CN111982853A - Straw nitrogen adsorption determination method and determination device - Google Patents
Straw nitrogen adsorption determination method and determination device Download PDFInfo
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- CN111982853A CN111982853A CN202010999690.1A CN202010999690A CN111982853A CN 111982853 A CN111982853 A CN 111982853A CN 202010999690 A CN202010999690 A CN 202010999690A CN 111982853 A CN111982853 A CN 111982853A
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- straw
- ammonium
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- 239000010902 straw Substances 0.000 title claims abstract description 793
- 238000001179 sorption measurement Methods 0.000 title claims abstract description 455
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 408
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 209
- 238000000034 method Methods 0.000 title claims abstract description 97
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Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/002—Determining nitrogen by transformation into ammonia, e.g. KJELDAHL method
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N2021/3595—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using FTIR
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- Chemical & Material Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Molecular Biology (AREA)
- Fertilizers (AREA)
Abstract
The invention belongs to the technical field of measurement, and discloses a straw nitrogen adsorption determination method and a determination device, wherein the straw nitrogen adsorption determination method comprises the following steps: and (3) simulating field flowing water to scour the straws through a dynamic adsorption device, and dynamically measuring the adsorption capacity of the straws to the ammonium nitrogen. The invention starts from the adsorption performance of straws to nitrogen, adopts a method combining static adsorption and dynamic adsorption to analyze the microcosmic surface morphology and the surface functional group change before and after the straws adsorb the nitrogen, discusses two influence factors of the straws on the adsorption of ammonium nitrogen and researches on the adsorption thermodynamics and the adsorption kinetics of the straws on the nitrogen, establishes an adsorption thermodynamics model and a proper kinetics model and conjects the adsorption mechanism. The method is characterized by comprising the steps of determining the adsorption characteristics of straws on ammonium nitrogen, evaluating the fertilizer retention capacity of the two straws on the ammonium nitrogen fertilizer at the initial stage of water and fertilizer combination, and preliminarily disclosing the mechanism of the two straws for adsorbing the ammonium nitrogen.
Description
Technical Field
The invention belongs to the technical field of measurement, and particularly relates to a method and a device for measuring nitrogen adsorption of straws.
Background
At present, the main crop harvest index and annual agricultural production statistical data thereof counted by Food and Agricultural Organization (FAO) of the United nations show that the total yield of straws in the world is 51 hundred million tons in 2012, and the total dry matter of straws is nearly 10 hundred million tons in China, the first world of straw production, which accounts for about 20 percent of the total crop straws in the world. The element composition of the straws mainly comprises nitrogen, phosphorus, potassium, carbon, trace elements and the like, the returning of the crop straws to the field can release various element nutrients of the straws to the soil so as to supplement the soil element inventory, and meanwhile, the crops can obtain the nutrients stored in the soil by returning the straws to the field, so that the growth and development of the crops and the yield formation are promoted, and the crop straw returning method makes a great contribution to the element biogeochemical cycle of the agricultural ecosphere and the sustainable development thereof.
Nitrogen (N) is one of the essential macro-elements for crop growth and is also the most important nutrient element limiting yield formation. People generally pursue the goal of higher crop yield, but the soil nitrogen reservoir generally cannot meet the requirement of crops on nitrogen, and the purpose of increasing the yield is achieved by increasing the input of chemical nitrogen fertilizers in a habitual way. From 1980 to 2012, the applied nitrogen fertilizer amount is increased year by year, the nitrogen fertilizer amount is kept stable in 2012-2016 and slightly reduced, the agricultural nitrogen fertilizer application amount in 2016 is 2310.5 ten thousand tons, and is reduced by 51.1 ten thousand tons compared with 2015, but the annual nitrogen fertilizer amount in China is still large, the annual nitrogen fertilizer consumption accounts for 1/3 of the whole world, and the nitrogen fertilizer utilization rate is only 30-40%. Excessive application of nitrogen fertilizer not only wastes mineral resources, but also causes a part of nitrogen runoff and eluviation to flow into water, thus causing water eutrophication and overproof underground water nitrate; and the other part of nitrogen is volatilized in the form of nitrous oxide and ammonia gas, so that atmospheric haze, PM2.5 standard exceeding and the like are caused, the soil fertility of farmland and the quality of soil environment are reduced, and the safety of atmospheric water and the health of people are threatened.
According to statistical data, annual total amount of various crop straws is huge worldwide, and the total amount of Chinese straw resources is very rich and occupies 1/5 of the total amount of the whole world. The chemical components of cellulose, hemicellulose and lignin of different straws have different contents, but various functional groups such as hydroxyl, carboxyl and the like exist in the structure of the straw. When the fertilizer is applied to soil, the fertilizer can be used as a fertilizer, and also can be directly used as an adsorbent or used as an adsorbent after being improved; has both economic benefit and environmental benefit. The agricultural straw contains nitrogen, phosphorus, potassium and trace elements, and belongs to renewable resources. At present, straw returning is the most important and effective means and way for solving the problem of comprehensive utilization of straws. In developed countries, such as the united states, uk, canada and japan, straw returning measures have become a fundamental agricultural practice. In recent years, the country pays more attention to the behavior of punishing the straw burning and encourages the straw returning, the relevant research of the straw returning technology of scientific research personnel improves the cognitive level of farmers, and the agricultural department continuously popularizes and applies the straw returning measures, so that the straw returning measures are gradually a basic farming system in China. The research of the prior art shows that the combined application of the straws and the chemical fertilizer can not only improve the crop yield and the soil structure, but also play an important role in the aspects of water retention and fertilizer retention, in agricultural production and an agricultural ecological system, the decomposition and nutrient release rules of returning straws to fields under the condition of rape fields are researched, the influence of returning straws with different carbon-nitrogen ratios on soil nitrogen is determined, the adsorption mechanism of the straws on the nitrogen is preliminarily explored, the reasonable analysis and explanation are made for the phenomenon that inorganic nitrogen is adsorbed and fixed by high-carbon-nitrogen-ratio straws in the early stage of returning straws to the fields, and the sustainable development of efficient utilization of the nitrogen nutrients under the condition of returning straws to the fields is further promoted.
Through the above analysis, the problems and defects of the prior art are as follows: the prior art does not have a related determination method for nitrogen adsorption of straws.
The difficulty in solving the above problems and defects is: an effective evaluation method for scientifically evaluating the nitrogen retention capability of the straws is lacked.
The significance of solving the problems and the defects is as follows: the retention capacity of straw returning to the field on chemical fertilizers and soil active nitrogen is evaluated, and scientific basis can be provided for scientific application of nitrogen fertilizers, improvement of nitrogen fertilizer utilization efficiency and reduction of nitrogen environmental pollution.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method and a device for measuring nitrogen adsorption of straws.
The invention is realized in such a way that the straw nitrogen adsorption determination method comprises the following steps:
step one, taking straws as an adsorbent raw material, taking an ammonium chloride solution as an adsorbate, and measuring the nitrogen adsorption capacity of the straws by adopting a dynamic adsorption method;
and step two, simulating field flowing water to scour the straws through a dynamic adsorption device, and dynamically measuring the adsorption capacity of the straws to the ammonium nitrogen.
Further, in the second step, the dynamic measurement method for the adsorption amount of the straw to the ammonium nitrogen comprises the following steps:
1) cutting the straws into 1-2 cm long, washing dust on the surfaces of the straws by using ultrapure water, and naturally drying the straws;
2) weighing 2.5g of naturally air-dried straws, putting into an absorption device, wherein the lower layer is a quartz sand baffle plate, and the upper layer is covered by glass beads;
3) controlling the flow rate of a peristaltic pump, connecting each device by a silica gel fine hose, and preparing an ammonium chloride solution with the concentration of 16 mg/L; enabling the ammonium chloride solution to flow through the straw adsorption device at the speed of 5ml/min, and collecting effluent liquid at different times;
4) and (3) measuring the ammonium nitrogen concentration of the collected liquid by using an AA3 continuous flow analyzer, calculating the straw nitrogen adsorption amount based on the measured liquid ammonium nitrogen concentration, and drawing a curve of the concentration and the time.
Further, in step 3), the collecting the effluent liquid at different times includes: one sample was collected every 5min for the first 60min and every 10min for the last 60 min.
Further, in the step 4), the calculation formula of the straw nitrogen adsorption amount is as follows:
4.1) total adsorption amount of straw ammonium nitrogen:
4.2) total amount of ammonium nitrogen flowing through the adsorption column:
QT＝C0*V*t
4.3) adsorption rate of straw to ammonium nitrogen:
R(％)＝Qt/QT*100％
4.4) adsorption capacity of the straw per unit mass to ammonium nitrogen:
qr＝Qt/m
wherein Q istIs the total adsorption quantity of the ammonium nitrogen in the straws, Delta C is the concentration difference, QT is the total quantity of the ammonium nitrogen flowing through the adsorption column, R is the adsorption rate of the straws to the ammonium nitrogen, qrIs the adsorption capacity of the straw to ammonium nitrogen per unit mass, C0The initial solution concentration is shown as m, the straw dosage (g) is shown as V, the control flow rate of the peristaltic pump is shown as V, and t is the adsorption time.
The invention also aims to provide a straw nitrogen adsorption measuring device for implementing the straw nitrogen adsorption measuring method.
By combining all the technical schemes, the invention has the advantages and positive effects that:
the method disclosed by the invention has the advantages that the influence factors, the kinetic adsorption characteristics and the thermodynamic adsorption characteristics of the straw for adsorbing the ammonium nitrogen are determined by adopting an indoor culture research means, the method has a relatively important significance for understanding the adsorption behavior of the straw to the nitrogen, and a scientific basis can be provided for the technology of returning the straw to the field and efficiently utilizing the nitrogen.
The invention starts from the adsorption performance of straws to nitrogen, adopts a method combining static adsorption and dynamic adsorption to analyze the microcosmic surface morphology and the surface functional group change before and after the straws adsorb the nitrogen, discusses two influence factors of the straws on the adsorption of ammonium nitrogen and researches on the adsorption thermodynamics and the adsorption kinetics of the straws on the nitrogen, establishes an adsorption thermodynamics model and a proper kinetics model and conjects the adsorption mechanism. The method is characterized by comprising the steps of determining the adsorption characteristics of straws on ammonium nitrogen, evaluating the fertilizer retention capacity of the two straws on the ammonium nitrogen fertilizer at the initial stage of water and fertilizer combination, and preliminarily disclosing the mechanism of the two straws for adsorbing the ammonium nitrogen.
The present invention uses static adsorption as a comparative material. The invention adopts a dynamic adsorption method, and can be more suitable for the actual field situation.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained from the drawings without creative efforts.
FIG. 1 is a flow chart of a straw nitrogen adsorption determination method provided by the embodiment of the invention.
FIG. 2 is a schematic diagram of straw nitrogen adsorption measurement provided by the embodiment of the invention.
FIG. 3 is a schematic diagram of accumulated temperature and rainfall in the straw decomposition process provided by the embodiment of the invention.
FIG. 4 is a schematic diagram of the residual amount of covered field straws, the decomposition rate, and the temperature accumulation and rainfall change in the decomposition process provided by the embodiment of the invention.
FIG. 5 is a schematic diagram of the characteristics of carbon content, residual carbon content and cumulative carbon release rate of straws under a condition of mulching and returning.
FIG. 6 is a schematic diagram of the characteristics of the nitrogen content, nitrogen residual amount and nitrogen cumulative release rate of the straw under the condition of mulching and returning to the field provided by the embodiment of the invention.
FIG. 7 is a schematic diagram of the time sequence variation characteristics of the carbon-nitrogen ratio of the straw under the condition of covering and returning to the field provided by the embodiment of the invention.
FIG. 8 is a diagram illustrating the characteristics of the phosphorus content, phosphorus residual amount and phosphorus cumulative release rate of straws under the condition of mulching and returning.
FIG. 9 is a schematic diagram of characteristics of potassium content, potassium residual amount and potassium cumulative release rate of straw under a condition of mulching and returning provided by an embodiment of the invention.
FIG. 10 is a schematic diagram of the effect of straw addition with different C/N ratios on soil ammonium nitrogen provided by the embodiment of the invention.
FIG. 11 is a schematic diagram of the effect of adding straw with different C/N ratios on soil nitrate nitrogen provided by the embodiment of the invention.
FIG. 12 is a schematic diagram of the effect of straws with different C/N ratios on soil mineral nitrogen provided by the embodiment of the invention.
FIG. 13 is a schematic diagram illustrating the effect of straw usage on the amount of ammonium nitrogen adsorbed according to an embodiment of the present invention.
Fig. 14 is a graph showing the effect of the initial concentration on the amount of ammonium nitrogen adsorbed according to the example of the present invention.
Fig. 15 is a schematic diagram illustrating the effect of temperature on the amount of ammonium nitrogen adsorbed according to an embodiment of the present invention.
FIG. 16 is a schematic diagram showing the effect of pH on the straw adsorption amount (a) and surface potential (b) according to the embodiment of the present invention.
Fig. 17 is a schematic view showing the influence of the adsorption time on the amount of ammonium nitrogen released (a) and the amount of ammonium nitrogen adsorbed (b) according to the example of the present invention.
FIG. 18 is a front and rear surface structure view of straw adsorption provided in an embodiment of the present invention;
in the figure: a, soaking undisturbed rice straws b in pure water for 4 hours before adsorption, and c, soaking the rice straws in 20mg/L ammonium chloride for 4 hours; d, soaking the original rape straws e in pure water for 4 hours before adsorption, and soaking the rape straws f in 20mg/L ammonium chloride for 4 hours.
FIG. 19 is the infrared spectra before and after the adsorption of ammonium nitrogen by the rape straw (a) and the rice straw (b) according to the embodiment of the present invention.
FIG. 20 is a graph showing the adsorption kinetics of rape straw (a) and rice straw (b) according to the present invention.
FIG. 21 is a schematic view of adsorption isotherms of rape straw (a) and rice straw (b) according to an embodiment of the present invention.
