TWI719887B - Method for producing ammonium magnesium phosphate hexahydrate by using livestock manure - Google Patents

Abstract

The present invention relates to a method for producing ammonium magnesium phosphate hexahydrate by using livestock manure, including steps of: (1) anaerobic digestion for nutrient release, (2) solid-liquid separation, (3) adjustment of element ratio of digestive effluent, (4) decalcification and (5) magnesium ammonium phosphate precipitate. The method of the invention provides high element dissolution rate, appropriate ratio of synthesizable ammonium phosphate and removes crystal interference factors, which maximize the efficiency of recovering nutrients in livestock manure by the ammonium magnesium phosphate precipitation.

Description

Method for producing magnesium ammonium phosphate hexahydrate by using poultry and livestock manure

The present invention relates to a method for producing magnesium ammonium phosphate hexahydrate by using poultry and livestock manure, especially a method using anaerobic digestion and precipitation of magnesium ammonium phosphate.

Recovery of phosphorus in solids (such as manure, litter) in livestock wastes transfers phosphates from the solid part to the liquid part through active means (for example, dissolving insoluble phosphates, or mineralizing organophosphates and keeping them in In solution), the phosphate dissolved in the liquid can be recovered by adding chemicals to produce phosphate crystals or through the assimilation of phosphate phagocytic microorganisms. Among the recovered solids, the biogas residue can be used as a soil amendment, and the phosphate crystals can be used as phosphate fertilizer to return to agricultural land. The low-phosphorus residual biogas slurry is discharged into the environment and there is no risk of eutrophication, reducing excessive phosphate the effect on the environment. However, how to effectively recover phosphorus from poultry and livestock manure for use has always had different problems in the existing technology.

In the composting process, microorganisms will cause part of the nitrogen to be volatilized in the form of gas during the composting process, which cannot be effectively recycled and reused. Moreover, due to the low concentration of nutrients in manure, a higher application rate is required during fertilization. The ratio of nitrogen, phosphorus and potassium (NPK) cannot be adjusted to the nutritional requirements of crops. There is a problem of insufficient nitrogen but excessive phosphorus; part of the phosphorus will be formed. The insoluble phosphorus salt is fixed in the soil, and part of the phosphorus is scattered to the environment due to leaching, resulting in eutrophication. In addition, the composting process often has problems such as foul smell, breeding of mosquitoes, too long maturity, and the need for larger land area. While the granulation method and the heap-free method are heating and drying the feces or treating them with enzymes. Although they can reduce the risk of residual disease vectors and improve the odor problem, there is a concern that the degree of mineralization of nutrient elements is insufficient, and The problem of heavy metal residues still cannot be solved.

When anaerobic digestion produces natural gas, certain manure sources (such as chicken manure) will produce excessively high ammonium concentration, which inhibits the growth of methane bacteria and limits the production of biogas. In addition, excessively high magnesium ammonium phosphate will cause fouling on the pipe wall, and additional equipment maintenance costs must be paid. In recent years, co-digestion has gradually become a significant study of waste treatment and natural gas production. However, if co-digestion conditions are not properly controlled, it is easy to cause excessive acidification of the digestion environment and limit methane production.

When the magnesium ammonium phosphate precipitation method is used to recover the nutrient elements in the manure of laying hens, the dissolution rate of phosphorus is low during the anaerobic digestion process, and most of the phosphorus is still stored in the solid, resulting in poor phosphorus recovery efficiency. This is because the phosphorus species in layer manure is mainly insoluble calcium and phosphorus, which not only limits the phosphorus dissolution rate, but also limits the availability of phosphorus in the residual biogas residue. The proportions of phosphorus, ammonium, and magnesium dissolved in wastes from different sources are different, which limits the efficiency of recovering magnesium ammonium phosphate (ie struvite). To solve this problem, many technologies are supplemented by additional phosphorus, ammonium, and magnesium. In order to obtain an appropriate dosage ratio, maximize the crystallization efficiency of magnesium ammonium phosphate hexahydrate. However, additional phosphorus, ammonium, and magnesium supplementation will increase recycling costs. The complex composition in the effluent of anaerobic digestion will interfere with the crystallization reaction of magnesium ammonium phosphate, reduce the purity of the crystal, and even form a precipitate of non-magnesium ammonium phosphate.

