A method for treating domestic sewage containing perfluorinated compounds using bacteria-algae symbiotic aerobic granular sludge

Abstract

The application discloses a method for treating domestic sewage containing perfluorinated compounds by using bacteria-algae symbiotic aerobic granular sludge. The bacteria-algae symbiotic aerobic granular sludge is cultivated through an SBR biological reactor, the concentration of PFOA is gradually increased to establish the tolerance of the bacteria-algae symbiotic aerobic granular sludge, and the synchronous removal of PFOA, organic matter, total phosphorus and total nitrogen is realized, and the removal rates of PFOA, TN, COD, TP and total nitrogen are 56.8%, 85.2%, 80.5% and 84.5% respectively. The application firstly uses the novel bacteria-algae symbiotic aerobic granular sludge to treat domestic sewage containing PFOA, and the performance of the reactor is stable during operation, and the granular sludge form and the settling performance are not obviously affected. The bacteria-algae symbiotic aerobic granular sludge method can solve the problems of high energy consumption, large yield and large occupied area of the traditional activated sludge method, and also provides a feasible scheme for realizing the synchronous removal of denitrification, phosphorus removal and PFOA.

Description

Technical Field

[0001] The present invention belongs to the field of biological sewage treatment, and specifically relates to a method for treating domestic sewage containing perfluorinated compounds by utilizing bacteria-algae symbiotic aerobic granular sludge, which is applicable to the field of domestic sewage treatment containing perfluorinated compounds. Background Art

[0002] Perfluorinated compounds (PFCs), as typical new pollutants, are widely present in various environmental media due to their environmental persistence, difficulty in degradation and bioaccumulation. PFCs enter the environment and migrate and transform through various pathways. Currently, there is almost no environment with zero PFC background value in the world, and it has been detected even in the Arctic and Antarctic regions. Perfluorooctanoic acid (PFOA) is one of the most typical representatives of PFCs and is also the final degradation product of many long-chain PFCs. PFOA has high water solubility (solubility of 3.4g / L) and a high detection rate in various environmental media. PFOA is carcinogenic and can disrupt endocrine system, so many countries and regions strictly control the use of PFOA. my country's new version of the "Standard for Drinking Water Quality" (GB5749-2022) has put forward control requirements for PFCs for the first time, with PFOA and PFOS limit values ​​of 80 and 40ng / L, respectively. The effluent from sewage treatment plants is one of the main pathways for wastewater to enter the natural environment. Therefore, using appropriate treatment processes to reduce the content of PFCs in the effluent from sewage treatment plants is the primary measure to reduce PFCs in the environment.

[0003] Common treatment methods used in wastewater treatment plants include membrane treatment technology, adsorption, advanced oxidation processes, and biological methods. Biological methods can effectively remove some PFCs from wastewater through biological adsorption and degradation, making them relatively environmentally friendly and cost-effective. However, the traditional activated sludge method currently used suffers from suboptimal removal performance and is plagued by issues such as large amounts of excess sludge, high material and energy consumption, and the need for new microbial methods to effectively remove PFCs. Algal-bacterial aerobic granular sludge (ABGS), a novel wastewater treatment process, offers advantages over traditional activated sludge, including a dense microbial structure, excellent settling properties, simultaneous nitrification and denitrification, and strong resistance to high organic matter content. ABGS is considered a promising alternative to traditional activated sludge. ABGS utilizes microalgae to absorb organic matter in the water and CO2 released by bacteria to produce oxygen, thereby reducing aeration intensity, improving nitrogen and phosphorus removal, and lowering aeration volume and wastewater treatment plant operating costs. In addition, the complex biological structure and synergistic multi-mechanism of ABGS have good prospects in the removal of new pollutants.

