Iron-mediated EGSB-type pd / anammox-feps coupled system and wastewater treatment method

Abstract

The application discloses an iron-mediated EGSB type PD / anammox-FePs coupling system and a wastewater treatment method, and belongs to the technical field of wastewater treatment. The iron-mediated EGSB type PD / anammox-FePs coupling system comprises an EGSB reactor and a water inlet system. The water outlet end of the water inlet system is communicated with the bottom of the EGSB reactor. The water inlet system comprises an organic carbon source storage tank, an iron source storage tank, a nitrogen-containing wastewater storage tank, a pump body and pipelines. The organic carbon source storage tank, the iron source storage tank and the nitrogen-containing wastewater storage tank are respectively communicated with the bottom of the EGSB reactor through the pipelines. The pipelines are provided with a reflux pump and a circulating fan to optimize the flow state distribution. The iron mediation improves the nitrogen metabolism intensity and the electron transfer capacity of the system, optimizes the microbial community structure, promotes the formation of high-efficiency mass transfer particles, and then realizes the simultaneous and efficient removal of nitrogen and phosphorus under the condition of low HRT.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment, and particularly relates to an iron-mediated EGSB type PD / anammox-FePs coupling system and a wastewater treatment method. BACKGROUND

[0002] The traditional biological denitrification process of sewage combines nitrification and denitrification. In the nitrification process, NH4 + -N is converted into NO2 - -N by ammonia-oxidizing bacteria, and then NO2 - -N is converted into NO3 - -N by nitrite-oxidizing bacteria. Subsequently, NO3 - -N is gradually converted into N2 under the action of denitrifying bacteria. Since the nitrification process requires a large amount of aeration, and the denitrification process requires an external carbon source, the traditional biological denitrification process has a high cost. The traditional biological phosphorus removal utilizes phosphate-accumulating microorganisms, and the phosphorus release and phosphorus absorption processes exhibited under anaerobic conditions and aerobic or anoxic conditions achieve the removal of phosphorus in sewage. The biological phosphorus removal is achieved by absorbing more phosphorus in the aerobic stage than releasing phosphorus in the anaerobic stage, and by removing the excess sludge containing high polymer content. This traditional biological phosphorus removal process requires external aeration and carbon source, and there is secondary removal of phosphorus in the excess sludge, resulting in a high cost.

[0003] Since the discovery of anaerobic ammonium oxidation (anammox) in the 1990s, anammox has attracted widespread attention due to its environmentally friendly characteristics. In an anaerobic environment, pollutants NH4 + -N and NO2 - -N are removed in the form of N2, without aeration and with less excess sludge, greatly saving energy input. In practical applications, the anammox process is often combined with partial nitrification (PN) or partial denitrification (PD) to provide stable NO2 - -N for the anammox process. However, due to the difficulty of stable inhibition of NOB in the PN / anammox system, it is difficult to provide stable NO2 - -N, and the effluent cannot avoid the problem of residual NO3 - -N. Therefore, PD / anammox has more advantages, and the specific reaction equation is as follows.

[0004] Partial denitrification (PD):

[0005] NO3 -+0.083 C6H 12 O6→ NO2 - +0.5 CO2+0.5 H2O

[0006] Anammox:

[0007] NH4 + +1.32 NO2 - +0.066 HCO3 - +0.13 H + →0.066 CH2O 0.5 N 0.15 +1.02 N2+0.26 NO3 -

[0008] +2.03 H2O

[0009] (1) Denitrification process based on PD / anammox process

[0010] The existing heterotrophic PD / anammox process is a wastewater treatment technology based on the synergistic effect of denitrification and anammox. It mainly includes the following aspects: first, denitrification provides reaction substrates for anammox. In the process of denitrification, NO3 - -N acts as an electron acceptor and is converted into NO2 - -N under the action of enzyme. By inhibiting NO2 - -N reductase, it reduces the generation of N2O and consumes organic matter to generate CO2. Second, part of the denitrification consumes dissolved oxygen in the process of consuming organic matter, providing a low-oxygen environment for anammox, and the CO2 generated by denitrification can be used as an inorganic carbon source for anammox. At the same time, anammox consumes intermediate product NO2 - -N, reducing the impact of NO2 - -N accumulation on the denitrification process and avoiding the further reduction of NO2 - -N to N2O. Anammox uses NO2 - -N and NH4 + -N as reaction substrates, and finally converts them into N2, and the released energy is used for CO2 synthesis of organic matter and life activities.

[0011] Currently, the application of PD / anammox process is still limited to the treatment of low load wastewater using sequential batch reactor (SBR), because SBR has complete mixing characteristics, which can avoid the problem of high concentration at the bottom of upflow reactor, however, due to the need for intermittent water feeding and drainage, SBR cannot be continuously operated, and has a long hydraulic retention time, which cannot meet the requirements of large flow wastewater treatment. At present, although some upflow reactors can increase the treatment load to a certain extent, they often face the problems of sludge floating and uneven influent concentration leading to inhibition of anammox process by high concentration of organic matter. Therefore, it is of great significance to reform the existing PD / anammox process to enable it to stably treat high load sewage.