In view of the shortcomings of the above-mentioned technology, the existing technology must develop a method of high efficiency, high element dissolution rate, appropriate synthesis ratio of magnesium ammonium phosphate and removal of crystallization interference factors, so as to maximize the production of magnesium ammonium phosphate and recover poultry manure. Of nutrients.

1.5；(4)脫鈣：添加有機酸至該混合消化液，使脫鈣後之該混合消化液的鈣/鎂之莫耳比

0.25；及(5)磷酸銨鎂沉澱：將該脫鈣後之該混合消化液，調整pH值至8.0~10.0，回收沉澱物，得到磷酸銨鎂六水合物。 Therefore, the present invention provides a method for producing magnesium ammonium phosphate hexahydrate using poultry manure. The steps include: (1) Anaerobic digestion: anaerobic digestion of poultry manure and an organic carbon source from the first aqueous solution , And carry out anaerobic digestion of poultry manure in the second aqueous solution at 50℃~70℃; (2) solid-liquid separation: solidify the first aqueous solution and the second aqueous solution of step (1) anaerobic digestion Liquid separation to obtain biogas residue, first digestion juice and second digestion juice respectively; (3) Digestion juice element ratio adjustment: mix the first digestion juice and the second digestion juice to obtain a mixed digestion juice, and confirm the mixed digestion juice The molar ratio of nitrogen/phosphorus>1 and the molar ratio of magnesium/nitrogen

1.5; (4) Decalcification: add organic acid to the mixed digestive juice to make the molar ratio of calcium/magnesium in the mixed digestive juice after decalcification

0.25; and (5) Magnesium ammonium phosphate precipitation: adjust the pH value of the mixed digestive solution after decalcification to 8.0~10.0, and recover the precipitate to obtain magnesium ammonium phosphate hexahydrate.

In a preferred embodiment, the organic carbon source is selected from the group consisting of straw, mushroom buns, rice, raw food waste, molasses, glycerin, sucrose, glucose and fructose.

In a preferred embodiment, the first aqueous solution in the step (1) is subjected to anaerobic digestion at 20°C to 50°C.

In a preferred embodiment, the weight ratio of the poultry manure in the step (1) to the weight of the first aqueous solution and the second aqueous solution is 0.5wt%-20wt%.

In a preferred embodiment, the ratio of the weight of the organic carbon source to the weight of the livestock manure is 1-5.

In a preferred embodiment, this step (2) is to perform solid-liquid separation by gravity sedimentation, belt filter dehydration, plate filter press dehydration, or screw extrusion dehydration.

In a preferred embodiment, the biogas residue obtained in this step (2) is further dried and granulated at a temperature higher than 60-75°C to form soil conditioning materials.

In a preferred embodiment, the biogas residue is further added with thermophilic enzymes or colonized with thermostable bacteria.

In a preferred embodiment, the organic acid in this step (4) is selected from the group consisting of carboxyl-containing organic acids of succinic acid, malic acid, fumaric acid, citric acid, lactic acid and oxalic acid.

In a preferred embodiment, the residual digestion solution after the completion of step (5) is further passed into an anaerobic digestion tank to produce biogas.

In a preferred embodiment, the addition amount of the organic acid is controlled by monitoring the electrical conductivity (EC).

The method for producing magnesium ammonium phosphate hexahydrate by using poultry and livestock manure of the present invention has high efficiency, high element dissolution rate, proper synthesis of magnesium ammonium phosphate and a method for removing crystallization interference factors, which can maximize the crystallization of magnesium ammonium phosphate The method can recover the efficiency of nutrient elements in poultry and livestock manure; at the same time, it can increase the phosphorus availability rate of the remaining biogas residue, so that the biogas residue can be used as an alternative source of phosphorus in agricultural land, so that the waste can be recycled and reused. The residual biogas slurry with low phosphorus, ammonium, magnesium and neutral partial alkali can be further used as a nutrient source for the methanation step, reducing the risk of tube wall fouling, and improving the yield and quality of natural gas.

The following embodiments should not be regarded as excessively limiting the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can modify and change the embodiments discussed herein without departing from the spirit or scope of the present invention, and still fall within the scope of the present invention.

The terms "one" and "one" in this article represent one or more than one (ie at least one) grammatical objects in this article.

