Method for treating toilet wastewater by using in-situ bacteria and algae for short-cut nitrification and denitrification nitrogen removal

Abstract

The present invention discloses a method for treating toilet wastewater by using in-situ bacteria and algae for short-cut nitrification and denitrification to remove nitrogen. By gradually increasing the influent ammonia nitrogen concentration, the invention inhibits nitrite-oxidizing bacteria in the activated sludge system, so that the initial ammonia nitrogen is oxidized into nitrite nitrogen to initiate a short-cut nitrification activated sludge system. After the system is stable, in-situ algae are cultured under suitable light conditions to construct a short-cut in-situ bacteria-algae system. The method of the present invention can reduce the aeration and carbon source costs in the traditional biological nitrogen removal process, solve the problem of poor adaptability of exogenous microalgae, and can also be applied to the efficient, low-energy-consumption and rapid nitrogen removal of other high-ammonia-nitrogen wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage resource treatment processes, and relates to a method for treating toilet wastewater by using in-situ bacteria and algae for short-cut nitrification and denitrification nitrogen removal. Background Art

[0002] With the rapid development of public transportation such as high-speed railways and aviation, a large amount of toilet wastewater containing high concentrations of ammonia nitrogen has been generated. Biological nitrogen removal processes have been proven to be an effective method for removing ammonia nitrogen from toilet wastewater through conventional nitrification and denitrification means. However, this method requires aeration and the addition of carbon sources, and due to the increased treatment cost and the lack of consideration for nitrogen recovery, it limits its large-scale application. Therefore, it is necessary to develop a technology for simultaneously treating toilet wastewater and recovering resources.

[0003] The bacteria-algae symbiotic system forms a good symbiotic relationship based on complementary metabolic functions, and the synergistic effect between the two has great potential in improving nutrient removal and reducing the cost of wastewater treatment (such as the energy consumption of aeration and carbon sources). Based on the water quality characteristics of toilet-collected wastewater with high ammonia-nitrogen concentration and low C / N ratio, it is suitable to be treated by the shortcut biological nitrogen removal technology. At present, there are few relevant studies on the treatment of toilet-collected wastewater by the shortcut bacteria-algae process combining microalgae and the shortcut biological nitrogen removal technology. It has been reported that the shortcut bacteria-algae can further reduce the energy cost in the biological process, especially for wastewater with low C / N, including anaerobic pig manure fermentation broth and landfill leachate in References 1 and 2 (Wang Meng, Yang Han, Ergas Sarina J, et al. A novel shortcut nitrogen removal process using an algal-bacterial consortium in a photo-sequencing batch reactor (PSBR) [J]. Water Research, 2015, 87: 38-48; Wu Lina, Li Zhi, Zhao Chen, et al. A novel partial-denitrification strategy for post-anammox to effectively remove nitrogen from landfill leachate [J]. Science of the Total Environment, 2018, 633: 745-751). At present, most of the studies on the shortcut bacteria-algae use methods such as free ammonia (FA), free nitrous acid (FNA), and low dissolved oxygen (DO) to first achieve shortcut nitrification and enrich ammonia-oxidizing bacteria (AOB), and then use the co-culture of AOB and pure algae. However, this method has poor adaptability of algae, and the stability of the nitrification system and the denitrification efficiency are limited. Therefore, it is necessary to study the startup and stable maintenance of the shortcut bacteria-algae. Summary of the Invention

[0004] To solve the above problems and minimize the aeration and carbon source costs required in the traditional biological nitrogen removal process and solve the problem of poor adaptability of exogenously added microalgae, the present invention provides a method for treating toilet-collected wastewater by using in-situ bacteria-algae shortcut nitrification and denitrification nitrogen removal. This method constructs in-situ shortcut bacteria-algae and synchronously realizes the cultivation of in-situ bacteria-algae and the efficient removal of nitrogen and phosphorus.

