A method for improving the settling property and sewage treatment efficiency of algal-bacterial granular sludge

Abstract

The application discloses a method for improving stability and sewage treatment efficiency of alga-bacterium granular sludge, which is related to the type of added trace elements, the cultivation mode of algae and environmental conditions. The application provides a method for constructing stable alga-bacterium granular sludge symbiotic relationship and reducing mutual competition and inhibition relationship. Exogenous introduction of boric acid can affect the structural stability of cells and the efficiency of photosynthesis, regulate the growth and stability of alga-bacterium granules, ensure the sewage treatment efficiency of alga-bacterium granular sludge, and improve the stability of alga-bacterium granular sludge, so that the alga-bacterium granular sludge can be applied to actual working environment. Compared with other regulation factors such as AHLs or AI-2 signal molecules, the price of boron is reduced by 1000 times. When the boron concentration in the system is maintained at 80-200 muM, no environmental impact and health hazards are caused, and the method is a green technology method.

Description

Technical Field

[0001] This invention relates to the technical field of algae-bacterial granular sludge wastewater treatment, specifically to a method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge. Background Technology

[0002] In the field of wastewater treatment, algae-bacterial granular sludge technology, compared with the traditional activated sludge process, features low energy consumption, high treatment efficiency, and low greenhouse gas emissions, making it a green and sustainable wastewater treatment technology. The foundation of this process lies in the mutually beneficial symbiotic relationship of nutrient exchange and metabolic complementarity: microalgae absorb nutrients such as nitrogen and phosphorus from wastewater, converting them into biomass, and producing oxygen and organic matter through photosynthesis. Bacteria, through respiration, absorb organic matter produced by mineralized algae and organic matter in wastewater, producing CO2, which is then supplied to the algae as raw materials for photosynthesis, forming a mutually beneficial material cycle. This interaction not only solves the problems of small flocs and poor settling properties when using microalgae alone, but also reduces CO2 emissions and improves dissolved oxygen utilization through biological carbon sinks and in-situ oxygen production. However, when the nutrients in the environment cannot simultaneously meet the growth needs of both microalgae and bacteria, they will compete for nutrients. Furthermore, microalgae can produce algal toxins and extracellular secretions (amino acids, antibiotics) that inhibit bacterial growth or harm bacteria; bacteria can also release bacterial toxins that inhibit microalgal cell growth and even lyse algal cells, exhibiting an algicidal effect. This competitive or inhibitory relationship not only alters the composition of the algal-bacterial community but also affects the healthy material and energy cycle between them. Therefore, maintaining the mutually beneficial symbiotic relationship between algae and bacteria, especially strengthening the symbiotic relationship and maintaining system stability in the face of adverse conditions such as fluctuating environmental conditions and insufficient nutrients, is currently a key technical challenge of this process.

[0003] Although research on algae-bacterial granular sludge has been conducted, most studies remain in the laboratory stage and have not yet been applied on a large scale. A core issue is how to establish a stable symbiotic relationship between algae and bacteria. The interaction between microalgae and bacteria is complex, including both mutually beneficial symbiotic relationships involving the use of metabolic products and competitive and inhibitory relationships regarding nutrients. Studies have shown that signal transduction is an important way to regulate the interaction between algae and bacteria, and the growth and stability of algae-bacterial granules can be regulated using interspecific signaling molecules. Previous studies have largely focused on the regulation of algae-bacterial granules by intraspecific N-acylated homoserine lactones (AHLs) through quorum sensing (QS), neglecting the important role of interspecific furanoborates (AI-2) in the later stages of granule maturation. In granular sludge systems, mature granules are mainly regulated by AI-2 signaling molecules, while AHLs primarily play a role in granule formation. In practical applications, the method of directly adding AHL-type or AI-2-type signaling molecules is unsustainable due to problems such as high cost and easy degradation by the system.

[0004] Boron, as a key component of AI-2 precursors, can directly stimulate AI-2 production. Furthermore, boron is essential for algal growth and development, participating in the metabolism of hormones such as indole-3-acetic acid (IAA). Exogenous boron significantly enhances the photosynthetic efficiency of green algae, while boron deficiency restricts plant growth and hinders IAA transport. Therefore, boron has a dual impact on both metabolism and signaling, and can strengthen algal-microbe symbiotic systems. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of existing algae-bacterial granular sludge systems, such as poor particle stability and deterioration of wastewater treatment effect after long-term operation, thereby providing an enhanced method to improve the stability and operational efficiency of algae-bacterial granular sludge systems. To solve the above problems, this application achieves this through the following technical solution:

[0006] A method for improving the settling properties and wastewater treatment efficiency of algae-bacteria granular sludge includes the following steps: S1, adding aerobic granules and synthetic wastewater into a reactor, and cultivating mature algae-bacteria granular sludge under light and aerobic conditions;

[0007] S2. Add the mature algae-bacteria granular sludge from step S1, the synthesized wastewater and boric acid into the reactor, and operate it under light, aeration or zero aeration. After settling, the treated purified water is obtained.

