Method for removing nitrogen in reclaimed water by using manganese ion to reinforce constructed wetland filler bed

Abstract

The method for strengthening the nitrogen removal in reclaimed water by using manganese ions to reinforce the artificial wetland filler bed belongs to the technical field of urban sewage regeneration and utilization, and comprises the following steps: (1) using vertical partition plates to separate the artificial wetland filler bed into several areas, and making water flow into the first area from the bottom of the filler bed and sequentially enter each area along the partition plates; (2) after the artificial wetland is started and stabilized, adding ammonia nitrogen in the influent to adjust the total inorganic nitrogen concentration of the influent, and operating under the set total inorganic nitrogen concentration for a set time; (3) stopping adding ammonia nitrogen in the influent, and starting to add manganese ions in the influent, and adjusting the manganese ion concentration according to the concentration gradient change amount when the ammonia nitrogen is added. The present application enriches manganese-oxidizing bacteria in the filler bed by adding manganese ions in the reclaimed water, and improves the biodegradability of the reclaimed water and strengthens the denitrification effect under the mediation of the bacteria.

Description

Technical Field

[0001] This invention belongs to the field of urban wastewater reuse technology, specifically relating to a method for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing beds. Background Technology

[0002] Reclaimed water is the effluent discharged after deep treatment at urban wastewater treatment plants, characterized by its large and stable volume. Reclaimed water replenishing nearby natural water bodies is a crucial pathway for the resource utilization of urban wastewater and an effective method to alleviate problems such as river drying up and ecological degradation. In recent years, wastewater treatment plants in various provinces, cities, and regions have successively implemented stricter "quasi-IV" discharge standards, building upon the Class A discharge standard of the "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants" (GB18918-2002). This means that, except for total nitrogen, major conventional indicators such as COD, ammonia nitrogen, and total phosphorus must meet the Class IV standards of the "Environmental Quality Standard for Surface Water" (GB3838-2002). Although the "quasi-IV" standard does not restrict total nitrogen, the nitrate nitrogen concentration (approximately 10 mg / L) differs significantly from the concentration in natural Class I-IV surface water bodies. High nitrogen input poses a risk of eutrophication to receiving water bodies.

[0003] Constructed wetlands are widely used in advanced wastewater treatment, water pollution control, and aquatic ecological restoration. They are water quality improvement technologies that enhance natural purification functions through engineering methods, forming an ecosystem primarily composed of a packing bed, plants, and microorganisms. Aquatic plants absorb pollutants from the water, while microorganisms purify pollutants through metabolism. However, due to the very low COD concentration in reclaimed water, sufficient electrons cannot be provided for microbial denitrification, hindering its effective nitrogen removal. Secondly, aquatic plants are not very effective at absorbing nitrate nitrogen, especially during the autumn and winter months when temperatures drop, leading to plant death and reduced microbial activity, significantly inhibiting the pollutant removal capacity of constructed wetlands. The packing bed, as a crucial unit of constructed wetlands, not only provides attachment space for aquatic plants but also serves as a habitat for various microorganisms. In the past decade or so, researchers have focused on finding efficient and low-consumption packing materials, utilizing their excellent physicochemical properties to further improve the reduction and control of pollutants (ammonia nitrogen, phosphorus, microorganisms, and heavy metals) in constructed wetland systems. These fillers are mostly derived from natural materials (kaolin, volcanic rock, and zeolite), construction waste (bricks and concrete blocks), and industrial byproducts (coal slag and steel slag), making them inexpensive and readily available. However, these fillers themselves do not have the ability to remove nitrate nitrogen.

[0004] For advanced nitrate nitrogen removal, denitrification is typically achieved in the purification unit by adding an external organic carbon source electron donor. However, this method complicates the process, increases operating costs and sludge production, and also introduces secondary COD pollution, increasing subsequent management difficulties. Therefore, some researchers have used iron or manganese ore as constructed wetland packing beds, leveraging the electron transfer process of variable-valence metal ions such as iron or manganese ions to enhance nitrate nitrogen removal. However, the efficiency of nitrate nitrogen removal still depends on the concentration of the COD carbon source. Reclaimed water has a low carbon-to-nitrogen ratio (C / N), and the residual COD is difficult for microorganisms to directly utilize. Therefore, without an external COD carbon source, the denitrification process is difficult to complete, resulting in insufficient system denitrification efficiency. Summary of the Invention

