Method for enhancing denitrification and dephosphorization of low carbon-nitrogen ratio sewage by algal-bacterial granular sludge

Abstract

This invention discloses a method for enhanced nitrogen and phosphorus removal from wastewater with low carbon-to-nitrogen ratio using algae-bacterial granular sludge, comprising the following steps: inoculating an algae-bacterial symbiotic sludge into a sequencing batch reactor; introducing domestic sewage, performing low-DO aeration, subjecting the reactor to light treatment, and operating the reactor in an anaerobic / aerobic / anoxic mode, thereby forming algae-bacterial symbiotic sludge into algae-bacterial granular sludge; and controlling the dissolved oxygen concentration of the low-DO aeration to 0.4–0.6 mg·L⁻¹. ‑1 The inoculated sludge concentration is 4000-5000 mg / L. This invention employs low dissolved oxygen aeration combined with lighting to drive algae and bacteria granular sludge to achieve endogenous carbon compensation, significantly reducing the carbon source demand in the denitrification and phosphorus removal process of low carbon-to-nitrogen ratio wastewater, lowering wastewater treatment operating costs, and avoiding secondary pollution caused by carbon source addition.

Description

Technical Field

[0001] This invention relates to a wastewater treatment method, and more particularly to a method for nitrogen and phosphorus removal from wastewater with enhanced algae and bacteria granular sludge and low carbon-to-nitrogen ratio. Background Technology

[0002] Currently, urban wastewater treatment plants and some industrial wastewater treatment plants face the prominent problem of low influent carbon-to-nitrogen ratios. This is caused by factors such as urbanization, changes in residents' water usage habits, and infiltration from municipal pipe networks. Wastewater with low carbon-to-nitrogen ratios cannot meet the organic carbon source requirements of traditional nitrification-denitrification processes. In existing technologies, the main way to solve this problem is to add external carbon sources (such as sodium acetate or methanol), but this significantly increases operating costs. Furthermore, excessive addition of carbon sources or incomplete degradation can easily lead to the emission of greenhouse gases such as N2O, causing secondary pollution.

[0003] Algal-bacterial granular sludge is a granular microbial aggregate formed by the spontaneous flocculation of microalgae and bacteria. It achieves simultaneous pollutant removal through the synergistic metabolism of algae and bacteria. Microalgae fix CO2 and produce oxygen through photosynthesis, while bacteria degrade organic matter and convert nitrogen and phosphorus. It is an ideal technology carrier for treating wastewater with a low carbon-to-nitrogen ratio. Low-DO aeration represents an energy-saving optimization direction in wastewater treatment and can promote simultaneous nitrification and denitrification.

[0004] However, existing low-DO aeration technologies are mostly applied to single bacteria or pure algae systems. They have not yet achieved system regulation of the symbiotic characteristics of algae and bacteria granular sludge, nor have they revealed the mechanism of low-DO aeration synergistic with light-driven endogenous carbon compensation. They have problems such as algae-bacteria ratio imbalance, poor sludge granulation stability, and limited improvement in nitrogen and phosphorus removal efficiency, making it difficult to achieve engineering application in low carbon-nitrogen ratio wastewater treatment. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for enhancing nitrogen and phosphorus removal in wastewater with low carbon-to-nitrogen ratio using algae and bacteria granular sludge, which can be adapted to the characteristics of algae and bacteria granular sludge, and can drive endogenous carbon compensation through low DO aeration and light synergy, without the need for external carbon sources.

[0006] Technical solution: The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge as described in this invention includes the following steps:

[0007] Inoculate algae-bacterial symbiotic sludge into a sequencing batch reactor;

[0008] Domestic sewage is introduced, and low-DO aeration is carried out. The reactor is treated with light and operated in an anaerobic / aerobic / anoxic mode. The algae-bacterial symbiotic sludge forms algae-bacterial granular sludge.

[0009] The dissolved oxygen concentration in the low-DO aeration is controlled at 0.4-0.6 mg·L⁻¹. -1 The concentration of inoculated sludge is 4000-5000 mg / L.

[0010] The reaction time in the anaerobic / aerobic / anoxic process stages is 1:2:2 for the anaerobic stage: aerobic stage: anoxic stage.

