CN114516766B - Method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer and application of method - Google Patents
Method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer and application of method Download PDFInfo
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Abstract
The invention discloses a method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer and application thereof. According to the invention, a novel strategy for efficiently and rapidly recycling phosphorus is realized by adding calcium chloride and sodium carbonate solution into low-phosphate sewage and utilizing in-situ calcium carbonate microspheres. The in-situ generation calcium carbonate microsphere phosphate fertilizer technology provided by the invention can very effectively capture phosphate ions and self-assemble into composite calcium carbonate microspheres; under the optimized condition, 98% of phosphate can be recovered within 30min, and the residual phosphate amount is 0.2mg-P/L, so that the time is saved compared with the existing method. Importantly, with this novel calcium carbonate in situ recovery strategy, 20.8wt.% of high quality phosphate fertilizer can be obtained, with a content of 4 times that of the calcite calcium carbonate nanoparticles prepared. The yield of the fast-growing vegetable cabbage is increased by 58.9% by adopting the prepared sodium carbonate in-situ phosphate fertilizer. The method provides a new way for recycling the low-concentration phosphate fertilizer.
Description
Technical Field
The invention relates to a technology for removing low-concentration phosphate and preparing high-efficiency phosphate fertilizer on the basis of the technology, in particular to a method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer and application of the method.
Background
The national economy continues to develop, and the environmental problem is increasingly prominent. The river, the lake and the sea as well as the underground water are polluted in different areas and different degrees, so that the ecological environment is endangered, and the human health is endangered more. Phosphate is a typical contaminant that when released into the aquatic environment can lead to eutrophication. While phosphorite is now depleting at a remarkable rate as a non-renewable resource, it supports a huge and growing population on earth. Thus, recovery of phosphate from wastewater (P-recovery) is becoming an increasingly urgent global environmental issue, playing a key role in human sustainable development (Desmidt et al, 2014).
At present, high-concentration phosphate wastewater is generally effectively removed by means of a biological method, a chemical recovery method and the like. Biological phosphorus recovery can capture phosphate, producing phosphorus-containing sludge (Shuai et al 2021), but the phosphate concentration in the sludge is too low to be useful as a phosphorus fertilizer (Egle et al 2016; tarayre et al 2016). Chemical recovery methods (Ye et al, 2017) capture phosphate ions from water quickly and simply by adding calcium (Bouzas et al, 2019), iron (Wilfert et al, 2015), or aluminum (Ma et al, 2018). However, iron and aluminum chemicals are not suitable for agricultural applications because they bind too strongly to phosphates and are not readily absorbed by plants (Abel, 2017). Since calcium agents have proven to be safe in soil remediation, calcium chemicals or materials are more suitable for use as phosphate fertilizers. However, the addition of calcium reagent is generally only suitable for treating high concentration phosphate wastewater, such as struvite formation, whereas the phosphate concentration in municipal wastewater is only on the order of mg/L (Desmodt et al, 2013; kataki et al, 2016). Achieving low concentration phosphorus recovery with calcium reagent still has a pressing need for a more efficient strategy.
Disclosure of Invention
The invention aims at overcoming the defects and shortcomings of the prior art and providing a method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer.
The invention also aims to provide application of the method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer.
The aim of the invention is achieved by the following technical scheme:
a method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer comprises the following steps:
(1) Adding a calcium chloride solution into the phosphorus-containing solution in a stirring state to obtain a mixed solution A;
(2) Adding sodium carbonate into the mixed solution A in a stirring state, and continuously stirring to react to obtain mixed solution B;
(3) And (3) carrying out solid-liquid separation on the mixed solution B, and drying the separated solid to obtain the calcium carbonate microsphere phosphate fertilizer generated in situ.
The phosphorus-containing solution in the step (1) is preferably a phosphorus-containing solution with a concentration of 1-80 mg/L in terms of phosphorus; more preferably a phosphorus-containing solution having a concentration of 10mg/L or less in terms of phosphorus; most preferably a phosphorus-containing solution having a concentration of 1 to 10mg/L in terms of phosphorus.
The phosphorus-containing solution in the step (1) is preferably sodium dihydrogen phosphate solution or sewage.
The sewage is preferably urban sewage.
