15 mg / L, chlorine dioxide or potassium permanganate is added during pre-oxidation to remove iron and manganese; when the manganese content of the source water is higher than 0.15 mg / L, potassium permanganate is added to remove iron and manganese or potassium permanganate and chlorine dioxide are combined to remove manganese, and the addition of chlorine dioxide does not exceed 1.0 mg / L; pre-oxidizing and inhibiting the flea and the cyclops in the source water by using chlorine dioxide; cO2 needs to be added to reduce the pH of the source water. The method has the beneficial effects that the using effect of sodium hypochlorite is optimized, iron-manganese composite micro-pollution is effectively removed, high plankton is inhibited and killed, the pH value of source water is adjusted, the aluminum content is controlled, the water treatment efficiency and economical efficiency are improved, the adaptability is high, popularization is easy, and the method has important significance for guaranteeing drinking water safety and improving the water treatment efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of tap water treatment, and in particular to a method for treating water from a complex micro-pollution source with high algae content, high plankton content, and iron and manganese content in central Yunnan. Background Art

[0002] Reservoir source water in central Yunnan often faces problems such as high algae, high plankton (such as fish fleas, copepods, etc.), and iron-manganese complex micro-pollution. The reproduction of algae also causes the pH of the source water to rise. The increase in pH will bring great difficulties to the disinfection effect of sodium hypochlorite and the control of aluminum in the water leaving the factory, which brings huge challenges to the water treatment process of the tap water plant.

[0003] 1. Application and Challenges of Sodium Hypochlorite Disinfection of Drinking Water: Currently, water utilities that previously used chlorine disinfection are gradually changing their disinfection methods, with the majority switching to sodium hypochlorite solution. Sodium hypochlorite offers a more efficient and relatively safe disinfection process and has become the mainstream disinfection process for water treatment. However, sodium hypochlorite also presents some challenges during the disinfection process. During the use of sodium hypochlorite disinfection, we discovered that some water utilities lack a deep understanding of the properties of sodium hypochlorite, potential reactions during storage, and the resulting disinfection byproducts such as chlorates, chlorites, trihalomethanes, and haloacetic acids, all of which contribute to ensuring effective disinfection.

[0004] (1) Sodium hypochlorite is prone to hydrolysis and may undergo chemical reactions during storage

[0005] 1. Hydrolysis reaction

[0006] Sodium hypochlorite is an unstable oxidant that can undergo a variety of chemical reactions in solution. It hydrolyzes in water to produce hypochlorous acid, a reversible reaction. Its composition and oxidizing properties vary with pH. The lower the pH, the higher the proportion of HClO, and the stronger the oxidizing and disinfecting abilities:

[0007]

[0008] At the same time, sodium hypochlorite may undergo decomposition and disproportionation reactions during storage, resulting in a continuous decrease in the effective chlorine concentration. The disproportionation reaction also produces a by-product, chlorate, and an intermediate product, chlorite, as shown in formulas (1) and (2):

[0009] 2. Decomposition reaction and disproportionation reaction

[0010] Decomposition reaction: 2NaClO=2NaCl+O2↑(1)

[0011] Disproportionation reaction: 3NaClO = 2NaCl + NaClO3 (2)

[0012] The disproportionation reaction is presumably divided into two-step ion reactions, as shown in Equations (3) and (4):

[0013] 2ClO - →ClO2 - +Cl - (3)

[0014] ClO2-+ClO - →ClO3 - +Cl - (4)

[0015] Decomposition and disproportionation reactions can occur simultaneously, and which reaction predominates depends on the reaction conditions. Generally speaking, light favors decomposition, while heating promotes disproportionation. However, decomposition can also occur at excessively high temperatures. This is why a water plant in Yunnan Province, which uses sodium hypochlorite instead of chlorine dioxide, has detected significant levels of chlorite in its water supply.

[0016] (2) Source water pH has an impact on the disinfection effect of sodium hypochlorite

[0017] In 2022, the five water plants in Yunnan Province that used sodium hypochlorite for disinfection encountered the problem in different seasons that the free chlorine in the factory water had reached 0.60 mg / L, and the contact time was more than 30 minutes, but the total colony count and total coliform group of the factory water and pipe network water (free chlorine was between 0.10 and 0.30 mg / L) still exceeded the standard from time to time. Some also had excessive pH and residual aluminum. After careful analysis of the inspection reports, a common point was found: the pH of the source water of the five water plants was above 8.10, ranging from 8.10 to 8.50. pH has the greatest influence on the bactericidal effect of sodium hypochlorite. The bactericidal effect of sodium hypochlorite mainly depends on the concentration of undecomposed hypochlorous acid in the solution. Hypochlorite (ClO - ) has a weak bactericidal ability. According to literature reports, based on experiments on Escherichia coli, hypochlorite ions (ClO - ) has a sterilization efficiency of only 1 / 80 of that of hypochlorous acid, while HClO and ClO - The relative proportion mainly depends on the pH value. The lower the pH value of the solution, the more undecomposed hypochlorous acid there is. As the pH rises, more and more hypochlorous acid decomposes into hydrogen and hypochlorite ions. When the pH is greater than 10, OCl - Close to 100%, when pH < 5, HClO close to 100%. When pH = 7.54, HClO and ClO - When pH=8.20, ClO - Close to 80%.