[0011] The aeration intensity was controlled at 7-13 mL / min. -1 ·L -1 .

[0012] The photosynthetic photon flux density on the inner wall of the reactor was maintained at 400-600 μmol·m⁻¹. -2 ·s -1 .

[0013] The aeration and illumination time provide an anaerobic environment for the system and inhibit excessive growth of microalgae, thereby adjusting the algae-to-bacterial ratio of the algae-bacterial granular sludge to 0.85-1.08 and enhancing nitrate removal.

[0014] The conditions for the formation of algae-bacterial granular sludge are as follows: when the sludge settling volume index for 30 min is controlled at 41.5-46.8 mL / g, and granular sludge with a diameter >200 μm accounts for more than 50% of the total sludge volume, algae-bacterial granular sludge is considered to have formed.

[0015] The total nitrogen concentration in the effluent is less than 7.5 mg / L, i.e., 5.9-7.5 mg / L, and the phosphate removal rate is greater than 72.0%, i.e., 72.0-76.8%.

[0016] This invention provides a method for enhancing nitrogen and phosphorus removal in wastewater with low carbon-to-nitrogen ratio by driving endogenous carbon compensation in algae-bacterial granular sludge using a low dissolved oxygen (DO) aeration and synergistic light strategy. The core of this method lies in using low DO aeration and light duration as environmental selection pressures to optimize the algae-to-bacterial ratio in algae-bacterial granular sludge, enhance extracellular polymer secretion and sludge granulation stability, enrich nitrogen and phosphorus removal functional bacteria, and ultimately achieve the synergistic effect of simultaneous nitrification, endogenous denitrification, and phosphorus removal. This solves the problems of insufficient carbon source, high aeration energy consumption, and poor algae-bacterial synergy in wastewater with low carbon-to-nitrogen ratio.

[0017] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0018] (1) The present invention adopts a low dissolved oxygen aeration and light regulation strategy to drive algae and bacteria granular sludge to achieve endogenous carbon compensation, which greatly saves the carbon source demand and power consumption caused by aeration in the process of denitrification and phosphorus removal of low carbon-nitrogen ratio wastewater, reduces the operating cost of wastewater treatment, and avoids secondary pollution caused by carbon source addition.

[0019] (2) By switching between A / O and A / O / A operating modes in stages, the present invention can accurately control the aeration and light duration, achieve optimized control of the algae-bacteria ratio of 0.85-1.08, promote the granulation of algae-bacteria symbiotic sludge, solve the technical problems of poor algae-bacteria synergy and excessive proliferation of microalgae under low carbon-nitrogen ratio sewage conditions, and strengthen the synergistic effect of algae-bacteria photosynthetic oxygen production and bacterial nitrogen and phosphorus conversion. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the structure of the sequencing batch algae and bacteria granular sludge reactor of the present invention.

[0021] Figure 2 shows the change in the algae-to-bacterial ratio of the algae-to-bacterial granular sludge during the two-stage operation of the present invention;

[0022] Figure 3 shows the COD removal efficiency variation curve during the two-stage operation of this invention;

[0023] Figure 4 shows the nitrogen removal efficiency variation curve during the two-stage operation of the present invention;

[0024] Figure 5 shows the change curve of phosphate removal efficiency during the two-stage operation of the present invention;

[0025] Figure 6 shows the nitrogen removal efficiency variation curve during the two-stage operation of Comparative Example 1.

[0026] Figure 7 shows the change curve of phosphate removal efficiency during the two-stage operation of Comparative Example 1.

[0027] Figure 8 shows the nitrogen removal efficiency variation curve during the two-stage operation of Comparative Example 2.

[0028] Figure 9 shows the change curve of phosphate removal efficiency during the two-stage operation of Comparative Example 2. Detailed Implementation

[0029] The present invention will now be described in further detail.

