Nitrogen and phosphorus removal method based on sand filtration in-situ optimization

Abstract

The invention discloses a nitrogen and phosphorus removal method based on sand filtration in-situ optimization, which comprises the following steps: (1) mixing green algae obtained by centrifuging a green algae bacterial solution with a sodium alginate solution to obtain a sodium alginate and green algae mixed solution; preparing a metal cation solution; (2) spraying the sodium alginate and green alga mixed solution into a sand filter filled with a sand filter filler for 1-2 times; then spraying the metal cation solution into the sand filter for 1-2 times, and curing to obtain a modified sand filter filler of which the surface is coated with microbial hydrogel; (3) feeding sewage to be treated into the sand filter, and carrying out nitrogen and phosphorus removal purification; and (4) after the sand filter runs for 15-30 days every time, draining sewage in the sand filter, and repeating the steps (1)-(3). Hydrogel is formed through the cross-linking reaction of sodium alginate and metal cations, green algae are fixed to the outer layer of quartz sand, microbial hydrogel is formed, the quartz sand can be protected against erosion and abrasion in the filtering process, and meanwhile the nitrogen and phosphorus removal effect is improved.

Description

Technical Field

[0001] The present application relates to the technical field of water treatment, and in particular to a method for removing nitrogen and phosphorus based on in-situ optimization of sand filtration. Background Art

[0002] Nitrogen and phosphorus are the main factors that cause algae to multiply and water eutrophication. In nature, eutrophic water is a phenomenon of ecosystem imbalance, which may cause the complete extinction of species in the water ecosystem. When natural water bodies accept nitrogen and phosphorus wastewater, they will promote the rapid reproduction of autotrophic microorganisms, which will shorten their life cycle due to their fast growth rate. After the algae die, nitrogen and phosphorus elements will remain in the water and be absorbed by other algae. The eutrophic water environment promotes the prosperity of various algae, especially those with strong reproductive capacity. The increase in the number of these algae not only poses a threat to human health, seriously affects water quality and produces bad odors, but also poses a threat to the safety of drinking water. According to research reports, trace amounts of potential carcinogens may be generated when chlorinating algae. When aquatic animals ingest toxins produced by cyanobacteria, the results can be fatal. In addition, toxins produced by red tide bacteria pose a potential threat to human health. In addition, eutrophication of water bodies will also have a negative impact on the water supply system, resulting in increased operating costs, which in turn has an adverse impact on the fishery industry and causes significant losses to the aquaculture industry. Therefore, denitrification and phosphorus removal in the water treatment process are very critical.

[0003] At present, the infrastructure construction of municipal sewage treatment in my country has been gradually improved, and the water treatment efficiency has been improved, but the reclaimed water still has the problem of residual nitrogen and phosphorus nutrients, which further increases the risk of eutrophication of rivers, lakes and landscape water bodies. The denitrification process and phosphorus removal process of the traditional denitrification and phosphorus removal process are independent. Polyphosphate bacteria and denitrifying bacteria are both heterotrophic bacteria, so there is a problem of competition for carbon sources between the two. In addition, there are contradictions in the process principle of biological denitrification and phosphorus removal. The growth of nitrifying bacteria requires a long sludge age, while the phosphorus removal of polyphosphate bacteria requires a short sludge age, which makes it extremely difficult to control the working conditions of simultaneous denitrification and phosphorus removal in the biochemical system. Conventional municipal sewage treatment processes often cooperate with deep treatment technologies such as flocculation and adsorption. Although they can achieve the deep treatment goal of total phosphorus below 0.3 mg / L, it is difficult to quantitatively and targetedly remove organic phosphorus. The inefficient addition of excessive agents greatly increases the drug consumption and cost of sewage treatment plants, which runs counter to the development direction of sewage treatment to reduce pollution and carbon emissions and green environmental protection. Therefore, it is becoming increasingly important to develop advanced and cost-effective high-efficiency denitrification and phosphorus removal technologies.