[0005] To address the problems of existing technologies, this invention discloses a method for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing beds. The aim is to provide an operational method for deep denitrification of reclaimed water using manganese ion-enhanced constructed wetland packing beds. By adding manganese ions to the reclaimed water, manganese-oxidizing bacteria are enriched in the packing bed. Under the mediation of these bacteria, the biodegradability of the reclaimed water is improved, and the denitrification effect is enhanced.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland bed packing material is applicable to deep denitrification of reclaimed water with COD concentration less than 30 mg / L, total nitrogen concentration less than 10 mg / L, and carbon-to-nitrogen ratio (C / N) less than 3. The method includes the following steps:

[0008] (1) The artificial wetland filler bed is divided into several areas by vertical partitions. Water flows from the bottom of the filler bed into the first area and then into each area in sequence along the partitions.

[0009] (2) After the artificial wetland is started and stabilized, ammonia nitrogen is added to the influent to adjust the total inorganic nitrogen concentration of the influent, and the wetland is run for a set time at the set total inorganic nitrogen concentration.

[0010] (3) Stop adding ammonia nitrogen to the influent and start adding manganese ions to the influent. Adjust the concentration of manganese ions according to the change in concentration gradient when adding ammonia nitrogen.

[0011] Preferably, in step (1), the artificial wetland packing bed is divided into at least 3 areas by vertical partitions, each area forming a separate reactor. The vertical partitions and the inner wall of the packing bed form an "S"-shaped water flow channel, which connects the reactors in series. The upper part of the outer end of the last reactor is provided with a water outlet.

[0012] Preferably, in step (1), the hydraulic retention time of the constructed wetland is 3 days, and the surface hydraulic load is 0.6-1.0 m. 3 / (m 2 *h).

[0013] Preferably, step (2) includes: after the constructed wetland has been running stably for 145 days, when the total inorganic nitrogen removal rate is maintained at 9%, the total inorganic nitrogen concentration in the influent is adjusted to three concentration gradients of 10 mg / L, 12 mg / L and 14 mg / L by adding ammonia nitrogen to the influent, and the constructed wetland is operated for 9 days under each ammonia nitrogen concentration gradient.

[0014] Preferably, step (3) includes: when the constructed wetland has been in operation for 182 days, ammonia nitrogen is stopped being added to the influent, and manganese ions are started being added to the influent, with an initial manganese ion concentration of 2 mg / L.

[0015] Preferably, step (3) further includes: the concentration gradient change when adding ammonia nitrogen is 2 mg / L. Under the condition that the manganese ion concentration in the effluent is less than 0.1 mg / L, starting from the initial manganese ion concentration of 2 mg / L, the concentration gradient change is 2 mg / L as the increment, and the manganese ion concentration is adjusted to 4 mg / L, 6 mg / L and 8 mg / L, a total of 3 manganese ion concentration gradients. The constructed wetland operates for 24 days under each manganese ion concentration gradient.

[0016] The beneficial effects of this invention on nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing beds are as follows:

[0017] 1. Manganese ions chelate with residual natural organic matter in reclaimed water to form complexes, effectively improving the biodegradability of the reclaimed water. This process is achieved by controlling the reaction rate. The manganese ion complexes increase the migration rate of organic matter to the bacterial surface, thereby prolonging the decomposition time of organic matter.

[0018] 2. Experiments have shown that adding Mn to the influent... 2+ At a concentration of 8 mg / L, the system's total inorganic nitrogen removal rate increased to between 40% and 45%, and the effluent Mn... 2+ With a concentration of <0.1 mg / L, this invention provides an effective data range for wastewater treatment using packed beds.

[0019] 3. The addition of manganese ions enhances the denitrification efficiency of the system and makes up for the problem of insufficient utilization of residual organic matter in reclaimed water. The total inorganic nitrogen removal can be estimated based on 0.4 times the manganese ion removal, so as to reduce the detection of nitrogen indicators.

[0020] Instruction manual illustrations

[0021] Figure 1: Working principle diagram of an artificial wetland device for deep denitrification of reclaimed water.

[0022] Figure 2 : Effect diagram of deep denitrification of reclaimed water by constructed wetland with manganese ore and quartz sand composite packing bed.