[0018] Therefore, during disinfection, care should be taken to control the pH of the water. It should not be too high, as this will produce an excess of hypochlorite ions and a decrease in hypochlorous acid, which would affect sterilization efficiency. Five water plants adjusted the source water pH to between 7.00 and 7.50, ensuring effective disinfection with minimal microbial, pH, or aluminum overload. Why not adjust the pH to less than 7.00? A pH below 7.00 in the outlet water can exacerbate corrosion in the pipe network and shorten its service life. It's worth noting that sodium hypochlorite (NaClO) is a strong base with a weak acid salt. Adding 1mg / L to 3mg / L of sodium hypochlorite can raise the outlet water pH by 0.15 to 0.45.

[0019] (3) Issues with chlorate and chlorite, by-products of sodium hypochlorite disinfection

[0020] Currently, water plants use two types of sodium hypochlorite disinfectants. One uses finished sodium hypochlorite solutions, typically with an available chlorine content of 10% to 13%. The other uses a sodium hypochlorite generator to electrolyze salt to produce a low-concentration sodium hypochlorite solution of approximately 0.8% for on-site disinfection. Improper use of sodium hypochlorite disinfection methods often results in excessive levels of chlorate and chlorite, byproducts of drinking water disinfection. Both 10% to 13% finished sodium hypochlorite and 0.8% sodium hypochlorite produced on-site by generators present chlorate byproducts. The chlorate content of sodium hypochlorite produced by on-site generators depends on the generator's performance, electrolysis conditions, storage time, and storage conditions. Research into the changes in chlorate in finished sodium hypochlorite revealed that a Yunnan water plant used a finished sodium hypochlorite stock solution with an available chlorine content of approximately 13%. On-site follow-up studies revealed that the sodium hypochlorite sampled from the tank trucks entering the plant contained chlorate, ranging from 363.45 to 720.32 mg / L. After three days of storage, the chlorate content in the sodium hypochlorite solution sampled from the storage tank rose to 4627.35 mg / L. After five days of storage, the chlorate content in the sodium hypochlorite solution sampled from the storage tank rose to 8463.75 mg / L. After 10 days of storage, the chlorate content in the sodium hypochlorite solution sampled from the storage tank rose to 10005.37 mg / L. If the dosage of available chlorine of sodium hypochlorite in the water plant is 2-3 mg / L, and the available chlorine content of sodium hypochlorite decreases during storage and transmission (to be discussed in the next point), the chlorate content in the water leaving the factory may exceed 0.7 mg / L, which poses a great risk of exceeding the standard.

[0021] (IV) Special attention should be paid to the attenuation trend of the effective chlorine concentration of sodium hypochlorite solution during storage

[0022] As mentioned in the second sub-point of the first point above, sodium hypochlorite solution may undergo decomposition and disproportionation reactions during storage, resulting in a continuous decrease in the effective chlorine concentration. Many water plants have not paid enough attention to this issue, and greater attention is needed. While guiding a Yunnan water plant to address the issue of unsatisfactory disinfection effectiveness of sodium hypochlorite solution, which occasionally exceeded microbial indicators, we studied the changing trends of effective chlorine in the plant's sodium hypochlorite during storage. The plant used a finished sodium hypochlorite solution with an effective chlorine content of approximately 13%. When the tank truck was unloaded, a sample of the sodium hypochlorite solution showed an initial effective chlorine concentration of 12.92%. This concentration dropped to 11.96% on the fourth day, 11.42% on the seventh day, and 10.81% on the eleventh day, an average daily decrease of 0.194%, reaching 9.32% on the twentieth day. It can be seen from this that the longer the sodium hypochlorite solution is stored, the more the effective chlorine concentration continues to decrease. During the storage process, the effective chlorine concentration of the sodium hypochlorite solution shows a downward trend. By the 20th day, the effective chlorine concentration of the sodium hypochlorite has dropped to 75% to 80% of the initial concentration. This means that in order to achieve the same disinfection effect, more sodium hypochlorite solution needs to be added, which also brings the risk of increased chlorate concentration in the effluent. This is also one of the reasons why the water plant maintains the same dosage but sometimes exceeds the microbial indicators. According to the literature, if the differences in other factors are not taken into account, the effective chlorine concentration of the diluted sodium hypochlorite solution decreases more slowly than that of the original solution. Relevant studies have shown that the decomposition rate of sodium hypochlorite with a low content of effective chlorine of about 5% is much slower than that of 10%.

[0023] II. Research on Excessive Aluminum in Water Plant Outlet Water: Excessive aluminum in water plant outlet water has become a major challenge for many water plants, and improper handling can compromise drinking water safety. Currently, most domestic water plants use aluminum salts as flocculants. During their use, it has been discovered that algae blooms in source water during summer and autumn can increase the pH of the source water. This can lead to the hydrolysis of the Al(OH)3 colloid produced when aluminum salt flocculants are used under conventional water treatment processes, potentially resulting in excessive aluminum in the outlet water.

[0024] 3. How to inhibit and kill high-level plankton in raw water (such as fish fleas, cyclops, etc.)

