Method for treating wastewater through cooperation of modified agricultural waste and pyrrhotite

Abstract

The invention belongs to the technical field of wastewater treatment, and provides a method for treating wastewater by modified agricultural wastes and pyrrhotite. The method comprises the following steps: mixing modified corncobs and pyrrhotite, inoculating sulfur autotrophic denitrification sludge to obtain a mixture, and carrying out nitrogen and phosphorus removal treatment on wastewater by the mixture to obtain treated wastewater, the mass ratio of the modified corncob to the pyrrhotite is 1: (85-95). Heterotrophic denitrification and autotrophic denitrification coexist in the mixed nutrition type reactor, synchronous nitrogen and phosphorus removal of low-pollution water lacking organic carbon is achieved, and the modified corncobs and the pyrrhotite have a good removal effect on nitrogen and phosphorus pollution in tail water of an urban sewage treatment plant under the synergistic action of the modified corncobs and the pyrrhotite. In a continuous dynamic experiment, the denitrification kinetics is zero level, which indicates that the reaction rate is kept consistent under the determined concentration, and the denitrification process is in an efficient and stable state.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for treating wastewater by using modified agricultural waste in conjunction with pyrrhotite. Background Art

[0002] The denitrification process requires organic carbon to provide electron donors to convert NO3 - -N is reduced to NO2 - -N, then NO2 - -N is reduced to N2 to achieve nitrogen removal, but the organic carbon concentration in the tail water of the sewage treatment plant is very low, which makes the deep denitrification and phosphorus removal of the tail water very poor. Adding carbon sources is an effective way to increase the carbon-nitrogen ratio of the tail water and improve the denitrification effect. Agricultural waste, which has a wide range of sources, is low-cost and easy to obtain. It is a natural cellulose solid carbon source. Its stable organic carbon release over a long period of time and its rough and porous surface structure make it an ideal choice for denitrification solid carbon sources. The use of agricultural waste in the process of deep denitrification and phosphorus removal not only solves the problem of low organic carbon content in the tail water, but also makes resource utilization of agricultural waste.

[0003] Adding a carbon source is one of the solutions to the problem that alkalinity is consumed during the autotrophic denitrification of pyrrhotite, causing the pH of the system to decrease. Ideally, the introduction of a carbon source will cause partial heterotrophic denitrification in the system. Heterotrophic denitrification can effectively reduce the production of by-products in the autotrophic denitrification process, thereby maintaining a relatively balanced state of the system. Denitrification using two different nutritional methods can be carried out stably and effectively.

[0004] Therefore, it is of great significance to study a method for treating wastewater by using modified agricultural waste in combination with pyrrhotite and to improve the effects of nitrogen removal and phosphorus removal. Summary of the invention

[0005] The purpose of the present invention is to provide a method for treating domestic sewage by using modified agricultural waste in order to overcome the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for treating wastewater by using modified agricultural waste in combination with pyrrhotite, comprising the following steps:

[0008] The modified corn cob and pyrrhotite are mixed and then inoculated with sulfur autotrophic denitrification sludge to obtain a mixture, and the mixture is used to remove nitrogen and phosphorus from wastewater to obtain treated wastewater;

[0009] The mass ratio of modified corncob to pyrrhotite is 1:85-95.

[0010] Preferably, the particle size of the pyrrhotite is 3-5 mm; and the mixing temperature is 20-30°C.

[0011] Preferably, the modified corn cob is obtained by alkali treatment of corn cob, the reagent for alkali treatment is sodium hydroxide solution, the mass concentration of sodium hydroxide solution is 1.8-2.2%, the temperature of alkali treatment is 33-37°C, and the time is 18-22h.

[0012] Preferably, the preparation process of the sulfur autotrophic denitrification sludge is: activated sludge and liquid culture medium are mixed and enriched and cultured in an anaerobic environment to obtain sulfur autotrophic denitrification sludge; the volume ratio of activated sludge to liquid culture medium is 1:3.5-4.5.

[0013] Preferably, the temperature of the enrichment culture is 20-30° C., and the time of the enrichment culture is 16-20 days.

