CN113603229A

CN113603229A - Method for removing nitrogen and phosphorus from domestic sewage

Info

Publication number: CN113603229A
Application number: CN202110972536.XA
Authority: CN
Inventors: 徐建玲; 刘姣; 王汉席; 盛连喜
Original assignee: Northeast Normal University
Current assignee: Northeastern University China; Northeast Normal University
Priority date: 2021-08-24
Filing date: 2021-08-24
Publication date: 2021-11-05

Abstract

The invention relates to the technical field of sewage treatment, in particular to a method for removing nitrogen and phosphorus from domestic sewage. The invention utilizes domestic sewage to carry out water culture on wetland plants, and utilizes the absorption function, the photosynthesis and the rhizosphere microorganism function of the wetland plants to purify and remove pollutants in the water body.

Description

Method for removing nitrogen and phosphorus from domestic sewage

Technical Field

The invention relates to the technical field of sewage treatment, in particular to a method for removing nitrogen and phosphorus from domestic sewage.

Background

Eutrophication of water bodies causes many problems, and the ecological environment and the production and life of human beings are seriously affected. The harm mainly comprises the following aspects: (1) eutrophication of water generally causes a great amount of algae to propagate, reduces the transparency of the water and seriously hinders the photosynthesis of deep plants, thereby reducing the content of dissolved oxygen in the water, accelerating the death of animals and plants in the water and reducing the stability and diversity of aquatic organisms; (2) the eutrophic water contains partial toxic substances, such as nitrite, nitrate and the like, and if people use the water with the excessive content of the toxic substances as drinking water for a long time, partial diseases and even poisoning can be caused; (3) eutrophication causes water quality deterioration, which can seriously affect the ecological environment, cause aquatic ecosystem degradation and affect ecological landscape.

The treatment of domestic sewage mainly comprises three main categories: physical, chemical and biological methods. The basic principle of the physical method is to remove nitrogen and phosphorus in water through physical or mechanical action; the basic principle of the chemical method is to add chemical substances into the sewage, separate and recover the substances in the sewage by utilizing chemical reaction, or convert the substances into harmless substances, such as adding coagulant, algaecide and the like; the basic principle of the biological method is to utilize the metabolism of microorganisms to oxidize and degrade nitrogen and phosphorus in the wastewater into harmless substances, such as an activated sludge method, a biological filter, an oxidation pond and the like. However, although the physical adsorption method and the chemical method have the advantages of high adsorption speed, simple operation and the like, the physical adsorption method is only suitable for low-concentration nitrogen and phosphorus wastewater, the adsorption material has the problems of difficult recovery and small recycling space, and the chemical method is easy to cause secondary pollution. Although the biological method avoids the shortages of the two methods, large-scale process facilities occupy large area and are not suitable for in-situ repair.

Phytoremediation uses green plants (terrestrial plants, wetland plants, etc.) to transfer, contain and transform pollutants to render them environmentally benign. The mechanism of action is to fully exert the metabolic activity of the plants and the rhizosphere indigenous microorganisms thereof so as to absorb, accumulate, degrade or convert pollutants in the environment. Compared with the traditional water environment restoration technology, the plant restoration technology has the advantages of low cost, good effect, environmental aesthetics and the like; however, different wetland plants have different purification effects on nutrient elements in sewage due to different growth speeds, root types and accumulation capacities, so that the technical problems of slow restoration speed, insignificant effects and the like still exist.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for removing nitrogen and phosphorus from domestic sewage. The purpose of purifying the domestic sewage is realized by performing nitrogen and phosphorus removal on the static water culture wetland plants in the domestic sewage.

The domestic sewage denitrifying and dephosphorizing method is to perform denitrifying and dephosphorizing treatment on static water culture wetland plants in the domestic sewage, wherein the wetland plants are one or more of Siberian iris, acorus calamus and cress.

Furthermore, the wetland plants are placed in clear water for culturing for 10-14 days after being cleaned by clear water, transferred into nutrient solution for culturing for 10-14 days, and transferred into sewage for domestication to be used for nitrogen and phosphorus removal of domestic sewage.

Further, the culture conditions in the clear water, in the nutrient solution and in the acclimatization process are as follows: the ambient temperature is 15-21 ℃, and the illumination time is 8 am to 5 pm;

the nutrient solution comprises the following components in percentage by weight: 920-950mg/L of calcium nitrate, 500-520mg/L of potassium nitrate, 50-100mg/L of ammonium nitrate, 120-150mg/L of monopotassium phosphate, 450-500mg/L of magnesium sulfate, 2-3mL/L of iron salt solution and 5mL/L of trace element solution;

in the iron salt solution: 5-6g/L of ferrous sulfate and 7-8g/L of sodium ethylene diamine tetracetate;

in the trace element solution: 0.75-1mg/L of potassium iodide, 6-7mg/L of boric acid, 21-25mg/L of manganese sulfate, 8-10mg/L of zinc sulfate, 0.2-0.3mg/L of sodium molybdate, 0.02-0.03mg/L of copper sulfate and 0.02-0.03mg/L of cobalt chloride.

Further, the domestication in the sewage specifically comprises:

a low-concentration sewage domestication stage: culturing in clear water, culturing wetland plants in low-concentration sewage for 1-2 days every 2-3 days, and culturing in low-concentration sewage for 3-4 times to convert into medium-concentration sewage acclimation stage;

and (3) a medium-concentration sewage domestication stage: culturing in clear water, placing wetland plants in medium-concentration sewage for culturing for 1-2 days every 2-3 days, culturing for 4-5 times in medium-concentration sewage, and transferring to high-concentration sewage acclimatization stage;

high-concentration sewage domestication stage: culturing in low-concentration sewage, culturing in high-concentration sewage for 1-2 days every 2-3 days, and culturing in high-concentration sewage for 4-5 times to complete acclimation;

wherein the concentration of pollutants in the low-concentration sewage is not higher than: TN 7.5mg/L, NH₄ ⁺-N＝5mg/L，NO₃ ^--N2.5 mg/L, TP 0.5mg/L, COD 30 mg/L; the concentration of pollutants in the medium-concentration sewage is not higher than: TN 10mg/L, NH₄ ⁺-N＝10mg/L，NO₃ ^--N-5 mg/L, TP-1 mg/L, COD-60 mg/L; the concentration of pollutants in the high-concentration sewage is not higher than: TN 30mg/L, NH₄ ⁺-N＝20mg/L，NO₃ ^--N＝10mg/L，TP＝2mg/L，COD＝120mg/L。

Further, the low-concentration sewage, the medium-concentration sewage and the high-concentration sewage also contain an element stock solution with the volume fraction of 0.1%; in the element stock solution: 120mg/L of calcium chloride 110, 420mg/L of magnesium sulfate 400, 12-15mg/L, EDTA 15-20mg/L, KI 0.5.5-1 mg/L of ferrous sulfate, 6-8mg/L of boric acid, 21-24mg/L of manganese sulfate, 8-9mg/L of zinc sulfate, 0.1-0.3mg/L of ammonium molybdate, 0.01-0.03mg/L of copper sulfate and 0.01-0.03mg/L of copper chloride.

Before the water culture wetland plants are subjected to sewage treatment, the wetland plants are domesticated, so that the tolerance of the plants can be improved to a great extent, and the sewage purification capacity is improved while the survival rate of the sewage water culture wetland plants is ensured.

Furthermore, wetland plants are fixedly planted in the fly ash ceramsite matrix, and nitrogen and phosphorus removal is carried out on the wetland plants statically hydroponically in the domestic sewage.

Further, the fly ash ceramsite matrix is of a porous structure, and comprises the following raw materials in parts by weight: 10-20 parts of attapulgite, 10-20 parts of straw, 50-80 parts of fly ash, 10-20 parts of calcium oxide and 1-2 parts of gypsum.

