Deep denitrification method for secondary effluent of sewage plant

Abstract

The invention relates to the technical field of environmental pollution treatment, in particular to a deep denitrification method for secondary effluent of a sewage plant. Comprising the following steps: S1, volcanic rock and sulfur particles are taken as filler for attachment of a biological membrane, a biological filter column is started, and functional microorganisms in the biological membrane after successful starting comprise Thiobacillus and Candidate Kuenia; s2, the effluent of the primary sedimentation tank and the secondary effluent are mixed according to the volume ratio of (4.5-y) / (x-4. 5)-(5.5-y) / (x-5. 5) to obtain a mixed solution, x and y are the ammonia nitrogen concentration of the effluent of the primary sedimentation tank and the ammonia nitrogen concentration of the secondary effluent respectively, and the unit is mg / L; s3, carrying out denitrification treatment by taking the mixed solution as to-be-treated inlet water, and monitoring the quality of treated outlet water; and S4, judging whether to adjust the treatment process or not according to the nitrogen content in the effluent. According to the method, deep denitrification of the secondary effluent of the sewage plant can be realized, and the treatment cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of environmental pollution control, and in particular to a method for deep denitrification of secondary effluent from a sewage plant. Background Art

[0002] At present, water pollution control is still the top priority of my country's environmental protection work. As the "last line of defense" for pollutants to enter the water environment, the effluent quality of sewage treatment plants directly or indirectly affects the quality of the water environment. Many regions in China have proposed to improve the quality of tail water from urban sewage treatment plants, and implement total nitrogen control in many cities and eutrophic lakes, requiring total nitrogen <1.5mg / L. At present, most sewage treatment plants use secondary processes for biological denitrification, but the effluent after treatment still contains some nitrate nitrogen and a small amount of ammonia nitrogen. Therefore, deep denitrification of the secondary effluent of sewage treatment plants is a technical problem that needs to be urgently solved to improve the quality of sewage treatment plants.

[0003] The secondary effluent from urban sewage treatment plants has a low ammonia nitrogen concentration and a high nitrate nitrogen concentration. It also contains trace amounts of difficult-to-degrade organic matter and is a typical low C / N wastewater. It is difficult to achieve deep denitrification using traditional processes. The patent application with the announcement number CN116874084A discloses a reactor for deep denitrification of urban tail water, and specifically discloses a method for denitrification using the reactor, by detecting the nitrate content in the raw water, adding a carbon source 5 times the nitrate nitrogen value to treat the tail water, the total nitrogen removal efficiency reaches more than 60%, and the total nitrogen in the effluent is about 4.5 mg / L; the patent application with the announcement number CN110342639A discloses an enhanced denitrification MBR sustainable biological denitrification device and method, using anhydrous sodium acetate as a carbon source, maintaining a carbon-nitrogen ratio of 3:1 to treat the tail water, the total nitrogen removal efficiency reaches 95±5%, and the total nitrogen in the effluent is about 1.5 mg / L; the patent application with the announcement number CN106315980A discloses a deep treatment system for secondary effluent of domestic sewage, including an anaerobic biological filter and an aerated biological filter connected in series, after the tail water is deeply treated by the two-stage biological filter, the total nitrogen removal efficiency reaches 90%, and the total nitrogen in the effluent is 1.5 mg / L. All of the above technologies require an external organic carbon source, have high operating costs, and the total nitrogen in the effluent is ≥1.5mg / L, which still has room for improvement and does not meet the current requirements of energy conservation and consumption reduction in sewage treatment and "carbon peak" and "carbon neutrality". Therefore, it is of great significance to propose a low-cost and high-efficiency technology for deep denitrification of secondary effluent from sewage treatment plants.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a method for deep denitrification of secondary effluent from a sewage treatment plant, so as to solve the technical problems in the prior art that deep denitrification requires an external carbon source, is costly, and the total nitrogen content in the effluent after denitrification is still high. The method of the present invention uses the effluent from the primary sedimentation tank of the sewage treatment plant to provide an ammonia nitrogen matrix for the biological filter column, and after mixing with the secondary effluent, the Thiobacillus and Candidatus Kuenenia flora in the filter column work together to complete the simultaneous removal of ammonia nitrogen and nitrate nitrogen; during operation, the addition ratio of the effluent from the primary sedimentation tank, the water inlet flow rate or the update of the filler are adjusted in time according to the effluent water quality. The whole process does not require the addition of any additional matrix, the operating cost is low, and the average value of the total nitrogen in the effluent can be guaranteed to be less than 1.5 mg / L. During stable operation, the average value of the total nitrogen in the effluent is less than 1.0 mg / L, and the total nitrogen removal rate is greater than 90%, meeting the requirements of deep denitrification.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0007] A method for deep denitrification of secondary effluent from a sewage treatment plant comprises the following steps:

