Rapid culture and stable operation method for low-concentration municipal sewage aerobic granular sludge

Abstract

The invention relates to the technical field of sewage treatment, and particularly discloses a low-concentration municipal sewage aerobic granular sludge rapid culture and stable operation method which comprises the following steps: adding sodium acetate, monopotassium phosphate and allyl thiourea into low-concentration municipal sewage of which the COD (Chemical Oxygen Demand) is less than or equal to 200mg / L; after addition, the COD concentration of the inlet water is increased by 100-200mg / L, the PO4 < 3->-P concentration is increased by 2.5-5.0 mg / L, and the ATU concentration is increased by 5-10mg / L; then inoculating activated sludge of a common municipal sewage treatment plant into the reactor, wherein the concentration of the activated sludge is 3000-6000 mg MLSS / L; culturing the aerobic granular sludge, wherein the time length of each period is 3-4 hours, and water feeding, stirring, aerating, precipitating and water discharging are performed in sequence; the volume exchange ratio of each period is 33%-50%; when the granulation rate reaches 80% or above, a stable operation period is started; at the moment, only low-concentration municipal sewage is used for feeding water, each period is 4-6 hours, and the volume exchange ratio of each period is increased to 50%-75%. The invention aims to solve the problems that the starting period is long and the aerobic granular sludge is difficult to maintain stably when low-concentration municipal sewage is used for culturing the aerobic granular sludge.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for rapid cultivation and stable operation of aerobic granular sludge of low-concentration municipal sewage. Background Art

[0002] Aerobic granular sludge is a microbial aggregate formed by the principle of microbial self-flocculation. Compared with the traditional activated sludge method, the aerobic granular sludge method has many advantages such as good mud-water separation performance, high volumetric load, simultaneous nitrogen and phosphorus removal, and resistance to shock load and toxic substances. It can save about 75% of the floor space and about 50% of the operating energy consumption. It can also extract high value-added products such as alginate polymers from aerobic granular sludge. It is recognized as a new generation of sewage biological treatment technology.

[0004] Practice has shown that it often takes more than half a year to completely granulate aerobic granular sludge using low-concentration municipal sewage. There are three main reasons: ① It is difficult for low-concentration sewage to create an ideal "feast-hunger" alternating environment, which is one of the necessary conditions for the formation of aerobic granular sludge (except for special cases such as nitrifying granular sludge); ② The actual low-concentration urban sewage has complex components, with a large proportion of granular COD, but very limited high-quality carbon sources, which is not conducive to microorganisms storing it as an internal carbon source, thereby affecting the granulation process; ③ The current operation mode used in the case of aerobic granular sludge method for treating actual urban sewage is basically the same as the operation mode used in the small-scale test based on artificial water distribution. There is no targeted improvement and optimization. Although aerobic granular sludge can eventually be formed, the startup period is long and difficult to maintain stably. Summary of the invention

[0005] In view of the shortcomings of the existing technology, the technical problem solved by the present invention is to provide a method for rapid cultivation and stable operation of aerobic granular sludge using low-concentration municipal sewage, thereby solving the problem that the start-up period of the existing technology using low-concentration municipal sewage to cultivate aerobic granular sludge is long and difficult to maintain stably.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is: a method for rapid cultivation and stable operation of aerobic granular sludge of low-concentration municipal sewage, comprising the following steps:

[0007] S100 influent: Add sodium acetate, potassium dihydrogen phosphate and propylene thiourea to low-concentration municipal sewage with COD ≤ 200 mg / L; after addition, the COD concentration of the influent increases by 100-200 mg / L, PO4 3- -P concentration increased by 2.5-5.0 mg / L, ATU concentration increased by 5-10 mg / L;

[0008] S200 sludge inoculation: The reactor is inoculated with activated sludge from ordinary municipal sewage treatment plants at a concentration of 3000-6000 mg MLSS / L;

[0009] Cultivation of S300 aerobic granular sludge: The duration of each cycle of the reactor during the cultivation period is 3 to 4 hours, and it is operated in the order of slow water inflow, stirring, aeration, sedimentation, and drainage in an upflow manner; the water inflow is 60 minutes, stirring is 0 to 60 minutes, sedimentation is 3 to 50 minutes, and drainage is 3 to 10 minutes. The aeration duration is determined by subtracting the four periods of water inflow, stirring, sedimentation, and drainage from the duration of each cycle; the volume exchange ratio of each cycle is 33% to 50%;