FIG. 22 is a schematic view of a dynamic adsorption self-made testing apparatus provided in an embodiment of the present invention.
FIG. 23 is a schematic view of the dynamic adsorption curves of the rape straw (a) and the rice straw (b) at different concentrations.
FIG. 24 is a schematic diagram showing the effect of different flow rates on the dynamic adsorption of rape straw (a) and rice straw (b) according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Aiming at the problems in the prior art, the invention provides a method for measuring straw nitrogen adsorption, which is described in detail below with reference to the accompanying drawings.
As shown in fig. 1, the method for determining straw nitrogen adsorption provided by the embodiment of the invention comprises the following steps:
s101, taking straws as an adsorbent raw material and an ammonium chloride solution as an adsorbate, carrying out SEM observation and infrared spectrum detection on microscopic surface morphology and surface functional groups before and after straw adsorption, and determining the nitrogen adsorption capacity of the straws by adopting a static adsorption method;
s102, simulating field flowing water to scour the straws through the dynamic adsorption device, and dynamically measuring the adsorption capacity of the straws to the ammonium nitrogen.
In step S101, the straw provided in the embodiment of the present invention is rape straw or rice straw.
In step S101, the SEM observation and infrared spectrum detection of the microscopic surface morphology and surface functional groups before and after straw adsorption provided by the embodiment of the present invention includes:
transferring 12mg/L ammonium chloride solution into a 500mL beaker, adding 2.5g of straw into each bottle, wrapping gauze with a weight, putting into water, completely soaking for 4h, taking the solution to be tested, testing the nitrogen concentration, keeping the temperature at 25 +/-2 ℃, and repeating for 4 times; and (3) collecting the straws adsorbed for 4h, observing a part of the straws by using a scanning electron microscope for the microscopic morphology of the straw surface, and measuring the structural change of the straws before and after the residue is adsorbed by using a Fourier transform infrared spectrometer.
In step S101, the method for statically measuring the nitrogen adsorption capacity of straw provided in the embodiment of the present invention includes the following steps:
weighing 0.25g of straws in a clean small white bottle, respectively adding 50mL of 12mg/L ammonium chloride solution, keeping the pH value of the solution between 7 and 9, and putting the solution into an incubator; completely soaking for 4 hours, repeating for 4 times, respectively filtering the obtained solutions to be tested, and testing the nitrogen concentration of the filtrate; and calculating the adsorption quantity of the straw to adsorb the ammonium nitrogen based on the nitrogen concentration in the filtrate obtained by the test.
The temperature of the incubator provided by the embodiment of the invention is 25-40 ℃.
The calculation formula of the ammonium nitrogen adsorption amount of the straw provided by the embodiment of the invention is as follows:
(1) calculating formula of ammonium nitrogen adsorption amount:
in the formula: t represents adsorption reaction time; qtRepresents the adsorption amount in the t period; v represents solution volume (mL); m represents the straw usage amount; c0Represents the mass concentration of the initial liquid phase adsorbate; ctRepresenting the mass concentration of the adsorbate over a period of t;
(2) lagergren quasi-first order kinetic equation:
ln(Qe-Qt)＝lnQe-K1t
in the formula: qeRepresents the equilibrium adsorption amount; k1Represents the adsorption rate constant;
(3) langergren quasi-second order kinetic equation:
in the formula: k2Represents the adsorption rate constant; h is0Represents the initial adsorption rate;
(4) elovich kinetic model: used for showing that the adsorption rate exponentially decreases with the increase of the adsorption amount and reflects the exchange adsorption of ions;
in the formula, t 01/α · β; α represents the initial adsorption rate; β represents a constant related to the surface coverage and activation energy;
(5) intragranular diffusion model:
qt＝kit1/2+C
wherein, KiRepresents the intrinsic diffusion rate constant;
(6) langmuir equation:
wherein, CeRepresents the mass concentration of adsorbate in the liquid phase at equilibrium; qmRepresents the saturated adsorption amount of monolayer adsorption; b represents an adsorption equilibrium constant relating to the heat of adsorption;
(7) freundlich equation:
wherein, KfRepresents the saturated adsorption amount of monolayer adsorption; n represents a constant relating to the adsorption strength of the adsorbent;
(8) constant temperature and pressure, the free energy for adsorption is set as delta G, the enthalpy change is delta H, and the entropy change is delta S, then the following components are provided:
△G＝△H-TΔS
wherein the content of the first and second substances,
represents a dispersion coefficient; Δ H represents enthalpy; deltaS represents entropy; t represents an absolute temperature; r represents a gas constant; the values of Δ H and Δ S are calculated from the data
To pair
The slope and intercept of the line obtained by plotting are obtained.
In step S102, the method for dynamically measuring the amount of adsorption of ammonium nitrogen by straw provided in the embodiment of the present invention includes:
1) cutting the straws into 1-2 cm long, washing dust on the surfaces of the straws by using ultrapure water, and naturally drying the straws;
2) weighing 2.5g of naturally air-dried straws, putting into an absorption device, wherein the lower layer is a quartz sand baffle plate, and the upper layer is covered by glass beads;
3) controlling the flow rate of a peristaltic pump, connecting each device by a silica gel fine hose, and preparing an ammonium chloride solution with the concentration of 16 mg/L; enabling the ammonium chloride solution to flow through the straw adsorption device at the speed of 5ml/min, and collecting effluent liquid at different times;
4) and (3) measuring the ammonium nitrogen concentration of the collected liquid by using an AA3 continuous flow analyzer, calculating the straw nitrogen adsorption amount based on the measured liquid ammonium nitrogen concentration, and drawing a curve of the concentration and the time.
In step 3), collecting the effluent liquid at different times provided by the embodiment of the present invention includes: one sample was collected every 5min for the first 60min and every 10min for the last 60 min.
In the step 4), the calculation formula of the nitrogen adsorption amount of the straw provided by the embodiment of the invention is as follows:
4.1) total adsorption amount of straw ammonium nitrogen:
4.2) total amount of ammonium nitrogen flowing through the adsorption column:
QT＝C0*V*t
4.3) adsorption rate of straw to ammonium nitrogen:
R(％)＝Qt/QT*100％
4.4) adsorption capacity of the straw per unit mass to ammonium nitrogen:
qr＝Qt/m
wherein Q istIs the total adsorption quantity of the ammonium nitrogen in the straws, Delta C is the concentration difference, QT is the total quantity of the ammonium nitrogen flowing through the adsorption column, R is the adsorption rate of the straws to the ammonium nitrogen, qrIs the adsorption capacity of the straw to ammonium nitrogen per unit mass, C0The initial solution concentration is shown as m, the straw dosage (g) is shown as V, the control flow rate of the peristaltic pump is shown as V, and t is the adsorption time.
The technical solution of the present invention is further illustrated by the following specific examples.
Example 1:
3 rice straw mulching returning decomposition and nutrient release characteristics
3.1 introduction to the beginning
Crop straws are an important natural resource. According to statistics, the amount of straw resources generated in China every year is 8.4 hundred million tons, which accounts for about 19 percent of the total amount of straws in the world. Researches show that the straws are rich in cellulose, lignin, nitrogen, phosphorus, potassium and other nutrient elements, and returning the straws to the field can play a great role in updating soil humus, maintaining the balance of soil organic matters and improving soil, and can improve soil fertility. Especially under the condition of shortage of potash fertilizer resources in China, the straw potassium can be used as a good potash fertilizer resource. The research of returning the straws to the field in the rape season also shows that the straw returning field has the functions of preserving the moisture of the dry land, preserving the heat in winter and improving the soil fertility. Under the conditions of modern, mechanized and industrialized production of a large amount of straws, the future agricultural cultivation mode will provide requirements of higher efficiency and higher standard for straw returning, so that the more difficult challenge is faced in straw returning, the research on the decomposition process and nutrient release rule of the straws is very important, and the decomposition process and the nutrient release characteristic of the straws in the soil must be clearly and deeply understood.
The previous researches on the decomposition of the straws and the release of nutrients in the straws under the condition of returning the straws to the field have been carried out, and the research result of the prior art 1 shows that the relative water content of the soil has great influence on the decomposition degree of the wheat straws and the corn straws, and the two straws greatly promote the increase of the C, N content of the soil, improve the organic matter content and the active microorganism content of the soil and improve the soil environment. The results of the prior art 2, which adopts a nylon bag method to simulate the decomposition of the straws in the paddy field, show that the decomposition rates of the tested straws are shown to be faster in the early stage of the culture and gradually slower in the later stage. The release rate of nutrients in the straws is represented by K > P > C > N, and the release amount is represented by K > C > N > P. In the prior art 3, rice straws are respectively subjected to undisturbed, chopped and decomposed agent adding and chopped farmyard manure adding treatment in a nylon bag, and the decomposition and nutrient release rate of the straws under the outdoor condition are researched, so that the results show that after decomposition for a period of time, each treatment is decomposed by more than 50%, and the decomposition of the rice straws can be accelerated by the treatment of adding the decomposed agent and the farmyard manure after straw chopping, and the release of nitrogen, phosphorus and potassium nutrients is improved. The decomposition of the field straws and the release of nutrients are greatly influenced by environmental factors, and the method is taken as an entry point, and the characteristics of straw decomposition and nutrient release under the rape season straw coverage are researched by combining accumulated temperature and rainfall so as to provide a theoretical basis for rape season straw coverage and returning and nutrient resource management.
3.2 materials and methods
3.2.1 general description of the test area
The test was conducted in Meerchun Town, Wujing, Hubei, from 2016 to 2017, at 5 months (115 ° 59.7 '51.2 "for east longitude, 30 ° 12' 5" for northern latitude). The test point belongs to a typical subtropical monsoon humid climate, and by referring to rainfall conditions of Chinese meteorolite and sunny new sites in 2013-2016 year and 4 year rape planting season, the average 24h rainfall in each year rape planting season is more than 10mm, and the number of times is 20-30. The agricultural production in this area is mainly rice-oil twice a year. The soil type is rice soil formed by the development of Yangtze river alluvial substance. Basic physicochemical properties of the soil to be tested: the pH value is 5.37, the organic matter is 26.71g/kg, the total nitrogen is 1.45g/kg, the quick-acting phosphorus is 8.20mg/kg, and the quick-acting potassium is 62.14 mg/kg.
3.2.2 test stalks
After 2016, collecting rice straws, crushing the rice straws to 5-10 cm, air-drying and storing for later use. The water content and the nutrient content of the tested straws are measured before the test, and the nutrient content is respectively as follows: 41.7 percent of C, 0.54 percent of N, 0.07 percent of P and 2.42 percent of K.
3.2.3 test methods
The decomposition and carbon, nitrogen, phosphorus and potassium release characteristics of rape field covered rice straws under field conditions are researched by adopting a nylon mesh bag method. After the rice is harvested, the crushed straws are put into a nylon mesh bag with 200 meshes (the mesh bag is 25cm long and 20cm wide), and the water content of the straws is measured at the same time. The thickness of the straw filled in the mesh bag is basically consistent with the actual covering thickness (about 2cm), and each bag is filled with 20g of straw, and the total amount is 90 bags. The 90 nylon mesh bags are evenly put into the rape field, and no fertilizer is applied to the area. Randomly selecting 3 mesh bags according to rainfall, wherein the rainfall is mainly field runoff, and if no runoff exists, sampling is not carried out. If no rainfall was produced at the sampling interval for one month, 3 mesh bags were randomly selected. The sample was taken back, dried at 60 ℃ and weighed. And (4) determining the decomposition rate of the straws by a weight loss method. Sampling is carried out 18 times in the decomposition period of the straws, 3 mesh bags are randomly taken each time, and 54 mesh bags are taken.
The plant sample determination method comprises the following steps: the plant total carbon is titrated by ferrous sulfate by a potassium dichromate volumetric method; total nitrogen, phosphorus and potassium are digested by H2SO4-H2O2, nitrogen and phosphorus are measured by AA3 flow injection, and total potassium is measured by flame photometry.
Straw decomposition rate (%) - (original straw weight-straw residue)/original straw weight x 100
The nutrient release rate (%) (total amount of original straw nutrients-total amount of residual straw nutrients/total amount of original straw nutrients x 100, wherein the total amount of straw nutrients is the mass of straw x the content of straw nutrients
3.2.4 data statistics
The experimental data were processed with Excel and SPSS software for statistics and mapping, and the level of differential significance (P <0.05) was examined using the least significant method (LSD, P < 0.05).
3.3 results and analysis
3.3.1 residual amount of straw decomposition and decomposition rate
The residual quantity of the straws is in a descending trend along with the growth period of the rapes, and the decomposition rate of the straws is consistent with the trend of accumulated temperature of more than 0 ℃ and rainfall change (figure 4). For the decomposition rate of the straws, the rainfall amount is less in the early stage of decomposition (0-157 days), but the temperature is basically more than 10 ℃, so that the decomposition rate of the straws has a relatively gentle increasing trend, and the average decomposition rate is 0.156%/d. In the later stage of decomposition (157-228 days), along with the increase of rainfall and accumulated temperature, the decomposition of the straws has a rapid decomposition stage compared with the earlier stage. When the rape is harvested, the decomposition rate of the straws reaches 56.9 percent, the average decomposition rate reaches 0.456 percent/d, and the decomposition rate reaches 3 times of the earlier decomposition rate.
3.3.2 straw decomposition carbon content, carbon residue and straw carbon cumulative release rate change characteristics
Figure 5 shows the varying characteristics of the straw carbon release. Test results show that the carbon content of the straws is generally in a continuous descending trend from 0 to 228 days, the carbon content is totally reduced by 9.2 percentage points, the accumulated carbon residue in the straws is reduced by 4.45g, and the reduction amplitude is 64.5%. With the lapse of decay time, the cumulative release rate of carbon in the straw shows a gradually increasing trend, and the maximum value of the cumulative release rate appears at 75% when the rape is harvested.