[0023] Figure 3 Linear relationship between manganese ion removal and total inorganic nitrogen removal in constructed wetlands.

[0024] 1. Inlet tank; 2. Peristaltic pump; 3. Valve; 4. Reactor; 5. Baffle plate; 6. Outlet; 7. Collection tank. Detailed Implementation

[0025] The following description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0026] The following embodiments can be understood as illustrating a part of the structure or method of the present invention individually, or as combining the embodiments to explain the broader structure or method of the present invention.

[0027] Example 1

[0028] Methods for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing beds, such as... Figure 1-3 As shown, the method described is suitable for deep denitrification of reclaimed water with a COD concentration of less than 30 mg / L, a total nitrogen concentration of less than 10 mg / L, and a carbon-to-nitrogen ratio (C / N) of less than 3, and includes the following steps:

[0029] (1) The artificial wetland filler bed is divided into several areas by vertical partitions. Water flows from the bottom of the filler bed into the first area and then into each area in sequence along the partitions.

[0030] (2) After the artificial wetland is started and stabilized, ammonia nitrogen is added to the influent to adjust the total inorganic nitrogen concentration of the influent, and the wetland is run for a set time at the set total inorganic nitrogen concentration.

[0031] (3) Stop adding ammonia nitrogen to the influent and start adding manganese ions to the influent. Adjust the concentration of manganese ions according to the change in concentration gradient when adding ammonia nitrogen.

[0032] Example 2

[0033] like Figure 1As shown, in step (1), the constructed wetland packing bed is divided into at least three areas by vertical partitions, each area constituting a separate reactor. An "S"-shaped water flow channel is formed between the vertical partitions and the inner wall of the packing bed. This "S"-shaped water flow channel connects the reactors in series, and a water outlet is provided at the upper outer end of the last reactor. Figure 1 As shown, the water flow channel first moves vertically upward, then vertically downward, and then vertically upward again, forming an "S" shape.

[0034] Example 3

[0035] like Figure 1-3 As shown, in step (1), the hydraulic retention time of the constructed wetland is 3 days, and the surface hydraulic load is 0.6-1.0 m. 3 / (m 2 *h).

[0036] Example 4

[0037] like Figure 1-3 As shown, step (2) includes: after the constructed wetland has been running stably for 145 days, when the total inorganic nitrogen removal rate is maintained at 9%, the total inorganic nitrogen concentration in the influent is adjusted to three concentration gradients of 10 mg / L, 12 mg / L and 14 mg / L by adding ammonia nitrogen to the influent. The constructed wetland runs for 9 days under each ammonia nitrogen concentration gradient.

[0038] Example 5

[0039] like Figure 1-3 As shown, step (3) includes: when the artificial wetland has been in operation for 182 days, ammonia nitrogen is stopped being added to the influent and manganese ions are started being added to the influent, with an initial manganese ion concentration of 2 mg / L.

[0040] like Figure 1-3 As shown, step (3) further includes: the concentration gradient change when adding ammonia nitrogen is 2 mg / L. Under the condition that the manganese ion concentration in the effluent is less than 0.1 mg / L, the manganese ion concentration is adjusted to three manganese ion concentration gradients of 4 mg / L, 6 mg / L and 8 mg / L, starting from the initial manganese ion concentration of 2 mg / L and using the concentration gradient change as the increment. The constructed wetland operates for 24 days under each manganese ion concentration gradient.

[0041] Example 6

[0042] The constructed artificial wetland packing bed device, such as Figure 1 As shown, the reactor is constructed using transparent acrylic sheets, and its dimensions (length × width × height) are 0.9 × 0.3 × 0.5 m. The effective volume is 0.135 m³. 3The reactor is divided into three compartments (A, B, and C) using vertical partitions, with water flow channels between compartments A and B, and between compartments B and C, thus connecting the three compartments in series. The reactor packing bed is filled from bottom to top with pebbles (10cm), manganese ore (20cm), and quartz sand (20cm). The packing bed operates under the following conditions: hydraulic retention time of 3 days and surface hydraulic load of 0.6-1.0m. 3 / (m 2 *h), according to the technical solution of the present invention, the operation phase of the example constructed wetland device includes a start-up operation phase, an ammonia nitrogen addition phase, and a manganese ion addition phase.

