CN110395824B - Advanced phosphorus removal and phosphorus recovery device and method for secondary effluent of sewage treatment plant - Google Patents

Advanced phosphorus removal and phosphorus recovery device and method for secondary effluent of sewage treatment plant Download PDF

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CN110395824B
CN110395824B CN201910787634.9A CN201910787634A CN110395824B CN 110395824 B CN110395824 B CN 110395824B CN 201910787634 A CN201910787634 A CN 201910787634A CN 110395824 B CN110395824 B CN 110395824B
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hap
crystallization
zone
induced crystallization
phosphorus
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CN110395824A (en
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聂小保
陆洲
刘阳
梁军
蒋昌波
隆院男
金筱英
胡明睿
周梨
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Zhejiang Industry Design & Research Inst
Changsha University of Science and Technology
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Zhejiang Industry Design & Research Inst
Changsha University of Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/58—Treatment of water, waste water, or sewage by removing specified dissolved compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F2001/5218—Crystallization
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/105—Phosphorus compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2201/00—Apparatus for treatment of water, waste water or sewage
    • C02F2201/002—Construction details of the apparatus
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/06—Controlling or monitoring parameters in water treatment pH
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/18—PO4-P

Abstract

The invention discloses a deep phosphorus removal and recovery device and a deep phosphorus removal and recovery method for secondary effluent of a sewage treatment plant, which fluidize a large number of small HAP crystal seed particles by means of ascending water flow in a fluidized bed to form an induced crystallization zone; low concentration PO in secondary effluent4 3‑And OH added‑And Ca2+Firstly generating HAP molecular clusters in an induced crystallization zone, and rapidly agglomerating and crystallizing the molecular clusters and HAP seed crystal particles under the action of ascending water flow to generate a crystallization product HAP which is deposited at the bottom of a fluidized bed; and a small amount of broken crystallization product enters a buffer zone of the fluidized bed under the action of ascending water flow, the speed gradually decreases along the way, and the broken crystallization product returns to the induced crystallization zone again under the action of gravity, so that ascending-descending circulation occurs, and the broken crystallization product gradually grows in the circulation, finally falls into the induced crystallization zone to serve as new seed crystals, and the seed crystals lost due to HAP (hydrogen-induced phosphate) discharge of the crystallization product are supplemented. The invention has the advantages of good treatment effect and high phosphorus recycling value.

Description

Advanced phosphorus removal and phosphorus recovery device and method for secondary effluent of sewage treatment plant
Technical Field
The invention relates to the technical field of sewage dephosphorization and phosphorus recovery, in particular to a device and a method for deeply dephosphorizing and recovering phosphorus from secondary effluent of a sewage treatment plant.
Background
In order to comprehensively restrain water environment pollution and control water eutrophication, the improvement of standards of sewage plants is being comprehensively developed in China, and the effluent standard is improved from primary B to primary A in pollutant discharge Standard of urban Sewage treatment plant (GB 18918-. The limits for phosphorus in the primary B and primary A standards were 1.0mg/L and 0.5mg/L, respectively.
At present, more mature sewage and wastewater phosphorus control technologies and equipment, such as coagulation phosphorus removal, membrane filtration, ion exchange and the like, exist at home and abroad, can meet the phosphorus removal requirement in the standard improvement and transformation process of sewage plants, but have the problems of high cost, complex operation, secondary pollution and the like. Wherein, more coagulant is needed to be added for the coagulation and phosphorus removal, and a large amount of phosphorus-containing sludge is generated and is difficult to treat; the membrane filtration can greatly remove phosphorus in the sewage, and the removal efficiency can be further improved after the membrane filtration and coagulation are combined, but the treatment cost is high, and the risk of membrane pollution exists; ion exchange requires frequent regeneration of the exchange resin, the regeneration cost is high, and secondary pollution is easily caused by the regenerated waste liquid; and the method can not realize the recycling of the phosphorus in the sewage.