[0010] S400 stable operation period: When the mass fraction of granular sludge in the reactor is measured to be more than 80% of the total sludge, the reactor enters the stable operation period, the particle size of the granular sludge is greater than 0.2mm, and the reactor enters the stable operation period; at this time, the influent only uses low-concentration municipal sewage with COD≤200mg / L, and each cycle of the stable operation period lasts 4 to 6 hours, and it operates in the order of slow upflow water inflow, stirring, aeration, sedimentation, and drainage; wherein the water inflow is 60 to 90 minutes, stirring is 0 to 90 minutes, sedimentation is 3 to 25 minutes, and drainage is 3 to 10 minutes. The aeration time is determined by subtracting the four time periods of water inflow, stirring, sedimentation and drainage from the length of each cycle; the volume exchange ratio of each cycle is increased to 50% to 75%.

[0011] The technical principles and beneficial effects of this solution are:

[0012] 1) During the granular sludge cultivation period, a composite agent of sodium acetate, phosphate and allylthiourea is added, wherein sodium acetate is a common carbon source, which is easily converted into an internal carbon source by microorganisms in the activated sludge, such as polyphosphate bacteria and polysaccharide bacteria; potassium dihydrogen phosphate is to maintain a suitable C / P ratio, so that the formed granular sludge is more enriched with polyphosphate bacteria, thereby better removing phosphorus; allylthiourea can inhibit nitrification reaction, avoid rbCOD in the influent being consumed by denitrifying bacteria, thereby affecting the proliferation of polyphosphate bacteria and polysaccharide bacteria. In short, the composite agent promotes the proliferation of polyphosphate bacteria through the above multiple effects. Polyphosphate bacteria are typical slow-growing microorganisms, which are conducive to the formation of compact granular sludge and can quickly cultivate aerobic granular sludge. At the same time, the enrichment of polyphosphate bacteria also provides a guarantee for efficient phosphorus removal.

[0013] 2) During the granular sludge cultivation period and stable operation period, by controlling the stirring time of each cycle, the external carbon source is converted into the internal carbon source of the microorganism to the maximum extent, avoiding various negative effects caused by the aerobic degradation of rbCOD, such as the rapid growth of ordinary heterotrophic bacteria (OHOs), sludge finger growth and even sludge filamentous bacteria expansion, which leads to slow and / or unstable granular sludge formation.

[0014] 3) During the stable operation period, the nitrate nitrogen and nitrite nitrogen (NO x - ) to reduce its impact on polyphosphate bacteria; by controlling dissolved oxygen, relying on the characteristics of aerobic granular sludge to achieve simultaneous nitrification and denitrification phosphorus removal, it not only ensures the effluent quality but also reduces NO in the reactor. x - And its adverse effects on the anaerobic phosphorus release process of polyphosphate bacteria.

[0015] 4) After experimental testing, during the aerobic granular sludge cultivation period, after 20 days of operation according to the set cycle and cultivation parameters, visible granular sludge appeared in the reactor, that is, the sludge particle size was greater than 0.2 mm. After 15 to 30 days of continuous operation, the mass fraction of granular sludge in the total sludge volume could reach more than 80%, SVI 30 <50mL / g, the sludge concentration MLSS in the reactor can reach more than 6000mg / L. The entire aerobic granular sludge cultivation process takes 35 to 50 days, which is much shorter than the more than 6 months required for granulation under the current low-concentration municipal sewage conditions.

[0016] After 130 days of operation according to the set cycle and cultivation parameters during the stable operation period, the granular sludge in the system remained stable, and the average particle size increased to 0.64mm. The average removal rates of COD, ammonia nitrogen, total nitrogen and total phosphorus in the system were 88%, 94%, 76% and 99% respectively.

[0017] Furthermore, in step S300 and step S400, the stirring time is controlled so that the content of bCOD in the mixed solution is less than 20% of the total bCOD at the end of stirring. The control of the stirring time is mainly to ensure that the removal rate of bCOD in the anaerobic stage is not less than 80%. If the condition that the content of bCOD in the mixed solution is less than 20% of the total bCOD is met, stirring is not required.

