Method for improving settleability of algae-bacterium granule sludge and sewage treatment efficiency

Abstract

The invention discloses a method for improving stability of algae-bacteria granular sludge and sewage treatment efficiency. The method is related to types of added trace elements, culture modes of algae and environmental conditions. The invention provides a method for constructing a stable algae-bacterium granule sludge symbiotic relationship and reducing a mutual competition and inhibition relationship, boric acid is introduced from an external source, so that the structural stability of cells and the efficiency of photosynthesis can be influenced, and the growth and stability of algae-bacterium granules are regulated and controlled, namely the sewage treatment efficiency of the algae-bacterium granule sludge is ensured; the stability of the algae-bacteria granular sludge can be improved, so that the algae-bacteria granular sludge can be applied to an actual working environment. Compared with other regulatory factors, such as AHLs or AI-2 signal molecules, the price cost of the boron element is reduced by 1000 times. And when the boron concentration of the system is maintained at 80-200 [mu] M, environmental influence and health hazard are not generated, and the method is a green technical method.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment with algae-bacteria granular sludge, and in particular to a method for improving the sedimentation property of algae-bacteria granular sludge and sewage treatment efficiency. Background Art

[0002] Compared with the traditional activated sludge method, the algae-bacteria granular sludge technology in the field of sewage treatment has the characteristics of low energy consumption, high treatment efficiency and low greenhouse gas emissions. It is a green and sustainable sewage treatment technology. The mutually beneficial symbiotic relationship of nutrient exchange and metabolic complementarity is the basis of this process: microalgae absorb nutrients such as nitrogen and phosphorus in sewage and convert them into biomass, and produce oxygen and organic matter through photosynthesis. Bacteria absorb organic matter produced by mineralized algae and organic matter in sewage through respiration and produce CO2, which is supplied to algae as raw materials for photosynthesis, forming a mutually beneficial material cycle. This interaction not only solves the problem of small flocs and poor sedimentation when microalgae are used 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 meet the growth needs of microalgae and bacteria at the same time, the two will compete for nutrients. In addition, microalgae can produce algal toxins and extracellular secretions (amino acids, antibiotic substances) that inhibit bacterial growth or poison bacteria; bacteria can also release bacterial toxins to inhibit the growth of microalgae cells, and even lyse algae cells, showing an algaecidal effect. This competitive or inhibitory relationship will not only change the composition of the algae-bacteria community, but also affect the benign material and energy cycle between algae and bacteria. Therefore, how to maintain the mutually beneficial symbiotic relationship between algae and bacteria, especially to strengthen the symbiotic relationship and maintain system stability in the face of adverse conditions such as fluctuating environmental conditions and insufficient nutrients, is the current technical difficulty of this process.

[0003] Although research on algae-bacteria granular sludge has been carried out, most of them are still in the laboratory stage and have not been put into practical use on a large scale. The core issue is how to build a stable symbiotic relationship between algae and bacteria. The interaction between microalgae and bacteria is relatively complex, including both a mutually beneficial symbiotic relationship of mutual utilization of metabolites and a mutual competition and inhibition relationship for 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-bacteria granules can be regulated by using algae-bacteria signal molecules. Previous studies have focused on the regulation of algae-bacteria granules by intraspecific N-acylated homoserine lactones (Acyl Homoserine Lactones, AHLs) signal molecules in quorum sensing (QS), while ignoring the important role of interspecific furan borate esters (AI-2) signal molecules in the late stage of granule maturation. In the granular sludge system, mature granules are mainly regulated by AI-2 signal molecules, while AHLs signal molecules mainly play a role in granule formation. In practical applications, the direct addition of AHL or AI-2 signal molecules is unsustainable due to high cost and easy degradation by the system.