[0014] Preferably, during the enrichment culture, the liquid culture medium is replaced every 4 days.

[0015] Preferably, the liquid culture medium uses sodium thiosulfate as a sulfur source.

[0016] Preferably, the hydraulic retention time of the denitrification and dephosphorization treatment is 22 to 26 days.

[0017] 1) Heterotrophic and autotrophic denitrification coexist in the mixed nutrition reactor of the present invention. Pyrrhotite has a good effect on phosphorus removal in the tail water of sewage treatment plants. By synergistically modifying corn cobs and pyrrhotite, low-pollution water lacking organic carbon can be denitrified and dephosphorized simultaneously. The concentration gradient method is used to enable the modified corn cob to cooperate with the pyrrhotite reactor to achieve rapid startup, short biofilm formation time, good biofilm activity, and good denitrification effect in the medium term, with a nitrate removal rate of more than 82%. The method of the present invention has a good effect in the treatment of low-pollution water.

[0018] 2) With the increase of influent nitrate concentration, the denitrification rate of the co-reactor also increased, and the highest denitrification rate was 2.34 mg / (L·h), when the influent nitrate concentration was 80 mg / L. With the increase of influent phosphate concentration, the phosphorus removal rate also increased, and the highest phosphorus removal rate reached 0.28 mg / (L·h), when the influent phosphate concentration was 12 mg / L, but the denitrification of the co-reactor was poor at this concentration.

[0019] 3) After the co-reactor had been running stably for a period of time, the COD effluent concentration was no higher than 40 mg / L. The acid-base balance was well maintained during the operation of the co-reactor, so that the denitrification process was always in a stable state. The sulfate concentration showed a downward trend over time, indicating that the problem of sulfate production by autotrophic denitrification of pyrrhotite can be improved by using modified corn cobs to coordinate pyrrhotite denitrification.

[0020] 4) The scanning electron microscopy results show that before the denitrification and phosphorus removal reaction, the surfaces of the modified corn cob and pyrrhotite showed a rough and porous morphology, which provided good conditions for the attachment of the biofilm, allowing the biofilm to firmly adhere to the surface. At the same time, the porous structure helps to increase the specific surface area of ​​the material, thereby improving the adsorption of phosphate. After the reaction, the surfaces of the modified corn cob and pyrrhotite were almost covered with biofilm, which indicates that during the experiment, the biofilm grew well and the modified corn cob and pyrrhotite synchronous denitrification and phosphorus removal denitrification reactor operated stably.

[0021] 5) In a continuous 15-day dynamic experiment of simulated urban sewage treatment plant tailwater with HRT = 24h, influent nitrate concentration of 15mg / L, influent phosphate concentration of 3mg / L, the average effluent nitrate concentration was 2.05mg / L, the average removal rate was 86.98%, the average effluent phosphate concentration was 0.40mg / L, the average removal rate was 86.98%, and the pH was stable at 7.0-7.6, indicating that the modified corncob and pyrrhotite have a good removal effect on nitrogen and phosphorus pollution in the tailwater of urban sewage treatment plants. In the continuous dynamic experiment, the denitrification kinetics is zero order, indicating that the reaction rate remains consistent at a certain concentration, and the denitrification process is in an efficient and stable state. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a photo of corncob and pyrrhotite of the present invention;

[0023] Figure 2 The modified corncob cooperative pyrrhotite reactor of the present invention;

[0024] Figure 3 The concentration and removal rate of nitrate nitrogen in the effluent of the reactor during the biofilm formation stage in Example 1 vary with time;

[0025] Figure 4 is the nitrate concentration and average removal effect of the effluent from the co-reactor at different HRTs;

[0026] Figure 5 are the nitrite and ammonia nitrogen concentrations of the effluent from the co-reactor at different HRTs;

[0027] Figure 6 is the phosphate concentration and removal rate of the effluent from the co-reactor at different HRTs;

[0028] Figure 7 is the nitrate nitrogen concentration of the effluent from the co-reactor under different nitrate nitrogen influent concentrations;

[0029] Figure 8 are the nitrite and ammonia nitrogen concentrations of the effluent from the co-reactor at different nitrate influent concentrations;