The amount of calcium chloride added in step (1) is preferably calculated as calcium in the calcium chloride: the mole ratio of phosphorus in the solution is calculated as 2:1-10:1; more preferably as calcium of calcium chloride: the mole ratio of phosphorus in the solution is calculated as 4:1-10:1; most preferably as calcium of the calcium chloride: the molar ratio of phosphorus in the solution was calculated to be 6:1.
The amount of sodium carbonate added in step (2) is preferably the amount of calcium in the calcium chloride in step (1): the molar ratio of carbonate radicals in the sodium carbonate is calculated as 3:1-1:2; more preferably calcium of the calcium chloride in step (1): the molar ratio of carbonate radicals in the sodium carbonate is calculated as 2:1-1:2; most preferred is calcium from the calcium chloride of step (1): the molar ratio of carbonate groups in the sodium carbonate is calculated to be 1-1.
The reaction time in the step (2) is preferably 0 to 24 hours, and the end point value of 0 is not contained; more preferably 30min to 24h; most preferably 30min to 2h; most preferably 30min.
The solid-liquid separation mode in the step (3) comprises filtration, standing or centrifugation.
The filtration is preferably carried out using a microfiltration membrane of 0.22. Mu.m.
The standing is to utilize gravity sedimentation to separate solids and liquids to obtain solids.
The drying condition in the step (3) is preferably that the drying is carried out at 50-150 ℃ until the drying is complete; more preferably at 80 c to complete drying.
The method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer is applied to recycling phosphate in sewage.
The sewage is preferably urban sewage; particularly preferably sewage with a phosphorus concentration of 10mg/L or less; most preferably, the concentration of the sewage is 1-10 mg/L in terms of phosphorus.
The calcium carbonate microsphere phosphate fertilizer is generated in situ and is obtained by the method; can be used as phosphate fertilizer.
Compared with the prior art, the invention has the following advantages:
(1) The method for in-situ generation of calcium carbonate microsphere phosphate fertilizer to recycle low-concentration phosphate in sewage can effectively recycle phosphorus element in phosphate water solution with concentration as low as 10mg/L in a short time.
(2) The technology of in-situ generation of calcium carbonate microsphere phosphate fertilizer can very effectively capture phosphate ions and self-assemble into composite calcium carbonate microspheres. Under the optimized condition, 98% of phosphate can be recovered within 30min, and the residual phosphate amount is 0.2mg-P/L, so that the time is greatly saved compared with the prior method.
(3) By this method P can be produced 2 O 5 High-phosphorous fertilizers in an amount exceeding 20wt.% are used in an amount of 4 times the amount of the ultra-fine calcium carbonate solid powder.
(4) The high-phosphorus fertilizer has an obvious forward promotion effect on the growth of the cabbages, and the yield of the fast-growing vegetable cabbages can be increased by 58.9% by adopting an in-situ generation calcium carbonate microsphere phosphate fertilizer method as the phosphate fertilizer, thereby being beneficial to agricultural growth.
Drawings
FIG. 1 is a scanning electron micrograph of the product prepared in example 1; wherein a is in-situ generated calcium carbonate microsphere phosphate fertilizer (calcite/vaterite microsphere) with the size of 10 μm; b is in-situ generation of calcium carbonate microsphere phosphate fertilizer (calcite/vaterite microsphere) with the size of 500nm; c is a calcium carbonate phosphate fertilizer (calcite) prepared by a traditional method, and the size is 2 mu m; d is the calcium carbonate phosphate fertilizer (calcite) prepared by the traditional method, and the size is 500nm.
FIG. 2 is a graph of the X-ray diffraction results of the product prepared in example 1.
FIG. 3 is a chart showing the results of the Fourier transform infrared absorption spectrum of the product prepared in example 1.
FIG. 4 is a graph showing the effect of dephosphorization of different Ca/P molar ratios in the method of changing in-situ generation of calcium carbonate microsphere phosphate fertilizer in example 2.
FIG. 5 is a schematic diagram showing the variation of Ca in the in situ calcium carbonate microsphere phosphate fertilizer process according to example 3 2+ /CO 3 2- Concentration molar ratio dephosphorization effect graph.
FIG. 6 is a graph showing the comparison of the dephosphorization effect of the two methods at different reaction times in example 4.