Further, the preparation method of the fly ash ceramsite comprises the following steps: crushing straws, sieving the crushed straws with a 100-mesh sieve, and uniformly mixing the crushed straws with fly ash, calcium oxide, desulfurized gypsum and attapulgite; placing the mixture in a granulator, and spraying water for granulation to obtain ceramsite green balls; and calcining the ceramsite raw ball at the temperature of 500 plus 800 ℃ and the temperature of 1000 plus 1200 ℃ to obtain the fly ash ceramsite.

Further, the heat treatment time at 800 ℃ of 500-DEG C is 1-3h, and the calcination time at 1200 ℃ of 1000-DEG C is 0.5-1 h.

Furthermore, the particle size of the raw ceramsite spheres is 5-15 mm.

Compared with the prior art, the invention has the beneficial effects that:

the invention utilizes domestic sewage to carry out water culture on wetland plants, and utilizes the absorption function, the photosynthesis and the rhizosphere microorganism function of the wetland plants to purify and remove pollutants in the water body.

The Siberian iris in wetland is cold-resistant and heat-resistant, can grow well in shallow water, wetland, shade, dry land or potted plant, has strong disease resistance, particularly resists root rot, and is one of iris with strong adaptability; the acorus calamus grows on the water side with the elevation of 2600 meters or below, the marsh wetland or the lake floating island and has stronger stress resistance; the cress generally grows on low-humidity wetlands, shallow swamps and river banks or in paddy fields, is fond of moist and fertile soil, has strong waterlogging resistance and cold resistance, generally adopts asexual propagation and has higher survival rate. The Siberian iris, the acorus calamus and the cress are planted in a combined mode in a water planting process, and are matched according to the difference of self physiological forms and the difference of nutrient absorption capacity, so that the interaction among plants can be generated, and the removal rate is increased.

The matrix is introduced in the water culture process to construct a water culture plant-matrix combined purification system, on one hand, the matrix can provide a carrier for plant growth, and the removal effect is influenced by influencing the growth of plants, on the other hand, the matrix can directly absorb nitrogen and phosphorus in sewage and is used for the growth and reproduction of microorganisms, and most importantly, a biological film can be formed on the surface layer of the matrix to become a carrier attached by the microorganisms, so that the nitrification and denitrification are facilitated. In the technical scheme, the substrate is prepared into ceramsite green balls by selecting attapulgite, straws, fly ash, calcium oxide and gypsum as raw materials, then two sections of roasting treatment at different temperatures are carried out, the straws absorb water and expand to occupy ceramsite space, the straws are promoted to be predecomposed by one-time roasting, more pore structures are generated inside the ceramsite, gases such as carbon dioxide and the like generated at the same time are adsorbed by calcium oxide to generate solid structures such as calcium carbonate and the like, and the calcium carbonate and the like are decomposed to release the carbon dioxide again by secondary roasting, so that the pore structures of the ceramsite are more abundant and uniform; the attapulgite has a high specific surface area structure and a high water absorption performance, the fly ash is a light material rich in various substance components such as silicon dioxide, aluminum oxide, ferric oxide and the like, and the ceramic prepared by mixing the straw, the calcium oxide, the gypsum and the straw and the calcium oxide can improve the speed of system stability, so that the purification effect is better when the attapulgite is used for high-concentration sewage.

Drawings

FIG. 1 shows the variation of TN concentration in sewage of different concentrations in example 1 of the present invention, wherein (a), (b), (c), and (d) are high, medium, and low concentrations and lake water of a park in this order;

FIG. 2 shows NH in wastewater with different concentrations in example 1 of the present invention₄ ⁺-N concentration variations, wherein (a), (b), (c), (d) are high, medium, low concentration and park lake water in sequence;

FIG. 3 shows NO in wastewater with different concentrations in example 1 of the present invention₃ ^--N concentration variations, wherein (a), (b), (c), (d) are high, medium, low concentration and park lake water in sequence;

FIG. 4 is a graph showing the variation of TP concentration in sewage of different concentrations in example 1 of the present invention, wherein (a), (b), (c), and (d) are high, medium, and low concentrations and lake water of a park in sequence;

FIG. 5 is a graph showing the change of COD concentration in sewage of different concentrations in example 1 of the present invention, wherein (a), (b), (c), and (d) are high, medium, and low concentrations in sequence, and park lake water;

FIG. 6 shows the removal rates of the respective contamination indexes in example 1 of the present invention, in which (a) shows the removal rate of TN and (b) shows NH₄ ⁺Removal rate of-N, in FIG. (c) NO₃ ^-The concentration of N varies, graph (d) shows the removal rate of TP, and graph (e) shows the removal rate of COD;

FIG. 7 is a graph showing the results of the contents of nitrogen and phosphorus in plants in example 1 of the present invention, wherein (a) is the nitrogen content in plants and (b) is the phosphorus content in plants;

FIG. 8 is scanning electron micrographs of the fly ash ceramsite in example 2 before and after the experiment, wherein A and C are before the experiment, and B and D are after the experiment;

FIG. 9 shows the variation of TN concentration in sewage of different concentrations in example 2 of the present invention, wherein (a), (b), and (c) are sequentially high, medium, and low concentrations;

FIG. 10 shows NH in wastewater with different concentrations in example 2 of the present invention₄ ⁺-N, wherein (a), (b), (c) are high, medium, low concentration in sequence;

FIG. 11 shows NO in wastewater with different concentrations in example 2 of the present invention₃ ^--N, wherein (a), (b), (c) are high, medium, low concentration in sequence;

FIG. 12 shows NO in wastewater with different concentrations in example 2 of the present invention₂ ^--N, wherein (a), (b), (c) are high, medium, low concentration in sequence;

FIG. 13 shows the concentration variation of TP in sewage of different concentrations in example 2 of the present invention, wherein (a), (b), and (c) are sequentially high, medium, and low concentrations;

FIG. 14 shows the change of COD concentration in sewage of different concentrations in example 2 of the present invention, wherein (a), (b), and (c) are high, medium, and low concentrations in sequence;

FIG. 15 shows the removal rate of each contamination index in example 2 of the present invention, in which (a) shows the removal rate of TN and (b) shows NH₄ ⁺Removal rate of-N, in FIG. (c) NO₃ ^-Concentration change of N, graph (d) shows the removal rate of TP, graph (c)e) The removal rate of COD is obtained;

FIG. 16 is a graph showing the results of the contents of nitrogen and phosphorus in plants in example 2 of the present invention, wherein (a) represents the nitrogen content in plants and (b) represents the phosphorus content in plants.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

The wetland plants Siberian iris, acorus calamus and cress used in the invention are purchased from the internet, and the roots and leaves of the plants are cleaned by clean water after being purchased, so that the interference to the experiment is prevented. Then putting the wetland plants into clear water for culturing for two weeks to adapt to a new environment, then transferring the wetland plants into nutrient solution for culturing for two weeks, and finally performing sewage acclimation; wherein, the concentration of the nutrient solution is as follows: 945mg/L of calcium nitrate, 500mg/L of potassium nitrate, 80mg/L of ammonium nitrate, 135mg/L of monopotassium phosphate, 500mg/L of magnesium sulfate, 2.5mL/L of iron salt solution and 5mL/L of trace element solution; in the iron salt solution: 5.5g/L of ferrous sulfate and 7.5g/L of sodium ethylene diamine tetracetate; in the trace element solution: potassium iodide 0.8mg/L, boric acid 6.5mg/L, manganese sulfate 23mg/L, zinc sulfate 8.5mg/L, sodium molybdate 0.25mg/L, copper sulfate 0.025mg/L, and cobalt chloride 0.025 mg/L.

