A method for in-situ ultra-deep denitrification of a mixed nutrient system

Abstract

The present application relates to sewage biological treatment technical field, disclose a kind of mixed nutrient system in situ ultra-deep denitrification method.The method comprises the following steps: (1) to anaerobic digestion sludge from municipal wastewater treatment plant is carried out physical dewatering treatment, and the dewatered sludge with moisture content <80% is obtained;(2) the above-mentioned dewatered sludge is put into anaerobic ammonia oxidation reactor, and in situ ultra-deep denitrification treatment is carried out, while adjusting the dewatered sludge dosage according to effluent nitrate concentration.Compared with the use of organic carbon source in sewage, the dewatered sludge as solid carbon source is easy to control in the method provided by the present application;Compared with the traditional sludge treatment method of landfill and incineration, the method provided by the present application enables dewatered sludge to realize internal circulation in wastewater treatment plant, and better realizes sludge resource.

Description

Technical Field

[0001] This invention relates to the field of wastewater biological treatment technology, specifically to a method for in-situ ultra-deep denitrification of a mixed nutrient system. Background Technology

[0002] Anaerobic ammonia oxidation is a highly efficient and energy-saving biological nitrogen removal method for wastewater. Compared with traditional nitrification and denitrification processes, it has the advantages of significantly reducing operating energy consumption and greenhouse gas emissions such as CO2 and N2O.

[0003] However, in practical applications, nitrate accumulation is one of the key issues restricting the anammox process. Currently, much research focuses on how to solve the technical problem of nitrate residue in the effluent from anammox. As shown in the following formula, the reaction theoretically produces approximately 11% nitrate:

[0004] NH4 + +1.32NO2 - →1.02N2+0.26NO3 - .

[0005] Since anaerobic ammonium oxidation is an autotrophic denitrification process, the organic matter content in the influent and effluent is usually low. Therefore, a common method is to add an external organic carbon source, such as sodium acetate, to remove nitrates through denitrification, thereby achieving the goal of meeting total nitrogen discharge standards. However, this increases the cost of wastewater treatment and also easily increases the activity of heterotrophic denitrifying bacteria, which compete with anaerobic ammonium oxidizing bacteria for electron acceptors such as nitrite.

[0006] Anaerobic digestion of waste sludge from urban wastewater treatment plants is a technical means to reduce, render harmless, and utilize the resources of sludge. The small-molecule organic matter produced, such as volatile fatty acids, can be used as a carbon source for denitrification. However, there are still some problems in using the organic matter generated by anaerobic digestion to remove nitrates through denitrification, such as the separation, collection, and utilization of organic matter. Therefore, there are technical difficulties in using the organic matter in sludge digestion liquid to remove nitrates.

[0007] Although anaerobic digestion of sludge has converted most organic matter into final products such as methane, the anaerobic digested sludge itself still contains a certain amount of unused organic carbon sources. Meanwhile, in recent years, nutrient and energy recovery has gradually become a goal of wastewater treatment plants, with carbon source recovery being one of the core issues. However, currently, no research has been conducted to develop a mixed-nutrient, in-situ deep denitrification technology based on anaerobic ammonia oxidation, utilizing the solid carbon sources in anaerobic digested sludge. Summary of the Invention

[0008] The purpose of this invention is to solve the problem of insufficient total nitrogen in the effluent due to residual nitrates in existing anaerobic ammonia oxidation processes, and also to provide a way for the resource utilization of sludge, a byproduct of wastewater treatment.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for in-situ ultra-deep denitrification of a mixed nutrient system, the method comprising the following steps:

[0010] (1) Anaerobic digestion sludge from urban sewage treatment plants is physically dewatered to obtain dewatered sludge with a moisture content of <80%;

[0011] (2) The above-mentioned dewatered sludge is put into the anaerobic ammonia oxidation reactor for in-situ ultra-deep denitrification treatment. The amount of dewatered sludge added is adjusted according to the nitrate concentration in the effluent.

[0012] Preferably, in step (2), the nitrogen load in the anaerobic ammonia oxidation reactor is 0.2–0.3 kg N / m³. 3 / d.

[0013] More preferably, in step (2), the amount of dewatered sludge added is determined according to the nitrate concentration and hydraulic retention time of the effluent from the anaerobic ammonia oxidation reactor, and the ratio of the amount of dewatered sludge added to the effluent nitrate concentration is 3 to 20.

[0014] In a preferred embodiment, in step (2), the operating cycle of the anaerobic ammonia oxidation reactor is 48 to 72 hours, and the amount of dewatered sludge added is 0.2 to 1.4 g / L.

