A method for recovering phosphorus resources in sewage based on bamboo-based biofilm filler

Abstract

The application discloses a method for recovering phosphorus resources in sewage and waste water based on bamboo-based biomembrane fillers, and takes bamboo-based biomembrane fillers saturated with adsorption after a period of operation as the recovery object, wherein the fillers take bamboo-based materials from bamboo subfamily plants as substrates, form porous carbon skeletons through carbonization treatment, and are loaded with metal oxide modified layers; the form of the fillers includes one or more of a spherical shape, an ellipsoidal shape, a cylindrical shape, a drum shape, a butterfly shape, a flat plate shape and a rope shape, the whole fillers are taken out, phosphorus is recovered through incineration ash extraction, acid leaching or alkali leaching, calcium phosphate, hydroxyapatite, ammonium magnesium phosphate or slow-release phosphate fertilizer is prepared, and the metal oxide components such as iron and lanthanum recovered can be recycled to prepare new fillers, and the method is suitable for recovering and recycling phosphorus resources in urban domestic sewage, rural domestic sewage, industrial waste water and aquaculture waste water treatment systems, realizes zero waste cycle of phosphorus storage and replacement recovery, the purity of the recovery product is high, the recovery product can be used as a phosphorus chemical raw material or a phosphate fertilizer production raw material, enters a phosphorus resource commodity circulation system, and realizes high-value cyclic utilization of phosphorus resources in sewage.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource recycling technology, and in particular to a method for recovering phosphorus resources from wastewater based on bamboo-based biofilm packing material. Background Technology

[0002] Phosphate rock is a precious, non-renewable resource on Earth, listed as a "critical raw material" by the European Union and a "critical mineral" by the U.S. Geological Survey. Global phosphate rock reserves are limited and extremely unevenly distributed. At the current rate of extraction, global phosphate rock reserves can only last for 50-100 years, making the phosphorus crisis a global resource security issue. In my country, millions of tons of phosphorus resources are lost annually through wastewater discharge, causing the dual problems of eutrophication and resource waste. Traditional wastewater treatment processes primarily remove phosphorus through chemical precipitation (addition of aluminum, iron, and calcium salts) or biological phosphorus removal (excessive phosphorus uptake by polyphosphate-accumulating bacteria). Ultimately, phosphorus enters landfills or incinerators as chemical or biological sludge, failing to achieve resource recovery.

[0003] In recent years, technologies for recovering phosphorus from wastewater have gradually gained attention, mainly including: Struvite (magnesium ammonium phosphate) crystallization method: In anaerobic digestion sludge supernatant or high-phosphorus wastewater, by controlling the Mg content... 2+ NH4 + PO4 3- Concentration and pH value cause struvite to crystallize and precipitate. This method requires a specialized crystallization reactor and precise process control, resulting in large equipment investment and high operating costs, making it difficult to promote in small and medium-sized wastewater treatment plants.

[0004] Chemical precipitation: Calcium or magnesium salts are added at the end of wastewater treatment to precipitate phosphorus as calcium phosphate or struvite. This method requires additional chemical additives, increasing operating costs, and the precipitate has low purity, making it difficult to use directly.

[0005] Adsorption method: Phosphorus is adsorbed using adsorbents such as activated carbon, zeolite, and metal oxides, but the adsorption capacity is low, regeneration is difficult, and the adsorbent itself is expensive.

[0006] However, the existing phosphorus recovery technologies mentioned above have the following problems: 1. Existing adsorbents have limited functionality: For example, the iron-lanthanum composite modified biomass adsorbent disclosed in Chinese patent document CN109311728A, although possessing a certain adsorption capacity, is mostly in powder or granular form, possessing only a single adsorption function and lacking the function of a biofilm carrier. In practical applications, separating the adsorbent from the sludge mixture is difficult, the operation is complex, and the recovery purity is low.

[0007] 2. Separation of phosphorus recovery from wastewater treatment processes: Struvite crystallization, chemical precipitation, and other methods require additional specialized reactors and chemical reagents, resulting in large equipment investments and high operating costs, making them unsuitable for small and medium-sized wastewater treatment plants and decentralized treatment facilities.