The specific domestication process is as follows:

a low-concentration sewage domestication stage: culturing in clear water, culturing the wetland plants in low-concentration sewage for 1 day every 3 days, and culturing the low-concentration sewage for 3 times to convert the plants into a medium-concentration sewage acclimation stage;

and (3) a medium-concentration sewage domestication stage: culturing in clear water, culturing wetland plants in medium-concentration sewage for 2 days every 3 days, culturing in medium-concentration sewage for 4 times, and transferring to a high-concentration sewage acclimatization stage;

high-concentration sewage domestication stage: culturing in low-concentration sewage, culturing in high-concentration sewage for 2 days every 3 days, and culturing in high-concentration sewage for 4 times to complete domestication;

wherein the concentration of pollutants in the low-concentration sewage is not higher than: TN 7.5mg/L, NH₄ ⁺-N＝5mg/L，NO₃ ^--N2.5 mg/L, TP 0.5mg/L, COD 30 mg/L; the concentration of pollutants in the medium-concentration sewage is not higher than: TN 10mg/L, NH₄ ⁺-N＝10mg/L，NO₃ ^--N-5 mg/L, TP-1 mg/L, COD-60 mg/L; the concentration of pollutants in the high-concentration sewage is not higher than: TN 30mg/L, NH₄ ⁺-N＝20mg/L，NO₃ ^--N-10 mg/L, TP-2 mg/L, COD-120 mg/L. The low-concentration sewage, the medium-concentration sewage and the high-concentration sewage also contain element stock solutions with volume fractions of 0.1%; in the element stock solution: 111mg/L of calcium chloride, 410mg/L of magnesium sulfate, 13.9mg/L, EDTA 18.65.65 mg/L, KI 0.83.83 mg/L of ferrous sulfate, 6.2mg/L of boric acid, 22.3mg/L of manganese sulfate, 8.6mg/L of zinc sulfate, 0.25mg/L of ammonium molybdate, 0.025mg/L of copper sulfate and 0.025mg/L of copper chloride.

Example 1

(1) Selecting domesticated wetland plants with similar plant height, biomass, growth condition and the like, putting the plants into water culture boxes according to the content in table 1, putting cut white foam into each water culture box to fix the plants, drilling holes (5cm) on a foam pad at equal intervals to enable plant roots to penetrate through the foam pad, fixing the plants by using sponge to prevent the plants from toppling over, planting 4 plants in each water culture box, placing 4 plants in each wetland plant in a plant system, and placing two plants in each wetland plant in a plant two-two mixed system.

The ambient temperature range during the study was 28-21 ℃. Plant growth lamps were selected to simulate light, 8 am to 5 pm each day. The initial water quality index of the water used in the experimental process is shown in table 2.

In addition, the addition of elemental stock solution to the system was configured according to the Hoagland nutrient solution standard to ensure normal plant growth, the amount of stock solution was in accordance with the volume of wastewater: volume of element stock solution is 1000: 1, namely adding 1ml of stock solution into every 1L of sewage, wherein the indexes of the element stock solution are as follows: 111mg/L of calcium chloride, 410mg/L of magnesium sulfate, 13.9mg/L, EDTA 18.65.65 mg/L, KI 0.83.83 mg/L of ferrous sulfate, 6.2mg/L of boric acid, 22.3mg/L of manganese sulfate, 8.6mg/L of zinc sulfate, 0.25mg/L of ammonium molybdate, 0.025mg/L of copper sulfate and 0.025mg/L of copper chloride.

TABLE 1

TABLE 2

(2) Collecting and determining a water sample: before sampling, the water quality indexes needing on-site measurement comprise pH, dissolved oxygen and water temperature DO by adopting a handheld DO instrument. Before collecting a water sample, the sewage in the incubator is uniformly stirred by a glass rod, and then the water sample is collected by 50mL at the position of 5cm in water depth by an injector. The water body indexes comprise conductivity, Total Nitrogen (TN) and ammonia Nitrogen (NH)₄ ⁺-N), nitrate Nitrogen (NO)₃ ^--N), Total Phosphorus (TP) and Chemical Oxygen Demand (COD), the conductivity is measured by a conductivity meter, and the other indexes are measured by a Green-Kary water quality detector. The water lost by sample collection and evaporation was replenished with distilled water every day.

Collecting and measuring plant samples. Before the experiment, 5 plants of each plant are randomly selected to measure the plant height and the maximum root length, and finally the average number of the plants is taken as an initial value, and the plant height and the maximum root length are measured by using a flexible rule. Randomly selecting a plant to measure the fresh weight, the dry weight and the nitrogen and phosphorus content in the body (dividing into an overground part and an underground part for measurement). Fresh weight and dry weight determination: filtering out water on the surface of the plant by using filter paper, then weighing the plant on an electronic balance, after weighing is finished, putting the plant into a drying oven, deactivating enzyme for 30min at 105 ℃, then drying to constant weight at 80 ℃, and weighing the plant on the electronic balance to obtain the dry weight of the plant. And (3) measuring the total nitrogen content of the plant sample: (1) grinding the plant sample which is dried to constant weight into powder by using a mortar, accurately weighing 0.5g of the plant dry sample, putting the plant dry sample into a digestion tube, and adding 5mL of sulfuric acid (overnight or standing for at least 1 hour); (2) adding 2mL of hydrogen peroxide, standing for a period of time, adding 2mL of hydrogen peroxide once again, heating at 275 ℃ for 7min on a digestion furnace, cooling to room temperature, adding 2mL of hydrogen peroxide, and heating at 370 ℃ for about 1h until a sample in the digestion tube is transparent; (3) and cooling the digestion tube and the digestion solution to room temperature, washing residual digestion solution in the digestion tube into a volumetric flask with 100mL for many times by using a small amount of water, diluting with water to a constant volume of 100mL, and filtering or clarifying to be tested. Simultaneously, the sample blank is digested. The clarified or filtered solution can be used for analyzing total nitrogen and phosphorus.

And (3) determining the water sample by three times of treatment (because the precision of an instrument for determining the water sample is higher, the numerical values of the three repeated treatments are basically consistent, and the difference cannot be reflected). Data statistics and processing were performed using Microsoft Excel 2016, and results were plotted using Origin 9.0. The relative growth rates are expressed as:

wherein, W₁The biomass of the individual plant before the experiment is shown in g, W₂The biomass of the individual plants after the end of the experiment is indicated in g, and t is the time interval between the two measurements, in days.

(3) Analysis of results

Changes of water temperature, pH, DO and conductivity: during the experiment, the water temperature of the water purification system is maintained at 17-21 ℃, DO undergoes the process of first decreasing and then increasing, the pH of the system is maintained in a neutral range, the conductivity does not fluctuate greatly, and the DO slowly decreases along with the time.

Variation of TN concentration: referring to FIG. 1, TN in each system was significantly removed after 30 days of the experiment. In high-concentration sewage, the concentration of TN is always in a descending trend, except for a blank control group, the concentration of TN in other groups is greatly reduced, particularly in an HIA group, and the concentration of TN is already reduced to a class V standard of surface water environmental quality standard. In medium-concentration and low-concentration sewage, the change trend of TN is slightly different from that of high-concentration water, TN is subjected to a slow increasing process, and is reduced after 10 days and gradually becomes stable after 25 days. TN removal effect of MAO group in medium concentration water body is best, and MI group is worst. In the low-concentration water body, the TN concentration at the end of the experiment is from large to small in sequence: LO > LA > LI > LIA > LAO > LIO > LCK. The TN concentration in the park lake water body experimental group is always in a descending trend, and the TN concentration is reduced to be below 0.5mg/L by the end of the experiment, so that the standard of the surface water environment quality standard II is achieved. In general, the removal effect of TN in the high-concentration water body is better than that of TN in the medium-low concentration water body.

③NH₄ ⁺Variation in the concentration of N: see FIG. 2, results show NH in each system₄ ⁺Significant removal of-N was observed. In high concentration sewage, NH⁴⁺the-N concentration always decreased, except for the blank group, the remaining group NH₄ ⁺The N concentrations had all been reduced to a lower level, except for the blank, and the NH levels in the remaining groups₄ ⁺The concentration of N reaches the standard of 'surface water environmental quality standard' class II. In medium and low concentration sewage, NH₄ ⁺The trend of the N goes through a process of increasing and then decreasing. In the medium-concentration water body, the effect of removing the calamus and cress groups is the best. In low concentration sewage, the change is similar to that of high concentration water body, except that the blank experiment group and the rest NH groups₄ ⁺The concentration of N-N is reduced to below 0.5mg/L, which reaches the II-class standard of surface water environmental quality standard. At the end of the experiment, all appeared to be NH in the system of the growing plants₄ ⁺The concentration of-N is lower than that of the blank. NH in lake water of park₄ ⁺The concentration of N shows a tendency to decrease first and then to increase and decrease again, NH by the end of the experiment₄ ⁺the-N concentrations had all dropped below 0.15mg/L, and the removal was similar for each group. Overall, NH in high and low concentrations of wastewater₄ ⁺The removal effect of-N is obvious and is superior to that of middle-concentration sewage and NH in water of parks and lakes₄ ⁺The concentration of N reaches the category I standard of surface water environmental quality standard.