[0004] Prior to this, patent CN116986712A disclosed the coupling of AGS technology with the advantageous features of the bacteria-algae symbiotic system to construct a bacteria-algae symbiotic aerobic granular sludge (MBGS) system. However, the patent did not explore the treatment effect of using this system for treating wastewater containing PFCs. However, Yang et al. (Interaction between perflfluorooctanoic acid and aerobic granular sludge.Water Research, Volume 169, 2020, 115249, ISSN0043-1354) studied the treatment of wastewater containing PFOA with aerobic granular sludge. The study found that PFOA significantly reduced the sedimentation of granular sludge and the biological denitrification and phosphorus removal effects. And under PFOA stress, a large number of filamentous hairs grew on the surface of aerobic granular sludge, which seriously affected its sedimentation performance. Ji et al. (Perflfluorooctane sulfonate decreases the performance of a sequencing batch reactor system and changes the sludgemicrobial community.Chemosphere, Volume 279, 2021, 130596, ISSN 0045-6535) studied the effect of perfluorooctane sulfonic acid (PFOS) on the operating efficiency of aerobic granular sludge system. The study found that the presence of PFOS caused sludge swelling, reduced the settling performance of granular sludge, and significantly reduced the abundance of microorganisms in the system, thereby reducing the removal effect of COD and ammonia nitrogen by the system. Based on the above research, it is often difficult to obtain satisfactory results by directly using aerobic granular sludge (AGS) to treat domestic sewage containing typical PFCs (such as PFOA). Therefore, finding a suitable treatment process to effectively reduce the content of PFCs in the effluent of sewage treatment plants while maintaining / improving the stability of the system is still a problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the primary objective of the present invention is to provide a method for treating domestic wastewater containing typical PFCs (such as PFOA) using aerobic granular sludge generated by bacterial and algal symbiosis, effectively reducing the PFC content in the effluent. The use of granular sludge in this invention not only addresses the current problems of activated sludge processes in sewage treatment plants, such as high energy consumption, large sludge production, large floor space requirements, and excessive reliance on the coupling and superposition of multiple wastewater treatment processes, but also reduces construction and maintenance costs, providing a feasible solution for the integrated treatment of nitrogen and phosphorus in sewage treatment plants. The wastewater treatment method of the present invention is simple, low-cost, and highly operational.

[0006] Another object of the present invention is to provide an application of the water treatment method.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for treating PFC-containing domestic sewage using bacteria-algae symbiotic aerobic granular sludge comprises the following specific steps:

[0009] (1) Cultivation of bacteria-algae symbiotic aerobic granular sludge: Activated sludge is inoculated into the SBR reactor for aerobic treatment, and the operation mode is as follows: the reactor operates according to a set cycle every day, and the operation process of each cycle includes water inlet, anaerobic, aerobic, sedimentation and drainage. The reactor uses artificial synthetic wastewater containing ammonia nitrogen, total phosphorus and COD and added with trace elements; a lamp is installed on the outside of the reactor to simulate sunlight, and a light and dark alternating cycle strategy is adopted until regular bacteria-algae symbiotic aerobic granular sludge is formed;

[0010] (2) Start the first stage: Based on step (1), take some mature algae-bacteria symbiotic aerobic granular sludge and place it in another SBR reactor. No perfluorinated compounds are added in the first stage. The reactor is operated according to the mode described in step (1) for 30-40 days to allow the algae-bacteria symbiotic aerobic granular sludge to adapt to the new SBR reactor. The effluent indicators are tested every day until the removal rates of TN, COD and TP in the reactor effluent remain stable.

[0011] (3) Starting the second stage: Based on step (2), perfluorinated compounds are added, and the reactor is operated according to the mode described in step (1) for preliminary acclimation, and the effluent indicators are tested every day until the removal rates of TN, COD, TP and perfluorinated compounds in the reactor effluent remain stable;

[0012] (4) Start the third stage: Based on step (3), the concentration of perfluorinated compounds is further increased, and the reactor is operated according to the mode described in step (1) to further domesticate the bacteria-algae symbiotic aerobic granular sludge. The effluent indicators are tested every day until the removal rates of TN, COD, TP and perfluorinated compounds in the reactor effluent remain stable.

[0013] In step (1), the activated sludge is taken from the aeration tank of a sewage treatment plant and is in the form of flocs.

[0014] In steps (1) to (4), the reactor is operated daily in the following mode according to a set cycle: a hydraulic retention time of 6 hours is one cycle, and the reactor is operated for 4 cycles per day; one cycle operation includes five stages: water inlet (3 minutes), anaerobic reaction (115 minutes), aerobic reaction (115 minutes), sedimentation (4 minutes), and drainage (3 minutes). During the entire operation, the temperature is maintained at 25±1°C, the pH is maintained at 7.5-8.5, and the dissolved oxygen range is controlled at 7-8 mg / L during the aeration stage.

[0015] In steps (1) to (4), the artificial synthetic wastewater contains a nitrogen source, a phosphorus source, a carbon source, magnesium chloride, ferrous sulfate, CaCl2, NaHCO3 and KH2PO4; wherein the nitrogen source is provided by ammonium chloride, the phosphorus source is provided by KH2PO4, the carbon source is provided by sodium acetate, NaHCO3 is used to buffer the pH of the reactor, and CaCl2, ferrous sulfate and magnesium chloride are required to maintain particle structure and microbial growth; the initial concentration of the nitrogen source in the wastewater is 28-32 mg / L, the initial concentration of the phosphorus source is 2.8-3.2 mg / L, the initial concentration of COD is 280-320 mg / L, the initial concentration of NaHCO3 is 190-200 mg / L, the initial concentration of CaCl2 is 37-40 mg / L, the initial concentration of ferrous sulfate is 8-10 mg / L, and the initial concentration of MgCl2 is 49-51 mg / L; and the pH of the wastewater is adjusted to 7.5-8.5 with hydrochloric acid and sodium hydroxide solution, and the most suitable pH is 7.5.

