Method for advanced nitrogen removal of secondary effluent of sewage plant

Abstract

The present application relates to the technical field of environmental pollution treatment, in particular to a method for advanced denitrification of secondary effluent of sewage plant, comprising the following steps: S1. taking volcanic rock and sulfur particles as the filler for biofilm adhesion, starting the biofilter column, and after successful start, the functional microorganisms in the biofilm include Thiobacillus and Candidatus Kuenenia; S2. mixing the primary sedimentation tank effluent and the secondary effluent according to the volume ratio of (4.5-y) / (x-4.5)~(5.5-y) / (x-5.5) to obtain the mixed liquor, wherein x and y are the ammonia nitrogen concentrations in the primary sedimentation tank effluent and the secondary effluent respectively, and the unit is mg / L; S3. taking the mixed liquor as the water to be treated for denitrification treatment, and monitoring the water quality of the treated effluent; S4. judging whether to adjust the treatment process according to the nitrogen content in the effluent. The present method can realize the advanced denitrification of the secondary effluent of sewage plant, and has low treatment cost.

Description

Technical Field

[0001] This invention relates to the field of environmental pollution control technology, and more specifically, to a method for deep denitrification of secondary effluent from a wastewater treatment plant. Background Technology

[0002] Currently, water pollution control remains a top priority in my country's environmental protection efforts. Wastewater treatment plants, as the "last line of defense" against pollutants entering the aquatic environment, directly or indirectly affect water quality through their effluent. Many regions in China have proposed upgrading the standards and quality of effluent from urban wastewater treatment plants and implementing total nitrogen control measures in several cities and eutrophic lakes and reservoirs, requiring total nitrogen levels to be <1.5 mg / L. Currently, most wastewater treatment plants use secondary biological denitrification processes; however, the treated effluent still contains some nitrate nitrogen and a small amount of ammonia nitrogen. Therefore, advanced denitrification of secondary effluent from wastewater treatment plants is a crucial technical issue that urgently needs to be addressed to improve the efficiency and standards of wastewater treatment plants.

[0003] The secondary effluent from urban wastewater treatment plants has low ammonia nitrogen concentrations and high nitrate nitrogen concentrations, while also containing trace amounts of recalcitrant organic matter. It is a typical low C / N wastewater, and traditional processes are insufficient to achieve deep denitrification. Patent application CN116874084A discloses a deep denitrification reactor for urban effluent and specifically discloses a denitrification method using this reactor. By detecting the nitrate content in the raw water, five times the amount of carbon source is added to treat the effluent based on the nitrate nitrogen value, achieving a total nitrogen removal efficiency of over 60% and an effluent total nitrogen of approximately 4.5 mg / L. Patent application CN110342639A discloses a sustainable biological denitrification device and method for enhanced denitrification MBR, using anhydrous sodium acetate as the carbon source and maintaining a carbon-to-nitrogen ratio of 3:1 to treat the effluent, achieving a total nitrogen removal efficiency of 95±5% and an effluent total nitrogen of approximately 1.5 mg / L. Patent application CN106315980A discloses a deep treatment system for secondary effluent of domestic sewage, including anaerobic biological filters and aerated biological filters connected in series. After deep treatment of the effluent through two stages of biological filters, the total nitrogen removal efficiency reaches 90%, and the effluent total nitrogen is 1.5 mg / L. All of the above technologies require external organic carbon sources, resulting in high operating costs. Furthermore, the total nitrogen in the effluent is ≥1.5 mg / L, leaving room for improvement. These technologies do not meet the current requirements for energy conservation, emission reduction, carbon peaking, and carbon neutrality in wastewater treatment. Therefore, proposing a low-consumption, high-efficiency technology for deep nitrogen removal from secondary effluent of wastewater treatment plants is of great significance.