[0008] 3. Low purity of recovered products and difficulty in direct utilization: Existing technologies for recovering phosphorus from municipal sludge incineration ash (such as those used in Germany and Japan) use municipal sludge as raw material and have problems such as high risk of heavy metal pollution, high cost of pathogen inactivation, and uneven phosphorus enrichment concentration. The recovered products have low purity and need to be further purified before they can be used, which limits their agricultural application.

[0009] 4. Limited packing material morphology: Existing biofilm packing materials (such as Chinese patent document with publication number CN111547198A) mostly use a mixture of polymer and mineral powder for granulation, resulting in a single morphology. This makes it difficult to meet the special requirements of fixed bed, A² / O and other processes for suspended or stacked packing materials (such as rope-like materials), thus limiting the application scenarios.

[0010] Therefore, developing a phosphorus resource recovery method that can integrate phosphorus removal and storage, is easy to operate, produces high-purity products, and is adaptable to various processes is a pressing technical problem that needs to be solved. Summary of the Invention

[0011] The purpose of this invention is to solve the above-mentioned problems by providing a method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing, which achieves zero-waste recycling by removing phosphorus and storing phosphorus, and by replacing materials and recovering phosphorus, while improving the purity of the recovered products and reducing the recovery cost.

[0012] To achieve the above objectives, the present invention provides the following technical solution: The present invention discloses a method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material, comprising the following steps: The adsorption-saturated bamboo-based biofilm packing material uses bamboo-based materials derived from Bambusoideae plants as the substrate, which are carbonized to form a porous carbon skeleton and loaded with a metal oxide modified layer. After operating in a wastewater treatment system for a period of time, the packing material becomes saturated with adsorption, and its adsorption capacity for phosphate reaches 12-35 mgP / g. At the same time, it serves as a biofilm carrier, supporting functional microorganisms such as nitrifying bacteria and denitrifying bacteria, and exerting a synergistic decontamination function of biodegradation and chemical adsorption. The morphology of the packing material includes one or more of the following: spherical, ellipsoidal, cylindrical, drum-shaped, butterfly-shaped, flat, and rope-shaped.

[0013] The packing material was tested and found to be free of pathogen contamination, with heavy metal content below the standard limit for agricultural sludge, and uniform phosphorus enrichment. It is fundamentally different from the ash content of municipal sludge incineration, and the recycled raw materials have high purity. The recycled products can be directly used in agricultural production. (2) Remove the saturated packing material from the wastewater treatment system and transport it to the phosphorus recovery and treatment site; (3) The saturated filler removed is subjected to phosphorus resource recovery treatment by one of the following methods: incineration ash extraction, acid leaching or alkaline leaching, to obtain the recovered product, which includes one or more of calcium phosphate, hydroxyapatite, magnesium ammonium phosphate and slow-release phosphate fertilizer.

[0014] Furthermore, the metal oxide modified layer is a metal oxide modified layer containing iron and lanthanum elements, and the packing material becomes saturated with adsorption after 3 to 5 years of operation in the wastewater treatment system.

[0015] Furthermore, the rope-shaped packing has a diameter of 2mm to 50mm and a length of 50mm to 6000mm. It is made of multiple strands of bamboo fiber twisted and woven together, with a spiral or straight surface. It is suitable for use as a suspended or stacked packing in fixed beds, biological contact oxidation tanks, aerated biofilm reactors, or anaerobic / anoxic / aerobic processes. The rope-shaped packing includes an auxiliary support skeleton, the skeleton material of which is one of bamboo sticks, nylon rope, stainless steel wire, or polypropylene rope. The skeleton material only serves a supporting function, while the bamboo fiber is the main functional component.

[0016] Furthermore, the wastewater treatment system includes a biological contact oxidation tank, a biological filter, a fixed bed, an aerated biofilm reactor, an anaerobic tank, an anoxic tank, an aerobic tank, or a side-flow treatment unit; the addition rate of the packing material is 20% to 60% of the effective volume of the tank.

[0017] Furthermore, the incineration ash extraction method described in step (3) includes the following steps: The adsorption-saturated filler was incinerated at 600℃~900℃, and the bamboo fiber matrix was converted into ash. Iron and lanthanum were enriched in the ash in the form of oxides, and phosphorus existed in the form of pyrophosphate. The ash was leached with a hydrochloric acid or sulfuric acid solution with a mass fraction of 5% to 20%, the solid-liquid ratio was 1:5 to 1:15, the leaching temperature was 50℃ to 80℃, and the leaching time was 2h to 8h. After filtration, calcium or magnesium salts are added to the leachate to adjust the pH to 8-10, and hydroxyapatite or calcium phosphate is recovered by precipitation.