[0016] In steps (1) to (4), the addition of trace elements refers to the addition of a trace element stock solution, which is prepared by adding trace elements to tap water, wherein the volume ratio of trace elements to tap water is 1 mL / 1 L, and the trace element components and their contents are ZnSO4 0.12-0.13 g / L, MnCl2·4H2O 0.12-0.13 g / L, (NH4)6Mo7O 24 ·4H2O0.07-0.09g / L, CuSO4·5H2O 0.03-0.05g / L, CoCl2·6H2O 0.15-0.16g / L, NiCl2 0.10-0.12g / L, EDTA 0.06-0.08g / L, KI 0.18-0.20g / L and H3BO3 0.10-0.11g / L.

[0017] In steps (1) to (4), the light and dark alternating cycle strategy is adopted, specifically, the continuous light time is 12 hours and the continuous dark time is 12 hours per day, that is, the light-dark ratio is 12:12, and the light intensity is 6000xl. This alternating cycle is used to simulate sunlight, and it is operated in this way for 2-3 months until the algae and bacteria are entangled and combined with each other to form a regular elliptical-shaped algae symbiotic aerobic granular sludge.

[0018] In steps (1) to (4), the reactor is an SBR bioreactor. The bacteria-algae symbiotic aerobic granular sludge in the reactor is mainly composed of green algae, diatoms, and Chlorella, and bacteria in the activated sludge. The algae grow on the outside of the granular sludge, enveloping the granular sludge, and the bacteria are inside the granular sludge. The main functional bacteria in the reactor are nitrogen and phosphorus removal functional bacteria. The reactor uses a peristaltic pump to control water inlet and outlet, with water inlet at the bottom and water outlet in the middle, and the water inlet volume and water outlet volume are both half the volume of the reactor; the water inlet system includes an inlet valve, an inlet pipe, an inlet bucket and an inlet pump, and the water outlet system includes an outlet pipe, an outlet bucket and an outlet pump; the inlet bucket and the reactor body are connected by an inlet pipe, and the inlet valve and the inlet pump are arranged on the inlet pipe; the reactor body and the outlet bucket are connected by an outlet pipe, and the outlet pump is arranged on the outlet pipe; the water inlet system and the outlet system are both provided with sampling valves and sampling tubes; the material of the reactor body is preferably plexiglass; the inlet pump and the outlet pump are preferably peristaltic pumps.

[0019] In steps (1) to (4), the aeration treatment refers to the air pump in the reactor pumping air into the reactor through the microporous aeration disk at the bottom of the reactor to form numerous and uniform small bubbles.

[0020] In steps (1) to (4), in order to ensure that the water quality does not change significantly, the inlet water should be replaced at the same time every day as much as possible, and a trace element dilution solution should be introduced before the inlet water is introduced.

[0021] In steps (2) to (4), the MLSS of the bacteria-algae symbiotic aerobic granular sludge in the reaction system is 4.8-5.2 g / L, the MLVSS / MLSS is 0.88-0.93, and the mass ratio of C:N:P is 100:10:1.

[0022] In steps (3) and (4), the added pollutant is PFOA. PFOA is a characteristic pollutant in municipal wastewater, and the present invention uses it to stably remove PFOA and remove nitrogen and phosphorus from domestic wastewater containing PFOA. In step (3), the concentration of PFOA added is 0.09-0.1 mg / L, and the reactor is operated for 40-45 days; in step (4), the concentration of PFOA added is 0.9-1 mg / L, and the reactor is operated for 40-45 days.

[0023] The present invention utilizes a method for treating domestic sewage containing perfluorinated compounds by utilizing bacteria-algae symbiotic aerobic granular sludge. The perfluorinated compounds are not limited to PFOA, but are also applicable to other perfluorinated compounds with similar structures, and can achieve good removal effects.

[0024] In step (2), a portion of the mature algae granular sludge cultured in step (1) was placed in another SBR reactor, with the sludge concentration controlled at 5 g / L and the particle size at 2 mm. The operating conditions and water distribution conditions were identical to those in the culture stage. Steps (3) and (4) were based on the previous step, with all other conditions remaining unchanged, except for the PFOA concentration in the influent.