[0012] (2) Anammox-based phosphorus removal process

[0013] In terms of phosphorus recovery, biological mineralization technology combined with anammox shows great potential. Although the anammox process in a completely anaerobic system limits the growth and reproduction of phosphate-accumulating microorganisms. In recent years, it has been found that by adding metal ions Ca 2+ to the anammox reactor, the alkalinity is generated near the cells during the biological reaction process, and under the conditions of high concentration of Ca 2 + and PO4 3- , the calcium phosphate solution tends to be saturated near the cell wall, inducing the formation of crystal nucleus and the growth of minerals, and the phosphorus is recovered in the form of hydroxyapatite (Ca 10 (PO4)6(OH)2, HAP), and HAP can provide habitat for microorganisms, allowing biomass and crystals to grow synchronously, forming an anammox-HAP multi-layer particle structure, which provides new possibilities for anammox phosphorus recovery. Although biological mineralization technology has opened up a new direction for phosphorus removal, due to the high alkalinity of HAP suitable for pH range (> 8), it is difficult to generate HAP under neutral and acidic conditions, which limits the efficiency of phosphorus removal. On the other hand, the required reaction substrates for anammox are NO2 - -N and NH4 + -N, and the content of NO2 - -N in natural water bodies or contaminated water bodies is relatively low, which cannot provide stable reaction substrates for anammox, so the anammox process alone cannot be applied to the treatment of actual wastewater.

[0014] The existing PD / anammox process is difficult to cope with stable operation under high nitrogen load:

[0015] Due to the coupling of partial denitrification and anammox, it depends on the NO3 --N is reduced to NO2 - -N, so that sufficient organic carbon source is needed to meet the first step of the denitrification reduction process. Therefore, when the one-stage heterotrophic PD / Anammox process is applied to treat high-nitrogen load wastewater, the COD load therein is inevitably too high, thereby causing inhibition to anammox. Therefore, the existing one-stage heterotrophic PD / anammox process is difficult to meet the high-nitrogen load treatment requirement, and the current PD / anammox treatment sewage load is concentrated below 3 g N / L / d. The SBR has high stability during operation, but the HRT is long, and high load demand cannot be met. The upflow reactor shortens the HRT to meet the high load requirement, but the current upflow reactor is often affected by the inhibition of high-concentration organic matter to anammox, sludge floating and other problems, and cannot be stably operated.

[0016] The pure PD / anammox process or the anammox-HAP process cannot realize simultaneous denitrification and phosphorus removal in actual application:

[0017] During the operation of the pure PD / anammox process, the alternation of aerobic and anaerobic conditions is not involved, so that simultaneous phosphorus removal cannot be realized under the anaerobic condition required for denitrification. Although the anammox-HAP process can promote phosphorus removal and particle formation by adding Ca 2+ - -N content in the conventional water body is extremely low, which cannot meet the actual nitrogen removal of anammox, and Ca 2+ has no promoting effect on nitrogen removal. The existing technology cannot produce coupling particles of denitrifying bacteria, anammox bacteria and inorganic minerals. SUMMARY

[0018] The purpose of the present application is to provide an iron-mediated EGSB type PD / anammox-FePs coupling system and a wastewater treatment method, so as to overcome at least one of the above-mentioned defects in the prior art.

[0019] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0020] The iron-mediated EGSB type PD / anammox-FePs coupling system provided by the present application comprises an EGSB reactor and a water inlet system, the water outlet end of the water inlet system is in communication with the bottom of the EGSB reactor, and the water inlet system comprises an organic carbon source storage tank, an iron source storage tank, a nitrogen-containing wastewater storage tank, a pump body and a pipeline, the organic carbon source storage tank, the iron source storage tank and the nitrogen-containing wastewater storage tank are respectively in communication with the bottom of the EGSB reactor through the pipeline, and the pipeline is provided with the pump body.

[0021] ​Preferably, the system further comprises a circulating fan and a circulating air pipe, the circulating air pipe is communicated with the exhaust port at the top of the EGSB reactor, the circulating air pipe has two outlets, one of which is externally discharged, and the other is communicated with the bottom of the EGSB reactor, and the circulating air pipe is provided with the circulating fan.

[0022] Preferably, the system further comprises a backflow pump, a backflow pipe, a circulating pump and a circulating water pipe, the EGSB reactor comprises a reaction zone and a three-phase separation zone, the three-phase separation zone is located above the reaction zone, the three-phase separation zone has two water outlets, one of the water outlets of the three-phase separation zone is communicated with the backflow pipe, the other end of the backflow pipe is communicated with a pipe close to the bottom of the EGSB reactor, the backflow pipe is provided with the backflow pump, the upper end of the circulating water pipe is communicated with the upper part of the reaction zone, the lower end of the circulating water pipe is communicated with the lower part of the reaction zone, and the circulating water pipe is provided with the circulating pump.

[0023] Preferably, the EGSB reactor is an upflow EGSB reactor, a sequencing batch EGSB reactor or a two-stage EGSB reactor.