④NO₃ ^-Variation in the concentration of N: see FIG. 3, NO in high concentration wastewater₃ ^-The N concentration had already decreased to a minimum at day 5 and then appeared to increase slowlyThe trend gradually decreases again to the later stage of the experiment. In medium concentration wastewater, except for blank control group, NO₃ ^-The concentration of N shows a gradually decreasing trend in the first 10 days, gradually increases again after the 10 th day and gradually stabilizes after the 25 th day. In low concentration wastewater, except blank control group, the rest groups contain NO₃ ^-The concentration of N is reduced to the minimum value on the fifth day and then gradually increased, and the concentration of N tends to be stable after 25 days, and NO in lake water of a park is stable₃ ^-The trend of the concentration of N is similar to that of sewage with medium and low concentration, but NO is in the later stage of the experiment₃ ^-The concentration of N decreases all the time, and NO in the PI and PA groups at the end of the experiment₃ ^-NO of PO group with N concentration already reduced below 0.1mg/L₃ ^-The concentration of-N has also dropped below 0.4 mg/L.

TP concentration change: referring to FIG. 4, TP decreased in the placebo group at all times in the high concentration wastewater, but increased significantly over time and decreased gradually by 15 days. The concentration of TP in a system for planting plants is in a trend of decreasing after being slightly increased and is obviously reduced to the end of an experiment, wherein the HO group removal effect is best, the concentration of TP is reduced to 0, and the concentrations of HA and HIA group TP are also reduced to 0.01mg/L, thereby reaching the class I standard of surface water environment quality standard. In medium concentration wastewater, the concentration of TP is increased and then decreased, and at the end of the experiment, the concentration of TP in several systems is higher than the initial concentration, the best removal effect is achieved by MAO group, and the concentration of TP is already decreased to 0.14mg/L at the end of the experiment. The change trend of the concentration of TP in the low-concentration sewage is similar to the medium concentration, except that the concentration of TP in each system is lower than the initial concentration at the end of the experiment, the removal effect is the LAO group with the best removal effect, and the LIO group is the LIO group, and the TP removal effect of the mixed plant group is better than that of single plant. The concentration of TP in the lake water of the park is basically in a descending trend all the time, and the TP in each system is basically and completely removed when the experiment is finished.

Sixthly, the change of the COD concentration: see fig. 5. In high-concentration sewage, the COD concentration in a system planted with plants is reduced to below 25mg/L on the 5 th day of the experiment, the COD is slowly reduced subsequently, the COD tends to slowly increase by the last 10 days of the experiment, and the COD concentration in the system planted with plants is reduced to below 20mg/L at the end of the experiment. The change trend of COD in sewage with medium concentration and low concentration is similar to that of high concentration, and at the 5 th day, except for a blank control group, the COD concentration in the other systems planted with plants is reduced to the lowest level of the whole experiment, and then slowly rises along with the lapse of time, but the fluctuation is not large, so that the removal effect of the MIO and LIO groups is the best. In the low-concentration sewage, except the LIO group which has a sharp rise at the 25 th day, the COD concentration of the other groups shows the trend of first decreasing and then rising and falling. The COD in the lake water in the park is low in initial value and tends to fluctuate up and down during the whole experiment, but the amplitude is small, and the COD concentration is still below 24mg/L at the end of the experiment. In general, except the HCK, MO and MIA groups, the COD concentration in other systems reaches the IV-class standard of surface water environmental quality standard at the end of the experiment, namely the COD concentration is below 30 mg/L.

Removing rate of each pollution index: FIG. 6, in which graph (a) shows the removal rate of TN and graph (b) shows NH₄ ⁺Removal rate of-N, in FIG. (c) NO₃ ^-The change in the concentration of N, the removal rate of TP in graph (d), and the removal rate of COD in graph (e). From fig. 7, it can be seen that:

in high concentration wastewater, the systems grown with plants had higher removal rates for TN except for the placebo group, with the highest removal rate for the HIA group. The removal rate of TN in the sewage with medium concentration is obviously lower than that of TN with high concentration, the highest removal rate is MAO group, and the worst removal rate is MI group. Compared with medium-concentration sewage and medium-concentration sewage, the removal rate of TN in each system in the low-concentration sewage is greatly different, wherein the removal rate of TN in the LAO group is a negative value, namely the concentration of TN in the system is higher than the initial value at the end of the experiment, and the removal rate of TN in the other systems is very low although the removal rate is not a negative value. The removal rate of TN by three plants in lake water of the park is higher, which is shown as follows: PI (87.31%) > PA (82.84%) > PO (61.94%), which is easier to remove considering the low initial concentration of contaminants in the water body. In general, the removal rate of TN in high-concentration sewage is obviously better than that of medium-low concentration sewage, and the high-concentration nitrogen provides enough nitrogen source for the growth of plants considering that enough nitrogen is needed for the growth period of the plants to maintain the growth of the plants.

NH in sewage with different concentrations₄ ⁺The removal rate of-N is different from TN, namely NH in sewage with high, medium and low concentration₄ ⁺The removal rate of-N is higher. In high-concentration sewage, the rest groups except the blank control group are NH⁴⁺The removal rate of-N reaches more than 98 percent. NH in sewage with medium concentration₄ ⁺The removal rate of-N is lower than that of high-concentration sewage, the highest removal rate is MAO group, and the worst removal rate is MCK group. NH in low concentration wastewater₄ ⁺The removal rate of-N is similar to that of TN, and the removal rates of the rest groups are about 97% except for LCK group and LI group. In general, compared with TN, NH is treated in sewage with high, medium and low concentration₄ ⁺And N is better removed, wherein the removal rate of the sewage with high and low concentration is higher.

Except high-concentration and park and lake sewage, NO in medium-low concentration sewage₃ ^-The removal rates of-N are all negative values. High concentration of NO in sewage₃ ^-The magnitude of the removal rate of-N is expressed as: HIA (84.96%) > HA (77.73%) > HI (76.30%) > HO (65.46%) > HAO (63.70%) > HCK (60.00%) > HIO (57.90%). NO in medium and low concentration sewage₃ ^-The removal rates of-N are all negative values. In lake water in park, NO₃ ^-The removal rate of-N is expressed as: HI (96.51%) > HA (95.35%) > HO (60.47%).

In high-concentration sewage, except for blank control, the removal rate of TP by other systems reaches over 80 percent, wherein the removal rate of TP by HO group reaches 100 percent, and the removal rate of HA and HIA group also reaches over 99 percent. In medium concentration sewage, except HAO for obviously removing TP, the removal rate of TP by other systems is very low. Except LCK and LI groups, the TP removal rate of other systems in the low-concentration sewage is equivalent to that of the low-concentration sewage, and is over 68 percent. In the lake water in the park, the removal rate of TP by PA and PO groups reaches 100 percent, and the removal rate of TP by PI groups also reaches 85.71 percent. In general, the removal rate of TP in high-concentration sewage is better than that of medium-concentration sewage and low-concentration sewage.

COD in high, medium and low sewage is removed to a certain extent. In general, the removal effect of the high-concentration sewage is the best, except for blank control, the removal rates of other groups to COD are all over 80%, the highest removal rate is the HIA group, and the removal rates of other groups are similar. The removal rate of COD in the sewage with medium concentration and low concentration is obviously lower than that of the sewage with high concentration. In the sewage with medium concentration, the removal rate of the IO group is the highest, and in the sewage with low concentration, the removal rate of the AO group is the highest. The initial COD concentration of the lake water body in the park is low, the removal rate of COD is 0 at the end of the experiment, but the pollution level is still low.