[0018] The ash after incineration is rich in phosphorus, iron, and lanthanum oxides, with a P2O5 content of not less than 10 wt%; the phosphorus recovery rate is not less than 80%, and the purity of the recovered product is not less than 80%.

[0019] Furthermore, the acid leaching method described in step (3) includes the following steps: The adsorption-saturated filler is directly immersed in a 0.5-2 mol / L hydrochloric acid or sulfuric acid solution with a solid-liquid ratio of 1:5-1:10, and stirred for 2-8 hours at room temperature or 50-80℃. Iron and lanthanum, along with adsorbed phosphorus, are dissolved simultaneously, with a phosphorus concentration of 2–8 g / L in the leachate; Iron, lanthanum, and phosphorus are separated by stepwise precipitation or extraction, with phosphorus recovered as calcium phosphate or magnesium ammonium phosphate.

[0020] The stepwise precipitation process includes first adding an oxidant to the leachate to oxidize any low-valent iron to high-valent iron, adjusting the pH to 4-5 to precipitate and separate the iron; then further adjusting the pH to 7.5-8.5, adding calcium salts to precipitate and recover calcium phosphate; or adding magnesium salts and ammonia to adjust the pH to 8.5-9.5, precipitating and recovering magnesium ammonium phosphate (struvite).

[0021] Furthermore, the alkaline leaching method described in step (3) includes the following steps: The adsorption-saturated filler was immersed in a 1-3 mol / L sodium hydroxide solution with a solid-liquid ratio of 1:8-1:15 and stirred for 2-6 hours at room temperature or 40-80℃. Phosphorus is selectively leached, iron loss rate is ≤8%, lanthanum loss rate is ≤5%, and iron and lanthanum mainly remain in the filler skeleton in the form of hydroxides; Calcium salts are added to the leachate, or carbon dioxide gas is introduced and calcium salts are added to adjust the pH to 8-10, and calcium phosphate or hydroxyapatite is precipitated and recovered; the remaining bamboo fiber matrix is ​​washed and dried and used as biomass fuel or soil conditioner.

[0022] Compared with the prior art, the present invention has significant advantages, as can be seen from the above technical solution: 1. Phosphorus removal and storage simultaneously: Iron-lanthanum modified bamboo-based biofilm packing simultaneously adsorbs and removes phosphates during wastewater treatment. After 3 to 5 years of operation and adsorption saturation, the phosphorus resources enriched in the packing are equivalent to a small phosphate mine, realizing the enrichment of phosphorus resources through "treatment and storage". 2. Replacement and recycling: After the saturated packing is removed as a whole, phosphorus can be recovered by incineration ash extraction, acid leaching or alkali leaching. No special recycling equipment or additional chemical agents are required. The recycling process is simple and low cost. 3. Three recycling routes are available: Depending on the regional resource conditions and the demand for recycled products, the following methods can be flexibly selected: incineration ash extraction (to recover hydroxyapatite), acid leaching (to recover calcium phosphate or struvite), or alkaline leaching (to recover calcium phosphate), which is highly adaptable. 4. Iron and lanthanum recycling: The recovered iron and lanthanum components can be recycled to prepare new iron and lanthanum modified bamboo-based biofilm fillers, reducing the production cost of fillers by 30% to 50% and realizing a closed-loop resource cycle.

[0023] 5. High purity of recovered products, directly applicable to agriculture: The packing material is tested and found to be free of pathogen contamination, with heavy metal content below the standard limit for agricultural sludge. The recovered products (hydroxyapatite, calcium phosphate, and struvite) can be directly used as raw materials for phosphate fertilizer or slow-release fertilizer, with a purity of over 80%. Magnesium ammonium phosphate is used as a slow-release nitrogen and phosphorus compound fertilizer. Attached Figure Description

[0024] Figure 1 This is a flowchart of the phosphorus resource recovery method in wastewater based on bamboo-based biofilm packing material according to the present invention.