In this article, the magnesium ammonium phosphate hexahydrate (MgNH ₄ PO _{4 .6H 2} O) is a crystal of magnesium ammonium phosphate, referred to as Magnesium ammonium phosphate (MAP), commonly known as struvite.

1.5；(4)脫鈣S4：添加有機酸6至該混合消化液，使脫鈣後之該混合消化液的鈣/鎂之莫耳比

0.25， 有機酸會與脫出的鈣形成有機酸鈣7；及(5)磷酸銨鎂沉澱S5：將該脫鈣後之該混合消化液，使用pH調整液8調整pH值至8.0~10.0，回收沉澱物，得到磷酸銨鎂六水合物9。進一步地，本發明之方法可包含步驟(6)厭氧消化S6：將該步驟(5)完成後之殘餘消化液(圖中未示)通入一厭氧消化槽以生產沼氣10。 Please refer to Figure 1. The method for producing magnesium ammonium phosphate hexahydrate from livestock manure of the present invention includes: (1) Anaerobic digestion S1: Poultry manure 1 and an organic carbon source 2 are combined in the first aqueous solution 3 Carry out anaerobic digestion, and carry out anaerobic digestion of poultry manure 1 in the second aqueous solution 4 at 50℃~70℃; (2) solid-liquid separation S2: the first aqueous solution of step (1) anaerobic digestion 3 and the second aqueous solution 4 undergo solid-liquid separation to obtain biogas residue 5, a first digestion liquid (not shown in the figure) and a second digestion liquid (not shown in the figure) respectively; (3) Digestion liquid element ratio adjustment S3: Mix the first digestive juice and the second digestive juice to obtain a mixed digestive juice, and confirm that the molar ratio of nitrogen/phosphorus in the mixed digestive juice>1 and the molar ratio of magnesium/nitrogen in the mixed digestive juice

1.5; (4) Decalcification S4: Add organic acid 6 to the mixed digestive juice to make the calcium/magnesium molar ratio of the mixed digestive juice after decalcification

0.25, the organic acid will form organic acid calcium 7 with the desorbed calcium; and (5) magnesium ammonium phosphate precipitation S5: use the pH adjustment solution 8 to adjust the pH value to 8.0~10.0 for the mixed digestion solution after decalcification, The precipitate was recovered, and magnesium ammonium phosphate hexahydrate 9 was obtained. Further, the method of the present invention may include step (6) anaerobic digestion S6: the residual digestion solution (not shown in the figure) after the step (5) is passed into an anaerobic digestion tank to produce biogas 10.

In the step (1) anaerobic digestion S1, the weight ratio of the poultry manure 1 to the first aqueous solution 3 and the second aqueous solution 4 is 0.5wt%-20wt%, preferably 2.5-10wt% , More preferably 10wt%, such as 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% , 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, and the present invention is not limited to these, but the second aqueous solution 4 In, increasing the content of poultry and livestock manure can significantly increase the yield of ammonium nitrogen. The poultry manure 1 in this article can be any source of poultry manure, such as pig manure, cow manure, sheep manure, chicken manure, duck manure, etc., and the manure that has been pelletized can be used, such as but not limited to Chicken manure. The time of anaerobic digestion S1 may be 8-25 days, preferably 8-15 days, more preferably 10 days.

The first aqueous solution 3 is used to generate a first digestive solution whose main elements are phosphorus, magnesium, and calcium, and it contains phosphate ions (PO ₄ ^3- ), calcium ions (Ca ²⁺ ), and magnesium ions (Mg ^{2 +} ); The first digestion liquid is obtained by removing the biogas residue 5 from the first aqueous solution 3 through solid-liquid separation. In this step (1) anaerobic digestion S1, the first aqueous solution 3 is subjected to anaerobic digestion with the addition of an organic carbon source 2 and a temperature of 20°C to 50°C, and preferably 35 to 40°C, more preferably 37°C, specifically for example 30°C, 33°C, 35°C, 37°C, 40°C, 43°C, 45°C, 47°C or 50°C, and the present invention is not limited to these; but when the temperature is too high or too low , Will limit the efficiency of phosphorus dissolution.