[0025] 4. Seasonal iron and manganese problems in reservoirs: Excessive manganese in water leaving the water plant has become a major problem in water treatment for many water plants. If manganese removal cannot be carried out properly, it will cause yellow water in the pipe network, affecting the safety of drinking water. Yunnan's special geographical, geological, landform, soil and climatic conditions make the water temperature stratification of source water obvious in spring and summer, forming a density barrier. The upper and lower water bodies are separated by the thermocline and lack convection movement, making it difficult for oxygen on the surface of the reservoir to enter the reservoir bottom through the thermocline. At the same time, the original dissolved oxygen at the bottom of the reservoir is not only decomposed by organic matter, but also consumed by reducing pollutants, resulting in a decrease in dissolved oxygen in the bottom layer, a drop in pH, and the MnO2 in the sediment at the bottom of the reservoir being reduced to soluble Mn 2+ Therefore, it is necessary to study the removal measures of manganese and iron in water production.

[0026] 5. The problem of alum flocs mixed with algae being difficult to settle: In the process of treating high-algae and low-turbidity source water in central Yunnan, the problem of alum flocs being poorly flocculated and difficult to settle, and the aluminum content easily exceeding the standard (the solution has been discussed in the second point above) often occurs. When the pH value is high, the algae are high, and the turbidity is low, there are problems of poor flocculation and difficulty in settling alum flocs, and there is a water quality risk of aluminum content being difficult to control. Summary of the Invention

[0027] In order to solve the above-mentioned technical problems existing in the prior art, the present invention provides a method for treating water from high-algae, high-plankton, and iron-manganese composite micro-pollution sources in central Yunnan. The method optimizes the use effect by reasonably controlling the storage period, strengthening monitoring, and adjusting the pH value. In response to the problem of excessive aluminum in the effluent from the water plant, the optimal pH control range is determined through beaker coagulation and stirring experiments, effectively reducing the aluminum content. Pre-oxidants such as chlorine dioxide and potassium permanganate are used, and the dosage is strictly controlled to achieve good iron and manganese removal effects and avoid excessive disinfection by-products.

[0028] To achieve the above object, the present invention provides the following technical solutions:

[0029] A method for treating water with high algae, high plankton, and iron and manganese composite micro-pollution in central Yunnan, comprising the following steps:

[0030] S1. When unloading the sodium hypochlorite solution, dilute the 10% to 13% sodium hypochlorite stock solution to about 5% for storage;

[0031] S2. Testing sodium hypochlorite during storage using a portable chlorate detector;

[0032] S3. When the manganese content of the source water is lower than 0.15 mg / L, chlorine dioxide or potassium permanganate is added during pre-oxidation to remove iron and manganese; when the manganese content of the source water is higher than 0.15 mg / L, potassium permanganate is added to remove iron and manganese, or potassium permanganate and chlorine dioxide are added to remove iron and manganese, and the amount of chlorine dioxide added shall not exceed 1.0 mg / L;

[0033] S4. When the number of fish fleas and cyclops fleas in the source water is high, use chlorine dioxide for pre-oxidation inhibition, and the inhibition dosage should not exceed 1.0 mg / L of chlorine dioxide solution;

[0034] S5. When the pH of the source water is high, CO2 needs to be added to lower the pH of the source water.

[0035] Furthermore, in step S1, during storage and use of the purchased finished sodium hypochlorite solution or the low-concentration sodium hypochlorite solution of about 0.8% prepared on-site using a sodium hypochlorite generator, the effective chlorine concentration is monitored more strictly and the dosage is adjusted in a timely manner.

[0036] Furthermore, in step S1, the optimal storage conditions of the sodium hypochlorite solution are determined according to the local climate conditions and the production conditions of the water plant to slow down the rate of decrease of the effective chlorine concentration during storage.

[0037] Furthermore, in step S2, the purchased sodium hypochlorite disinfectant is stored at room temperature, and the supply cycle is about 7-10 days.

[0038] Furthermore, in step S2, before adding new reagent to the storage tank or storage pool, the reagent in the storage tank or storage pool is used up, and the storage tank or storage pool is emptied and cleaned regularly to reduce the impact of residual liquid on the quality of sodium hypochlorite.

[0039] Furthermore, in step S2, the pre-warehousing inspection of the purchased finished sodium hypochlorite solution is strengthened, and the chlorate content and heavy metal ion content in the sodium hypochlorite solution before entering the tank pool are strictly controlled.

[0040] Furthermore, in step S3, a complete potassium permanganate dosing system is selected to ensure the accuracy of the potassium permanganate dosage.

[0041] Furthermore, in step S4, the fish fleas and copepods in the raw water are first inhibited and killed by pre-oxidation with chlorine dioxide, and then disinfected with sodium hypochlorite solution.

[0042] Furthermore, in step S5, kaolin is added to adjust the turbidity of the source water, and at the same time, the pH of the source water is adjusted to decrease from 8.13 to 7.49.

[0043] Furthermore, in step S5, under the conditions of algae outbreak in the source water and the use of strong base and weak acid salt sodium hypochlorite solution for disinfection in the water plant, the changes in the pH value of the source water and the increase in the pH value of the process water caused by the sodium hypochlorite solution are continuously detected and observed.