[0025] Figure 2 This is a process flow diagram of phosphorus recovery by incineration ash extraction method according to the present invention.

[0026] Figure 3 This is a process flow diagram of phosphorus recovery by acid leaching according to the present invention.

[0027] Figure 4 This is a process flow diagram of phosphorus recovery by alkaline leaching according to the present invention.

[0028] Figure 5 This is a process flow diagram of the iron-lanthanum recycling process of the present invention. Detailed Implementation

[0029] The following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing proposed in this invention: Example 1: Phosphorus recovery by incineration ash extraction method (municipal wastewater treatment plant) See Figure 1-2 The present invention discloses a method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing, comprising the following steps: Step 1: Provide bamboo-based biofilm packing material that is saturated with adsorption.

[0030] Iron-lanthanum modified bamboo-based biofilm packing material (cylindrical, 100mm outer diameter, 150mm length) that had been operating for 3 years in the biological contact oxidation tank of a municipal wastewater treatment plant was used. This packing material uses bamboo fiber as the base material and undergoes a two-step carbonization process, with an iron-lanthanum composite oxide functional layer (Fe:La=4:1, iron loading 10wt%, lanthanum loading 5wt%) loaded on the surface. The packing material is dark brown in appearance, with a large amount of phosphate precipitate accumulated on its surface and in its pores. Testing showed that the packing material was free of pathogen contamination, its heavy metal content was below the standard limit for agricultural sludge, and phosphorus was uniformly enriched. The dosage of this packing material in the biological contact oxidation tank was 40% of the tank's effective volume.

[0031] Step 2: Remove the saturated packing material from the biological contact oxidation tank as a whole and transport it to the phosphorus recovery and treatment site; Step 3 involves recovering phosphorus resources from the removed saturated packing material using an incineration ash extraction method, including the following steps: (1) Ash extraction from incineration: The adsorption-saturated packing material was placed in a rotary kiln and incinerated at 800℃ at a rate of 5℃ / min under air atmosphere for 2 hours. After incineration, grayish-white ash was obtained, with a mass of approximately 25% of the original packing material mass. X-ray fluorescence spectroscopy (XRF) analysis showed that the ash contained 18.5wt% P2O5, 22.3wt% Fe2O3, 15.6wt% La2O3, and 8.2wt% CaO (from the co-precipitation of calcium ions and phosphate ions in the influent).

[0032] (2) Acid leaching purification: The ash was mixed with a 15% hydrochloric acid solution at a solid-liquid ratio of 1:10 and leached at 60°C for 4 hours with stirring. After filtration, a phosphorus-containing leachate was obtained, in which the phosphorus concentration was 4.2 g / L (as PO4). 3- (Calculation). Saturated lime milk (Ca(OH)2) was slowly added to the leachate to adjust the pH to 9.5. The mixture was stirred at room temperature for 2 hours to form hydroxyapatite precipitate. After filtration, washing, and drying, the hydroxyapatite product was obtained with a purity of 92.3% and a phosphorus recovery rate of 87.6%.

[0033] The resulting hydroxyapatite can be sold to fertilizer plants as a raw material for phosphate fertilizer, or further crushed and used directly as a slow-release phosphate fertilizer in surrounding farmland. Based on the plant's processing capacity of 100,000 tons / day and a filler filling rate of 40%, approximately 20 tons of phosphorus resources (calculated as P2O5) can be recovered over three years. At a market price of 3,500 yuan / ton for phosphate rock, the recovery value is approximately 70,000 yuan. Simultaneously, the cost of chemical phosphorus removal agents (PAC / Alum) saved over three years is approximately 2 million yuan, demonstrating significant overall economic benefits.

[0034] Example 2: Phosphorus recovery by acid leaching (aquaculture wastewater treatment plant) See Figure 1 , 3 The present invention discloses a method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing, comprising the following steps: Step 1: Provide bamboo-based biofilm packing material that is saturated with adsorption.

[0035] Iron-lanthanum modified bamboo-based biofilm packing material (spherical, 100mm in diameter, made of bamboo fiber, Fe:La=3:1, iron loading 12wt%, lanthanum loading 6wt%) was taken from the aerobic tank of a certain aquaculture wastewater treatment plant and had been in operation for 4 years. Testing showed that the packing material was free of pathogen contamination, its heavy metal content was below the standard limit for agricultural sludge, and its phosphorus was uniformly enriched. The dosage of this packing material in the aerobic tank was 35% of the effective volume of the tank.