[0008] In step S1, the aerobic particles have a particle size of 1.0~1.4 mm, SV 30 / SV5=0.86~0.94.

[0009] In step S1, the synthetic wastewater includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH adjuster.

[0010] The concentrations of NaAc, NH4Cl, and KH2PO4 were 515–520 mg / L, 150–155 mg / L, and 20–23 mg / L, respectively.

[0011] The synthetic wastewater also includes MgSO4·7H2O, CaCl2, and FeSO4·7H2O.

[0012] The concentrations of MgSO4·7H2O were 48–52 mg / L; the concentrations of CaCl2 were 19–21 mg / L; and the concentrations of FeSO4·7H2O were 9–11 mg / L.

[0013] The synthetic wastewater also includes a trace element solution with a concentration of 0.9~1.1 mg / L; the trace element solution consists of 10000 mg / L EDTA, 100 mg / L MnSO2·H2O, 30 mg / L CuSO2·5H2O, 120 mg / L ZnSO2·7H2O, 60 mg / L Na2MoO4·2H2O, 180 mg / L KI, and 150 mg / L CoCl2·6H2O.

[0014] The synthetic wastewater has a COD concentration of 385-430 mg / L and an NH4+ concentration of... + -N was 36.5~43.5 mg / L, PO4 3- -P is 4.5~5.5 mg / L, pH is 7~8.

[0015] In step S1, the ratio of aerobic particles to synthetic wastewater is 2.9~3.1g:1L.

[0016] In step S1, the reactor is a cylindrical sequencing batch reactor; the water exchange cycle of the reactor is 2 times / day, the water inlet time of each cycle is 18~22min, the aeration time is 655~665min, the settling time is 18~22min, and the drainage time is 19~21min. Preferably, in step S1, the water exchange volume is 0.2~0.5L.

[0017] In step S1, the light intensity is 190~210 μmol•m. -2 •s -1 .

[0018] In step S1, the aerobic condition is a dissolved oxygen concentration of 2.5~3.0 mg / L.

[0019] In step S1, the particle size of the mature algae-bacteria granular sludge is 1.0~1.5mm.

[0020] Preferably, in step S1, the culture time is 30-40 days.

[0021] Preferably, in step S1, the light-dark cycle ratio is 12h / 12h.

[0022] In step S2, the ratio of mature algae-bacterial granular sludge to synthetic wastewater is 4~4.5g:1L.

[0023] In step S2, the synthetic wastewater includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH adjuster.

[0024] The concentrations of NaAc, NH4Cl, and KH2PO4 were 145–520 mg / L, 150–155 mg / L, and 20–23 mg / L, respectively.

[0025] The synthetic wastewater also includes MgSO4·7H2O, CaCl2 and FeSO4·7H2O;

[0026] The concentrations of MgSO4·7H2O were 48–52 mg / L, CaCl2 was 19–21 mg / L, and FeSO4·7H2O was 9–11 mg / L.

[0027] The synthetic wastewater also includes a trace element solution with a concentration of 0.9–1.1 mg / L. The trace element solution consists of 10,000 mg / L EDTA, 100 mg / L MnSO₂·H₂O, 30 mg / L CuSO₂·5H₂O, 120 mg / L ZnSO₂·7H₂O, 60 mg / L Na₂MoO₄·2H₂O, 180 mg / L KI, and 150 mg / L CoCl₂·6H₂O.

[0028] The synthetic wastewater has a COD concentration of 110~430 mg / L and an NH4+ concentration of... + -N was 36.5~43.5 mg / L, PO4 3- -P is 4.5~5.5 mg / L, pH is 7~8.

[0029] Preferably, in step S2, the reactor is a cylindrical sequencing batch reactor; the reactor has a water exchange cycle of 4 times / day, with an influent time of 18-22 minutes, an aeration or zero aeration operation time of 295-305 minutes, a sedimentation time of 18-22 minutes, a drainage time of 19-21 minutes, and a water exchange volume of 0.2-0.5 L per cycle.

[0030] Preferably, in step S2, boric acid is added once every 24 hours, with a boric acid:sewage ratio of 80~200 μmol:1L.

[0031] Preferably, in step S2, the light intensity is 190~210 μmol•m -2 •s -1 The light-dark cycle ratio is 12h / 12h.

[0032] Preferably, in step S2, the dissolved oxygen concentration is 2.5~3.0 mg / L during aeration, and only oscillation is performed during zero aeration, with an oscillation rate of 120~130 rpm.