[0008] S1. Using volcanic rocks and sulfur particles as fillers for biofilm attachment, starting the biofilter column, after which the functional microorganisms in the biofilm of the biofilter column include Thiobacillus and Candidatus Kuenenia;

[0009] S2. The effluent from the primary sedimentation tank and the secondary effluent of the sewage treatment plant are mixed to obtain a mixed solution, wherein the volume ratio of the effluent from the primary sedimentation tank to the secondary effluent is (4.5-y) / (x-4.5) to (5.5-y) / (x-5.5), wherein x is the ammonia nitrogen concentration in the effluent from the primary sedimentation tank, and y is the ammonia nitrogen concentration in the secondary effluent, both in mg / L;

[0010] S3. operating the biofilter column, denitrifying the mixed solution as the influent to be treated, and monitoring the quality of the treated effluent;

[0011] S4. During operation, determine whether to adjust the treatment process based on the nitrogen content in the effluent.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] Since the secondary effluent of the sewage treatment plant contains almost no ammonia nitrogen, the present invention uses a small amount of effluent from the primary sedimentation tank to provide an ammonia nitrogen matrix for the growth of microorganisms in the biological filter column. The Thiobacillus bacteria in the filter column reduce part of the nitrate nitrogen to nitrous oxide, and directly reduce the other part of the nitrate nitrogen to nitrogen gas for removal, while Candidatus Kuenenia converts ammonia nitrogen and nitrous oxide into nitrogen gas for discharge;

[0014] The method of the present invention does not require any additional substrate to be added during operation. Only a combination of effluents from different units of a sewage treatment plant is used to achieve deep denitrification of secondary effluent, with low treatment cost. By reasonably controlling the initial mixing ratio of the effluent from the primary sedimentation tank and the secondary effluent, the average total nitrogen concentration in the treated effluent is <1.5 mg / L. During stable operation, the average total nitrogen concentration in the effluent is <1 mg / L, meeting the requirements for deep denitrification. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 This is a graph showing the change in nitrogen concentration of the inlet and outlet water during the tail water treatment operation in Example 1 of the present invention;

[0017] Figure 2 This is a graph showing the change in total nitrogen removal rate of actual tail water treated in Example 1 of the present invention;

[0018] Figure 3 This is a diagram of the microbial composition of the biofilter column in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0020] The present invention provides a method for deep denitrification of secondary effluent from a sewage treatment plant, comprising the following steps:

[0021] S1. Using volcanic rocks and sulfur particles as fillers for biofilm attachment, the biofilter column was started. After startup, the functional microorganisms in the biofilm of the biofilter column included Thiobacillus and Candidatus Kuenenia;

[0022] S2. The effluent from the primary sedimentation tank and the secondary effluent of the sewage treatment plant are mixed to obtain a mixed solution, and the volume ratio of the mixed effluent from the primary sedimentation tank and the secondary effluent is (4.5-y) / (x-4.5) to (5.5-y) / (x-5.5), wherein x is the ammonia nitrogen concentration in the effluent from the primary sedimentation tank, and y is the ammonia nitrogen concentration in the secondary effluent, both in mg / L;

[0023] S3. Run the biofilter column to denitrify the mixed solution as the influent to be treated, and monitor the quality of the treated effluent;

[0024] S4. During operation, determine whether the treatment process needs to be adjusted based on the nitrogen content in the effluent.

