Ferrous sulfide microparticle reinforced subsurface flow constructed wetland and application thereof

Abstract

The application belongs to the field of ecological water treatment, and relates to a ferrous sulfide particle reinforced subsurface flow constructed wetland and application thereof. A ferrous sulfide particle suspension is added to the subsurface flow constructed wetland by using a reverse circulation injection method; the reverse circulation injection method comprises the following steps: a. injection from the water outlet of the subsurface flow constructed wetland; b. collection and discharge of the effluent from the water inlet of the subsurface flow constructed wetland, and re-injection of the effluent into the water outlet of the subsurface flow constructed wetland; wherein the b process is at least circulated once; the ratio of the particle size of the filler in the subsurface flow constructed wetland to the particle size of the ferrous sulfide particles is 1-10:1-100, cm:nm. The application can effectively introduce the ferrous sulfide particles into the subsurface flow constructed wetland, thereby effectively reinforcing the simultaneous reduction of heavy metals and nitrate nitrogen in the subsurface flow constructed wetland, so that the application can be used for treating industrial wastewater, mining wastewater, tail water of a sewage treatment plant and the like, and controlling the ecological environment health hazards caused by combined wastewater pollution of heavy metals and nitrate nitrogen.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ecological water treatment, and relates to a ferrous sulfide particle reinforced subsurface flow constructed wetland and application thereof. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing the understanding of the general background of the application and does not necessarily constitute an admission or any kind of suggestion that this information forms the general prior art previously visualized by those working in the field.

[0003] In the subsurface flow constructed wetland, the substrate as a component of the constructed wetland can adsorb pollutants in water and provide a good attachment carrier for microorganisms during the operation of the subsurface flow constructed wetland. According to the research and understanding of the inventors, at present, the main substrate used in the subsurface flow constructed wetland is gravel and crushed stone material, which has low cost but is easy to block, has low adsorption capacity for heavy metals, weak adsorption capacity, low electron transfer efficiency between microorganisms, low microbial activity, and poor effect of simultaneous removal of nitrate nitrogen, which cannot meet the demand of the subsurface flow constructed wetland for wastewater treatment. SUMMARY

[0004] In order to solve the problems in the prior art, the present application aims to provide a ferrous sulfide particle reinforced subsurface flow constructed wetland and application thereof, which can effectively introduce ferrous sulfide particles into the subsurface flow constructed wetland, thereby effectively reinforcing the simultaneous reduction of heavy metals and nitrate nitrogen in the subsurface flow constructed wetland, so as to be used for treating industrial wastewater, mining wastewater, tail water of sewage treatment plant, etc., and controlling the ecological environment health hazards caused by combined wastewater pollution of heavy metals and nitrate nitrogen.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] On the one hand, a ferrous sulfide particle reinforced subsurface flow constructed wetland adopts a reverse circulation injection method to add ferrous sulfide particle suspension liquid into the subsurface flow constructed wetland;

[0007] The reverse circulation injection method is as follows: a. injection from the effluent port of the subsurface flow constructed wetland; b. collection of discharge liquid from the influent port of the subsurface flow constructed wetland and re-injection of the discharge liquid into the effluent port of the subsurface flow constructed wetland; wherein the process b is at least circulated once;

[0008] The particle size ratio of the filler in the subsurface flow constructed wetland to the particle size of the ferrous sulfide particles is 1-10:1-100, cm:nm.

[0009] The present application selects ferrous sulfide particles to strengthen the subsurface flow constructed wetland, mainly because the ferrous sulfide particles have high adsorption capacity and strong adsorption ability for heavy metals, and the ferrous sulfide particles can improve the microbial sulfur autotrophic denitrification capacity in the subsurface flow constructed wetland and simultaneously strengthen the removal of heavy metals and nitrate nitrogen in the subsurface flow constructed wetland.