The organic carbon source 2 is selected from the group consisting of straw, mushroom buns, rice, raw food waste, molasses, glycerin, sucrose, glucose and fructose, and the present invention is not limited to these. The organic carbon source 2 Co-digestion can achieve the effect of biological acidification, thereby increasing the dissolution rate of phosphorus, magnesium and calcium in the first aqueous solution 3. Simple organic carbon sources (such as molasses, glycerol, sucrose, glucose and fructose) are compared to complex organic carbon Sources (such as rice straw, mushroom buns, rice, raw kitchen waste) have a significant effect on the dissolution of calcium, and sucrose and fructose have the best dissolution effect. However, due to the cost of sugar and waste recycling, straw should be preferred , Mushroom buns, rice, raw kitchen waste and other high-carbon wastes. The weight of the organic carbon source 2/the weight of the poultry manure 1 feces is 1 to 5, such as 1, 2, 3, 4, or 5, and the present invention is not limited to these.

The second aqueous solution 4 is used to generate a second digestive solution whose main component is nitrogen, which contains ammonium nitrogen (NH ₄ ⁺ -N); the second digestive solution is a solid-liquid separation of the second aqueous solution 4 Obtained after removing the biogas residue 5. In this step (1) anaerobic digestion S1, the second aqueous solution 4 is subjected to anaerobic digestion at 50°C to 70°C, and preferably 50 to 60°C, more preferably 55°C, for example, 50°C, 53°C °C, 55 °C, 58 °C, 60 °C, 63 °C, 65 °C, 68 °C or 70 °C, and the present invention is not limited to these.

In the step (2) solid-liquid separation S2, the solid-liquid separation system intends to separate the solid and liquid completed in the step (1) anaerobic digestion S1 for subsequent recovery and reuse procedures; the solid is the biogas residue 5. The liquid is the first digestive juice and the second digestive juice. The solid-liquid separation method includes gravity sedimentation, belt-type dehydration, plate-type filter press dehydration, or screw extrusion type dehydration, etc., and the present invention is not limited to these.

After the step (2) solid-liquid separation S2, the biogas residue 5 can be dried at high temperature and granulated (step S21) as the soil conditioning material 11; the temperature of the high temperature drying is 60~75°C, preferably 70°C, and the present invention is not limited to this. The purpose of high temperature drying is to inactivate pathogens and reduce moisture content, and supplemented with high temperature enzymes or high temperature resistant bacteria (such as but not limited to Bacillus subtilis) to increase deodorization, mineralization and promote crop growth And other effects. The biogas residue 5 can form easily soluble calcium and phosphorus (dicalcium phosphate) in an environment with a pH of 5.5 to 4.0, thereby improving the phosphorus availability of the biogas residue 5.

1.5；此係因經過發明人以純系統驗證組成比例，對於磷酸銨鎂結晶合成的影響，找出邊界條件，顯示在pH值至8.0~10.0下，此比例足以形成磷酸銨鎂結晶；及，以純系統證實鈣含量過高(Ca/Mg之莫耳比>0.5)會干擾磷酸銨鎂結晶，形成無定型化合物。 In this step (3) the element ratio adjustment S3 of the digestive juice, the first digestive juice and the second digestive juice are mixed so that the molar ratio of nitrogen/phosphorus in the digestive juice>1 and the molar ratio of magnesium/nitrogen in the digestive juice Ear ratio

1.5; This is because the inventor has verified the composition ratio with a pure system, and found out the boundary conditions for the influence of the synthesis of magnesium ammonium phosphate crystals. It shows that at a pH value of 8.0~10.0, this ratio is sufficient to form magnesium ammonium phosphate crystals; and, with pure The system confirmed that too high calcium content (Ca/Mg molar ratio>0.5) will interfere with the crystallization of magnesium ammonium phosphate and form amorphous compounds.

In this step (4) decalcification S4, the organic acid 6 is selected from the group consisting of carboxyl-containing organic acids of succinic acid, malic acid, fumaric acid, citric acid, lactic acid and oxalic acid, and the present invention does not Limited to these; among them, oxalic acid is preferred, because oxalic acid has a higher specificity for calcium and does not affect the concentration of magnesium. The amount of organic acid 6 added can be controlled by monitoring the electrical conductivity (EC). In the method of the present invention, the step (4) decalcification S4 is to remove excess calcium ions, because the excess calcium ions will affect the step (5) the crystallization reaction of magnesium ammonium phosphate precipitation S5; when the amount of calcium ions is too much, The phosphate in the mixed digestion liquid easily reacts with calcium ions to generate calcium phosphate, that is, the generation of the magnesium ammonium phosphate hexahydrate 9 is reduced.