[0004] Sand filtration process Filtration technology is a rapid method for separating insoluble substances in water in water treatment and wastewater treatment. In order to obtain high-quality effluent, filtration technology is widely used in the deep treatment of sewage (wastewater). Filtration technology is usually used after chemical coagulation and biochemical treatment. It is a water treatment operation process that allows water to pass through a bed of porous media such as sand, coal particles or diatomaceous earth to separate suspended matter in water. Its main function is to remove inorganic and organic particles in a dispersed suspended state in water, including various plankton, bacteria, filterable viruses, floating oil, emulsified oil, etc. However, sand filtration has limited removal effect on some tiny particles and soluble substances. In order to maintain the filtration effect, the quartz sand filter material needs to be replaced regularly, which increases the operating cost and maintenance workload. In addition, sand filtration has high requirements for water quality. If the water quality is poor, it may cause premature clogging or reduced filtration effect. Therefore, it is necessary to optimize the sand filtration process to improve its sewage treatment efficiency and reduce maintenance costs.

[0005] Patent CN118529889A has established a resource treatment system for lithium iron phosphate production wastewater. A sand filter and sand filter backwash system are added after the clear water tank to filter out impurities such as fine particles, suspended matter, colloids, and organic matter brought by the incoming water. The filtering mechanism is to form a dense filter membrane on the upper part of the filter layer through the filter layer, and the impurities in the water are trapped in the filter layer through the filter membrane, thereby ensuring excellent effluent water quality. However, the setting of the sand filter backwash system increases the complexity of the process, and also increases the cost and daily maintenance expenses.

[0006] Patent CN118420173A designs a potassium permanganate catalytic oxidation-bioactivated carbon feed water deep treatment method, which can replace ozone oxidation-bioactivated carbon, be applied to the intermediate carbon pool process, and achieve the water quality target of deep water treatment, effectively guarantee the requirements of effluent turbidity, and eliminate the water quality safety risk caused by the microorganisms carried by the effluent of the bioactivated carbon. The purified water after the activated carbon layer treatment is subjected to sand filtration to form the intermediate carbon pool process of "raw water → pre-oxidation → coagulation and sedimentation → potassium permanganate-catalytic membrane floating ceramsite cage-bioactivated carbon → sand filtration". Although the risk of microorganisms carried by the effluent of the bioactivated carbon can be further eliminated, the saturation of the filter material in the sand filter is not taken into account, and regular replacement or backwashing is required. Summary of the invention

[0007] The present application provides a method for denitrification and phosphorus removal based on in-situ optimization of sand filtration, which utilizes the cross-linking reaction of sodium alginate and metal cations to form a hydrogel, fixes green algae on the outer layer of quartz sand, and forms a microbial hydrogel. On the one hand, the quartz sand can be protected from erosion and wear during the filtration process; on the other hand, the hydrogel contains green algae, which can carry out photosynthesis and has a good denitrification and phosphorus removal effect on the water body; in addition, the technology optimizes sand filtration in situ and can simultaneously achieve denitrification and phosphorus removal of sewage.

[0008] A method for removing nitrogen and phosphorus based on in-situ optimization of sand filtration, characterized by comprising:

[0009] (1) mixing the green algae obtained by centrifuging the green algae liquid with a sodium alginate solution to obtain a sodium alginate green algae mixed liquid; preparing a metal cation solution;

[0010] (2) pouring the sodium alginate green algae mixed solution into a sand filter tank filled with sand filter filler 1 to 2 times; then pouring the metal cation solution into the sand filter tank 1 to 2 times for solidification, and after solidification, the surface of the sand filter filler is coated with microbial hydrogel;

[0011] (3) sending the wastewater to be treated into the sand filter tank for nitrogen and phosphorus removal;

[0012] (4) After the sand filter tank has been running for 15 to 30 days, the sewage in the sand filter tank is drained and steps (1) to (3) are repeated.

[0013] In view of the problems existing in the prior art, the present application designs a method for denitrification and phosphorus removal based on in-situ optimization of sand filtration. Sodium alginate and metal cation solution containing green algae are sequentially added to the sand filter, and a layer of microbial hydrogel is directly covered on the surface of quartz sand. The microbial hydrogel can not only reduce the loss of quartz sand filler, but the green algae inside can also further denitrify and remove phosphorus from the sewage. In addition, the hydrogel has high mechanical strength and wear resistance, so the interval between the next pouring of sodium alginate and metal cation solution is long, maintenance takes less time, the process is simple, and the cost is low.

[0014] Several optional methods are also provided below, but they are not intended to be additional limitations on the above-mentioned overall solution, but are merely further supplements or preferences. Under the premise that there are no technical or logical contradictions, each optional method can be combined with the above-mentioned overall solution separately, and multiple optional methods can also be combined.