Changing physiological characteristics of plants: after the experiment is finished, the physiological characteristics of the plants are changed to a certain extent. During the whole experiment, the phenomena of massive death and withering of the plants are not found, and the normal growth of the plants is not influenced except that the leaf tips of the plants in an extremely individual system are yellowed. The physiological changes of the plants are shown in table 3. The plant height changes mostly in acorus calamus and next in Siberian iris, the maximum root length of cress is increased greatly, and the maximum root length of cress in high-concentration sewage is increased by more than 17 cm. During the experiment, new leaves were observed to grow on all three plants, and there were also more new roots on Acorus calamus and Oenanthe stolonifera. The table shows the biomass change of the plant as a single plant, the amount of plant growth is the change in biomass before and after the plant was transplanted, and the amount of plant growth is the difference between the biomass of the plant at the end of the experiment and the biomass of the plant before the start of the experiment, calculated as the biomass of the single plant. The growth of the acorus calamus is the greatest in all systems, and it is also observed during the experiment that the growth of the acorus calamus is better than that of the other two plants.

The relative growth rate is an important mark for reflecting the growth condition of the plants, and the influence of different pollution loads on the growth of the plants can be seen by observing the change of the relative growth rate. Under the condition of high concentration, the RGRs of Siberian iris, acorus calamus and cress are respectively 0.020, 0.043 and 0.031/day, under the condition of medium concentration, the RGRs of the three plants are respectively 0.028, 0.045 and 0.037/day, under the condition of low concentration, the RGRs of the three plants are respectively 0.021, 0.042 and 0.029/day, and in the experimental group of water bodies in lakes of parks, the RGRs of the three plants are respectively 0.010, 0.022 and 0.020/day. In general, the relative growth rate of the acorus calamus is the largest under the conditions of three concentrations and lake water in the park.

TABLE 3

Ninthly, nitrogen and phosphorus contents in the plant body: the results are shown in FIG. 7, where (a) is the nitrogen content in the plant and (b) is the phosphorus content in the plant. The plants assimilate the nitrogen and phosphorus in the sewage into self substances through self absorption so as to maintain the normal growth of the plants, thereby removing the nitrogen and phosphorus in the sewage. Under the condition of high concentration, the concentration of nitrogen elements in Siberian iris, acorus and cress respectively reaches the maximum value when Siberian iris-cress mixed seeds, Siberian iris-acorus mixed seeds and acorus-cress mixed seeds are planted. Under the condition of medium concentration, the condition that the concentration of nitrogen elements in the three plants reaches the maximum value is consistent with the condition of high concentration. Under the condition of low concentration, nitrogen elements in the three plants respectively reach the maximum values when Siberian iris-cress are mixed, Siberian iris-acorus calamus is mixed and cress is single. Under three pollution load conditions, the nitrogen content in the three wetland plants is larger in the underground part than in the overground part. Under the condition of high pollution load, except for the mixed planting system of acorus calamus-cress, the nitrogen element concentrations of the overground part and the underground part of the plant are different, which shows that the nitrogen element concentrations of the underground part of the plant are higher than that of the overground part by 10mg/g, and the nitrogen element concentrations of the underground part and the overground part of the plant in other systems are close. Under medium pollution load, the nitrogen element concentration of the overground part and the underground part of the plants in each system has almost the same difference. Under low pollution load, it is shown that the nitrogen concentration in the underground part of iris single and calamus single systems is much higher than that in the above ground part, wherein the underground part of calamus is 21mg/g higher than that in the above ground part.

Under the condition of high concentration, phosphorus elements in Siberian iris, acorus and cress respectively reach the maximum value when Siberian iris-cress mixed seeds, acorus-cress mixed seeds and Siberian iris-cress mixed seeds are planted. Under the condition of medium concentration, the condition that the concentration of phosphorus element in the three plants reaches the highest value is consistent with the high concentration. Under the condition of low concentration, the concentration of phosphorus in the three plants respectively reaches the maximum value when the Siberian iris-cress are mixed, the calamus is single and the cress is single. The phosphorus content of Siberian iris in vivo under three pollution load conditions is shown to be that the above-ground part is larger than the below-ground part, but except the Siberian iris-cress mixed planting system under the low concentration condition, the phosphorus element concentration difference of the above-ground part and the below-ground part in the rest systems is very little. The concentration of phosphorus in the acorus calamus appears to be greater in the underground part than in the above ground part under three pollution load conditions. Cress exhibits a greater phosphorus content in the aerial parts than in the underground parts under high pollution load conditions and a greater phosphorus content in the underground parts than in the aerial parts under medium and low pollution load conditions.

The removal effect of three wetland plants and combination thereof on nitrogen, phosphorus and COD in domestic sewage is researched by constructing a hydroponic plant purification system and measuring the quality of sewage and plant physiological indexes in the water, and the following conclusion is mainly obtained:

(1) the three wetland plants and the combination thereof have good removal effect on nitrogen, phosphorus and COD in the sewage. Under the condition of high concentration, each system has higher removal rate on nitrogen, phosphorus and COD, and the removal effect of the system for planting plants on pollutants is better than that of a blank control group; under the condition of medium concentration, each system is paired with TN and NH₄ ⁺N and COD have certain removal effect; at low concentration, to H₄ ⁺N and COD have better removal effect. (2) Different plants and combinations thereof have different removal effects on pollutants under the same pollution load. Under the condition of high pollution load, the Siberian iris and acorus calamus system has a good removal effect on pollutants, and under the condition of medium and low pollution load, the Siberian iris and acorus calamus system has a high removal rate on pollutants in sewage. (3) The same plant or combination pairThe pollutants under different pollution load conditions have different removal effects. For single plants, Siberian iris under high pollution load conditions has a nitrogen removal rate lower than that of the neutral low pollution load, and the removal effect of phosphorus and COD is better than that of the neutral low pollution load; the removal rate of nitrogen, phosphorus and COD of the calamus and cress under the condition of high pollution load is higher than that of the calamus and cress under the condition of medium and low pollution load. For plant mixed planting, the removal effect of the nitrogen, phosphorus and COD by the system of the three plants mixed planting in pairs is shown to be superior to that of the medium and low pollution load. (4) During the whole experiment, all plants can normally grow under three pollution load conditions, and the phenomena of death and withering do not occur. The plant height change is the calamus, the maximum root length is cress, the growth amount of the maximum root length under the high pollution load condition exceeds 17cm, and the roots of cress are obviously increased after the experiment is finished. The biomass increased most with acorus calamus, and during the experiment it was also observed to grow better than the other two plants, with a significant increase in leaf length and leaf surface area. (5) From the relative growth rate of the plants, the tolerance capacity of the three wetland plants to the pollution load is as follows: rhizoma Acori Calami > Oenanthe stolonifera > Siberian Iris. The relative growth rate of the plants under the condition of high pollution load is lower than that of the plants under the condition of medium and low pollution load, which indicates that the high pollution load has certain inhibiting effect on the growth of the plants. (6) The accumulation amounts of nitrogen and phosphorus in the three plants have certain difference. Under three pollution load conditions, the nitrogen content in Siberian iris is greater in the underground part than in the aerial part, and the phosphorus content is opposite in the aerial part than in the underground part. The nitrogen and phosphorus contents in the acorus calamus body are consistent in specific gravity, and the underground part is larger than the overground part. The content of phosphorus in cress is larger than that of the underground part under high pollution load, and the content of nitrogen and phosphorus in cress is larger than that of the underground part under other conditions.

Example 2

(1) Preparing a matrix: weighing 20 parts of raw materials, namely attapulgite, 20 parts of straws, 50 parts of fly ash, 15 parts of calcium oxide and 2 parts of gypsum; crushing straws, sieving the crushed straws with a 100-mesh sieve, and uniformly mixing the crushed straws with fly ash, calcium oxide, desulfurized gypsum and attapulgite; placing the mixture in a granulator, and spraying water for granulation to obtain ceramsite green balls with the particle size of 10 mm; heating the raw ceramsite balls to 800 ℃ at a speed of 10 ℃/min for heat treatment for 2h, heating to 1200 ℃ at a speed of 20 ℃/min, and calcining for 0.5h to obtain the fly ash ceramsite.