[0030] Fig. 9 is the phosphate concentration of the effluent from the co-reactor at different nitrate influent concentrations;

[0031] Fig.10 is the nitrate nitrogen concentration and average removal rate of the effluent of the co-reactor under different phosphate influent concentrations;

[0032] Fig.11 are the nitrite nitrogen and ammonia nitrogen concentrations of the effluent from the co-reactor at different phosphate influent concentrations;

[0033] Fig.12 It is the change of COD concentration and pH in the whole process of the coordinated reactor;

[0034] Fig.13 It is the change of sulfate concentration in the effluent of the coordinated reactor during the whole reaction process;

[0035] Fig.14 The scanning electron microscope images of modified corncobs and pyrrhotite before being added to the reactor, wherein A and B are modified corncobs, and C and D are pyrrhotite;

[0036] Fig.15 The scanning electron microscope images of the modified corncob and pyrrhotite after the reactor was denitrified and dephosphorized, wherein A, B, and C are modified corncobs, and D, E, and F are pyrrhotite;

[0037] Fig.16 The effect of modified corncob in synergistic pyrrhotite reactor on dynamic removal of nitrate;

[0038] Fig.17 The effect of modified corncob in synergistic pyrrhotite reactor on dynamic removal of phosphate;

[0039] Fig.18 Dynamic pH of a modified corncob-synergistic pyrrhotite reactor. DETAILED DESCRIPTION

[0040] The present invention provides a method for treating wastewater by using modified agricultural waste in combination with pyrrhotite, comprising the following steps:

[0041] The modified corn cob and pyrrhotite are mixed and then inoculated with sulfur autotrophic denitrification sludge to obtain a mixture, and the mixture is used to remove nitrogen and phosphorus from wastewater to obtain treated wastewater;

[0042] The mass ratio of modified corncob to pyrrhotite is 1:85-95.

[0043] In the present invention, the mass ratio of modified corncob to pyrrhotite is preferably 1:88-92, and more preferably 1:90.

[0044] In the present invention, the particle size of the pyrrhotite is preferably 3-5 mm, more preferably 3.5-4.5 mm, and more preferably 4 mm; the mixing temperature is preferably 20-30°C, more preferably 22-28°C, and more preferably 24-25°C.

[0045] In the present invention, the modified corn cob is preferably obtained by alkali treatment of corn cob, the alkali treatment reagent is preferably sodium hydroxide solution, the mass concentration of the sodium hydroxide solution is preferably 1.8-2.2%, more preferably 2%, the alkali treatment temperature is preferably 33-37°C, more preferably 35°C, and the alkali treatment time is preferably 18-22h, more preferably 20h.

[0046] In the present invention, the preparation process of the sulfur autotrophic denitrification sludge is preferably: activated sludge and liquid culture medium are mixed and enriched and cultured in an anaerobic environment to obtain sulfur autotrophic denitrification sludge; the volume ratio of activated sludge to liquid culture medium is preferably 1:3.5-4.5, and more preferably 1:4.

[0047] In the present invention, the temperature of the enrichment culture is preferably 20 to 30° C., more preferably 23 to 27° C., and more preferably 25° C., and the time of the enrichment culture is preferably 16 to 20 days.

[0048] In the present invention, during the enrichment culture, the liquid culture medium is preferably replaced every 4 days.

[0049] In the present invention, the liquid culture medium preferably uses sodium thiosulfate as a sulfur source.

[0050] In the present invention, the hydraulic retention time of the denitrification and dephosphorization treatment is preferably 22 to 26 days, more preferably 23 to 25 hours, and even more preferably 24 hours.

[0051] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0052] In the present invention, total nitrogen (TN) was determined by potassium persulfate oxidation-ultraviolet spectrophotometry, total phosphorus (TP) was determined by potassium persulfate digestion, and ammonium nitrogen (NH4 + -N) was determined by Nessler's reagent spectrophotometry, chemical oxygen demand (COD) was determined by potassium dichromate digestion UV spectrophotometry, and pH was determined by METTLER FE28 pH meter.