[0033] The principle of this invention is as follows:

[0034] 1. Cultivation of mature algae-bacteria particles

[0035] Aerobic granules were added to a cylindrical sequencing batch reactor containing synthetic wastewater to achieve a granule concentration of 2.9–3.1 g / L. The dissolved oxygen concentration was controlled to maintain aerobic conditions of 2.5–3.0 mg / L. Light-emitting diodes (LEDs) were used to monitor the photosynthetic photon flux density (PPFD) at 190–210 μmol•m⁻¹. -2 •s -1 The reactor was irradiated under a light / dark cycle ratio of 12h / 12h. After 30-40 days of cultivation and operation, the algae-bacteria granular sludge gradually matured, exhibiting a typical green color and a particle size of 1.0-1.5mm.

[0036] In step 1, the aerobic particles have a particle size of 1.0~1.4mm, SV 30 / SV5=0.86~0.94.

[0037] In step 1, the synthesized wastewater uses NaAc as the carbon source, NH4Cl as the nitrogen source, KH2PO4 as the phosphorus source, and NaHCO3 as the pH adjuster. The COD concentration is 385~430 mg / L, and the NH4... + -N concentration was 36.5~43.5 mg / L, PO4 3- -P concentration is 4.5~5.5 mg / L, and system pH is 7~8.

[0038] The operating conditions of the reactor in step 1 are as follows: the water exchange cycle is 2 times / day, the water inlet time is 18~22 min, the aeration time is 655~665 min, the settling time is 18~22 min, the drainage time is 19~21 min, and the water exchange rate is 50%; the reactor is operated at room temperature, with a temperature of 23~27℃.

[0039] 2. Construction of Algae-Fungus Particle Enhancement System

[0040] The mature algae-bacterial granules from step 1 are added to a cylindrical sequencing batch reactor containing synthetic wastewater to achieve an algae-bacterial granule concentration of 4–4.5 g / L. 80–200 μM boric acid is added to the reactor every 24 hours. The control system is kept in either aeration or zero-aeration mode, using light-emitting diodes (LEDs) at a photosynthetic photon flux density (PPFD) of 190–210 μmol•m³. -2 •s -1 The reactor was irradiated under a light / dark cycle ratio of 12h / 12h. The reactor can operate stably for a long time. Compared with the reactor without boric acid, the reactor has higher treatment efficiency for ammonia nitrogen and phosphorus, and the algae-bacterial sludge particles have better settling properties.

[0041] The wastewater quality synthesized in step 2 is suitable under both normal C / N ratio (C / N ratio > 4) and low C / N ratio (C / N ratio < 4) conditions. Under normal C / N ratio conditions: NaAc is used as the carbon source, NH4Cl as the nitrogen source, KH2PO4 as the phosphorus source, and NaHCO3 as the pH adjuster; the COD concentration is 385~430 mg / L, and NH4... + -N concentration was 36.5~43.5 mg / L, PO4 3- -P concentration is 4.5~5.5 mg / L, system pH is 7-8; at a low carbon-to-nitrogen ratio: NaAc is used as the carbon source, NH4Cl as the nitrogen source, KH2PO4 as the phosphorus source, NaHCO3 as the pH adjuster, COD concentration is 110~130 mg / L, NH4... + -N concentration was 36.5~43.5 mg / L, PO4 3— The P concentration is 4.5~5.5 mg / L and the system pH is 7-8.

[0042] The system in step 2 can be operated in two modes: aeration or zero aeration. When aeration is performed, the dissolved oxygen concentration is above 2.5~3.0 mg / L. When zero aeration is performed, no additional aeration is required; the system simply shakes on the vibrator at a speed of 120~130 rpm.

[0043] The long-term operation mentioned in step 2 refers to stable operation for more than 50 days, with a significant increase in the removal rates of ammonia nitrogen and phosphate in the system, and a significant enhancement in the settling properties of algae-bacterial sludge particles in the system.

[0044] The operating conditions of the reactor in step 2 are as follows: the water exchange cycle is 4 times / day, the water inlet time is 18~22 min per cycle, the aeration or shaking time is 295~305 min, the settling time is 18~22 min, the drainage time is 19~21 min, and the water exchange rate is 50%; the reactor is operated at room temperature, with a temperature of 23℃~27℃.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] 1. The purpose of this invention is to utilize boric acid to enhance the symbiotic relationship between algae and bacteria particles (especially under zero aeration) and the system's shock resistance, and to provide a method to simultaneously promote the metabolism of algae and bacteria, thereby achieving a stable symbiotic relationship, improving sludge settling and stability, and ensuring the wastewater treatment efficiency of algae-bacterial particle sludge, thus enabling its application in actual working environments.