[0043] During the start-up and operation period, the system's total inorganic nitrogen removal rate increased from 0% to about 6%. On day 144, the effluent concentration of total inorganic nitrogen was 7.31 mg / L, and the system removal rate stabilized at about 9%.

[0044] Within 145-181 days, the ammonia nitrogen concentration in the reactor influent was controlled in stages at 2 mg / L, 4 mg / L, and 6 mg / L. Under these conditions, the reactor was operated for 9 days at each concentration gradient, and the total inorganic nitrogen removal rates in the effluent were 17.62%, 28.32%, and 39.70%, respectively.

[0045] Starting from day 182, manganese ions were added to the reactor with an initial concentration of 2 mg / L. With the effluent manganese ion concentration less than 0.1 mg / L, the concentration was gradually increased to 4 mg / L, 6 mg / L, and 8 mg / L. At this point, the total inorganic nitrogen removal rate gradually increased to approximately 43%. Subsequently, the influent manganese ion concentration was adjusted to 5 mg / L, and the total inorganic nitrogen removal rate decreased to below 40%.

[0046] Appendix Figure 3 This indicates a positive correlation between the removal of total inorganic nitrogen and the removal of manganese ions, with a correlation coefficient of 0.4. On the one hand, when manganese ions directly act as electron donors for denitrification, the theoretical relationship between nitrogen removal and manganese removal is 0.1, indicating that manganese ions do not directly participate in denitrification. Furthermore, combined with the attached... Figure 1 During the stable operation phase of the reactor, denitrification contributed only about 9% to nitrogen removal. This further demonstrates that manganese ions indirectly enhance the denitrification process.

Claims

1. A method for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing beds, characterized by: The method described is suitable for deep denitrification of reclaimed water with a COD concentration of less than 30 mg / L, a total nitrogen concentration of less than 10 mg / L, and a carbon-to-nitrogen ratio (C / N) of less than 3, and includes the following steps: (1) The artificial wetland filler bed is divided into several areas by vertical partitions. Water flows from the bottom of the filler bed into the first area and then into each area in sequence along the partitions. (2) After the constructed wetland is started and stabilized, ammonia nitrogen is added to the influent to adjust the total inorganic nitrogen concentration of the influent, and the wetland is run for a set time at the set total inorganic nitrogen concentration. (3) Stop adding ammonia nitrogen to the influent and start adding manganese ions to the influent. Adjust the concentration of manganese ions according to the change in concentration gradient when adding ammonia nitrogen. Step (3) includes: when the constructed wetland has been in operation for 182 days, the addition of ammonia nitrogen to the influent is stopped, and the addition of manganese ions to the influent is started, with an initial manganese ion concentration of 2 mg / L; The step (3) further includes: the concentration gradient change when adding ammonia nitrogen is 2 mg / L. Under the condition that the manganese ion concentration in the effluent is less than 0.1 mg / L, the manganese ion concentration is adjusted to three manganese ion concentration gradients of 4 mg / L, 6 mg / L and 8 mg / L, starting from the initial manganese ion concentration of 2 mg / L and using the concentration gradient change as the increment. The constructed wetland is operated for 24 days under each manganese ion concentration gradient.

2. The method for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing bed as described in claim 1, characterized in that: In step (1), the artificial wetland packing bed is divided into at least 3 areas by vertical partitions, each area forming a separate reactor. The vertical partitions and the inner wall of the packing bed form an "S"-shaped water flow channel, which connects the reactors in series. The upper part of the outer end of the last reactor is provided with a water outlet.

3. The method for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing bed as described in claim 2, characterized in that: In step (1), the hydraulic retention time of the constructed wetland is 3 days, and the surface hydraulic load is 0.6-1.0 m. 3 / (m 2 *h).

4. The method for nitrogen removal from reclaimed water using manganese ion-enhanced constructed wetland packing bed as described in claim 3, characterized in that: Step (2) includes: after the constructed wetland has been running stably for 145 days, when the total inorganic nitrogen removal rate is maintained at 9%, the total inorganic nitrogen concentration in the influent is adjusted to three concentration gradients of 10 mg / L, 12 mg / L and 14 mg / L by adding ammonia nitrogen to the influent. The constructed wetland is run for 9 days under each ammonia nitrogen concentration gradient.

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