[0053] The contents of each component in the liquid culture medium are: KH2PO4 20mg / L, NH4Cl 5mg / L, NaHCO3 10mg / L, MgSO4·7H2O 10mg / L, Na2S2O3·5H2O 50mg / L, FeSO4·7H2O 0.1mg / L, NaNO3 20mg / L; trace elements 1mL / L; the contents of each component in the trace elements are: C 10 H 16 N2O850mg / L, CaCl2·2H2O 55mg / L, (NH4)6Mo7O 24 ·4H2O11mg / L, FeSO4·7H2O50mg / L, ZnSO4·7H2O 22mg / L, MgSO4·7H2O 50mg / L, NiSO4·6H2O4.2mg / L, MnCl2·4H2O 50mg / L, CoCl2·6H2O 16mg / L, CuSO4·5H2O 16mg / L.

[0054] The activated sludge was taken from the denitrification sludge of a sewage treatment plant in Shunyi District, Beijing, with a water content of 99%; the pyrrhotite was collected from the natural pyrrhotite in Jinan City, Shandong Province, with a particle size of 3 to 5 mm.

[0055] Example 1

[0056] Wash and dry the corn cobs and break them into 1 cm pieces. 3 The corn cob was soaked in a sodium hydroxide solution with a mass concentration of 2% at 35° C. for 20 hours, and then washed and neutralized, and then dried and weighed again to obtain a modified corn cob.

[0057] 100 mL of activated sludge was inoculated in a thread-mouth bottle, and 400 mL of liquid culture medium was replaced every 4 days at 25°C. After each replacement, nitrogen was introduced for 5 minutes to exclude air and maintain an anaerobic state. After 5 replacements, sulfur autotrophic denitrification sludge was obtained. During the enrichment culture, NaHCO3 was added to meet the needs of sulfur autotrophic denitrification for inorganic carbon while maintaining the pH of the reactor stable, sodium thiosulfate was added to meet the needs of sulfur autotrophic denitrification for sulfur, and sodium acetate was added to meet the needs of heterotrophic denitrification for organic carbon.

[0058] After 25g of modified corn cob and 2250g of pyrrhotite were mixed evenly, they were added to a plexiglass column reactor (450mm high, 5cm from the bottom of the water inlet, and 10cm from the top of the water outlet), and the enriched sulfur autotrophic denitrification sludge was inoculated into the corn cob synergistic pyrrhotite reactor (synergistic reactor). The reaction temperature was 25°C. The biofilm was started according to the parameters shown in Table 1. After the biofilm was successfully formed, 300mL of simulated wastewater was added to the reagent bottle and placed in a constant temperature shaking incubator with the temperature set to 35°C and the speed set to 80r / min.

[0059] Table 1 Water quality of the influent in the start-up phase of the biofilm formation in the co-reactor

[0060]

[0061] The first stage of biofilm formation in the collaborative reactor lasted for 8 days, with an influent COD of 600 mg / L and a carbon-nitrogen ratio of 3.87. The biofilm began to recover its denitrification function. The second stage lasted for 7 days, with the influent COD adjusted to 400 mg / L and a carbon-nitrogen ratio of 2.58. The carbon-nitrogen ratio decreased in this stage, but the nitrate concentration in the effluent increased slightly compared with the first stage, indicating that the biofilm gradually adapted to the organic carbon released by sodium acetate and modified corn cobs as carbon sources. The third stage lasted for 5 days, with the influent COD continuing to decrease to 200 mg / L and the carbon-nitrogen ratio of 1.29. The carbon-nitrogen ratio was further reduced on the basis of the previous stage. The carbon-nitrogen ratio in this stage did not meet the theoretical value of 2.86 for heterotrophic denitrification, heterotrophic denitrification was affected, and the average effluent concentration of nitrate nitrogen increased significantly. When the COD concentration was 200 mg / L, the theoretically reducible sulfate concentration was 69.93 mg / L, and the actual reduced nitrate nitrogen concentration was 131.73 mg / L, indicating that the organic carbon released by the modified corn cob provided electron donors for the biofilm in the reactor and began to reduce nitrate. At this time, the co-reactor successfully formed biofilm.