In this step (5) magnesium ammonium phosphate precipitation S5, after the mixed digestion solution is adjusted to pH 8.0~10.0, an upflow crystallization bed can be used for precipitation reaction, and the present invention is not limited to this. In this step, the pH adjustment liquid 8 can use an alkaline solution, such as sodium hydroxide solution, but is not limited thereto.

Due to the differences in dietary habits, feeding methods and production purposes of different animals, their feed formulas are also different, that is, the difference in the ratio of elements in the manure discharged by different animals is also very different, which has led to the conventional technology in the recovery of livestock. When manure is used to produce magnesium ammonium phosphate hexahydrate, additional sources of phosphorus, magnesium or nitrogen need to be added to obtain an appropriate element ratio to react to form magnesium ammonium phosphate hexahydrate. However, unlike the conventional technology, the method of the present invention produces a first digestion solution with a high concentration of phosphorus, calcium and magnesium through this step (1) anaerobic digestion S1, and a second digestion solution with a high concentration of ammonium nitrogen The mixing method is used to adjust the mixed digestive liquid to have an appropriate element ratio close to the synthetic magnesium ammonium phosphate hexahydrate, which can effectively reduce the cost of additional phosphorus, magnesium or nitrogen sources. The mixed digestive liquid of the present invention only After this step (4) and step (5), after decalcification and pH adjustment are completed, the reaction precipitates to generate magnesium ammonium phosphate hexahydrate 9.

In this step (6) anaerobic digestion S6, the concentration of calcium, phosphorus, magnesium, and ammonium nitrogen in the residual digestion solution is low, which can avoid the generation of wall fouling in the tank (the composition of wall fouling) Divided into magnesium ammonium phosphate or calcium phosphate) to reduce maintenance costs. In addition, due to the low concentration of ammonium nitrogen, when the biogas 10 is generated, the growth of methane archaea will not be inhibited by ammonium nitrogen, which can increase the methane yield. Therefore, the present invention can be incorporated into the conventional pollution treatment system to reduce costs and create additional added value.

[ Specific embodiment ]

Hereinafter, the present invention will be further described with detailed description and examples. However, it should be understood that these examples are only used to help make the present invention easier to understand and not to limit the scope of the present invention.

Example 1. In the first aqueous solution, straw (RS) Adding amount to the dissolution rate of phosphorus, magnesium, calcium and pH Impact

Use 22.5 g pelleted chicken manure to 900 mL deionized water to prepare a 2.5% chicken manure aqueous solution (CM), add 0 g, 22.5 g, 45 g, 67.5 g and 90 g of rice straw to obtain the content of 0 g respectively. %, 2.5%, 5%, 7.5%, 10% concentration of rice straw 2.5% chicken manure aqueous solution; each group is 2.5% CM, 2.5% CM + 2.5% RS, 2.5% CM + 5% RS, 2.5% CM + 7.5% RS and 2.5% CM +10% RS. Subsequently, the anaerobic digestion reaction was carried out at 37°C for 25 days, and the first digestion liquid was obtained after solid-liquid separation.

The test results are shown in Figures 2 to 4: On the 10th day of anaerobic digestion, as shown in Figure 2, the phosphorus concentrations were 138 mg/L, 189 mg/L, 234 mg/L, 299 mg/L and 305 mg/L; as shown in Figure 3, the calcium concentrations are 163 mg/L, 533 mg/L, 614 mg/L, 901 mg/L and 861 mg/L; as shown in Figure 4, the magnesium concentrations are 162 mg/L, 227 mg/L, 249 mg/L, 297 mg/L and 310 mg/L. When the amount of rice straw (RS) added is increased to 4 times, the dissolution of phosphorus, calcium and magnesium can be increased by about 2.2, 5.3 and 1.9 times. That is, when organic carbon source is added, the phosphorus and calcium after anaerobic digestion can be increased. And the dissolution of magnesium.

In addition, as shown in Figure 5, as the amount of rice straw (RS) added increases, the pH also decreases after the fifth day of the anaerobic digestion reaction.