FIG. 7 is a graph showing the effect of coexisting ions on the dephosphorization process in example 5.
FIG. 8 is a graph showing the effect of temperature on the dephosphorization process in example 6.
FIG. 9 is a graph showing the effect of final pH of wastewater in example 7 on phosphorus removal efficiency.
FIG. 10 is a graph showing the results of X-ray photoelectron spectroscopy analysis of the in-situ generated calcium carbonate microsphere phosphate fertilizer and the conventionally prepared calcium carbonate phosphate fertilizer in example 1; wherein a is in-situ generated calcium carbonate microsphere phosphate fertilizer, b is in-situ generated calcium carbonate microsphere phosphate fertilizer, c is conventionally prepared calcium carbonate phosphate fertilizer, and d is conventionally prepared calcium carbonate phosphate fertilizer.
FIG. 11 is a graph showing the results of in-situ calcium carbonate microspheres obtained in example 1 in comparison with the plant height, root length, fresh weight of stem and dry weight of stem obtained after the application to growth of cabbage in example 11.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but embodiments of the present invention are not limited thereto.
Example 1
1. In-situ generation of calcium carbonate microsphere phosphate fertilizer
By simulating sewage (NaH) from low concentrations 2 PO 4 The method for preparing the in-situ generated calcium carbonate microsphere phosphate fertilizer by enriching phosphorus element in solution, 10 mg-P/L) comprises the following steps:
preparing sodium dihydrogen phosphate (NaH) with concentration of 38.73mg/L 2 PO 4 ) The solution (total phosphorus is 10mg/L in terms of P) simulates a low-concentration phosphorus-containing water body (more phosphorus-containing water bodies with the phosphorus concentration exceeding 10mg-P/L are generally researched, and less related researches are carried out on sewage with lower phosphorus concentration, so that sewage with the phosphorus concentration less than or equal to 10mg-P/L is defined as the water body with low phosphorus concentration). Under the condition of conventional stirring, firstly adding calcium chloride (CaCl) 2 1 mol/L) solution until CaCl in the system 2 The concentration was 214.8mg/L, and sodium carbonate (Na 2 CO 3 1 mol/L) solution until Na in the system 2 CO 3 The concentration was 205.2mg/L, and stirring was stopped after the reaction was continued for 30 minutes. The solution was filtered using a quick filter paper, and after the filtration was completed, the phosphorus content of the filtered water sample was measured with reference to GB 11893-89. The solid obtained by filtration is placed in an oven at 80 DEG CAnd (5) drying. The obtained powder is the calcium carbonate microsphere phosphate fertilizer generated in situ.
2. Calcium carbonate phosphate fertilizer produced by traditional sewage treatment process
By comparison, we simulated a phosphorus-containing water body (NaH) from a low concentration with traditional calcite crystal form ultrafine calcium carbonate powder (commercial nano calcium carbonate, particle size less than or equal to 100 nm) 2 PO 4 Solution, 10 mg-P/L) of phosphorus element, comprising the following steps:
preparing sodium dihydrogen phosphate (NaH) with concentration of 38.73mg/L 2 PO 4 ) The solution (total phosphorus in P is 10 mg/L) simulates a low concentration phosphorus-containing water body. 200mg/L of ultrafine calcium carbonate powder was added thereto and stirred for 30 minutes. And (3) filtering by using quick filter paper, determining the phosphorus content of a water sample obtained by filtering by referring to GB11893-89, and drying the obtained solid to obtain the calcium carbonate phosphate fertilizer produced by the traditional sewage treatment process.
3. Detection result
A and b in fig. 1 are graphs of Scanning Electron Microscope (SEM) results of in-situ generation of calcium carbonate microsphere phosphate fertilizer, and c and d are graphs of Scanning Electron Microscope (SEM) photographs of conventional method calcium carbonate phosphate fertilizer; wherein a is measured at a magnification of 2K, b is measured at a magnification of 50K, c is measured at a magnification of 10K, and d is measured at a magnification of 50K. SEM shows that the in-situ formed calcium carbonate microsphere phosphate fertilizer consists of microspheres with diameters of 2-10 microns, when the microspheres are amplified into single spheres, tiny nano particles can be observed on the surfaces of the particles, the particle diameter is about 50 nanometers, and the in-situ formed calcium carbonate microsphere phosphate fertilizer is formed by tiny vaterite CaCO 3 Nanoparticles are agglomerated, and phosphate ions may be coated between adjacent nanoparticles. Ultrafine calcium carbonate consists of nanoparticles of smaller particle size (about 50nm and narrower distribution in situ calcium carbonate microspheres form larger microspheres more favorable for phosphate recovery than conventional calcium carbonate anchors consisting of nanoparticles of smaller particle size and narrower distribution.