[0010] However, there are not only sulfur autotrophic denitrifying microorganisms in the subsurface flow constructed wetland, and only the ferrous sulfide particles and the sulfur autotrophic denitrifying microorganisms can improve the microbial sulfur autotrophic denitrification capacity. Therefore, it is necessary to make the ferrous sulfide particles more evenly distributed in the subsurface flow constructed wetland. In order to make the distribution uniform, it is necessary to ensure the uniform diffusion and fixation of the ferrous sulfide particles. The present application first adopts the reverse circulation injection method to make the ferrous sulfide particles uniformly diffuse in the subsurface flow constructed wetland, so that more ferrous sulfide particles can contact the sulfur autotrophic denitrifying microorganisms in the anaerobic section. In order to make more ferrous sulfide particles in the anaerobic section be fixed, the present application further researches and finds that the combination of the above-mentioned filler particle size and the ferrous sulfide particle size is beneficial to the fixation of the ferrous sulfide particles, so that the ferrous sulfide particles are more evenly distributed in the subsurface flow constructed wetland, thereby achieving the simultaneous strengthening of the removal of heavy metals and nitrate nitrogen in the subsurface flow constructed wetland.

[0011] On the other hand, the above-mentioned ferrous sulfide particle strengthened subsurface flow constructed wetland is applied to treat industrial wastewater, mining wastewater or tail water of a sewage treatment plant, and the industrial wastewater, mining wastewater or tail water of the sewage treatment plant contains heavy metal ions and nitrate nitrogen.

[0012] The present application has the following beneficial effects:

[0013] The present application introduces the ferrous sulfide particles into the subsurface flow constructed wetland system by the reverse circulation injection method. Since the ferrous sulfide particles have high adsorption capacity and strong adsorption ability for heavy metals, and the ferrous sulfide particles serve as the electron donor of autotrophic denitrification, the microbial sulfur autotrophic denitrification capacity in the wetland system is improved, and the removal of heavy metals and nitrate nitrogen in the artificial wetland is simultaneously strengthened. By controlling the particle size of the ferrous sulfide particles and combining the reverse circulation injection method, the injected ferrous sulfide particles are uniformly distributed in the subsurface flow constructed wetland, thereby effectively strengthening the simultaneous reduction of heavy metals and nitrate nitrogen in the subsurface flow constructed wetland. The present application is suitable for treating industrial wastewater, mining wastewater, tail water of a sewage treatment plant and the like, and controlling the ecological environment health hazards caused by the combined pollution of heavy metals and nitrate nitrogen. BRIEF DESCRIPTION OF DRAWINGS

[0014] The drawings constituting a part of the specification of the present application serve to provide a further understanding of the present application, and the schematic embodiments of the present application and the description thereof serve to explain the present application and do not constitute an improper limitation on the present application.

[0015] Figure 1 A flowchart for the process of synchronously reducing heavy metals and nitrate nitrogen in the ferrous sulfide particle reinforced subsurface constructed wetland in the embodiments of the present application is shown in the figure;

[0016] Figure 2 A figure showing the concentration change of nitrate nitrogen in the water in and out of the subsurface constructed wetland with or without the introduction of ferrous sulfide particles in the embodiments of the present application is shown in the figure;

[0017] Figure 3 A comparison figure for the removal of heavy metals by the subsurface constructed wetland system in the embodiments of the present application is shown in the figure;

[0018] Figure 4 A distribution figure of ferrous sulfide particles with different particle size ranges in the subsurface constructed wetland filled with 4-6mm gravel in the embodiments of the present application is shown in the figure. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0020] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0021] In view of the problems of weak adsorption capacity for heavy metals and poor effect of removing nitrate nitrogen in the existing subsurface constructed wetland, the present application provides a ferrous sulfide particle reinforced subsurface constructed wetland and its application.

[0022] In a typical embodiment of the present application, a ferrous sulfide particle reinforced subsurface constructed wetland is provided, and a reverse circulation injection method is used to add ferrous sulfide particle suspension into the subsurface constructed wetland.

[0023] The reverse circulation injection method is as follows: a. injection from the water outlet of the subsurface constructed wetland; b. collection of the discharge liquid from the water inlet of the subsurface constructed wetland and re-injection of the discharge liquid into the water outlet of the subsurface constructed wetland; wherein the process b is repeated at least once.