[0062] The changes of nitrate nitrogen concentration and removal rate of the reactor effluent in the biofilm formation stage of Example 1 over time are shown in the following table: Figure 3 As shown, during the initial 8-day adaptation period, the nitrate removal rate increased from 42.36% to 82.25%, and the effluent concentration decreased from 89.34 mg / L to 27.62 mg / L, indicating that the activated sludge was gradually recovering its denitrification function during this stage, and biofilm gradually began to form on the surfaces of modified corn cobs and pyrrhotite. During 9-21 days, the reactor maintained an average removal rate of 82.88%, and the average nitrate effluent concentration was 26.59 mg / L. During 22-25 days, the amount of sodium thiosulfate added as a sulfur source was very small, and no organic carbon source was added to the reactor. During this period, the average nitrate effluent concentration was 27.12 mg / L, and the removal rate was 82.58% on average. It was already possible to clearly observe the appearance of yellow-brown biofilm on the surfaces of modified corn cobs and pyrrhotite particles, and the synergistic reactor successfully formed a biofilm.

[0063] Example 2

[0064] After the biofilm was successfully formed in Example 1, the nitrogen and phosphorus removal effects of the co-reactor were tested at different HRTs of 24 h, 12 h and 18 h, respectively, and the nitrate concentration of the influent was 15 mg / L.

[0065] The nitrate concentration and average removal effect of the effluent from the co-reactor at different HRTs are shown in Figure 2. Figure 4 As shown. The HRT of the co-reactor was controlled to be 24h, 12h, and 18h ​​in sequence, and the average nitrate nitrogen effluent concentrations were 2.13mg / L, 6.55mg / L, and 5.31mg / L, respectively, and the average removal rates were 85.8%, 56.3%, and 64.6%, respectively; when the HRT was 24h, the co-reactor had the best denitrification removal effect; the nitrate removal rates were basically the same when the HRT was 12h and 18h, and shortening the HRT reduced the mass transfer time of nitrate nitrogen to the biofilm on the surface of the modified corn cob and pyrrhotite particles. When the HRT was 12h, the carbon release of the modified corn cob was insufficient under the shorter HRT conditions, and the sulfur release in the pyrrhotite was also insufficient, the denitrification reaction was not fully carried out, and the denitrification rate was low, resulting in the highest nitrate nitrogen effluent concentration.

[0066] The concentrations of nitrite and ammonia nitrogen in the effluent of the co-reactor at different HRTs are as follows: Figure 5 As shown. At different HRTs, the nitrite effluent concentration does not exceed 1 mg / L. Except for a brief peak at 1 to 2 days, the concentration is extremely low at other times. This shows that a relatively complete denitrification reaction occurs in the co-reactor, and nitrite is quickly and thoroughly reduced to nitrogen. A longer HRT is conducive to the reduction of nitrite, while a shorter HRT will lead to the accumulation of nitrite in the mixed denitrification reactor. When the HRT is 24h, the concentration of ammonia nitrogen in the effluent is high, and the concentration is low for most of the other time. Pyrrhotite is introduced into the denitrification system as a sulfur source. The introduction of sulfide in the sulfur autotrophic system will lead to the enhancement of DNRA. DRNA bacteria will compete with denitrifying bacteria for nitrate and use pyrrhotite as an electron donor to dissimilate nitrate into ammonium.

[0067] Phosphate concentration and removal rate of the effluent from the co-reactor at different HRTs Figure 6As shown. The phosphate inlet concentration was 3.26 mg / L. Within the initial 4 days, the average phosphate outlet concentration of the co-reactor was reduced to 0.74 mg / L under the condition of HRT = 24 h, and the average removal rate was 77.3%; when HRT = 12 h, the average phosphate outlet concentration was 1.29 mg / L, and the average removal rate was 60.4%; when HRT = 18 h, the average phosphate outlet concentration was 0.78 mg / L, and the average removal rate was 76.1%. When HRT = 24 h and 18 h, the phosphate outlet concentration was basically the same, and the difference was not large when HRT was 12 h, 24 h and 18 h, and it had a good phosphorus removal effect overall. In the initial stage of the reaction in the column reactor (0-20 days), the HRT of this stage is 24h. Pyrrhotite fails to release enough iron ions to precipitate phosphate, resulting in unsatisfactory phosphate removal effect. However, as the reaction proceeds, more iron ions are released through the denitrification reaction on the surface of pyrrhotite. This process improves the phosphate removal rate and ultimately basically completely removes the phosphate.