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

[0005] The purpose of this invention is to provide a method for deep denitrification of secondary effluent from wastewater treatment plants, addressing the technical problems of existing deep denitrification technologies that require external carbon sources, are costly, and still result in high total nitrogen content in the effluent after denitrification. This invention uses the effluent from the primary sedimentation tank of the wastewater treatment plant as a substrate for ammonia nitrogen in a biological filter column. After mixing with the secondary effluent, the Thiobacillus and Candidatus Kuenenia bacteria in the filter column work together to simultaneously remove ammonia and nitrate nitrogen. During operation, the proportion of primary sedimentation tank effluent, the influent flow rate, or the packing material is adjusted in a timely manner according to the effluent quality. The entire process requires no additional substrate, has low operating costs, and ensures that the average total nitrogen in the effluent is less than 1.5 mg / L. During stable operation, the average total nitrogen in the effluent is <1.0 mg / L, and the total nitrogen removal rate is greater than 90%, meeting the requirements for deep denitrification.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] A method for advanced nitrogen removal in secondary effluent from a wastewater treatment plant includes the following steps:

[0008] S1. Using volcanic rock and sulfur particles as packing material for biofilm attachment, the biofilter column is started. After start-up, 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 effluent from the secondary sedimentation tank of the wastewater treatment plant are mixed to obtain a mixed liquid, wherein the volume ratio of the effluent from the primary sedimentation tank and the effluent from the secondary sedimentation tank is (4.5-y) / (x-4.5)~(5.5-y) / (x-5.5), where x is the ammonia nitrogen concentration in the effluent from the primary sedimentation tank and y is the ammonia nitrogen concentration in the effluent from the secondary sedimentation tank, both in mg / L;

[0010] S3. Operate the biological filter column, use the mixed liquid as the influent to be treated for denitrification, and monitor 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 beneficial effects of the present invention are as follows:

[0013] Since the secondary effluent from the wastewater treatment plant contains almost no ammonia nitrogen, this invention utilizes a small amount of primary sedimentation tank effluent to provide an ammonia nitrogen substrate for the growth of microorganisms in the biological filter column. Thiobacillus bacteria in the filter column reduce some nitrate nitrogen to nitrous oxide and directly reduce another part of nitrate nitrogen to nitrogen gas for removal. Candidatus Kuenenia converts ammonia nitrogen and nitrous oxide into nitrogen gas for emission.

[0014] The method of this invention does not require the addition of any additional substrate during operation. It achieves deep denitrification of secondary effluent simply by combining the effluent from different units of the wastewater treatment plant. The treatment cost is low. By reasonably controlling the initial mixing ratio of the primary sedimentation tank effluent 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, which meets the requirements for deep denitrification. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a graph showing the changes in nitrogen concentration in the influent and effluent during the tailwater treatment operation in Embodiment 1 of the present invention;

[0017] Figure 2 This is a graph showing the change in total nitrogen removal rate of the actual effluent 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 Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

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

[0021] S1. Volcanic rock and sulfur particles are used as packing material for biofilm attachment. The biofilter column is started. After startup, the functional microorganisms in the biofilm of the biofilter column include Thiobacillus and Candidatus Kuenenia.

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

[0023] S3. Operate the biological filter column, use the mixed liquor as the influent to be treated for denitrification, 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 secondary effluent from wastewater treatment plants contains almost no ammonia nitrogen, the method of this invention utilizes a small amount of primary sedimentation tank effluent to provide an ammonia nitrogen substrate for the growth of microorganisms within the filter column. Thiobacillus bacteria within the filter column reduce some nitrate nitrogen to nitrous oxide and another portion of nitrate nitrogen directly to nitrogen gas for removal. Candidatus Kuenenia converts ammonia nitrogen and nitrous oxide into nitrogen gas for emission. By rationally 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, highly efficient removal of ammonia nitrogen and nitrate nitrogen from the secondary effluent is achieved. This method requires no additional substrate during operation; deep denitrification of the secondary effluent is achieved simply by combining effluent from different units of the wastewater treatment plant. Compared to traditional treatment methods that require the addition of organic carbon sources, this significantly reduces treatment costs.