3.3.3 straw nitrogen content, nitrogen residual quantity and straw nitrogen cumulative release rate under the condition of covering and returning to field
The change of nitrogen content and its release during straw decomposition is shown in fig. 6. Test results show that the nitrogen content of the straws shows a slow increasing trend along with the decay time from 0 th to 228 th days, the nitrogen content of the straws is 0.85 percent when the rape is harvested, the nitrogen content is increased by 0.31 percent compared with the original straws, and the increasing rate is 57.4 percent. The nitrogen residual quantity of the straws shows a trend of slowly increasing and then rapidly decreasing along with the decay time, and the total nitrogen residual quantity of the straws is reduced by 0.03g in a cumulative way from 0 to 228 days, and the reduction amplitude is 32.4%. The cumulative release rate of nitrogen in the straws is in a trend of slightly decreasing (0-108 days) and then significantly increasing (108-228 days) along with the decay time, and the cumulative release rate of the nitrogen in the straws reaches 66% when the rape is harvested. In the early stage of straw decomposition, the nitrogen content fluctuation is large, probably caused by the nitrogen competition effect between the straw decomposition process and soil microorganisms, and the result shows that the release of straw nitrogen is not facilitated in the early stage after straw covering.
FIG. 7 shows the variation of the carbon-nitrogen ratio of the straw with the decay time. The carbon-nitrogen ratio of the straws in the initial returning to the field is 77.11. With the lapse of the growth period of the rape, the carbon-nitrogen ratio of the straws shows a trend of remarkably reducing, the carbon-nitrogen ratio of the straws is 24.79 when the rape is harvested, and the reduction range reaches about 68 percent compared with the original returning-to-field straws.
3.3.5 the change characteristics of the content of decomposed phosphorus in the straws, the residual amount of phosphorus and the cumulative release rate of phosphorus in the straws
FIG. 7 shows the variation of the phosphorus nutrient content and its release from straw. Test results show that the phosphorus content of the straws fluctuates greatly along with the decay time from 0 th to 228 th day without obvious change characteristics; the phosphorus residue of the straws shows a trend of slightly increasing and then gradually decreasing along with the decay time, and the total amount of phosphorus remaining in the straws is reduced by 0.005g in a cumulative way from 0 to 228 days, and the reduction range is 47.2%; with the lapse of the decomposition time, the cumulative release rate of phosphorus in the straws also shows the trend of firstly decreasing (0-108 days) and then increasing (108-228 days), until the cumulative release rate of phosphorus in the decomposed straws reaches 55.3% when the rapes are harvested. Research results show that the low cumulative release rate of the phosphorus in the straws in the early stage of decomposition is probably related to the certain adsorption effect of the straws on the phosphorus.
3.3.6 straw decomposing potassium content, potassium residual quantity and straw potassium accumulated release rate change characteristics
FIG. 9 shows the variation of the potassium nutrient content and its release from straw. The change of the potassium content of the straws shows a trend of obvious reduction, the potassium content is released quickly in the early stage (0-159 days) of the decomposition of the straws, and the potassium content in the straws tends to be gentle in the later stage (159-228 days), when the rape is harvested, the potassium content in the straws is only 0.17%, and compared with the potassium content in the straws returned to the field initially, the reduction range reaches 93.0%, which indicates that the condition that the straws are covered by the straws is favorable for supplementing potassium deficiency of soil. The release rate of potassium shows a trend of increasing remarkably at the early stage of decomposition, and by the time of rape harvest, the release rate of potassium in the straws reaches over 96 percent and is released basically and completely.
3.4 discussion
3.4.1 factors affecting decomposition of straw
The decomposition rate of the covering straw reaches 56.9 percent after 228 days of decomposition, which is basically consistent with the previous research. From the whole decomposition process of the straw, the straw is greatly influenced by precipitation. Although the range of water that can be accommodated by the soil microflora participating in straw decomposition is wide, too high or too low a soil water content can adversely affect straw decomposition. The research result of the prior art 4 shows that when the soil moisture content of the corn straw reaches 16% -20%, the decomposition rate is the fastest, and when the soil moisture content is too high or too low, the decomposition rate is reduced. The temperature also has a remarkable influence on the decomposition of the straws, because the temperature is crucial to the activity of soil microorganisms, and the activity of the microorganisms can be inhibited or weakened when the temperature is too high or too low, so that the decomposition of the straws is influenced. In addition, the carbon-nitrogen ratio of the straws has the same influence on the decomposition of the returned straws, the decomposition rate of the returned straws is slowed down if the carbon-nitrogen ratio of the straws is larger, and the decomposition rate of the straws is accelerated if the carbon-nitrogen ratio of the straws is smaller. The carbon-nitrogen ratio of the invention shows a trend of remarkably reducing along with the decay time, which shows that the decay of the straw tends to be easy. There are many factors that affect the decomposition of straw, such as the degree of crushing of straw, etc. The invention discusses the law of field straw decomposition by combining the factors of external environment (rainfall and temperature) and provides a basis for the practice of straw returning production.
3.4.2 comparison of differences in nutrient release rates from straw
Returning straws to the field inputs part of nutrients output by crops into soil to a certain extent, and in recent years, many researches are developed aiming at C, N, P, K nutrient content, and basic results show that returning straws to the field reduces the loss of nutrients in soil N, K; returning the straws to the field can quickly release nutrients C and N, and improve the organic matter level of the soil; NPK nutrients released by the straws can be directly absorbed and utilized by crops. The results of the invention show that the release characteristics of the carbon and the potassium in the straws are more obvious than that of nitrogen and phosphorus, the carbon and the potassium both have an increasing trend along with the decay time, and the potassium is released more obviously, because the potassium in the straws mainly exists in an ionic state and is greatly influenced by moisture, the potassium is released more quickly. The carbon release may be in the early stage in the form of carbon dioxide released by the action of microorganisms, while in the later stage the accumulation of organic matter in the soil. About 40% of the organic carbon in the straw is lost during the decomposition of wheat straw and corn stover in the form of carbon dioxide, and the rest can supplement the carbon source in the soil carbon reservoir in the form of organic carbon. The release rate of nitrogen and phosphorus in the straws is not changed greatly, but the nitrogen content in the straws shows a trend of increasing in the early stage of decomposition, probably because the nitrogen competing effect with microorganisms is required to meet the self decomposition in the early stage of decomposition of the straws. The content of phosphorus in the straws is low, the rule of the accumulated release rate of phosphorus in the decomposition period is similar to that of nitrogen, a negative release value appears in the early stage, which is possibly related to the living consumption of microorganisms and the straw adsorption, and the result is similar to that of the prior art that nitrogen and phosphorus in the straw decomposition are firstly enriched and then released in the cold temperature zone and the dynamic characteristics of red soil and moisture soil.
3.5 summary
1. The late stage of the decomposition rate of the straws is 3 times that of the early stage, the decomposition rate of the straws in the later stage is improved by the sudden increase of accumulated temperature and rainfall, the carbon-nitrogen ratio of the straws shows a trend of remarkably reducing along with the lapse of decomposition time, and the decomposition of the straws is promoted by the 3 factors.
2. From the time of returning the straws to the field to the end of the rape growth period, the cumulative release rate of the nutrients in the straws is sequentially K > N > P; the release rate of the potash fertilizer is fastest, and the state of soil potassium deficiency can be relieved to a certain extent. The fluctuation of the content of nitrogen and phosphorus in the straw is not obvious, and the NP release rate in the early stage of decomposition is negative, because the straw adsorbs nitrogen and phosphorus or microorganisms consume and utilize nitrogen and phosphorus.
Influence of 4 different C/N rice straws on soil mineral nitrogen conversion
4.1 introduction to the public
Nitrogen mineralization is the conversion of nitrogen from an organic state to mineral Nitrogen (NH)4 +Or NH3) The process of (1). Mineral Nitrogen Compound (NH)4 +，NH3， NO3 -，NO2 -) Transformation ofThe process of organic nitrogen is defined as the holding effect of nitrogen. The mineralization of soil nitrogen determines the effective amount of soil nitrogen, and is a key link of nitrogen circulation of an ecosystem. The mineralization process is carried out by heterotrophic soil microorganisms that utilize organic matter as an energy source. Remineralization of nitrogen refers to the normal death of a population of microorganisms or competition between different populations which in turn allows the release of a portion of the immobilized nitrogen. Factors affecting the nitrogen mineralization process of soil include not only biological factors such as soil animals and microorganisms, but also non-biological factors (such as plant or residue C/N, pH value, temperature, moisture, and fertilizer application management factors). The content of organic nitrogen in soil is generally above 90%, and the organic nitrogen can be absorbed and utilized by crops only after being converted into inorganic nitrogen. In the fertilization, a fertilization measure of returning straws to the field and applying a chemical fertilizer is usually adopted, the concentration of inorganic nitrogen in the soil can be improved by mineralization of organic nitrogen in the returning straws to the field, and the decomposition of the straws can be judged into 3 stages (namely, a mineralization stage, a holding-mineralization stage and a holding stage) according to the difference between the content of the inorganic nitrogen in the soil after returning the straws to the field and the purification mineralization quantity. Generally, the more obvious the accumulation of the straw mineralization process along with the prolonging of the straw decomposition time, the different growth periods of different crops are affected in the actual production. The C/N of the straw is an important influence factor for the mineralization of the nitrogen in the soil. The optimal C/N ratio of the microorganism participating in the decomposition of the organic matters is 25:1, wherein 5 units of carbon of the microorganism is derived from the microorganism, and the other 20 units of carbon are external energy sources in the growth and reproduction process of the microorganism. Because the C/N of the returning crop straws is higher than 25:1, the growth, the propagation and the metabolic activity of the microbial community are determined by the amount of the nitrogen source. The invention adopts two soil treatments of long-term straw returning and straw non-returning for sterilization and non-sterilization culture in the long-term positioning test of the Hunan Cassia occidentalis, researches the influence of straw nitrogen source on soil ammonium nitrogen, nitrate nitrogen and mineral nitrogen by adding straws with different C/N, and improves the theoretical basis for improving the utilization rate of straw returning nitrogen.
4.2 materials and methods
4.2.1 test materials
4.2.1.1 test soil
The test soil is obtained from yellow in the city of Taoism of Hunan provinceThe fertilization test point (112 degrees 80 'in northern latitude and 28 degrees 37' in east longitude) is positioned in Jinxiang for a long time. The test point starts in 1981, the rainfall is relatively high, the annual average is 1370mm, the annual average temperature is 17 ℃, and the annual average frost-free period is 300 d. The test soil is rice soil developed by quaternary red clay. The fertilizer is urea (nitrogen fertilizer), calcium superphosphate (phosphate fertilizer) and potassium chloride (potassium fertilizer). In the period of 1981-2014, the fertilization conditions are as follows: the application amount of the nitrogen fertilizer is 150kg N/hm of early rice2And late rice 180kg N/hm2The application amount of the phosphate fertilizer is 45kg of P in each season of the early and late rice2O5/hm2The application amount of the potash fertilizer is 120kg K in each season of the early and late rice2O/hm2. The early rice and late rice are conventional early rice and hybrid late rice respectively. The field management measures are consistent with local farmers.
According to the method, two processed soil samples of 0-20 cm plough layers are collected after 2014 late rice is harvested: (1) long-term fertilizer application (NPK); (2) applying fertilizer for a long time in combination with straw returning treatment (NPKS), wherein the straw returning amount is 2100 kg/hm/season of early and late rice2. The basic physicochemical properties and nitrogen contents of different forms of soil samples (0-20 cm) are shown in Table 5-1, and the determination method refers to the soil agricultural chemical analysis method. The organic matter is subjected to a potassium chromate heating volumetric method; titrating total nitrogen by a semi-micro Kelvin method and standard acid; quick-acting phosphorus is treated with 0.5moL/L NaHCO3Leaching-molybdenum-antimony colorimetric resisting method; 1mol/L NH for quick-acting potassium4And (3) OAc leaching-flame photometry, measuring ammonium nitrogen by using a distillation method, measuring nitrate nitrogen by using a reduction distillation method, wherein the pH value is determined according to the water-soil ratio of 2.5: 1, potentiometric measurement.
TABLE 4-1 test soil different forms of nitrogen content and basic physicochemical properties (0-20 cm, 2014)
4.2.1.2 test Nitrogen sources
The organic nitrogen fertilizer adopts rice straws treated by different nitrogen fertilizers, the C, N content in the straws is simultaneously measured, the measurement result and the calculated carbon-nitrogen ratio are as follows, the carbon content and the nitrogen content of the straws are respectively 43.0 percent and 1.79 percent, and the carbon-nitrogen ratio is about 24; the carbon content and the nitrogen content of the straw are respectively 42.8 percent and 1.19 percent, and the carbon-nitrogen ratio is about 36; the carbon content and the nitrogen content of the straw are respectively 42.3 percent and 0.77 percent, and the carbon-nitrogen ratio is about 55. The straws are cut into 5mm after being air-dried and are uniformly mixed with the soil, and the inorganic nitrogen fertilizer adopts common urea.
4.2.2 test design
The indoor culture method is adopted in the test, two groups of main treatments of sterilization and non-sterilization are respectively set for long-term positioning test soil (NPK and NPKS), and each group of main treatments are respectively provided with 5 auxiliary treatments: (ii) Control (CK); ② adding 150kg of urea N/hm2Culturing (Urea); ③ adding 150kg of rice straw with 24C/N2Culturing (Straw C/N24); adding 150kg N/hm of rice straw with C/N of 362Culturing (Straw C/N36), adding rice Straw 150kg N/hm with C/N552Culturing (Straw C/N55). Each treatment was repeated 4 times. Weighing 30.0g of air-dried soil sample (passing through a 2mm sieve), fully and uniformly mixing the soil sample with an additive (straw or urea), bottling, adjusting the water content of the soil to 25% by using deionized water, placing in a constant-temperature incubator at 25 ℃, sealing by using an aseptic sealing film, and leaving a plurality of small holes on the film. And adding deionized water into the bottle every 3-4 days, weighing, and keeping the water content of the soil unchanged during the culture period. The sterilized soil and straw are sterilized by ethylene oxide method for 24h, and the glass bottle, medicine spoon and the like required by cultivation are wiped with 75% ethanol for sterilization. The sterilized and non-sterilized treatments are respectively placed in different incubators for cultivation. Samples were taken on days 0, 5, 10, 20, 30, 50, 90, and 130 of the culture to determine the ammonium nitrogen and nitrate nitrogen contents.