[0068] Example 3

[0069] After the biofilm was successfully formed in Example 1, the reactor was operated for 20 days at an HRT of 24 h and the nitrate nitrogen concentrations of the influent were 15 mg / L, 40 mg / L and 80 mg / L, respectively, to test the effects of different nitrate influent concentrations on the denitrification and phosphorus removal performance of the synergistic reactor.

[0070] The nitrate nitrogen concentration in the effluent of the co-reactor under different nitrate nitrogen influent concentrations is as follows Figure 7 When the concentration is 15 mg / L, the average effluent concentration is 1.26 mg / L, and the average denitrification rate is 0.66 mg / (L·h); when the concentration is 40 mg / L, the average effluent concentration is 2.77 mg / L, and the average denitrification rate is 1.70 mg / (L·h); when the concentration is 80 mg / L, the average effluent concentration is 24.41 mg / L, and the average denitrification rate is 2.34 mg / (L·h).

[0071] Changes of nitrite and ammonia nitrogen concentrations in the effluent of the co-reactor under different nitrate influent concentrations Figure 8 The nitrite nitrogen effluent concentration remained at a low level during the reaction and did not fluctuate significantly, indicating that the reduction of nitrate to nitrite nitrogen was the limiting step of denitrification in the co-reactor.

[0072] The phosphate concentration of the effluent from the co-reactor under different nitrate influent concentrations is as follows: Fig. 9When the nitrate nitrogen concentration was 40mg / L, 80mg / L and 15mg / L, and the average phosphate influent concentration was 3.11mg / L, the average phosphate effluent concentration was 0.46mg / L, 0.41mg / L and 0.43mg / L, and the average removal rates were 85.21%, 86.82% and 86.17%, respectively. With the increase of nitrate influent concentration, the phosphate removal rate increased slightly, and Fe 2+ and Fe 3+ Iron ions are the key factors affecting the phosphorus removal effect of the reactor. The increase of nitrate concentration can promote the decomposition of pyrrhotite and the production of iron ions, and can precipitate and flocculate more phosphates. However, for the removal of low-concentration phosphates, the phosphate removal rates of 15 mg / L nitrate-nitrogen influent concentrations are basically the same as those of 80 mg / L nitrate-nitrogen influent concentrations. A nitrate influent concentration of 15 mg / L can meet the requirements for phosphorus removal in low-pollution water.

[0073] Example 4

[0074] After the biofilm was successfully formed in Example 1, the reactor was operated for 15 days at HRT of 24 h and the phosphate concentrations of the influent were 3 mg / L, 6 mg / L and 12 mg / L, respectively, to test the effects of different phosphate influent concentrations on the denitrification and phosphorus removal performance of the synergistic reactor.

[0075] The nitrate nitrogen concentration and average removal rate of the effluent of the co-reactor under different phosphate influent concentrations are shown in Figure 2. Fig.10 As shown. When the phosphate concentration is 3 mg / L and the nitrate concentration is 15.7 mg / L, the average nitrate effluent concentration is 2.16 mg / L, and the average removal rate is 86.24%; when the phosphate concentration is 6 mg / L and the nitrate concentration is 16.7 mg / L, the average nitrate effluent concentration is 1.96 mg / L, and the average removal rate is 88.26%; when the phosphate concentration is 3 mg / L and the nitrate concentration is 15.2 mg / L, the average nitrate effluent concentration is 7.18 mg / L, and the average removal rate is 52.76%. The denitrification effect of the synergistic reactor is basically the same when the phosphate influent concentration is 3 mg / L and 6 mg / L. When the phosphate concentration is increased to 12 mg / L, the denitrification effect of the reactor becomes worse. The reason is that the pores on the surface of pyrrhotite are blocked when the phosphate concentration is too high, which reduces the mass transfer of sulfur in pyrrhotite and makes it difficult for the biofilm to obtain sulfur sources, resulting in poor denitrification effect.