[0044] Beneficial effects of the present invention:

[0045] Compared with the existing technology, the method for treating water with high algae, high plankton, and iron and manganese composite micro-pollution in central Yunnan Province described in the present invention has the following technical characteristics or beneficial effects:

[0046] (1) Optimizing the effectiveness of sodium hypochlorite: By diluting the high-concentration sodium hypochlorite stock solution to about 5% for storage, its decomposition and disproportionation reaction during storage is slowed down, reducing the rate of decrease in the effective chlorine concentration, thereby ensuring the stability and durability of the disinfection effect. At the same time, through real-time monitoring by a portable chlorate detector, the dosage of sodium hypochlorite can be adjusted in a timely manner, avoiding the problem of excessive levels of disinfection by-products such as chlorate and chlorite, and improving the safety of drinking water.

[0047] (2) Effectively remove iron and manganese combined micro-pollution: Depending on the manganese content of the source water, chlorine dioxide and potassium permanganate are flexibly selected as pre-oxidants. This not only effectively removes iron and manganese pollutants, but also avoids the problem of disinfection by-products caused by excessive addition. The use of a complete potassium permanganate dosing system ensures the accuracy of the dosage, further improving the iron and manganese removal effect.

[0048] (3) Inhibit and kill high-level plankton: By adding chlorine dioxide for pre-oxidation, high-level plankton such as fish fleas and water fleas in the raw water are effectively inhibited and killed, reducing their impact on the water treatment process and ensuring the clarity and hygiene of the effluent water quality.

[0049] (4) Adjusting the pH of the source water and controlling the aluminum content: By adding CO2 to lower the pH of the source water, not only does it optimize the disinfection effect of sodium hypochlorite, but it also avoids the problem of excessive aluminum content caused by excessive pH. Adding kaolin to adjust the turbidity of the source water also further adjusts the pH value, making the effluent water quality more stable and safe.

[0050] (5) Improved water treatment efficiency and economic efficiency: The technical solution of this invention comprehensively considers multiple aspects of sodium hypochlorite, including storage, use, and monitoring, as well as iron and manganese removal, plankton elimination, and pH adjustment, to form a complete and efficient water treatment process. By precisely controlling various parameters and dosage, it not only improves water treatment efficiency but also reduces operating costs, achieving a win-win situation in both economic and environmental benefits.

[0051] (6) Strong adaptability and easy promotion: The technical solution of the present invention proposes a targeted treatment strategy for complex water quality problems such as high algae and plankton levels, and iron and manganese complex micro-pollution in central Yunnan. Furthermore, the technical solution is simple to operate and easy to control, has strong adaptability to changes in water quality, and is easy to promote and apply in water treatment plants in similar areas.

[0052] In summary, the present invention provides a scientific, efficient and economical technical solution for the treatment of micro-pollution in reservoir source water in central Yunnan, which is of great significance for ensuring the safety of drinking water and improving water treatment efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort. Among them:

[0054] Figure 1 This is a graph showing changes in the aluminum content of filtered water and the turbidity of settled water with pH;

[0055] Figure 2 This is a curve diagram of the change of aluminum content and turbidity in water after filtration with pH according to the conventional treatment process of the present invention. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Figure 1-2 The method for treating water from high-algae, high-plankton, and iron-manganese composite micro-pollution sources in central Yunnan is further explained, and the technical solutions in the embodiments of this application are clearly and completely described; obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0057] Example 1

[0058] To address the problem of chlorate and chlorite, byproducts of sodium hypochlorite disinfection, this embodiment adopts the following measures:

[0059] 1. The sodium hypochlorite disinfectants currently purchased are all stored at room temperature. The recommended purchasing cycle is about 7 days, and generally should not exceed 10 days, because the amount of chlorate generated is closely related to the storage time. The longer the storage time, the higher the chlorate concentration.

[0060] 2. In order to prevent the sodium hypochlorite base liquid in the storage tank from being stored for too long, before adding new reagents to the storage tank (pool), the reagents in the storage tank (pool) should be used up as much as possible, and the storage tank (pool) should be emptied and cleaned regularly to reduce the impact of residual liquid on the quality of sodium hypochlorite.

[0061] 3. Strengthen the pre-warehousing inspection of purchased finished sodium hypochlorite solution, and strictly control the chlorate content and heavy metal ion content in the sodium hypochlorite solution before entering the tank pool.

[0062] 4. Commercial sodium hypochlorite will undergo chemical reactions such as decomposition and disproportionation during storage. It is recommended to use a portable chlorate detector.

[0063] Example 2

[0064] To address the issue of attenuation of the effective chlorine concentration of sodium hypochlorite solution during storage, this embodiment adopts the following measures:

[0065] 1. Whether it is the finished sodium hypochlorite solution purchased or the low-concentration sodium hypochlorite solution of about 0.8% prepared on-site using a sodium hypochlorite generator, the effective chlorine concentration should be monitored more strictly during storage and use, and the dosage should be adjusted in time to ensure the water quality of the effluent.

[0066] 2. Determine the optimal storage conditions for sodium hypochlorite solution based on local climatic conditions and the production situation of the water plant to slow down the rate of decrease in the effective chlorine concentration during storage.

[0067] 3. You can try to dilute the 10% to 13% sodium hypochlorite stock solution to about 5% when unloading and store it for later use.

[0068] Example 3

[0069] Given the problem of excessive aluminum in waterworks' effluent, it's crucial to investigate control measures for aluminum content in waterworks. This beaker coagulation and stirring experiment, using reservoir water from a waterworks in central Yunnan, investigated the effect of pH on aluminum content in drinking water and how to control it.