[0004] Boron, as an important component of AI-2 precursors, can directly stimulate the production of AI-2. In addition, boron is an essential element for algae growth and development, and is involved in the metabolism of hormones such as indole-3-acetic acid (IAA). Exogenous introduction of boron significantly enhances the photosynthesis efficiency of green algae, while a lack of boron will limit plant growth and hinder the transport of IAA. Therefore, boron has a dual effect on material metabolism and signal communication, and can strengthen the algae-bacteria symbiotic system. Summary of the invention

[0005] The technical problem solved by the present invention is to overcome the defects of the existing algae-bacteria granular sludge system in that the granules are poorly stable and the sewage treatment effect is deteriorated after long-term operation, thereby providing a method for enhancing the stability of the algae-bacteria granular sludge system and the system operation efficiency. In order to solve the above problems, the present application is implemented through the following technical solutions: A method for improving the sedimentation property of algae-bacteria granular sludge and the sewage treatment efficiency, comprising the following steps: S1, adding aerobic granules and synthetic sewage into a reactor, and cultivating mature algae-bacteria granular sludge under light and aerobic conditions; S2. Add the mature algae-bacteria granular sludge, synthetic sewage and boric acid in step S1 into the reactor, operate under light, aeration or zero aeration, and obtain treated purified water after sedimentation.

[0006] The aerobic particles in step S1 have a particle size of 1.0-1.4 mm, SV 30 / SV5=0.86~0.94.

[0007] In step S1, the synthetic sewage includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH regulator; Among them, the concentration of NaAc is 515~520 mg / L, the concentration of NH4Cl is 150~155 mg / L, and the concentration of KH2PO4 is 20~23 mg / L; The synthetic sewage also includes MgSO4·7H2O, CaCl2 and FeSO4·7H2O. Among them, the concentration of MgSO4·7H2O is 48~52 mg / L; the concentration of CaCl2 is 19~21 mg / L, and the concentration of FeSO4·7H2O is 9~11 mg / L; The synthetic sewage also includes a trace element solution, the concentration of the trace element solution is 0.9-1.1 mg / L; the trace element solution comprises 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 COD concentration of the synthetic sewage is 385~430mg / L, NH4 + -N is 36.5~43.5mg / L, PO4 3- -P is 4.5~5.5mg / L, pH is 7~8.

[0008] In the step S1, the ratio of aerobic particles to synthetic sewage is aerobic particles: synthetic sewage = 2.9-3.1 g: 1 L.

[0009] In the step S1, the reactor is a cylindrical sequencing batch reactor; the water change cycle of the reactor is 2 times / day, the water inlet time of each cycle is 18-22 minutes, the aeration operation time is 655-665 minutes, the sedimentation time is 18-22 minutes, and the drainage time is 19-21 minutes. Preferably, in the step S1, the water change amount is 0.2-0.5L.

[0010] In step S1, the intensity of the illumination is 190-210 μmol•m -2 •s -1 .

[0011] In step S1, the aerobic condition is a dissolved oxygen concentration of 2.5-3.0 mg / L.

[0012] In the step S1, the particle size of the mature algae-bacteria granular sludge is 1.0-1.5 mm.

[0013] Preferably, in step S1, the culture time is 30 to 40 days.

[0014] Preferably, in step S1, the light-dark cycle ratio of illumination is 12h / 12h.

[0015] In the step S2, the ratio of the mature algae-bacteria granular sludge to the synthetic sewage is: mature algae-bacteria granular sludge: synthetic sewage = 4-4.5 g: 1 L.

[0016] In step S2, the synthetic sewage includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH regulator; Among them, the concentration of NaAc is 145~520 mg / L, the concentration of NH4Cl is 150~155 mg / L, and the concentration of KH2PO4 is 20~23 mg / L; The synthetic sewage also includes MgSO4·7H2O, CaCl2 and FeSO4·7H2O; Among them, the concentration of MgSO4·7H2O is 48~52 mg / L, the concentration of CaCl2 is 19~21 mg / L, and the concentration of FeSO4·7H2O is 9~11 mg / L; The synthetic sewage also includes a trace element solution, the concentration of the trace element solution is 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, 150 mg / L CoCl2·6H2O, The COD concentration of the synthetic sewage is 110~430mg / L, NH4 + -N is 36.5~43.5mg / L, PO4 3- -P is 4.5~5.5mg / L, pH is 7~8.

[0017] Preferably, in step S2, the reactor is a cylindrical sequencing batch reactor; the water change cycle of the reactor is 4 times / day, the water inlet time of each cycle is 18~22min, the aeration or zero aeration operation time is 295~305min, the sedimentation time is 18~22min, the drainage time is 19~21 min, and the water change volume is 0.2~0.5L.