4.2.3 assay methods
Measuring the total nitrogen of the soil by adopting a Kjeldahl azotometer method; extracting inorganic nitrogen in soil by 2mol/L KCl, measuring ammonium nitrogen by using a distillation method, and measuring nitrate nitrogen by using a reduction distillation method.
4.2.4 calculation method and data processing
(1) Soil ammonium nitrogen content and soil nitrate nitrogen content:
W(NH4 +-N/NO3 --N)＝(V-V0)×C×14×1000/m/v (1)
in the formula, W (NH)4 +-N/NO3 --N) the content of soil ammonium nitrogen and soil nitrate nitrogen in mg/kg; v is titration starting point volume, ml; v0Titration end point volume, ml; c, the concentration of the hydrochloric acid standard solution is mol/L; m is the mass of the air-dried soil sample, g; v is sample volume, ml;
(2) soil mineral nitrogen content:
TMN＝W(NH4 +-N)+W(NO3 --N) (2)
TMN-content of mineral nitrogen in soil in mg/kg
The experimental data were analyzed for variance using SPSS 20 software, and graphed using Excel 2013 software and origin 2017 software.
4.3 results and analysis
4.3.1 Change in the content of ammonium Nitrogen in soil
Under the non-sterilization condition, the content of the NPK and NPKS soil ammonium nitrogen is rapidly increased in 0-5 days, slowly increased in 5-50 days and reaches a peak value, and gradually decreased in 50-130 days (figures 10a and b). Under the sterilization condition, the content of the NPK and NPKS soil ammonium nitrogen is rapidly increased in 0-5 days, slowly increased after 5-50 days, slightly increased in 50-130 days and tends to be stable. The content difference of the ammonium nitrogen in the soil between different exogenous nitrogen treatments is obvious, and the integral expression is as follows: urea addition (Urea) > Straw with C/N24 addition (Straw C/N24) > Straw with C/N36 addition (Straw C/N36) > Straw with C/N55 addition (Straw C/N55) > Control (Control). Under the same culture condition, the treatment of the soil (NPKS) ammonium nitrogen by long-term straw returning is obviously higher than the treatment of the soil (NPK) by long-term straw not returning. On day 50, the NPKS treated groups increased in ammonium nitrogen by 15.40, 51.33, 57.28, 55.11 and 6.39mg kg/kg in the Control, Urea, Straw C/N24, Straw C/N36 and Straw C/N55 treatments, respectively, as compared to the NPK treated groups without sterilization-1Increases of 34.49%, 29.93%, 36.78%, 40.26% and 6.10%; under the sterilization condition, the treatment is respectively increased by 11.39, 19.71, 37.79, 18.33 and 10.68mg kg-1The amplifications were 12.14%, 7.86%, 20.71%, 11.51% and 7.20%.
4.3.2 Change in nitrate Nitrogen content in soil
The change characteristics of the soil nitrate nitrogen content after adding different C/N straws are shown in figure 11. Under different culture environments, the content of the nitrate nitrogen in the soil of NPKS and NPK groups is represented by Urea & gtStraw C/N24 & gtStraw C/N36 & gtStraw C/N55 & gtcontrol, and the content of the nitrate nitrogen in the soil treated by exogenous nitrogen is remarkably different (P & lt 0.05). The nitrate nitrogen content of each treatment was significantly higher under non-sterile conditions (fig. 11a, b) than the corresponding treatment under sterile conditions (fig. 11c, d). During the culture for 0-50 days under the non-sterilization condition, the nitrate nitrogen in each treatment is in a slow increasing trend and is lower than 20mg/kg, and the nitrate nitrogen is rapidly increased in 50-130 days; and the change trends of the sterilization conditions are different, the treatment nitrate nitrogen content is slowly increased within 0-90 days, only two treatment nitrate nitrogen contents of Urea and Straw C/N24 are rapidly increased within 90-130 days (the highest value is lower than 60mg/kg), and the other 3 treatments have no obvious increase trend and keep a lower level (the maximum value of the content is lower than 10 mg/kg). When the cultivation is carried out till 130 days, the treatment of the soil (NPKS) ammonium nitrogen by long-term straw returning is obviously higher than that by long-term straw non-returning (NPK) under the same cultivation condition. For example, under the non-sterilization condition, the nitrate nitrogen content of the NPKS group treated by Urea, Straw C/N24, Straw C/N36, Straw C/N55 and Control is increased by 17.75, 23.94, 13.97, 12.5 and 15.39mg/kg and the amplification is 7.87%, 12.96%, 7.82%, 7.03% and 13.09% respectively compared with the corresponding treatment of the NPK group. Under the sterilization condition, the corresponding treatment increases 8.68, 2.63, 1.32, 1.2 and 5.42mg/kg respectively, and the amplification increases 17.99%, 9.01%, 16.01%, 20.62% and 65.49%.
4.3.3 Change in mineral Nitrogen content in soil
As shown in fig. 12, the difference in soil mineral nitrogen content between treatments with different exogenous nitrogen additions was significant. The overall performance is as follows: urea addition (Urea) > C/N24 Straw addition (Straw C/N24) > C/N36 Straw addition (Straw C/N36) > C/N55 Straw addition (Straw C/N55) > Control (Control). The mineral nitrogen content of each soil treated is rapidly increased in 0-30 days in the early stage of culture, slowly increased after 30-90 days, slightly increased in 90-130 days and reaches the maximum value after the culture is finished. On day 130 of culture, the mineral nitrogen content of each treatment is significantly higher on the basis of NPKS non-sterilization (a) than that of NPK non-sterilization (b), and the mineral nitrogen content of the treatments of Control, Urea, Straw C/N24, Straw C/N36 and Straw C/N55 is respectively increased by 5.56, 13.11, 21.17, 11.67 and 5.08mgkg-14.14%, 4.66%, 9.93%, 5.71% and 2.57% amplification; under sterilization conditions, each of the NPKS treatments increased 23.2, 51.5, 66.3, 59.83, and 49.5mg kg-1, with 20.00%, 15.76%, 29.69%, 34.44%, and 28.66% increases, respectively, over the NPK treatment.
4.4 discussion
4.4.1. Influence of long-term straw returning soil on soil nitrogen conversion
Mineral nitrogen is consumed by microbial assimilation and plant absorption, inorganic nitrogen is converted into microbial nitrogen by microbes in soil through assimilation, the microbial nitrogen is used for growth and propagation of the microbes, and the inorganic nitrogen is released after the microbes are killed for a period of time, and the process is the conversion process of soil nitrogen in the mineral nitrogen and the microbes. The prior art discovers that the returning time of the straws is prolonged and the using amount of the straws is increased through a 3-year continuous straw returning test. The accumulation amount of ammonium nitrogen and nitrate nitrogen content of 3 layers of soil (0-5 cm, 5-15 cm and 15-25 cm) after 3 years of continuous straw returning is gradually increased. In the early stage of covering and returning the straws to the field, the content of ammonium nitrogen and nitrate nitrogen in the soil tends to decrease; in the later stage of straw decomposition, the contents of ammonium nitrogen and nitrate nitrogen in the straws are gradually released, and the yield of crops is increased. Compared with long-term straw returning-to-field soil NH4 +The content of N and the organic matter of the soil are obviously improved, and the pH value of the soil is kept at a relatively stable level. The addition of urea and the treatment of straws can improve the NH content of soil4 +-N、NO3 -N content and mineral nitrogen content, due to the increased nitrogen content of the soil, which greatly promotes mineralization. The soil property and the property of the returned straws influence the release process of decomposed nitrogen of the returned straws. The soil of the long-term positioning test point has good soil physical and chemical properties and high organic matter content, and correspondingly, the nitrogen content is higher than that of the long-term straw non-return soil, and the soil microbial biomass is also higher than that of the non-return soil, so that NH is promoted4 +-N、NO3 -Increase in N content and mineral nitrogen content. In the test, NH was treated under non-sterile conditions4 +N content compared with the content of the corresponding treatment under sterile conditionsThe change of the bacteria treatment is very obvious after 50 days of culture, the content of ammonium nitrogen is greatly reduced, and NO is reduced3 -The content of-N is greatly increased, the content of ammonium nitrogen is slightly increased and stably kept in sterilization treatment, and NO is reduced3 -The content of N is increased in a small range because the quantity of soil nitrobacteria is reduced due to sterilization, the soil nitrification is reduced, and the conversion process of ammonium nitrogen to nitrate nitrogen is inhibited. The accumulation of mineral nitrogen in the culture process keeps steadily increasing, and the straw develops towards the mineralization process of the nitrogen along with the prolongation of the decay time.
4.4.2. Influence of straws with different C/N on soil nitrogen conversion
The C/N ratio of the soil microorganism decomposed organic matter is 25:1, and most straws have C/N higher than the optimal value. When the C/N ratio of the straws is too high, the carbon source is relatively excessive, and the nitrogen source is relatively insufficient; along with the reduction of the C/N ratio, the nitrogen source is relatively excessive, the growth and development of microorganisms are promoted, and the mineralization of nitrogen is utilized. In the actual field agricultural production, attention needs to be paid to returning straws to fields, a certain amount of nitrogen fertilizer needs to be applied, and the reasonable carbon-nitrogen ratio of soil is kept. In the invention, for the same soil treatment, after the materials are added, the contents of ammonium nitrogen, nitrate nitrogen and mineral nitrogen in the materials converted into soil are correspondingly increased compared with the contents of the ammonium nitrogen, the nitrate nitrogen and the mineral nitrogen in the soil, which shows that the addition of urea or straws promotes the nitrogen mineralization process of the test soil and increases the contents of the ammonium nitrogen, the nitrate nitrogen and the mineral nitrogen in the soil. The nitrogen fertilizer is applied in a proper amount, the microbial propagation and the carbon-nitrogen mineralization and decomposition process of plant residues are promoted, the nitrogen competition between microbes and crops is avoided, the decomposition of crop straws is accelerated, and the content of effective nitrogen in soil is increased. In addition, the easier the straws with relatively small carbon-nitrogen ratio are decomposed in the soil, and the more beneficial the contents of ammonium nitrogen, nitrate nitrogen and mineral nitrogen in the soil are increased. Similar to the research results of the prior art, the carbon-nitrogen ratio of the rice straws is large and is applied to the soil in the early stage, the carbon source stimulates the microorganisms to fix and utilize the mineral nitrogen in the straws, and as the carbon-nitrogen ratio of the straws is reduced, the nitrogen in the soil is relatively surplus, so that the mineral nitrogen in the soil is increased rapidly after the microorganisms are consumed. When the fertilizer is normally applied, the content of available nitrogen in soil of a plough layer is supplemented, and sufficient nitrogen source utilization can be provided for microorganisms, but in the early stage process of straw decomposition after straw returning, because the C/N of the returned crop straws is too high, and meanwhile, the original nitrogen in the soil needs to be consumed when the microorganisms decompose the crop straws, the content of mineral nitrogen in the soil is greatly reduced. The decomposition of organic substances is different to a great extent due to different types of organic materials, the carbon-nitrogen ratio of the organic materials is 25-30, and the process of decomposing and utilizing nutrients in the straws by microorganisms is promoted. In the (NPKS) long-term straw returning soil and the (NPK) straw not returning soil, the carbon and nitrogen ratio of the added straw is more approximate to 25, the more beneficial the adjustment of the carbon-nitrogen ratio of the soil is, and the straw nitrogen mineralization is promoted.
4.5 nubs
1. Under the condition of NPK and NPKS in free combination with sterilized and non-sterilized soil, the differences of ammonium nitrogen, nitrate nitrogen and mineral nitrogen in post-treatment by adding different exogenous nitrogen are obvious, and the integral expression is as follows: urea addition (Urea) > Straw with C/N24 addition (Straw C/N24) > Straw with C/N36 addition (Straw C/N36) > Straw with C/N55 addition (Straw C/N55) > Control (Control). The straw with smaller C/N is beneficial to the mineralization of straw nitrogen.
2. When the soil is cultured for 50 days, the content of ammonium nitrogen in the soil (NPKS) treated by long-term straw returning is obviously higher than that in the soil treated by long-term straw not returning (NPK); at the end of the culture (day 130), the content of nitrate nitrogen and mineral nitrogen in the soil (NPKS) treated by long-term straw returning is obviously higher than that in the soil (NPK) treated by long-term straw not returning. The long-term straw returning treatment of the soil is beneficial to the mineralization of the straws, and the accumulation of mineral nitrogen in the soil is promoted.
5 static adsorption characteristic of nitrogen in rice and rape stalks
5.1 introduction to the public
Ammonium nitrogen is an important part of the nitrogen cycle in soil and water and is also the mineral nitrogen form directly utilized by many ammoniacal plants. The nitrogen contents of different types of crop straws are different, wherein the nitrogen contents of the straws, the rape straws, the corn straws and the like are respectively 0.34-1.12%, 0.56-0.90% and 0.48-0.77%, and the straw nitrogen can also be supplied to a farmland system for utilization, so that the growth of crops and the formation of yield are promoted. In recent years, the measures of returning the straws to the field are gradually paid more attention by the government in China. The nitrogen in the straws is brought into the soil by returning the straws to the field, the straws adsorb inorganic nitrogen in the solid-liquid phase of the soil, and the straws can adsorb aqueous solution with the weight 3-5 times of the self weight when the water is sufficient. After the straw is returned to the field, the solution in the soil can be adsorbed, so that part of nitrogen is stored. The carbon-nitrogen ratio of the straws is higher at the initial stage of returning the straws to the field, and the microorganisms decompose the straws to consume excessive nitrogen sources, so that the nitrogen fertilizer is generally applied to the returning of the straws to the field. When the water and fertilizer supply is sufficient in the early stage of returning the straws to the field, part of nitrogen can be adsorbed, but influence factors for adsorbing the nitrogen by the straws and an adsorption mechanism of the nitrogen by the straws are not clear. Therefore, the connection between the straws and the nitrogen nutrients is necessary to be researched, so that the straw returning field is used for replacing part of nitrogen fertilizers, the normal requirements of crops are met, and the theoretical possibility is provided.