[0070] (1) Overview of water plant technology and water quality

[0071] The design scale of the second phase of a water plant in central Yunnan is 50,000 m 3 / d. The source water is taken from a reservoir in the area. The water plant adopts the conventional water treatment process: source water → mixing → grid reaction → inclined tube sedimentation → siphon filter → chlorination disinfection → clear water tank → effluent. The flocculant is liquid polyaluminum chloride and the disinfectant is sodium hypochlorite solution. The inlet pH is 8.00±0.28. In the summer when the temperature is high and algae are high, the pH can reach 8.40-8.50. The turbidity is 3.0±2.0NTU and the algae are as high as 5.8×10 8Cells / L, the aluminum content of the source water is 0.0092 mg / L, and the aluminum content of the water leaving the water plant is occasionally close to 0.20 mg / L at certain times. Especially since the use of strong base and weak acid sodium hypochlorite solution for disinfection in the second half of 2022 will cause the pH to rise, aluminum control has become particularly important. In order to solve this water treatment technology problem, we conducted a series of beaker coagulation and stirring experiments on high-pH source water to determine the optimal pH control range of the water after the coagulation reaction. In production, we used the existing hydrochloric acid addition process to adjust the pH to the optimal control range, successfully solving the practical problem of aluminum content sometimes approaching the standard in production, and meeting the standard requirements for high-quality water.

[0072] (2) Experimental water quality

[0073] The source water from a reservoir at a water plant in central Yunnan during a certain period of time was used as the experimental water. Some conventional indicators are shown in Table 1.

[0074] Table 1 Source water quality

[0075] Serial number project unit Detection value 1 Turbidity NTU 4.62 2 Ammonia (as N) mg / L 0.09 3 <![CDATA[Permanganate index (calculated as O2)]]> mg / L 2.54 4 pH … 8.13 5 water temperature ℃ 25.6 6 aluminum mg / L 0.0092 7 Total phytoplankton density Cells / L <![CDATA[5.8*10 8 ]]>

[0076] (3) Effect of pH on aluminum content

[0077] 1. Beaker coagulation stirring experiment

[0078] The beaker coagulation and stirring experiment was conducted with the source water from a reservoir in central Yunnan as the sample. Six cups of 1L source water were taken and the pH was adjusted artificially to conduct the beaker coagulation and stirring experiment to explore the relationship between pH and the aluminum content of the filtered water. # , 2 # , 3 # , 4 # CO2 and 5 # , 6 # Add appropriate amount of NaOH solution. The quality of the experimental source water is shown in Table 1. The dosage of liquid polyaluminium chloride is 18.0 mg / L. The experimental phenomena and results are shown in Table 2. The curves of turbidity, aluminum content after filtration and turbidity of water after precipitation with pH are shown in Table 2. Figure 1 .

[0079] Table 2 Experimental phenomena and results

[0080]

[0081] From Table 2 and Figure 1It can be seen that as the pH of the source water gradually increases, the alum flocs become smaller and difficult to settle, and the aluminum content in the filtered water and the turbidity of the settled water also gradually increase. When the pH of the source water is less than 7.30, the aluminum content in the filtered water is relatively low, ranging from 0.09 to 0.14 mg / L, which is less than the national standard requirement of 0.2 mg / L. When the pH of the source water is greater than 7.30, the aluminum content in the filtered water also increases. When the pH of the source water is 7.50 to 8.54, the aluminum content is between 0.20 and 0.30 mg / L, both exceeding the national standard requirement of 0.2 mg / L.

[0082] The reason why aluminum content increases with the increase of pH is that when pH is less than 7.50, aluminum salts hydrolyze to generate a large amount of Al(OH)3 colloid condensed solids, which are easy to sink, causing the residual aluminum content in the water to drop to the lowest point. When pH is greater than 7.50, more Al(OH)4 - The amount of aluminum remaining in the dissolved form increases with increasing pH.

[0083] The beaker test results show that under the condition of adding a certain amount of liquid polyaluminium chloride, the pH conditions of the coagulation reaction have a significant impact on the aluminum content. Improper pH control can easily cause the aluminum content of the filtered water to exceed the standard. Therefore, in actual water plant production, the amount of lime or CO2 added should be controlled based on the pH of the water after the coagulation reaction being controlled between 7.00 and 7.30. At the minimum, the pH of the water after the reaction must be kept below 7.50, otherwise the aluminum content in the effluent will easily exceed the standard.

[0084] 2. Production practice operation test

[0085] According to the beaker test results, water from a reservoir in central Yunnan was used as source water many times in production. The pH was adjusted with hydrochloric acid to a range of 7.05 to 7.62. The changes in the aluminum content and turbidity of the filtered water after conventional treatment process with pH were shown in the table below. Figure 2 .

[0086] Depend on Figure 2 It can be seen that the aluminum content in filtered water changes with pH in production, similar to the results of the beaker stirring experiment. Both increase with rising pH, and when the pH exceeds 7.50, the aluminum content in filtered water easily exceeds the limit of 0.2 mg / L. Therefore, in actual production, it is best to control the amount of HCl (CO2) or lime added based on the pH of the water after the coagulation reaction between 7.10 and 7.30 to keep the aluminum content at a low and safe level.