[0047] 2. This invention is applicable to algae-bacteria granular sludge systems under aeration or zero aeration conditions.

[0048] 3. This invention is applicable to algae-bacteria granular sludge systems that treat water with normal carbon-nitrogen ratio (carbon-nitrogen ratio > 4) or low carbon-nitrogen ratio (carbon-nitrogen ratio < 4).

[0049] 4. This invention primarily utilizes added boric acid to address the algae-bacterial granular sludge system, enabling stable operation for over 50 days, especially under zero aeration conditions. This invention leverages boron to simultaneously promote the growth of both bacteria and algae, which is beneficial for maintaining the algae-bacterial symbiotic relationship and enhancing shock resistance. Boric acid can stimulate Al-2 production and promote photosynthetic efficiency. However, high concentrations of boric acid can cause boron toxicity. This invention determines the optimal boric acid addition level to be 80-200 μmol / L. At a boric acid addition level of 80-200 μmol / L, nitrogen and phosphorus removal efficiency and particle settling properties are significantly improved. Attached Figure Description

[0050] Figure 1 This is a graph showing the effect of boric acid concentration on pollutant removal under zero aeration and normal carbon-to-nitrogen ratio.

[0051] Figure 2 The graph shows the effect of aeration, normal carbon-to-nitrogen ratio, and boric acid concentration on pollutant removal.

[0052] Figure 3 This is a graph showing the effect of boric acid concentration on pollutant removal under aeration and low carbon-to-nitrogen ratio conditions. Detailed Implementation

[0053] Unless otherwise specified, the following examples are tested in accordance with national standards: Drying method: CJ / T 221-2005 Sludge testing method for urban wastewater treatment plants, rapid digestion spectrophotometric method HJT399-2007, HJ533-2009 Nessler's reagent spectrophotometric method, HJ 632-2011 Determination of total phosphorus in soil by alkaline fusion-molybdenum antimony resist spectrophotometric method.

[0054] The aerobic granules were purchased from Jiangsu Shangshan Environmental Protection Technology Co., Ltd., and the aerobic granule size is 1.0~1.5mm.

[0055] Example 1

[0056] A method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge specifically includes the following steps:

[0057] (1) Cultivation of mature algae-bacteria granular sludge

[0058] A cylindrical sequencing batch reactor (SBR) was selected as the experimental setup. The reactor was 40 cm high, with an inner diameter of 6 cm and a height-to-diameter ratio of 6:1, and an effective volume of 1 L. Aerobic granules were added to the reactor containing synthetic wastewater to achieve a concentration of 3.0 g / L. External illumination was provided at an intensity of 190–210 μmol·m⁻². -2 •s -1 A light source with a light-dark cycle ratio of 12h / 12h was used for cultivation under aerobic conditions at 24℃ and a dissolved oxygen concentration of 2.5mg / L. After 35 days of cultivation, mature algae-bacteria granular sludge was obtained, exhibiting a typical green color and a particle size of 1.0~1.5mm.

[0059] In step (1), the aerobic particle size is 1.0~1.4mm, SV 30 / SV5=0.86~0.94.

[0060] In step (1), the composition of the synthetic wastewater is as follows: NaAc concentration is 520 mg / L, NH4Cl concentration is 153 mg / L, KH2PO4 concentration is 22 mg / L, MgSO4·7H2O concentration is 50 mg / L, CaCl2 concentration is 20 mg / L, FeSO4·7H2O concentration is 10 mg / L, and trace element solution concentration is 1 mg / L; the composition of the trace element solution is 10000 mg / L EDTA, 100 mg / L MnSO2·H2O, 30 mg / L CuSO2·5H2O, 120 mg / L ZnSO2·7H2O, 60 mg / L Na2MoO4·2H2O, 180 mg / L KI, and 150 mg / L CoCl2·6H2O.

[0061] In step (1), the synthetic wastewater uses NaAc as the carbon source, NH4Cl as the nitrogen source, KH2PO4 as the phosphorus source, and NaHCO3 as the pH adjuster. The COD concentration is 400 mg / L, and the NH4Cl concentration is 400 mg / L. + -N concentration was 40 mg / L, PO4 3- -P concentration is 5 mg / L, system pH is 7.5.

[0062] In step (1), the hydraulic retention time of the reactor is 24 hours, the water exchange cycle is 2 times / day, the water inlet time is 20 minutes, the aeration time is 660 minutes, the settling time is 20 minutes, the drainage time is 20 minutes, and the water exchange volume is 50% (0.5L).