According to the part, rice straws and rape straws are used as adsorbent raw materials, an ammonium chloride solution is used as an adsorbate, SEM observation and infrared spectrum detection are carried out on microscopic surface forms and surface functional groups before and after the two straws are adsorbed, a static adsorption method is adopted, influence factors of the two straws on the adsorption of ammonium nitrogen are researched, an adsorption thermodynamic model is fitted through research on adsorption thermodynamics and adsorption kinetics of the straws on nitrogen, and a proper kinetic model is established and an adsorption mechanism is presumed. The method aims to determine the adsorption characteristics of the two straws on the ammonium nitrogen, evaluate the fertilizer retention capacity of the two straws on the ammonium nitrogen fertilizer at the initial stage of water and fertilizer combination, and preliminarily disclose the mechanism of the two straws for adsorbing the ammonium nitrogen.
5.2 materials and methods
5.2.1 test materials
In the test, rape straws and rice straws are obtained in 2016, the rape straws and the late rice straws are cut into 2-3 cm long, the straws are washed by ultrapure water, and the straws are naturally dried and stored for later use. The hydrochloric acid, sodium hydroxide, ammonium chloride, potassium nitrate, potassium sodium tartrate, potassium iodide, mercury hydroxide and other chemical reagents used in the test are analytically pure, and water is ultrapure water.
The apparatus used for the test is shown in Table 5-1.
TABLE 5-1 test apparatus
5.2.2 test design
(1) Static test of influence factors of straw adsorbing ammonium nitrogen
Firstly, preparing 1000mg/L stock solution of ammonium chloride, adding 1-2 drops of chloroform, and storing for later use. The solution is prepared into solution with required concentration and is ready for use.
Influence of straw dosage on adsorption
0.05 g, 0.15 g, 0.25g, 0.35 g and 0.45g of rape (or rice) straws are respectively weighed into a clean white bottle, 50mL of 20mg/L ammonium chloride solution and deionized water (contrast) are respectively added, the straws float on the water surface, are half-soaked for 2 hours, and the temperature is kept at 25 +/-2 ℃. Repeat 4 times. And (4) filtering the solutions to be tested in the steps, and testing the nitrogen concentration of the filtrate.
Influence of initial concentration on straw adsorption of ammonium nitrogen
Transferring 50mL of ammonium chloride solution of 4mg/L, 8mg/L, 12mg/L, 16mg/L and 20mg/L into a small white bottle, using deionized water as a control, placing 0.25g of rape (or rice) straws into each bottle, floating the straws on the water surface, soaking for half 2 hours, and keeping the temperature at 25 +/-2 ℃. Repeat 4 times. And (4) filtering the solutions to be tested in the steps, and testing the nitrogen concentration of the filtrate.
Influence of temperature on straw adsorption of ammonium nitrogen
0.25g of rape (or rice) straws are weighed into a clean small white bottle, 50mL of 20mg/L ammonium chloride solution and deionized water (contrast) are respectively added into the bottle, the bottle is placed into incubators with different temperatures of 278K (5 ℃), 298K (25 ℃) and 313K (40 ℃), the straws float on the water surface, and the bottle is half-soaked for 2 hours. Repeat 4 times. And (4) filtering the solutions to be tested in the steps, and testing the nitrogen concentration of the filtrate.
Influence of pH on straw adsorption of ammonium nitrogen
Respectively filling prepared 20mg/L ammonium chloride solution into 5 small white bottles of 100mL, adjusting the pH value by using 0.01mol/L hydrochloric acid and sodium hydroxide, testing the pH value to be 3, 5, 7, 9 and 11 by using a pH meter, adding 0.25g of rape (or rice) straws into each bottle, floating the straws on the water surface, semi-soaking for 2 hours, and keeping the temperature at 25 +/-2 ℃. Repeat 4 times. And respectively filtering the solutions to be tested in the steps, testing the nitrogen concentration of the filtrate, and testing the Zeta Potential of the filtrate to be used as the surface Potential of the straw.
Influence of adsorption time on straw (complete soaking) adsorption of ammonium nitrogen
2.5g of rape (or rice) straws are well packaged by a clean gauze, a weight is bound and put into a 500mL beaker filled with 20mg/L ammonium chloride solution, deionized water is used as a contrast, the completely soaked state is kept, 10mL of the deionized water is taken out as a liquid to be tested after 0.1, 0.5, 1, 2, 3 and 4 hours, and the temperature is kept at 25 +/-2 ℃. Repeat 4 times. And (4) filtering the solutions to be tested in the steps, and testing the nitrogen concentration of the filtrate.
(2) Dynamic change of straw adsorbing ammonium nitrogen and difference of surface appearance and structure of straw
Respectively transferring 0mg/L, 4mg/L, 12mg/L and 20mg/L ammonium chloride solutions into 500mL beakers, adding 2.5g of rape straws or rice straws into each bottle, wrapping gauze with a weight, putting the gauze in water, completely soaking, taking the solution to be tested, testing the nitrogen concentration after 0.1, 0.5, 1, 2, 3 and 4 hours, and keeping the temperature at 25 +/-2 ℃. Repeat 4 times. Collecting the straws adsorbed for 4h, observing the micro morphology of the surfaces of the straws by using a scanning electron microscope (JSM-6390LV, NTC Japan), and measuring the structural changes before and after the straw residues are adsorbed by using a Fourier transform infrared spectrometer (Nexus, Thermo Nicolet USA) on the other part.
(3) Thermodynamic characteristics of straw for adsorbing ammonium nitrogen
0.25g of rape straws or rice straws is weighed into a clean small white bottle, 50mL of ammonium chloride solutions of 0mg/L, 4mg/L, 8mg/L, 12mg/L, 16mg/L and 20mg/L are respectively added into the bottle, the bottle is placed into incubators with different temperatures of 278K (5 ℃), 298K (25 ℃) and 313K (40 ℃), the straws float on the water surface, and the bottle is half soaked for 2 hours. Repeat 4 times. And (4) filtering the solutions to be tested in the steps, and testing the nitrogen concentration of the filtrate.
5.2.3 assay method
The pH of the solution was measured using a portable pH meter, the ambient temperature was measured using a thermometer, and the ammonium nitrogen concentration was measured using flow injection analysis.
5.2.4 calculation method
The method indirectly calculates the adsorption quantity of the straw to adsorb the ammonium nitrogen by measuring the content of the ammonium nitrogen in the solution. The experimental data are analyzed by using Excel 2013, an equation is fitted to an adsorption characteristic curve of the straws to the ammonium nitrogen by using Origin 2017, and the variance analysis is carried out on the experimental data by using SPSS 20 software. The specific calculation method is as follows:
(1) formula for calculating ammonium nitrogen adsorption amount
In the formula: t: adsorption reaction time; qt: adsorption amount (mg/g) at time t; v: volume of solution (mL); m: the using amount of the straw (g); c0: mass concentration of the initial liquid phase adsorbate (mg/L); ct: mass concentration of adsorbate (mg/L) over time period t;
(2) quasi first order equation of dynamics of Lagergren
ln(Qe-Qt)＝lnQe-K1t (2)
In the formula: qe: equilibrium adsorption capacity (mg/g); k1: adsorption Rate constant (min)-1)
(3) Quasi-second order kinetic equation of Lagergren
In the formula: k2: adsorption rate constant, g/(mg. min); h is0: initial adsorption Rate, mg/(g min)
(4) Elovich kinetic model
Indicating that the adsorption rate decreases exponentially with the increase in the amount of adsorption for exchange adsorption of reactive ions.
In the formula t 01/α · β; α: initial adsorption Rate (mg/(g min))-1(ii) a Beta: a constant (g/mg) related to surface coverage and activation energy;
(5) intragranular diffusion model
qt＝kit1/2+C (5)
Ki: intrinsic diffusion rate constant, (mg ((g:) min)0.5))-1)
(6) Langmuir equation
Ce: mass concentration (mg/L) of adsorbate in the liquid phase at equilibrium; qm: saturated adsorption capacity (mg/g) of monolayer adsorption; b: adsorption equilibrium constant (L/mg) relating to heat of adsorption
(7) Freundlich equation
Kf: saturated adsorption capacity (mg/g) of monolayer adsorption; n: constant (L/mg) relating to adsorption strength of adsorbent
(8) Constant temperature and pressure, the free energy for adsorption is set as delta G, the enthalpy change is delta H, the entropy change is delta S, and then
△G＝△H-TΔS (8)
Δ H and Δ S can be obtained from Van't Hoff equation:
wherein the content of the first and second substances,
is a dispersion coefficient (L.g)-1) (ii) a Delta H-represents enthalpy (KJ. mol)-1) (ii) a Δ S-represents entropy; (J. mol. K)-1)；
T-absolute temperature (K);
r-gas constant (8.314J. mol. K)-1)；
The values of Δ H and Δ S are calculated from the data
To pair
The slope and intercept of the line obtained by plotting were determined.
5.3 results and analysis
5.3.1 influencing factors of straw to adsorb ammonium nitrogen
(1) Influence of straw dosage on ammonium nitrogen adsorption
FIG. 13 is a graph showing the trend of the effect of different dosages of straws on the adsorption amount of ammonium nitrogen in nitrogen solutions with the same concentration. The content of ammonium nitrogen adsorbed by the rice straws and the rape straws in unit mass is gradually reduced along with the increase of the using amount of the straws, and when the using amount of the straws reaches 0.25g, the unit adsorption amount of the two straws is not reduced along with the continuous increase of the using amount of the straws, so that the straws tend to be stable. The adsorption capacity of the ammonium nitrogen in the rice straw per unit mass is slightly higher than the average value of the adsorption capacity of the ammonium nitrogen in the rape straw, but the difference is not large. The use amount of 0.25g of straws is a turning point of the unit straws with the absorption amount being changed from reduction to stabilization, at the moment, the absorption amount of the rape straws is 0.20 +/-0.07 mg/g, and the absorption amount of the rice straws is 0.27 +/-0.08 mg/g.
(2) Effect of initial concentration on ammonium Nitrogen adsorption
FIG. 14 is a graph showing the variation trend of the influence of solutions with different initial ammonium nitrogen concentrations on the ammonium nitrogen adsorption amount per unit mass of straw. With the increase of the initial concentration, the content of ammonium nitrogen adsorbed by the rice straws and the rape straws in unit mass is gradually increased, when the initial concentration reaches 12mg/L, the initial concentration is continuously increased, and the unit adsorption amount of the rice straws has no great difference. When the initial concentration is increased from 4mg/L to 20mg/L, the adsorption capacity of the rice straw per unit mass is increased by 0.13mg/g, the amplification is 104.1%, and the adsorption capacity of the rape straw per unit mass is increased by 0.08mg/g and 61.4%. The adsorption capacity of the rice straws is more sensitive to the change of the initial concentration, and under the condition of the same initial concentration, the adsorption capacity of the rice straws is higher than that of the rape straws.
(3) Influence of temperature on adsorption of ammonium nitrogen
The effect of different environmental temperatures on the amount of ammonium nitrogen adsorbed by the straw is shown in fig. 15. Along with the rise of the environmental temperature, the ammonium nitrogen adsorption amount of the two straws is increased in different degrees, and the rise of the temperature is favorable for the straws to adsorb nitrogen. The straw adsorption capacity is obviously increased from 5 ℃ to 40 ℃, the rape straw adsorption capacity is increased by about 0.15mg/g, the amplification is 142.2%, the rice straw adsorption capacity is increased by 0.09mg/g, the amplification is 40.3%, and the rape straw ammonium nitrogen adsorption capacity is more sensitive to temperature change. Under the condition of the same temperature, the adsorption amount of the ammonium nitrogen in the rice straws is obviously larger than that of the rape straws.
4) Influence of pH on straw adsorption of ammonium nitrogen and zeta surface potential
FIG. 16 is a graph showing the trend of the change (a) of the adsorption of ammonium nitrogen by rape and rice straws in different pH environmental solutions and the change (b) of Zeta Potential on the surfaces of the rape and rice straws. The Zeta potential approximately represents the potential of the electrostatic charge carried by the straw on its surface in solution. Generally, a zeta potential <0 indicates that the material surface has a static negative charge (the amount of negative charge is much larger than the amount of positive charge). The higher the Zeta potential, the more stable the dispersion. As can be seen from fig. 16a, as the pH of the solution increases, the adsorption amounts of ammonium nitrogen in both straw gradually increase, and the values change from negative to positive. In the same pH environment, the adsorption capacity of the ammonium nitrogen in the rice straws is greater than that of the rape straws. When the pH value is 11, the adsorption quantity of the ammonium nitrogen in the rice straws reaches the maximum value, namely 1.45mg/g, and is increased by about 1.19mg/g and the amplification is 465.0% relative to the pH value of 7; the adsorption quantity of the ammonium nitrogen of the rape straws reaches the maximum value of 0.98 mg/g, and is increased by 0.77mg/g relative to the pH value of 7, and the amplification degree is 369.1%. When the pH is 9, the adsorption capacity of the rice straws and the rape straws is increased by 7 relative to the pH respectively. The result shows that the adsorption quantity of the ammonium nitrogen in the rice straw is more sensitive to the change of pH. When the pH value is less than 7, the ammonium nitrogen adsorption amount of the two straws is negative. In an acidic environment, this may be due to H in solution+And NH4 +With competing adsorption relationship to seize the surface of straw togetherThe adsorption sites, also possibly at pH < 7, affect the activity of certain functional groups on the surface of the straw. When the pH value is in a neutral to slightly alkaline condition, the straw has the optimal adsorption effect on the ammonium nitrogen, and the adsorption quantity of the ammonium nitrogen of the straw is greatly improved. As shown in FIG. 16b, the Zeta Potential on the straw surface is negative, i.e., negatively charged, when the pH is between 3 and 11. Along with the increase of the pH value, the more negative charge quantity accumulated on the surface of the straw is, the more favorable the adsorption of positive charge group ion group ammonium ions is, and the test result of the increase of the adsorption quantity of the ammonium nitrogen of the straw per unit mass is synchronously explained. The surface potential of the straw is between 20 mv and 30mv, and the solution dispersion system is relatively stable. When the pH value is 7, the Zeta potential on the surface of the rape straw is-16.53 +/-3.98 mv, and the Zeta potential on the surface of the rice straw is-26.80 +/-2.50 mv. When the pH value is increased to 9, the Zeta potential on the surface of the rape straw is increased to-26.67 +/-2.68 mv, and the Zeta potential on the surface of the rice straw is increased to-28.60 +/-0.96 mv.