[0025] Since the secondary effluent of the sewage treatment plant contains almost no ammonia nitrogen, the method of the present invention uses a small amount of primary sedimentation tank effluent to provide an ammonia nitrogen matrix for the growth of microorganisms in the filter column. The Thiobacillus bacteria in the filter column reduce part of the nitrate nitrogen to nitrous acid, and directly reduce the other part of the nitrate nitrogen to nitrogen gas for removal. Candidatus Kuenenia converts ammonia nitrogen and nitrous acid into nitrogen gas for discharge. By reasonably controlling the initial mixing ratio of the primary sedimentation tank effluent and the secondary effluent, coupled with the synergistic effect of the two bacterial communities, efficient removal of ammonia nitrogen and nitrate nitrogen in the secondary effluent is achieved together. During the operation of the method of the present invention, no additional matrix needs to be added. Only the combination of effluents from different units of the sewage treatment plant is used to achieve deep denitrification of the secondary effluent. Compared with the traditional treatment method that requires the addition of an organic carbon source, the treatment cost is significantly reduced.

[0026] In the effluent treated by the method of the present invention, the average value of total nitrogen concentration during operation is less than 1.5 mg / L, and during stable operation, the average value of total nitrogen concentration is less than 1 mg / L, which meets the requirements of deep denitrification.

[0027] In some specific embodiments of the present invention, the effluent from the primary sedimentation tank and the effluent from the secondary sedimentation tank come from the same sewage treatment plant.

[0028] In some specific embodiments of the present invention, in step S1, the volume ratio of volcanic rock to sulfur particles is 0.5 to 2, for example, it can be any point value or a range value consisting of any two point values ​​among 0.5, 0.8, 1, 1.2, 1.5, 1.8, and 2. The ratio of sulfur to volcanic rock in the filter column will affect the abundance ratio of Thiobacillus and Candidatus Kuenenia, and thus affect the denitrification effect. Therefore, the ratio range of sulfur particles to volcanic rock needs to be reasonably controlled.

[0029] In some specific embodiments of the present invention, in step S1, after the biofilter column is started, the relative abundance of Thiobacillus and Candidatus Kuenenia flora are both greater than 5%. For example, the relative abundance of the two flora can be independently selected from 6%, 6.3%, 7%, 7.5%, 8%, 8.5% or 9%, etc.

[0030] In some specific embodiments of the present invention, in step S1, after the biofilter column is started, the relative abundance ratio of Thiobacillus and Candidatus Kuenenia is 1 to 3, for example, it can be any point value among 1, 1.5, 2, 2.5, 3 or a range value consisting of any two point values.

[0031] The method of the present invention ensures the path of synergistic denitrification in the biofilter column by reasonably controlling the relative abundance of Thiobacillus and Candidatus Kuenenia flora and the abundance ratio of the two, thereby achieving efficient removal of ammonia nitrogen and nitric nitrogen in the secondary effluent of the sewage treatment plant.

[0032] In some specific embodiments of the present invention, in step S2, the pH of the secondary effluent is 6.5-7.5, the nitrate nitrogen concentration is 5-15 mg / L, the ammonia nitrogen concentration is 0-4 mg / L, and the nitrous acid concentration is <0.5 mg / L.

[0033] In some specific embodiments of the present invention, in step S3, the nitrogen concentration in the effluent is detected once a day to monitor the effluent water quality.

[0034] In some specific embodiments of the present invention, in step S4, if the nitrate nitrogen and ammonia nitrogen in the effluent are always less than 1 mg / L, there is no need to adjust the treatment process, and at least part of the sulfur particles in the biofilter column are replaced every 50 to 100 days to ensure sufficient sulfur source supply in the filter column. The replacement amount each time is preferably (45V~55V)g, where V is the volume of the biofilter column.

[0035] In some embodiments, typically but not limiting, for example, during operation, the time interval for replacing sulfur particles can be any point value among 50 days, 60 days, 70 days, 80 days, 90 days, and 100 days, or a range value consisting of any two point values; the replacement amount each time can be any point value among 45Vg, 48Vg, 50Vg, 52Vg, and 55Vg, or a range value consisting of any two point values.