[0005] The technical solution of the present invention is as follows:

[0006] A method for treating toilet-collected wastewater by using in-situ bacteria-algae shortcut nitrification and denitrification nitrogen removal, comprising the following steps:

[0007] (1) Using the toilet wastewater with a gradient ammonia nitrogen concentration as the influent of the SBR reactor to domesticate the activated sludge in the SBR reactor until the accumulation of nitrite nitrogen in the reactor is stable and the nitrite accumulation rate > 90%, obtaining a shortcut nitrification activated sludge system;

[0008] (2) Applying light to the shortcut nitrification activated sludge system with a light intensity of 0.0188 kJ·mg / VSS, and at the same time introducing the toilet wastewater into the SBR reactor to achieve shortcut nitrification denitrification biological nitrogen removal and microbial assimilation synchronously.

[0009] Preferably, in step (1) or (2), the reactor operates using the SBR process, including the processes of influent, anoxic, aerobic, sedimentation, and drainage. More preferably, in the SBR process cycle, the influent time is 2 min, the anoxic time is 240 min, the aerobic time is 480 min, the sedimentation time is 50 min, and the drainage time is 5 min.

[0010] Preferably, in step (1), the gradient ammonia nitrogen concentrations of the toilet wastewater are successively: stage I 100 - 150 mg / L, stage II 150 - 200 mg / L, stage III 200 - 250 mg / L, stage IV 250 - 300 mg / L.

[0011] Preferably, in step (1), when the ammonia nitrogen in the stage effluent of the toilet wastewater with each gradient ammonia nitrogen concentration is lower than 15 mg / L, it enters the next concentration gradient.

[0012] In step (1), when the accumulation of nitrite nitrogen in the reactor is stable and the nitrite accumulation rate > 90%, it is regarded as the successful start of shortcut nitrification. The nitrite accumulation rate formula is is the nitrite concentration in the effluent, is the nitrate nitrogen concentration in the effluent.

[0013] Preferably, in step (2), the initial concentration of the shortcut nitrification activated sludge is 3000 - 3500 mg / L.

[0014] In step (2), in order to reduce unnecessary energy consumption, the actual light condition evaluation is based on the formula P is the light power (W), T is the light time (h), V is the actual working volume of the reactor (L), MLVSS is the sludge concentration (mg / L), and Es is maintained within the range of 0.0188 kJ·mg / VSS. Within this range, the activity of nitrite oxidizing bacteria (NOB) can be inhibited, the activity of AOB can be slowly stimulated, and the stability of the shortcut system can be effectively maintained.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) First, the present invention domesticates the activated sludge in the SBR reactor with the centralized toilet wastewater of gradient ammonia nitrogen concentration, inhibits the activity of NOB by the alternating action of FA and FNA, constructs a short-cut nitrification activated sludge system, and then realizes the selective stimulation of AOB and the inhibition of NOB by applying appropriate light conditions, which is the main factor to maintain the short-cut in the short-cut in-situ bacteria-algae system. At the same time, the algal-derived organic matter secreted by algae can be used for denitrification and bacterial metabolism, improving the availability of carbon sources in the short-cut in-situ bacteria-algae system.

[0017] (2) Compared with other existing methods that only consider the light intensity, the present invention comprehensively considers factors such as light power, light time, and sludge. The algal-derived organic matter generated after the in-situ algae enrichment can supply denitrification, promoting the progress of denitrification and maintaining the stability of the short-cut system. For the in-situ bacteria-algae system constructed by the method of the present invention, the average removal rate of ammonia nitrogen reaches more than 90%, and the NAR also remains about 90%.

[0018] In summary, the present invention uses light in a specific light range to enrich in-situ algae, promotes the biomass accumulation of the symbiotic system, constructs an in-situ bacteria-algae system, maintains the stability of the short-cut system, and at the same time realizes the effective removal of ammonia nitrogen, greatly reducing the reaction cost, which has very important significance for promoting the low-carbon resource treatment of sewage. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the reactor and the control system;

[0020] Figure 2 It is the change of the three nitrogen and pH within one cycle before culturing in-situ algae;

[0021] Figure 3 It is the change of the in-situ bacteria-algae biomass in the reactor (a) is chlorophyll, (b) is the change of the appearance morphology of bacteria-algae;