[0026] The average total nitrogen concentration in the effluent treated by the method of this invention is <1.5 mg / L during operation and <1 mg / L during stable operation, which meets the requirements for 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 wastewater 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 one value from 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, or a range of any two values. The ratio of sulfur to volcanic rock in the filter column affects the abundance ratio of the two bacterial communities, Thiobacillus and Candidatus Kuenenia, and thus affects the denitrification effect. Therefore, it is necessary to reasonably control the range of the ratio of sulfur particles to volcanic rock.

[0029] In some specific embodiments of the present invention, in step S1, after the biofilter is started, the relative abundance of Thiobacillus and Candidatus Kuenenia is greater than 5%. For example, the relative abundance of the two bacterial groups 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 ratio of the relative abundance of Thiobacillus and Candidatus Kuenenia is 1 to 3. For example, it can be any one value among 1, 1.5, 2, 2.5, and 3, or a range of any two point values.

[0031] The method of this invention ensures the synergistic denitrification pathway within the biofilter column by rationally controlling the relative abundance of Thiobacillus and Candidatus Kuenenia and their abundance ratio, thereby achieving efficient removal of ammonia nitrogen and nitrate nitrogen from the secondary effluent of wastewater treatment plants.

[0032] In some specific embodiments of the present invention, in step S2, the pH of the secondary effluent is 6.5 to 7.5, the nitrate nitrogen concentration is 5 to 15 mg / L, the ammonia nitrogen concentration is 0 to 4 mg / L, and the nitrous oxide 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 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, then there is no need to adjust the treatment process. At least part of the sulfur particles in the biological filter 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 to 55V) g, where V is the volume of the biological filter column.

[0035] In some implementations, typically but not limitingly, for example, during operation, the time interval for replacing sulfur particles can be any one of 50 days, 60 days, 70 days, 80 days, 90 days, 100 days, or a range of any two of these values; the replacement amount each time can be any one of 45Vg, 48Vg, 50Vg, 52Vg, 55Vg, or a range of any two of these 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. Depending on the effluent quality, there are three main scenarios, each requiring different process parameters. The specific adjustment process is as follows:

[0037] When the ammonia nitrogen in the effluent is >1 mg / L and the nitrate nitrogen is <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 <1 mg / L.

[0038] When the nitrate nitrogen in the effluent is >1 mg / L and the ammonia nitrogen is <1 mg / L for 2-4 consecutive days, the influent flow rate in step S2 is reduced. If the nitrate nitrogen in the effluent is still >1 mg / L when the influent flow rate is reduced to 0.8 times the original value, the sulfur particles in the biological filter column are replaced at least partially to refresh the sulfur source. As an example, the amount of sulfur particles replaced is 20-50 g / L (the mass of sulfur replaced per unit filter column volume). For example, it can be any one value or a range of any two values ​​from 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, and 50 g / L.

[0039] When nitrate nitrogen and ammonia nitrogen in the effluent are consistently above 1 mg / L for 2–4 consecutive days, reduce the influent flow rate in step S2 and increase effluent recirculation. This involves mixing the treated effluent with the influent again before flowing it into the biological filter column for further treatment. Effluent recirculation not only returns signal molecules from the effluent to the reactor to enhance microbial activity but also returns dissolved microbial products from the effluent to the filter column to provide an endogenous carbon source for denitrifying bacteria. Furthermore, it extends the reaction time of the effluent, improving treatment efficiency. During the adjustment process, the increase in effluent recirculation should be equal to the decrease in influent flow rate until the ammonia nitrogen or nitrate nitrogen in the effluent drops below 1 mg / L. Then, adjust according to the appropriate adjustment steps for the corresponding water quality until both ammonia nitrogen and nitrate nitrogen in the effluent are less than 1 mg / L.