[0015] More preferably, in step (2), the conditions for the in-situ ultra-deep denitrification treatment are: light protection, dissolved oxygen <0.2mg / L, and reaction system temperature of 30~37℃.

[0016] The method provided by this invention also has at least the following beneficial effects:

[0017] First, the method provided by this invention does not require the addition of an additional organic carbon source, thus saving wastewater treatment costs. Second, compared with utilizing organic carbon sources in wastewater, such as volatile fatty acids in anaerobic digestion liquid, the dewatered sludge produced by the method provided by this invention is smaller in volume, easier to transport, and can be added quantitatively in a better manner.

[0018] Secondly, the method provided by this invention is conducive to developing dewatered sludge into a commercial carbon source. It is expected to transform waste sewage sludge, which originally required additional costs to process, into an economically valuable commercial carbon source simply through dewatering. Compared with the traditional method of using residual sludge fermentation to produce volatile fatty acids as an organic carbon source, this invention has greater scalable commercial value and feasibility.

[0019] Finally, compared with traditional sludge treatment methods such as landfill and incineration, the method provided by this invention has the potential to transform dewatered sludge into an economically valuable organic carbon source, enabling it to circulate internally within the wastewater treatment system and better achieve the goal of sludge resource utilization. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the in-situ ultra-deep denitrification principle of the mixed nutrient system of the present invention. By adding dewatered sludge, the nitrate generated by the anaerobic ammonia oxidation reaction is reduced to nitrite by denitrifying bacteria, and then supplied to the anaerobic ammonia oxidation bacteria for further reaction, thereby achieving in-situ ultra-deep denitrification. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] In this invention, the principle of using sludge as an organic carbon source for in-situ ultra-deep denitrification in a mixed nutrient system lies in the difference in the oxidizing properties of nitrates and nitrites: based on the difference in the biodegradability of nitrates and nitrites as electron acceptors, sludge organic carbon sources are divided into three types: the first type is easily biodegradable carbon sources, such as volatile fatty acids like acetic acid, which can be oxidized by nitrates and nitrites; the second type is short-range carbon sources, which can be oxidized by nitrates but not by nitrites; and the third type is difficult-to-biodegrade carbon sources, which cannot be oxidized by either nitrates or nitrites.

[0023] In this invention, the dosage ratio is calculated based on the amount of dewatered sludge added in the experiment. Specifically, the dosage of dewatered sludge is 0.2–1.4 g / L. When the dosage of dewatered sludge is 1.4 g / L, the ratio of the dosage of dewatered sludge to the nitrate concentration in the effluent is... When the dosage of the dewatered sludge is 0.2 g / L, the ratio of the dosage of the dewatered sludge to the nitrate concentration in the effluent is: That is, the ratio of the amount of dewatered sludge added to the effluent nitrate concentration in this invention is 3 to 20, and the ratio of the amount of dewatered sludge added to the effluent nitrate concentration is preferably 18.

[0024] In this invention, the process from the influent to the effluent of the anaerobic ammonia oxidation reactor constitutes one operating cycle.

[0025] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials are all commercially available products.

[0026] In the following examples, unless otherwise specified, physical dewatering treatment refers to the conventional sludge dewatering process in wastewater treatment plants, which must meet the standard of moisture content <80% before it can be transported off-site. The dewatered sludge used in this patent experiment was obtained by freeze-drying, with a freeze-drying time of 2 to 3 days.

[0027] Example 1

[0028] This example provides a method for in-situ ultra-deep nitrogen removal in a mixed nutrient system, and the method includes the following steps:

[0029] (1) The raw anaerobic digestion sludge from the urban sewage treatment plant is placed in a freeze dryer for physical dewatering treatment to obtain dewatered sludge with a default moisture content of 0.

[0030] The physical dehydration process is carried out by freeze drying, and the conditions for the physical dehydration process are: time is 3 days, and temperature is < -40℃.

[0031] (2) The above-mentioned dewatered sludge is fed into the anaerobic ammonia oxidation reactor through the return port or other areas (the nitrogen load in the influent is 0.22 kg N / m³). 3 / d), in-situ ultra-deep denitrification treatment is carried out. The physicochemical indicators of the effluent from the anaerobic ammonia oxidation reactor are tested according to the reactor operation cycle. The reactor has been operating stably for more than six months (8 months).

[0032] The amount of dewatered sludge added is determined based on the nitrate concentration and hydraulic retention time of the effluent from the anaerobic ammonia oxidation reactor. The ratio of the amount of dewatered sludge added to the effluent nitrate concentration is 20:1. In this embodiment, the effluent nitrate concentration is 70 mg N / L, the hydraulic retention time is 72 h, and the amount of dewatered sludge added is 1.4 g / L.