The induced crystallization phosphorus removal technology is applied to the treatment and resource utilization of high-concentration phosphorus-containing wastewater, and can be used for removing phosphorus greatly and recovering phosphorus efficiently. The technology is also applied to urban sewage plants, for example, Chinese patent of invention (CN 105540770A) discloses a method and a device for removing and recovering phosphorus in sewage by magnetic induction crystallization, wherein the phosphorus in sludge dewatering filtrate and sludge nitrifying liquid is removed and recovered, the concentration of the phosphorus in inlet water is between 5.9 and 60mg/L, and the concentration of the phosphorus in outlet water is between 0.66 and 3.2 mg/L; chinese invention patent (CN 104973723A) discloses a device and a method for recovering induced crystallization phosphorus, wherein calcite is used as a crystal seed to induce phosphorus in sewage to be recovered in a calcium Hydroxyphosphate (HAP) crystal form, the concentration of phosphorus in inlet water is 38.8-45.9mg/L, and the concentration of phosphorus in outlet water is below 8.0 mg/L. In the method, the phosphorus concentration of the inlet water is far higher than that of the secondary outlet water of the sewage plant (about 1 mg/L), and the phosphorus concentration of the outlet water exceeds the primary A standard limit value by 0.5mg/L, so that the method cannot be directly applied to the phosphorus removal requirement of the sewage plant for upgrading and reconstruction.
Chinese invention patent (CN 104310641A) discloses a method for deep phosphorus removal from low-phosphorus water, which takes modified coral sand as a seed crystal, and can reduce the phosphorus in secondary effluent to below 0.2mg/L through primary fluidized bed crystallization and secondary fixed bed crystallization, and simultaneously the phosphorus is recovered in the form of a crystallization product HAP. However, the method adopts a series connection mode of a fluidized bed and a fixed bed, the hydraulic retention time reaches 5.46h and 4.58h respectively, and the required equipment or structure is large in size. At 10 ten thousand meters3For example, the total volume of the required equipment or structures reaches 4 ten thousand meters in a sewage plant3This is clearly undesirable in upgrading sewage plants.
In a word, no technical method for advanced phosphorus removal and recovery of phosphorus from secondary effluent with strong suitability has been reported so far, wherein the technical method is improved aiming at sewage plants, can meet the requirement of a first-level A standard on the limit value of phosphorus concentration, and can recycle phosphorus.
Disclosure of Invention
The present application is directed to solving at least one of the problems in the prior art. Therefore, the invention aims to provide a device and a method for deeply removing phosphorus and recovering phosphorus from secondary effluent of a sewage treatment plant. The device and the method adopt a fluidized bed structure form, and realize deep phosphorus removal and phosphorus recovery of secondary effluent of a low-phosphorus-concentration sewage treatment plant through high-density induced crystallization.
In order to solve the technical problem, the following technical scheme is adopted in the application:
a method for deeply removing phosphorus and recovering phosphorus from secondary effluent of a sewage treatment plant is characterized in that a large amount of fine HAP crystal seed particles are fluidized by means of ascending water flow in a fluidized bed to form an induced crystallization zone;
low concentration PO in secondary effluent4 3-And OH added-And Ca2+Firstly generating molecular clusters of HAP and precursor thereof in an induced crystallization zone, rapidly agglomerating and crystallizing the molecular clusters and HAP seed crystal particles under the action of ascending water flow to generate crystallization products HAP and precursor thereof, and depositing the crystallization products HAP and precursor thereof at the bottom of a fluidized bedA section;
and a small amount of broken crystallization product enters a buffer zone of the fluidized bed under the action of ascending water flow, the speed gradually decreases along the way, and the broken crystallization product returns to the induced crystallization zone again under the action of gravity, so that ascending-descending circulation occurs, and the broken crystallization product gradually grows in the circulation, finally falls into the induced crystallization zone to serve as new seed crystals, and the seed crystals lost due to HAP (hydrogen-induced phosphate) discharge of the crystallization product are supplemented.
Further, the fluidized bed is sequentially divided into a concentration and aging area, an induced crystallization area and a buffer area from bottom to top, and secondary effluent, alkali liquor and calcium salt are introduced into the fluidized bed from the bottom of the induced crystallization area.
The inventor researches and discovers that after the reaction is stable, when the quantity of HAP seed crystals in an induced crystallization zone is controlled to be 10-60 g/L, preferably 20-50 g/L, and the average particle size is controlled to be 45-200 mu m, preferably 50-150 mu m, the phosphorus concentration of effluent can be controlled to be below 0.3 mg/L. And when the particle size is less than 45 mu m, the seed crystal has certain loss, when the particle size is more than 200 mu m or the number of the seed crystal is less than 10g/L, the phosphorus concentration of effluent cannot be stabilized below 0.3mg/L, and when the number of the seed crystal is more than 60g/L, the water head loss of a crystallization area is obviously increased, and the energy consumption is larger.