[0036] In some specific embodiments of the present invention, in step S4, if the ammonia nitrogen in the effluent is >1 mg / L for 2-4 consecutive days, and / or the nitrate nitrogen is >1 mg / L for 2-4 consecutive days, the treatment process needs to be adjusted. There are mainly three situations according to the different effluent water quality. Different process parameters need to be adjusted for different water quality conditions. The specific adjustment process is as follows:

[0037] When the ammonia nitrogen in the effluent is greater than 1 mg / L and the nitrate nitrogen is less than 1 mg / L for 2 to 4 consecutive days, the mixing ratio of the effluent from the primary sedimentation tank in step S2 is reduced to reduce the ammonia nitrogen content in the effluent until the ammonia nitrogen in the effluent is less than 1 mg / L;

[0038] When the nitrate nitrogen in the effluent is greater than 1 mg / L and the ammonia nitrogen is less than 1 mg / L for 2 to 4 consecutive days, the inlet flow rate in step S2 is reduced. If the nitrate nitrogen in the effluent is still greater than 1 mg / L when the inlet flow rate is reduced to 0.8 times of the original value, the sulfur particles in the biofilter column are at least partially replaced to renew the sulfur source. As an example, the replacement amount of sulfur particles is 20-50 g / L (the mass of sulfur replaced per unit filter column volume), for example, it can be any point value among 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, or a range value composed of any two point values.

[0039] When the nitrate nitrogen in the effluent is greater than 1 mg / L for 2 to 4 consecutive days, and the ammonia nitrogen is greater than 1 mg / L, the inlet flow rate in step S2 is reduced, and the effluent reflux is increased, that is, the treated effluent is mixed with the influent again and flows into the biological filter column for treatment. The effluent reflux can not only return the signal molecules in the effluent to the reactor to enhance the activity of microorganisms, but also return the soluble microbial products in the effluent to the filter column to provide an endogenous carbon source for denitrifying bacteria. On the other hand, it can extend the reaction time of the effluent and improve the treatment effect. During the adjustment process, the increase in the effluent reflux is equal to the decrease in the inlet flow rate until the ammonia nitrogen or nitrate nitrogen in the effluent drops below 1 mg / L, and then the adjustment steps applicable to the corresponding water quality are adjusted until the ammonia nitrogen and nitrate nitrogen in the effluent are less than 1 mg / L.

[0040] This method can not only flexibly adjust the fluctuation of effluent water quality caused by the fluctuation of reactor performance, but also timely adjust the fluctuation of effluent concentration caused by the change of influent substrate concentration. The adjustment is timely and the reactor reacts quickly, which can maintain long-term stable operation. After the effluent water quality is adjusted to be stable by the above method, the average value of total nitrogen concentration in the effluent can be less than 1mg / L, which meets the requirements of deep denitrification. In addition, this method does not require any additional substrate to be added during the adjustment process, and the operating cost is low.

[0041] The present invention makes adjustments only when any of the above-mentioned water quality conditions that require adjustment occur for 2-4 consecutive days. For example, the adjustment can be made when any of the above-mentioned conditions occur for 2 consecutive days, 3 consecutive days or 4 consecutive days. The main reason is that the water quality is tested once a day during operation. The situation in which the water quality needs to be adjusted on a certain day may be an accidental fluctuation or a detection error. If the adjustment is only made after this situation has occurred for too long in succession, the time for unqualified water discharge will be prolonged, affecting the average level of water quality of the effluent during the treatment process.

[0042] In some specific embodiments of the present invention, when the ammonia nitrogen in the effluent is >1 mg / L for 2 to 4 consecutive days and the nitric nitrogen is <1 mg / L, it is necessary to reduce the mixing ratio of the primary sedimentation tank effluent, and the specific adjustment process is: the average concentration of the ammonia nitrogen in the effluent for 2-4 days is recorded as m, in mg / L, and the volume ratio of the primary sedimentation tank effluent and the secondary effluent is first adjusted to (5.5-my) / (x-5.5+m), and the operation is continued and the nitrogen content in the effluent is monitored. If the ammonia nitrogen is <1 mg / L and the water quality is stable, the adjustment is stopped; if the ammonia nitrogen is still >1 mg / L for 2-4 consecutive days after the adjustment, the average ammonia nitrogen concentration in the effluent for 2-4 days after the adjustment is >1 mg / L is taken as the new m value, and adjustment is performed again, and this is repeated until the ammonia nitrogen in the effluent is <1 mg / L.