(5) Influence of adsorption time on release and adsorption of straw ammonium nitrogen
FIG. 17 is a graph showing the change of release of ammonium nitrogen (a) and adsorption of ammonium nitrogen (b) in the initial 4 hours of two straws completely soaked in 20mg/L ammonium chloride solution. As can be seen from FIG. 17a, the release amount of straw ammonium nitrogen gradually increases with the time, but the release law of rape straw ammonium nitrogen is obviously different from that of rice straw ammonium nitrogen. The release rate of the ammonium nitrogen in the rice straw is high within the first 1h, and the increase rate is slow or the change is small after the release period of the ammonium nitrogen in the rice straw is 3 h. Within 0-1 h, the release amount of rape straws is increased by 0.34mg/g, the release rate is 0.34mg/g/h, the release amount of rice straws is increased by 0.12mg/g, and the release rate is 0.12 mg/g/h; within 1-4 h, the release amount of rape straws is increased by 0.13mg/g, the release rate is 0.04mg/g/h, the release amount of rice straws is increased by 0.05mg/g, and the release rate is 0.01 mg/g/h. And in the 4 th hour, the release amount of the two straws reaches the maximum value, the release amount of the rape straws is 0.47mg/g, the release amount of the rice straws is 0.16mg/g, and the release amount of the ammonium nitrogen of the rape straws is 1.92 times higher than that of the rice straws. As can be seen from FIG. 17b, with the time advance, the adsorption amounts of ammonium nitrogen in the two straws gradually increase from 0h to 2h, and then keep a relatively stable trend from 2h to 4 h. The adsorption amount of the rape straw ammonium nitrogen in the first 2h is increased by about 0.79mg/g, the adsorption rate is about 0.40mg/g/h, the adsorption amount of the rice straw ammonium nitrogen is increased by about 2.02mg/g, and the adsorption rate reaches 1.01 mg/g/h. Compared with the balance adsorption capacity of the straw floating test when the concentration is 20mg/L, the straw is completely soaked in the solution, and the unit mass straw ammonium nitrogen adsorption capacity is greatly increased. It is shown that the increase of the solid-liquid contact area increases the unit adsorption amount of the solid to the liquid phase. Before the adsorption balance is achieved, the straw release and adsorption actions are usually carried out, a certain amount of ammonium ions can be released from the surface of the straw, and a part of the ammonium ions are also adsorbed, wherein the adsorption balance is mainly determined by the release and adsorption rates.
5.3.2 kinetic characteristics of straw to adsorb ammonium nitrogen
(1) Appearance shape change characteristic of straw after absorbing ammonium nitrogen
The property of the adsorbent is most important to the adsorption effect, and the microstructure of the adsorbent and the surface functional group of the adsorbent can be studied to provide evidence for the adsorption effect intuitively. By electron microscope scanning and infrared spectrum identification, surface topography maps before and after the rape and rice straws adsorb ammonium nitrogen are compared (fig. 18). Compared with rape straws (fig. 18 d-f), the surfaces of the rice straws (fig. 18 a-c) are smoother, have more mastoids, larger specific surface area and more obvious pores, which greatly influences the adsorption capacity of the rice straws. Compared with the original straws, the straw surface is changed to different degrees after being soaked in pure water and ammonium chloride solution for 4 hours. After being soaked in 20mg/L ammonium chloride for 4h (FIG. 18c), the rape stalks have regular strip-shaped structures on the surface and rough surface compared with pure water (FIG. 18b), and a similar phenomenon occurs after the rice adsorbs ammonium nitrogen (FIG. 18c and FIG. 18 b). In addition, when the straw adsorbs water, nitrogen can be adsorbed by the straw on the surface of the straw along with the water. The change of the surface structures such as the microporous structure and the like indicates that the straw adsorbs nitrogen physically.
(2) Change characteristic of straw surface functional group after straw adsorbs ammonium nitrogen
In organic molecules, atoms constituting chemical bonds or functional groups are constantly vibratedThe frequency is equivalent to the vibration frequency of infrared light, and the vibration of peaks at different positions on an infrared spectrogram represents chemical bond and functional group information. FTIR can determine compound classes, determine functional groups, infer molecular structure and quantify analysis. The absorption peak detected represents a specific vibrational mode of a certain functional group in the adsorbent. As shown in FIG. 19, caulis et folium Brassicae campestris (a) is at 3344, 2903, 2342, 685cm-1Obvious functional group change can be seen, a wide absorption peak is arranged at 3344 before adsorption, the position is shifted to the right after adsorption, the position is caused by stretching vibration of hydrogen bonds among cellulose molecules and is possibly subjected to combination or substitution reaction with adsorbents, a new peak appears at 2903 and is related to C-H stretching vibration, a small displacement is arranged at 2342 after the peak is adsorbed, the vibration of a C-N bond appears, and the N-H vibration at 685 is formed. The rice straw (b) is 3306, 2920, 1638, 1366 and 1030cm-1Has obvious changed absorption peak, and the straw after absorbing the ammonium has obvious vibration of 3306cm-1Phenolic hydroxyl groups or alcoholic hydroxyl groups (-OH). 2920cm-1、2903cm-1C-H stretching vibration, 1638/1366cm-1N-H bending vibration, 1030cm-1Strong absorption peak (C-O absorption), increased functional groups, new stable structure, and strong evidence for rice straw to absorb ammonium ions. The whole map shows that the intensity and the position of the characteristic peak of the straw are changed before and after the straw is adsorbed, which indicates that the adsorption process has the functions of chemical reaction, ion exchange, substitution reaction and the like.
(3) Dynamics curve for adsorbing ammonium nitrogen by straw and adsorption mechanism analysis
FIG. 20 is a graph of straw sorption kinetics for different initial concentrations when fully soaking straw. As can be seen from the figure, the straw adsorbs ammonium nitrogen through 3 processes: a rapid adsorption period is set within 0-1 h, and under the action of solute pushing force, ammonium ions rapidly reach the adsorption sites on the outer surfaces of the straws; in the stage that the adsorption rate of ammonium nitrogen is gradually reduced within 1-2 h, adsorbate enters straw pores for diffusion. And (4) adsorbing ammonium nitrogen in 2-4h to enter a relative balance stage, and attaching adsorbates to the inner surface of the straw. In the equilibrium stage, the equilibrium adsorption capacities of 4mg/L, 12mg/L and 20mg/L rape straws are 0.33mg/g, 0.61mg/g and 0.79mg/g in sequence, and the equilibrium adsorption capacities of rice straws are 0.39mg/g, 1.29mg/g and 2.49mg/g in sequence.
Fitting the kinetic data of the rape straws and the rice straws for adsorbing ammonium nitrogen with different concentrations through a quasi-first-level adsorption kinetic equation, a quasi-second-level adsorption kinetic equation, an elovich model and an intra-particle diffusion model, and solving the characteristic parameters of the adsorption reaction, wherein the results are shown in a table 5-2. Quasi first order kinetic equation (R)2Between 0.9120 and 0.9940) and quasi-second order kinetic equation (R)2Between 0.9008-0.9870) is determined2The two dynamic equations are both suitable for the invention, wherein the actual adsorption capacity of the straws is similar to the adsorption capacity predicted by the quasi-first-order dynamic model, so the quasi-first-order dynamic equation is the best model for describing the straw adsorption dynamics. The quasi-second order kinetics is based on the basic assumption that the adsorption rate is controlled by a chemical adsorption mechanism, and the electron sharing and the electron transfer of straw and ammonium nitrogen are involved. The Elovich model is suitable for describing the adsorption process (R) of an adsorbent with uneven surface20.8529-0.9532) is suitable for the process with larger activation energy in the reaction process, and the rape straws are more suitable for the nitrogen adsorption process than the rice straws. Fitting the results (R) from the intra-granular diffusion model straight line20.7781-0.9105), the equation does not conform to the linear equation, and intercept exists on the Y axis, so that the ammonium nitrogen adsorption process of the straw does not belong to single internal diffusion, and the adsorption of a straw solution interface layer also exists. And from the slope of the fitted curve, the diffusion rate in the rice straw is fast first and then slow, while the diffusion rate in the rape straw is not changed greatly.
TABLE 5-2 two straw ammonium nitrogen adsorption kinetics fitting parameters
5.3.3 thermodynamic characteristics of straw for adsorbing ammonium nitrogen
FIG. 21 is a thermodynamic curve of straw adsorption after straw is half-soaked in ammonium chloride solutions of different concentrations at different temperatures. As can be seen from the figure, when the equilibrium concentration is 0-8 mg/L, the adsorption capacity of the ammonium nitrogen in the rape straws is rapidly increased, and when the equilibrium concentration exceeds 8mg/L, the adsorption capacity of the ammonium nitrogen in the rape straws is slightly increased or kept stable. When the equilibrium concentration is 0-12 mg/L, the ammonium nitrogen adsorption amount of the rice straw rapidly rises, and when the equilibrium concentration continues to increase, the ammonium nitrogen adsorption amount of the rice straw keeps stable. In the balance stage, the balance adsorption capacity of 278K, 298K and 313K rape straws is 0.11mg/g, 0.20mg/g and 0.25mg/g in sequence, and the balance adsorption capacity of rice straws is 0.23mg/g, 0.26mg/g and 0.32mg/g in sequence.
And (3) fitting thermodynamic data of the rape and rice straws absorbing ammonium nitrogen with different concentrations by applying Langmuir and Freundlich adsorption isothermal equations, and solving characteristic parameters of adsorption reaction, wherein the results are shown in tables 5-3. R of Langmuir adsorption isothermal equation of rice straws at different temperatures2Between 0.95 and 0.97, R of Freundlich adsorption isotherm equation2Between 0.84 and 0.92, and the rape straw Langmuir adsorbs R of the isothermal equation2Between 0.69 and 0.90, Freundlich adsorption isotherm equation2Between 0.48 and 0.84. In general, the law that the straws adsorb ammonium nitrogen at different temperatures can be better described by applying the Langmuir adsorption isothermal equation, and the Langmuir adsorption isothermal equation and the Freund adsorption isothermal model of the rice straws have better effects than the simulation effect of the rape straws. Langmuir adsorption isotherms assume that the adsorption is a monolayer and that the coverage is not large and that the solid surface is relatively uniform. The Freundlich model simulation parameter 1/n is less than 1, which indicates that the straw is benign in adsorption of ammonium nitrogen.
Table 5-3 two straw ammonium nitrogen adsorption isothermal equation fitting parameters
The thermodynamic parameter delta G of the straw for adsorbing the ammonium nitrogen can be calculated by a Gibbs free energy formula. The values of Δ H, Δ S and Δ G for the adsorption of ammonium nitrogen by rape and rice stalks at different temperatures are shown in tables 5-4. The delta H is more than 0, which indicates that the straw absorbs the ammonium nitrogen and absorbs the heat from the outside. In the invention, the Delta H is expressed as that rice straws are smaller than rape straws, which shows that the rape straws absorbing the same amount of ammonium nitrogen need more external heat, and the result is consistent with the test result that the adsorption amount of the rape straws is more sensitive to temperature rise. Delta S is more than 0, which shows that the messiness of the whole adsorption system is increased after the straws adsorb ammonium nitrogen. And Delta S is expressed as rice straw being smaller than rape straw. Under the temperature of 278K, 298K and 313K, the free energy of the straw to ion ammonium adsorption Gibbs is-3.79 to-9.46 KJ.mol-1In the process, namely the Delta G is less than 0, the process of adsorbing ammonium nitrogen by the two straws is spontaneous, and the Delta G | shows a gradually increasing trend along with the rise of the temperature, the value of the Delta G | reflects the magnitude of the adsorption driving force, if the Delta G | is larger, the adsorption driving force is larger, otherwise, the adsorption driving force is smaller. Under the isothermal condition, the | Delta G | shows that the rice straws are larger than the rape straws, and indirectly verifies that the adsorption performance of the rice straws is stronger than that of the rape straws. From the above, the adsorption of the straw to the ammonium nitrogen is mainly physical adsorption.
TABLE 5-4 two thermodynamic parameters for straw ammonium nitrogen adsorption
5.4
The straw returning technology is widely applied to agriculture, but most agricultural straw returning tests relate to the research on the returning effect of straw returning, and influence on the growth, yield and quality of crops and physical, chemical and biological properties of soil, or the conversion of straw returning nitrogen, and the adsorption performance of the straw returning nitrogen is generally researched through straw modification. The invention develops the adsorption performance of rape and rice straws on ammonium nitrogen, and completes the adsorption of straws on the ammonium nitrogen under the conditions of proper dosage, concentration, moisture, pH, time and temperature.
