Method for rapidly culturing aerobic granular sludge by directly aerating low-concentration domestic sewage

Abstract

The invention discloses a method for quickly culturing aerobic granular sludge by directly aerating low-concentration domestic sewage, which is characterized in that a sequencing batch reactor (SBR) is adopted, and 100 mL of anhydrous calcium chloride with the concentration of 22.3 g / L is added in the 5th minute of an aeration mixing stage after water feeding of the SBR from the 3rd day, and 100 mL of polyacrylamide with the concentration of 0.27 g / L is added in the 10th minute of the aeration mixing stage after water feeding of the SBR; the low-concentration domestic sewage is domestic sewage with the pH value of 7-8, the COD (Chemical Oxygen Demand) of 200 mg / L, the ammonia nitrogen of 50 mg / L and the total phosphorus of 5 mg / L. According to the method, sludge inoculation is not needed, anhydrous calcium chloride and PAM are added after water enters the reactor to promote coagulation among sludge flocs to culture AGS with a compact structure, and the defect that only the sludge settling performance is improved but sludge screening at different settling velocities cannot be realized by adding a flocculating agent before precipitation is avoided; compared with the addition of the flocculating agent before precipitation, the addition of the PAM after water inflow does not affect the hydraulic screening process of the sludge, and the method has the characteristics of rapidness, low operation cost and high reliability.

Description

Technical Field

[0001] The invention relates to the technical field of biological treatment of low-concentration domestic sewage, and in particular to a method for rapidly cultivating aerobic granular sludge by directly aerating low-concentration domestic sewage. Background Art

[0002] Aerobic granular sludge (AGS) is a granular biopolymer formed by spontaneous aggregation and proliferation of microorganisms under harsh conditions. It has many advantages that ordinary activated sludge cannot match, such as regular shape, good sedimentation performance, compact structure, ability to withstand high volumetric load, single-stage simultaneous nitrogen and phosphorus removal, high toxicity resistance, etc. Thanks to these advantages, AGS has become a research hotspot in the field of wastewater treatment and is considered to be a wastewater biological treatment technology with great development prospects in the 21st century. However, the conditions for the formation of aerobic granular sludge are harsh, and it is necessary to gradually screen out sludge with fast sedimentation and strong flocculation ability through the regulation of operating parameters, and finally form AGS through their proliferation. Studies have shown that when simulated wastewater is used as the matrix, the cultivation of AGS in most studies takes 40 to 60 days; if actual wastewater is used as the substrate, this process often takes longer. Activated sludge is the most commonly used inoculated sludge in the cultivation process of AGS, but in the process of gradually shortening the sedimentation time, most of the activated sludge will be discharged from the reactor, which invisibly causes serious waste of resources. AGS formation requires a higher volumetric load, and the appropriate COD volumetric load should be 2.4 kg / m 3 ·d or more, it is obvious that low-concentration domestic sewage cannot provide such a high volumetric load, which is also one of the limiting factors for the difficulty in cultivating AGS in the traditional activated sludge method. Although low COD volumetric load can also cultivate AGS, it often takes longer.

[0003] By summarizing the reported literature, the existing AGS rapid culture strategies mainly include four categories: First, improve the composition of the influent matrix to promote aerobic granulation, such as using a higher influent Ca 2+ Mg 2+ , Fe 3+Plasma concentration; second, adding carriers as inducing nuclei to accelerate the process of aerobic granulation, such as adding mycelial balls, powdered activated carbon, silica gel, etc. However, whether the biological aggregates formed after adding carriers can be classified as AGS is still debatable; third, changing the composition of inoculated sludge to promote aerobic granulation. Many studies have been carried out in this regard, such as inoculating anaerobic granular sludge, pre-inoculating partially mature AGS, inoculating partially broken AGS, etc.; fourth, adding flocculants or special bacterial agents to promote sludge granulation. Among them, flocculants are almost always added before sedimentation and drainage, and the price of microbial agents is often tens of thousands of yuan per ton. Whether the economic cost of adding special bacterial agents during application is acceptable still needs to be tested. Usually, these rapid culture modes can shorten the time of aerobic granulation to less than 30 days. However, the sewage used in these rapid cultures is basically medium-to-high concentration sewage, which can provide sufficient organic load for the proliferation of microorganisms, while the organic load provided by low-concentration domestic wastewater is limited, and a large amount of sludge is required during hydraulic screening, making the rapid cultivation of AGS still challenging. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the above-mentioned prior art and to provide a method for rapidly cultivating aerobic granular sludge by aerating low-concentration domestic sewage without the need for inoculating sludge, by adding anhydrous calcium chloride and flocculant polyacrylamide (PAM) after water inflow to promote microbial coagulation and proliferation and improve sedimentation performance to cultivate densely structured AGS.