[0040] This method not only flexibly adjusts for fluctuations in effluent water quality caused by reactor performance variations, but also promptly adjusts for fluctuations in effluent concentration caused by changes in influent substrate concentration. The adjustment is timely, and the reactor reacts rapidly, enabling long-term stable operation. After adjusting to stable effluent water quality using the above method, the average total nitrogen concentration in the effluent is <1 mg / L, meeting the requirements for deep denitrification. Furthermore, this method does not require the addition of any additional substrate during the adjustment process, resulting in low operating costs.

[0041] This invention only makes adjustments when one of the aforementioned water quality conditions requiring adjustment occurs for 2-4 consecutive days. For example, adjustments can be made only after one of the aforementioned conditions occurs for 2, 3, or 4 consecutive days. The main reason is that water quality is tested once a day during operation. If water quality requires adjustment on a particular day, it may be due to occasional fluctuations or testing errors. However, if adjustments are made only after such conditions have occurred for an extended period, it will prolong the time of unqualified effluent and affect the average level of effluent quality during the treatment process.

[0042] In some specific embodiments of the present invention, when the ammonia nitrogen in the effluent is >1 mg / L and the nitrate nitrogen is <1 mg / L for 2-4 consecutive days, and it is necessary to reduce the mixing ratio of the primary sedimentation tank effluent, the specific adjustment process is as follows: the average concentration of ammonia nitrogen in the effluent for 2-4 consecutive days >1 mg / L is recorded as m, with the unit being mg / L. First, the volume ratio of the primary sedimentation tank effluent and the secondary effluent is adjusted to (5.5-my) / (x-5.5+m). The operation continues 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 for 2-4 consecutive days after the adjustment is taken as the new m value, and the adjustment is performed again. This process 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 shows "nitrate nitrogen > 1 mg / L and ammonia nitrogen < 1 mg / L" or "nitrate nitrogen > 1 mg / L and ammonia nitrogen > 1 mg / L" for 2-4 consecutive days, the influent flow rate in step S2 needs to be reduced. The influent flow rate is adjusted as follows: During the adjustment process, the daily influent flow rate is calculated using the formula VQ / (V+0.5Q), where V is the volume of the biological filter column and Q is the influent flow rate of the previous day. That is, during adjustment, the influent flow rate is first changed to VQ / (V+0.5Q), where Q is the influent flow rate of the previous day. After one day of adjustment, if nitrate nitrogen is still greater than 1 mg / L, or both ammonia nitrogen and nitrate nitrogen are greater than 1 mg / L, then the adjustment continues based on the influent flow rate of the previous day, and this process is repeated.

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

[0045] The following detailed description of some embodiments of the present invention is provided in conjunction with specific examples. Unless otherwise specified, all raw materials used in the embodiments are commercially available.

[0046] Example 1

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

[0048] Effluent from the primary sedimentation tank and secondary sedimentation tank of the municipal wastewater treatment plant (i.e., wastewater effluent, also known as secondary effluent) was collected. Measurements showed that the ammonia nitrogen concentration in the primary sedimentation tank effluent was 55.2 mg / L, and the nitrate nitrogen concentration was 1.2 mg / L. The ammonia nitrogen concentration in the secondary sedimentation tank effluent was 0, and the nitrate nitrogen concentration was approximately 8.1 mg / L. The primary sedimentation tank effluent (A) and the secondary sedimentation tank effluent (B) were mixed at a volume ratio of approximately 1:10. After thorough mixing, the average ammonia nitrogen concentration in the wastewater (mixture) at this stage was 4.6 mg / L, the nitrate nitrogen concentration was 9.3 mg / L, and the nitrite concentration was 0. The nitrogen concentration changes during operation are shown in [see figure]. Figure 1 and Figure 2 This is a selection of representative operational data.