Fig. 2 is an X-ray diffraction (XRD) result graph of in situ formation of calcium carbonate microsphere phosphate fertilizer and conventional process calcium carbonate phosphate fertilizer. XRD showed that in situ formation of calcium carbonate microsphere phosphate fertilizer consisted of calcite (JCPDS card No. 05-0586) and vaterite (JCPDS card No. 33-0268), conventional waterThe superfine calcium carbonate powder used in the treatment process is prepared from calcite CaCO 3 (JCPDS card No. 05-0586) mineral is crushed and has low reactivity.
FIG. 3 is a graph showing the results of Fourier transform infrared absorption spectroscopy (FTIR) of in-situ generated calcium carbonate microsphere phosphate fertilizer and conventional calcium carbonate phosphate fertilizer. In-situ generation of 1048cm calcium carbonate microsphere phosphate fertilizer -1 And 576cm -1 In the FTIR spectrum of (c), there is a distinct phosphate absorption peak. Phosphate ions exist in an amorphous state in situ to form calcium carbonate microsphere phosphate fertilizer, and vaterite crystalline phase calcium carbonate plays a vital role in phosphate recovery. FTIR of the traditional calcium carbonate phosphate fertilizer is 1048cm -1 And 576cm -1 The absorption peak intensity at the position is obviously weaker than that of the in-situ generated calcium carbonate microsphere phosphate fertilizer, which means that the phosphate content is obviously lower than that of the in-situ generated calcium carbonate microsphere phosphate fertilizer.
In the same time, the recovery rate of the recovered phosphorus by the in-situ generation of calcium carbonate microsphere phosphate fertilizer method reaches 98 percent, and the total phosphorus content of the effluent reaches 0.2mg-P/L and reaches the national first grade A standard of sewage discharge; the traditional method uses the calcium carbonate ultrafine powder as the dephosphorizing agent, the recovery rate of phosphorus is only 17 percent, and the total phosphorus content of the effluent is 8.3mg-P/L, which does not reach the national first grade A standard of sewage discharge.
Example 2
The in-situ generation of calcium carbonate microsphere phosphate fertilizer under different Ca/P molar ratios and the dephosphorization effect of the traditional synthetic calcium carbonate method comprise the following steps:
(1) In-situ generation of calcium carbonate microsphere phosphate fertilizer, and dephosphorization with different Ca/P molar ratios. While stirring, the mixture was stirred to a volume of 1L and a concentration of 38.73mg/L of sodium dihydrogen phosphate (NaH) 2 PO 4 ) CaCl was added to the solutions (10 mg/L total phosphorus as P) one after the other 2 Solution until CaCl in system 2 Concentrations of 71.6, 143.2, 179, 214.8, 286.4 and 358mg/L, after 30min of reaction, the phosphorus content was determined by sampling and Na was added separately 2 CO 3 Solution until Na in the system 2 CO 3 The concentrations were 68.4, 136.8, 171, 205.2, 273.6 and 342mg/L, and stirring was stopped after the reaction was continued for 30 minutes. The water sample is filtered, the content of phosphorus is measured, and the total phosphorus is measured according to GB11893-89 and molybdic acid spectrophotometry.
(2) In contrast, the conventional calcium carbonate micropowder addition method removes phosphorus at different Ca/P molar ratios as follows. While stirring, the mixture was stirred to a volume of 1L and a concentration of 38.73mg/L of sodium dihydrogen phosphate (NaH) 2 PO 4) solution (total phosphorus in terms of P is 10 mg/L), adding calcium carbonate micropowder 65, 129, 161, 194, 258, 323mg/L respectively, reacting for 30min, and continuing reacting for 30min. The water sample was filtered and the phosphorus content was determined with reference to GB 11893-89.