[0024] The application also provides a wastewater treatment method, which uses the EGSB type PD / anammox-FePs coupling system to treat wastewater, and comprises the following steps: S1, inoculating short-cut denitrification and anaerobic ammonia oxidation composite sludge in the EGSB reactor; S2, feeding nitrogen-containing wastewater into the EGSB reactor, and then feeding an organic carbon source and an iron source into the EGSB reactor, so that the short-cut denitrification and anaerobic ammonia oxidation composite sludge and phosphorus in the nitrogen-containing wastewater spontaneously couple to form PD / anammox-FePs particles under biological induction by the mediation of the external iron source, so as to realize the denitrification and phosphorus removal treatment of the nitrogen-containing wastewater.

[0025] Preferably, the organic carbon source is C2H3O2Na·3H2O, and the iron source is zero-valent iron, divalent iron or an iron-containing mineral; when the iron source is divalent iron, the iron source is FeSO4·7H2O-EDTA.

[0026] Preferably, the total nitrogen concentration of the nitrogen-containing wastewater is 170-190 mg / L, the NO3 - -N concentration is 90-110 mg / L, the NH4 + -N concentration is 70-90 mg / L, and the iron concentration of the iron source is 30-40 mg / L.

[0027] Preferably, the hydraulic retention time of the EGSB reactor is 0.60-0.65 h, the nitrogen load is 6.74-6.94 g N / L / d, the backflow ratio is 1.6-2.0:1, the reaction pH value is 7.5-7.8, the reaction temperature is 33-37℃, the EGSB reactor is an upflow EGSB reactor, and the upflow velocity is 1.63-1.83 m / h.

[0028] Preferably, the PD / anammox-FePs granules have a particle size of at least one of <2 mm, 2-4 mm, >4 mm.

[0029] Preferably, the PD / anammox-FePs granules have a surface attached with a biofilm, the biofilm includes a bacterial flora and EPS secreted by sludge, the inside of the PD / anammox-FePs granules has a FePs and biomass coupling body, the bacterial flora includes anaerobic ammonia oxidation bacteria and denitrifying bacteria, the anaerobic ammonia oxidation bacteria are wrapped in the denitrifying bacteria.

[0030] The beneficial effects of the present application are:

[0031] 1. The iron-mediated EGSB-type PD / anammox-FePs coupling system reduces the demand for organic carbon sources in the denitrification process, reduces the inhibition of organic carbon sources on the anammox flora, and meets the treatment needs of high-concentration pollutants, while efficiently removing nitrogen and reducing carbon emissions.

[0032] 2. The PD / anammox-FePs coupling system improves key enzyme activity under iron mediation, improves system electron transfer capacity, and promotes faster reactions to meet the efficient removal of pollutants under short HRT conditions.

[0033] 3. In the PD / anammox-FePs coupling system, by adding iron, physical, chemical and biological mineralization is achieved, efficient phosphorus removal is achieved on the basis of simultaneous nitrogen removal, phosphorus is intercepted in the reactor in the form of FePs minerals, the formed crystals provide points for microbial attachment and promote sludge granulation, and a unique granular structure of denitrifying bacteria on the outside and anammox bacteria on the inside is formed, which can protect anammox from environmental impact and provide a basis for efficient material and electron exchange.

[0034] 4. The iron-mediated EGSB-type PD / anammox-FePs coupling system realizes a better collaborative mode of denitrification process (partial denitrification, complete denitrification and autotrophic denitrification) and anammox flora, and realizes stable operation under high load. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a structural diagram of the iron-mediated EGSB-type PD / anammox-FePs coupling system of the present application.

[0036] Figure 2 is a sludge structure diagram in the iron-mediated EGSB-type PD / anammox-FePs coupling system of the present application.

[0037] Figure 2 a is a sludge morphology diagram of the first stage of the present application.

[0038] Figure 2 b is a sludge morphology map of the Vth stage of the present application.

[0039] Figure 2 c is an overlay fluorescence sludge map of denitrifiers and anammox bacteria in the Vth stage sludge of the present application.

[0040] Figure 2 d is a sludge map of the Vth stage of the present application with denitrifier probe labeled (blue).

[0041] Figure 2 e is a sludge map of the Vth stage of the present application with Amx820 probe labeled (red).

[0042] Figure 2 f is an optical microscope observation map of the Vth stage sludge of the present application.

[0043] Figure 2 g is a SEM map of the Vth stage sludge of the present application.

[0044] Figure 2 h is an EDS observation map (C) of the Vth stage sludge of the present application.

[0045] Figure 2 i is an EDS observation map (O) of the Vth stage sludge of the present application.

[0046] Figure 2 j is an EDS observation map (P) of the Vth stage sludge of the present application.

[0047] Figure 2 k is an EDS observation map (Fe) of the Vth stage sludge of the present application.

[0048] Figure 2 1 is an internal division map of the Vth stage SEM observed sludge granule of the present application.

[0049] Figure 3 is a micro-characterization map of the three particle sizes of PD / anammox-FePs granules of the present application.