[0024] The ratio of the particle size of the filler in the subsurface constructed wetland to the particle size of the ferrous sulfide particles is 1-10:1-100, cm:nm.

[0025] In some embodiments, the process b is repeated 4-5 times, which can ensure more ferrous sulfide particles to enter the subsurface constructed wetland.

[0026] In some embodiments, the concentration of the ferrous sulfide particle suspension is 10-50 g / L. In this case, the effect of simultaneous reduction of heavy metals and nitrate nitrogen is better.

[0027] In some embodiments, the particle size of the filler in the subsurface constructed wetland is 1-3 mm, and the particle size of the ferrous sulfide particles is 1-30 nm. In this case, the uniformity of the distribution of the ferrous sulfide particles in the subsurface constructed wetland can be better ensured.

[0028] In some embodiments, the particle size of the filler in the subsurface constructed wetland is 4-6 mm, and the particle size of the ferrous sulfide particles is 30-60 nm. In this case, the uniformity of the distribution of the ferrous sulfide particles in the subsurface constructed wetland can be better ensured.

[0029] In some embodiments, the particle size of the filler in the subsurface constructed wetland is 7-10 mm, and the particle size of the ferrous sulfide particles is 60-100 nm. In this case, the uniformity of the distribution of the ferrous sulfide particles in the subsurface constructed wetland can be better ensured.

[0030] In some embodiments, the speed of injection of the ferrous sulfide particle suspension into the subsurface constructed wetland is 5-10 times the normal flow rate of the wetland. In this case, the efficiency of the subsurface constructed wetland can be ensured, and the distribution of the original microorganisms in the subsurface constructed wetland can be avoided.

[0031] The ferrous sulfide particles can be obtained commercially or by self-preparation. Ferrous sulfide is easily oxidized, and therefore the cost of obtaining the required ferrous sulfide particles is high. Therefore, the ferrous sulfide particles are preferably obtained by self-preparation. In some embodiments, the preparation process of the ferrous sulfide particles is as follows: under anaerobic conditions, a ferrous salt solution and a sulfide solution are prepared, the sulfide solution is added to the ferrous salt solution containing carboxymethyl cellulose, the reaction is continued under stirring, then deoxygenated water is used for washing, and freeze-drying is performed to obtain the ferrous sulfide particles. The preparation process of the present application can avoid the oxidation of the ferrous sulfide particles and affect the application effect. The anaerobic conditions in the present application refer to conditions without oxygen or with a small amount of oxygen, such as inert gas atmosphere conditions, vacuum conditions, etc. The dropping process is carried out under stirring.

[0032] In one or more embodiments, the concentration of the ferrous salt solution is 0.1-0.5 M, the concentration of the sulfide solution is 0.1-0.5 M, the dropping speed of the sulfide solution is 0.01-0.15 mL / s, the content of the carboxymethyl cellulose is 0.1-0.3 ωt. % of the mass of the ferrous salt solution, the stirring speed is 100-300 r / min, and the stirring time is 10-30 minutes. Through the combination of the concentration, the dropping speed of the sulfide solution, the adding amount of the carboxymethyl cellulose, the stirring speed, and the stirring time, the ferrous sulfide microparticles that meet the particle size condition can be obtained, the waste of raw materials is reduced, and the cost is saved. The faster the dropping speed of the sulfide solution, the less the adding amount of the carboxymethyl cellulose, the slower the stirring speed, and the shorter the stirring time, the larger the particle size of the ferrous sulfide microparticles. For example, when the adding amount of the carboxymethyl cellulose is 0.1-0.15 ωt. %, the stirring speed is 100-200 r / min, the dropping speed of the sulfide solution is 0.1-0.15 mL / s, and the stirring time is 10-20 minutes, the particle size of the ferrous sulfide microparticles is in the range of 60-100 nm; when the adding amount of the carboxymethyl cellulose is 0.15-0.2 ωt. %, the stirring speed is 200-250 r / min, the dropping speed of the sulfide solution is 0.05-0.1 mL / s, and the stirring time is 20-25 minutes, the particle size of the ferrous sulfide microparticles is in the range of 30-60 nm; when the adding amount of the carboxymethyl cellulose is 0.2-0.3 ωt. %, the stirring speed is 250-300 r / min, the dropping speed of the sulfide solution is 0.01-0.05 mL / s, and the stirring time is 25-30 minutes, the particle size of the ferrous sulfide microparticles is in the range of 1-30 nm.