[0025] The above-mentioned method of treating domestic sewage containing PFCs using bacterial-algal symbiotic aerobic granular sludge has a PFOA removal rate of about 50%, and the total nitrogen removal rate is more than 40% higher than the removal rate in the stage without PFOA addition. Under the stress of 1 mg / L PFOA, the total nitrogen removal rate of the bacterial-algal granular sludge is about 85%, and the phosphorus removal capacity is almost unaffected by PFOA, with a total phosphorus removal rate of about 84.5%.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] The method of the present invention enables the startup and stable operation of a symbiotic aerobic granular sludge system suitable for PFOA-containing domestic wastewater, while simultaneously achieving stable PFOA removal and simultaneous nitrogen and phosphorus removal. Furthermore, the present invention provides an effective solution to the potential adverse effects of PFCs in wastewater on the symbiotic aerobic granular sludge system. The present invention first utilizes a suitable concentration gradient of PFOA to induce stress memory in the symbiotic aerobic granular sludge, enabling it to adapt to PFOA-containing domestic wastewater. This prevents irreversible damage to the symbiotic aerobic granular sludge caused by high PFOA concentrations and improves its tolerance to PFOA. Furthermore, the synergistic interaction between algae and bacteria provides a new pathway for systemic nitrogen and phosphorus removal. Furthermore, the symbiotic aerobic granular sludge significantly improves TN removal under PFOA stress. Furthermore, the algae use photosynthesis to provide oxygen to the granular sludge, reducing energy consumption. The symbiotic aerobic granular sludge exhibits excellent settling properties, strong resistance to shock loads, and exhibits no sludge bulking in response to PFOA stimulation. Compared to traditional multi-stage coupled denitrification processes for municipal wastewater, the present invention's bacterial-algal symbiotic granular denitrification system offers significant engineering application prospects, offering a new, low-energy, efficient, and stable method for treating PFOA-containing wastewater. By leveraging the synergistic effects of PFOA concentration gradient stress and bacterial-algal symbiotic aerobic granular sludge, this system not only optimizes the efficiency of nitrogen and phosphorus removal but also enhances the overall stability of the system, demonstrating significant innovation and practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a diagram of the operating device of the SBR reactor of the present invention;

[0029] Figure 21. is a graph showing the concentration of ammonia nitrogen in the inlet and outlet water and the removal efficiency of the bacteria-algae granular sludge system in the SBR reactor of the present invention;

[0030] Figure 3 Graph showing total nitrogen inlet and outlet concentrations and removal efficiency of the bacteria-algae granular sludge system in the SBR reactor of the present invention;

[0031] Figure 4 Graph showing the COD inlet and outlet concentrations and removal efficiency of the bacteria-algae granular sludge system in the SBR reactor of the present invention;

[0032] Figure 5 2. It is a graph showing the total phosphorus inlet and outlet concentration and removal efficiency of the bacteria-algae granular sludge system in the SBR reactor of the present invention;

[0033] Figure 6 This is a graph showing changes in ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and phosphorus concentrations during a typical cycle of operation of the bacteria-algae granular sludge system in the SBR reactor of the present invention;

[0034] Figure 7 This is a graph showing changes in PFOA removal rates during operation of the bacteria-algae granular sludge system in the SBR reactor of the present invention;

[0035] Figure 8 This is a morphological characteristic diagram of granular sludge during operation of the bacteria-algae granular sludge system in the SBR reactor of the present invention. DETAILED DESCRIPTION

[0036] The technical solutions of the present invention are further described below with reference to the accompanying drawings and specific embodiments. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0037] Please refer to Figure 1 The method for treating domestic sewage containing PFCs with aerobic granular sludge using bacteria-algae symbiotic sludge of the present invention adopts an SBR reactor as the reactor body, and its working volume is 1L. There is a microporous aeration disk at the bottom of the SBR reactor, with an effective volume of 6L. The suspended solids concentration of the inoculated sludge mixture is maintained at 5000mg / L, and the drainage ratio is 50%. The reactor body includes a water inlet 4 and water outlets 5 and 6; the water inlet 4 of the reactor body 11 is connected to the external water distribution barrel 1 through the water inlet peristaltic pump 2; the water outlet 5 of the reactor body 11 is connected to the external water outlet barrel 9 through the water outlet peristaltic pump 7; the aeration of the reactor body 11 adopts an aeration pump 13 to control the release through the aeration disk 10 at the bottom of the reactor body 11 through the rotor flowmeter 12. The specific operating principle is as follows: Figure 1As shown in the figure, the hydraulic retention time (HRT) constituted one cycle, the SBR reactor had a drainage ratio of 50%, and four cycles were run daily. Each cycle consisted of five stages: water inlet (3 minutes), anaerobic reaction (115 minutes), aerobic reaction (115 minutes), sedimentation (4 minutes), and drainage (3 minutes). The temperature was maintained at 25±1°C throughout the operation, the pH was maintained between 7.5 and 8.5, and the dissolved oxygen range during the aeration phase was controlled at 7-8 mg / L.