[0050] Figure 3 a is a micro-characterization map of PD / anammox-FePs granules of the present application (small granule).

[0051] Figure 3 b is a micro-characterization map of the first surface biofilm of PD / anammox-FePs granules of the present application (small granule).

[0052] Figure 3 c is a micro-characterization map of the second surface biofilm of PD / anammox-FePs granules of the present application (small granule).

[0053] Figure 3 d is a micro-characterization of the PD / anammox-FePs granules of the present application (large granules).

[0054] Figure 3 e is a micro-characterization of the PD / anammox-FePs granules biofilm and internal structure of the present application (large granules).

[0055] Figure 3 f is a micro-characterization of the FePs existing form in the PD / anammox-FePs granules of the present application (large granules).

[0056] Figure 3 g is a micro-characterization of the PD / anammox-FePs granules of the present application (ultra-large granules).

[0057] Figure 3 h is a micro-characterization of the first surface biofilm of the PD / anammox-FePs granules of the present application (ultra-large granules).

[0058] Figure 3 i is a micro-characterization of the second surface biofilm of the PD / anammox-FePs granules of the present application (ultra-large granules).

[0059] Figure 4 is the phosphorus binding state composition diagram of the sludge granules at different stages of the present application.

[0060] Figure 5 is the XRD spectrum of the sludge granules at different stages of the present application.

[0061] Figure 6 is the XPS spectrum (Fe2p) of the sludge granules at the first stage of the present application.

[0062] Figure 7 is the XPS spectrum (Fe2p) of the sludge granules at the fifth stage of the present application.

[0063] The marks in the drawing are: 1-EGSB reactor, 2-influent system, 21-organic carbon source storage tank, 22-iron source storage tank, 23-nitrogen-containing wastewater storage tank, 24-pump body, 25-pipeline, 3-circulating fan, 4-circulating air pipe, 5-backflow pump, 6-backflow pipe, 7-circulating pump, 8-circulating water pipe, 11-reaction zone, 12-three-phase separation zone. DETAILED DESCRIPTION

[0064] The present application will be further described in conjunction with the drawings and specific embodiments.

[0065] Contents not described in detail in this specification are prior art known to those skilled in the art. In the description of this invention, it should be understood that terms such as "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, terms such as "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0066] like Figure 1 As shown, the iron-mediated EGSB-type PD / anammox-FePs coupling system provided in this embodiment includes an EGSB reactor 1 and an influent system 2. The outlet of the influent system 2 is connected to the bottom of the EGSB reactor 1. In this embodiment, the EGSB reactor 1 is an upflow EGSB reactor 1. The influent system 2 includes an organic carbon source storage tank 21, an iron source storage tank 22, a nitrogen-containing wastewater storage tank 23, a pump body 24, and a pipeline 25. The organic carbon source storage tank 21, the iron source storage tank 22, and the nitrogen-containing wastewater storage tank 23 are respectively connected to the bottom of the EGSB reactor 1 through the pipeline 25, and the pump body 24 is installed in the pipeline 25.

[0067] This invention relates to the construction of an iron-mediated expanded granular sludge bed (EGSB) type PD / anammox system under high nitrogen loading conditions and the efficient nitrogen and phosphorus removal process of biologically induced PD / anammox-FePs mineral particle self-formation. The system is optimized based on EGSB type PD / anammox, with exogenous iron addition; in this embodiment, divalent iron (Fe(II)) is added exogenously. This achieves the combination of inorganic and organic electron donors, reducing the demand for organic carbon sources while reducing the inhibitory effect of organic matter on anammox. Simultaneously, utilizing the physical, chemical, and biomineralization processes involving Fe, phosphorus removal is achieved simultaneously with efficient nitrogen removal, promoting particle formation and further enhancing the operational stability of EGSB reactor 1. Compared to the traditional SBR type PD / anammox system process, the system process of this invention achieves simultaneous nitrogen and phosphorus removal, increasing the applicable nitrogen loading range. Compared to the anammox-HAP system process, the system process of this invention is more feasible in application, providing a stable source of NO2 for anammox. - -N supply enables simultaneous promotion of nitrogen removal.

[0068] The circulating fan 3 and the circulating air pipe 4 are further included, the exhaust port at the top of the EGSB reactor 1 is communicated with the circulating air pipe 4, the circulating air pipe has two outlets, one of which is externally discharged, and the other is communicated with the bottom of the EGSB reactor, and the circulating air pipe 4 is provided with the circulating fan 3. Through the setting of the circulating fan 3 and the circulating air pipe 4, the gas circulation is achieved, and the particle formation and mass transfer are promoted.