[0063] (2) Construction of algae-bacterial granular sludge enhancement system under zero aeration and normal carbon-nitrogen ratio conditions

[0064] Five identical cylindrical sequencing batch reactors were selected as the experimental setup. Each reactor had a volume of 600 mL, with an effective volume of 400 mL, an inner diameter of 8 cm, and a height of 18 cm. Mature algae-bacterial granular sludge from step (1) was distributed into the five reactors containing synthetic wastewater, resulting in an algae-bacterial granule concentration of 4.3 g / L. Boric acid was added to the five reactors every 24 hours at concentrations of 0 µmol / L, 50 µmol / L, 80 µmol / L, 200 µmol / L, and 2000 µmol / L, respectively. An external light intensity of 190–210 μmol•m was added. -2 •s -1 A light source with a light-dark cycle ratio of 12h / 12h was used, and the reactor was operated for 60 days in a zero-aeration mode at room temperature of 23~27℃.

[0065] In step (2), the composition and quality of the synthetic wastewater are the same as in step (1).

[0066] In step (2), no additional aeration is required during zero aeration. The reactor is simply placed in a constant temperature shaking culture device with a shaking speed of 120-130 rpm and shaken.

[0067] In step (2), the hydraulic retention time of the reactor is 12h, the water exchange cycle is 4 times / day, the water inlet time is 20min, the oscillation time is 300min, the settling time is 20min, the drainage time is 20min, and the water exchange volume is 50% (0.2L).

[0068] (3) Stability of algae-bacterial granular sludge and wastewater treatment efficiency under zero aeration and normal carbon-nitrogen ratio conditions

[0069] The sludge concentration (MLSS) and sludge volume index (SVI5) of the algae-bacterial granular sludge were determined: sludge concentration was determined by drying method; after obtaining the sludge mixture, the sludge settling ratio (SV5) at 5 min was measured, and SVI5 = SV5 / MLSS (mL / g); COD was determined by rapid digestion spectrophotometry, ammonia nitrogen by Nessler's reagent spectrophotometry, and phosphate by molybdenum-antimony anti-phosphate spectrophotometry. The results are shown in Table 1.

[0070] Table 1 Comparison of sludge concentration and SVI5 concentration

[0071]

[0072] Please refer to Figure 1 Under normal C / N ratio conditions with zero aeration, the sludge concentration in the reactor system with added boric acid was significantly higher than that in the reactor without added boric acid, indicating that adding boric acid can significantly promote the growth of algae-bacterial granular sludge. The SVI5 of the reactor without added boric acid was significantly higher than that of other groups, indicating that adding boric acid can significantly improve the settling properties of algae-bacterial granular sludge. When adding 80 µmol / L and 200 µmol / L boric acid, the algae-bacterial granular sludge in the reactor system showed a significant growth advantage, high stability, and the best settling performance. The addition of boric acid did not significantly promote COD removal, and the COD removal rate was above 80%. The addition of 80 µmol / L and 200 µmol / L boric acid can significantly improve the removal efficiency of ammonia nitrogen and phosphate in wastewater, with an ammonia nitrogen removal rate above 90% and a phosphate removal rate above 88%.

[0073] Example 2

[0074] A method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge specifically includes the following steps:

[0075] (1) Cultivation of mature algae-bacteria granular sludge

[0076] A cylindrical photocatalytic batch reactor was selected as the experimental setup. The reactor was 40 cm high, with an inner diameter of 6 cm and a height-to-diameter ratio of 6:1, and an effective volume of 1 L. Aerobic granules were added to the reactor containing synthetic wastewater to achieve a concentration of 2.9–3.1 g / L. External light intensity was added at 190–210 μmol•m. -2 •s -1 The algae-bacteria granular sludge was cultured under a light source with a light / dark cycle ratio of 12h / 12h, at 24℃, and under aerobic conditions with a dissolved oxygen concentration of 2.5mg / L. After 35 days of cultivation, mature algae-bacteria granular sludge was obtained, which was typically green and had a particle size of 1.0~1.5mm.

[0077] In step (1), the aerobic particle size is 1.0~1.4mm, SV30 / SV5=0.86~0.94.

[0078] In step (1), the composition of the synthetic wastewater is as follows: NaAc concentration is 520 mg / L, NH4Cl concentration is 153 mg / L, KH2PO4 concentration is 22 mg / L, MgSO4·7H2O concentration is 50 mg / L, CaCl2 concentration is 20 mg / L, FeSO4·7H2O concentration is 10 mg / L, and trace element solution concentration is 1 mg / L; the composition of the trace element solution is 10000 mg / L EDTA, 100 mg / L MnSO2·H2O, 30 mg / L CuSO2·5H2O, 120 mg / L ZnSO2·7H2O, 60 mg / L Na2MoO4·2H2O, 180 mg / L KI, and 150 mg / L CoCl2·6H2O.