(2) A plastic basket was added to the original apparatus of example 1 to hold the substrate, and a substrate mass of 660g (about 1cm in thickness) was added to each system.

The initial water quality index of the experimental water body is shown in a table 4; the rest of the experimental procedures and statistics of the results are the same as example 1.

TABLE 4

(3) And (4) counting results:

analyzing the shape of a substrate: as shown in fig. 8, from the results of the scanning electron microscope, it can be seen that the fly ash ceramsite before the experiment has a rough surface and a porous interior, which is beneficial to adsorbing pollutants, and the fly ash ceramsite after the experiment has a smooth surface.

Variation of water temperature, DO, pH and conductivity: variation of water temperature, DO, pH and conductivity in wastewater of different concentrations. The water temperature is basically maintained between 17 ℃ and 19.5 ℃, and the method is suitable for the growth of plants. The DO concentration change is obvious, the DO concentration in high-concentration sewage is in a linear descending trend in the first six days and then slowly increases, the change trend of the medium-low concentration sewage is similar, the DO concentration in the high-concentration sewage is in a linear descending trend in the first three days and then gradually increases. The pH value is decreased within the first three days, and then is increased to be stable and basically stabilized between 7.5 and 8.5, and the sewage is in a more neutral state and cannot influence the growth of plants. The conductivity tends to be stable basically at the later stage except for a low state at the beginning, and does not fluctuate too much.

③ change of TN concentration: referring to fig. 9, in the high-concentration wastewater, the concentration of TN in each system in the first six days of the experiment is in a straight-line decreasing trend, except for the HCK and HAO groups, the concentration of TN in the other groups is slowly decreased after the sixth day and finally tends to be stable, while the concentration of TN in the HCK group is increased by a small margin at the time of day 12 and then tends to decrease, the concentration of TN in the HAO group tends to fluctuate after the sixth day and tends to be stable after day 12, and the removing effect is shown as follows: HIA > HAO > HI > HIO > HO > HCK > HA. In medium concentration wastewater, except MI and MAO groups, the rest groups showed straight reduction in the first six days, and then fluctuated up and down, wherein MI group was always reduced along with the progress of the experiment, but slightly increased at the end of the experiment, MAO group was always reduced, MIO group had the best removal effect, and MA experiment group had the worst removal effect. The concentration change trend of TN in the low-concentration sewage is similar to that of high-concentration sewage, except for an LO group, other groups are linearly reduced in the first six days, and fluctuate up and down in the later period, the concentration of TN in the LO group is always reduced, and is reduced to the lowest value in the 12 th day, and is increased after the experiment is finished, so that the LO removal effect is the worst when the experiment is finished, and the TN removal effect is the best by the LIA group.

④NH₄ ⁺Variation in the concentration of N: see FIG. 10, NH in high concentration wastewater at the early stage of the experiment₄ ⁺The concentration of N is in a linear decreasing trend, NH starting from the sixth day₄ ⁺The concentration of-N tends to be stable, and the removal effect is expressed as: HCK > HA > HO > HAO > HIA > HIO > HI. NH in sewage with medium concentration₄ ⁺The concentration of N varied in a similar manner to that of the high concentration test group, except that the removal of the plant-grown system was superior to that of the blank control group, the MA group showed the best removal, and NH was added at the end of the test₄ ⁺The concentration of-N is reduced to 0.21mg/L, which reaches the standard of 'surface water environmental quality standard' class II, and then MIA and MI, NH thereof₄ ⁺The concentration of N reaches the IV-class standard of surface water environmental quality. NH in low concentration wastewater₄ ⁺The trend of the concentration of N varies from high to medium concentration, with a first increase followed by a linear decrease and finally a gradual trend, except for the blank, NH₄ ⁺The concentration of-N is reduced to below 1mg/L, which reaches the III-class standard of surface water environmental quality standard, wherein the LI groupThe best effect is achieved, its NH₄ ⁺The concentration of-N reaches the II standard.

⑤NO₃ ^-Variation in the concentration of N: see FIG. 11, NO of high concentration wastewater₃ ^-The concentration of N and NH₄ ⁺the-N trend is similar and shows a straight-line decline in the early stage and a gentle decline in the later stage, except that the plant-planted system NO₃ ^-The concentration of-N is lower than that of the blank control group, except the blank control group, the NO of the other groups^3-The N concentration is reduced to below 0.1mg/L, and the removal effect is shown as follows: HIA > HI > HIO ═ HA > HAO > HO > HCK. NO in sewage with medium concentration₃ ^-The trend of the concentration of N is different from the high concentration, NO in the four MCK, MIA, MIO and MAO groups₃ ^-The concentration of N decreased until the first nine days, reached the lowest value at the ninth day and then increased, and NO in the MCK group₃ ^-The concentration of-N decreased again at the end of the experiment, and NO in the remaining three groups₃ ^-The concentration of-N then shows a tendency to decrease first and then to increase, then to decrease and then to increase again at the end of the experiment, reaching the lowest value also on the ninth day of the experiment. In low concentration wastewater, except LCK group, NO in other groups₃ ^-The concentration of N is relatively consistent, and shows a trend that the concentration is increased slowly and then decreased and then increased, and reaches a minimum value on the ninth day, and similar to the medium concentration, the LCK group is increased slowly all the first six days, and finally is decreased to the minimum value on the ninth day and then increased, and shows a trend that the concentration is decreased linearly at the end of the experiment.

⑥NO₂ ^-Concentration variation of N, see FIG. 12, configured for NO in artificial wastewater₂ ^-The contents of N and NO being 0 in each case over time₂ ^-The concentration of-N is also increasing, which is related to the conversion of nitrogen elements in water. In high concentration wastewater, the rest of the groups showed a tendency of increasing, then slowly decreasing, and then gradually increasing, except for the HCK and HO groups, which increased much more at the sixth day than the group grown with plants. NO in medium concentration sewage in MI, MA and MIA groups₂ ^-Concentration of-NThe degree increases with time, and the rest groups show a trend of gradual increase in the early stage and gradual decrease in the later stage. In low concentration wastewater, NO was observed in the first nine days of the experiment₂ ^-The concentration of-N was consistently low and did not increase significantly, and then LCK group showed a tendency to increase first and then decrease, LI group showed a slow decrease and then increase, and the rest of groups showed a continuous increase in the later stages of the experiment, considering the increase in DO in water, promoting nitrification.

Concentration change of TP: referring to fig. 13, the TP concentration in the high, medium and low concentration sewage varies more regularly, and the TP has decreased to a lower level on the third day, and then the TP concentration has become stable with the passage of time. In high-concentration sewage, the removal effect of each system on TP in the sewage is equivalent, the best performance is HAO group, the concentration of TP is reduced to 0.23mg/L after the experiment is finished, the III standard of surface water environment quality standard is reached, and the concentration of TP in other groups also reaches the V standard. In the medium-concentration sewage, except for the HIA group, the concentration of TP shows a trend of decreasing along with the progress of the experiment, the concentration of TP in the HIA group is increased to some extent at the ninth day, but then shows a trend of decreasing, and by the end of the experiment, the concentration of TP in each system is reduced to below 0.15mg/L, thereby reaching the III-class standard of surface water environmental quality standard. In low-concentration sewage, the concentration of TP in each system is reduced to be less than 0.1mg/L after the experiment is finished, the II-class standard of surface water environmental quality standard is reached, wherein TP in Siberian iris experiment group is reduced to 0, and the integral removal effect is shown as follows: LI > LA > LAO ═ LO > LIA > LIO > LCK.