[0022] Figure 4 It is the morphology of bacteria-algae, (a) is the morphology of bacteria-algae under the microscope, (b) is the morphology of bacteria-algae under the electron microscope;

[0023] Figure 5 It is the change of the species of microalgae in the reactor;

[0024] Figure 6 It is the result of the possibility of microalgae secreting organic matter;

[0025] Figure 7 It is the change of the sludge concentration in the short-cut in-situ bacteria-algae system and the short-cut nitrification activated sludge system. Detailed Embodiments

[0026] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0027] The reagents used in the following examples are all commercially available.

[0028] Example 1

[0029] Construction of a short-cut nitrification activated sludge system:

[0030] Taking the collected toilet wastewater as the research object, the water quality components are as follows: total nitrogen (TN) 6501 - 6729 mg / L, ammonia nitrogen 6473 - 6648 mg / L, nitrite 0.06 - 0.21 mg / L, nitrate 0.04 - 0.12 mg / L, total phosphorus 383.4 - 376.9 mg / L, chemical oxygen demand 6210 - 6431 mg / L, pH 9.18 - 9.29. As Figure 1 shown, the selected photobioreactor has an effective volume of 0.5 L, and the denitrification reaction and domestication are carried out in the SBR mode. The specific process is as follows:

[0031] Inoculate the nitrifying sludge that has been domesticated for a long time into the reactor to make the sludge concentration reach 3000 - 3500 mg / L. Dilute the toilet wastewater as the reactor inlet water, and gradually increase the inlet ammonia nitrogen concentration in four stages: Ⅰ (100 - 150 mg / L), Ⅱ (150 - 200 mg / L), Ⅲ (200 - 250 mg / L), Ⅳ (250 - 300 mg / L). Each stage stays for 7 - 10 days, specifically determined according to the effluent level and nitrite accumulation. Carry out nitrification and denitrification in the SBR mode. Each cycle includes inlet water - anoxic - aerobic - precipitation - drainage. The mixed liquor is mixed evenly by a magnetic stirrer, and the nitrification stage is aerated by an air pump with an aeration stone. The pH of the whole reaction process is controlled at 7.0 - 7.5, the dissolved oxygen (DO) is controlled at 2 - 3 mg / L, and NOB shows a certain sensitivity under the gradually increasing nitrogen load, and the accumulation of nitrite nitrogen is gradually formed.

[0032] As Figure 2 shown, on the 70th day of the early cultivation, in the anoxic stage (0 - 4 hours), the ammonia nitrogen concentration remained relatively stable, but as the denitrification process proceeded, due to the continuous increase in pH value (from 7.28 to 7.85), FA continuously increased from 1.64 mg / L to 5.86 mg / L. Subsequently, during the period of 4 - 12 h, since ammonia nitrogen was continuously oxidized to nitrite during the aerobic process and this process consumed alkalinity resulting in a decrease in pH, FA began to decrease. The combination of nitrite accumulation and pH change led to a sharp increase in FNA from 0.002 mg / L at 4 hours to 0.028 mg / L at 12 hours. Therefore, this system presented the alternating action of FA and FNA to inhibit the activity of NOB.

[0033] Example 2

[0034] Enrichment of in-situ algae and cultivation of short-cut in-situ bacteria-algae:

[0035] For a short-cut sludge system that has been acclimated for a long time, light (Es: 0.0188 kJ·mg / VSS) was applied. The reactor still carried out nitrification and denitrification in the SBR mode. One cycle included 2 minutes of influent feeding, 240 minutes of anoxic phase, 480 minutes of aerobic phase, 50 minutes of sedimentation, and 5 minutes of effluent drainage. The mixed liquor was evenly mixed by a magnetic stirrer. The pH of the whole reaction process was controlled at 7.0 - 7.5, and aeration was carried out through an air pump with an aeration stone, and the dissolved oxygen (DO) was controlled at 2 - 3 mg / L. After about 1 month, green color could be seen in the reactor. As Figure 3 shown, the measured chlorophyll a content was 2.91 μg / mL and the chlorophyll b content was 2.22 μg / mL. As the cultivation time increased, in-situ algae were gradually enriched, and the external color of the bacteria-algae flocs gradually deepened. Observed under a microscope and an electron microscope, as Figure 4 shown, abundant algae were found in the sludge flocs and the suspension, and in-situ algae were cultivated in the system. As Figure 5 shown, Tetradesmus obliquus (72.2%) and Desmodesmus sp. (26.8%) were the dominant algal species of in-situ algae, and the proportions were similar at different times.