[0018] Preferably, in step S2, boric acid is added once every 24 hours, and the ratio of boric acid to sewage is 80-200 μmol to 1 L.

[0019] Preferably, in step S2, the light intensity is 190-210 μmol•m -2 •s -1 , the light-dark cycle ratio is 12h / 12h.

[0020] Preferably, in step S2, during aeration, the dissolved oxygen concentration is 2.5-3.0 mg / L, and during zero aeration, only oscillation is performed, and the oscillation rate is 120-130 rpm.

[0021] The principle of the present invention is as follows: 1. Cultivation of mature algae-bacteria particles Aerobic particles were added into a cylindrical sequencing batch reactor filled with synthetic sewage to make the concentration of aerobic particles in the reactor 2.9-3.1 g / L. The dissolved oxygen concentration of the system was controlled to be 2.5-3.0 mg / L under aerobic conditions. A light emitting diode (LED) was used to detect the photosynthetic photon flux density (PPFD) of 190-210 μmol•m -2 •s -1 The reactor was irradiated under the condition of a light-dark cycle ratio of 12h / 12h. After 30-40 days of cultivation in the reactor, the algae-bacteria granular sludge gradually matured and showed a typical green color with a particle size of 1.0-1.5mm.

[0022] In step 1, the aerobic particle size is 1.0~1.4mm, SV 30 / SV5=0.86~0.94.

[0023] In step 1, the synthetic wastewater uses NaAc as carbon source, NH4Cl as nitrogen source, KH2PO4 as phosphorus source, and NaHCO3 as pH regulator, with COD concentration of 385~430 mg / L, NH4 + -N concentration is 36.5~43.5mg / L, PO4 3- -P concentration is 4.5~5.5 mg / L and system pH is 7~8.

[0024] The operating conditions of the reactor in step 1 are: water change cycle is 2 times / day, water inlet time per cycle is 18~22 min, aeration time is 655~665 min, sedimentation time is 18~22 min, drainage time is 19~21 min, and water change volume is 50%; the reactor is operated at room temperature, with a temperature of 23~27°C.

[0025] 2. Construction of algae-bacteria particle enhancement system The mature algae-bacteria particles in step 1 were added to a cylindrical sequencing batch reactor filled with synthetic sewage to make the concentration of algae-bacteria particles in the reactor system 4-4.5 g / L. 80-200 μM boric acid was added to the reactor every 24 hours. The control system was in an aerated or zero aeration state, and a light emitting diode (LED) was used to illuminate the system at a photosynthetic photon flux density (PPFD) of 190-210 μmol•m -2 •s -1 The reactor was irradiated under the condition of a light-dark cycle ratio of 12h / 12h. The reactor can operate stably for a long time. Compared with the reactor without adding boric acid, the reactor has higher ammonia nitrogen and phosphorus treatment efficiency, and the algae-bacteria sludge particles have better sedimentation properties.

[0026] The synthetic wastewater quality in step 2 is applicable under normal carbon-nitrogen ratio (carbon-nitrogen ratio>4) or low carbon-nitrogen ratio (carbon-nitrogen ratio<4). Under normal carbon-nitrogen ratio: NaAc is used as carbon source, NH4Cl is used as nitrogen source, KH2PO4 is used as phosphorus source, NaHCO3 is used as pH regulator, COD concentration is 385~430mg / L, NH4 + -N concentration is 36.5~43.5 mg / L, PO4 3- -P concentration is 4.5~5.5mg / L, system pH is 7-8; when the carbon-nitrogen ratio is low: NaAc is used as the carbon source, NH4Cl is used as the nitrogen source, KH2PO4 is used as the phosphorus source, and NaHCO3 is used as the pH regulator. The COD concentration is 110~130 mg / L, NH4 + -N concentration is 36.5~43.5mg / L, PO4 3— The P concentration is 4.5~5.5 mg / L and the system pH is 7-8.

[0027] The system in step 2 can be operated in two modes: aeration or zero aeration. During aeration, the dissolved oxygen concentration is above 2.5~3.0 mg / L. During zero aeration, no additional aeration is required and only shaking on the oscillator is required, with an oscillation speed of 120~130 rpm.

[0028] The long-term operation described in step 2 refers to stable operation for more than 50 days, the ammonia nitrogen and phosphate removal rates of the system are significantly improved, and the settling properties of the algae-bacteria sludge particles in the system are significantly enhanced.