Example 2. The influence of different organic carbon sources on the dissolution rate of phosphorus, magnesium and calcium in the first aqueous solution

Use 22.5 g pelletized chicken manure to 900 mL deionized water to prepare a 2.5% chicken manure aqueous solution (chicken manure, CM), and add the aforementioned organic carbon source, each group is 1 times sucrose S1, 2 times sucrose S2 , 1 times glucose G1, 2 times glucose G2, 1 times fructose F1, 2 times fructose F2, and waste liquids 1 to 3 after general anaerobic digestion treatment (no carbon source added), and pig manure sludge (Pig sludge, PS); And, the control group con without adding organic carbon source. Subsequently, the anaerobic digestion reaction was carried out at 37°C for 25 days, and the first digestion liquid was obtained after solid-liquid separation.

The test results are shown in Figures 6 to 7 respectively: Compared with the control con, the phosphorus dissolution of 1x sucrose S1 and 2x sucrose S2 increased by 3.4 and 7.8 times, the magnesium dissolution increased by 1.7 and 1.8 times, and the calcium dissolution increased by 54.9 and 78.5. Times. Compared with the control group con, 1 times glucose G1, 2 times glucose G2, phosphorus dissolution increased by 3.5 and 3.8 times, magnesium dissolution increased by 1.2 and 1.6 times, and calcium dissolution increased by 42.9 and 73.3 times; compared to the control group (con), The phosphorus dissolution of 1 times fructose F1 and 2 times fructose F2 increased by 3.3 and 10.1 times, magnesium dissolution increased by 1.3 and 2.0 times, and calcium dissolution increased by 46.4 and 100.8 times. The dissolution rates of calcium, phosphorus, and magnesium in the waste liquids 1 to 3 and the pig manure sludge PS after anaerobic digestion treatment are not much different from those of the control group.

Example 3. In the second aqueous solution, the effect of temperature on the yield of ammonium nitrogen

Add 90g of pelletized chicken manure to 900mL of deionized water, perform batch anaerobic digestion at 25, 37, and 55°C respectively, and obtain a second digestion solution after solid-liquid separation. The test results are shown in Figure 8. The anaerobic digestion can reach the highest ammonium nitrogen yield on the 10th day; the ammonium concentration of the digestion solution at 25, 37, and 55°C is 624, 873, and 1006 mg/L respectively, that is, high temperature digestion. (55℃) Compared with low temperature digestion (25℃), it can increase the yield of ammonium nitrogen nearly twice. That is, when the temperature is increased, the yield of ammonium nitrogen can be significantly increased.

Example 4. In the second aqueous solution, the influence of poultry manure content on the yield of ammonium nitrogen

22.5g and 90g of pelletized chicken manure were added to 900mL of deionized water to prepare 2.5% and 10% chicken manure aqueous solutions (2.5% GCM and 10% GCM, respectively), and perform anaerobic digestion at 37°C , After solid-liquid separation, the second digestion liquid under different conditions is obtained. The test results are shown in Figure 9. The ammonium nitrogen concentrations of 2.5% GCM and 10% GCM on the 10th day were 129 and 873 mg/L, respectively. That is, when the content of livestock manure increases, the yield of ammonium nitrogen can be significantly increased.

Example 5. Mixed digestive juice

1.5)。 After mixing the first digestion solution obtained by double fructose (F2) in the above Example 2 and the second digestion solution (1) with high ammonium nitrogen obtained in the above Example 3 in a ratio of 1:1, as shown in Table 1 , The mixed digestive juice produced has a molar ratio of nitrogen/phosphorus of 1.1, a molar ratio of magnesium/nitrogen of 1.2, and a molar ratio of calcium/magnesium of 5.8; except for the molar ratio of calcium/magnesium, nitrogen/ Both the molar ratio of phosphorus and the molar ratio of magnesium/nitrogen are the safe ranges for the synthesis of magnesium ammonium phosphate hexahydrate (MAP) (the molar ratio of nitrogen/phosphorus>1 and the molar ratio of magnesium/nitrogen)

1.5).