[0036] On the one hand, appropriate light conditions achieved selective stimulation of AOB and inhibition of NOB, which was the main factor maintaining the short-cut in the short-cut in-situ bacteria-algae system. The light energy density applied to nitrifying bacteria could regulate the metabolism of AOB, such as strengthening the activity of the electron transport system, enhancing the activity of key enzymes (i.e., AMO), upregulating gene expression (such as amoA), and energy production (such as reduced ATP consumption). On the other hand, due to insufficient carbon sources for denitrification and microbial assimilation, the sludge biomass in the reactor continued to decline. In addition, the carbon sources determined by three-dimensional fluorescence (EEM) were mainly composed of humic acid (about 70%) and tryptophan (about 30%), and these two substances were regarded as non-ideal carbon sources because they were difficult to biodegrade. Algae could produce organic matter, which could be used for denitrification and bacterial metabolism, thus improving the availability of carbon sources in the short-cut in-situ bacteria-algae system. As Figure 6 shown, after separation, in-situ algae were confirmed to have the possibility of secreting organic matter during their growth, and this kind of organic matter could be used as a biological carbon source for short-cut denitrification, avoiding nitrite oxidation in the reactor, and ultimately maintaining the stability of the short-cut in the short-cut in-situ bacteria-algae system.

[0037] Comparing with the continuously operating short-cut nitrifying activated sludge system without adding light, as Figure 7 shown, due to the carbon source problem, the sludge volume continued to decline, and the nitrogen removal performance gradually deteriorated until the system collapsed.

[0038] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0039] In addition, it should be noted that, in the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0040] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. Method for treating toilet wastewater by in-situ bacteria and algae short-cut nitrification and denitrification nitrogen removal, Characterized in that, It includes the following steps: (1) Using toilet wastewater with gradient ammonia nitrogen concentration as the influent of the SBR reactor, domesticating the activated sludge in the SBR reactor until the accumulation of nitrite nitrogen in the reactor is stable and the nitrite accumulation rate > 90% to obtain a short-cut nitrification activated sludge system; (2) Applying light to the short-cut nitrification activated sludge system, with a light density of 0.0188 kJ∙mg / VSS, enriching in-situ algae. At the same time, introducing toilet wastewater into the SBR reactor. The algal organic matter generated after the enrichment of in-situ algae can supply denitrification, synchronously realizing short-cut nitrification and denitrification biological nitrogen removal and microbial assimilation.

2. The method according to claim 1, Characterized in that, In step (1) or (2), the reactor operates using the SBR process, including the processes of influent, anoxic, aerobic, sedimentation, and drainage.

3. The method according to claim 2, Characterized in that, In the SBR process cycle, the influent time is 2 min, the anoxic time is 240 min, the aerobic time is 480 min, the sedimentation time is 50 min, and the drainage time is 5 min.

4. The method according to claim 1, Characterized in that, In step (1), the gradient ammonia nitrogen concentrations of the toilet wastewater are successively: stage I 100 - 150 mg / L, stage II 150 - 200 mg / L, stage III 200 - 250 mg / L, stage IV 250 - 300 mg / L.

5. The method according to claim 1, Characterized in that, In step (1), when the effluent ammonia nitrogen of the toilet wastewater at each gradient ammonia nitrogen concentration is lower than 15 mg / L, it enters the next concentration gradient.

6. The method according to claim 1, Characterized in that, In step (2), the initial concentration of the short-cut nitrification activated sludge is 3000 - 3500 mg / L.

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