[0038] The wastewater used in the present examples is synthetic wastewater, primarily composed of CH₃COONa, NH₄Cl, KH₂PO₄, NaHCO₃, MgSO₄·7H₂O, CaCl₂, and FeSO₄·7H₂O. The main components of the synthetic wastewater are shown in Table 1. The influent pH was controlled at 7.5. Before daily inflow, 1 mL of trace elements per liter of water was added to prepare a trace element stock solution. The composition and content of the trace elements are shown in Table 2. PFOA is a typical PFC.

[0039] Table 1 Main components of synthetic wastewater

[0040]

[0041] Table 2 Trace element stock solution components

[0042]

[0043] The activated sludge described in the embodiment of the present invention is an activated sludge obtained by acclimating and culturing aerobic flocculent sludge from the aerobic aeration tank of the Guangzhou Lijiao Sewage Treatment Plant for about 800 days. The denitrification efficiency is maintained at above 95%, and the MLSS of the activated sludge in the reaction system is 5 g / L, and the MLVSS / MLSS is 0.5.

[0044] Example 1: Cultivation and stable operation of bacterial-algal symbiotic aerobic granular sludge

[0045] The flocculent activated sludge collected from the aeration tank of Leijiao sewage treatment plant in Guangzhou was inoculated into the SBR reactor for aerobic treatment. The SBR reactor had a micro-porous aeration disc at the bottom, and the effective volume was 6 L. The suspended solid concentration of the inoculated sludge was maintained at 5 g / L. The pH of the reaction system was adjusted to 7.5-8.5, and the drainage ratio was 50%. The following mode was used for operation: 6 h of hydraulic retention time as one cycle, 4 cycles per day; one cycle operation included five stages: water feeding (3 min), anaerobic (115 min), aerobic reaction (115 min), sedimentation (4 min), and drainage (3 min). The temperature was controlled at 25±1℃ during the whole operation period, the pH was maintained at 7.5-8.5, and the dissolved oxygen range was controlled at 7-8 mg / L during the aeration stage. In order to meet the needs of microbial growth, the trace element solution was dissolved in the water bucket through the water feeding pipe according to the method of adding 1 ml of trace element stock solution per 1 L of water.

[0046] The water feeding was performed by a peristaltic pump at a rate of 180-200 mL / min. The synthetic wastewater contained nitrogen source, phosphorus source, carbon source, magnesium chloride, ferrous sulfate, CaCl2, NaHCO3, and KH2PO4. Among them, the nitrogen source was provided by ammonium chloride, the phosphorus source was provided by KH2PO4, the carbon source was provided by sodium acetate, NaHCO3 was used to buffer the pH of the reactor, and CaCl2, ferrous sulfate, and magnesium chloride were required for maintaining the structure of the particles and microbial growth; the initial concentration of the nitrogen source in the wastewater was 30 mg / L, the initial concentration of the phosphorus source was 3 mg / L, the initial concentration of COD was 300 mg / L, the initial concentration of NaHCO3 was 200 mg / L, the initial concentration of CaCl2 was 40 mg / L, the initial concentration of ferrous sulfate was 10 mg / L, and the initial concentration of MgCl2 was 51 mg / L; the pH of the wastewater was preferably 7.5. A lamp was installed outside the SBR reactor, and the light time was 12 h and the dark time was 12 h, which were alternately cycled to simulate sunlight. In this way, the operation was carried out until the algae and bacteria were intertwined and combined to form regular ellipsoidal-shaped bacterial-algal symbiotic aerobic granular sludge (the whole process took about 2-3 months), and thus the bacterial-algal symbiotic aerobic granular sludge was formed.

[0047] The above-mentioned bacterial-algal symbiotic aerobic granular sludge system, without the addition of PFOA, stably maintained the removal rate of ammonia nitrogen at more than 98%, the removal rate of TN at 60%, the removal rate of COD at about 85%, and the removal rate of TP at about 85%.