FIG. 4 is a graph showing the effect of dephosphorization of different Ca/P molar ratios in the in situ calcium carbonate microsphere phosphate fertilizer process of example 2. The results showed that even if the Ca/P molar ratio was increased from 2/1 to 10/1, caCl was added 2 Hardly any phosphate can be removed from the wastewater. The conventional calcium carbonate micropowder can remove about 12% of phosphate because the reaction time is short, and even if the amount is increased, the total phosphorus removal rate is not significantly improved. Forming CaCO in situ 3 In the microsphere phosphorus recovery process, the residual phosphate was reduced from 10mg-P/L to 4.87mg-P/L when the Ca/P molar ratio was 2/1, and further reduced to 0.20mg-P/L when the Ca/P molar ratio was increased to 6/1. The concentration not only meets the wastewater discharge standard (0.5 mg-P/L), but also meets the Chinese surface water (III) standard (0.2 mg-P/L).
Example 3
Different Ca in-situ generation method of calcium carbonate microsphere phosphate fertilizer 2+ /CO 3 2- The dephosphorization effect of the mole ratio comprises the following steps:
referring to the procedure of example 1, sodium dihydrogen phosphate (NaH) was added in an amount of 1L by volume and a concentration of 38.73mg/L under stirring 2 PO 4) solution (10 mg/L total phosphorus based on P) to which CaCl was added 2 Solution until CaCl in system 2 The concentration is 214.8mg/L, the sample is taken to determine the phosphorus content, and Na is added respectively 2 CO 3 Solution until Na in the system 2 CO 3 The concentrations were 68.4, 102.6, 136.8, 307.8 and 410.4mg/L, and stirring was stopped after continuing the reaction for 30 minutes. After the reaction is completed, the water sample is filtered, and the phosphorus content is measured.
FIG. 5 is a graph showing the in situ formation of calcium carbonate microsphere phosphate fertilizer of example 3 2+ /CO 3 2- Mole ratio dephosphorization effect graph. The result shows that the insufficient carbonate leads to the obvious reduction of the phosphorus recovery efficiency, the excessive carbonate content leads to the slight reduction of the phosphorus recovery rate, ca 2+ /CO 3 2- The optimal molar ratio of (2) is 1/1, i.e. the theoretical CaCO is produced 3 Thus, equimolar reaction between calcium ion and carbonate ion forms CaCO 3 Is very important for improving the recovery process.
Example 4
Influence of reaction time on dephosphorization effect in situ generation of calcium carbonate microsphere phosphate fertilizer
(1) While stirring, the mixture was stirred to a volume of 1L and a concentration of 38.73mg/L of sodium dihydrogen phosphate (NaH) 2 PO 4 ) CaCl was added to the solution (10 mg/L total phosphorus as P) 2 The solution (1 mol/L) is reacted for 30min until the concentration of calcium chloride is 214.8mg/L, and Na is added 2 CO 3 The reaction was continued for 30min, 1h, 2h, 6h, 12h and 24h, with a solution (1 mol/L) to a sodium carbonate concentration of 205.2 mg/L. At the above reaction time points, the water sample was filtered and the phosphorus content was measured to evaluate the effect of the reaction time on the phosphorus removal efficiency.
(2) As a control, sodium dihydrogen phosphate (NaH) was added to a volume of 1L and a concentration of 38.73mg/L under stirring 2 PO 4 ) Adding traditional calcite crystal form superfine calcium carbonate powder (commercial nanometer calcium carbonate, 100 nm) to 200mg/L into the solution (total phosphorus calculated by P is 10 mg/L), and continuing to react for 30min, 1h, 2h, 6h, 12h and 24h. At the reaction time point, filtering the water sample, and measuring the phosphorus content.
FIG. 6 is a graph showing the effect of phosphorus removal at different reaction times in the two calcium carbonate processes of example 4. The result shows that the residual phosphate level of the traditional method for synthesizing calcium carbonate is continuously reduced from 10mg-P/L to 2.92mg-P/L, and conversely, for the in-situ generation of calcium carbonate microsphere phosphate fertilizer, caCO is used for the preparation of the calcium carbonate microsphere phosphate fertilizer 3 After 30 minutes of in situ formation, the residual phosphate reached a minimum (0.2 mg-P/L) and after that the residual phosphate continued to increase slowly, reaching 0.54mg-P/L within 24 hours. Thus, in situ CaCO 3 Should be separated from the treated water as soon as possible to obtain a high phosphorus recovery efficiency.