[0069] The reflux pump 5, the reflux water pipe 6, the circulating pump 7 and the circulating water pipe 8 are further included, the EGSB reactor 1 includes a reaction zone 11 and a three-phase separation zone 12, the three-phase separation zone 12 is located above the reaction zone 11, the three-phase separation zone 12 has two water outlets, one of the water outlets of the three-phase separation zone 12 is communicated with the reflux water pipe 6, the other end of the reflux water pipe 6 is communicated with the pipe 25 close to the bottom of the EGSB reactor 1, the reflux water pipe 6 is provided with the reflux pump 5, the upper end of the circulating water pipe 8 is communicated with the upper part of the reaction zone 11, the lower end of the circulating water pipe 8 is communicated with the lower part of the reaction zone 11, and the circulating water pipe 8 is provided with the circulating pump 7. Through the setting of the reflux pump 5 and the reflux water pipe 6, combined with the setting of the reflux ratio, the water is uniformly mixed, and the mass transfer capacity of the upflow EGSB reactor 1 is improved. Through the setting of the circulating pump 7 and the circulating water pipe 8 in the reaction zone 11, the flow state distribution is optimized, so that the nitrogen-containing wastewater and the sludge are fully mixed.

[0070] The application further provides a wastewater treatment method, which adopts the EGSB type PD / anammox-FePs coupling system to treat wastewater.

[0071] S1: inoculating short-cut denitrification and anaerobic ammonia oxidation composite sludge in the EGSB reactor 1.

[0072] S2: sending the nitrogen-containing wastewater into the EGSB reactor 1, then sending the organic carbon source and the iron source into the EGSB reactor 1, through the mediation of the external iron source, the short-cut denitrification and anaerobic ammonia oxidation composite sludge and the phosphorus in the nitrogen-containing wastewater are spontaneously coupled to form the PD / anammox-FePs particles under the biological induction, so that the nitrogen and phosphorus removal treatment of the nitrogen-containing wastewater is realized.

[0073] The organic carbon source of the embodiment is C2H3O2Na·3H2O, the iron source is FeSO4·7H2O-EDTA, NH4 + -N is provided by (NH4)2SO4, NO3 - -N is provided by NaNO3. The total nitrogen concentration of the nitrogen-containing wastewater is 180 mg / L, wherein the NO3 - -N concentration is 100 mg / L, NH4 +- N concentration 80 mg / L, iron source iron concentration 40 mg / L. In order to realize the requirement of high load treatment, the hydraulic retention time of EGSB reactor 1 is set to be short, which is 0.63 h. The nitrogen load is 6.84 g N / L / d, and the reflux ratio is 1.8:1. The reaction pH value is 7.5, and the reaction temperature is 35℃. The EGSB reactor 1 is an upflow EGSB reactor 1, and the upflow velocity is 1.73 m / h.

[0074] Denitrification and phosphorus removal performance of iron-mediated EGSB type PD / anammox-FePs coupled system:

[0075] In order to verify the denitrification and phosphorus removal performance of the system, according to the different Fe(II) dosing concentrations, the long-term experiment is divided into five stages, and the Fe(II) dosing amounts are 0, 10, 20, 30 and 40 mg / L respectively. The specific operation data are shown in Table 1.

[0076] Table 1 Denitrification and phosphorus removal performance of iron-mediated EGSB type PD / anammox-FePs coupled system

[0077]

[0078]

[0079] Stage I corresponds to the treatment effect of heterotrophic PD / anammox system under high nitrogen load, and the nitrogen and phosphorus removal rates are relatively low. With the increase of Fe(II) dosing amount, the total nitrogen removal rate (NRE) continuously rises, the anammox denitrification contribution rate continuously rises, and the phosphorus removal rate (PRE) continuously rises. When the Fe(II) concentration is 40 mg / L, NRE is 85.96%, NRR is 5.88 g N / L / d, anammox contribution rate is 88.3%, and PRE is 88.8%, realizing high-efficiency simultaneous denitrification and phosphorus removal. At the same time, in the running process, the COD removal rate (COD-RE) continuously decreases, which is due to the introduction of inorganic electron donor by Fe(II) dosing, reducing the demand for organic carbon source, realizing high-efficiency performance while reducing carbon emission. Enzyme activity determination of nitrate reductase (NAR), nitrite reductase (NIR) and hydrazine dehydrogenase (HDH) at the end of each stage shows that the sludge enzyme activity is improved. Monitoring the electron transport system (ETS) of sludge in each stage shows that the sludge ETS increases from 1.26 mg / (g SS·h) to 5.70 mg / (g SS·h), improving the electron transfer capacity of the system and promoting the faster occurrence of the reaction.

[0080] High load operation was achieved by high concentration of substrate and shortening HRT. The stable operation of the EGSB-type PD / anammox-FePs coupled system under high load conditions was mainly due to two aspects. First, the adaptability to high concentration of pollutants was enhanced. The addition of iron provided an additional inorganic electron donor for the system, which reduced the input of organic carbon source to a certain extent, reduced the inhibition of anammox, and at the same time, low concentration of Fe(II) could enhance the activity of anammox and improve the adaptability to high concentration of organic matter. Second, the reaction rate was accelerated to adapt to the short HRT condition. The addition of iron improved the key enzyme activity and electron transfer capacity of the system, promoted the faster reaction, and achieved efficient removal of pollutants under low HRT condition.