In order to form a high-density induced crystallization area, the small initial seed crystal particle size and the large adding amount are selected, the initial seed crystal particle size is about 75 mu m, and the adding amount of the initial seed crystal is 50 g/L.
Preferably, in order to ensure the dispersed suspension and secondary nucleation of the seed crystals in the high-density induced crystallization area and simultaneously strengthen the rapid agglomeration crystallization process, the ascending flow rate of the induced crystallization area is controlled to be 12-24 m/h.
Preferably, Ca is added to enhance the formation of HAP molecular clusters in the high density induced crystallization region2+The adding amount is controlled to be 20-50 mg/L, and the pH value of the middle part of the high-density induced crystallization area is controlled to be 7.5-9.5, and is further preferably 8.0-9.0.
The inventor further researches and discovers that the hydraulic retention time in the induced crystallization zone is controlled to be 5-10 min, and the ascending flow speed at the top of the buffer zone is controlled to be 6-12 m/h. When the hydraulic retention time is less than 5min, the crystallization process is insufficient, and when the hydraulic retention time is more than 10min, the required volume of a crystallization area is large, and the manufacturing cost of the device is increased; when the ascending flow velocity is lower than 12m/h, the fluidization of the crystal seeds in the crystallization area is insufficient, and when the ascending flow velocity is higher than 24m/h, the potential risk of crystal seed loss exists. When the flow velocity at the top of the buffer zone is lower than 6m/h or higher than 12m/h, the crushed crystalline product cannot be effectively circulated in the buffer zone and gradually grows into new crystal nuclei.
Further, the calcium salt includes calcium chloride, calcium nitrate, calcium sulfate, calcium carbonate and the like, and calcium chloride or calcium nitrate is selected because calcium sulfate and calcium carbonate have low solubility and are not suitable for selection. The alkali liquor comprises sodium hydroxide, potassium hydroxide and calcium hydroxide, and the calcium hydroxide with low solubility is not suitable for use, and sodium hydroxide or potassium hydroxide can be selected.
A secondary effluent deep phosphorus removal and phosphorus recovery device of a sewage treatment plant comprises a fluidized bed reactor, wherein the fluidized bed reactor is sequentially divided into a concentration curing zone, an induced crystallization zone and a buffer zone from bottom to top;
the bottom of the induced crystallization area is provided with a water inlet, an alkali liquor feeding port and a calcium salt feeding port, and the induced crystallization area is also provided with an HAP seed crystal feeding port;
the buffer area is a conical upward expansion section;
and a pH detector for monitoring the pH value in the induced crystallization area.
Furthermore, a water collecting tank communicated with an overflow port of the buffer area is arranged above the buffer area, the concentration curing area is in an inverted cone shape, and a slag discharging pipe with a slag discharging valve is arranged at the bottom of the cone.
Further, CaCl communicated with the calcium salt feeding port through a medicine feeding pipe2And the dosing pipe is provided with a dosing pump and a dosing valve.
Further, the device also comprises a pipeline mixer and a NaOH solution tank;
the water inlet and the alkali liquor feeding port share the same inlet, one liquid inlet of the pipeline mixer is communicated with the water inlet pipe, the other liquid inlet of the pipeline mixer is communicated with the liquid outlet pipe of the NaOH solution tank, and the liquid outlet of the pipeline mixer is communicated with the water inlet;
the water inlet pipe is provided with a water inlet valve and a water inlet pump, the liquid outlet pipe is provided with a pH controller, and the pH controller controls the adding amount of the NaOH solution tank according to the monitoring result of the pH detector.
Principles and advantages
The inventor researches and discovers that the phosphorus concentration in secondary effluent is low (generally in the range of 0.6-2.0 mg/L), the HAP supersaturation degree of a solution system is low, the driving force of crystallization reaction is insufficient, and PO is4 3-And OH added-And Ca2+In the induced crystallization zone, the product HAP cannot be directly crystallized4 3-、OH-And Ca2+The nanometer HAP molecular cluster exists in water to generate the molecular cluster of HAP and precursor thereof.