Example 5
Influence of coexisting ions on in situ formation of calcium carbonate microspheres
Uniformly preparing NaF and NaHCO with the concentration of 2mol/L 3 、Na 2 SO 4 、NaNO 3 And NaCl solution to a volume of 1L, and total phosphorus concentration of 10mg-P/L sodium dihydrogen phosphate (NaH) 2 PO 4 ) The amount of the interfering anionic substances added into the solution is 10 times and 60 times of that of the phosphate ions respectively (the mixed group is that the anionic substances are mixed according to the equimolar ratio); when the Ca/P mole ratio is 6/1, caCl is firstly added under the stirring state of 300-500rpm 2 The concentration of the solution is 214.8mg/L, and Na is added after 30min of reaction 2 CO 3 The concentration of the solution is 205.2mg/L, the reaction is carried out for 30min, a water sample is filtered, and the phosphorus content is measured.
FIG. 7 is a graph showing the effect of in situ formation of calcium carbonate microsphere phosphate fertilizer in the removal of phosphorus under interfering anions in example 5. The results show that the coexisting ions (10 times of P) at low concentrations, including Cl - 、F - 、HCO 3 - 、NO 3 - And SO 4 2- Little adverse effect. The amounts of chloride, nitrate and sulfate substances have no significant adverse effect even when they reach a 60-fold high concentration of phosphate. Although not commonly encountered, when F in sewage - 、HCO 3 - When the amount of the substance reaches 60 times that of the phosphate, a remarkable adverse effect is generated. Overall, the method of forming calcium carbonate microspheres in situ has good resistance to salt interference.
Example 6
The effect of temperature on the dephosphorization process of in situ formation of calcium carbonate microspheres comprising the steps of:
at 15 deg.C, 20 deg.C, 25 deg.C and 30 deg.C, at Ca/P molar ratio of 6/1, stirring at 300-500rpm, adding sodium dihydrogen phosphate (NaH) with total phosphorus concentration of 10mg-P/L in terms of P 2 PO 4 ) Adding CaCl into the solution 2 The concentration of the solution is 214.8mg/L, and Na is added 2 CO 3 The concentration of the solution is 205.2mg/L, the reaction is carried out for 30min, a water sample is filtered, and the phosphorus content is measured.
FIG. 8 is a graph showing the effect of in situ formation of calcium carbonate microsphere phosphate fertilizer of example 6 on dephosphorization at different temperatures. The result shows that the temperature (from 15 ℃ to 30 ℃) has little influence on the reaction, the phosphorus recovery rate is more than 95% after treatment, the total phosphorus content of the effluent is less than 0.5mg/L, the national sewage discharge grade 1A standard is reached, and the wastewater treatment device has good temperature interference resistance.
Example 7
The effect of endpoint pH on the dephosphorization process of in situ formation of calcium carbonate microspheres comprising the steps of:
preparing sodium dihydrogen phosphate (NaH) with total phosphorus concentration of 10mg-P/L calculated by P 2 PO 4 ) Solution, by adding 1.0mol/L NaOH and HCl solution, adjusting the equilibrium pH value of the solution to obtain different end point pH values (from 7.5 to 13), adding sodium dihydrogen phosphate (NaH) with total phosphorus concentration of 10mg-P/L in terms of P to 1L in a stirring state of 300-500 revolutions per minute when the Ca/P molar ratio is 6/1 2 PO 4 ) Adding CaCl into the solution 2 The solution was brought to a calcium chloride concentration of 214.8mg/L, and Na was added 2 CO 3 The solution was stirred at room temperature for 30min at a concentration of 205.2mg/L, the final pH was determined, and the water sample was filtered to determine the phosphorus content.