[0005] The purpose of the present invention is achieved through the following technical solutions: A method for rapidly cultivating aerobic granular sludge by directly aerating low-concentration domestic sewage, using a sequencing batch reactor (SBR), adding 100 mg / L of anhydrous calcium chloride with a concentration of 22.3 g / L from the 5th minute of the aeration and mixing stage after the SBR completes water inflow from the 3rd day, and adding 100 mL of polyacrylamide (PAM) with a concentration of 0.27 g / L from the 10th minute; the low-concentration domestic sewage is domestic sewage with a pH of 7-8, COD of 200 mg / L, ammonia nitrogen of 50 mg / L, and total phosphorus of 5 mg / L.

[0006] Furthermore, the dosage of the polyacrylamide is determined by a sedimentation test, and the specific method is: 1000 mL of activated sludge on the second day in 5 batches of reactors are respectively measured, and 0.2%, 0.4%, 0.8%, 1.2%, and 1.6% PAM are respectively added (that is, 0.2 mg, 0.4 mg, 0.8 mg, 1.2 mg, and 1.6 mg of PAM are respectively added to 1 L of water), the mixing measuring cylinder is repeatedly inverted for 2 minutes, and the sedimentation is allowed to stand. The time taken for complete sedimentation is compared, and the dosage of PAM with the shortest time is the optimal value, and 100 mL of solution is prepared and added at the 10th minute of the aeration mixing section.

[0007] Furthermore, the cycle of the sequencing batch reactor SBR is 12-4 hours, including: water intake, aeration mixing, anoxic stirring, aeration, sedimentation and drainage.

[0008] Beneficial effects of the present invention: The present invention does not need to inoculate sludge. After water enters the reactor, anhydrous calcium chloride and PAM are added to promote coagulation between sludge flocs. The coagulated sludge proliferates and grows. In the process of gradually shortening the sedimentation time, the sludge flocs with poor sedimentation performance are further washed out, and finally the AGS with a dense structure is cultivated, thereby avoiding the disadvantage that the addition of flocculants before precipitation only improves the sludge sedimentation performance but cannot achieve the sludge screening with different sedimentation speeds. Compared with the addition of flocculants before precipitation, the addition of PAM after water inflow does not affect the hydraulic screening process of the sludge, and the present invention has the characteristics of rapidity, low operating cost and high reliability, and provides an effective new method for the rapid cultivation of AGS in low-concentration domestic sewage. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a graph showing the sludge morphology changes at different times in the R1 controlled reactor in Example 1 of the present invention; Figure 2 This is a diagram showing the sludge morphology changes at different times in the R2 control reactor in Example 1 of the present invention; Figure 3 This is a graph showing the sludge floating in the R2 control reactor on the 15th day in Example 1 of the present invention; Figure 4 This is a graph showing the change in sludge granulation rate in the R1 control reactor in Example 1 of the present invention; Figure 5 This is a graph showing the change in sludge granulation rate in the R2 control reactor in Example 1 of the present invention. DETAILED DESCRIPTION

[0010] The content of the present invention is further described below in conjunction with the accompanying drawings and embodiments. Example 1

[0011] AGS was rapidly cultured in two SBR reactors respectively; R1 was a control reactor using the technical solution of the present invention, and R2 was a control reactor.