The invention is based on the general idea of deep phosphorus removal and phosphorus recovery by induced crystallization of rapid agglomeration crystallization, a phosphorus removal and recovery device adopts a fluidized bed structure form, a large amount of HAP with fine particles is put into a fluidized bed to be used as seed crystals to form a high-density induced crystallization area with high particle number density, then molecular clusters and the seed crystals HAP with high particle number density are subjected to rapid agglomeration crystallization under the action of ascending water flow to generate a crystallization product HAP and a precursor thereof, and phosphorus is removed from secondary effluent.
In the application, secondary effluent, alkali liquor and calcium salt are introduced into the fluidized bed from the bottom of the induced crystallization zone, a large amount of HAP fine particles are put into the induced crystallization zone to serve as seed crystals, and OH in the alkali liquor-And Ca in calcium salts2+And low-concentration PO in secondary effluent4 3-And (2) carrying out molecular cluster reaction to generate nano HAP molecular clusters, carrying out rapid agglomeration crystallization on the HAP molecular clusters and HAP seed crystal particles under the action of ascending water flow to generate crystallization products HAP and precursors thereof, gradually increasing the particle sizes of the crystallization products HAP and the precursors thereof along with the progress of agglomeration crystallization, and finally overcoming the jacking of the ascending water flow under the action of gravity and sinking to the bottom of the crystallization products to form sludge.
In the invention, because of the high particle number density characteristic of the crystallization area, the number density of corresponding crystallization product particles is also higher, the crystallization products in the induced crystallization area are mutually rubbed and collided under the action of ascending water flow, a small amount of crystallization products are crushed to form new crystal nuclei, namely secondary nucleation, the new crystal nuclei enter a buffer area along with the ascending water flow, the flow velocity of the corresponding ascending water flow is reduced along the way as the cross section area of a channel of the buffer area is increased along the way, when the new crystal nuclei rise to the precipitation area, the new crystal nuclei overcome the jacking of the ascending water flow under the action of gravity and fall back to the induced crystallization area again, so that an ascending-sinking cycle occurs and gradually grows in the cycle, finally fall into the induced crystallization area to serve as new crystal seeds to supplement the crystal seed loss caused by HAP discharge of the crystallization products, clear water after solid-liquid separation in the buffer area is discharged from an overflow port, and in the secondary effluent treatment process, and new seed crystals do not need to be added again.
In the application, a crystallization product concentration and curing area is arranged at the bottom of a fluidized bed, the particle size of a crystallization product HAP and a precursor thereof is gradually increased along with the proceeding of agglomeration and crystallization, and finally the particle size overcomes the jacking of ascending water flow under the action of gravity and sinks to a crystallization product concentration and curing discharge area to form sludge; the HAP precursor in the crystallized product gradually removes the crystal water along with the extension of the concentration time, the HAP with high sphericity is aged, the crystallized product discharged by the final device is more compact, the sphericity is higher, and the recycling value is high.
OH in water as the crystallization process of the upper half area of the high density induced crystallization area and the buffer area continues-And the pH value of the final effluent is less than 9.0 after the final effluent is continuously consumed, and the final effluent meets the primary A standard of pollutant discharge Standard of urban Sewage treatment plant (GB 18918-2002).
Although the prior art of induced crystallization also uses external seed crystal, the working mechanism is completely different from the present application, for example, in patent document CN 104310641A, modified coral sand is used as seed crystal, PO4 3-、OH-And Ca2+And accumulating and crystallizing on the surface of the seed crystal in the form of crystal forming ions one by one. This process involves PO4 3-、OH-And Ca2+Mass transfer from the liquid phase main body to the liquid film on the solid surface, mass transfer in the liquid film, crystallization reaction and other steps, the overall crystallization rate is low, and correspondingly, the phosphorus removal effect is improvedIf the hydraulic retention time is as long as several hours, the required reaction equipment is large in size.
However, in the present application, the seed Crystal addition amount is greatly increased and the seed Crystal particle size is reduced, the addition amount is as high as 50g/L, the particle size is only 75 μm, a high-density induced crystallization region with high particle number density is formed, and because the seed Crystal particle number density is high, the seed Crystal particle frequently collides with a nano HAP molecular cluster, and is rapidly crystallized in an agglomerated crystallization form described in patent literature, namely, a Crystal product HAP with the seed Crystal particle as a core and a precursor thereof are generated, and phosphorus in secondary effluent of a sewage plant with low phosphorus concentration is removed. Meanwhile, the crystallized product enters a crystallized product concentration, curing and discharge area to be densified and spheroidized, so that the water content is greatly reduced, and the crystallized product can be directly recycled as a phosphate fertilizer.