5.4.1 influencing factors of straw for adsorbing ammonium nitrogen
The use amount of the straws of 0.25g is a turning point for changing the absorption amount of the straws per unit from a reduction trend to a stable one under the test condition, the use amount of the straws is continuously increased to be unfavorable for absorption, and the release amount of the straws is increased more probably because the use amount of the straws is too large. The initial concentration of the solution promotes the adsorption process between the solid phase and the liquid phase, which is an important influence factor for adsorption in the test, and the improvement of the initial concentration of the solution is beneficial to the improvement of the adsorption capacity of the straw to nitrogen. The adsorption capacity of the rice straws is more sensitive to the change of the initial concentration, and under the condition of the same initial concentration, the adsorption capacity of the rice straws is larger than that of the rape straws. The temperature is increased at 5-40 ℃, so that the adsorption process of the straw on the ammonium nitrogen is facilitated, the straw can be supposed to absorb heat from the outside when adsorbing the ammonium nitrogen, and the thermodynamic analysis also supports the point. Under the condition of the same temperature, the adsorption amount of the ammonium nitrogen in the rice straws is obviously larger than that of the rape straws. Under the condition that the pH value is less than 7, the adsorption quantity of the straw to the ammonium nitrogen is a negative value, and the nitrogen release quantity is larger than the adsorption quantity. Under the conditions that the pH is neutral and alkaline, the adsorption amounts of the ammonium nitrogen of the two straws are obviously improved, and the possible reason is that along with the increase of the pH, the Zeta potential on the surface of the straw is negative potential and the absolute value is gradually increased, the amount of negative charges accumulated on the surface of the straw is increased, the adsorption of the ammonium nitrogen with positive charges is facilitated, and certain organic groups on the surface of the straw adsorb the ammonium nitrogen through the charge adsorption effect. The unit adsorption amount of the straw to the ammonium nitrogen can be increased by increasing the contact time of solid and liquid. The recommended conditions of the test for adsorbing ammonium nitrogen by straws in the test are as follows: the using amount of the straws is 0.25g, the temperature is 25-40 ℃, the initial concentration is high, the pH is 7-9, the adsorption time is 4 hours, and the straws are in a complete contact state.
5.4.2 mechanism analysis of straw for adsorbing ammonium nitrogen
The invention discovers that the adsorption mechanism of the rape straws and the rice straws is complex, and comprises physical adsorption, chemical adsorption, ion exchange and the like. Adsorption is caused by the attractive forces between the ammonium nitrogen and the straw, including van der waals forces, chemical bonding forces, and electrostatic attractive forces. Physisorption and chemisorption can interact and can be linked to each other as conditions change, but there are primary and secondary relationships. Straw adsorption kinetics are more suitable for applying quasi-first-stage and quasi-second-stage adsorption kinetics equations. The Langmuir isothermal adsorption equation can describe the thermodynamic characteristics of straw adsorption.
(1) Physical adsorption is through the adsorption between straw and ammonium nitrogen through intermolecular attraction (i.e., van der waals forces). Physical adsorption generally occurs mainly at low temperature, and the physical adsorption can form a monomolecular adsorption layer or a polymolecular adsorption layer. The ammonium nitrogen is not fixed on the specific position of the surface of the straw, but can freely move in the interface range of the straw and the ammonium nitrogen solution, the adsorption mode is not as firm as chemical adsorption or even reversible, so that the phenomenon that the straw can release the ammonium nitrogen and adsorb the ammonium nitrogen occurs, the adsorption has a dynamic balance, the Jeps free energy calculated by adsorption thermodynamics is a negative value, the reaction is carried out spontaneously, and the absolute value of the free energy of the rice straw is greater than that of the rape straw, which indicates that the reaction is carried out spontaneously and has stronger driving force. The free energy of the two straws varies between-3.79 and-9.46 KJ.mol < -1 >, and although the boundary between physical adsorption and chemical adsorption is not obvious, the standard free energy of physical adsorption is generally considered to be within-20 KJ.mol < -1 >. So that the two straws mainly adsorb the ammonium nitrogen by physical adsorption.
(2) The chemical adsorption takes place between the straw and the ammonium nitrogen, and the adsorption behavior is promoted by the chemical reaction effect caused by chemical bonds. The chemical adsorption generally has higher requirement on temperature and larger heat of adsorption, which is equivalent to the heat of chemical reaction, and the standard free energy of the chemical adsorption is generally considered to be-80 to-500 (KJ. mol.)-1) Within. An adsorbent can only chemically adsorb one or more adsorbates, and the chemical adsorption is selective. Since chemisorption is performed by a chemical bond between the adsorbent and the adsorbate, adsorption can only form a monomolecular adsorption layer. Before and after the straw is adsorbed, the intensity and the position of the characteristic peak of the infrared spectrogram are changed, and a new functional group appears due to the stretching vibration of the hydrogen bond. Indicating that a chemical reaction exists during the adsorption process. The straw also has a chemical adsorption mode for adsorbing nitrogen.
(3) The ion exchange adsorption is to adsorb ammonium nitrogen ions in an ammonium nitrogen solution through a charged point on the surface of the straw by using electrostatic attraction, and simultaneously release equivalent cations to perform ion exchange, so that the ion charge is a determining factor of the exchange. In the research, the Zeta potential on the surface of the straw changes along with the change of the pH value of the solution, and potassium ions are possibly released on the surface of the straw to leave a plurality of cation adsorption sites, and the cation adsorption sites are replaced by ammonium ions.
5.5
(1) The amount of straw, the initial concentration of the solution, the environmental temperature, the pH value of the solution and the contact time can all influence the ammonium nitrogen adsorption amount of the straw in unit mass. The initial concentration of the solution is improved, the environmental temperature is properly increased, the solution is in a neutral or alkaline environment, the adsorption time and the contact area are increased, and the straw adsorption quantity is favorably improved.
(2) Adsorption kinetics results: under the condition of complete soaking, from low concentration to high concentration (4-12-20 mg/L), the balanced adsorption capacity of the rape straws per unit mass is 0.33mg/g, 0.61mg/g and 0.79mg/g in sequence, and the balanced adsorption capacity of the rice straws per unit mass is 0.39mg/g, 1.29mg/g and 2.49mg/g in sequence; under the condition of floating, the balanced adsorption amounts of the rape straws from low temperature to high temperature (278K-298K-313K) are 0.12mg/g, 0.20mg/g and 0.25mg/g in sequence, and the balanced adsorption amounts of the rice straws are 0.23mg/g, 0.26mg/g and 0.32mg/g in sequence. The whole adsorption process of the two straws to the ammonium nitrogen can be described by adopting a quasi-first-stage, a quasi-second-stage, an Elovich and an intra-particle diffusion equation, but the actual adsorption quantity of the straws is similar to the adsorption quantity predicted by a quasi-first-stage kinetic model, so that the quasi-first-stage kinetic equation is an optimal model for describing straw adsorption kinetics.
(3) Through the detection research of a scanning electron microscope and a Fourier infrared spectrum, the invention discovers the changes of the surface forms and the functional groups of the two straws before and after adsorption. The results of the thermodynamic study of adsorption are shown below, where the adsorption isotherm of rice straw is expressed by the Langmuir adsorption isotherm (R)20.95-0.97), and the adsorption isothermality equation (R) of the rape straws is used for the rape straws20.69-0.90) is good. Application of Langmuir adsorption isothermal equation can better describe that straws adsorb ammonium nitrogen at different temperaturesAccording to the rule, the Langmuir adsorption isothermal equation and Freundlich adsorption isothermal model effect of the rice straw is superior to the simulation effect of the rape straw.
The process of absorbing ammonium nitrogen by the straws is a spontaneous process of enthalpy change (delta H is more than 0) (reaction endotherm) entropy change (delta S is more than 0) (the reaction tends to be stable). Combining the two studies, the adsorption of the straw may not be single physical or chemical adsorption, but is the result of combining several adsorption processes, but the physical adsorption is the main one.
6 dynamic adsorption characteristic of nitrogen in rice and rape stalks
6.1
The crop straws contain rich nitrogen resources, the nitrogen contents of the straws and the rape straws are respectively 0.34-1.12% and 0.56-0.90% according to statistics, after the straws are returned to the field, the potassium nutrients in the straws are quickly released, and the nitrogen in the straws mainly exists in the form of organic nitrogen and is slowly released in the early stage. The prior art finds that under certain rainfall conditions, the crop straws can intercept 29% of rainfall at most; according to the research result of rice straw water absorption dynamics reported in the prior art, the straw is basically saturated after being soaked for 150min, and the maximum water absorption capacity is 3.88g/g, which is nearly 4 times of the self weight. The crop straws have stronger water retention performance, and the previous section of research shows that the phenomenon of adsorbing ammonium nitrogen exists while adsorbing water. Therefore, the influence of the adsorption time on the adsorption of ammonium nitrogen by the straw needs to be further refined. The dynamic adsorption test can monitor the change of the adsorption condition of more precise and fine time nodes, so that the dynamic adsorption test of the straws on the ammonium nitrogen is carried out.
Dynamic adsorption is a common straw adsorption mode. The concentration and flow rate affect the adsorption amount and adsorption rate of the whole adsorption process, and are two indispensable physical quantities in the dynamic adsorption test, and the most common adsorption models, namely the BDST model and the Thomas model, have to provide the two parameters. Therefore, rape straws and rice straws are mainly utilized in the chapter, a laboratory self-made dynamic adsorption device is used for simulating field flowing water to wash the straws, and the difference of the adsorption condition of the straws on ammonium nitrogen in a short time interval is explored under the conditions of solutions with different concentrations and different flow rates.
6.2 materials and methods
6.2.1 test materials
In the test, rape straws and rice straws are harvested in 2016, the straws are cut into 1-2 cm long, surface dust of the straws is washed by ultrapure water, and the straws are naturally air-dried and stored for later use. The ammonium chloride, potassium sodium tartrate, potassium iodide, mercury hydroxide and other chemical reagents used in the test are all analytically pure. Schematic diagram 22 of the dynamic adsorption test apparatus.
6.2.2 test design
Weighing 2.5g of straws, placing the straws into an absorption device, covering the lower layer with a quartz sand baffle plate and the upper layer with glass beads, preparing initial solutions (ammonium chloride) with different concentrations, controlling the flow rate of a peristaltic pump, collecting effluent liquid at different times, collecting a sample every 5min in the first 60min, and collecting a sample every 10min in the last 60 min. The concentration of ammonium nitrogen was measured and plotted against time.
The method comprises the steps of putting rape straws and rice straws which are cut into 1-2 cm sections into an adsorption device, controlling the flow rate of a system through a peristaltic pump, connecting each device through a silica gel thin hose, enabling an initial solution to be an ammonium nitrogen solution, enabling the solution to flow through the straw adsorption device, and carrying out a dynamic adsorption test. Referring to other research results, the dynamic test selects a 90% (Ct/C0 ═ 0.90) breakthrough point, and correlation analysis is carried out on the effluent liquid ammonium nitrogen concentration and time.
(1) Influence of initial solution concentration
The peristaltic pump flow rate was adjusted to 5ml/min (66.5rpm) and initial solution concentrations were set at 8mg/L, 16mg/L, 32 mg/L.
(2) Influence of flow velocity
The flow rates were set to 4ml/min (55.5rpm), 5ml/min (66.5rpm), 6ml/min (80rpm), and the initial solution concentration was set to 16 mg/L.
6.2.3 measurement method
Ammonium nitrogen concentration was measured on a continuous flow AA3 analyzer machine.
6.2.4 calculation method
1. Total adsorption amount of straw ammonium nitrogen
2. Total amount of ammonium nitrogen flowing through the adsorption column
QT＝C0*V*t (2)
3. Adsorption rate of straw to ammonium nitrogen
R(％)＝Qt/QT*100％ (3)
4. Adsorption capacity of unit mass of straw to ammonium nitrogen
qr＝Qt/m (4)
Wherein Q istThe total adsorption quantity of the ammonium nitrogen in the straws, the Delta C is the concentration difference, QT is the total quantity of the ammonium nitrogen flowing through the adsorption column, R is the adsorption rate (%) of the straws to the ammonium nitrogen, and qrIs the adsorption capacity of the straw to ammonium nitrogen per unit mass, C0The initial solution concentration is m, the straw dosage (g) is m, the peristaltic pump control flow rate (ml/min) is V, and t is the adsorption time (min).
6.3 results and analysis
6.3.1 Effect of different initial concentrations on straw adsorption
FIG. 23a shows that the concentration of the effluent liquid of the ammonium nitrogen solution passing through the rape straws is stable after gradually decreasing within 0-120 min. Solutions with initial concentrations of 32mg/L, 16mg/L and 8mg/L respectively need about 40min, 50min and 55min to be reduced to concentrations equal to the initial concentrations through rape straws, the concentrations are respectively reduced by 2.41 mg/L, 3.17 mg/L and 4.37mg/L, and the reduction rates are respectively 0.06 mg/L, 0.06 mg/L and 0.08 mg/L/min. FIG. 23b shows that the concentration of the effluent liquid of the initial solution with different concentrations passing through the rice straw is gradually increased within 0-120 min until the concentration of the effluent liquid is the same as that of the original initial solution, and then the effluent liquid is kept unchanged. The initial concentration of the solution is from high to low (32-16-8 mg/L), the time of reaching the penetration point (0.9C0) is about 30min, 50min and 70min respectively, at the moment, compared with the first observation (0-5 min), the ammonium nitrogen concentration of the effluent is respectively increased by 1.83, 3.17 and 1.65mg/L, and the concentration increasing rate is respectively 0.061, 0.063 and 0.024 mg/L/min.