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

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

[0051] During days 26-28, both ammonia nitrogen and nitrate nitrogen in the effluent exceeded 1 mg / L. Therefore, on the evening of day 28, the effluent recirculation was increased while the influent flow rate was decreased. The influent flow rate was changed from 0.08 L / h to 0.077 L / h, and the effluent recirculation flow rate was increased from 0 to 0.023 L / h. On day 29, both ammonia nitrogen and nitrate nitrogen in the effluent decreased, but neither fell below 1 mg / L. Considering that more than 50 days had passed since the last sulfur replacement (including start-up time), 50 g of sulfur was replaced on day 30. On day 31, nitrate nitrogen decreased to approximately 0.7 mg / L. On day 32, both ammonia nitrogen and nitrate nitrogen concentrations in the effluent decreased to 0 mg / L, and thereafter maintained stable operation with effluent ammonia nitrogen <1 mg / L, effluent nitrate nitrogen <1 mg / L, and an average total nitrogen removal rate of 0.6 mg / L, resulting in an average total nitrogen removal rate of 95%.

[0052] Example 2

[0053] A mixture of volcanic rock and sulfur particles was used as the packing material for biofilm attachment, with a volume ratio of 2:1. The biofilter column was started up with an effective volume of 1 L. The start-up time was 25 days. After start-up, the main functional microorganisms in the biofilm of this filter column included Thiobacillus (8.5%) and Candidatus Kuenenia (6.3%). For detailed microbial composition, see [link to relevant documentation]. Figure 3 ;

[0054] After the biological filter column was started and operated stably, it was used to treat the effluent from the secondary sedimentation tank of the Shuangqiao Sludge Treatment Plant in Zhengzhou. Measurements showed that the ammonia nitrogen in the secondary sedimentation tank effluent was 0.3 mg / L, nitrate nitrogen was 10.4 mg / L, and nitrite was 0 mg / L. The ammonia nitrogen in the primary sedimentation tank effluent was 31.1 mg / L, nitrate nitrogen was 1.7 mg / L, and nitrite was 0.6 mg / L. Primary sedimentation tank effluent: The initial volume ratio of the secondary sedimentation tank effluent was 1:6. After thorough mixing, it was treated using the aforementioned biological filter column. During operation from day 15 to 17, the effluent nitrate nitrogen was greater than 1 mg / L for three consecutive days, while ammonia nitrogen was less than 1 mg / L. The influent flow rate was reduced from 0.083 L / h to 0.08 L / h, and the effluent nitrate nitrogen decreased to 0.4 mg / L. During operation from day 24 to 26, the effluent ammonia nitrogen was greater than 1 mg / L for three consecutive days, while nitrate nitrogen was less than 1 mg / L. The influent ratio A:B was changed to 1:8, and subsequently, the effluent ammonia nitrogen decreased to approximately 0.5 mg / L. During the operation of this batch of water, there were no instances where both ammonia nitrogen and nitrate nitrogen were greater than 1 mg / L simultaneously. During operation, adjustments are made promptly based on the effluent water quality. The filter column can operate stably for a long period of time. During stable operation, the average effluent ammonia nitrogen is 0.2 mg / L, the average effluent nitrate nitrogen is 0.4 mg / L, the average effluent total nitrogen 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 granules was used as the packing material for biofilm attachment, with a volume ratio of volcanic rock to sulfur granules of 1.5. After the biofilter column was started and operated stably, the biofilm contained 9.1% Thiobacillus and 7.5% Candidatus Kuenenia, and was used to treat the effluent from the secondary sedimentation tank of the Shuangqiao Sludge Treatment Plant in Zhengzhou. Measurements showed that the ammonia nitrogen in the secondary sedimentation tank effluent was 0.5 mg / L, nitrate nitrogen was 9.5 mg / L, and nitrous oxide was 0, while the ammonia nitrogen in the primary sedimentation tank effluent was 43.2 mg / L, nitrate nitrogen was 1.6 mg / L, and nitrous oxide was 0.2 mg / L. The initial volume ratio of the mixed liquor was 1:8, where the effluent from the primary sedimentation tank was effluent from the secondary sedimentation tank. After thorough mixing, the mixture was treated using the aforementioned biological filter column. During operation, adjustments were made promptly based on the effluent quality according to the method of this invention. The filter column was able to operate stably for a long period. During stable operation, the average effluent ammonia nitrogen was 0.5 mg / L, the average effluent nitrate nitrogen was 0.4 mg / L, the average effluent total nitrogen was 0.9 mg / L, and the average total nitrogen removal rate was 94%.