[0081] Formation of high-efficiency mass transfer granules in the EGSB-type PD / anammox-FePs coupled system mediated by iron

[0082] As shown in Figure 2 , during the operation of the system, the formation of granules was promoted, and a relatively stable PD / anammox-FePs granular structure was formed. The sludge morphology in the first and fifth stages is shown in Figure 2 a-2b, and the Fe(II) induced the formation of an obvious orange-brown shell on the surface of the sludge. In order to further study the granular structure, the spatial distribution of microorganisms and chemical elements in the sludge granules was explored by fluorescence in situ hybridization (FISH) and SEM experiments. According to the FISH staining results Figure 2 c-2e), it was found that a granular structure of denitrifying bacteria wrapping anammox bacteria was formed in the distribution of bacterial flora. This structure not only reduces the sensitivity of anammox bacteria to the external environment, but also accelerates the exchange of substrates between anammox bacteria and denitrifying bacteria. The same spatial distribution was also observed under an optical microscope Figure 2 f), pink anammox bacteria were wrapped in brownish denitrifying bacteria, and the part not stained by FISH may be non-biological substances. The composition of substances in the sludge was further analyzed by SEM and EDS. The results showed that in the fifth stage, crystals mainly composed of Fe, P and O elements were formed in the sludge, combined with the transformation process of phosphorus classification, it can be inferred that FePs inorganic matter was formed, and biological matter represented by C element was distributed around FePs inorganic minerals Figure 2 g-2l). Based on Figures 4-7 , it can be found that with the addition of Fe(II), Ca-P and Al-P in the sludge granules gradually transform into Fe-P, and based on XPS, it is found that Fe(II) promotes the increase of Fe content in the sludge, and the Fe in the sludge is mainly Fe(II).

[0083] The microstructure of single sludge particle was observed by SEM to explore the spatial distribution model of PD / anammox biomass and FePs inorganic minerals. Figure 3 SEM images of sludge of three particle sizes (<2 mm, 2-4 mm and >4 mm, named as small particle, large particle and super large particle respectively). As shown in FIG. 1, the surface of the small particle was covered by a layer of biofilm, and the biofilm included bacteria and EPS secreted by sludge. The interior of the small particle had FePs and biomass coupling body, and the bacteria included anammox bacteria and denitrifying bacteria, and the anammox bacteria were wrapped in the denitrifying bacteria. The large particle and the super large particle had similar microstructure, and the surface of the large particle and the super large particle was covered by a layer of biofilm, and the biofilm included bacteria and EPS secreted by sludge. The interior of the large particle and the super large particle had FePs and biomass coupling body, and the bacteria included anammox bacteria and denitrifying bacteria, and the anammox bacteria were wrapped in the denitrifying bacteria. Figure 3 As shown in FIG. 3a-3i, the three particles all had complete particle structure. The surface of the PD / anammox-FePs particle was attached with a biofilm, the biofilm included bacteria and EPS secreted by sludge, the interior of the PD / anammox-FePs particle had FePs and biomass coupling body, the bacteria included anammox bacteria and denitrifying bacteria, and the anammox bacteria were wrapped in the denitrifying bacteria. Specifically, the coupling PD / anammox-FePs particle had obvious spatial structure, the surface of the sludge of the three particle sizes was attached with a layer of biofilm, and the biofilm included bacteria and EPS secreted by sludge. The EPS of the biofilm on the surface of the small particle was more, the biofilm on the surface of the large particle and the super large particle was mainly gathered with bacteria, and the rich EPS on the surface of the small particle was helpful for sludge aggregation. Cracks were seen on the surface of the large particle, and the structure around and in the cracks was observed to find that there was different spatial model between the interior of the sludge and the surface biofilm, and FePs was only found in the interior of the sludge, and the bacteria and EPS were attached around the FePs. In the cross-sectional microstructure of the super large particle, cluster crystal groups with dense network structure were found, and there was almost no bacteria and EPS structure around the crystal, which might be due to insufficient internal substrate mass transfer, and the microorganism could not survive to form the crystal network core. Therefore, the addition of Fe promoted the removal of phosphorus, combined the phosphorus in the sludge in the form of FePs mineral, promoted the granulation of sludge, and improved the stability of the system.

[0084] Changes in microbial structure in the iron-mediated EGSB type PD / anammox system:

[0085] In anammox, the addition of Fe(II) helped the enrichment of Candidatus_Kuenenia, whose abundance increased from 35.2% in the first stage to 65.0% in the fourth stage, strengthening the dominant role of the anammox pathway in denitrification. In the partial denitrification process, Fe(II) promoted the enrichment of Thauera. In autotrophic denitrification, the enrichment of Hydrogenophaga and Azospira was found in the fourth and fifth stages. Hydrogenophaga is related to facultative hydrogen-type autotrophic denitrification, and Azospira is related to the NAFO process. The addition of Fe(II) promoted the autotrophic denitrification of the system, reduced the demand for organic carbon sources, and reduced the inhibition of high-concentration COD on anammox. In complete denitrification, the abundance of Comamonas decreased, indicating that the addition of Fe(II) helped to inhibit the complete denitrification process, thereby reducing the competition between complete denitrification and anammox for NO2 - -N.