[0087] (IV) Treatment measures

[0088] 1. The excessive aluminum content in the effluent from the water plant is mainly caused by soluble aluminum, which is closely related to the form of aluminum. The form of aluminum is related to the pH of the water. When algae in the source water break out and the water plant uses strong base and weak acid sodium hypochlorite solution for disinfection, it is necessary to pay close attention to the changes in the pH of the source water and the situation where the sodium hypochlorite solution causes the pH of the process water to rise.

[0089] 2. When the inlet pH is greater than 7.50, carbon dioxide dosing equipment or direct addition of liquid CO2 is usually used in production to lower the pH. HCl can also be added to adjust the pH to achieve the same effect, but it has the disadvantages of being difficult to control, dangerous in storage and operation, releasing harmful fumes, being corrosive, and increasing the salt content in the water.

[0090] 3. In the actual production of water plants, the amount of HCl (CO2) or lime added should be controlled based on the pH of the water after coagulation reaction being controlled between 7.00 and 7.30 to reduce the aluminum content of the process water. At the very least, the pH of the reaction water must be kept below 7.50, otherwise the aluminum content in the effluent will easily exceed the standard.

[0091] Example 4

[0092] Regarding how to inhibit and kill high-level plankton (such as fish fleas and copepods) in raw water: From 2020 to 2022, at a water plant in Yunnan, we studied the use of sodium hypochlorite solution and chlorine dioxide to inhibit and kill fish fleas and copepods in raw water. The results showed that adding 1.0 mg / L of chlorine dioxide solution was able to kill fish fleas and copepods in raw water, while adding 2.5 mg / L of sodium hypochlorite solution did not achieve this effect. Therefore, special attention should be paid to the research on the combination of sodium hypochlorite solution with chlorine dioxide and potassium permanganate. Therefore, it is recommended to strengthen the pre-oxidation with chlorine dioxide and potassium permanganate to inhibit and kill fish fleas and copepods in raw water, and then use sodium hypochlorite solution for disinfection.

[0093] Example 5

[0094] In response to the seasonal iron and manganese problems in reservoirs, experiments have found that when sodium hypochlorite is selected as a pre-oxidant, the manganese removal effect is not ideal, and the turbidity and permanganate index content of the filtered water are relatively high; when chlorine dioxide is selected as a pre-oxidant, the iron and manganese removal effects are improved compared to sodium hypochlorite, but the content of the disinfection by-product chlorite is very easy to exceed the standard, and the turbidity and permanganate index content of the filtered water are high; when potassium permanganate is selected as a pre-oxidant, the iron and manganese removal effects are obvious, and the content of the disinfection by-product chlorite is low, but the dosage of potassium permanganate needs to be strictly controlled, otherwise "red water incidents" are likely to occur; when potassium permanganate and chlorine dioxide are selected as pre-oxidants, although the iron and manganese removal effects are better, the cost is higher than adding potassium permanganate alone, and the dosage of potassium permanganate still needs to be controlled.

[0095] The treatment measures are as follows: 1. When the manganese content of the source water is lower than 0.15 mg / L, chlorine dioxide or potassium permanganate can be added during pre-oxidation to remove iron and manganese, and the content of disinfection by-product chlorite is not easy to exceed the standard at this time; when the manganese content of the source water is higher than 0.15 mg / L, in order to prevent the content of disinfection by-product chlorite from exceeding the standard, it is recommended to add potassium permanganate to remove iron and manganese or potassium permanganate and chlorine dioxide to remove manganese. The dosage of chlorine dioxide and potassium permanganate needs to be strictly controlled. Excessive addition will not only cause waste, but also easily lead to the factory water being slightly reddish and the manganese content exceeding the standard and the chlorite content exceeding the standard. In actual production operation, the dosage needs to be preliminarily determined according to the beaker coagulation and stirring experiment, because in addition to Mn 2+ In addition to consuming potassium permanganate, there are other reducing substances that will consume potassium permanganate to a greater or lesser extent. The content of these reducing substances in different source water areas is different, and the amount of potassium permanganate consumed is also inconsistent.

[0096] 2. The use of potassium permanganate can effectively remove iron and manganese from source water. At the same time, this method has the advantages of simple manganese removal, less required facilities, less investment and less land in actual production applications in water plants. The by-products are easy to control and can be used as one of the preferred methods for removing iron and manganese during pre-oxidation.

[0097] 3. Selecting a complete set of potassium permanganate dosing system with accurate dosage can ensure that the potassium permanganate dosage obtained from the beaker coagulation and stirring experiment is more consistent with the actual production operation.

[0098] Example 6

[0099] To address the difficulty in settling alum flocs mixed with algae, we used kaolin as a coagulant and added CO2 to adjust the pH range. Using liquid polyaluminum chloride as a flocculant, we conducted beaker coagulation and stirring experiments to study flocculation, sedimentation, turbidity of settled water, and aluminum content. A water plant in central Yunnan uses reservoir water as its source water. Due to the continued high temperatures and drought in recent years, algae outbreaks have been severe, resulting in a high pH in the source water. The plant uses conventional water treatment processes:

[0100] Source water → mixing → grid reaction → inclined tube sedimentation → siphon filter → chlorination disinfection → clear water tank → outlet water, which uses liquid polyaluminum chloride for flocculation and sodium hypochlorite for disinfection. At high pH, ​​high algae levels, and low turbidity, water production faces challenges such as poor flocculation and difficult alum floc settling, as well as water quality risks associated with difficult-to-control aluminum content. To address this water treatment technology challenge, the present invention primarily addresses reservoir source water with high algae levels and low turbidity. By adding kaolin as a coagulant aid and using CO2 to adjust the source water pH, this improves flocculation conditions, achieving high-quality water standards at a lower treatment cost.