[0079] In step (1), the synthetic wastewater uses NaAc as the carbon source, NH4Cl as the nitrogen source, KH2PO4 as the phosphorus source, and NaHCO3 as the pH adjuster. The COD concentration is 400 mg / L, and the NH4Cl concentration is 400 mg / L. + -N concentration was 40 mg / L, PO4 3- -P concentration is 5 mg / L, system pH is 7.5.

[0080] In step (1), the hydraulic retention time of the reactor is 24 hours, the water exchange cycle is 2 times / day, the water inlet time is 20 minutes, the aeration time is 660 minutes, the settling time is 20 minutes, the drainage time is 20 minutes, and the water exchange volume is 50% (0.5L).

[0081] (2) Construction of an algae-bacterial granular sludge enhancement system under aeration and normal carbon-nitrogen ratio conditions

[0082] Five identical cylindrical sequencing batch reactors were selected as the experimental setup. Each reactor had a volume of 600 mL, with an effective volume of 400 mL, an inner diameter of 8 cm, and a height of 18 cm. Mature algae-bacterial granular sludge from step (1) was distributed into the five reactors containing synthetic wastewater, resulting in an algae-bacterial granule concentration of 4.3 g / L. Boric acid was added to the five reactors every 24 hours at concentrations of 0 µmol / L, 50 µmol / L, 80 µmol / L, 200 µmol / L, and 2000 µmol / L, respectively. An external light intensity of 190–210 μmol•m was added. -2 •s -1 A light source with a light-dark cycle ratio of 12h / 12h was used, and the reactor was operated for 60 days at room temperature of 23~27℃ using an aeration method.

[0083] In step (2), the composition and quality of the synthetic wastewater are the same as in step (1).

[0084] In step (2), the dissolved oxygen concentration during aeration is 2.5~3.0 mg / L.

[0085] In step (2), the hydraulic retention time of the reactor is 12h, the water exchange cycle is 4 times / day, the water inlet time is 20min, the aeration time is 300min, the settling time is 20min, the drainage time is 20min, and the water exchange volume is 50% (0.2L).

[0086] (3) Stability of algae-bacterial granular sludge and wastewater treatment efficiency under aeration and normal carbon-nitrogen ratio conditions

[0087] The sludge concentration (MLSS) and sludge volume index (SVI5) of the algae-bacterial granules were determined: sludge concentration was determined by drying method; after obtaining the sludge mixture, the sludge settling ratio (SV5) at 5 min was measured, and SVI5 = SV5 / MLSS (mL / g); COD was determined by rapid digestion spectrophotometry, ammonia nitrogen by Nessler's reagent spectrophotometry, and phosphate by molybdenum-antimony anti-phosphate spectrophotometry. The results are shown in Table 2.

[0088] Table 2 Comparison of sludge concentration and SVI5 concentration

[0089]

[0090] Please refer to Figure 2 Under normal aeration and C / N ratio conditions, the sludge concentration in the reactor system with added boric acid was significantly higher than that in the reactor without added boric acid, indicating that adding boric acid can significantly promote the growth of algae-bacterial granular sludge. The SVI5 of the reactor without added boric acid was significantly higher than that of other groups, indicating that adding boric acid can significantly improve the settling properties of algae-bacterial granular sludge. When adding 80 µmol / L and 200 µmol / L boric acid, the algae-bacterial granular sludge in the reactor system showed a significant growth advantage, high stability, and optimal settling performance. The addition of boric acid did not significantly promote COD removal, with COD removal rates exceeding 85%. Adding 80 µmol / L and 200 µmol / L boric acid significantly improved the removal efficiency of ammonia nitrogen and phosphate in wastewater, with ammonia nitrogen removal rates exceeding 95% and phosphate removal rates exceeding 92%.

[0091] Example 3

[0092] A method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge specifically includes the following steps:

[0093] (1) Cultivation of mature algae-bacteria granular sludge

[0094] A cylindrical photocatalytic batch reactor was selected as the experimental setup. The reactor was 40 cm high, with an inner diameter of 6 cm and a height-to-diameter ratio of 6:1, and an effective volume of 1 L. Aerobic granules were added to the reactor containing synthetic wastewater to achieve a concentration of 2.9–3.1 g / L. External light intensity was added at 190–210 μmol•m. -2 •s -1 A light source with a light-dark cycle ratio of 12h / 12h was used for cultivation under aerobic conditions at 23~27℃ and a dissolved oxygen concentration of 2.5mg / L. After 35 days of cultivation, mature algae-bacteria granular sludge was obtained, exhibiting a typical green color and a particle size of 1.0~1.5mm.

[0095] In step (1), the aerobic particle size is 1.0~1.4mm, SV 30 / SV5=0.86~0.94.