[0029] The operating conditions of the reactor in step 2 are: water change cycle is 4 times / day, water inlet time per cycle is 18~22 min, aeration or oscillation time is 295~305 min, sedimentation time is 18~22 min, drainage time is 19~21 min, and water change volume is 50%; the reactor is operated at room temperature, and the temperature is 23℃~27℃.

[0030] Compared with the prior art, the present invention has the following beneficial effects: 1. The purpose of the present invention is to use boric acid to strengthen the symbiotic relationship between algae and bacteria (especially under zero aeration) and the impact resistance of the system, and to provide a method for synchronously promoting the metabolism of algae and bacteria, so as to achieve the purpose of stabilizing the symbiotic relationship and improving the sedimentation and stability of sludge, and on this basis, to ensure the sewage treatment efficiency of algae-bacteria granular sludge, so that it can be applied to actual working environments.

[0031] 2. The present invention can be applied to algae-bacteria granular sludge systems under aerated or zero aeration conditions.

[0032] 3. The present invention can be applied to algae-bacteria granular sludge systems for treating water with normal carbon-nitrogen ratio (carbon-nitrogen ratio>4) or low carbon-nitrogen ratio (carbon-nitrogen ratio<4).

[0033] 4. The present invention mainly uses added boric acid to solve the algae-bacteria granular sludge system, especially under zero aeration conditions, it can operate stably for more than 50 days. The present invention uses boron to simultaneously promote the growth of bacteria and algae, which is beneficial to the maintenance of the algae-bacteria symbiotic relationship and impact resistance. Boric acid can stimulate the production of AI-2, and it can also promote the efficiency of photosynthesis. High concentrations of boric acid will produce boron toxicity. The present invention determines that the amount of boric acid added is 80~200 μmol / L. When the amount of boric acid added is 80~200 μmol / L, the nitrogen and phosphorus removal effect and particle sedimentation are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a graph showing the effect of boric acid concentration on pollutant removal at zero aeration and normal carbon-nitrogen ratio; Figure 2 is aeration, normal carbon-nitrogen ratio is the effect of boric acid concentration on pollutant removal; Figure 3 This is a graph showing the effect of boric acid concentration on pollutant removal under aeration and low carbon-nitrogen ratio. DETAILED DESCRIPTION

[0035] Unless otherwise specified, the following examples are tested with reference to national standards: drying method: CJ / T 221-2005 Municipal sewage treatment plant sludge inspection method, rapid digestion spectrophotometry HJT399-2007, HJ533-2009 Nessler reagent spectrophotometry, HJ 632-2011 Determination of total phosphorus in soil alkali fusion-molybdenum antimony anti-spectrophotometry.

[0036] Aerobic particles were purchased from Jiangsu Shangshan Environmental Protection Technology Co., Ltd., and the size of the aerobic particles was 1.0-1.5 mm.

[0037] Example 1 A method for improving the sedimentation performance of algae-bacteria granular sludge and sewage treatment efficiency, specifically comprising the following steps: (1) Cultivation of mature algae-bacteria granular sludge A cylindrical sequencing batch reactor was selected as the experimental device. The reactor was 40 cm high, 6 cm in inner diameter, and had a height-to-diameter ratio of 6:1. The effective volume was 1 L. Aerobic particles were added to the reactor containing synthetic sewage to a concentration of 3.0 g / L. The external light intensity was 190-210 μmol•m -2 •s -1 , a light source with a light-dark cycle ratio of 12h / 12h, and aerobic conditions of 24℃ and a dissolved oxygen concentration of 2.5mg / L. After 35 days of cultivation, mature algae-bacteria granular sludge was obtained, which was typical green in color and had a particle size of 1.0~1.5mm.

[0038] In step (1), the aerobic particles have a particle size of 1.0-1.4 mm, and SV 30 / SV5=0.86~0.94.

[0039] In step (1), the composition of the synthetic sewage is: 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 the 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.

[0040] In step (1), the synthetic sewage has NaAc as carbon source, NH4Cl as nitrogen source, KH2PO4 as phosphorus source, NaHCO3 as pH regulator, COD concentration is 400 mg / L, NH4 + -N concentration is 40mg / L, PO4 3- -P concentration is 5 mg / L and system pH is 7.5.