[0015] In step (1):

[0016] Optionally, the mass percentage concentration of sodium alginate in the sodium alginate green algae mixed solution is 0.1-0.5%. If the concentration is too low, it is not easy to form a hydrogel with the metal cation solution, and if the concentration is too high, it is easy to form agglomerates on the surface of quartz sand, affecting the effect of removing suspended matter in the water body.

[0017] Optionally, the mass percentage concentration of green algae in the sodium alginate green algae mixture is 5-15%. If the proportion of green algae is too low, the effect of nitrogen removal and phosphorus removal will be unsatisfactory, while if it is too high, the bacterial solution will be wasted and the growth and metabolism of bacteria will be inhibited.

[0018] Optionally, the metal cation in the metal cation solution is a copper, calcium, barium or strontium cation. Preferably, it is a CaCl2 solution; because Ca 2+ The cross-linking effect with sodium alginate is better and more conducive to the formation of hydrogel.

[0019] Optionally, the mass percentage concentration of the metal cation solution is 2%-3%. If the concentration of the cation solution is too low, the hydrogel is not completely formed, and if the concentration is too high, it is easy to enter the water body and cause pollution.

[0020] Optionally, the green algae liquid is a liquid of one or more of the genus Chlorella, Chlamydomonas, Hydrodictyon, Volvox, Spirogyra, Agaricus or Pteridium, and the OD of the green algae liquid is 600 1-2. Green algae can photosynthesize and remove nutrients such as nitrogen and phosphorus from water.

[0021] Optionally, the green algae is pretreated as follows:

[0022] The green algae liquid is centrifuged at a certain speed and time, resuspended with distilled water to the original scale, centrifuged again and repeated 1-2 times. Preferably, the centrifugal speed is 4000-8000 r min -1 , the centrifugation time is 5-15min.

[0023] In step (2):

[0024] Optionally, the sand filter filler is quartz sand.

[0025] Optionally, the volume ratio of the sodium alginate green algae mixture to the sand filter filler is 1:10 to 1:25; the volume ratio of the metal cation solution to the sand filter filler is 2:10 to 4:10; and the curing time is 10-15 hours. If the curing time is too short, the formed hydrogel will have insufficient mechanical strength and be easily damaged. If the curing time is too long, the activity of the green algae will deteriorate.

[0026] Optionally, the microbial hydrogel coated on the surface of the sand filter filler has a thickness ranging from 0.5 to 2 mm. Under the above-mentioned preferred combination of conditions, the microbial hydrogel formed on the surface of the quartz sand has a thickness ranging from 0.5 to 2 mm. If the thickness is too thin, it is easy to fall off, and if the thickness is too thick, it will affect the transferability.

[0027] As the sand filter is running, the microbial hydrogel formed on the surface of the quartz sand will be lost. Therefore, the quartz sand is wrapped again after the sand filter has been running for a certain period of time. The timing of wrapping again can be determined based on the state of the microbial hydrogel (such as wrapping integrity, wrapping thickness, hydrogel elasticity, etc.). Generally, after 15 to 30 days of operation, the state of the microbial hydrogel decreases significantly and needs to be re-wrapped. When wrapping again, the concentration of sodium alginate and metal ions can also be appropriately adjusted within the aforementioned ratio range according to the state of the hydrogel on the surface of the quartz sand.

[0028] Optionally, the dosage of the sand filter filler is 20-40% of the volume of the sand filter tank.

[0029] In step (3):

[0030] Optionally, the hydraulic retention time in the sand filter is 10 to 15 hours.

[0031] Optionally, the sewage to be treated is sewage after secondary treatment in a sewage treatment plant. The sand filter is used for deep nitrogen and phosphorus removal after secondary treatment.

[0032] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0033] (1) The method of the present application is simple and low-cost: the optimization is performed in situ, which is simple, easy to operate and low-cost.

[0034] (2) The method of the present application can reduce the wear and tear of quartz sand: microbial hydrogel is formed on the surface of quartz sand, which can resist external impact and wear, and reduce the replacement and consumption of sand filter media.

[0035] (3) The method of the present application can enhance the activity of green algae: by utilizing the cross-linking reaction between sodium alginate and metal cations, the green algae are fixed on the outside of quartz sand to form a microbial hydrogel, thereby maintaining the biological activity of the bacteria and reducing the toxic effects of difficult-to-degrade organic matter on the bacteria.