[0096] In step (1), the composition of the synthetic wastewater is as follows: NaAc concentration is 520 mg / L, NH4Cl concentration is 153 mg / L, KH2PO4 concentration is 22 mg / L, MgSO4·7H2O concentration is 50 mg / L, CaCl2 concentration is 20 mg / L, FeSO4·7H2O concentration is 10 mg / L, and trace element solution concentration is 1 mg / L; the composition of the trace element solution is 10000 mg / L EDTA, 100 mg / L MnSO2·H2O, 30 mg / L CuSO2·5H2O, 120 mg / L ZnSO2·7H2O, 60 mg / L Na2MoO4·2H2O, 180 mg / L KI, and 150 mg / L CoCl2·6H2O.

[0097] In step (1), the synthetic wastewater uses NaAc as the carbon source, NH4Cl as the nitrogen source, KH2PO4 as the phosphorus source, and NaHCO3 as the pH adjuster. The COD concentration is 400 mg / L, and the NH4Cl concentration is 400 mg / L. + -N concentration was 40 mg / L, PO4 3- -P concentration is 5 mg / L, system pH is 7.

[0098] In step (1), the hydraulic retention time of the reactor is 24 hours, the water exchange cycle is 2 times / day, the water inlet time is 20 minutes, the aeration time is 660 minutes, the settling time is 20 minutes, the drainage time is 20 minutes, and the water exchange volume is 50% (0.5L).

[0099] (2) Construction of an algae-bacterial granular sludge enhancement system under aeration and low carbon-nitrogen ratio conditions

[0100] Five identical cylindrical sequencing batch reactors were selected as the experimental setup. Each reactor had a volume of 600 mL, with an effective volume of 400 mL, an inner diameter of 8 cm, and a height of 18 cm. Mature algae-bacterial granular sludge from step (1) was distributed into the five reactors containing synthetic wastewater, resulting in an algae-bacterial granule concentration of 4.3 g / L. Boric acid was added to the five reactors every 24 hours at concentrations of 0 µmol / L, 50 µmol / L, 80 µmol / L, 200 µmol / L, and 2000 µmol / L, respectively. An external light intensity of 190–210 μmol•m was added. -2 •s -1 A light source with a light-dark cycle ratio of 12h / 12h was used, and the reactor was operated for 60 days at room temperature of 23℃~27℃ using an aeration method.

[0101] In step (2), the composition of the synthetic wastewater is as follows: NaAc concentration is 150 mg / L, NH4Cl concentration is 153 mg / L, KH2PO4 concentration is 22 mg / L, MgSO4·7H2O concentration is 50 mg / L, CaCl2 concentration is 20 mg / L, FeSO4·7H2O concentration is 10 mg / L, and trace element solution concentration is 1 mg / L; the composition of the trace element solution is 10000 mg / L EDTA, 100 mg / L MnSO2·H2O, 30 mg / L CuSO2·5H2O, 120 mg / L ZnSO2·7H2O, 60 mg / L Na2MoO4·2H2O, 180 mg / L KI, and 150 mg / L CoCl2·6H2O.

[0102] In step (2), the synthesized wastewater uses NaAc as the carbon source, NH4Cl as the nitrogen source, KH2PO4 as the phosphorus source, and NaHCO3 as the pH adjuster. The COD concentration is 120 mg / L, and the NH4Cl concentration is 120 mg / L. + -N concentration was 40 mg / L, PO4 3- -P concentration is 5 mg / L, system pH is 7.5.

[0103] In step (2), the dissolved oxygen concentration during aeration is 2.5~3.0 mg / L.

[0104] In step (2), the hydraulic retention time of the reactor is 12h, the water exchange cycle is 4 times / day, the water inlet time is 22min, the aeration time is 305min, the settling time is 22min, the drainage time is 21min, and the water exchange volume is 50% (0.2L).

[0105] (3) Stability of algae-bacteria particles and wastewater treatment efficiency under aeration and low carbon-nitrogen ratio conditions

[0106] The sludge concentration (MLSS) and sludge volume index (SVI5) of the algae-bacterial granules were determined: sludge concentration was determined by drying method; after obtaining the sludge mixture, the sludge settling ratio (SV5) at 5 min was measured, SVI5 = SV5 / MLSS (mL / g); COD was determined by rapid digestion spectrophotometry, ammonia nitrogen by Nessler's reagent spectrophotometry, and phosphate by molybdenum-antimony anti-phosphate spectrophotometry. The results are shown in Table 3.