[0041] In step (1), the hydraulic retention time of the reactor is 24 h, the water change cycle is 2 times / day, the water inlet time in each cycle is 20 min, the aeration time is 660 min, the sedimentation time is 20 min, the drainage time is 20 min, and the water change volume is 50% (0.5 L).

[0042] (2) Construction of algae-bacteria granular sludge intensification system under zero aeration and normal carbon-nitrogen ratio conditions Five identical cylindrical sequencing batch reactors were selected as experimental devices. The reactor volume was 600 mL, of which the effective volume was 400 mL, the inner diameter was 8 cm, and the height was 18 cm. The mature algae-bacteria granular sludge in step (1) was divided into five reactors filled with synthetic sewage, so that the concentration of algae-bacteria particles in the reactor system was 4.3 g / L; boric acid with concentrations of 0 µmol / L, 50 µmol / L, 80 µmol / L, 200 µmol / L, and 2000 µmol / L was added to the five reactors every 24 hours. The external light intensity was 190~210 μmol•m -2 •s -1 , the light source has a light-dark cycle ratio of 12h / 12h, and the reactor is operated for 60 days in a zero aeration mode at room temperature of 23~27℃.

[0043] In step (2), the composition and water quality of the synthetic sewage are the same as those in step (1).

[0044] In step (2), no additional aeration is required during zero aeration, and the reactor is simply placed in a constant temperature shaking culture device with an shaking speed of 120-130 rpm.

[0045] In step (2), the hydraulic retention time of the reactor is 12 h, the water change cycle is 4 times / day, the water inlet time in each cycle is 20 min, the oscillation time is 300 min, the sedimentation time is 20 min, the drainage time is 20 min, and the water change volume is 50% (0.2 L).

[0046] (3) Stability of algae-bacteria granular sludge and wastewater treatment efficiency under zero aeration and normal carbon-nitrogen ratio conditions The sludge concentration (MLSS) and sludge volume index SVI5 of algae-bacteria granular sludge were measured: the sludge concentration was measured by drying method; after obtaining the sludge mixed liquid, the sludge settling ratio (SV5) at 5 minutes was measured, SVI5=SV5 / MLSS, (mL / g); COD was determined by rapid digestion spectrophotometry, ammonia nitrogen was determined by Nessler reagent spectrophotometry, and phosphate was determined by molybdenum antimony anti-spectrophotometry. The results are shown in Table 1.

[0047] Table 1 Comparison of sludge concentration and SVI5 concentration

[0048] Please refer to Figure 1Under the conditions of zero aeration and normal carbon-nitrogen ratio, the sludge concentration in the reactor system with boric acid added was significantly higher than that in the reactor without boric acid, indicating that the addition of boric acid can significantly promote the growth of algae-bacteria granular sludge; the SVI5 of the reactor without boric acid added was significantly higher than that of other groups, indicating that the addition of boric acid can significantly improve the sedimentation of algae-bacteria granular sludge; when 80 µmol / L and 200 µmol / L of boric acid were added, the growth advantage of algae-bacteria granular sludge in the reactor system was obvious, with high stability and the best sedimentation performance. The addition of boric acid had no significant promoting effect on COD removal, and the COD removal rate was above 80%; the addition of 80 µmol / L and 200 µmol / L of boric acid can significantly improve the removal effect of ammonia nitrogen and phosphate in sewage, with ammonia nitrogen removal rate above 90% and phosphate removal rate above 88%.

[0049] Example 2 A method for improving the sedimentation performance of algae-bacteria granular sludge and sewage treatment efficiency, specifically comprising the following steps: (1) Cultivation of mature algae-bacteria granular sludge A cylindrical photo-sequential batch reactor was selected as the experimental device. The reactor was 40 cm high, 6 cm in inner diameter, with a height-to-diameter ratio of 6:1, and an effective volume of 1 L. Aerobic particles were added to the reactor filled with synthetic sewage to make the concentration of aerobic particles in the reactor 2.9-3.1 g / L. The external light intensity was 190-210 μmol•m -2 •s -1 The culture was carried out under aerobic conditions with a light source of 12h / 12h light-dark cycle, 24℃ and dissolved oxygen concentration of 2.5mg / L. After 35 days of culture, mature algae-bacteria granular sludge was obtained, which was typical green in color and had a particle size of 1.0~1.5mm.