[0036] Step 2: Remove the saturated packing material from the biological contact oxidation tank as a whole and transport it to the phosphorus recovery and treatment site; Step 3 involves acid leaching to recover phosphorus from the removed saturated packing material. This includes the following steps: (1) Acid leaching: The saturated filler was directly immersed in a 10% sulfuric acid solution with a solid-liquid ratio of 1:8, and leached at 50°C with stirring for 6 hours. The phosphorus concentration in the leachate was 3.8 g / L (as PO4). 3- (Calculated), the iron concentration is 2.1 g / L and the lanthanum concentration is 1.5 g / L.

[0037] (2) Stepwise precipitation separation: First, an oxidant is added to the leachate to oxidize any possible low-valent iron to high-valent iron. Then, ammonia is slowly added to adjust the pH to 4.5, and the iron (in the form of ferric hydroxide) is precipitated and separated. The pH is then adjusted to 8.5, and magnesium chloride and ammonia are added to precipitate and recover 3.2 kg of magnesium ammonium phosphate (struvite). The nitrogen and phosphorus recovery rate is ≥88%.

[0038] After filtration and drying, struvite slow-release fertilizer was obtained with a purity of 89.5% and a phosphorus recovery rate of 82.3%. The leached packing matrix, after washing and drying, can be re-functionalized with iron and lanthanum, achieving recycling of the packing matrix. The recovered iron and lanthanum solution, after concentration, can be used to prepare new iron and lanthanum modifiers.

[0039] Example 3: Phosphorus recovery by alkaline leaching (food industry wastewater treatment plant) See Figure 1 , 4 The present invention discloses a method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing, comprising the following steps: Step 1: Provide bamboo-based biofilm packing material that is saturated with adsorption.

[0040] A butterfly-shaped, iron-lanthanum modified bamboo-based biofilm packing material (Fe:La = 5:1, iron loading 8 wt%, lanthanum loading 4 wt%), which had been operating for 3.5 years in a biological filter of a food industry wastewater treatment plant, was tested. The packing material was found to be free of pathogen contamination, with heavy metal content below the standard limits for agricultural sludge, and phosphorus was uniformly enriched. The packing material was added to the aerobic tank at a rate of 30% of the tank's effective volume.

[0041] Step 2: Remove the saturated packing material from the biological contact oxidation tank as a whole and transport it to the phosphorus recovery and treatment site; Step 3 involves treating the removed saturated packing material using an alkaline leaching method to recover phosphorus resources. This includes the following steps: (1) Alkali leaching: The saturated filler was immersed in a 10% sodium hydroxide solution (solid-liquid ratio 1:10) and leached with stirring at room temperature for 4 hours. The phosphorus concentration in the leachate was 2.5 g / L (as PO4). 3-It exists in the form of sodium phosphate, with an iron concentration of 0.3 g / L (iron loss rate <5%) and a lanthanum concentration of 0.2 g / L (lanthanum loss rate <3%).

[0042] (2) Precipitation recovery: Calcium salt was added to the leachate and the pH was adjusted to 9.0. 4.8 kg of calcium phosphate product was obtained by precipitation, with a phosphorus recovery rate of 90%.

[0043] The remaining bamboo fiber matrix, after washing and drying, can be used as biomass fuel with a calorific value of approximately 18 MJ / kg. This route is suitable for scenarios requiring the recovery of iron and lanthanum ions; the leachate after alkaline leaching can be further used to recover iron and lanthanum.

[0044] Example 4: Application of rope-like (anamorphic aquatic plant) iron-lanthanum modified bamboo-based packing material in fixed bed phosphorus recovery See Figure 1 The present invention discloses a method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing, comprising the following steps: Step 1: Provide bamboo-based biofilm packing material that is saturated with adsorption.