[0048] Example 2: Removal of PFOA in domestic sewage and simultaneous denitrification and phosphorus removal by bacterial-algal symbiotic aerobic granular sludge under PFCs stress

[0049] The mature and stable aerobic granular sludge from the bacterial-algal symbiosis cultured in Example 1 was placed in an SBR reactor. The sludge concentration was controlled at 5 g / L and the particle size was 2 mm. The operating and water distribution conditions were identical to those in the culture stage. The temperature was controlled at 25 ± 1°C, the DO during the aeration phase was maintained at 2-8 mg / L, and the pH was maintained at 7.5-8.5. Synthetic wastewater was added for aeration, and the reactor effluent quality was monitored daily.

[0050] (1) Start-up Phase I: A portion of the mature algae-bacteria granular sludge was placed in another SBR reactor, with the sludge concentration controlled at 5 g / L and the particle size at 2 mm. The operating conditions and water distribution conditions were identical to those of the cultivation phase. In the first phase, the wastewater was set to be free of PFOA, i.e., the PFOA concentration was 0. The reactor was operated in this manner for 30 days to allow the algae-bacteria symbiotic aerobic granular sludge to adapt to the new SBR reactor. The effluent indicators were tested daily until the TN, COD, and TP removal rates of the reactor effluent remained stable. The TN, COD, and TP removal rates were 63.0%, 84.5%, and 87.6%, respectively.

[0051] (2) Start the second phase: Based on the first phase, the operating conditions of the SBR reactor remain unchanged. PFOA synthetic wastewater is added to the inlet bucket of the SBR reactor to increase the PFOA concentration in the inlet water to 0.1 mg / L. Under this condition, the reactor is operated for about 40 days for preliminary acclimation, stimulating the stress memory of the bacteria-algae symbiotic aerobic granular sludge system to PFOA and improving its tolerance to PFOA. The effluent indicators are tested every day until the removal rates of TN, COD, TP and PFOA in the reactor effluent remain stable. The removal rates of TN, COD and TP are 68.3%, 82.8% and 90.5% respectively, and the PFOA removal rate is stable at about 30%.

[0052] (3) Start the third stage: Based on the second stage, after the SBR reactor has been subjected to a low-concentration PFOA stress strategy, the operating conditions of the SBR reactor remain unchanged, and the PFOA concentration in the inlet bucket of the SBR reactor is increased to 1 mg / L. After about 40 days of operation, the bacteria-algae symbiotic aerobic granular sludge is further domesticated, and the effluent indicators are tested every day until the TN, COD, TP and PFOA removal rates of the reactor effluent remain stable. The removal rates of TN, COD and TP are 85.2%, 80.5% and 84.5% respectively, and the PFOA removal rate is about 50%.

[0053] After the SBR reactor was subjected to PFOA concentration gradient cycle stress, the bacteria-algae symbiotic aerobic granular sludge was able to adapt to domestic wastewater containing PFOA. The specific denitrification efficiency of the entire reactor process can be seen in Figure 2Compared with the stage without PFOA addition, the final ammonia nitrogen effluent concentration of the reactor of the bacteria-algae symbiotic aerobic granular sludge under 1mg / LP PFOA stress was maintained below 1mg / L, and the ammonia nitrogen removal rate reached 100%. Figure 3 As shown in the figure, after PFOA gradient stress, the stable TN removal rate of the bacteria-algae symbiotic aerobic granular sludge increased from 63.0% to 85.2%, with an increase rate of 35%. Figure 4 and Figure 5 As shown in the figure, the changes in the influent and effluent COD and TP removal rates of the system were not significantly affected by PFOA. The above results indicate that the system is suitable for the establishment of a high-efficiency nitrogen and phosphorus removal system using a bacterial-algal symbiotic aerobic granular sludge system for PFCs-containing wastewater.

[0054] In Example 2, the high-efficiency algae granular sludge suitable for treating PFOA-containing domestic wastewater can stably remove nitrogen and phosphorus. The changes in the concentrations of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen and sulfate ion in a typical cycle of the system are shown in the following figure: Figure 6 As shown in the figure, compared to the changes in ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the bacteria-algae granular sludge system without PFOA addition, the ammonia nitrogen concentration in the bacteria-algae granular sludge denitrification system under PFOA acclimation decreased with increasing PFOA concentration, indicating enhanced ammonia nitrogen removal capacity; nitrite nitrogen in the periodic effluent was almost zero and was not affected by PFOA; nitrate nitrogen in the periodic effluent decreased with increasing PFOA concentration, resulting in an increase in TN removal rate. This indicates that under long-term PFOA stress, the denitrification capacity of the bacteria-algae symbiotic aerobic granular sludge system is enhanced. Although phosphate release decreases during the anaerobic stage, it can still achieve a high removal rate during the aerobic stage.