As can be seen from tables 5-5, the total amount Qt of ammonium nitrogen adsorbed by the straw (area product enclosed by the graphic sum) was subtracted from the total amount Qt of ammonium nitrogen adsorbed by the straw at concentrations of 8mg/L, 16mg/L and 32mg/LPartial area of the release is obtained), the total amount of the rape straws adsorbing the ammonium nitrogen is 2.7mg, 5.5mg and 12.3 mg in sequence, the adsorption rate R of the rape straws to the ammonium nitrogen is 56.3%, 57.3% and 63.9% in sequence, and the adsorption capacity of the rape straws per unit mass is 1.1m in sequenceg/g. 2.2mg/g, 4.9 mg/g; the total amount of the rice straw is 4.0mg, 8.5mg and 17.3mg in sequence, the adsorption rate is 82.5%, 88.6% and 90.1% in sequence, and the adsorption capacity of the rice straw per unit mass is 1.6mg/g, 3.4mg/g and 6.9mg/g in sequence. The comparison result shows that the rice straws with the concentrations of 8mg/L, 16mg/L and 32mg/L are respectively improved by 48.0 percent, 54.5 percent and 40.7 percent in the total adsorption amount, respectively improved by 46.5 percent, 54.6 percent and 41.0 percent in the adsorption rate, respectively improved by 45.5 percent, 54.5 percent and 40.8 percent in the adsorption capacity of unit mass. The concentration is increased from 8mg/L to 32mg/L, the total amount, the adsorption rate and the unit adsorption capacity of the ammonium nitrogen in the rape straws are improved by 9.6mg, 7.6 percent and 3.8mg/g, and the amplification is 355.6 percent, 13.5 percent and 345.5 percent. The total adsorption amount, the adsorption rate and the unit adsorption amount of the rice straws are improved by 13.3mg, 7.6 percent and 5.3mg/g, and the amplification is 332.5 percent, 9.2 percent and 331.3 percent.
TABLE 5-5 dynamic adsorption parameters of oilseed rape and rice stalks on ammonium nitrogen at different concentrations
6.3.2 Effect of different flow rates on straw adsorption
FIG. 24a shows that, at 0-120 min, when the solution with the same concentration (16mg/L) flows through the rice straw at flow rates of 4ml/min, 5ml/min and 6ml/min, the concentration of the effluent liquid gradually decreases and then becomes stable. Solutions with the same initial concentration and flow rates of 6ml/min, 5ml/min and 4ml/min in sequence need about 40min, 50min and 60min to be respectively reduced to the concentration equal to the initial concentration after passing through the rape straws, and compared with the initial concentration, the ammonium nitrogen concentration of the equilibrium solution is reduced by 20.4%, 20.4% and 18.8%, due to the initial concentration of the system. FIG. 24b shows the solution (C) at different flow rates016mg/L) of the solution, the concentration of the effluent liquid is gradually increased until the concentration of the effluent liquid is equal to the original initial solution concentrationAnd then kept stable. When the solution with the same concentration flows through the rice straws at the flow rates of 6ml/min, 5ml/min and 4ml/min within 0-120 min, the solution reaches a penetration point (0.9C)0) The time periods of the two steps are respectively about 25 min, 45 min and 60min, at the moment, the concentration is respectively increased by 1.81mg/L, 2.86mg/L and 3.47mg/L, and the speed increases are respectively 0.0724, 0.0636 and 0.0578 mg/L/min.
As can be seen from the table 5-6, the total amount QT of the ammonium nitrogen passed by the adsorption column under the condition of different flow rates of the rape straws and the rice straws is 7.9mg, 9.6mg and 11.5mg respectively, and the total amounts QT are consistent. Under the flow rates of 4ml/min, 5ml/min and 6ml/min, the total amount of the ammonium nitrogen adsorbed by the rape straws is 3.9mg, 5.5mg and 7.5mg in sequence, the adsorption rates of the rape straws on the ammonium nitrogen are 50.3%, 57.3% and 64.8% in sequence, and the adsorption capacities of the rape straws per unit mass are 1.5mg/g, 2.2mg/g and 3.0mg/g in sequence; the total amount of the rice straw is 6.7mg, 8.5mg and 10.4mg in sequence, the adsorption rate is 86.6%, 88.6% and 90.3% in sequence, and the adsorption capacity of the rice straw per unit mass is 2.7mg/g, 3.8mg/g and 4.2mg/g in sequence. The comparison result shows that the total adsorption amount of the rice straws is respectively improved by 50.5%, 71.5% and 38.7% under the flow rates of 4ml/min, 5ml/min and 6ml/min, the adsorption rates are respectively improved by 72.2%, 71.4% and 39.4%, and the adsorption capacities of unit mass are respectively improved by 80.0%, 72.7% and 40.0%. The concentration is increased from 4ml/min to 6ml/min, the total adsorption amount, the adsorption rate and the unit adsorption amount of the ammonium nitrogen in the rape straws are improved by 3.6mg, 14.5 percent and 1.5mg/g, the amplification is 92.3 percent, 28.8 percent and 100.0 percent, the total adsorption amount, the adsorption rate and the unit adsorption amount of the ammonium nitrogen in the rice straws are improved by 3.7mg, 3.7 percent and 1.5mg/g, and the amplification is 55.2 percent, 4.3 percent and 55.6 percent.
TABLE 5-6 dynamic adsorption parameters for oilseed rape and rice straw at different flow rates
6.4 discussion
The adsorption curve of the dynamic adsorption test is influenced by a plurality of factors, such as concentration, flow rate, pH value, temperature, thickness of materials of the adsorption column and the infusion tube, and the like. The invention mainly inspects the influence of the initial solution concentration and the system flow rate on the adsorption of ammonium nitrogen by the two straws. The dynamic adsorption process of the straw to the ammonium nitrogen is an adsorption process from outside to inside, an adsorbate solution firstly contacts with the whole outer surface, namely solid-liquid interface adsorption, then enters the interior through micropores on the surface of the straw, and is internally diffused to find adsorption sites for adsorption. The stronger the driving force of the whole adsorption system, the shorter the time to reach the equilibrium point and the breakthrough point. The adsorbate concentration is the driving force for the adsorption process. The two straws have the same adsorption performance on ammonium nitrogen in the solution, the concentration of the ammonium nitrogen in the rape straws is in a descending trend, and the concentration of the ammonium nitrogen in the rice straws is in a gradually ascending trend. The reason for the decrease of the concentration in the rape straw dynamic adsorption test is analyzed: the release amount of the ammonium nitrogen released from the outer surface of the rape straw is more than that of the adsorbed ammonium nitrogen before 40min, 50min and 55 min. Both the straws can adsorb a certain amount of ammonium nitrogen, but the amount of the ammonium nitrogen released by the rape straws is more than that adsorbed by the straws in the first 1h, so that the solution concentration is greater than the initial solution concentration, and then the rape straws start to change that the adsorption amount is greater than the release amount, so that the concentration of effluent is less than the initial solution concentration. Different rice straws are adopted, the concentration of the effluent liquid does not reach the concentration of the initial solution all the time in the whole test time period, and the adsorption rate of the rice straws to the ammonium nitrogen is faster than the release rate of the rice straws when the peristaltic pump is started, so that the difference occurs 1h before the test of the rape straws and the rice straws. The rice straw has stronger adsorption performance on ammonium nitrogen than rape straw, the adsorption time is earlier, and the accumulation amount of the ammonium nitrogen of the rice straw is larger than that of the rape straw.
The initial concentration of the solution is the internal driving force of the whole solid-liquid adsorption system, the higher the concentration is, the stronger the penetrating power of the solution is, the stronger the capacity of actively searching for an adsorption site is, and the faster the change rate is, the easier the adsorption is. Under otherwise identical conditions. The higher the concentration, the higher the initialThe shorter the time required for the solution to be in an equal concentration, the faster the average rate of the straw to adsorb ammonium nitrogen. The initial solution concentration is increased, and the total straw adsorption amount and the unit straw adsorption amount are greatly increased. The prior art research shows that when the initial concentration of aniline is 8.7mg/L and 96.8mg/L, the penetration time is 119.1min and 11.1min respectively, and the adsorption capacity is 0.8mg/g and 1.1mg/g respectively. In the invention, the solution with initial concentration of 32mg/L, 16mg/L and 8mg/L can be reduced to the concentration equal to the initial concentration after passing through the rape straws for about 40min, 50min and 55min respectively. The initial concentration of the solution of the rice straw is changed from 32-16-8 mg/L and reaches a penetration point (0.9C)0) The time of (a) is about 30min, 50min and 70min respectively. The concentration is increased from 8mg/L to 32mg/L, the ammonium nitrogen adsorption total amount, the adsorption rate and the unit adsorption capacity of the rape straws are 355.6 percent, 13.5 percent and 345.5 percent respectively, and the amplification of the rice straws are 332.5 percent, 9.2 percent and 331.3 percent in sequence.
The flowing speed of the solution is the external driving force of the whole solid-liquid adsorption system, the faster the flowing speed is, the shorter the contact time of the adsorbent and the adsorbate is, so that the adsorption between the adsorbent and the adsorbate is stopped on a surface layer, the too short time can not reach the balance, and the adsorption speed is also faster. The flow rate is reduced, the adsorption time of the adsorbent and the adsorbate is prolonged, the adsorption efficiency is improved, but the flow rate is too low, and the adsorption capacity in unit time is also greatly reduced. The dynamic adsorption characteristics of the resin on polyphenol in the prior art show that when the flow rate is 0.5mL/min and 1.5mL/min, the adsorption capacity is not favorably improved, and the dynamic adsorption effect at 1mL/min is optimal. The research result of the prior art shows that when the flow rate is changed between 2mL/min and 4mL/min and 6mL/min, the penetration time of the adsorption column is 133min, 66min and 42 min. When the flow rates are respectively 4.8cm/min, 8.4cm/min and 11.82cm/min, the penetration times are respectively 62.0h, 12.4h and 2.1 h. In the invention, the solution of 6ml/min, 5ml/min and 4ml/min needs about 40min, 50min and 60min respectively after flowing through the rape straws to reach the concentration equal to the initial concentration, and the rice straws correspondingly reach the penetration point (0.9C) after being adsorbed0) For about 25, 45, 60min, respectively. The total amount of the ammonium nitrogen adsorbed by the rape straws, the adsorption rate and the unit adsorption capacity increase are respectively 92.3 percent, 28.8 percent and 100.0 percent when the concentration is increased from 4mL/min to 6mL/min, and the rice strawsThe amplification of the stalks is 55.2%, 4.3% and 55.6% in sequence. The lifting amplitude of the concentration and the flow velocity to the adsorption quantity can be known, the influence of the concentration is greater than the influence of the flow velocity, the concentration is increased and the flow velocity is accelerated, and the increase amplitude of the adsorption quantity of the rape straws is greater than that of the rice straws.
6.5 nubs
(1) Under the same flow rate, the adsorption effect of the straws with different initial concentrations of the solution is different. The higher the concentration, the shorter the time required to reach the equilibrium point or the breakthrough point, and the greater the amount of straw adsorbed per unit mass.
(2) Under the same initial solution concentration, the faster the flow rate, the shorter the time for the straw surface to reach saturation or equilibrium for the adsorption of ammonium nitrogen, and the larger the adsorption amount of the straw per unit mass.
(3) Under the same conditions, the adsorption performance of the rice straw is totally stronger than that of the rape straw. In the test, when the flow rate is 5ml/min and the concentration is 16mg/L, the adsorption rate of the rape straws to the ammonium nitrogen is 57.3 percent, and the unit mass adsorption capacity is 2.2 mg/g; the adsorption rate of the rice straws to the ammonium nitrogen is 88.6 percent, and the unit mass straw adsorption capacity is 3.4 mg/g.
The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.
Claims (6)
1. A straw nitrogen adsorption determination method is characterized by comprising the following steps:
and (3) simulating field flowing water to scour the straws through a dynamic adsorption device, and dynamically measuring the adsorption capacity of the straws to the ammonium nitrogen.
2. The method for measuring straw nitrogen adsorption according to claim 1, wherein the temperature of the incubator is 25 ℃.
3. The method for measuring the straw nitrogen adsorption according to claim 1, wherein the method for dynamically measuring the adsorption amount of the straw to the ammonium nitrogen comprises the following steps:
1) cutting the straws into 1-2 cm long, washing dust on the surfaces of the straws by using ultrapure water, and naturally drying the straws;
2) weighing 2.5g of naturally air-dried straws, putting into an absorption device, wherein the lower layer is a quartz sand baffle plate, and the upper layer is covered by glass beads;
3) controlling the flow rate of a peristaltic pump, connecting each device by a silica gel fine hose, and preparing an ammonium chloride solution with the concentration of 16 mg/L; the ammonium chloride solution flows through the straw adsorption device at the speed of 5ml/min, and effluent liquid is collected at different times;
4) and (3) measuring the ammonium nitrogen concentration of the collected liquid by using an AA3 continuous flow analyzer, calculating the straw nitrogen adsorption amount based on the measured liquid ammonium nitrogen concentration, and drawing a curve of the concentration and the time.
4. The straw nitrogen adsorption assay method of claim 3, wherein in step 3), the collecting effluent liquid at different times comprises: one sample was collected every 5min for the first 60min and every 10min for the last 60 min.
5. The straw nitrogen adsorption determination method according to claim 3, wherein in the step 4), the straw nitrogen adsorption amount calculation formula is as follows:
4.1) total adsorption amount of straw ammonium nitrogen:
4.2) total amount of ammonium nitrogen flowing through the adsorption column:
QT＝C0*V*t
4.3) adsorption rate of straw to ammonium nitrogen:
R(％)＝Qt/QT*100％
4.4) adsorption capacity of the straw per unit mass to ammonium nitrogen:
qr＝Qt/m
wherein Q istIs the total adsorption quantity of the ammonium nitrogen in the straws, Delta C is the concentration difference, QT is the total quantity of the ammonium nitrogen flowing through the adsorption column, R is the adsorption rate of the straws to the ammonium nitrogen, qrIs the adsorption capacity of the straw to ammonium nitrogen per unit mass, C0The initial solution concentration is shown as m, the straw dosage (g) is shown as V, the control flow rate of the peristaltic pump is shown as V, and t is the adsorption time.
6. A straw nitrogen adsorption measuring device for implementing the straw nitrogen adsorption measuring method according to any one of claims 1 to 5.
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