[0030] Example 1

[0031] A method for enhancing nitrogen and phosphorus removal from wastewater with algae and bacteria granular sludge in low carbon-to-nitrogen ratio conditions includes the following steps:

[0032] (1) Algal-bacterial symbiotic sludge, which had been domesticated in the laboratory for a long time, was used as inoculum sludge and injected into a sequencing batch reactor at a concentration of 4500 mg / L. For details of the algae and bacteria, please refer to the literature: Low-intensity aeration enhances algal–bacterial synergy to improve nitrogen removal from wastewater with low carbon-to-nitrogen ratio. Li, Y. etc. Bioresource Technology 445, 134055. https: / / doi.org / 10.1016 / j.biortech.2026.134055;

[0033] like Figure 1 As shown, the sequencing batch aerobic granular sludge reactor of the present invention includes a wastewater inlet tank 1, a biochemical reactor 2, and a wastewater outlet tank 11 connected in sequence; a peristaltic pump 3 is installed on the pipeline between the outlet of the wastewater inlet tank 1 and the inlet of the reactor 2; a light-emitting device 4 is installed on the outer side of the biochemical reactor 2; an air pump 5 is connected to an aeration disc 7 installed at the bottom of the biochemical reactor 2 for aerating the liquid in the reactor; a gas flow meter 6 is installed on the connecting pipeline between the air pump 5 and the aeration disc 7; a stirring device 8 is installed in the biochemical reactor 2; a sludge discharge port 9 is installed at the bottom of the biochemical reactor 2; a water outlet 10 is installed in the biochemical reactor 2; and a solenoid valve is installed on the pipeline between the water outlet 10 and the wastewater outlet tank 11.

[0034] (2) Low carbon-to-nitrogen ratio urban sewage is used as influent, with an influent COD concentration of 130-144 mg / L and NH4+ concentration of 100 mg / L. + -N concentration was 38-41 mg / L, PO4 3- -P concentration was 4.8-5.9 mg / L; reactor operating temperature was controlled at 25.0±3.0 ℃; low dissolved oxygen aeration was provided to the reactor through quartz sand aeration discs, with the aeration intensity stably controlled at 7-13 mL·min. -1 ·L -1 This maintains the aeration DO concentration at 0.4-0.6 mg / L; a full-spectrum LED lighting device provides illumination to the reactor, and the photosynthetic photon flux density on the reactor inner wall remains constant at 400-600 μmol·m⁻¹. -2 ·s -1 The total operating cycle of the reactor is 8 hours, and the operation is controlled in two stages. The entire process is controlled with 10 minutes of influent, 2 minutes of sedimentation, and 18 minutes of effluent. The remaining time is allocated according to the corresponding process stage, and the drainage ratio is 50%.

[0035] (3) The 0-30 days are the anaerobic / aerobic stage. The single cycle is operated in the following sequence: 10 min for influent, 90 min for anaerobic stage, 360 min for aerobic stage, 2 min for sedimentation, and 18 min for effluent. During the aerobic stage, the aeration and light synergy mode is adjusted in different time periods, namely aeration + light for 2 h, light only for 2 h, and aeration only for 2 h. In this stage, the algae and bacteria granular sludge achieves the initial adaptation to wastewater with low carbon-nitrogen ratio and removes nitrogen and phosphorus. The total nitrogen effluent concentration is controlled at 8.5-15.3 mg / L, and the phosphate removal rate is 48.6-60.4%. The algae-to-bacteria ratio of the algae and bacteria granular sludge formed in this stage is 1.22-1.27.

[0036] (4) The 30-60 days are the anaerobic / aerobic / anoxic stage. The single cycle is operated in the following sequence: 10 min for influent, 90 min for anaerobic stage, 180 min for aerobic stage, 180 min for anoxic stage, 2 min for sedimentation, and 18 min for effluent. Among them, the aerobic stage is controlled by aeration and light synergy mode, which is aeration + light for 2 h and light only for 1 h. Compared with the anaerobic / aerobic process stage, the energy consumed by aeration and light is reduced, and better nitrogen and phosphorus removal performance is achieved.

[0037] When the sludge settling volume index after 30 minutes is controlled at 41.5-46.8 mL / g, and granular sludge >200 μm accounts for more than 50% of the total sludge volume, it is considered that algae-bacterial granular sludge has formed. The algae-to-bacterial ratio of the algae-to-bacterial granular sludge formed in this stage is 0.85-1.08, see [reference needed]. Figure 2 .