[0055] The removal rate of PFOA during the operation of the reactor is shown in Figure 7 Under PFOA stress, the algae-bacteria granular sludge gradually adapted to the low concentration of PFOA, and the PFOA removal rate gradually increased. In the second stage, the PFOA removal rate reached 30%, and in the third stage, the PFOA removal rate of the algae-bacteria granular sludge reached about 50%.

[0056] The morphological characteristics of the aerobic granular sludge driven by bacteria-algae symbiosis in the reactor under PFOA stress are shown in Figure 8 It can be seen that under long-term PFOA acclimation with an appropriate concentration gradient, the particle size and morphology did not change significantly. The green filamentous algae on the surface of the bacteria-algae symbiotic aerobic granular sludge increased, and the surface showed many membrane-like structures. In addition, a large number of microorganisms attached to the algae surface, mainly bacilli and cocci, enriched the biological community of the bacteria-algae symbiotic aerobic granular sludge, and correspondingly improved the stability of the system.

[0057] It can be clearly seen that the use of this method can obtain a bacteria-algae symbiotic aerobic granular sludge efficient denitrification system suitable for treating domestic wastewater containing PFOA. The present invention adopts a new process of bacteria-algae symbiotic aerobic granular sludge driven by appropriate PFOA concentration gradient stress, which can not only solve the problems of high energy consumption, large sludge production and large floor space of the existing activated sludge method in sewage treatment plants, but also the use of bacteria-algae symbiotic aerobic granular sludge provides a feasible solution for the integrated treatment of nitrogen and phosphorus in sewage treatment plants. It also solves the technical bottleneck of over-reliance on the coupling and superposition of multiple wastewater treatment processes in the current domestic wastewater treatment, realizes the establishment of a bacteria-algae symbiotic aerobic granular sludge efficient denitrification system in a single structure, and improves the feasibility of engineering application. In addition, the effluent of the reactor designed by the present invention meets the TN, COD and TP emission standards in the Class A standard of the "Pollutant Discharge Standard for Urban Sewage Treatment Plants".

Claims

1. A method for treating domestic sewage containing perfluorinated compounds using bacterial-algal symbiotic aerobic granular sludge, characterized in that: The specific steps are: (1) Cultivation of aerobic granular sludge with bacterial and algal symbiosis: Activated sludge is inoculated into the SBR reactor for aerobic treatment. The operation mode is as follows: the reactor operates according to a set cycle every day. The operation process of each cycle includes water inlet, anaerobic, aerobic, sedimentation and drainage. The reactor uses artificial synthetic wastewater containing ammonia nitrogen, total phosphorus and COD and added with trace elements; The reactor is equipped with a lamp outside to simulate sunlight, and adopts a light and dark alternating cycle strategy until regular bacteria-algae symbiotic aerobic granular sludge is formed; (2) Start the first stage: Based on step (1), take some mature algae-bacteria symbiotic aerobic granular sludge and place it in another SBR reactor. In the first stage, no perfluorinated compounds are added. The reactor is operated according to the mode described in step (1) to allow the algae-bacteria symbiotic aerobic granular sludge to adapt to the new SBR reactor. The effluent indicators are tested every day until the removal rates of TN, COD and TP in the reactor effluent remain stable. (3) Start the second stage: Based on step (2), perfluorinated compounds are added, and the reactor is operated according to the mode described in step (1) for preliminary acclimation. The effluent indicators are tested every day until the removal rates of TN, COD, TP and perfluorinated compounds in the reactor effluent remain stable; (4) Start the third stage: Based on step (3), the concentration of perfluorinated compounds is further increased, and the reactor is operated according to the mode described in step (1) to further domesticate the bacterial-algal symbiotic aerobic granular sludge. The effluent indicators are tested every day until the removal rates of TN, COD, TP and perfluorinated compounds in the reactor effluent remain stable.

2. The method according to claim 1, characterized in that In step (1), the activated sludge is taken from the aeration tank of the sewage treatment plant and is in the form of flocs.