[0045] Take a wastewater treatment plant A in a certain town 2 The rope-like (aquatic plant-like) iron-lanthanum modified bamboo-based biofilm packing material, which has been in operation for 3 years in the / O process anaerobic tank, is 10mm in diameter and 500mm in length. It is made of 12 strands of bamboo fiber (0.5mm diameter per strand) twisted and woven together, with a spiral surface and a nylon rope as the skeleton support. The nylon rope serves only as an auxiliary support skeleton and can be replaced with bamboo skewers, stainless steel wire, polypropylene rope, or other inert materials. Bamboo fiber is the main functional component, with an iron-lanthanum composite oxide functional layer loaded on the surface. The iron-lanthanum modification imparts phosphorus absorption capability to the packing material, independent of the skeleton material. The packing material undergoes a two-step carbonization process, with an iron-lanthanum composite oxide functional layer (Fe:La=3:1, iron loading 10wt%, lanthanum loading 5wt%) loaded on the surface. The packing material is suspended in the anaerobic tank at 100mm intervals, with an addition rate of 35% of the tank's effective volume. The average total phosphorus concentration in the influent of this plant is 5.2mg / L, and the required total phosphorus concentration in the effluent is below 0.5mg / L. After adopting rope-shaped iron-lanthanum modified bamboo-based packing material, no additional chemical phosphorus removal agents are needed. The total phosphorus in the effluent is consistently below 0.5 mg / L, meeting the Class A standard. The packing material reaches adsorption saturation after 3 years of operation, at which point the total mass of the packing material in the tank is approximately 120 tons (dry weight). Testing showed that the packing material is free of pathogen contamination, the heavy metal content is below the standard limit for agricultural sludge, and phosphorus is uniformly enriched.

[0046] Step 2: Remove the saturated rope packing material as a whole and transport it to the phosphorus recovery and treatment site.

[0047] Step 3 involves recovering phosphorus resources from the removed saturated packing material using an incineration ash extraction method. This includes the following steps: (1) Incineration: Due to the compact structure of the rope-like packing, phosphorus recovery was achieved through incineration ash extraction: The ash was incinerated at 800℃ for 2 hours in a rotary kiln, yielding approximately 30 tons of ash. The P2O5 content in the ash was 19.2 wt%. (2) Acid leaching purification: The ash was mixed with a 15% hydrochloric acid solution at a solid-liquid ratio of 1:10 and leached at 60°C for 4 hours. After filtration, a phosphorus-containing leachate was obtained. Saturated lime milk (Ca(OH)2) was slowly added to the leachate to adjust the pH to 9.5. The mixture was stirred at room temperature for 2 hours to generate hydroxyapatite precipitate. After filtration, washing, and drying, the hydroxyapatite product was obtained with a purity of 91.5% and a phosphorus recovery rate of 88.2%.

[0048] This embodiment demonstrates that the rope-like (anamorphic aquatic plant) iron-lanthanum modified bamboo-based biofilm packing is also suitable for the phosphorus resource recovery method of the present invention, and due to its large specific surface area and uniform biofilm formation, it is suitable for use in fixed beds and A... 2 The / O process offers better phosphorus removal and higher phosphorus recovery value.

[0049] Example 5: Iron-Lanternium Recycling (Packaging Regeneration) like Figure 5 As shown, the method for recovering phosphorus by acid leaching and subsequent reuse of iron and lanthanum according to the present invention includes the following steps: Step 1: Provide bamboo-based biofilm packing material that is saturated with adsorption.

[0050] The same saturated packing material as in Example 2 was used (spherical iron-lanthanum modified bamboo-based biofilm packing material that has been running for 4 years in the aerobic tank of the aquaculture wastewater treatment plant, Fe:La=3:1, iron loading 12wt%, lanthanum loading 6wt%).

[0051] Step 2: Remove the saturated packing material from the wastewater treatment system and transport it to the phosphorus recovery and treatment site.

[0052] Same as step (2) in Example 2.

[0053] Step 3 involves using acid leaching to recover phosphorus from the removed saturated packing material, and further recycling the recovered iron and lanthanum components. This includes the following steps: (1) Acid leaching and stepwise precipitation to recover phosphorus: The acid leaching method of Example 2 was followed to obtain struvite product and iron- and lanthanum-containing recovery solution (i.e., the lanthanum-containing solution remaining after stepwise precipitation to separate iron and the solution after iron precipitation, which were actually combined for processing, but the iron- and lanthanum-containing solution after acid leaching was clearly used in this example).

