Method for improving denitrification nitrogen removal performance of corn or rice straw fermentation carbon source by using glucose

Abstract

The invention relates to the technical field of sewage treatment, in particular to a method for improving the denitrification nitrogen removal performance of a corn or rice straw fermentation carbon source by using industrial glucose. According to the method, the straws are soaked and pretreated by adopting calcium peroxide, and meanwhile, in the anaerobic fermentation process, the anaerobic condition is kept through nitrogen, and zero-valent iron is added to obtain the straw fermentation liquor. Fermentation liquor and industrial glucose are mixed to serve as a composite carbon source, the activity of microorganisms in a sludge system is stimulated through the usability of the glucose, and the utilization rate of the microorganisms to the rice and corn fermentation liquor carbon source is increased; anaerobic fermentation conditions of rice and corn straws are optimized, the carbon source release rate is increased, the complexity of carbon source composition of fermentation liquor is utilized, the diversity of microorganisms is improved, excessive propagation of the microorganisms is avoided, and the biological denitrification capacity is improved. The method disclosed by the invention is beneficial to resource utilization of agricultural wastes, reduces the biological denitrification cost of sewage with a low carbon-nitrogen ratio, and promotes green and low-carbon development of sewage treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to a method for improving the denitrification performance of corn or rice straw fermentation carbon source by using industrial glucose. Background Art

[0002] Sewage with a COD concentration lower than 200 mg / L and a COD / TN lower than 8 is usually referred to as low C / N sewage. Its sources are mainly domestic sewage and industrial production sewage. With the development of the economic society, the living standards of urban residents have been continuously improved, and the proportion of small-scale sewage treatment plants has increased nationwide. However, the supporting sewage collection and transportation systems are mostly imperfect, the infiltration of groundwater carrying dissolved oxygen into the pipe network and the incomplete separation of rainwater and sewage lead to the dilution of sewage, and the easily biodegradable organic matter is degraded by microorganisms before entering the sewage treatment plant, resulting in a decrease in the carbon-nitrogen ratio of domestic sewage. Industrial wastewater refers to a series of wastewater generated during the production and processing of industrial products. Common industrial wastewater includes textile wastewater, printing and dyeing wastewater, petroleum wastewater, etc. The organic matter components are complex (containing alcohols, aldehydes, esters, polycyclic aromatic hydrocarbons, etc.) and difficult to degrade, and the biodegradability is poor. Due to the large discharge of low carbon-nitrogen ratio sewage, sewage treatment plants often show low TN removal efficiency during biological denitrification, resulting in the effluent not meeting the first-class A standard of "GB18918 - 2002".

[0003] To solve this problem, sewage treatment plants usually adopt the method of adding external carbon sources to improve the efficiency of microbial denitrification. Currently, the commonly used external carbon sources in sewage treatment plants are mainly traditional carbon sources such as glucose, methanol, and sodium acetate. These small molecule carbon sources are easily absorbed and utilized by denitrifying bacteria. However, adding single molecule carbon sources is extremely likely to cause excessive reproduction of microorganisms, a decrease in community diversity, sludge bulking, clogging of process pipelines, affecting subsequent treatment, and the economic cost is also relatively high. Therefore, exploring new carbon sources that are efficient, inexpensive, and can "treat waste with waste" and optimizing the sewage treatment process are urgent problems that need to be solved by current sewage treatment plants.