Fig. 9 is a graph showing the effect of in situ formation of calcium carbonate microsphere phosphate fertilizer of example 7 on phosphorous removal at different endpoint pH. The result shows that the influence of the end point pH value (from 7.5 to 13) on the reaction is negligible, the phosphorus recovery rate is more than 97 percent after the treatment, the total phosphorus content of the effluent is less than 0.2mg/L, the national sewage discharge grade 1A standard is reached, and the wastewater treatment device has good acid-base interference resistance.
Example 8
Determination of in-situ generated calcium carbonate microsphere phosphate fertilizer and conventionally prepared calcium carbonate phosphorus content:
further analysis of the phosphate ions recovered from the in situ formation of calcium carbonate microsphere phosphate fertilizer in example 1 at CaCO was performed using the radiographic photoelectron spectroscopy (XPS) 3 In the form of the presence of a compound. XPS results indicated (as shown in FIG. 10), most of the phosphate ions were taken as HPO 4 2- (132.2 eV, 64%) and PO 4 3- (133.2 eV, 36%) was present in the in situ formed calcium carbonate microspheres. For conventionally synthesized calcium carbonate, phosphate ions are used as the active ingredientsHPO 4 2- (54％)、PO 4 2- (23％)、H 2 PO 4 1 (134.6 eV, 23%) are present. According to XPS results, the Ca/P molar ratio of the in situ formed calcium carbonate microspheres and the conventionally prepared calcium carbonate was 1.82:1 and 4.31:1. It follows that the solid form of in situ formation of calcium carbonate microspheres is: caCO (CaCO) 3 ·0.23Ca 3 (PO 4 ) 2 ·1.04CaHPO 4 ·16.48H 2 O; the solid form of the calcium carbonate synthesized by the traditional method is as follows: caCO (CaCO) 3 ·0.04Ca(H 2 PO 4 ) 2 ·0.16CaHPO 4 ·0.04Ca 3 (PO 4 ) 2 ·15.92H 2 O. After dissolving the sample in hydrochloric acid and testing the phosphate concentration in the solution, the P content in the in situ formed calcium carbonate microspheres is up to 20.80% (P) 2 O 5 Weight percent) of the calcium carbonate is 4 times that of the calcium carbonate synthesized by the traditional method. The phosphorus content of the calcium carbonate formed by the in-situ method is far higher than the phosphorus content standard (P) of qualified and high-quality calcium magnesium phosphate fertilizer in China 2 O 5 > 12% and > 18% by weight respectively) (GB 20412-2016, cn).
Example 9
In-situ calcium carbonate recovery method for phosphorus in septic tank sewage:
1L of water sample of the effluent of the septic tank is collected, and the initial total phosphorus concentration is measured to be 80mg-P/L, and pH=4.3.
Adding 5% (w/w) sodium hydroxide solution to a pH of 8, adding CaCl 2 The solution (1 mol/L) is added with Na until the concentration of calcium chloride is 1.2g/L 2 CO 3 The solution (1 mol/L) was reacted for 30 minutes until the concentration of sodium carbonate was 1.1g/L, and was filtered with a quick filter paper, and the phosphorus content of the effluent was 0.48mg-P/L as measured with reference to GB11893-89, and the phosphorus recovery was 99.4%.
Example 10
The in-situ calcium carbonate generation method is used for deep dephosphorization of the culture sewage:
1L of sewage discharged from a farm after biochemical treatment by an activated sludge method is collected, and the total phosphorus concentration is measured to be 5.6mg-P/L, and the pH=6.2.
Adding CaCl 2 Solution (1 mol/L) to calcium chloride concentration0.15g/L, na is added 2 CO 3 The solution (1 mol/L) was reacted for 30 minutes until the concentration of sodium carbonate was 0.14g/L, and then filtered through a quick filter paper, and the phosphorus content of the effluent was 0.41mg-P/L as measured with reference to GB11893-89, and the phosphorus recovery rate was 92.7%.
Example 11
An application of in-situ generated calcium carbonate microsphere phosphate fertilizer to growth of cabbages, comprising the following steps:
(1) Uniformly preparing a plurality of 100mL sodium dihydrogen phosphate (NaH) with the concentration of 38.73mg/L 2 PO 4 ) Solution (total phosphorus in P10 mg/L) sodium dihydrogen phosphate (NaH) having a total phosphorus concentration in P of 10mg-P/L 2 PO 4 ) A solution. Adding CaCl under stirring 2 Solution until CaCl in system 2 The concentration is 214.8mg/L, and Na is added after 30min of reaction 2 CO 3 Solution until Na in the system 2 CO 3 The concentration was 205.2mg/L, and stirring was stopped after the reaction was continued for 30 minutes. Filtering the precipitate, and drying and collecting the powder product to obtain the calcium carbonate microsphere phosphate fertilizer in situ.