Example 6. The effect of decalcification and pH adjustment on precipitation of magnesium ammonium phosphate

Use X-ray powder diffraction (XRD) to analyze the three types of mixed digestive juice of the present invention: (A) without decalcification, pH adjustment, (B) pH adjustment after decalcification, and (C) decalcification but no pH adjustment In this case, the pH adjustment solution of the precipitate obtained after the precipitation reaction of magnesium ammonium phosphate is 3N sodium hydroxide solution, and the pH value of the mixed digestion solution is adjusted to 9. As shown in Figure 10: (A) The precipitate obtained by adjusting the pH without decalcification has no obvious peak. It is speculated that the precipitate should be amorphous calcium phosphate. This result shows that it is not effective if the calcium content is too high. The formation of magnesium ammonium phosphate hexahydrate can explain the fact that the conventional technology does not have a decalcification step, that is, the product recovered and reused is mostly calcium phosphate instead of magnesium ammonium phosphate hexahydrate; (B) adjust pH after decalcification The precipitate has a clear peak, and compared to the peak spectrum of magnesium ammonium phosphate hexahydrate, it is confirmed that magnesium ammonium phosphate hexahydrate is successfully formed; (C) There is decalcification but no pH adjustment has a clear peak, but these The peak comparison is not magnesium ammonium phosphate hexahydrate, but other organic acid calcium crystals. That is, before the precipitation of magnesium ammonium phosphate, the mixed digestion solution should be decalcified and adjusted to a proper pH range to obtain magnesium ammonium phosphate hexahydrate.

Example 7. Oxalate decalcification ( Oxalic acid conductivity titration )

A 0.5M oxalic acid solution was added to the mixed digestive juice of the present invention, and the influence of the added amount of oxalic acid on the concentration of calcium and magnesium in the mixed digestive juice was analyzed. As shown in Figure 11, when the amount of oxalic acid added increases, the calcium concentration in the mixed digestive juice decreases, and it has no effect on the magnesium ion concentration. At the same time, it is also accompanied by a decrease in electrical conductivity, and the trend of decrease in electrical conductivity slows down when the calcium ions in the mixed digestive juice are exhausted, and it can be determined that the calcium ions in the solution have been completely removed. This result shows that the amount of oxalic acid required for decalcification can be controlled by monitoring the conductivity. This result proves that oxalic acid can effectively remove the calcium in the mixed digestive juice to achieve the effect of decalcification; in addition, as the amount of oxalic acid added increases, the magnesium concentration remains quantitative, that is, oxalic acid does not affect the magnesium concentration in the mixed digestive juice . It can be proved that oxalic acid can effectively remove calcium ions in the mixed digestive juice without affecting magnesium ions; furthermore, the use of oxalic acid for decalcification does not affect the subsequent synthesis of magnesium ammonium phosphate hexahydrate (MAP).

In summary, the method for producing magnesium ammonium phosphate hexahydrate by using poultry and livestock manure of the present invention has high efficiency, high element dissolution rate, a suitable ratio for synthesizing magnesium ammonium phosphate hexahydrate, and a method for removing crystallization interference factors. To maximize the efficiency of reclaiming nutrients in poultry manure by the magnesium ammonium phosphate crystallization method; at the same time, it can increase the phosphorus availability of the remaining biogas residue, so that the biogas residue can be used as an alternative source of phosphorus in agricultural land, so that the waste can be recycled. use. The residual biogas slurry with low phosphorus, ammonium, magnesium and neutral partial alkali can be further used as a nutrient source for the methanation step, reducing the risk of tube wall fouling, and improving the yield and quality of natural gas.

S1: Step (1) Anaerobic digestion S2: Step (2) solid-liquid separation S21: Drying and granulation S3: Step (3) Adjust the ratio of digestive juice elements S4: step (4) decalcification S5: Step (5) Precipitation of magnesium ammonium phosphate S6: step (6) anaerobic digestion 1: Livestock manure 2: Organic carbon source 3: The first aqueous solution 4: The second aqueous solution 5: Biogas residue 6: Organic acid 7: Calcium organic acid 8: pH adjustment solution 9: Magnesium ammonium phosphate hexahydrate 10: Biogas 11: Soil adjustment materials

Fig. 1 is a flow chart of the method for producing magnesium ammonium phosphate hexahydrate by using poultry and livestock manure according to the present invention.

Figure 2 is a graph of the amount of rice straw (RS) added in Example 1 versus the phosphorus dissolution rate.

Figure 3 is a graph showing the amount of rice straw (RS) added in Example 1 versus the calcium dissolution rate.

Figure 4 is a graph of the amount of rice straw (RS) added in Example 1 versus the magnesium dissolution rate.

Figure 5 is a graph showing the amount of rice straw (RS) added in Example 1 versus pH.