[0101] (1) Experimental water quality

[0102] The source water from a reservoir at a water plant in central Yunnan during a certain period of time was used as the experimental water. Some conventional indicators are shown in Table 3.

[0103] Table 3 Source water quality

[0104] Serial number project unit Detection value 1 Turbidity NTU 4.62 2 Ammonia (as N) mg / L 0.09 3 <![CDATA[Permanganate index (calculated as O2)]]> mg / L 2.54 4 pH … 8.13 5 water temperature ℃ 25.9 6 aluminum mg / L 0.0092 7 Total phytoplankton density Cells / L <![CDATA[9.9*10 7 ]]>

[0105] (2) Experimental results and discussion

[0106] 1. Effect of the dosage of flocculant liquid polyaluminium chloride on turbidity removal effect

[0107] Take 6 cups of 1L experimental water containing algae, add different amounts of liquid polyaluminum chloride to carry out beaker coagulation and stirring experiments. The water quality of the experimental source water is shown in Table 1. Observe the experimental phenomena, let it settle for 15 minutes, take the supernatant, and measure the turbidity of the water after sedimentation. The experimental phenomena and results are shown in Table 4.

[0108] Table 4 Experimental phenomena and results

[0109]

[0110]

[0111] As shown in Table 4, the turbidity decreases with the increase of the dosage of liquid polyaluminium chloride, but the decrease is not obvious. There are generally fine alum flowers, unsatisfactory sedimentation effect and excessive aluminium content.

[0112] 2. Effect of kaolin addition on the flocculation efficiency of liquid polyaluminium chloride flocculant

[0113] In order to improve the problems of poor flocculation and small alum flocs that are difficult to settle, kaolin was added to the experimental source water containing algae in amounts of (13.3, 22.5, 72.5) mg / L, and the turbidity of the experimental source water was increased from 4.62 to (10, 15, 33) NTU. Six cups of three different turbidities, totaling 18 cups of experimental source water (with kaolin), were taken, and different amounts of liquid polyaluminum chloride were added to carry out beaker coagulation and stirring experiments. The water quality of the experimental source water is shown in Table 1. The experimental phenomena were observed, and the water was allowed to settle for 15 minutes. The supernatant was taken and the turbidity of the water after sedimentation was measured. The experimental phenomena and experimental results are shown in Table 5.

[0114] Table 5 Experimental phenomena and results

[0115]

[0116]

[0117] Table 5 shows that adding kaolin to regulate source water turbidity improves mixed flocculation, making floc particles larger and denser, increasing their specific gravity and facilitating sedimentation. This significantly improves the effect. The turbidity of the settled water decreases with increasing amounts of liquid polyaluminum chloride and kaolin. Considering both treatment effectiveness and economic benefits, the method that minimizes kaolin dosage and maximizes its efficiency was chosen. Therefore, under the conditions of this experiment, the optimal kaolin dosage was 13.3 mg / L.

[0118] 3. Effects of adding kaolin and changing the pH of source water on turbidity removal

[0119] The optimal kaolin dosage of 13.3 mg / L improved mixing, flocculation, and sedimentation, but the aluminum content control was not ideal, as the aluminum content control is highly dependent on pH. Six 1L cups of experimental source water (added with kaolin and lowered to pH 7.49 with CO2) were used. The water quality of the experimental source water is shown in Table 1. Beaker coagulation and stirring experiments were conducted using liquid polyaluminum chloride at dosages of (18, 21, 24, 27, 30, and 33) mg / L. The experimental phenomena and results are shown in Table 6.

[0120] Table 6 Experimental phenomena and results

[0121]

[0122] From the above content, it can be seen that (1) adding kaolin to adjust the turbidity of the source water to aid coagulation and using CO2 to lower the pH can not only improve flocculation and sedimentation, but also further reduce the aluminum content of the effluent, and the aluminum content of the filtered water does not increase with the increase in the amount of liquid polyaluminum chloride added, and is maintained well. (2) adding 13.3 mg / L of kaolin to adjust the turbidity of the source water to 10NTU and using CO2 to lower the pH to 7.49, compared with adding 13.3 mg / L of kaolin to adjust the turbidity of the source water to 10NTU but not adjusting the pH to 8.13, under the condition of liquid polyaluminum chloride addition of 18.0 mg / L, the turbidity of the water after sedimentation in the first method is low, the aluminum content after filtration is low, and the treatment effect is better; (3) adding kaolin to adjust the turbidity of the source water to 10NTU and using CO2 to lower the pH to 7.49, the aluminum content control effect is better than the same dose of flocculant liquid polyaluminum chloride with only CO2 lowering the pH to 7.49.

[0123] (3) Treatment measures

[0124] 1. Adding kaolin to adjust the turbidity of source water and aid coagulation, and using CO2 to lower the pH of source water can not only better improve flocculation and sedimentation, make the floc particles larger and denser, increase the specific gravity, and be more conducive to sedimentation, but also further reduce the turbidity of the water after sedimentation, and better control the aluminum content of the effluent; under the condition of adding the same dose of flocculant liquid polyaluminum chloride, adding kaolin to adjust the turbidity of source water and adding CO2 to lower the pH within the appropriate range has better sedimentation effect and lower turbidity of the water after sedimentation than adding kaolin without lowering the pH of source water.