[0076] The concentrations of nitrite nitrogen and ammonia nitrogen in the effluent of the co-reactor under different phosphate influent concentrations are as follows: Fig.11 As shown. The nitrite nitrogen concentration in the reactor effluent did not exceed 0.4 mg / L, and the ammonia nitrogen concentration in the reactor effluent did not exceed 0.6 mg / L. The competition between denitrifying bacteria and DNRA bacteria for nitrate was not affected by the phosphate influent concentration, nor did it affect the nitrite nitrogen and ammonia nitrogen effluent concentrations.

[0077] Example 5

[0078] After the biofilm was successfully formed in Example 1, the biofilm was operated for a total of 126 days under the conditions of HRT of 24 h, nitrate concentration of the influent of 15 mg / L, and phosphate concentration of the influent of 3 mg / L. The COD concentration and pH changes over time were tested throughout the process. 10 mL of sample was taken every 24 h to test the COD concentration, pH change, and sulfate concentration of the effluent.

[0079] The COD concentration and pH changes during the whole reaction of the co-reactor are as follows Fig.12 As shown. After the co-reactor has been running stably for a period of time, the COD effluent concentration is stable at about 25 mg / L. The effluent pH value is 6.6-8, which is generally stable, indicating that the co-reactor can maintain the pH balance, which is conducive to the continuous denitrification process. There are two factors that determine the pH change in the reactor: (1) pyrrhotite autotrophic denitrification will produce acid, which will reduce the pH; (2) heterotrophic denitrification will produce alkalinity, which will increase the pH. It can be seen that the synergistic effect of heterotrophic and autotrophic denitrification can solve the problem of excessive acid or alkali production.

[0080] The change of sulfate concentration in the effluent of the co-reactor during the whole process is as follows Fig.13 On the first day of the synergistic reactor reaction, the sulfate concentration reached the highest value at this stage, which was 516.20 mg / L. The reason was that in order to meet the need for sulfur source for sulfur autotrophic denitrification in the biofilm stage, the added sodium thiosulfate was oxidized to produce a large amount of sulfate. As the process progressed, the sulfate concentration showed a gradual downward trend, indicating that compared with the use of pyrrhotite alone for autotrophic denitrification, the synergistic denitrification process helps to reduce the production of sulfate and the production of by-products.

[0081] Scanning electron microscope (SNE-4500M Plus) images of modified corncobs and pyrrhotite before addition to the reactor are shown in Fig.14 As shown, A and B are modified corncobs, and C and D are pyrrhotite. It can be observed in the figure that pyrrhotite particles and modified corncobs show similar surface morphology. Both modified corncobs and pyrrhotite show surface characteristics full of voids. Pyrrhotite has a honeycomb porous structure. In Figure D, it can be seen that there are voids on the surface that can penetrate into the pyrrhotite particles inside the ore. These voids are not only conducive to the attachment and growth of biofilms, but also more conducive to the adsorption of phosphorus by pyrrhotite.

[0082] The scanning electron microscope images of the modified corncob and pyrrhotite after the reactor was completed Fig.15As shown, A, B, and C are modified corn cobs, and D, E, and F are pyrrhotite. The synergistic reactor introduces pyrrhotite, combining heterotrophic and autotrophic denitrification, and the rough surfaces of pyrrhotite and modified corn cobs can fix microorganisms, especially the pyrrhotite surface has protrusions and grooves, which can better enable the biofilm to contact with the modified corn cob to obtain carbon source after mixing with the modified corn cob.

[0083] Example 6

[0084] After the biofilm formation in the reactor of Example 1 was completed, a dynamic experiment was carried out by continuous operation for 15 days under the conditions of HRT = 24h, nitrate nitrogen concentration of the inlet water of 15-17 mg / L, and phosphate concentration of the inlet water of 2.9-3.3 mg / L to test the dynamic denitrification and phosphorus removal effect of the modified corn cob in conjunction with the pyrrhotite reactor.