[0033] In one or more embodiments, the temperature of the process for preparing the ferrous sulfide microparticles is 25-30 °C.

[0034] In some embodiments, after the ferrous sulfide microparticle suspension is added to the subsurface constructed wetland by the reverse circulation injection method, the system is allowed to stand for 4-8 hours for stable operation. This can better fix the ferrous sulfide microparticles in the subsurface constructed wetland and ensure the stable operation of the subsurface constructed wetland reinforced by the ferrous sulfide microparticles when treating wastewater.

[0035] In another embodiment of the present application, the above-mentioned subsurface constructed wetland reinforced by ferrous sulfide microparticles is applied to treat industrial wastewater, mining wastewater, or tail water from a sewage treatment plant, wherein the industrial wastewater, mining wastewater, or tail water from a sewage treatment plant contains heavy metal ions and nitrate nitrogen.

[0036] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below with specific examples.

[0037] Example 1

[0038] I. Preparation of ferrous sulfide microparticles:

[0039] 1.1 Preparation of ferrous sulfide microparticles with a particle size range of 60-100 nm:

[0040] Under anaerobic conditions, 0.3 M FeCl2·4H2O and Na2S·9H2O solutions were prepared separately at a temperature of 25°C. 0.12 ωt.% carboxymethyl cellulose (CMC) was added to the FeCl2·4H2O solution, and the stirring speed was adjusted to 150 r / min. The Na2S·9H2O solution was titrated into the FeCl2·4H2O solution at a rate of 0.12 mL / s. After mixing, the stirring was continued for another 15 minutes. The ferrous sulfide suspension was repeatedly screened and washed with deoxygenated ultrapure water for 4 times. Ferrous sulfide microparticles with a particle size range of 60-100 nm were collected. The prepared ferrous sulfide microparticles were freeze-dried and stored under anaerobic conditions to avoid oxidation of the ferrous sulfide microparticles.

[0041] 1.2 Preparation of ferrous sulfide microparticles with a particle size range of 30-60 nm:

[0042] Under anaerobic conditions, 0.3 M FeCl2·4H2O and Na2S·9H2O solutions were prepared separately at a temperature of 25°C. 0.17 ωt.% CMC was added to the FeCl2·4H2O solution, and the stirring speed was adjusted to 230 r / min. The Na2S·9H2O solution was titrated into the FeCl2·4H2O solution at a rate of 0.07 ml / s. After mixing, the stirring was continued for another 23 minutes. The ferrous sulfide suspension was repeatedly screened and washed with deoxygenated ultrapure water for 4 times. Ferrous sulfide microparticles with a particle size range of 30-60 nm were collected. The prepared ferrous sulfide microparticles were freeze-dried and stored under anaerobic conditions to avoid oxidation of the ferrous sulfide microparticles.

[0043] 1.3 Preparation of ferrous sulfide microparticles with a particle size range of 1-30 nm:

[0044] Under anaerobic conditions, 0.3 M FeCl2·4H2O and Na2S·9H2O solutions were prepared separately at a temperature of 25°C. 0.25 ωt.% carboxymethyl cellulose was added to the FeCl2·4H2O solution, and the stirring speed was adjusted to 270 r / min. The Na2S·9H2O solution was titrated into the FeCl2·4H2O solution at a rate of 0.02 ml / s. After mixing, the stirring was continued for another 27 minutes. The ferrous sulfide suspension was repeatedly screened and washed with deoxygenated ultrapure water for 4 times. Ferrous sulfide microparticles with a particle size range of 1-30 nm were collected. The prepared ferrous sulfide microparticles were freeze-dried and stored under anaerobic conditions to avoid oxidation of the ferrous sulfide microparticles.