[0125] 2. When adding kaolin, the pH of the source water is adjusted from 8.13 to 7.49. While maintaining the same turbidity of the effluent, the amount of flocculant liquid polyaluminium chloride can be reduced by 9 mg / L.

[0126] 3. When algae in the source water breaks out and the water plant uses strong base and weak acid salt sodium hypochlorite solution for disinfection, it is necessary to pay close attention to the changes in the pH of the source water and the increase in the pH of the process water caused by the sodium hypochlorite solution.

[0127] In dealing with the problems of high algae, high plankton (such as fish fleas, sword water fleas, etc.), and iron-manganese composite micro-pollution faced by reservoir source water in central Yunnan, the present invention proposes a series of targeted treatment strategies through in-depth analysis and practical exploration. Although sodium hypochlorite disinfection has become the mainstream disinfection process, its properties are unstable and chemical reactions are prone to occur during storage, resulting in reduced effective chlorine concentration and disinfection by-products such as chlorate and chlorite. It is necessary to optimize the use effect by reasonably controlling the storage cycle, strengthening monitoring and adjusting the pH value. At the same time, in response to the problem of excessive aluminum in the effluent of the water plant, the present invention determined the optimal pH control range through beaker coagulation and stirring experiments, effectively reducing the aluminum content. In addition, for the treatment of high plankton and iron-manganese composite micro-pollution, the present invention recommends the use of pre-oxidants such as chlorine dioxide and potassium permanganate, and strictly controlling the dosage to achieve good iron and manganese removal effects and avoid excessive disinfection by-products. In summary, the present invention provides a scientific basis and technical support for solving the problem of micro-pollution of reservoir source water in central Yunnan, which is of great significance for ensuring the safety of drinking water. In the future, further research is needed to address more complex water quality challenges.

[0128] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for treating water from high algae, high plankton, iron and manganese composite micro-pollution sources in central Yunnan, characterized in that: Here are the steps: S1. When unloading the sodium hypochlorite solution, dilute the 10% to 13% sodium hypochlorite stock solution to 5% for storage; S2. Testing sodium hypochlorite during storage using a portable chlorate detector; S3. When the manganese content in the source water is lower than 0.15 mg / L, chlorine dioxide or potassium permanganate is added during pre-oxidation to remove iron and manganese; when the manganese content in the source water is higher than 0.15 mg / L, potassium permanganate is added to remove iron and manganese or potassium permanganate and carbon dioxide are combined to remove manganese, and the amount of chlorine dioxide added does not exceed 1.0 mg / L; S4. When the number of fish fleas and sword water fleas in the source water is high, use chlorine dioxide for pre-oxidation inhibition, and the inhibition dosage should not exceed 1.0 mg / L of chlorine dioxide solution; S5. When the pH of the source water is high, CO2 needs to be added to lower the pH of the source water.

2. The method for treating water from high algae, high plankton, iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S1, during storage and use of the purchased finished sodium hypochlorite solution or the low-concentration sodium hypochlorite solution of about 0.8% prepared on-site using a sodium hypochlorite generator, the effective chlorine concentration is monitored and the dosage is adjusted in time.

3. The method for treating water with high algae, high plankton, and iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S1, the optimal storage conditions of the sodium hypochlorite solution are determined according to the local climate conditions and the production conditions of the water plant to slow down the reduction rate of the effective chlorine concentration during storage.

4. The method for treating water from high algae, high plankton, iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S2, the purchased sodium hypochlorite disinfectant is stored at room temperature, and the purchase cycle is about 7-10 days.

5. The method for treating water with high algae, high plankton, and iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S2, before adding new reagents to the drug storage tank or drug storage pool, the reagents in the drug storage tank or drug storage pool are used up, and the drug storage tank or drug storage pool is emptied and cleaned regularly to reduce the impact of residual liquid on the quality of sodium hypochlorite.

6. The method for treating water with high algae, high plankton, and iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S2, the pre-warehousing inspection of the purchased finished sodium hypochlorite solution is strengthened, and the chlorate content and heavy metal ion content in the sodium hypochlorite solution before entering the tank pool are strictly controlled.

7. The method for treating water with high algae, high plankton, and iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S3, a complete potassium permanganate dosing system is selected to ensure the accuracy of the potassium permanganate dosage.

8. The method for treating water with high algae, high plankton, and iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S4, the fish fleas and sword water fleas in the raw water are first inhibited and killed by pre-oxidation with chlorine dioxide, and then disinfected with sodium hypochlorite solution.

9. The method for treating water from high algae, high plankton, iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 1, characterized in that: In step S5, kaolin is added to adjust the turbidity of the source water, and at the same time, the pH value of the source water is adjusted from 8.13 to 7.

49.

10. The method for treating water from high algae, high plankton, iron and manganese composite micro-pollution sources in central Yunnan as claimed in claim 9, characterized in that: In step S5, under the condition that the source water has an algae outbreak and the water plant uses a strong base and weak acid salt sodium hypochlorite solution for disinfection, the change in the source water pH and the increase in the process water pH caused by the sodium hypochlorite solution are continuously detected and observed.

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