[0043] In some specific embodiments of the present invention, when the effluent has the situation of "nitric nitrogen>1mg / L, and ammonia nitrogen<1mg / L" or "nitric nitrogen>1mg / L, and ammonia nitrogen>1mg / L" for 2 to 4 consecutive days, it is necessary to reduce the influent flow rate in step S2, and the influent flow rate is adjusted in the following manner: During the adjustment process, the daily influent flow rate is calculated according to the formula VQ / (V+0.5Q), where V is the volume of the biofilter column and Q is the influent flow rate of the previous day. That is, when adjusting, first change the influent flow rate to VQ / (V+0.5Q), where Q is the influent flow rate of the previous day. After one day of adjustment, if the nitric nitrogen is still greater than 1mg / L or both ammonia nitrogen and nitric nitrogen are greater than 1mg / L, continue to adjust according to the influent flow rate of the previous day, and repeat this process.

[0044] In some specific embodiments of the present invention, in step S4, the average value of the total nitrogen concentration in the effluent is less than 1.5 mg / L, the total nitrogen removal rate is greater than 90%, and during stable operation, the average value of the total nitrogen in the effluent is less than 1 mg / L, meeting the requirements for deep denitrification.

[0045] The following is a detailed description of some embodiments of the present invention in conjunction with specific examples. The raw materials used in the examples can be purchased from the market unless otherwise specified.

[0046] Example 1

[0047] A mixture of volcanic rock and sulfur particles was used as the filler for biofilm attachment. The volume ratio of volcanic rock to sulfur particles was 1. The biofilter column was started with an effective volume of 1L. The start-up time was 24 days. After the start-up, the main functional microorganisms in the biofilm of the filter column included Thiobacillus at 9.3% and Candidatus Kuenenia at 7.5%.

[0048] The effluent from the primary sedimentation tank and the secondary sedimentation tank of the municipal sewage treatment plant (i.e. the tail water of the municipal sewage treatment plant, also known as the secondary effluent) was taken. It was found that the concentration of ammonia nitrogen in the effluent of the primary sedimentation tank was 55.2 mg / L, and the concentration of nitrate nitrogen was 1.2 mg / L. The concentration of ammonia nitrogen in the effluent of the secondary sedimentation tank was 0, and the concentration of nitrate nitrogen was about 8.1 mg / L. The effluent of the primary sedimentation tank (A) and the effluent of the secondary sedimentation tank (B) were mixed at a volume ratio of A:B of about 1:10. After uniform mixing, the average concentration of ammonia nitrogen in the wastewater (mixed liquid) at this stage was 4.6 mg / L, the concentration of nitrate nitrogen was 9.3 mg / L, and the concentration of nitrous oxide was 0. The change of nitrogen concentration during the operation process is shown in Figure 1 and Figure 2 , which is a selection of representative operating data.

[0049] On the 7th day of operation, the effluent ammonia nitrogen was greater than 1 mg / L for three consecutive days, while the nitrate nitrogen was less than 1 mg / L. The average effluent ammonia nitrogen concentration from the 5th to the 7th day was 1.343 mg / L. Then on the 8th day, the influent ratio A:B was changed to 1:12, and then the effluent ammonia nitrogen decreased to about 0.5 mg / L.

[0050] Continue to operate until the 16th day. If the effluent nitrate nitrogen is greater than 1mg / L for three consecutive days and the effluent ammonia nitrogen is less than 1mg / L, then on the 17th day, reduce the inlet flow rate from 0.083L / h to 0.08L / h. On the 18th day, the effluent nitrate nitrogen is reduced to about 0.5mg / L.

[0051] When the operation continued until the 26th-28th day, the effluent ammonia nitrogen and nitrate nitrogen were both greater than 1mg / L. Then, on the evening of the 28th day, the effluent return flow was increased and the inlet flow was reduced at the same time. The inlet flow was changed from 0.08L / h to 0.077L / h, and the effluent return flow was increased from 0 to 0.023L / h. On the 29th day, the effluent ammonia nitrogen and nitrate nitrogen both decreased, but neither dropped below 1mg / L. Considering that it had been more than 50 days since the last sulfur replacement (including the start-up time), 50g of sulfur was replaced on the 30th day. On the 31st day, the nitrate nitrogen dropped to about 0.7mg / L. On the 32nd day, the effluent ammonia nitrogen and effluent nitrate nitrogen concentrations both dropped to 0mg / L, and since then, it has always maintained stable operation, with effluent ammonia nitrogen <1mg / L, effluent nitrate nitrogen <1mg / L, the average effluent total nitrogen was 0.6mg / L, and the average total nitrogen removal rate was 95%.