(iii) change in COD concentration: referring to fig. 14, the trend of the change in the high-concentration sewage and the medium-concentration sewage is similar. In the high-concentration sewage, except for the HCK group, all the other experimental groups are continuously reduced in the previous six days and then tend to be stable, the HCK group has a small-amplitude rise in the third day, the concentration of COD in the later experimental process is also reduced all the time, except for the HCK group and the HI group, the concentration of COD in all the other groups reaches the II-class standard of surface water environmental quality standard when the experiment is finished, and the removal effect is shown as follows: HIO > HAO > HIA > HO > HA > HCK. In medium-concentration sewage, except MCK groups, other groups show a linear descending trend in the first six days of the experiment, the concentration of COD in the MCK groups is also reduced all the time after the third day, the COD concentration is reduced to the lowest value in the 12 th day, the COD concentration in the MIA group is reduced to 0 in the 12 th day, but the COD concentration is increased to 22mg/L in the 12 th day, and the MAO group has the best removal effect when the whole experiment is finished, and all the other groups except MA and MIA groups reach the II-type standard. The COD concentration change trends in various systems in the low-concentration sewage are inconsistent, wherein the COD concentration in the LO group shows a trend of fluctuation up and down, the rest systems show a trend of descending all the previous nine days, then the LIA and LAO groups slowly ascend all the time, but the fluctuation is small, the rest systems show a slow ascending on the 12 th day and show a descending trend after the experiment is finished, and all the groups reach the II-type standard.

Ninthly, removal rate of each pollution index: FIG. 15 shows the removal rate of TN in graph (a) and NH in graph (b)₄ ⁺Removal rate of-N, in FIG. (c) NO₃ ^-The concentration of N varies, graph (d) shows the removal rate of TP, and graph (e) shows the removal rate of COD;

as can be seen from the figure, in the high-concentration sewage, each system has higher removal rate on TN, wherein the removal rate of TN by HIA groups is the highest, and the removal rate of TN by plant mixed species except HI groups is higher than that of single plant species. In the medium-concentration sewage, the removal rate of TN is lower than that of the high-concentration sewage on the whole, and the removal rate of the TN is higher than that of the medium-concentration sewage by using MIO and MAO groups. The removal rate of TN by the low-concentration sewage is lower than that by the high-concentration sewage and the medium-concentration sewage, and the removal rates of TN by other systems planted with plants except the LIA group are lower than that by the blank control group.

System to NH at various concentrations₄ ⁺There was some degree of removal of-N. In the whole view, NH in high-concentration sewage₄ ⁺The removal rate of-N is lower than that of medium-low concentration sewage. In high concentration sewage, each system is coupled to NH₄ ⁺The removal rate of-N is about 60%. Each system pair NH in medium concentration sewage₄ ⁺The removal rate of-N is different, and the removal rate of the plant system is higher than that of the blank control group. Low concentration sewage seed NH₄ ⁺The removal rate and the median concentration of N are comparable, with the highest removal rate being the LI group followed by the LAO group and also expressed as NH vs. plant grown systems₄ ⁺The removal rate of N is higher than that of a blank control group;

NO in sewage with different concentrations₃ ^-There is a large difference in the removal rate of-N. In high concentration sewage, each system is to NO₃ ^-The removal rate of-N reaches more than 85%, and the removal rate of the system planted with plants is higher than that of a blank control group. Medium concentration wastewater, except MCK, MIO and MAO groups, the other systems are NO₃ ^-The removal rates of-N were all 0. In low concentration wastewater, except for blank control group, other systems are used for NO₃ ^-The removal rates of-N are all negative values.

The removal rate of TP in the low-concentration sewage is higher than that of high-medium concentration sewage, and the removal rate of TP in the high-medium concentration sewage is basically equal. In high-concentration sewage, the highest removal rate is the HAO group, and the removal rates of other systems to TP are all up to more than 80%. In medium-concentration sewage, the MO group has the highest TP removal rate, and except the MI group, the TP removal rates of other groups planted with plants are higher than those of the blank control group. In the low-concentration sewage, except for the blank control, the removal rate of TP by other systems reaches over 90 percent, and the removal rate of TP by the system for planting plants is higher than that of the blank control due to the similarity of the medium concentration.

In the high-concentration sewage, each system has higher removal rate to COD, and the removal rate of mixed plant is higher than that of single plant, the removal rate of the system with the plant to the COD is higher than that of a blank control group, and the HIO group with the best removal effect is adopted. In the sewage with medium concentration, the removal rate of COD is lower than that of the sewage with high concentration as a whole, and the removal rate is represented as follows: MAO (93.94%) > MO (80.30%) > MIO ═ MCK (71.21%) > MIA (66.67%) > MA (63.64%). In low-concentration sewage, the removal rate of COD by each system is lower than that of high-concentration sewage, but the removal rate of COD by other systems except the LIA group also reaches more than 60%.

Change in physiological properties of plants in r: after the experiment is finished, the plant height, the maximum root length and the biomass of the plant are increased to a certain extent. During the whole experiment, the phenomena of massive plant death and withering are not found, and only a few plants have the condition of leaf rolling. The plant height, maximum root length and biomass changes are shown in Table 5. In general, the biggest plant height change is acorus calamus which is increased by more than 5cm, then Siberian iris and finally cress, especially in high-concentration and medium-concentration experimental groups, the plant height of the acorus calamus is obviously increased, the maximum root length of the acorus calamus and the cress is increased more, the maximum root length of the acorus calamus and the cress is increased by more than 10cm basically, and the maximum root length of the Siberian iris is increased less. It can be seen from the table that the growth of the acorus calamus is the largest in all experimental groups, which indicates that the acorus calamus has stronger stress resistance and can better adapt to different environments, and the growth of the acorus calamus is better than that of other two plants in the experimental process.

Under high concentration conditions, the RGRs of Iris sibirica, Acorus calamus and Oenanthe stolonifera are respectively 0.028, 0.092 and 0.056/day, under medium concentration conditions, the RGRs of the three plants are respectively 0.048, 0.096 and 0.072/day, and under low concentration conditions, the RGRs of the three plants are respectively 0.066, 0.082 and 0.084/day. The RGR of the three wetland plants under the medium concentration and low concentration conditions is greater than that under the high concentration condition, and the RGR of the acorus calamus is significantly greater than that of Siberian iris and slightly greater than that of cress.

TABLE 5

Nitrogen and phosphorus contents in plant bodies: see FIG. 16, where (a) is the nitrogen content in the plant and (b) is the phosphorus content in the plant. Different plants have different nitrogen contents in the plant body under the same pollution load condition. Under the condition of high load pollution, the nitrogen contents of the Siberian iris, the overground part and the underground part of the acorus calamus have no obvious difference, and the nitrogen content of the underground part of the cress has no obvious differenceThe amount of nitrogen element in the three plants is obviously higher than that in the overground part, the nitrogen element concentration in the three plants respectively reaches the maximum value when Siberian iris-cress mixed seeds, Siberian iris-acorus hybrid seeds and acorus-cress mixed seeds are mixed, and the maximum value is the same as that when no matrix is added. The conditions that the concentration of nitrogen elements in the three plants reaches the maximum value under the condition of medium and low concentration are also the same as those of the experimental group without adding the matrix. Under the condition of medium-load pollution, the nitrogen content in Siberian iris and Acorus calamus shows that the underground part is slightly larger than the overground part, and the cress shows that the overground part is slightly larger than the underground part, but the difference of the nitrogen element concentration of the overground part and the underground part of the plants in each experimental group is very little. Under the condition of low pollution load, the nitrogen content of the underground parts of the three plants is higher than that of the overground parts.