[0045] II. Construction of ferrous sulfide microparticle-enhanced subsurface flow constructed wetland:

[0046] Firstly, the subsurface flow constructed wetland system is constructed, the depth of the wetland substrate is 0.6 m, and the coarse gravel with a diameter of 4-6 mm (porosity 37%) is filled. Then, 20 g / L of 30-60 nm ferrous sulfide suspension is injected by reverse circulation injection method, i.e. from the effluent outlet to the reverse injection, and from the inlet to the effluent, and the effluent is collected; the injection speed is 8 times of the normal wetland operation flow rate; the effluent is injected into the system again to obtain new effluent, and the cycle is repeated for 5 cycles, until the concentration of suspended ferrous sulfide particles in the effluent is less than 1% of the concentration of injected particles. After the ferrous sulfide particles are immobilized in the interstices of the wetland filler, they are allowed to stand for 6 hours of stable operation, so that they are stably fixed in the interstices of the subsurface flow constructed wetland filler, and then the system can be operated normally. In the wetland, Acorus calamus is planted at a density of 20 plants / m 2 The Acorus calamus is planted in the wetland at a density of 20 plants / m

[0047] III. Treatment of wastewater:

[0048] The composite wastewater is injected into the wetland system through the water inlet device, passes through the wetland substrate from top to bottom, and the purified water is discharged from the water outlet. The overall process is shown in Figure 1

[0049] In the experiment, the wastewater entering the artificial wetland is synthetic wastewater containing nitrate nitrogen and heavy metals, the concentration of nitrate nitrogen in the influent is maintained at 30 mg / L, and as the subsurface flow constructed wetland operates, no heavy metals selenium and chromium are added for the first 12 weeks, chromium and selenium with a concentration of 100 μg / L are added at the 13th week, chromium and selenium with a concentration of 500 μg / L are added at the 20th week, and chromium and selenium with a concentration of 2000 μg / L are added at the 25th week. After treatment by the subsurface flow constructed wetland, the concentration of nitrate nitrogen in the effluent is 3 mg / L, and the average removal rate of nitrate nitrogen is 90%. Figure 2 As can be seen from the graphs of the concentration changes of nitrate nitrogen in the influent and effluent of the subsurface flow constructed wetland with and without the introduction of ferrous sulfide particles, as the operation time and heavy metal concentration increase, the removal rate of nitrate nitrogen by the subsurface flow constructed wetland system with the introduction of ferrous sulfide particles gradually increases and tends to be stable, and the removal rate of nitrate nitrogen is about 90%.

[0050] In the experiment, the wastewater entering the artificial wetland is synthetic wastewater containing nitrate nitrogen and heavy metals, the concentration of nitrate nitrogen in the influent is maintained at 30 mg / L, and as the subsurface flow constructed wetland operates, no heavy metals selenium and chromium are added for the first 12 weeks, chromium and selenium with a concentration of 100 μg / L are added at the 13th week, chromium and selenium with a concentration of 500 μg / L are added at the 20th week, and chromium and selenium with a concentration of 2000 μg / L are added at the 25th week. After treatment by the subsurface flow constructed wetland, the average removal rate of heavy metals chromium and selenium by the artificial wetland with the introduction of ferrous sulfide particles is about 77%, while the average removal rate of heavy metals chromium and selenium by the artificial wetland without the introduction of ferrous sulfide particles is about 15%, as shown in Figure 2 .​Figure 3 The contrast chart of the removal of heavy metals by the subsurface constructed wetland system can show that in different operation periods, the average removal rate of heavy metals by the subsurface constructed wetland system with the introduction of ferrous sulfide particles is about 77%, which is higher than that of the subsurface constructed wetland system without the introduction of ferrous sulfide particles, and it can be seen that the ferrous sulfide particles have high adsorption capacity and strong adsorption capacity for heavy metals.

[0051] From Figure 2 , Figure 3 It can be seen that the subsurface constructed wetland system with the introduction of ferrous sulfide particles can strengthen the removal of heavy metals and simultaneously remove nitrate nitrogen in the composite wastewater, and the ferrous sulfide particles can realize the simultaneous reduction of heavy metals and nitrate nitrogen in the subsurface constructed wetland.