[0018] Furthermore, the sedimentation time in step S300 is shortened by 0.5 to 1.5 minutes after every 6 to 8 cycles from the determined initial time, until the sludge with a sedimentation speed greater than 6 m / h is screened out. By gradually reducing the sedimentation time, hydraulic selective pressure can be formed to wash the sludge with poor sedimentation properties and screen out the sludge with good sedimentation properties, thereby shortening the aerobic granular sludge cultivation time.

[0019] Furthermore, in step S300, the dissolved oxygen concentration in the mixed solution is controlled at 1.5 to 2.5 mg / L during the aeration stage. When the dissolved oxygen concentration is maintained at 2.0±0.5 mg / L, sufficient oxygen can be provided for the polyphosphate bacteria to promote their growth and reproduction, thereby enhancing the phosphorus removal effect of the system.

[0020] Furthermore, in step S400, the initial dissolved oxygen concentration of each aeration cycle is controlled at 1.5-2.5 mg / L, and when the ammonia nitrogen concentration drops to 3 mg / L, the dissolved oxygen concentration drops to 0.2-0.8 mg / L. This promotes simultaneous nitrification and denitrification phosphorus removal, and can also reduce the NO retained in the reactor while obtaining high-quality effluent. x - The content should be as low as possible, thereby reducing its consumption of external carbon sources in the influent and enabling polyphosphate bacteria to release phosphorus more fully. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 4 is a SVI change curve diagram of an embodiment of the present invention.

[0022] Figure 2 This is a morphological diagram of cultured granular sludge according to an embodiment of the present invention.

[0023] Figure 3 The COD removal effect diagram of the embodiment of the present invention (COD an : Anaerobic final COD, COD eff : Outlet COD,).

[0024] Figure 4 The nitrogen and phosphorus in the effluent of the embodiment of the present invention. DETAILED DESCRIPTION

[0025] The following is further described in detail through specific implementation methods:

[0026] This example is a pilot test of using the present invention to treat low-concentration municipal sewage. The SBR reactor used in the experiment has a total height of 3 meters and an inner diameter of 43 cm. The components of the low-concentration municipal sewage treated are as follows (in mg / L): COD Cr 51~178; BOD532.1~76.4; NH3-N 10.2~29.1; TN 11.7~36.4; TP 0.72~2.81; SS 45~143. The activated sludge used for inoculation was taken from a full-scale sewage treatment plant that treated the sewage. The inoculated sludge concentration was MLSS=4300mg / L, and the sludge volume index SVI 30 =147 mg / L. The water temperature was 19-30°C and pH was 7.2-7.6 during the whole experiment.

[0027] S100 influent: Sodium acetate (NaAc), potassium dihydrogen phosphate (KH2PO4) and allylthiourea (ATU) are added to the above low-concentration municipal sewage. The concentrations after addition are 200mg / L COD, 5.0mg / L PO4 3- -P and 10mg / L ATU.

[0028] Sodium acetate is a common carbon source, which is easily converted into an internal carbon source by microorganisms in activated sludge (such as polyphosphate bacteria and polysaccharide bacteria); potassium dihydrogen phosphate is used to maintain a suitable C / P ratio, so that the formed granular sludge is more enriched with polyphosphate bacteria, thereby better removing phosphorus; allylthiourea can inhibit nitrification reaction, avoid rbCOD in the influent being consumed by denitrifying bacteria, thereby affecting the proliferation of polyphosphate bacteria and polysaccharide bacteria. The above effects are all conducive to the formation of granular sludge.

[0029] S200 sludge inoculation: activated sludge from a common municipal sewage treatment plant is inoculated into the reactor, and the inoculation sludge concentration MLSS = 4300 mg / L;

[0030] Cultivation of S300 aerobic granular sludge: The reactor operates according to the cultivation period cycle, each cycle lasts 3 hours, and operates in the order of slow upflow water inlet, stirring, aeration, sedimentation, and drainage. The water inlet is 60 minutes, the stirring is 30 minutes, and the sedimentation time is gradually reduced from 25 minutes to 10 minutes, which is reduced by 1 minute every day, that is, it is reduced by 1 minute every 8 cycles, and the drainage is 5 minutes. The aeration time is gradually increased from 60 minutes to 75 minutes, and it is extended by 1 minute every day. The volume exchange ratio of each cycle is 50%, the drain port is 1m away from the bottom of the reactor, and the liquid level is 2m high when the water inlet is completed. The details are as follows;