[0107] Table 3 Comparison of sludge concentration and SVI5 concentration

[0108]

[0109] Please refer to Figure 3 Under low C / N ratio aeration conditions, the sludge concentration in the reactor system with added boric acid was significantly higher than that in the reactor without added boric acid, indicating that adding boric acid can significantly promote the growth of algae-bacterial granular sludge. The SVI5 of the reactor without added boric acid was significantly higher than that of other groups, indicating that adding boric acid can significantly improve the settling properties of algae-bacterial granular sludge. When adding 80 µmol / L and 200 µmol / L boric acid, the algae-bacterial granular sludge in the reactor system showed a significant growth advantage, high stability, and optimal settling performance. The addition of boric acid did not significantly promote COD removal, with COD removal rates exceeding 75%. The addition of 80 µmol / L and 200 µmol / L boric acid significantly improved the removal efficiency of ammonia nitrogen and phosphate in wastewater, with removal rates of both ammonia nitrogen and phosphate exceeding 85%.

Claims

1. A method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge, characterized in that, Includes the following steps: S1. Aerobic granules and synthetic wastewater are added to the reactor and cultured under light and aerobic conditions to obtain mature algae-bacteria granular sludge. S2. Add the mature algae-bacterial granular sludge from step S1, the synthesized wastewater and boric acid to the reactor, and operate it under light, aeration or zero aeration. After settling, the treated purified water is obtained. In step S2, the ratio of boric acid to wastewater is 80~200 μmol: 1 L.

2. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S1, the synthetic wastewater includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH adjuster. The concentrations of NaAc, NH4Cl, and KH2PO4 were 515–520 mg / L, 150–155 mg / L, and 20–23 mg / L, respectively. The synthetic wastewater also includes MgSO4·7H2O, CaCl2, and FeSO4·7H2O. The concentrations of MgSO4·7H2O were 48–52 mg / L; the concentrations of CaCl2 were 19–21 mg / L; and the concentrations of FeSO4·7H2O were 9–11 mg / L. The synthetic wastewater also includes a trace element solution with a concentration of 0.9~1.1 mg / L; the trace element solution consists of 10000 mg / L EDTA, 100 mg / L MnSO2·H2O, 30 mg / L CuSO2·5H2O, 120 mg / L ZnSO2·7H2O, 60 mg / L Na2MoO4·2H2O, 180 mg / L KI, and 150 mg / L CoCl2·6H2O. The synthetic wastewater has a COD concentration of 385-430 mg / L and an NH4+ concentration of... + -N was 36.5~43.5 mg / L, PO4 3- -P is 4.5~5.5 mg / L, pH is 7~8.

3. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S1, the ratio of aerobic particles to synthetic wastewater is 2.9~3.1g:1L.

4. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S1, the reactor is a cylindrical sequencing batch reactor; the water exchange cycle of the reactor is 2 times / day, with an influent time of 18~22 minutes, an aeration time of 655~665 minutes, a settling time of 18~22 minutes, and a drainage time of 19~21 minutes per cycle.

5. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S1, the aerobic condition is a dissolved oxygen concentration of 2.5~3.0 mg / L.

6. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S2, the ratio of mature algae-bacterial granular sludge to synthetic wastewater is 4~4.5g:1L.

7. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S2, the synthetic wastewater includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH adjuster. The concentrations of NaAc, NH4Cl, and KH2PO4 were 145–520 mg / L, 150–155 mg / L, and 20–23 mg / L, respectively. The synthetic wastewater also includes MgSO4·7H2O, CaCl2 and FeSO4·7H2O; The concentrations of MgSO4·7H2O were 48–52 mg / L, CaCl2 was 19–21 mg / L, and FeSO4·7H2O was 9–11 mg / L. The synthetic wastewater also includes a trace element solution with a concentration of 0.9–1.1 mg / L. The trace element solution consists of 10,000 mg / L EDTA, 100 mg / L MnSO₂·H₂O, 30 mg / L CuSO₂·5H₂O, 120 mg / L ZnSO₂·7H₂O, 60 mg / L Na₂MoO₄·2H₂O, 180 mg / L KI, and 150 mg / L CoCl₂·6H₂O. The synthetic wastewater has a COD concentration of 110~430 mg / L and an NH4+ concentration of... + -N was 36.5~43.5 mg / L, PO4 3- -P is 4.5~5.5 mg / L, pH is 7~8.

8. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S2, the light intensity is 190~210 μmol•m -2 •s -1 .

9. The method for improving the settling properties and wastewater treatment efficiency of algae-bacterial granular sludge according to claim 1, characterized in that, In step S2, the reactor is a cylindrical sequencing batch reactor; the reactor has a water exchange cycle of 4 times / day, with an influent time of 18-22 minutes, an aeration or zero aeration operation time of 295-305 minutes, a sedimentation time of 18-22 minutes, a drainage time of 19-21 minutes, and a water exchange volume of 0.2-0.5L.

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