[0086] Mechanism summary of iron-mediated anammox coupled with mixed-nutrient denitrification system:

[0087] The system successfully regulated metabolic intensity, electron transport chain, and microbial community through exogenous Fe addition, and improved the nitrogen removal performance of the system with the help of Fe-N cycle. At the same time, through the participation of Fe in chemical precipitation, physical adsorption, and biological mineralization, efficient phosphorus removal was achieved, and a high-efficiency mass transfer PD / anammox-FePs coupled granule was formed.

[0088] ① Metabolic intensity regulation: Fe addition increased the key enzyme activities of NO3 - -N reduction, NO2 - -N reduction, and N2H4 dehydrogenation steps, increased the ATP content of the system, promoted energy metabolism, and achieved more efficient denitrification and anammox substance metabolism activity, adapting to efficient removal of pollutants under short HRT conditions.

[0089] ② Fe-N cycle optimization: Through exogenous Fe addition, the Fe(II) oxidation process dependent on NO3 - -N was introduced, creating a new reaction pathway for NO3 - -N reduction, realizing the coupling of autotrophic and heterotrophic denitrification, reducing the demand for external organic matter, and reducing the inhibition of organic matter on anammox.

[0090] ③Promote the formation of particles and phosphorus recovery: the addition of exogenous Fe promotes the formation of particles in the system, improves the sludge settling property, forms the PD / anammox-FePs coupling particles with a layer of biofilm including the internal structure of the outer layer, FePs crystals are formed in the particles, which promote phosphorus removal and improve the stability of the system. In terms of sludge coupling, a unique particle structure is formed with denitrifying bacteria on the outside and anammox bacteria on the inside, which ensures more suitable living conditions for anammox and reduces the inhibition of external conditions on anammox, while promoting efficient material and electron transfer between denitrifying bacteria and anammox bacteria.

[0091] ④Microbial synergy: Fe(II) achieves more stable microbial coupling, realizes the enrichment of partial denitrifying bacteria and autotrophic denitrifying bacteria, reduces the substrate competition of complete denitrification on the anammox process through the inhibition of complete denitrifying bacteria, realizes the transformation of electron donor from organic matter supply type to mixed nutrition type, and promotes the Candidatus_Kuenenia abundance from 35.2% to 49.0%. Autotrophic denitrifying bacteria and Fe(III) oxidizing bacteria have a positive correlation with anammox bacteria, and the enrichment of autotrophic denitrifying bacteria further realizes the dominant position of anammox bacteria.

[0092] Iron-mediated EGSB-type PD / anammox-FePs coupling system operation mode:

[0093] Based on the effect of upflow velocity and hydraulic shear in the upflow reactor, the formation of sludge particles is promoted, and in the PD / anammox system, the exogenous Fe is mediated to spontaneously couple with the phosphorus in the sewage under biological induction to form a PD / anammox-FePs particle structure.

[0094] PD / anammox-FePs particle structure:

[0095] In the iron-mediated EGSB-type PD / anammox-FePs coupling system, the formed sludge particles are monitored. In terms of microbial distribution, the coupling sludge forms a structure with denitrifying bacteria wrapping anammox bacteria. In terms of sludge structure, a structure is formed with a layer of biofilm wrapping the internal material on the outside, and FePs and biomass are mixed and distributed in the sludge, and the formed inorganic mineral crystals provide attachment sites for microorganisms.

[0096] High-efficiency denitrification and phosphorus removal mechanism of PD / anammox-FePs system:

[0097] On the one hand, the PD / anammox-FePs system has higher enzyme activity, material metabolism intensity, energy metabolism intensity and electron transfer capacity, realizing the synergy between partial denitrifying bacteria, autotrophic denitrifying bacteria, complete denitrifying bacteria and anammox bacteria.

[0098] On the other hand, the coupling particles formed in the PD / anammox-FePs system further promote the system to achieve more efficient denitrification and phosphorus removal. In terms of denitrification, the structure of denitrifying bacteria wrapping anammox bacteria protects anammox bacteria from external high-concentration COD inhibition, promotes the mass transfer of denitrifying bacteria and anammox bacteria, improves the upper limit of nitrogen load of the PD / anammox process, and the current nitrogen removal rate can reach 5.88 gN / L / d. In terms of phosphorus removal, the particles in the promotion system biomineralize sludge EPS and physically and chemically retain phosphorus in the form of FePs, achieving efficient phosphorus removal. In terms of sludge structure, inorganic minerals in PD / anammox-FePs provide attachment sites for biomass, improving particle stability.

[0099] The present application has the following advantages:

[0100] (1) The iron-mediated EGSB-type PD / anammox-FePs coupling system reduces the demand for organic carbon sources in the denitrification process, reduces the inhibition of organic carbon sources on anammox bacteria, and meets the treatment needs of high-concentration pollutants, while efficiently removing nitrogen and reducing carbon emissions.

[0101] (2) The PD / anammox-FePs coupling system improves key enzyme activity under iron mediation, improves system electron transfer capacity, and promotes faster reaction to meet the efficient removal of pollutants under short HRT conditions.