[0038] This stage achieves deep nitrogen and phosphorus removal from wastewater with a low carbon-to-nitrogen ratio, reducing the total nitrogen concentration in the effluent to 5.9-7.5 mg / L and the phosphate removal rate to 72.0-76.8%.

[0039] Comparative Example 1

[0040] (1) Similar to Example 1, the algae-bacteria symbiotic sludge that has been domesticated in the laboratory for a long time is used as inoculum sludge and injected into the sequencing batch reactor at a sludge concentration of 4500 mg / L.

[0041] (2) Low carbon-to-nitrogen ratio urban sewage is used as influent, with an influent COD concentration of 130-144 mg / L and NH4+ concentration of 100 mg / L. + -N concentration was 38-41 mg / L, PO4 3- -P concentration was 4.8-5.9 mg / L; reactor operating temperature was controlled at 25.0±3.0 ℃; high dissolved oxygen aeration was provided to the reactor through ceramic membrane aeration discs, with the aeration intensity stably controlled at 8.0-13.0 mL·min. -1 ·L -1This maintains the aeration DO concentration at 3.7-4.2 mg / L; a full-spectrum LED lighting device provides illumination to the reactor, and the photosynthetic photon flux density on the reactor inner wall remains constant at 400-600 μmol·m⁻¹. -2 ·s -1 The total operating cycle of the reactor is 8 hours, and the operation is controlled in two stages. The entire process is controlled with 10 minutes of influent, 2 minutes of sedimentation, and 18 minutes of effluent. The remaining time is allocated according to the corresponding process stage, and the drainage ratio is 50%.

[0042] (1) 0-30 days is the anaerobic / aerobic stage, and the single-cycle operation conditions are consistent with those in Example 1. The total nitrogen effluent concentration in this stage is controlled at 12.0-14.7 mg / L, and the phosphate removal rate is 40.8-49.6%.

[0043] (3) 30-60 days is the anaerobic / aerobic / anoxic stage, and the single-cycle operation conditions are consistent with those in Example 1. The total nitrogen effluent concentration in this stage is controlled at 9.3-10.5 mg / L, and the phosphate removal rate is 58.3-66.9%.

[0044] Comparative Example 2

[0045] (1) Similar to Example 1, the algae-bacteria symbiotic sludge that has been domesticated in the laboratory for a long time is used as inoculum sludge and injected into the sequencing batch reactor at a sludge concentration of 4500 mg / L.

[0046] (2) Low carbon-to-nitrogen ratio urban sewage is used as influent, with an influent COD concentration of 130-144 mg / L and NH4+ concentration of 100 mg / L. + -N concentration was 38-41 mg / L, PO4 3- -P concentration was 4.8-5.9 mg / L; reactor operating temperature was controlled at 25.0±3.0 ℃; aeration was provided to the reactor through quartz sand aeration discs, with the aeration intensity stably controlled at 75-90 mL·min. -1 ·L -1 This maintains the aeration DO concentration at 1.7-2.2 mg / L; a full-spectrum LED lighting device provides illumination to the reactor, and the photosynthetic photon flux density on the reactor inner wall remains constant at 400-600 μmol·m⁻¹. -2 ·s -1 The total operating cycle of the reactor is 8 hours, and the operation is controlled in two stages. The entire process is controlled with 10 minutes of influent, 2 minutes of sedimentation, and 18 minutes of effluent. The remaining time is allocated according to the corresponding process stage, and the drainage ratio is 50%.

[0047] (3) 0-30 days is the anaerobic / aerobic stage, and the single-cycle operation conditions are consistent with those in Example 1. The total nitrogen effluent concentration in this stage is controlled at 10.0-14.9 mg / L, and the phosphate removal rate is 42.4-51.9%.

[0048] (4) 30-60 days is the anaerobic / aerobic / anoxic stage, and the single-cycle operation conditions are consistent with those in Example 1. The total nitrogen effluent concentration in this stage is controlled at 8.2-11.0 mg / L, and the phosphate removal rate is 41.5-54.6%.

[0049] Depend on Figure 2 It can be seen that low DO aeration combined with light can regulate the biomass ratio of microalgae and bacteria in the system. By reducing the light intensity and aeration time of the system by 25% and 50% respectively in 30-60 days, the algae-bacteria ratio was adjusted from 1.22-1.27 to 0.85-1.08. This is mainly because low aeration intensity can enhance the synergistic effect between microalgae and bacteria, and the reduction of light time can inhibit the growth rate of microalgae, thus avoiding excessive growth of microalgae in wastewater with low carbon-nitrogen ratio.