[0050] In step (1), the aerobic particles have a particle size of 1.0-1.4 mm, and SV 30 / SV5=0.86~0.94.

[0051] In step (1), the composition of the synthetic sewage is: 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 the 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.

[0052] In step (1), the synthetic sewage has NaAc as carbon source, NH4Cl as nitrogen source, KH2PO4 as phosphorus source, NaHCO3 as pH regulator, COD concentration is 400 mg / L, NH4 + -N concentration is 40mg / L, PO4 3- -P concentration is 5 mg / L and system pH is 7.5.

[0053] In step (1), the hydraulic retention time of the reactor is 24 h, the water change cycle is 2 times / day, the water inlet time in each cycle is 20 min, the aeration time is 660 min, the sedimentation time is 20 min, the drainage time is 20 min, and the water change volume is 50% (0.5 L).

[0054] (2) Construction of algae-bacteria granular sludge intensification system under aeration and normal carbon-nitrogen ratio conditions Five identical cylindrical sequencing batch reactors were selected as experimental devices. The reactor volume was 600 mL, of which the effective volume was 400 mL, the inner diameter was 8 cm, and the height was 18 cm. The mature algae-bacteria granular sludge in step (1) was divided into five reactors filled with synthetic sewage, so that the concentration of algae-bacteria particles in the reactor system was 4.3 g / L; boric acid with concentrations of 0 µmol / L, 50 µmol / L, 80 µmol / L, 200 µmol / L, and 2000 µmol / L was added to the five reactors every 24 hours. The external light intensity was 190~210 μmol•m -2 •s -1 , the light source has a light-dark cycle ratio of 12h / 12h, and the reactor is operated for 60 days with aeration at room temperature of 23~27℃.

[0055] In step (2), the composition and water quality of the synthetic sewage are the same as those in step (1).

[0056] In step (2), the dissolved oxygen concentration during aeration is 2.5-3.0 mg / L.

[0057] In step (2), the hydraulic retention time of the reactor is 12 h, the water change cycle is 4 times / day, the water inlet time in each cycle is 20 min, the aeration time is 300 min, the sedimentation time is 20 min, the drainage time is 20 min, and the water change volume is 50% (0.2 L).

[0058] (3) Stability of algae-bacteria granular sludge and wastewater treatment efficiency under aeration and normal carbon-nitrogen ratio conditions The sludge concentration (MLSS) and sludge volume index SVI5 of algae-bacteria particles were measured: the drying method was used to determine the sludge concentration; after obtaining the sludge mixture, the sludge settling ratio (SV5) at 5 minutes was measured, SVI5 = SV5 / MLSS, (mL / g); COD was determined by rapid digestion spectrophotometry, ammonia nitrogen by Nessler reagent spectrophotometry, and phosphate by molybdenum antimony anti-spectrophotometry. The results are shown in Table 2.

[0059] Table 2 Comparison of sludge concentration and SVI5 concentration

[0060] Please refer to Figure 2 Under the condition of normal carbon-nitrogen ratio of aeration, the sludge concentration in the reactor system with boric acid added was significantly higher than that in the reactor without boric acid, indicating that the addition of boric acid can significantly promote the growth of algae-bacteria granular sludge; the SVI5 of the reactor without boric acid added was significantly higher than that of other groups, indicating that the addition of boric acid can significantly improve the sedimentation of algae-bacteria granular sludge; when 80 µmol / L and 200 µmol / L of boric acid were added, the growth advantage of algae-bacteria granular sludge in the reactor system was obvious, with high stability and the best sedimentation performance. The addition of boric acid had no significant promoting effect on COD removal, and the COD removal rate was above 85%; the addition of 80 µmol / L and 200 µmol / L of boric acid can significantly improve the removal effect of ammonia nitrogen and phosphate in sewage, with ammonia nitrogen removal rate above 95% and phosphate removal rate above 92%.