3. The method according to claim 1, wherein In steps (1) to (4), the artificial synthetic wastewater contains a nitrogen source, a phosphorus source, a carbon source, magnesium chloride, ferrous sulfate, CaCl2, NaHCO3 and KH2PO4; wherein the nitrogen source is provided by ammonium chloride, the phosphorus source is provided by KH2PO4, the carbon source is provided by sodium acetate, NaHCO3 is used to buffer the pH of the reactor, and CaCl2, ferrous sulfate and magnesium chloride are required to maintain particle structure and microbial growth; the initial concentration of the nitrogen source in the wastewater is 28-32 mg / L, the initial concentration of the phosphorus source is 2.8-3.2 mg / L, the initial concentration of COD is 280-320 mg / L, the initial concentration of NaHCO3 is 190-200 mg / L, the initial concentration of CaCl2 is 37-40 mg / L, the initial concentration of ferrous sulfate is 8-10 mg / L, and the initial concentration of MgCl2 is 49-51 mg / L; and the pH of the wastewater is adjusted to 7.5-8.5 using hydrochloric acid and sodium hydroxide solution.

4. The method according to claim 1, wherein In steps (1) to (4), the addition of trace elements refers to the addition of a trace element stock solution, which is prepared by adding trace elements to tap water, with a volume ratio of trace elements to tap water of 1 mL / 1 L, and the trace element components and their contents being ZnSO4 0.12-0.13 g / L, MnCl2·4H2O 0.12-0.13 g / L, (NH4)6Mo7O 24 ·4H2O 0.07-0.09 g / L, CuSO4·5H2O 0.03-0.05 g / L, CoCl2·6H2O 0.15-0.16 g / L, NiCl2 0.10-0.12 g / L, EDTA 0.06-0.08 g / L, KI 0.18-0.20 g / L and H3BO3 0.10-0.11 g / L; the reactor inlet water was replaced every day, and the trace element stock solution was introduced before the inlet water was introduced.

5. The method according to claim 1, wherein In steps (1) to (4), the five stages in one cycle of the reactor operation include water inlet for 3 minutes, anaerobic reaction for 115 minutes, aerobic reaction for 115 minutes, sedimentation for 4 minutes, and drainage for 3 minutes; during the entire operation, the temperature was maintained at 25±1°C, the pH was maintained at 7.5-8.5, and the dissolved oxygen range was controlled at 7-8 mg / L during the aeration stage.

6. The method according to claim 1, wherein In steps (1) to (4), the light and dark alternating cycle strategy is adopted, specifically, the continuous light time is 12 hours per day and the continuous dark time is 12 hours, and this alternating cycle is used to simulate sunlight. This operation is carried out for 2-3 months until the algae and bacteria are entangled and combined with each other to form a regular elliptical-shaped algae-symbiotic aerobic granular sludge.

7. The method according to claim 1, characterized in that In steps (1) to (4), the reactor is an SBR bioreactor, and the bacteria-algae symbiotic aerobic granular sludge in the reactor is mainly composed of green algae, diatoms, chlorella and bacteria in activated sludge. The algae grow on the outside of the granular sludge and wrap the granular sludge, and the inside of the granular sludge is bacteria. The reactor adopts a peristaltic pump to control water inlet and outlet, with water inlet at the bottom and water outlet in the middle. The water inlet volume and water outlet volume are both half of the volume of the reactor. The water inlet system includes an inlet valve, an inlet pipe, an inlet bucket and an inlet pump, and the water outlet system includes an outlet pipe, an outlet bucket and an outlet pump. The inlet bucket and the reactor body are connected by an inlet pipe, and the inlet valve and the inlet pump are arranged on the inlet pipe. The reactor body and the outlet bucket are connected by an outlet pipe, and the outlet pump is arranged on the outlet pipe. The water inlet system and the outlet system are both provided with a sampling valve and a sampling tube. The material of the reactor body is organic glass. The water inlet pump and the water outlet pump are peristaltic pumps.

8. The method according to claim 1, wherein In steps (2) to (4), the MLSS of the bacteria-algae symbiotic aerobic granular sludge in the reaction system is 4.8-5.2 g / L, the MLVSS / MLSS is 0.88-0.93, and the mass ratio of C:N:P is 100:10:

1.

9. The method according to claim 1, wherein In step (2), the reactor is operated for 30-40 days; in steps (3) to (4), the perfluorinated compound added is PFOA; wherein, in step (3), the concentration of PFOA added is 0.09-0.1 mg / L, and the reactor is operated for 40-45 days; and in step (4), the concentration of PFOA added is 0.9-1 mg / L, and the reactor is operated for 40-45 days.

10. The method according to any one of claims 1 to 9, characterized in that Using the above method to treat domestic wastewater containing PFOA, the PFOA removal rate was 50%, and the total nitrogen removal rate was more than 40% higher than that in the stage without PFOA addition; under the condition of 1 mg / L PFOA, the total nitrogen removal rate was 85% and the total phosphorus removal rate was 84.5%.

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