[0012] From day 1 to day 10, the two reactors were operated in the same way (cycle 6 hours, COD loading rate 0.48 kg / m 3·d), starting from the 3rd day, anhydrous calcium chloride was added in the 5th minute of the aeration mixing section after water inflow, and PAM was added in the 10th minute, and the settling time was between 5 and 3 minutes; on the 10th day, the mixed liquor sludge concentration (MLSS) in R1 and R2 was measured to be 3640 mg / L and 3685 mg / L, respectively, and the granulation rate exceeded 50% for the first time, reaching 51.67% and 53.34%, respectively.

[0013] From the 11th to the 20th day, R2 only added anhydrous calcium chloride and stopped adding PAM. Other operating modes were the same as R1 (cycle 4 hours, COD load rate 0.72 kg / m 3 ·d). After stopping the addition of PAM, the settling performance of R2 deteriorated significantly. Since the settling time was the same as that of R1 (the settling time continued to shorten), a large amount of sludge was discharged. After 15 days of operation, the reactor settling time was shortened to 2 minutes. The sludge concentrations of R1 and R2 were measured to be 3122 mg / L and 1084 mg / L, respectively. Figure 3 As shown, there is a lot of biological foam on the surface of R2, which is close to collapse. Then R2 is stopped and R1 is started; like Figure 4 , Figure 5 As shown, on the 20th day, the sludge concentration of R1 was measured to be 3252 mg / L, and the granulation rate was 74.44%; starting from the 26th day, the granulation rate of R1 exceeded 80% for the first time, reaching 81.08%, and then remained above 80%, with an average particle size of about 0.53 mm, successfully achieving AGS cultivation.

[0014] like Figure 1 As shown, in R1, on the first day, except for the impurities in the sewage from the septic tank, almost no sludge was observed. On the second day, many yellow flocculent sludges appeared in the reactor. On the third day, a large number of sludge flocs were observed, but these flocs were unstable and would be broken into sludge flocs after aeration. On the fifth day, a large number of sludge flocs were observed, mixed with some spherical particles. Thereafter, the number of particles continued to increase. On the 15th day, a large number of sludge flocs were formed in the reactor. On the 25th day, sludge flocs and particles in R1 were absolutely dominant. like Figure 2 As shown in the figure, the sludge morphology changes in R2 were similar to those in R1 in the first 10 days. On the 15th day, a large number of sludge flocs were formed in R2. Due to the larger sludge discharge volume, the particle proportion in R2 was significantly higher than that in R1.

[0015] It can be seen that the present invention successfully achieved aerobic granulation in the SBR in 26 days when the influent COD was 200 mg / L and without inoculation of sludge. The addition of anhydrous calcium chloride and PAM after the influent can accelerate the coagulation of flocculent sludge and improve its sedimentation performance, but does not affect the selective screening of sludge with different sedimentation performance during the sedimentation process, which provides a new method for the rapid start-up of the AGS reactor when treating low-concentration domestic sewage. Example 2