Compared with the prior art, the invention has the beneficial effects that:
1. the adaptability to sewage and wastewater with low phosphorus concentration is strong: by improving the number density of the seed crystal particles, a high-density induced crystallization area is formed, the crystallization process is controlled to be an agglomeration crystallization process between HAP molecular clusters and seed crystal particles by attaching and crystallizing the crystal-forming ions to the surface of the seed crystal one by one, so that the crystallization process can be realized under a lower HAP supersaturation degree, and the adaptability to low phosphorus concentration is improved.
2. The dephosphorization is efficient, and the effect is stable: the agglomerated crystals generated in the high-density induced crystallization area can control the concentration of discharged phosphorus to be stabilized below 0.3mg/L, the phosphorus removal efficiency is high, secondary nucleation is synchronously generated in the high-density induced crystallization area, a fluidized bed mode is adopted, the number density of particles in the induced crystallization area is high, secondary nucleation caused by mutual collision among crystal particles is generated under the action of ascending running water, new crystal nuclei grow into crystal seeds in a buffer area, the high particle number density level of the crystallization area is maintained, and the phosphorus removal effect is stable.
3. The medicine consumption is low, and the operation cost is low: PO4 3-、OH-And Ca2+The crystallization mode of (2) is the rapid agglomeration crystallization of HAP molecular clusters and seed crystals, and can be comparedThe process is completed under low HAP supersaturation, so that the medicine consumption of NaOH and a calcium-containing precipitator is correspondingly saved, and the operation cost is lower.
4. The system has simple structure, high integration and easy realization of automation: the whole device is provided with only a pH controller and a calcium-containing precipitator adding system as auxiliary systems except the fluidized bed main body, the system is simple in structure, the fluidized bed main body integrates the functions of high-density induced crystallization, circulating granulation, precipitation, crystallization product concentration and curing and the like, the high integration is realized, and the automatic control is easy to realize.
5. The purity of the crystallized product is high, and the phosphorus recycling value is high: HAP particles are innovatively adopted as an inducer in the industry for the first time; correspondingly, the crystallization product is HAP and a precursor thereof, and the purity of the crystallization product is high. Meanwhile, interstitial water and crystal water are removed from the crystallized product in the concentration and curing zone, and the compactness and sphericity of the crystallized product are improved, so that the phosphorus is high in recycling value and can be directly recycled as a high-quality phosphate fertilizer.
In conclusion, the recovery method has the characteristics of good treatment effect and high phosphorus recovery and utilization value. The recovery device has the characteristics of simple structure, high integration, low operation cost, high efficiency and stability.
Drawings
FIG. 1 is a schematic structural diagram of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the advanced phosphorus removal and recovery device for secondary effluent of a sewage treatment plant comprises a fluidized bed reactor, wherein the fluidized bed reactor is sequentially divided into a concentration and curing zone I, an induced crystallization zone II, a buffer zone III and a precipitation zone IV from bottom to top. The bottom of the induced crystallization area II is provided with a water inlet, an alkali liquor feeding port and a calcium salt feeding port, the induced crystallization area II is also provided with an HAP seed crystal feeding port, and the induced crystallization area II further comprises a pH detector 11 for monitoring the pH value in the induced crystallization area.
Wherein, the induced crystallization area II is a cylinder with a small diameter, a large amount of fine HAP particles are put in the cylinder to be used as seed crystals, the seed crystals are in a fluidized state under the action of ascending water flow to form a high-density induced crystallization area with high particle number density, the buffer area III is a cone, and the small opening end of the cone is connected with the high-density induced crystallization area II.
Referring to fig. 1, in this embodiment, the buffer zone III is designed as a conical cylinder, due to the high particle number density characteristic of the induced crystallization zone II, the number density of the corresponding crystallized product particles is also high, the crystallized products in the induced crystallization zone II rub and collide with each other under the action of the ascending water flow, a small amount of crystallized products are broken to form new crystal nuclei, i.e. secondary nucleation, the new crystal nuclei enter the buffer zone III along with the ascending water flow, as the buffer zone III is designed as a conical cylinder, the channel cross-sectional area of the buffer zone III increases along the way, the flow rate of the corresponding ascending water flow decreases along the way, when the new crystal nuclei rise to the precipitation zone IV, the new crystal nuclei overcome the ascending water flow jacking under the action of gravity and fall back to the induced crystallization zone II, so that an ascending-descending cycle occurs and grow gradually in the cycle, and finally fall to the induced crystallization zone to serve as new crystal seeds to supplement the crystal seeds caused by HAP discharge of the crystallized products, clear water after solid-liquid separation in the buffer zone is discharged from the overflow port, and new crystal seeds do not need to be added again in the secondary effluent treatment process.