[0052] From Figure 4 The distribution chart of ferrous sulfide with different particle size ranges in the subsurface constructed wetland filled with 4-6mm gravel can show that when the subsurface constructed wetland is filled with 4-6mm coarse gravel, the ferrous sulfide particles with the particle size ranges of 1-30nm and 60-100nm are unevenly distributed in the subsurface constructed wetland, the ferrous sulfide particles with the particle size range of 30-60nm are evenly distributed in the upper, middle and lower parts of the subsurface constructed wetland, which indirectly shows that the uniform distribution of ferrous sulfide particles in the subsurface constructed wetland is conducive to strengthening the removal of nitrate nitrogen by the subsurface constructed wetland system, which shows that the particle size of the introduced ferrous sulfide particles needs to be matched with the particle size of the filler of the subsurface constructed wetland.

[0053] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and the present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A ferrous sulfide microparticle enhanced subsurface flow constructed wetland characterized by, The ferrous sulfide microparticle suspension is injected into the subsurface constructed wetland by reverse circulation injection method; The reverse circulation injection method comprises: a. injecting from the effluent outlet of the subsurface constructed wetland; b. collecting the effluent from the influent inlet of the subsurface constructed wetland and re-injecting the effluent into the effluent outlet of the subsurface constructed wetland; wherein the process b is repeated at least once; The injection speed of the ferrous sulfide microparticle suspension into the subsurface constructed wetland is 5-10 times of the normal wetland operation flow rate of the subsurface constructed wetland; The particle size of the filler in the subsurface constructed wetland is 1-3 mm, and the particle size of the ferrous sulfide microparticle is 1-30 nm; Or, the particle size of the filler in the subsurface constructed wetland is 4-6 mm, and the particle size of the ferrous sulfide microparticle is 30-60 nm; Or, the particle size of the filler in the subsurface constructed wetland is 7-10 mm, and the particle size of the ferrous sulfide microparticle is 60-100 nm.

2. The ferrous sulfide particulate augmented subsurface flow constructed wetland of claim 1, wherein, The process b is repeated 4-5 times.

3. The ferrous sulfide particulate enhanced subsurface flow constructed wetland of claim 1, wherein, The concentration of the ferrous sulfide microparticle suspension is 10-50 g / L.

4. The ferrous sulfide particulate augmented subsurface flow constructed wetland of claim 1, wherein, The preparation process of the ferrous sulfide microparticle comprises: under anaerobic conditions, preparing a ferrous salt solution and a sulfide solution, adding the sulfide solution into the ferrous salt solution containing carboxymethyl cellulose, continuing to stir and react, then washing with deoxygenated water, and freeze-drying to obtain the ferrous sulfide microparticle.

5. The ferrous sulfide particulate enhanced subsurface flow constructed wetland of claim 4, wherein, The concentration of the ferrous salt solution is 0.1-0.5 M, the concentration of the sulfide solution is 0.1-0.5 M, the dropping speed of the sulfide solution is 0.01-0.15 mL / s, the content of the carboxymethyl cellulose is 0.1-0.3 ωt.% of the mass of the ferrous salt solution, the stirring speed is 100-300 r / min, and the stirring time is 10-30 minutes.

6. The ferrous sulfide particulate augmented subsurface flow constructed wetland of claim 4, wherein, The temperature of the preparation process of the ferrous sulfide microparticle is 25-30 ℃.

7. The ferrous sulfide particulate enhanced subsurface flow constructed wetland of claim 1, wherein, After the ferrous sulfide microparticle suspension is injected into the subsurface constructed wetland by the reverse circulation injection method, the system is allowed to stand for 4-8 hours for stable operation.

8. Application of the ferrous sulfide microparticle enhanced subsurface constructed wetland according to any one of claims 1-7 in treatment of industrial wastewater, mining wastewater or tail water of a sewage treatment plant, wherein the industrial wastewater, mining wastewater or tail water of the sewage treatment plant contains heavy metal ions and nitrate nitrogen.

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