[0036] (4) The method of the present application has the effect of removing nitrogen and phosphorus: it can further remove nutrients such as nitrogen and phosphorus in sewage. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The following is a flowchart of the operation of the method of this application. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0040] Example 1

[0041] The sand filter material used in this embodiment is quartz sand, with a sand particle size of 1 mm and a layer thickness of 0.7 m.

[0042] The specific preparation method is as follows:

[0043] (1) The purchased Chlorella (OD600 = 1, Chinese livestock, composite Chlorella species) was stirred at 4000 r min. -1 Centrifuge under the conditions of 10 min, resuspend with distilled water to the original scale, centrifuge again and repeat 2 times for later use;

[0044] (2) Preparation of sodium alginate solution: Add a certain amount of sodium alginate into distilled water to dissolve, heat to boil and then cool;

[0045] (3) Then, the chlorella after centrifugation in step (1) is added to the sodium alginate solution and stirred evenly to obtain a chlorella-sodium alginate mixed solution, wherein the mass percentage concentration of sodium alginate in the mixed solution is 0.1% and the mass percentage concentration of chlorella is 10%.

[0046] (4) preparing a 2 wt % CaCl2 solution;

[0047] (5) The chlorella-sodium alginate mixture obtained in step (3) is evenly poured into a sand filter tank filled with quartz sand (the volume ratio of quartz sand is 30%) for two times, and then the CaCl2 solution prepared in step (4) is poured, and the mixture is allowed to solidify for 12 hours. The volume ratio of the sodium alginate-green algae mixture to the sand filter filler is 1:15; the volume ratio of the metal cation solution to the sand filter filler is 3:10.

[0048] (6) Application of sewage treatment:

[0049] The sand filter treated in step (5) was directly used in the secondary treatment of the sewage treatment plant to purify the water again, with a hydraulic retention time of 12 hours. The treatment results are shown in Table 1.

[0050] (7) After running for a certain period of time, the state of the hydrogel wrapped on the surface of the quartz sand is observed, and steps (1) to (6) are repeated. In this embodiment, the wrapping is repeated after every 20 days of operation, and the wrapping is repeated three times. The results of the latter two treatments are close to the results of the first treatment.

[0051] Example 2

[0052] The sand filter material used in this embodiment is quartz sand, with a sand particle size of 1 mm and a layer thickness of 0.7 m.

[0053] The specific preparation method is as follows:

[0054] (1) The purchased Chlorella (OD600 = 1) was centrifuged at 6000 r min -1 and centrifuge under the conditions of 100 μl and 10 min, resuspend with distilled water to the original scale, centrifuge again and repeat 2 times for later use.

[0055] (2) Preparation of sodium alginate solution: Add a certain amount of sodium alginate into distilled water to dissolve, heat to boil and then cool.

[0056] (3) Then, the chlorella obtained by centrifugation in step (1) is added to the sodium alginate solution and stirred evenly to obtain a chlorella-sodium alginate mixed solution, wherein the mass percentage concentration of sodium alginate in the mixed solution is 0.5% and the mass percentage concentration of chlorella is 15%.

[0057] (4) preparing a 3 wt % CaCl2 solution;

[0058] (5) The chlorella-sodium alginate obtained in step (3) is evenly poured into a sand filter tank filled with quartz sand (the volume ratio of quartz sand is 35%) for two times, and then the CaCl2 solution prepared in step (4) is poured, and the mixture is allowed to stand and solidify for 12 hours. The volume ratio of the sodium alginate-green algae mixture to the sand filter filler is 1:10; the volume ratio of the metal cation solution to the sand filter filler is 4:10.

[0059] (6) Application of sewage treatment:

[0060] The sand filter treated in step (5) was directly used in the secondary treatment of the sewage treatment plant to purify the water again, with a hydraulic retention time of 12 hours. The treatment results are shown in Table 1.

[0061] (7) In this embodiment, the wrapping is repeated after every 20 days of operation, and steps (1) to (6) are repeated. The wrapping is repeated three times, and the results of the latter two treatments are close to the results of the first treatment.

[0062] Comparative Example 1

[0063] Single sand filtration, no other substances added, the rest is the same as Example 1.

[0064] Comparative Example 2

[0065] The sand filter material used in this comparative example is quartz sand, with a sand particle size of 1 mm and a layer thickness of 0.7 m.