It should be noted that, in practical design, the concentrated ripening zone I can be a conical cylinder, the lower part is connected with a slag discharge pipe 15 with a slag discharge valve 16, and the upper part is connected with the induced crystallization zone II.
In the embodiment, a concentration curing area I is arranged at the bottom of a fluidized bed, the particle sizes of a crystallization product HAP and a precursor thereof are gradually increased along with the proceeding of agglomeration crystallization, and finally the particle sizes overcome the jacking of ascending water flow under the action of gravity and sink to the crystallization product concentration curing area I to form sludge; the HAP precursor in the crystallized product gradually removes crystal water along with the extension of concentration time, and is aged into HAP with high sphericity, the crystallized product discharged by a final device is more compact, the sphericity is higher, the recycling value is high, the crystallized product is directly HAP, the crystallized product does not need to be subjected to post-treatment like in the patent document CN 104310641A, and the treatment cost is greatly reduced.
Referring to fig. 1, in the present application, a settling zone IV is further disposed above the buffer zone III, an overflow port and a water collection tank 13 are disposed on the settling zone IV, after the solid-liquid separated water from the buffer zone III is settled in the settling zone IV, the final clean water enters the water collection tank 12 through the overflow port, and is discharged through a water discharge pipe 13 and a water discharge valve 14.
Referring to fig. 1, as a preferred embodiment of the present application, the deep phosphorus removal and recovery apparatus further includes CaCl connected to the calcium salt feeding port through a medicine feeding pipe 62A solution tank 5, a pipeline mixer 4 and a NaOH solution tank 9, wherein a metering pump 7 and a medicine inlet valve 8 are arranged on a medicine inlet pipe 6. The water inlet and the alkali liquor feeding port share the same inlet, one liquid inlet of the pipeline mixer 4 is communicated with the water inlet pipe 1, the other liquid inlet of the pipeline mixer 4 is communicated with the liquid outlet pipe of the NaOH solution tank 9, and the liquid outlet of the pipeline mixer 9 is communicated with the water inlet; the water inlet pipe 1 is provided with a water inlet valve 3 and a water inlet pump 2, the liquid outlet pipe is provided with a pH controller 10, and the pH controller 10 controls the adding amount of the NaOH solution tank 9 according to the monitoring result of the pH detector 11.
In the embodiment, the secondary effluent is pumped by a water inlet pipe 1 through a water inlet pump 2, passes through a water inlet valve 3, is fully mixed with a NaOH solution from a pH controller 10 in a pipeline mixer 4, and then enters a high-density induced crystallization area II, the CaCl2 solution is pumped by a metering pump 7 and enters the high-density induced crystallization area II through a medicine inlet valve 8, the pH value in the middle of the high-density induced crystallization area II is continuously monitored on line by a pH detector 11, the pH controller 10 controls the adding amount of NaOH according to a monitoring result, and the pH value in the middle of the high-density induced crystallization area is stabilized within a set range, generally 7.5-9.5. In this embodiment, the NaOH solution and the second effluent are fully mixed by the pipeline mixer 4 before entering the high-density induced crystallization zone, which is beneficial to the subsequent cluster reaction.
Referring to fig. 1, the process of deep phosphorus removal and phosphorus recovery of secondary effluent of a sewage treatment plant by adopting the device is as follows:
the secondary effluent is pumped by a water inlet pipe 1 through a water inlet pump 2, passes through a water inlet valve 3, is fully mixed with NaOH solution from a pH controller 10 in a pipeline mixer 4, and then enters an induced crystallization area II, CaCl2 solution is pumped by a metering pump, passes through a medicine inlet valve and enters the induced crystallization area, and a large amount of HAP crystal seeds with small particles are put into the induced crystallization area through a crystal seed putting port and are fluidized under the action of ascending water flow.