Fig. 6 is a bar graph of the dissolution rate of nitrogen, phosphorus, and magnesium by different organic carbon sources in Example 2.

Fig. 7 is a bar graph showing the effect of different organic carbon sources on the dissolution rate of calcium in Example 2.

Fig. 8 is a graph showing the temperature vs. the dissolution rate of ammonium nitrogen in Example 3.

Fig. 9 is a graph showing the content of poultry manure versus the dissolution rate of ammonium nitrogen in Example 4.

Figure 10 shows the precipitation of the mixed digestive solution in Example 6 under three conditions of (A) without decalcification with pH adjustment, (B) with pH adjustment after decalcification, and (C) with decalcification but without pH adjustment. X-ray powder diffraction (XRD) spectrum of the object.

Fig. 11 is a graph showing the influence of oxalic acid decalcification (oxalic acid conductivity titration) on the concentration of calcium and magnesium in the mixed digestive juice in Example 7.

S1: Step (1) Anaerobic digestion

S2: Step (2) solid-liquid separation

S21: Drying and granulation

S3: Step (3) Adjust the ratio of digestive juice elements

S4: step (4) decalcification

S5: Step (5) Precipitation of magnesium ammonium phosphate

S6: step (6) anaerobic digestion

1: Livestock manure

2: Organic carbon source

3: The first aqueous solution

4: The second aqueous solution

5: Biogas residue

6: Organic acid

7: Calcium organic acid

8: pH adjustment solution

9: Magnesium ammonium phosphate hexahydrate

10: Biogas

11: Soil adjustment materials

Claims (10)

A method for producing magnesium ammonium phosphate hexahydrate by using livestock manure, the steps include: (1) 8-25 days of anaerobic digestion: poultry manure and an organic carbon are derived from the first aqueous solution at 20°C-50°C Anaerobic digestion is carried out under conditions, wherein the ratio of the weight of the organic carbon source to the weight of the livestock manure is 1 to 5; and, the livestock manure is subjected to anaerobic digestion at 50°C to 70°C in the second aqueous solution; (2) ) Solid-liquid separation: perform solid-liquid separation of the first aqueous solution and the second aqueous solution of step (1) anaerobic digestion to obtain biogas residue, first digestive liquid and second digestive liquid; (3) digestion liquid element ratio Adjustment: mix the first digestive juice and the second digestive juice to obtain a mixed digestive juice, and confirm that the molar ratio of nitrogen/phosphorus in the mixed digestive juice>1 and the molar ratio of magnesium/nitrogen

1.5; (4) Decalcification: add organic acid to the mixed digestive juice to make the molar ratio of calcium/magnesium in the mixed digestive juice after decalcification

0.25; and (5) Magnesium ammonium phosphate precipitation: adjust the pH value of the mixed digestion solution after decalcification to 8.0~10.0, recover the precipitate to obtain magnesium ammonium phosphate hexahydrate, and remove the precipitate after recovery The mixed digestive juice is the residual digestive juice. The method of claim 1, wherein the organic carbon source is selected from the group consisting of straw, mushroom buns, rice, raw food waste, molasses, glycerin, sucrose, glucose and fructose. According to the method of claim 1, wherein the first aqueous solution in the step (1) is subjected to anaerobic digestion at 20°C to 50°C. The method of claim 1, wherein the weight ratio of the poultry manure in the step (1) to the weight of the first aqueous solution and the second aqueous solution is 0.5 wt% to 20 wt%. Such as the method of claim 1, wherein the step (2) is solid-liquid separation by gravity sedimentation, belt-type dehydration, plate-type filter press dehydration or screw extrusion type dehydration. Such as the method of claim 1, wherein the biogas residue obtained in step (2) is further dried and granulated at a temperature higher than 60~75°C to form a soil conditioning material. Such as the method of claim 6, wherein the biogas residue is further added with thermophilic enzymes or colonized with thermostable bacteria. The method of claim 1, wherein the organic acid in step (4) is selected from the group consisting of carboxyl-containing organic acids of succinic acid, malic acid, fumaric acid, citric acid, lactic acid, and oxalic acid. According to the method of claim 1, wherein the residual digestion liquid after completion of step (5) is further passed into an anaerobic digestion tank to produce biogas. Such as the method of claim 1, wherein the addition amount of the organic acid is controlled by monitoring the electrical conductivity (EC).

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