(2) Sandy soil is collected from the local farmland as planting soil.
(3) Cabbage (Brassica campestris l.ssp.) was planted in a flowerpot containing 1.0kg of soil (available from hebei xing seed industry limited). 1g of prepared calcium carbonate microsphere phosphate fertilizer generated in situ is used as phosphate fertilizer (P-CaCO) 3 -in situ) is sprayed on the soil surface as a phosphate group; control (CK) was not fertilized; ten seeds were sown per group.
(4) After germination, 5 plants with average germination vigor are reserved for planting test. The water holding capacity during planting was kept at about 70% and the pots were placed in natural sunlight with 3 replicates per group. After 50 days, the plants were harvested and their stem height, root length and fresh weight were measured.
(5) The dry weight of the stems was determined after oven drying at 105 ℃ for 24 hours.
FIG. 11 is a graph showing the effect of in situ generation of calcium carbonate microsphere phosphate fertilizer of example 11 on the growth control of cabbage without phosphate fertilizer. The photographs show that after 50 days of planting, the plants of the fertilization group are obviously higher and the leaves are larger. After harvesting, the root system of the fertilizer application group is longer, which indicates that in-situ generation of calcium carbonate microsphere phosphate fertilizer promotes the growth of the root system. After weighing the plants, the yield of the fertilized group was found to increase by 58.9% (fresh weight) and the dry weight by 60.1%. Significant increases in plant yield indicate that in situ phosphorus recovery strategies are a potentially useful method to recover phosphorus from low concentration water to provide quality phosphate fertilizer.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (8)
1. The method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer is characterized by comprising the following steps:
(1) Adding a calcium chloride solution into the phosphorus-containing solution in a stirring state to obtain a mixed solution A;
(2) Adding sodium carbonate into the mixed solution A in a stirring state, and continuously stirring to react to obtain mixed solution B;
(3) Carrying out solid-liquid separation on the mixed solution B, and drying the separated solid to obtain in-situ generated calcium carbonate microsphere phosphate fertilizer;
the addition amount of the calcium chloride in the step (1) is as follows: the mole ratio of phosphorus in the solution is calculated as 2:1-10:1;
the addition amount of the sodium carbonate in the step (2) is based on the calcium in the calcium chloride in the step (1): the molar ratio of carbonate radicals in the sodium carbonate is calculated as 3:1-1:2;
the reaction time in the step (2) is 30 min-24 h.
2. The method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer according to claim 1, wherein the method comprises the following steps:
the addition amount of the calcium chloride in the step (1) is as follows: the mole ratio of phosphorus in the solution is calculated as 4:1-10:1;
the addition amount of the sodium carbonate in the step (2) is based on the calcium in the calcium chloride in the step (1): the molar ratio of carbonate radicals in the sodium carbonate is calculated as 2:1-1:2.
3. The method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer according to claim 1, wherein the method comprises the following steps:
the phosphorus-containing solution in the step (1) is a phosphorus-containing solution with the concentration of 1-80 mg/L in terms of phosphorus.
4. The method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer according to claim 3, wherein the method comprises the following steps:
the phosphorus-containing solution is a phosphorus-containing solution with the concentration of 1-10 mg/L calculated by phosphorus.
5. The method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer according to claim 1, wherein the method comprises the following steps:
the solid-liquid separation mode in the step (3) comprises filtration, standing or centrifugation;
the drying condition in the step (3) is that the drying is carried out at 50-150 ℃ until the drying is complete.
6. The method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer according to claim 5, wherein the method comprises the following steps:
the filtration is carried out by using a microfiltration membrane of 0.22 μm.
7. Use of the method for recovering phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer according to any one of claims 1-6 in recovery of phosphate in sewage.
8. The use according to claim 7, characterized in that: the sewage is sewage with the concentration of less than or equal to 10mg/L in terms of phosphorus.
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