Low concentration of PO4 3-With OH-And Ca2+Generating a molecular cluster reaction in the high-density induced crystallization area to generate a nano HAP molecular cluster; and the HAP molecular clusters and HAP seed crystal particles are subjected to rapid agglomeration crystallization to generate crystallization products HAP and precursors thereof, the crystallization products HAP with larger particles are deposited into a concentration and curing area, and the crystallization products HAP are discharged from a slag discharge pipe through a slag discharge valve after concentration and curing and are recycled as phosphate fertilizer.
And the high-density induced crystallization area II simultaneously generates secondary nucleation, new crystal nuclei enter the buffer area under the driving of ascending water flow, an ascending-descending cycle is generated, the new crystal nuclei gradually grow in the cycle, and finally fall into the high-density induced crystallization area to serve as new crystal seeds to supplement the crystal seed loss caused by the discharge of a crystallization product HAP.
After the ascending water flow passes through the buffer zone and enters the settling zone, the concentration of suspended particles in the water is further reduced, and finally, the clear water enters the water collecting tank 12 and is discharged after reaching the standard through the water discharging pipe 13 and the water discharging valve 14.
The present application will be described in detail with reference to specific examples.
Example 1
The phosphorus concentration of the inlet water is 1.0mg/L, and the average inlet water flow is 2m3The hydraulic retention time of an induced crystallization zone is 5min, the total hydraulic retention time of a fluidized bed is 10min, the rising flow rate of the induced crystallization zone is 16m/h, the rising flow rate of the top of a buffer zone is 8m/h, 75 mu m HAP particles are adopted as initial seed crystals, and the adding amount is 50 g/L; ca2+The pH value of the middle part of the induced crystallization area is controlled to be 9.0 when the adding amount is 50 mg/L. After the reaction is stable, the average grain diameter of the seed crystal in the induced crystallization area is maintained at 100 mu mThe amount was stabilized at 48 g/L.
Experimental results show that the phosphorus concentration of the effluent is stabilized below 0.2mg/L, the pH is stabilized at about 8.5, the first-class A standard of pollutant discharge standard of urban sewage treatment plant (GB 18918-.
Example 2
Different from the example 1, the phosphorus concentration of the feed water is 0.85-1.22 mg/L, 150 μm HAP particles are used as the initial seed crystal, the adding amount is 50g/L, and the rising flow velocity of the induced crystallization zone is 14 m/h. After the reaction is stable, the average grain diameter of the seed crystal in the induced crystallization area is maintained at 180 mu m, and the quantity is stabilized at about 48 g/L.
Experimental results show that the phosphorus concentration of the effluent is stabilized below 0.3mg/L, the pH is stabilized at about 8.8, the IV standard of the quality standard of surface water environment (GB 3838-.
Example 3
Different from the example 1, the phosphorus concentration of the inlet water is 1.22mg/L, the hydraulic retention time of the induced crystallization area is 8min, the total hydraulic retention time of the fluidized bed is 14min, the HAP particles with the particle size of 75 mu m are adopted as the initial seed crystals, and the adding amount is 20 g/L. After the reaction is stable, the average grain diameter of the seed crystal in the induced crystallization area is maintained at 100 mu m, and the quantity is stabilized at about 18 g/L.
The experimental result shows that the phosphorus concentration of the effluent is stabilized below 0.3mg/L, the pH is stabilized about 8.8, the first-class A standard of pollutant discharge Standard of municipal wastewater treatment plant (GB 18918-2002) is met, and the phosphorus recovery rate is more than 70%.
Example 4
Different from the example 1, the phosphorus concentration of the feed water is 1.1mg/L, and Ca is added2+The adding amount is 20mg/L, after the reaction is stable, the average grain diameter of the seed crystal in the induced crystallization area is maintained at 100 mu m, and the quantity is stabilized at about 48 g/L. Experimental results show that the phosphorus concentration of the effluent is stabilized below 0.3mg/L, the pH is stabilized at about 8.8, the IV standard of the quality standard of surface water environment (GB 3838-.
Example 5
Unlike example 1, the flow rate of the crystallization zone was induced to rise by 24m/h, and the flow rate of the buffer zone was induced to rise by 12 m/h. After the reaction is stable, the average grain diameter of the seed crystal in the induced crystallization area is maintained at 120 mu m, and the quantity is stabilized at about 42 g/L. Experimental results show that the phosphorus concentration of the effluent is stabilized below 0.25mg/L, the pH is stabilized at about 8.8, the first-class A standard of pollutant discharge Standard of municipal wastewater treatment plant (GB 18918-.