[0057] Comparative Example 1

[0058] A mixture of volcanic rock and sulfur particles was used as the packing material for biofilm attachment, with a volume ratio of 3:1. After starting the biofilter, the relative abundances of *Thiobacillus* and *Candidatus Kuenenia* in the filter were 2.3% and 8.1%, respectively. Even after three months of operation, it was impossible to achieve a relative abundance ratio between 1 and 3. Therefore, this filter was directly used to treat the wastewater effluent from the wastewater treatment plant. Measurements showed that the ammonia nitrogen concentration in the primary sedimentation tank effluent was 55.2 mg / L, and the nitrate nitrogen concentration was 1.2 mg / L. The ammonia nitrogen concentration in the secondary sedimentation tank effluent was 0, and the nitrate nitrogen concentration was approximately 8.1 mg / L. The primary sedimentation tank effluent (A) and the secondary sedimentation tank effluent (B) were mixed at a volume ratio of approximately 1:10. After thorough mixing, the average ammonia nitrogen concentration in the wastewater (mixture) at this stage was 4.6 mg / L, the nitrate nitrogen concentration was 9.3 mg / L, and the nitrite concentration 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, thus failing to achieve the deep denitrification effect of this invention.

[0059] Comparative Example 2

[0060] The same batch of wastewater was treated using the same biological filter column as in Example 3. Measurements showed that the ammonia nitrogen in the secondary sedimentation tank effluent was 0.5 mg / L, nitrate nitrogen was 9.5 mg / L, and nitrous oxide was 0 mg / L. The ammonia nitrogen in the primary sedimentation tank effluent was 43.2 mg / L, nitrate nitrogen was 1.6 mg / L, and nitrous oxide was 0.2 mg / L. The initial volume ratio of the mixed liquor was 1:12 (primary sedimentation tank effluent: secondary sedimentation tank effluent). After thorough mixing, the above-mentioned biological filter column was used for treatment. During operation, the effluent nitrate nitrogen level consistently exceeded 1 mg / L. Even after adjustments, it was impossible to achieve a simultaneous reduction of both ammonia nitrogen and nitrate nitrogen levels to below 1 mg / L. The average effluent nitrate nitrogen level was 3.2 mg / L. The analysis indicated that the primary sedimentation tank effluent was too low, failing to provide sufficient ammonia nitrogen substrate, thus inhibiting microbial activity.