The specific gravity of the phosphorus content in the plant body is different from the nitrogen content. Under the condition of high concentration, the phosphorus concentration in the three plants respectively reaches the maximum value when the Siberian iris-cress mixed seeds, the acorus calamus-cress mixed seeds and the cress are single seeds, and the conditions when the other two plants reach the maximum value except the cress are the same as those of an experimental group without the matrix. Under the condition of medium concentration, the nitrogen concentration in the three plants respectively reaches the maximum value when Siberian iris single species, calamus-cress mixed species and calamus-cress mixed species are planted. Under the condition of low concentration, the condition that the phosphorus element concentration in the three plants reaches the maximum value is the same as that of high concentration. Under three pollution load conditions, Siberian iris shows that the phosphorus content of the overground part is greater than that of the underground part, the phosphorus content in the calamus shows that the underground part is greater than that of the overground part, the phosphorus content in the cress under the high pollution load condition is greater than that of the underground part, and the phosphorus content in the water cress under the medium and low pollution load condition is greater than that of the underground part, but the difference is small.

In the embodiment, the selected fly ash ceramsite has larger specific surface area and porosity, and has better removal effect on pollutants. The addition of the matrix improves the speed of system stabilization, and compared with an experimental group without the matrix, the time for the system to achieve stabilization is shortened by one time. The addition of matrix afforded removal of a portion of the contaminants as compared to the experimental group without matrix additionIn the experimental group with the added matrix, the content of nitrogen and phosphorus in the plant body is obviously lower than that of the plant body without the added matrix, which indicates that a part of nitrogen and phosphorus is removed through the adsorption effect of the matrix, and particularly the removal of phosphorus is most obvious. Although the experimental time is doubled compared with the experimental time without adding the matrix, the experimental group with the fly ash ceramsite has NH₄ ⁺The removal rate of-N and TP is high.

Through constructing a water culture plant-substrate combined purification system, measuring the water quality of sewage and plant physiological indexes, the removal effect of three wetland plants and combination of the three wetland plants and the substrate on nitrogen, phosphorus and COD in the sewage is researched, and the following conclusion is mainly obtained:

(1) the fly ash ceramsite has a good adsorption effect on nitrogen and phosphorus in sewage, and compared with a system without adding the matrix, the addition of the matrix improves the removal effect of each system on pollutants, and improves the speed of the system to reach stability. From the result of a scanning electron microscope, a smooth biological film is formed on the surface layer of the substrate during the experiment, which is beneficial to the attachment of microorganisms, thereby improving the purification effect.

(2) The substrate has certain promotion effect on the growth of the three wetland plants. Compared with an experimental group without the added matrix, the relative growth rate of the three plants in the experimental group with the fly ash ceramsite is higher, which shows that the existence of the matrix provides a good environment for plant roots and promotes the growth of the plants.

(3) Different plants and combinations thereof have different removal effects on pollutants under the same pollution load. Under the condition of high pollution load, the system for the mixed planting of two plants has better removal effect on pollutants. Under the condition of medium pollution load, the better nitrogen removal effect is the siberian iris + cress and acorus + cress system, the better phosphorus removal effect is cress, the better COD removal effect is acorus + cress, and therefore, the better removal effect of acorus and cress on phosphorus in sewage can be obtained. Under the condition of low pollution load, the Siberian iris has better capacity of removing pollutants in domestic sewage.

(4) The same plant or combination has different removal effects on pollutants under different pollution load conditions. Overall, the system exhibited both nitrogen and COD removal rates as high pollution load greater than medium and low pollution load conditions. The removal of the phosphorus is shown to have stronger removal capacity under the condition of low pollution load, and the removal effect of the system on the phosphorus is similar under the conditions of high and medium pollution load.

(5) The addition of the matrix increases the growth rate of the plant in terms of the relative growth rate of the plant. The change rule is similar to that of an experimental group without adding a matrix, the RGR under the condition of high pollution load is smaller than that of a medium and low pollution load, and the RGR of the acorus calamus and the cress is obviously larger than that of the Siberian iris, which indicates that the Siberian iris has the worst tolerance capability to the pollution load.

(6) The contents of nitrogen and phosphorus in the three wetland plants are different. Under the conditions of high and medium load pollution, the nitrogen content in Siberian iris and Acorus calamus has no obvious difference, while the nitrogen content of the underground part of cress under the condition of high pollution load is slightly higher than that of the overground part, and the nitrogen content of the underground part of three plants is higher than that of the overground part under the condition of low pollution load. Under three pollution load conditions, Siberian iris shows that the phosphorus content of the overground part is greater than that of the underground part, the phosphorus content in the calamus shows that the phosphorus content of the underground part is greater than that of the overground part, and the phosphorus content difference between the overground part and the underground part of the cress is small.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.

Claims

1. The method for removing nitrogen and phosphorus from domestic sewage is characterized in that nitrogen and phosphorus are removed by statically water-culturing wetland plants in the domestic sewage, wherein the wetland plants are one or more of Siberian iris, acorus calamus and cress.

2. The method for removing nitrogen and phosphorus from domestic sewage according to claim 1, wherein the wetland plants are cleaned by clean water to remove nitrogen and phosphorus from the domestic sewage, and then cultured in clean water for 10-14 days, transferred into nutrient solution for 10-14 days, and then transferred into the sewage for acclimatization.

3. The method for removing nitrogen and phosphorus from domestic sewage according to claim 2,

the culture conditions in the clear water, in the nutrient solution and in the domestication process are as follows: the ambient temperature is 15-21 ℃, and the illumination time is 8 am to 5 pm;

4. The method for removing nitrogen and phosphorus from domestic sewage according to claim 2, wherein said acclimating in the sewage comprises:

wherein the concentration of pollutants in the low-concentration sewage is not higher than: TN 7.5mg/L, NH₄ ⁺-N＝5mg/L，NO₃ ^--N＝2.5mg/L，TP＝0.5mg/L，COD＝30 mg/L; the concentration of pollutants in the medium-concentration sewage is not higher than: TN 10mg/L, NH₄ ⁺-N＝10mg/L，NO₃ ^--N-5 mg/L, TP-1 mg/L, COD-60 mg/L; the concentration of pollutants in the high-concentration sewage is not higher than: TN 30mg/L, NH₄ ⁺-N＝20mg/L，NO₃ ^--N＝10mg/L，TP＝2mg/L，COD＝120mg/L。

5. The method of claim 4, wherein the low, medium and high concentration sewage further comprise a stock solution of elements with a volume fraction of 0.1%;

in the element stock solution: 120mg/L of calcium chloride 110, 420mg/L of magnesium sulfate 400, 12-15mg/L, EDTA 15-20mg/L, KI 0.5.5-1 mg/L of ferrous sulfate, 6-8mg/L of boric acid, 21-24mg/L of manganese sulfate, 8-9mg/L of zinc sulfate, 0.1-0.3mg/L of ammonium molybdate, 0.01-0.03mg/L of copper sulfate and 0.01-0.03mg/L of copper chloride.

6. The method for removing nitrogen and phosphorus from domestic sewage according to any one of claims 1 to 5, wherein wetland plants are planted in the fly ash ceramsite matrix, and nitrogen and phosphorus removal is performed on the wetland plants statically cultured in the domestic sewage.

7. The method for removing nitrogen and phosphorus from domestic sewage according to claim 6, wherein the fly ash ceramsite matrix has a porous structure, and comprises the following raw materials in parts by weight: 10-20 parts of attapulgite, 10-20 parts of straw, 50-80 parts of fly ash, 10-20 parts of calcium oxide and 1-2 parts of gypsum.

8. The method for removing nitrogen and phosphorus from domestic sewage according to claim 7, wherein the preparation method of the fly ash ceramsite comprises the following steps: crushing straws, sieving the crushed straws with a 100-mesh sieve, and uniformly mixing the crushed straws with fly ash, calcium oxide, desulfurized gypsum and attapulgite; placing the mixture in a granulator, and spraying water for granulation to obtain ceramsite green balls; and calcining the ceramsite raw ball at the temperature of 500 plus 800 ℃ and the temperature of 1000 plus 1200 ℃ to obtain the fly ash ceramsite.

9. The method for removing nitrogen and phosphorus from domestic sewage according to claim 8, wherein the heat treatment time at 500-800 ℃ is 1-3h, and the calcination time at 1000-1200 ℃ is 0.5-1 h.

10. The method for removing nitrogen and phosphorus from domestic sewage of claim 8, wherein the diameter of said ceramsite raw pellet is 5-15 mm.