Example 6
Different from the example 1, the adding amount of the initial seed crystal is 5g/L, the seed crystal adopts HAP particles with the particle size of 300 mu m, after the reaction is stable, the average particle size of the seed crystal in the induced crystallization area is 325 mu m, the quantity is stable at 4.8g/L, and the experimental result shows that the phosphorus concentration of the effluent is stable at about 0.6 mg/L.
Example 7
Different from example 1 in that Ca2+The adding amount is 8mg/L, the pH value of the middle part of the high-density induced crystallization area is controlled to be 7.0, after the reaction is stable, the average grain diameter of the seed crystals in the induced crystallization area is maintained at 90 mu m, the number is stable at 45g/L, and the experimental result shows that the concentration of the phosphorus in the effluent is stable at about 0.8 mg/L.
Example 8
Different from the embodiment 1, the rising flow rate of the induced crystallization zone is 40m/h, the rising flow rate of the buffer zone is 20m/h, after the reaction is stable, the average grain diameter of the seed crystal in the induced crystallization zone is maintained at 100 mu m, the number is stabilized at 33g/L, and the experimental result shows that the phosphorus concentration of the effluent is stabilized at about 0.9 mg/L.
The above examples are merely illustrative for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. Nor is it intended to be exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.

Claims (5)

1. A method for deeply removing phosphorus and recovering phosphorus from secondary effluent of a sewage treatment plant is characterized by comprising the following steps: fluidizing a plurality of fine HAP seed particles by means of an ascending current in the fluidized bed to form an induced crystallization zone;
low concentration PO in secondary effluent4 3-And OH added-And Ca2+Firstly generating molecular clusters of HAP and precursor thereof in an induced crystallization zone, and rapidly aggregating and crystallizing the molecular clusters and HAP seed crystal particles under the action of ascending water flow to generate crystallization products of HAP and precursor thereof, and depositing the crystallization products of HAP and precursor thereof at the bottom of a fluidized bed; the phosphorus concentration in the secondary effluent is 0.6-2.0 mg/L;
a small amount of crushed crystallization products enter a buffer zone of the fluidized bed under the action of ascending water flow, the speed gradually decreases along the way, and the crushed crystallization products return to the induced crystallization zone again under the action of gravity, so that ascending-descending circulation occurs, and the crushed crystallization products gradually grow in the circulation, finally fall into the induced crystallization zone to serve as new seed crystals, and supplement the seed crystals lost caused by HAP (hydrogen induced phosphate) discharge of the crystallization products;
after the reaction is stable, the quantity of HAP seed crystals in the induced crystallization zone is controlled to be 20-50 g/L, and the average particle size is controlled to be 50-150 μm.
2. The method of claim 1, wherein: ca in the induced crystallization region2+The concentration is controlled to be 20-50 mg/L, and the pH value is controlled to be 8.0-9.0.
3. The method according to claim 1 or 2, characterized in that: the ascending flow velocity of the induced crystallization zone is controlled to be 12-24 m/h, and the ascending flow velocity of the top of the buffer zone is controlled to be 6-12 m/h.
4. The method according to claim 1 or 2, characterized in that: the fluidized bed is sequentially divided into a concentration and curing zone, an induced crystallization zone and a buffer zone from bottom to top, and secondary effluent water and OH-And Ca2+Introducing the bottom of the self-induced crystallization zone into a fluidized bed.
5. The method according to claim 1 or 2, characterized in that: the Ca2+Is selected from CaCl2Said OH is-Selected from NaOH solution.
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Citations (2)

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Publication number Priority date Publication date Assignee Title
CN104973723A (en) * 2015-07-26 2015-10-14 安徽科技学院 Device and method for recycling phosphorus by virtue of induced crystallization
CN106938876A (en) * 2017-05-09 2017-07-11 北京市环境保护科学研究院 The preprocess method of waste water cleans in a kind of mineral water manufacturing enterprise

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104973723A (en) * 2015-07-26 2015-10-14 安徽科技学院 Device and method for recycling phosphorus by virtue of induced crystallization
CN106938876A (en) * 2017-05-09 2017-07-11 北京市环境保护科学研究院 The preprocess method of waste water cleans in a kind of mineral water manufacturing enterprise

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