[0102] (3) In the PD / anammox-FePs coupling system, by adding iron, physical, chemical and biological mineralization is achieved on the basis of simultaneous denitrification to achieve efficient phosphorus removal, and phosphorus is intercepted in the reactor in the form of FePs mineral formation. The formed crystals provide attachment sites for microorganisms, promote sludge granulation, and form a unique particle structure with denitrifying bacteria on the outside and anammox bacteria on the inside. On the one hand, it can protect anammox from environmental impact, and on the other hand, it provides a basis for efficient material and electron exchange.

[0103] (4) The iron-mediated EGSB-type PD / anammox-FePs coupling system realizes a better collaborative mode between denitrification processes (partial denitrification, complete denitrification, and autotrophic denitrification) and anammox bacteria, and realizes stable operation under high load.

[0104] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that; it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An iron-mediated EGSB-type PD / anammox-FePs coupling system, characterized in that: Including the EGSB reactor and influent system; The outlet of the water inlet system is connected to the bottom of the EGSB reactor; The water inlet system includes an organic carbon source storage tank, an iron source storage tank, a nitrogen-containing wastewater storage tank, a pump body, and pipelines; The organic carbon source storage tank, iron source storage tank, and nitrogen-containing wastewater storage tank are respectively connected to the bottom of the EGSB reactor through pipelines, and the pipelines are equipped with pumps; It also includes a return pump, a return water pipe, a circulation pump, and a circulation water pipe; The EGSB reactor includes a reaction zone and a three-phase separation zone, with the three-phase separation zone located above the reaction zone; The three-phase separation zone has two water outlets; One of the outlets of the three-phase separation zone is connected to a return water pipe, and the other end of the return water pipe is connected to the pipe near the bottom of the EGSB reactor. The return water pipe is equipped with a return pump. The upper end of the circulating water pipe is connected to the upper part of the reaction zone, and the lower end of the circulating water pipe is connected to the lower part of the reaction zone. The circulating water pipe is equipped with a circulating pump.

2. The iron-mediated EGSB-type PD / anammox-FePs coupling system according to claim 1, characterized in that: It also includes circulating fans and circulating ducts; The exhaust port at the top of the EGSB reactor is connected to a circulating air duct. The circulating air duct has two outlets, one of which discharges externally and the other is connected to the bottom of the EGSB reactor. The circulating air duct is equipped with a circulating fan.

3. The iron-mediated EGSB-type PD / anammox-FePs coupling system according to claim 1, characterized in that: The EGSB reactor is an upflow EGSB reactor, a sequencing batch EGSB reactor, or a two-stage EGSB reactor.

4. A wastewater treatment method, characterized in that, Processing using the iron-mediated EGSB-type PD / anammox-FePs coupling system according to any one of claims 1-3 includes the following steps: S1: Inoculate the EGSB reactor with a combined short-cut denitrification and anaerobic ammonium oxidation sludge; S2: Nitrogenous wastewater is fed into the EGSB reactor, and then organic carbon source and iron source are fed into the EGSB reactor. Through the mediation of exogenous iron, the combined sludge of short-cut denitrification and anaerobic ammonia oxidation spontaneously couples with phosphorus in nitrogenous wastewater under biological induction to form PD / anammox-FePs particles, thereby achieving nitrogen and phosphorus removal treatment of nitrogenous wastewater.

5. The wastewater treatment method according to claim 4, characterized in that: The organic carbon source is C2H3O2Na·3H2O; The iron source is zero-valent iron, divalent iron, or iron-containing minerals. When the iron source is divalent iron, the iron source is FeSO4·7H2O-EDTA.

6. The wastewater treatment method according to claim 4, characterized in that: The total nitrogen concentration of the nitrogen-containing wastewater is 170-190 mg / L, of which NO3... - -N concentration 90-110 mg / L, NH4 + -N concentration 70-90 mg / L; The iron source has an iron concentration of 30-40 mg / L.

7. The wastewater treatment method according to claim 4, characterized in that: The hydraulic retention time of the EGSB reactor is 0.60-0.65 h, the nitrogen loading is 6.74-6.94 g N / L / d, the reflux ratio is 1.6-2.0:1, the reaction pH is 7.5-7.8, and the reaction temperature is 33-37℃. The EGSB reactor is an upflow EGSB reactor with an upflow velocity of 1.63-1.83 m / h.

8. The wastewater treatment method according to claim 4, characterized in that: The particle size of the PD / anammox-FePs particles is at least one of < 2 mm, 2 - 4 mm, and > 4 mm.

9. The wastewater treatment method according to claim 4, characterized in that: The surface of the PD / anammox-FePs particles is covered with a biofilm, which includes microbial communities and EPS secreted by sludge. The interior of the PD / anammox-FePs particles contains FePs and biomass couplers. The microbial community includes anaerobic ammonia oxidizing bacteria and denitrifying bacteria, with the anaerobic ammonia oxidizing bacteria being encapsulated within the denitrifying bacteria.

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