[0061] Example 3 A method for improving the sedimentation performance of algae-bacteria granular sludge and sewage treatment efficiency, specifically comprising the following steps: (1) Cultivation of mature algae-bacteria granular sludge A cylindrical photo-sequential batch reactor was selected as the experimental device. The reactor was 40 cm high, 6 cm in inner diameter, with a height-to-diameter ratio of 6:1, and an effective volume of 1 L. Aerobic particles were added to the reactor filled with synthetic sewage to a concentration of 2.9-3.1 g / L. The external light intensity was 190-210 μmol•m -2•s -1 , a light source with a light-dark cycle ratio of 12h / 12h, and aerobic conditions of 23~27℃ and a dissolved oxygen concentration of 2.5mg / L. After 35 days of cultivation, mature algae-bacteria granular sludge was obtained, which was typical green in color and had a particle size of 1.0~1.5mm.

[0062] In step (1), the aerobic particles have a particle size of 1.0-1.4 mm, and SV 30 / SV5=0.86~0.94.

[0063] In step (1), the composition of the synthetic sewage is: 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 the trace element solution concentration is 1 mg / L; the trace element solution composition 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.

[0064] In step (1), the synthetic sewage has NaAc as carbon source, NH4Cl as nitrogen source, KH2PO4 as phosphorus source, NaHCO3 as pH regulator, COD concentration is 400 mg / L, NH4 + -N concentration is 40mg / L, PO4 3- -P concentration is 5 mg / L and system pH is 7.

[0065] In step (1), the hydraulic retention time of the reactor is 24 h, the water change cycle is 2 times / day, the water inlet time in each cycle is 20 min, the aeration time is 660 min, the sedimentation time is 20 min, the drainage time is 20 min, and the water change volume is 50% (0.5 L).

[0066] (2) Construction of algae-bacteria granular sludge intensification system under aeration and low carbon-nitrogen ratio conditions Five identical cylindrical sequencing batch reactors were selected as experimental devices. The reactor volume was 600 mL, of which the effective volume was 400 mL, the inner diameter was 8 cm, and the height was 18 cm. The mature algae-bacteria granular sludge in step (1) was divided into five reactors filled with synthetic sewage, so that the concentration of algae-bacteria particles in the reactor system was 4.3 g / L; boric acid with concentrations of 0 µmol / L, 50 µmol / L, 80 µmol / L, 200 µmol / L, and 2000 µmol / L was added to the five reactors every 24 hours. The external light intensity was 190~210 μmol•m -2 •s -1 , the light source has a light-dark cycle ratio of 12h / 12h, and the reactor is operated for 60 days under room temperature conditions of 23℃~27℃ with aeration.

[0067] In step (2), the composition of the synthetic sewage is: 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.

[0068] In step (2), the synthetic sewage has NaAc as carbon source, NH4Cl as nitrogen source, KH2PO4 as phosphorus source, NaHCO3 as pH regulator, COD concentration is 120 mg / L, NH4 + -N concentration is 40mg / L, PO4 3- -P concentration is 5 mg / L and system pH is 7.5.

[0069] In step (2), the dissolved oxygen concentration during aeration is 2.5-3.0 mg / L.

[0070] In step (2), the hydraulic retention time of the reactor is 12 h, the water change cycle is 4 times / day, the water inlet time in each cycle is 22 min, the aeration time is 305 min, the sedimentation time is 22 min, the drainage time is 21 min, and the water change volume is 50% (0.2 L).

[0071] (3) Stability of algae-bacteria particles and wastewater treatment efficiency under aeration and low carbon-nitrogen ratio conditions The sludge concentration (MLSS) and sludge volume index SVI5 of algae-bacteria particles were measured: the drying method was used to determine the sludge concentration; after obtaining the sludge mixture, the sludge settling ratio (SV5) at 5 minutes was measured, SVI5=SV5 / MLSS, (mL / g); COD was determined by rapid digestion spectrophotometry, ammonia nitrogen was determined by Nessler's reagent spectrophotometry, and phosphate was determined by molybdenum antimony anti-spectrophotometry. The results are shown in Table 3.