[0050] Depend on Figure 3 It can be seen that low-DO aeration combined with light can improve the COD removal capacity of algae and bacteria granular sludge systems.

[0051] Depend on Figure 4 It can be seen that low DO aeration combined with light can reduce the effluent concentration of nitrate nitrogen, thereby improving the total nitrogen removal capacity of the algae and bacteria granular sludge system.

[0052] Depend on Figure 5 It can be seen that low-DO aeration combined with light can improve the phosphate removal capacity of algae-bacterial granular sludge systems.

[0053] Depend on Figure 6 It can be seen that, in Comparative Example 1, high DO aeration combined with light can improve the total nitrogen removal capacity of the algae and bacteria granular sludge system, but the removal effect is weaker than that of the algae and bacteria granular sludge system under low DO aeration combined with light.

[0054] Depend on Figure 7 It can be seen that, in Comparative Example 1, high DO aeration combined with light can improve the removal capacity of phosphate in the algae and bacteria granular sludge system, but the removal effect is weaker than that of the algae and bacteria granular sludge system under low DO aeration combined with light.

[0055] Depend on Figure 8 It can be seen that, in Comparative Example 2, high-intensity aeration combined with light can improve the total nitrogen removal capacity of the algae and bacteria granular sludge system, but the removal effect is weaker than that of the algae and bacteria granular sludge system under low DO aeration combined with light.

[0056] Depend on Figure 9It can be seen that, in Comparative Example 2, high-intensity aeration combined with light can improve the total nitrogen removal capacity of the algae and bacteria granular sludge system, but the removal effect is weaker than that of the algae and bacteria granular sludge system under low DO aeration combined with light.

Claims

1. A method for nitrogen and phosphorus removal from wastewater with enhanced algae-bacterial granular sludge and low carbon-to-nitrogen ratio, characterized in that, Includes the following steps: Inoculate algae-bacterial symbiotic sludge into a sequencing batch reactor; Domestic sewage is introduced, and low-DO aeration is carried out. The reactor is treated with light and operated in an anaerobic / aerobic / anoxic mode. The algae-bacterial symbiotic sludge forms algae-bacterial granular sludge. The dissolved oxygen concentration in the low-DO aeration is controlled at 0.4-0.6 mg·L⁻¹. -1 The concentration of inoculated sludge was 4000-5000 mg / L.

2. The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge according to claim 1, characterized in that, The aeration intensity should be controlled at 7-13 mL / min. -1 ·L -1 .

3. The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge according to claim 1, characterized in that, The photosynthetic photon flux density on the inner wall of the reactor was maintained at 400-600 μmol·m -2 ·s -1 .

4. The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge according to claim 1, characterized in that, The reaction time in the anaerobic / aerobic / anoxic process stage is 1:2:2 for the anaerobic stage: aerobic stage: anoxic stage.

5. The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge according to claim 1, characterized in that, The low DO aeration and light exposure time provide an anaerobic environment for the system and inhibit excessive growth of microalgae. The algae-to-bacteria ratio of the algae-to-bacteria granular sludge is adjusted to 0.85-1.08, and nitrate removal is enhanced.

6. The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge according to claim 1, characterized in that, The conditions for the formation of algae-bacterial granular sludge are as follows: when the sludge settling volume index is controlled at 41.5-46.8 mL / g after 30 min, and granular sludge with a diameter >200 μm accounts for more than 50% of the total sludge volume, algae-bacterial granular sludge is considered to have formed.

7. The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge according to claim 1, characterized in that, The total nitrogen concentration in the effluent is less than 7.5 mg / L, and the phosphate removal rate is greater than 72.0%.

8. The method for enhanced nitrogen and phosphorus removal from low carbon-to-nitrogen ratio wastewater using algae-bacterial granular sludge according to claim 1, characterized in that, The total nitrogen concentration in the effluent was 5.9-7.5 mg / L, and the phosphate removal rate was 72.0-76.8%.

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