[0031] S301 water inlet: two dual-channel industrial peristaltic pumps are used to evenly pump water into the reactor from four symmetrical water inlets at the bottom for a total of 60 minutes;

[0032] S302 stirring; stirring can be achieved by stirring paddle or nitrogen aeration, wherein stirring paddle is suitable for full-scale sewage treatment plant, nitrogen aeration is suitable for small-scale test and pilot stage, and this embodiment adopts nitrogen aeration for stirring; nitrogen flow rate is 5L / min. After stirring for 30 minutes, take the mixed liquid and filter it with medium-speed qualitative filter paper, remove the sludge and measure COD, and determine that the bCOD content of the mixed liquid is less than 20% of the total bCOD, that is, the removal rate of bCOD in the anaerobic stage is not less than 80%.

[0033] S303 aeration: microporous aeration is used, and the aeration time is gradually increased from 60 minutes to 75 minutes. The main purpose of aeration in this stage is aerobic phosphorus absorption without considering nitrogen removal, and the dissolved oxygen is controlled at 2.0±0.5mg / L.

[0034] S304 sedimentation; due to the good sedimentation of the inoculated sludge, the initial sedimentation time was set at 25 minutes, corresponding to 2.4 m / h of sludge; then it was gradually shortened by 1 minute every day, and the sedimentation time was 10 minutes on the 16th day, and the sludge with a sedimentation speed greater than 6 m / h was screened out. Continuously shortening the sedimentation time can form hydraulic selective pressure to wash the sludge with poor sedimentation and screen out the sludge with good sedimentation.

[0035] S305 drainage; drainage time is 5 minutes, and water output is controlled by an electric valve.

[0036] like Figure 1-2 As shown in the figure, after 20 days of operation according to the above steps, visible granular sludge with good growth appeared in the reactor, that is, the sludge particle size was greater than 0.2 mm. After 21 days of operation, the mass fraction of granular sludge in the reactor, that is, the sludge particle size was greater than 0.2 mm, accounted for 81% of the total sludge, SVI 30 =31mL / g, SVI5 / SVI 30 ≈1. The sludge concentration in the reactor reaches 6500mg / L. The entire aerobic granular sludge cultivation process takes 41 days, which is much shorter than the more than 6 months required for granulation under the current low-concentration municipal sewage conditions.

[0037] S400 stable operation period: When the granulation reaches more than 80%, the reactor enters the stable operation period; this example enters the stable operation on the 49th day; each cycle of the stable operation period lasts 4 hours, and it operates in the order of slow upflow water inlet, stirring, aeration, sedimentation, and drainage. The water inlet is 90 minutes, stirring is 30 minutes, aeration is 100 minutes, sedimentation is 15 minutes, and drainage is 5 minutes. The volume exchange ratio of each cycle is increased to 60%, the drain port is 1m away from the bottom of the reactor, and the liquid level is 2.5m high when the water inlet is completed. The details are as follows;

[0038] S401 influent; low-concentration municipal sewage was used as influent, and sodium acetate, potassium dihydrogen phosphate and propylene thiourea were not added; the inhibited nitrification reaction was gradually restored; the influent time was 90 minutes in total. By increasing the volume exchange ratio, the nitrate nitrogen and nitrite nitrogen (NO x - ) to reduce its impact on polyphosphate bacteria.

[0039] S402: stirring; stirring by nitrogen aeration; nitrogen flow rate 5L / min. After 30 minutes of stirring, take the mixed liquid to measure COD, and determine that the bCOD content of the mixed liquid is less than 20% of the total bCOD, that is, the bCOD removal rate of the anaerobic stage is not less than 80%.

[0040] S403 aeration: microporous aeration is used for aeration, and the aeration time is 100 minutes. The main purpose of aeration in this stage is to achieve simultaneous nitrification, denitrification and phosphorus removal. The initial dissolved oxygen of each aeration cycle is controlled at 2.0±0.5mg / L. When the ammonia nitrogen concentration drops to 3mg / L, the dissolved oxygen drops to 0.5±0.3mg / L to promote simultaneous nitrification, denitrification and phosphorus removal. While obtaining high-quality effluent, it can also reduce the NO retained in the reactor. x -The content should be as low as possible, thereby reducing its consumption of external carbon sources in the influent and enabling polyphosphate bacteria to release phosphorus more fully.