[0054] (2) Iron and lanthanum recycling: The iron- and lanthanum-containing solutions after phosphorus recovery by acid leaching are concentrated by evaporation to Fe 3+ Concentration of 1.0 mol / L, La 3+The concentration was 0.3 mol / L. Freshly prepared bamboo fiber carbon skeletons (without iron and lanthanum loading, including cylindrical, spherical, and rope-like forms) were immersed in this concentrated solution and impregnated for 2 hours under a negative pressure of -0.08 MPa. After removal, in-situ precipitation with ammonia water was performed, the pH was adjusted to 9, and the mixture was aged at room temperature for 12 hours. After filtration and washing, the mixture was dried at 110℃. Finally, it was heat-treated at 400℃ for 2 hours under a nitrogen atmosphere. The resulting regenerated packing had an iron loading of 11 wt% and a lanthanum loading of 5.5 wt%, with performance comparable to fresh packing. The phosphate adsorption capacity was 28 mg P / g, meeting the requirements for engineering applications. This method achieves the recycling of iron and lanthanum resources and reduces the production cost of the packing by approximately 40%.

[0055] The economic benefits of phosphorus recovery from large-scale wastewater treatment plants are calculated as follows: Taking a municipal wastewater treatment plant with a treatment capacity of 100,000 tons / day as an example, iron-lanthanum modified bamboo-based biofilm packing material (including cylindrical, spherical, and rope-shaped mixed addition) is used as the biological contact oxidation tank and A 2 The filler material for the / O process has a filling rate of 40% of the effective volume of the tank.

[0056] The plant's influent total phosphorus concentration averaged 4.5 mg / L, and the effluent total phosphorus concentration was required to be below 0.5 mg / L. After adopting iron-lanthanum modified bamboo-based packing material, no additional chemical phosphorus removal agents were needed, and the effluent total phosphorus concentration remained consistently below 0.5 mg / L, meeting the Class A standard.

[0057] After 3 years of operation, the packing material becomes saturated with adsorption, at which point the total mass of the packing material in the tank is approximately 120 tons (dry weight). Based on an average P2O5 content of 18% in the ash, approximately 20 tons of P2O5 can be recovered over 3 years, equivalent to approximately 8.7 tons of phosphorus.

[0058] Comprehensive economic benefit calculation (3 years): (1) Value of recovered phosphorus products: Based on the market price of phosphate rock of RMB 3,500 / ton (P2O5), the value of recovered 20 tons of P2O5 is approximately RMB 70,000; (2) Save on chemical phosphorus removal agent costs: The original method of using PAC for phosphorus removal had a dosage of 150 mg / L, and the agent cost over 3 years was approximately RMB 2 million; (3) Reduce solid waste disposal costs: The original chemical sludge production was about 2,000 tons / year, with a disposal cost of 500 yuan / ton, and the cost over 3 years was about 3 million yuan; after adopting iron-lanthanum modified bamboo-based filler, the sludge volume was reduced by 40%, saving about 1.2 million yuan. (4) Iron and lanthanum recycling saves money: the cost of recycled filler is reduced by 40%, saving about RMB1.88 million in 3 years; (5) Overall economic benefits: approximately RMB 5.15 million / 3 years (conservative estimate). If multiple wastewater treatment plants are linked together and higher recovery rates are considered, the overall economic benefits can reach RMB 6 million / 3 years or more.

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material, characterized in that, Includes the following steps: (1) Provides bamboo-based biofilm packing material with adsorption saturation. The packing material is based on bamboo-based material derived from bamboo subfamily plants. It is carbonized to form a porous carbon skeleton and loaded with a metal oxide modified layer. The packing material is adsorbed saturation after running in the sewage treatment system for a period of time. The packing material is tested to be free of pathogen pollution, with heavy metal content lower than the standard limit for agricultural sludge, and phosphorus enrichment is uniform. (2) Remove the saturated packing material from the wastewater treatment system and transport it to the phosphorus recovery and treatment site; (3) The saturated filler removed is subjected to phosphorus resource recovery treatment by one of the following methods: incineration ash extraction, acid leaching or alkaline leaching, to obtain the recovered product, which includes one or more of calcium phosphate, hydroxyapatite, magnesium ammonium phosphate and slow-release phosphate fertilizer.

2. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 1, characterized in that: The metal oxide modified layer in step (1) is a metal oxide modified layer containing iron and lanthanum elements. The packing material becomes saturated with adsorption after 3 to 5 years of operation in the sewage treatment system.

3. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 1, characterized in that: The shape of the packing material in step (1) includes one or more of the following: spherical, ellipsoidal, cylindrical, drum-shaped, butterfly-shaped, flat, and rope-shaped.

4. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 3, characterized in that, The rope-shaped filler in step (1) has a diameter of 2mm to 50mm and a length of 50mm to 6000mm. It is made of multiple strands of bamboo fiber twisted and woven, and the surface is spiral or straight. The rope-shaped filler includes an auxiliary support skeleton, and the skeleton material is one of bamboo sticks, nylon rope, stainless steel wire or polypropylene rope.

5. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 1, characterized in that: The wastewater treatment system described in step (2) includes a biological contact oxidation tank, a biological filter, a fixed bed, an aerated biofilm reactor, an anaerobic tank, an anoxic tank, an aerobic tank, or a side-flow treatment unit; the addition rate of the packing material is 20% to 60% of the effective volume of the tank.

6. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 1 or 2, characterized in that... The incineration ash extraction method described in step (3) includes the following steps: The adsorption-saturated filler was incinerated at 600℃~900℃, and the bamboo fiber matrix was converted into ash, with iron and lanthanum enriched in the ash in the form of oxides. The ash was leached with a hydrochloric acid or sulfuric acid solution with a mass fraction of 5% to 20%, the solid-liquid ratio was 1:5 to 1:15, the leaching temperature was 50℃ to 80℃, and the leaching time was 2h to 8h. After filtration, calcium or magnesium salts are added to the leachate to adjust the pH to 8-10, and hydroxyapatite or calcium phosphate is recovered by precipitation.

7. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 6, characterized in that: The ash after incineration is rich in phosphorus, iron, and lanthanum oxides, with a P2O5 content of not less than 10 wt%; the phosphorus recovery rate is not less than 80%, and the purity of the recovered product is not less than 80%.

8. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 1 or 2, characterized in that: The acid leaching method described in step (3) includes the following steps: The adsorption-saturated filler is directly immersed in a 0.5-2 mol / L hydrochloric acid or sulfuric acid solution with a solid-liquid ratio of 1:5-1:10, and stirred for 2-8 hours at room temperature or 50-80℃. Iron and lanthanum, along with adsorbed phosphorus, are dissolved simultaneously, with a phosphorus concentration of 2–8 g / L in the leachate; Iron, lanthanum, and phosphorus are separated by stepwise precipitation or extraction, with phosphorus recovered as calcium phosphate or magnesium ammonium phosphate.

9. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 8, characterized in that: The stepwise precipitation process includes first adding an oxidant to the leachate to oxidize any low-valent iron to high-valent iron, adjusting the pH to 4-5 to precipitate and separate the iron; then further adjusting the pH to 7.5-8.5, adding calcium salts to precipitate and recover calcium phosphate; or adding magnesium salts and ammonia to adjust the pH to 8.5-9.5, precipitating and recovering magnesium ammonium phosphate.

10. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 1 or 2, characterized in that: The alkaline leaching method described in step (3) includes the following steps: The adsorption-saturated filler was immersed in a 1-3 mol / L sodium hydroxide solution with a solid-liquid ratio of 1:8-1:15 and stirred for 2-6 hours at room temperature or 40-80℃. Phosphorus is selectively leached, iron loss rate is ≤8%, lanthanum loss rate is ≤5%, and iron and lanthanum mainly remain in the filler skeleton in the form of hydroxides; Calcium salts are added to the leachate, or carbon dioxide gas is introduced and calcium salts are added to adjust the pH to 8-10, and calcium phosphate or hydroxyapatite is precipitated and recovered; the remaining bamboo fiber matrix is ​​washed and dried and used as biomass fuel or soil conditioner.

11. The method for phosphorus resource recovery from wastewater based on bamboo-based biofilm packing material according to claim 1 or 2, characterized in that: The recovered iron and lanthanum components are concentrated, precipitated, or extracted and then recycled to prepare new iron-lanthanum modified bamboo-based biofilm fillers.

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