[0033] The anaerobic ammonia oxidation reactor can operate stably for a long period of time (8 months), with an operating cycle of 72 hours, and the volume of the anaerobic ammonia oxidation reactor is 1L.

[0034] The conditions for the in-situ ultra-deep denitrification treatment are: protection from light, dissolved oxygen <0.2 mg / L, and reaction system temperature of 37±0.5℃.

[0035] Example 2

[0036] The method is carried out according to Example 1, except that in step (1), the residual sludge of the urban sewage treatment plant is used instead of the anaerobic digestion sludge of the urban sewage treatment plant, and the remaining steps and parameters are the same as in Example 1.

[0037] Example 3

[0038] The method of Example 1 is followed, except that in step (2), the amount of dewatered sludge added is 0.2 g / L, and the remaining steps and parameters are the same as in Example 1.

[0039] Example 4

[0040] The method of Example 1 is followed, except that in step (2), the amount of dewatered sludge added is 1.0 g / L, and the remaining steps and parameters are the same as in Example 1.

[0041] Comparative Example 1

[0042] The procedure was carried out according to Example 1, except that no dewatered sludge was added, and the remaining steps and parameters were the same as in Example 1.

[0043] Test Example 1

[0044] The concentrations of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the effluent from the anaerobic ammonia oxidation reactors of the above embodiments and comparative examples were tested, and the results are shown in Table 1.

[0045] Table 1

[0046]

[0047] As can be seen from the results in Table 1, the average total nitrogen removal rate in Example 1 of this invention is consistently >99.5%, and the average total nitrogen concentration in the effluent is consistently <2 mg N / L. As can be seen from the results in Table 1, the method of this invention can not only meet the Class A effluent total nitrogen standard, but also further stably meet the Class V water standard for total nitrogen in surface water. Moreover, the method of this invention uses sludge, a byproduct of wastewater treatment, as a carbon source, eliminating the need for external organic carbon sources, and can more effectively achieve in-situ ultra-deep denitrification in mixed nutrient systems.

[0048] Test Example 2

[0049] A long-term in-situ enrichment experiment was conducted on the raw anaerobic digestion sludge (i.e., anaerobic digestion sludge from a municipal wastewater treatment plant) that had not undergone physical dewatering treatment in Example 1 above. The specific method is as follows:

[0050] 200 mL of anaerobic digested sludge was inoculated into a 1 L anaerobic bottle, and deionized water was added to 1 L. Nitrogen was blown for 10 min to remove oxygen. The experimental group was treated with in-situ addition of nitrate, and the control group was treated with in-situ addition of nitrite. After long-term experiment, the organic carbon source of sludge gradually accumulated in the liquid phase. The experimental group was enriched with recalcitrant carbon source, while the control group was enriched with short-range carbon source and recalcitrant carbon source. The concentration of organic matter in the liquid phase was defined by chemical oxygen demand (COD). The COD concentration of the experimental group and the control group was calculated during the stable period after long-term operation. The content of short-range carbon source in the organic carbon source of sludge was found to be about 70%.

[0051] The calculation formula is: (COD of control group - COD of experimental group) / COD of control group * 100.

[0052] In this test case, a long-term in-situ enrichment experiment lasting 150 days showed that the content of short-range carbon sources in the sludge organic carbon source was about 70% (the calculation method does not include easily biodegradable carbon sources), which proved the feasibility of using sludge organic carbon sources for in-situ ultra-deep denitrification in a mixed nutrient system.

[0053] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for in-situ ultra-deep nitrogen removal in a mixed nutrient system, characterized in that, The method includes the following steps: (1) Anaerobic digestion sludge from urban sewage treatment plants is physically dewatered to obtain dewatered sludge with a moisture content of <80%; (2) The above-mentioned dewatered sludge is put into the anaerobic ammonia oxidation reactor for in-situ ultra-deep denitrification treatment. The amount of dewatered sludge added is adjusted according to the nitrate concentration in the effluent. In step (2), the amount of dewatered sludge added is determined according to the nitrate concentration and hydraulic retention time of the effluent from the anaerobic ammonia oxidation reactor, and the ratio of the amount of dewatered sludge added to the effluent nitrate concentration is 3 to 20. In step (2), the conditions for the in-situ ultra-deep denitrification treatment are: light protection, dissolved oxygen <0.2mg / L, and reaction system temperature of 30~37℃.

2. The method according to claim 1, wherein, In step (2), the nitrogen load in the anaerobic ammonia oxidation reactor is 0.2~0.3 kg N / m³. 3 / d.

3. The method according to claim 1, wherein, In step (2), the operating cycle of the anaerobic ammonia oxidation reactor is 48~72h, and the amount of dewatered sludge added is 0.2~1.4g / L.

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