[0041] S404 sedimentation; the sedimentation time is set to 15 minutes, which is slightly longer than the sedimentation time on the last day of the granular sludge culture period. The flocculent sludge that still maintains a sedimentation rate of less than 6m / h will flow out of the reactor with the effluent.

[0042] S405 drainage; drainage time is 5 minutes, and water output is controlled by an electric valve.

[0043] like Figure 3-4 As shown in the figure, the above steps were followed for 91 days, and the granular sludge in the system remained stable, with the average particle size increasing to 0.64 mm. The average removal rates of COD, ammonia nitrogen, total nitrogen and total phosphorus were 88%, 94%, 76% and 99% respectively.

[0044] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for rapid cultivation and stable operation of aerobic granular sludge from low-concentration municipal sewage, characterized by: The following steps are involved: S100 influent: Add sodium acetate, potassium dihydrogen phosphate and propylene thiourea to low-concentration municipal sewage with COD ≤ 200 mg / L; after addition, the COD concentration of the influent increases by 100-200 mg / L, PO4 3- -P concentration increased by 2.5-5.0 mg / L, ATU concentration increased by 5-10 mg / L; S200 sludge inoculation: Inoculate the reactor with activated sludge from ordinary municipal sewage treatment plants at a concentration of 3000-6000 mgMLSS / L; Cultivation of S300 aerobic granular sludge: The duration of each cycle of the reactor during the cultivation period is 3 to 4 hours, and it is operated in the order of slow water inflow, stirring, aeration, sedimentation, and drainage in an upflow manner; the water inflow is 60 minutes, stirring is 0 to 60 minutes, sedimentation is 3 to 50 minutes, and drainage is 3 to 10 minutes. The aeration duration is determined by subtracting the four periods of water inflow, stirring, sedimentation, and drainage from the duration of each cycle; the volume exchange ratio of each cycle is 33% to 50%; S400 stable operation period: When the mass fraction of granular sludge in the reactor reaches more than 80% of the total sludge, the reactor enters the stable operation period, and the particle size of the granular sludge is greater than 0.2mm; at this time, the influent only uses low-concentration municipal sewage with COD≤200mg / L, and each cycle of the stable operation period lasts 4 to 6 hours, and it operates in the order of slow upflow water inflow, stirring, aeration, sedimentation, and drainage; wherein the water inflow is 60 to 90 minutes, stirring is 0 to 90 minutes, sedimentation is 3 to 25 minutes, and drainage is 3 to 10 minutes. The aeration time is determined by subtracting the four time periods of water inflow, stirring, sedimentation and drainage from the length of each cycle; the volume exchange ratio of each cycle is increased to 50% to 75%.

2. The method for rapid cultivation and stable operation of aerobic granular sludge from low-concentration municipal sewage according to claim 1, characterized in that: In the step S300, the stirring time is controlled so that at the end of the stirring, the content of bCOD in the mixed solution is less than 20% of the total bCOD.

3. The method for rapid cultivation and stable operation of aerobic granular sludge from low-concentration municipal sewage according to claim 1, characterized in that: In the step S300, the sedimentation time is shortened by 0.5 to 1.5 minutes after every 6 to 8 cycles from the determined initial time, until sludge with a sedimentation speed greater than 6 m / h is screened out.

4. The method for rapid cultivation and stable operation of aerobic granular sludge from low-concentration municipal sewage according to claim 1, characterized in that: In step S300, the dissolved oxygen concentration in the mixed solution is controlled to be between 1.5 and 2.5 mg / L during the aeration stage.

5. The method for rapid cultivation and stable operation of aerobic granular sludge from low-concentration municipal sewage according to claim 1, characterized in that: In step S400, the initial dissolved oxygen concentration of each aeration cycle is controlled at 1.5-2.5 mg / L, and when the ammonia nitrogen concentration drops to 3 mg / L, the dissolved oxygen concentration drops to 0.2-0.8 mg / L.

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