[0061] Comparative Example 3

[0062] The same batch of wastewater was treated using the same biological filter column as in Example 3. The ammonia nitrogen in the secondary sedimentation tank effluent was 0.5 mg / L, nitrate nitrogen was 9.5 mg / L, and nitrous oxide was 0 mg / L. The ammonia nitrogen in the primary sedimentation tank effluent was 43.2 mg / L, nitrate nitrogen was 1.6 mg / L, and nitrous oxide was 0.2 mg / L. The initial volume ratio of the mixed liquor was 1 / 5 of the primary sedimentation tank effluent to the secondary sedimentation tank effluent. After thorough mixing, the above-mentioned biological filter column was used for treatment. After two months of adjustment, it was still impossible to guarantee that the effluent ammonia nitrogen was less than 1 mg / L for a continuous week. Even after a long period of adjustment, a stable operating effect of effluent ammonia nitrogen and nitrate nitrogen being less than 1 mg / L simultaneously could not be achieved. The average effluent ammonia nitrogen during the adjustment period was 2.1 mg / L. The reason for this was that the primary sedimentation tank effluent 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 understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall 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 wastewater treatment plant, characterized in that, Includes the following steps: S1. Using volcanic rock and sulfur particles as packing material for biofilm attachment, the biofilter column is started. After start-up, 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 effluent from the secondary sedimentation tank of the wastewater treatment plant are mixed to obtain a mixed liquid, wherein the volume ratio of the effluent from the primary sedimentation tank to the effluent from the secondary sedimentation tank is (4.5-y) / (x-4.5)~(5.5-y) / (x-5.5), where x is the ammonia nitrogen concentration in the effluent from the primary sedimentation tank and y is the ammonia nitrogen concentration in the effluent from the secondary sedimentation tank, both in mg / L; S3. Operate the biological filter column, use the mixed liquid as the influent to be treated for denitrification, and monitor the quality of the treated effluent; S4. During operation, determine whether to adjust the treatment process based on the nitrogen content in the effluent; if the nitrate nitrogen and ammonia nitrogen in the effluent are consistently less than 1 mg / L, no adjustment is needed, and at least some of the sulfur particles in the biological filter column should be replaced every 50-100 days; 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, then the treatment process needs to be adjusted. The adjustment process includes: When the ammonia nitrogen in the effluent is >1 mg / L and the nitrate nitrogen is <1 mg / L for 2-4 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 <1 mg / L. If the nitrate nitrogen in the effluent is >1 mg / L and the ammonia nitrogen is <1 mg / L for 2-4 consecutive days, the influent flow rate in step S2 is reduced. If the nitrate nitrogen in the effluent is still >1 mg / L when the influent flow rate is reduced to 0.8 times the original value, the sulfur particles in the biological filter column are replaced at least partially to refresh the sulfur source. If the nitrate nitrogen level in the effluent is >1 mg / L and the ammonia nitrogen level is >1 mg / L for 2-4 consecutive days, then reduce the influent flow rate in step S2 and increase the effluent recirculation. The increase in effluent recirculation should be equal to the decrease in influent flow rate until the ammonia nitrogen or nitrate nitrogen level in the effluent drops below 1 mg / L. Then, adjust according to the adjustment steps applicable to the corresponding water quality until both ammonia nitrogen and nitrate nitrogen levels in the effluent are less than 1 mg / L.

2. The method for deep denitrification of secondary effluent from a wastewater 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 to 2.

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

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

5. The method for deep denitrification of secondary effluent from a wastewater 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 nitrite concentration is <0.5 mg / L.

6. The method for deep denitrification of secondary effluent from a wastewater treatment plant according to claim 1, characterized in that, When reducing the mixing ratio of the primary sedimentation tank effluent, the average concentration of ammonia nitrogen in the effluent that is continuously >1 mg / L for 2-4 days is recorded as m. The volume ratio of the primary sedimentation tank effluent to the secondary effluent is adjusted to (5.5-my) / (x-5.5+m). The operation continues and the nitrogen content in the effluent is monitored. If the ammonia nitrogen is still >1 mg / L for 2-4 consecutive days after adjustment, the average ammonia nitrogen concentration on the 2nd to 4th day after adjustment is taken as the new value of m, and the adjustment is repeated until the ammonia nitrogen in the effluent is <1 mg / L.

7. The method for deep denitrification of secondary effluent from a wastewater treatment plant according to claim 1, characterized in that, When reducing the influent flow rate in step S2, the adjustment is made 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 biological filter column and Q is the influent flow rate of the previous day.

8. The method for deep denitrification of secondary effluent from a wastewater treatment plant according to any one of claims 1-7, characterized in that, In step S4, the average total nitrogen concentration in the effluent is <1.5 mg / L, and the total nitrogen removal rate is >90%.

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