[0052] Example 2

[0053] A mixture of volcanic rock and sulfur particles was used as the filler for biofilm attachment. The volume ratio of volcanic rock to sulfur particles was 2. The biofilter column was started with an effective volume of 1 L. The start-up time was 25 days. After the start-up, the main functional microorganisms in the biofilm of the filter column included Thiobacillus at 8.5% and Candidatus Kuenenia at 6.3. The specific microbial composition is shown in Figure 3 ;

[0054] After the biofilter was started and operated stably, it was used to treat the effluent from the secondary sedimentation tank of Zhengzhou Shuangqiao Sludge Treatment Plant. According to the test, the ammonia nitrogen in the effluent of the secondary sedimentation tank was 0.3 mg / L, the nitrate nitrogen was 10.4 mg / L, and the nitrous acid was 0. The ammonia nitrogen in the effluent of the primary sedimentation tank was 31.1 mg / L, the nitrate nitrogen was 1.7 mg / L, and the nitrous acid was 0.6 mg / L. The initial volume ratio of primary sedimentation tank effluent: secondary sedimentation tank effluent was 1:6. After evenly mixing, the above-mentioned biofilter column was used for treatment. On the 15th-17th day of operation, the effluent nitrate nitrogen was greater than 1 mg / L for three consecutive days, and the ammonia nitrogen was <1 mg / L. The inlet flow rate was reduced from 0.083 L / h to 0.08 L / h, and the effluent nitrate nitrogen was reduced to 0.4 mg / L. On the 24th-26th day of operation, the effluent ammonia nitrogen was greater than 1 mg / L for three consecutive days, and the nitrate nitrogen was <1 mg / L. The inlet ratio A:B was changed to 1:8, and then the effluent ammonia nitrogen was reduced to about 0.5 mg / L. During the operation of this batch of water, there was no situation where ammonia nitrogen and nitrate nitrogen were greater than 1 mg / L at the same time. During operation, timely adjustments are made according to the effluent water quality, and the filter column can operate stably for a long time. During stable operation, the average effluent ammonia nitrogen value is 0.2 mg / L, the average effluent nitrate nitrogen value is 0.4 mg / L, the average effluent total nitrogen value is 0.6 mg / L, and the average total nitrogen removal rate is 96%.

[0055] Example 3

[0056] A mixture of volcanic rock and sulfur particles was used as filler for biofilm attachment, with a volume ratio of volcanic rock to sulfur particles of 1.5. After the biofilter column was started and operated stably, the biofilm contained 9.1% Thiobacillus and 7.5% CandidatusKuenenia. It was used to treat the effluent from the secondary sedimentation tank of Zhengzhou Shuangqiao Sludge Disposal Plant. According to the measurement, the ammonia nitrogen in the effluent of the secondary sedimentation tank was 0.5mg / L, the nitrate nitrogen was 9.5mg / L, and the nitrous acid was 0. The ammonia nitrogen in the effluent of the primary sedimentation tank was 43.2mg / L, the nitrate nitrogen was 1.6mg / L, and the nitrous acid was 0.2mg / L. The initial volume ratio of the mixed liquor is 1:8 according to the effluent from the primary sedimentation tank: the effluent from the secondary sedimentation tank. After being evenly mixed, the biological filter column is used for treatment. During operation, the filter column is adjusted in time according to the method of the present invention according to the effluent water quality. The filter column can operate stably for a long time. During the stable operation, the average ammonia nitrogen content of the effluent is 0.5 mg / L, the average nitrate nitrogen content of the effluent is 0.4 mg / L, the average total nitrogen content of the effluent is 0.9 mg / L, and the average total nitrogen removal rate is 94%.