[0016] This example uses a sequencing batch reactor (SBR) with an inner diameter of 19 cm, a height of 100 cm, an effective water level of 80 cm, an effective volume of 22.67 L, a water exchange rate of 60%, and an SBR cycle of 12-4 hours, including: water inlet, aeration mixing, anoxic stirring, aeration, sedimentation and drainage; On day 0, 9 L of actual septic tank sewage was inoculated into the SBR; Starting from the first day, about 13.6 L of simulated domestic sewage (pH 7-8, COD 200 mg / L, ammonia nitrogen 50 mg / L, total phosphorus 5 mg / L) was added to the effective water level in each cycle. The cycle time was 12 hours, including water inlet (3 min), aeration (685 min), sedimentation (30 min), and drainage (2 min). The liquid level rose by 4 cm after aeration. The activated sludge was cultivated through continuous aeration for about 685 min in the cycle. Starting from the second day, the reactor cycle time was reduced to 6 hours, including: 3 minutes of water inlet, 15 minutes of aeration and mixing, 45 minutes of anoxic stirring, 290-292 minutes of aeration, 5-3 minutes of sedimentation, and 2 minutes of drainage. The COD loading rate was 0.48 kg / m 3 ·d. Add anhydrous calcium chloride in the 5th minute and PAM in the 10th minute of the aeration and mixing section after each water inflow. The dosage of anhydrous calcium chloride is 2.23 grams, and the dosage of PAM is 1.2%, that is, 1.2 mg of PAM is added per liter of sewage; During operation, the settling time was gradually shortened to wash out the sludge flocs with poor settling performance. When the mud-water interface reached 60% of the drain outlet, the sludge could be drained. On the 10th day, the sludge granulation rate exceeded 50% for the first time, and the operation cycle was shortened to 4 hours, including: 3 minutes of water intake, 15 minutes of aeration and mixing, 45 minutes of anoxic stirring, 170-172 minutes of aeration, 5-3 minutes of sedimentation, and 2 minutes of drainage. The COD load rate was 0.72 kg / m 3 d, the settling time of the next cycle decreases by about 20 s compared with the previous cycle, and it will not be shortened after the settling time is reduced to 2 minutes; The dosage of PAM was determined by sedimentation test. 1000 mL of activated sludge was taken with a measuring cylinder, and 0.2%, 0.4%, 0.8%, 1.2%, and 1.6% of PAM were added respectively (that is, 0.2, 0.4, 0.6, 0.8, 1, and 1.2 mg of PAM were added to 1 L of sewage). The mixing measuring cylinder was repeatedly inverted for 2 minutes, and the mixture was allowed to settle. The time taken for complete sedimentation was compared. It was found that as the dosage increased from 0.2% to 1.2%, the sludge flocs gradually increased and the sedimentation time gradually decreased from 5 min to 10 s. However, when the dosage was above 1.2%, the sedimentation time remained within 10 s. Therefore, the dosage of 1.2% was the optimal value, which was the PAM dosage at the 10th minute of the aeration mixing stage, that is, 1.2 mg of PAM was added to 1 L of sewage, and 100 mL of solution was prepared for use. The sludge granulation rate continued to increase during the cultivation process. On the 26th day, the granulation rate before the reaction exceeded 80% for the first time, that is, the mass of particles larger than 0.2 mm accounted for 80% of the total sludge volume, which was considered a successful cultivation.

[0017] The above-described embodiments are merely descriptions of preferred embodiments of the present invention, and are not limitations on the protection scope of the present invention. Without departing from the design spirit of the present invention, various equivalent modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field all fall within the protection scope of the present invention.

Claims

1. A method for rapidly cultivating aerobic granular sludge by directly aerating low-concentration domestic sewage, characterized in that: A sequencing batch reactor (SBR) was used. From the third day, 100 mg / L of anhydrous calcium chloride with a concentration of 22.3 g / L was added in the 5th minute of the aeration and mixing stage after the SBR completed the water intake, and 100 mL of polyacrylamide with a concentration of 0.27 g / L was added in the 10th minute; the low-concentration domestic sewage was domestic sewage with a pH of 7-8, COD of 200 mg / L, ammonia nitrogen of 50 mg / L, and total phosphorus of 5 mg / L.

2. The method of rapidly cultivating aerobic granular sludge by directly aerating low-concentration domestic sewage according to claim 1, characterized in that: The dosage of the polyacrylamide is determined by a sedimentation test, and the specific method is: 1000 mL of activated sludge on the second day in 5 batches of reactors are respectively measured, and 0.2%, 0.4%, 0.8%, 1.2%, and 1.6% polyacrylamide are respectively added, the mixing measuring cylinder is repeatedly inverted for 2 minutes, and the sedimentation is allowed to stand. The time taken for complete sedimentation is compared, and the dosage of PAM with the shortest time is the optimal value, and 100 mL of solution is prepared and added at the 10th minute of the aeration mixing section.

3. A method for rapidly cultivating aerobic granular sludge by directly aerating low-concentration domestic sewage according to claim 1 or 2, characterized in that: The cycle of the sequencing batch reactor SBR is 12-4 hours, including: water intake, aeration mixing, anoxic stirring, aeration, sedimentation and drainage.

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