[0085] Dynamic nitrate removal effect of modified corncob in synergistic pyrrhotite reactor Fig.16 As shown. Within 15 days of continuous reaction, the modified corncob synergistic pyrrhotite reactor has a good performance in the removal of nitrate. When the inlet nitrate concentration is 15-17 mg / L, the outlet concentration can reach below 2 mg / L, with an average removal rate of 86.98% and a maximum removal rate of 89.25%, indicating that the modified corncob synergistic pyrrhotite reactor is suitable for deep denitrification of low-pollution water.

[0086] Effect of modified corncob and pyrrhotite reactor on dynamic removal of phosphate Fig.17 As shown. Within 15 days of continuous reaction, the modified corncob synergistic pyrrhotite reactor has a good effect on phosphate. When the influent phosphate concentration is 2.9-3.3 mg / L, the effluent concentration can reach below 0.5 mg / L, with an average removal rate of 86.98% and a maximum removal rate of 89.25%, indicating that the modified corncob synergistic pyrrhotite reactor is suitable for deep phosphorus removal in low-pollution water.

[0087] Dynamic pH value of modified corncob pyrrhotite reactor Fig.18 The pH of the reactor with modified corncob and pyrrhotite did not change much during the continuous reaction for 15 days, and the reactor remained in a stable state, indicating that the modified corncob and pyrrhotite can avoid autotrophic denitrification SO4 2- The problem of low pH value caused by excessive effluent is beneficial to the removal of nitrogen and phosphorus from the tail water of urban sewage treatment plants.

[0088] The present invention uses agricultural waste corn cobs as a solid carbon source for heterotrophic denitrification after being treated with alkali and modified, and uses pyrrhotite as an electron donor for sulfur autotrophic denitrification to achieve mixed nutrition denitrification, and achieves the simultaneous removal of nitrogen and phosphorus elements during the denitrification process, thereby solving the problems of low content of electron donors such as organic matter in the tail water of urban sewage treatment plants, slow denitrification rate, and weak phosphorus removal capacity. In a continuous dynamic experiment of modified corn cobs in coordination with pyrrhotite, when the hydraulic retention time is 24h and the influent nitrate and phosphate concentrations are 15mg / L and 3mg / L respectively, the pH is generally stable between 7.0 and 7.5. The surface modified corn cobs in coordination with pyrrhotite can maintain a stable pH, which is conducive to the progress of denitrification, and has a good treatment effect on the tail water of urban sewage treatment plants.

[0089] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for treating wastewater by using modified agricultural waste in combination with pyrrhotite, characterized in that: The following steps are included: The modified corn cob and pyrrhotite are mixed and then inoculated with sulfur autotrophic denitrification sludge to obtain a mixture, and the mixture is used to remove nitrogen and phosphorus from wastewater to obtain treated wastewater; The mass ratio of modified corncob to pyrrhotite is 1:85-95.

2. The method according to claim 1, characterized in that The particle size of the pyrrhotite is 3-5 mm; the mixing temperature is 20-30°C.

3. The method according to claim 1 or 2, characterized in that: The modified corn cob is obtained by alkali treatment of the corn cob, the reagent for the alkali treatment is a sodium hydroxide solution, the mass concentration of the sodium hydroxide solution is 1.8-2.2%, the temperature of the alkali treatment is 33-37° C., and the time is 18-22 hours.

4. The method according to claim 1, characterized in that: The preparation process of the sulfur autotrophic denitrification sludge is as follows: activated sludge and liquid culture medium are mixed and then enriched and cultured in an anaerobic environment to obtain sulfur autotrophic denitrification sludge; the volume ratio of activated sludge to liquid culture medium is 1:3.5-4.

5.

5. The method according to claim 4, characterized in that The temperature of the enrichment culture is 20-30° C., and the time of the enrichment culture is 16-20 days.

6. The method according to claim 5, characterized in that During the enrichment culture, the liquid culture medium was replaced every 4 days.

7. The method according to claim 6, characterized in that The liquid culture medium uses sodium thiosulfate as a sulfur source.

8. The method according to claim 7, characterized in that The hydraulic retention time of the denitrification and dephosphorization treatment is 22 to 26 days.

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