[0057] Comparative Example 1

[0058] A mixture of volcanic rock and sulfur particles was used as filler for biofilm attachment. The volume ratio of volcanic rock to sulfur particles was 3. After starting the biofilter column, the relative abundances of Thiobacillus and Candidatus Kuenenia in the filter column were 2.3% and 8.1%, respectively. Even after three months of operation, the relative abundance ratio of the two could not reach an operating state between 1 and 3. The filter column was directly used to treat the tail water of the sewage plant. It was found that the concentration of ammonia nitrogen in the effluent of the primary sedimentation tank was 55.2 mg / L, and the concentration of nitrate nitrogen was 1.2 mg / L. The concentration of ammonia nitrogen in the effluent of the secondary sedimentation tank was 0, and the concentration of nitrate nitrogen was about 8.1 mg / L. The effluent of the primary sedimentation tank (A) and the effluent of the secondary sedimentation tank (B) were mixed at a volume ratio of A:B of about 1:10; after uniform mixing, the average concentration of ammonia nitrogen in the wastewater (mixed liquor) at this stage was 4.6 mg / L, the concentration of nitrate nitrogen was 9.3 mg / L, and the concentration of nitrous oxide was 0. However, during the two-month operation, no matter how the operating parameters were adjusted, the effluent ammonia nitrogen could not be less than 1 mg / L for three consecutive days, the nitrate nitrogen was always greater than 1 mg / L, and the effluent total nitrogen was greater than 3 mg / L, and the deep denitrification effect of the present invention could not be achieved.

[0059] Comparative Example 2

[0060] The same batch of wastewater was treated with the same biofilter column as in Example 3. It was determined that the ammonia nitrogen in the effluent of the secondary sedimentation tank was 0.5 mg / L, the nitrate nitrogen was 9.5 mg / L, and the nitrous acid was 0. The ammonia nitrogen in the effluent of the primary sedimentation tank was 43.2 mg / L, the nitrate nitrogen was 1.6 mg / L, and the nitrous acid was 0.2 mg / L. The initial volume ratio of the mixed solution was 1:12 according to the effluent of the primary sedimentation tank: the effluent of the secondary sedimentation tank. After uniform mixing, the above-mentioned biofilter column was used for treatment. During the operation, the effluent nitrate nitrogen was always greater than 1 mg / L. Even after adjustment, the effect of effluent ammonia nitrogen and effluent nitrate nitrogen being less than 1 mg / L at the same time could not be achieved. The average effluent nitrate nitrogen was 3.2 mg / L. The reason for the analysis was that the effluent of the primary sedimentation tank was too little, and it could not provide sufficient ammonia nitrogen matrix, and the microbial activity was inhibited.

[0061] Comparative Example 3

[0062] The same batch of wastewater was treated with the same biological filter column as in Example 3. The ammonia nitrogen in the effluent of the secondary sedimentation tank was 0.5 mg / L, the nitrate nitrogen was 9.5 mg / L, and the nitrous acid was 0. The ammonia nitrogen in the effluent of the primary sedimentation tank was 43.2 mg / L, the nitrate nitrogen was 1.6 mg / L, and the nitrous acid was 0.2 mg / L. The initial volume ratio of the mixed solution was 1 / 5 of the effluent of the primary sedimentation tank: the effluent of the secondary sedimentation tank. After uniform mixing, the above-mentioned biological filter column was used for treatment. After two months of adjustment, it was still impossible to ensure that the effluent ammonia nitrogen was less than 1 mg / L for a week. Even after a long period of adjustment, the stable operation effect of the effluent ammonia nitrogen and effluent nitrate nitrogen being less than 1 mg / L at the same time could not be achieved. The average value of the effluent ammonia nitrogen during the adjustment period was 2.1 mg / L. The reason for the analysis was that the effluent of the primary sedimentation tank provided excessive ammonia nitrogen, which could not be completely removed by anaerobic ammonia oxidation.

[0063] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for deep denitrification of secondary effluent from a sewage treatment plant, characterized in that: The following steps are involved: S1. Using volcanic rocks and sulfur particles as fillers for biofilm attachment, starting the biofilter column, after which the functional microorganisms in the biofilm of the biofilter column include Thiobacillus and Candidatus Kuenenia; S2. The effluent from the primary sedimentation tank and the secondary effluent of the sewage treatment plant are mixed to obtain a mixed solution, wherein the volume ratio of the effluent from the primary sedimentation tank to the secondary effluent is (4.5-y) / (x-4.5) to (5.5-y) / (x-5.5), wherein x is the ammonia nitrogen concentration in the effluent from the primary sedimentation tank, and y is the ammonia nitrogen concentration in the secondary effluent, both in mg / L; S3. operating the biofilter column, denitrifying the mixed solution as the influent to be treated, and monitoring the quality of the treated effluent; S4. During operation, determine whether to adjust the treatment process based on the nitrogen content in the effluent.

2. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 1, characterized in that: In step S1, the volume ratio of the volcanic rock to the sulfur particles is 0.5-2.

3. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 1, characterized in that: In step S1, after the biofilter column is started, the relative abundances of the Thiobacillus and the Candidatus Kuenenia are both greater than 5%.

4. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 1, characterized in that: In step S1, after the biofilter column is started, the relative abundance ratio of the Thiobacillus and the Candidatus Kuenenia is 1-3.

5. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 1, characterized in that: In step S2, the pH of the secondary effluent is 6.5-7.5, the nitrate nitrogen concentration is 5-15 mg / L, the ammonia nitrogen concentration is 0-4 mg / L, and the nitrous acid concentration is less than 0.5 mg / L.

6. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 1, characterized in that: In step S4, the nitrate nitrogen and ammonia nitrogen in the effluent are always less than 1 mg / L, and there is no need to adjust the treatment process. At least part of the sulfur particles are replaced every 50 to 100 days.

7. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 1, characterized in that: In step S4, if the ammonia nitrogen in the effluent is greater than 1 mg / L for 2-4 consecutive days, and / or the nitrate nitrogen is greater than 1 mg / L for 2-4 consecutive days, the treatment process needs to be adjusted, and the adjustment process includes: When the ammonia nitrogen in the effluent is greater than 1 mg / L and the nitrate nitrogen is less than 1 mg / L for 2 to 4 consecutive days, the mixing ratio of the effluent from the primary sedimentation tank in step S2 is reduced until the ammonia nitrogen in the effluent is less than 1 mg / L; When the nitrate nitrogen in the effluent is greater than 1 mg / L and the ammonia nitrogen is less than 1 mg / L for 2 to 4 consecutive days, the inlet flow rate in step S2 is reduced. If the nitrate nitrogen in the effluent is still greater than 1 mg / L when the inlet flow rate is reduced to 0.8 times of the original, the sulfur particles in the biofilter column are at least partially replaced to renew the sulfur source; When the nitrate nitrogen in the effluent is greater than 1 mg / L and the ammonia nitrogen is greater than 1 mg / L for 2 to 4 consecutive days, the inlet flow rate in step S2 is reduced, and the effluent reflux is increased, and the increase in the effluent reflux is equal to the decrease in the inlet flow rate, until the ammonia nitrogen or nitrate nitrogen in the effluent drops below 1 mg / L, and then adjustments are made according to the adjustment steps applicable to the corresponding water quality until the ammonia nitrogen and nitrate nitrogen in the effluent are both less than 1 mg / L.

8. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 7, characterized in that: When reducing the mixing ratio of the effluent from the primary sedimentation tank, the average concentration of ammonia nitrogen in the effluent for 2-4 consecutive days greater than 1 mg / L is recorded as m, and the volume ratio of the effluent from the primary sedimentation tank and the secondary effluent is adjusted to (5.5-my) / (x-5.5+m), and the operation is continued to monitor the nitrogen content in the effluent; if the ammonia nitrogen is still greater than 1 mg / L for 2-4 consecutive days after the adjustment, the average concentration of ammonia nitrogen on the 2nd to 4th day after the adjustment is taken as the new m value, and adjustment is made again until the ammonia nitrogen in the effluent is less than 1 mg / L.

9. The method for deep denitrification of secondary effluent from a sewage treatment plant according to claim 7, characterized in that: When reducing the water inlet flow rate in step S2, the adjustment is performed in the following manner: during the adjustment process, the daily water inlet flow rate is calculated according to the formula VQ / (V+0.5Q), wherein V is the volume of the biofilter column and Q is the water inlet flow rate of the previous day.

10. The method for deep denitrification of secondary effluent from a sewage treatment plant according to any one of claims 1 to 9, characterized in that: In step S4, the average value of the total nitrogen concentration in the effluent water is less than 1.5 mg / L, and the total nitrogen removal rate is greater than 90%.

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