[0072] Table 3 Comparison of sludge concentration and SVI5 concentration

[0073] Please refer to Figure 3 Under the condition of aeration and low carbon-nitrogen ratio, the sludge concentration in the reactor system with boric acid added was significantly higher than that in the reactor without boric acid, indicating that the addition of boric acid can significantly promote the growth of algae-bacteria granular sludge; the SVI5 of the reactor without boric acid added was significantly higher than that of other groups, indicating that the addition of boric acid can significantly improve the sedimentation of algae-bacteria granular sludge; when 80 µmol / L and 200 µmol / L of boric acid were added, the growth advantage of algae-bacteria granular sludge in the reactor system was obvious, with high stability and the best sedimentation performance. The addition of boric acid had no significant promoting effect on COD removal, and the COD removal rate was above 75%; the addition of 80 µmol / L and 200 µmol / L of boric acid could significantly improve the removal effect of ammonia nitrogen and phosphate in sewage, and the removal rates of ammonia nitrogen and phosphate were both above 85%.

Claims

1. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency, characterized in that: The following steps are involved: S1. Adding aerobic particles and synthetic sewage into a reactor, and cultivating mature algae-bacteria granular sludge under light and aerobic conditions; S2. Add the mature algae-bacteria granular sludge, synthetic sewage and boric acid in step S1 into the reactor, operate under light, aeration or zero aeration, and obtain treated purified water after sedimentation.

2. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency according to claim 1, characterized in that: In step S1, the synthetic sewage includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH regulator; Among them, the concentration of NaAc is 515~520 mg / L, the concentration of NH4Cl is 150~155 mg / L, and the concentration of KH2PO4 is 20~23 mg / L; The synthetic sewage also includes MgSO4·7H2O, CaCl2 and FeSO4·7H2O. Among them, the concentration of MgSO4·7H2O is 48~52 mg / L; the concentration of CaCl2 is 19~21 mg / L, and the concentration of FeSO4·7H2O is 9~11 mg / L; The synthetic sewage also includes a trace element solution, the concentration of the trace element solution is 0.9-1.1 mg / L; the trace element solution comprises 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 COD concentration of the synthetic sewage is 385~430mg / L, NH4 + -N is 36.5~43.5mg / L, PO4 3- -P is 4.5~5.5 mg / L, and pH is 7~8.

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

4. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency according to claim 1, characterized in that: In step S1, the reactor is a cylindrical sequencing batch reactor; the water change cycle of the reactor is 2 times / day, the water inlet time of each cycle is 18-22 minutes, the aeration operation time is 655-665 minutes, the sedimentation time is 18-22 minutes, and the drainage time is 19-21 minutes.

5. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency 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. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency according to claim 1, characterized in that: In the step S2, the ratio of the mature algae-bacteria granular sludge to the synthetic sewage is: mature algae-bacteria granular sludge: synthetic sewage = 4-4.5 g: 1 L.

7. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency according to claim 1, characterized in that: In step S2, the synthetic sewage includes NaAc as a carbon source, NH4Cl as a nitrogen source, KH2PO4 as a phosphorus source, and NaHCO3 as a pH regulator; Among them, the concentration of NaAc is 145~520 mg / L, the concentration of NH4Cl is 150~155 mg / L, and the concentration of KH2PO4 is 20~23 mg / L; The synthetic sewage also includes MgSO4·7H2O, CaCl2 and FeSO4·7H2O; Among them, the concentration of MgSO4·7H2O is 48~52 mg / L, the concentration of CaCl2 is 19~21 mg / L, and the concentration of FeSO4·7H2O is 9~11 mg / L; The synthetic sewage also includes a trace element solution, the concentration of the trace element solution is 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, 150 mg / L CoCl2·6H2O, The COD concentration of the synthetic sewage is 110~430mg / L, NH4 + -N is 36.5~43.5mg / L, PO4 3- -P is 4.5~5.5mg / L, pH is 7~8.

8. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency according to claim 1, characterized in that: In the step S2, boric acid: sewage = 80-200 μmol: 1L.

9. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency according to claim 1, characterized in that: In step S2, the light intensity is 190-210 μmol•m -2 •s -1 .

10. A method for improving the settling properties of algae-bacteria granular sludge and sewage treatment efficiency according to claim 1, characterized in that: In step S2, the reactor is a cylindrical sequencing batch reactor; the water change cycle of the reactor is 4 times / day, the water inlet time of each cycle is 18-22 minutes, the aeration or zero aeration operation time is 295-305 minutes, the sedimentation time is 18-22 minutes, the drainage time is 19-21 minutes, and the water change volume is 0.2-0.5L.

Images