[0066] The specific preparation method is as follows:

[0067] (1) Preparation of sodium alginate solution: Prepare a sodium alginate solution with a mass percentage concentration of 0.5% by adding a certain amount of sodium alginate into distilled water to dissolve it, heat it to boil and then cool it.

[0068] (2) preparing a 3 wt % CaCl2 solution;

[0069] (3) The sodium alginate obtained in step (1) is evenly poured into a sand filter tank filled with quartz sand (the volume ratio of quartz sand is 35%) for two times, and then the CaCl2 solution prepared in step (2) is poured, and the mixture is allowed to stand and solidify for 12 hours. The volume ratio of the sodium alginate and green algae mixed solution to the sand filter filler is 1:15; the volume ratio of the metal cation solution to the sand filter filler is 3:10.

[0070] (4) Application of sewage treatment:

[0071] The sand filter treated in step (3) was directly used in the secondary treatment of the sewage treatment plant to purify the water again, with a hydraulic retention time of 12 hours. The treatment results are shown in Table 1.

[0072] (5) After every 20 days of operation, repeat steps (1) to (3).

[0073] Comparative Example 3

[0074] Chlorella at a concentration of 10% of the sewage mass was directly added to the sand filter according to the sewage volume. The hydraulic retention time was 12 hours. The treatment results are shown in Table 1.

[0075] Table 1 Nitrogen, phosphorus and suspended matter removal of Examples 1-2 and Comparative Examples 1-3

[0076] Effect example Total nitrogen removal Total phosphorus removal Example 1 14.7mg / L→11.5mg / L 0.49mg / L→0.3mg / L Example 2 14.9mg / L→12mg / L 0.48mg / L→0.25mg / L Comparative Example 1 14.8mg / L→14.5mg / L 0.47mg / L→0.45mg / L Comparative Example 2 14.5mg / L→13.3mg / L 0.48mg / L→0.41mg / L Comparative Example 3 14.6mg / L→13.1mg / L 0.46mg / L→0.37mg / L

[0077] As can be seen from Table 1, the optimized sand filtration method of the present invention can significantly remove total nitrogen, total phosphorus and suspended solids while protecting the sand filter filler, and the effect is significantly better than that of the comparative example.

[0078] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for nitrogen and phosphorus removal based on in-situ optimization of sand filtration, characterized in that: include: (1) mixing the green algae obtained by centrifuging the green algae liquid with a sodium alginate solution to obtain a sodium alginate green algae mixed liquid; preparing a metal cation solution; (2) pouring the sodium alginate green algae mixed solution into a sand filter tank filled with sand filter filler 1 to 2 times; then pouring the metal cation solution into the sand filter tank 1 to 2 times for solidification, and after solidification, the surface of the sand filter filler is coated with microbial hydrogel; (3) sending the wastewater to be treated into the sand filter tank for nitrogen and phosphorus removal; (4) After the sand filter tank has been running for 15 to 30 days, the sewage in the sand filter tank is drained and steps (1) to (3) are repeated.

2. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (1), in the sodium alginate-green algae mixed solution: the mass percentage concentration of the sodium alginate is 0.1-0.5%; the mass percentage concentration of the green algae is 5-15%.

3. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (1), the mass percentage concentration of the metal cation solution is 2%-3%; the metal cations in the metal cation solution are cations of copper, calcium, barium or strontium.

4. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (1), the green algae liquid is a liquid of one or more of the genus Chlorella, Chlamydomonas, Hydrodictyum, Volvox, Spirogyra, Agaricus or Pteridium; the OD of the green algae liquid is 600 is 1-2.

5. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (2), the sand filter filler is quartz sand.

6. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (2), the volume ratio of the sodium alginate green algae mixed solution to the sand filter filler is 1:10 to 1:25; the volume ratio of the metal cation solution to the sand filter filler is 2:10 to 4:10; and the curing time is 10-15 hours.

7. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (2), the thickness of the microbial hydrogel coated on the surface of the sand filter filler is in the range of 0.5-2 mm.

8. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (2), the amount of the sand filter filler added is 20-40% of the volume of the sand filter tank.

9. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (3), the hydraulic retention time in the sand filter is 10 to 15 hours.

10. The method for denitrification and dephosphorization according to claim 1, characterized in that: In step (3), the sewage to be treated is sewage after secondary treatment in a sewage treatment plant.

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