[0004] Cellulose-based agricultural waste is mainly composed of lignin, cellulose, hemicellulose, etc., and has a high carbon content. It is considered a potential alternative carbon source for low carbon-nitrogen sewage treatment. However, due to the complex composition of rice, corn and other straws, in addition to volatile fatty acids (VFAs) that are easily utilized by microorganisms, their fermentation broth also contains a large amount of refractory carbon, resulting in low carbon source utilization rate, unstable denitrification rate, and easy problems such as nitrite accumulation and clogging of the packing layer. Current research on soil microecology has found that the input of fresh and easily biodegradable organic matter can stimulate the activity of microorganisms and enhance their decomposition rate of refractory organic matter in the soil, which is called the "priming effect". Therefore, it is urgent to explore a method to improve the biological denitrification ability of agricultural waste fermentation carbon source. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose. Aiming at the disadvantages of traditional industrial carbon sources and agricultural waste fermentation carbon sources in sewage treatment with low carbon-nitrogen ratio, the method of the present invention utilizes the "priming effect" theory of microbial ecology, and uses the easy utilization of industrial carbon source (glucose) to stimulate the activity of microorganisms in the sludge system, improve the utilization rate of rice and corn fermentation broth carbon sources by microorganisms; optimize the anaerobic fermentation conditions of rice and corn straws, improve the carbon source release rate, and utilize the complexity of the carbon source composition of the fermentation broth to increase the microbial diversity, avoid excessive reproduction of microorganisms, and improve the biological denitrification ability. The specific technical solutions are as follows: A method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose, comprising the following steps: Step (1), pretreat corn or rice straws, dry the corn or rice straws and then crush them through a 100-mesh sieve; Step (2), add calcium peroxide to the pretreated straws at a ratio of 0.06-0.2 g / g, add water to submerge the straws and soak for 24 h, then mix the straws with anaerobic sludge at a mass ratio of 1:4, add 3-10 g / L of zero-valent iron, adjust the pH value to 6.5-7.5, and ferment under anaerobic conditions with nitrogen purging. The fermentation temperature is 34-36 °C and the fermentation time is 5-15 days to obtain a fermentation broth; Step (3), add industrial glucose to the corn or rice straw fermentation broth obtained in Step 2, and adjust the carbon-nitrogen ratio of the mixed solution to 8-12 to obtain a denitrification carbon source; Step (4), dilute the denitrification carbon source obtained in Step (3) to a COD of 3000 mg / L, add it to the SBR reactor, control the dissolved oxygen concentration in the anoxic section of the reactor to be <0.5 mg / L and the dissolved oxygen concentration in the aerobic section to be >2.0 mg / L, the total hydraulic retention time is 24 h, each cycle is 12 h, and the reactor drainage ratio is 0.5; Further, the anaerobic sludge in Step (2) is selected from the anoxic tank of the A2O process, and is washed with tap water and stored at -4 °C when taken.

[0006] Further, the addition amount of zero-valent iron in Step (2) is 5 g / L, and the fermentation time is 9 days.

[0007] Further, the addition amount of industrial glucose in Step (3) is 10-30% of the COD of the corn or rice straw fermentation broth calculated by COD.

[0008] Further, the addition of the denitrification carbon source in Step (4) is determined based on the C / N of the wastewater treated in the SBR reactor, and the C / N in the SBR reactor is controlled to be 4-6.

[0009] Further, control the C / N in the SBR reactor to be 5.

[0010] The beneficial effects of the present invention are as follows: The present invention uses calcium peroxide to soak and pretreat straw. When CaO2 dissolves in an aqueous medium, in addition to the slow release of O2 and H2O2 at a "controllable" rate, the formation of alkali (Ca(OH)2) also occurs. These alkaline substances are beneficial to the destruction of the ether bonds and ester bonds between hemicellulose and cellulose. At the same time, during the anaerobic fermentation process, anaerobic conditions are maintained by nitrogen and zero-valent iron is added; the adverse effects brought by the strong oxidation of calcium peroxide to anaerobic fermentation can be effectively inhibited, and the residual oxidants can be rapidly reduced; at the same time, during the anaerobic fermentation process, the pH can be increased, providing a good living environment for anaerobic digestion bacteria; it can also increase the activities of enzymes related to the hydrolysis acidification process such as dehydrogenase, improving the efficiency of degrading organic matter; and it can promote the hydrogen production and acetic acid production process and the homoacetogenesis process, and accelerate the conversion of macromolecular organic substances such as propionic acid and butyric acid into acetic acid.

[0011] The present invention utilizes the easy utilization of industrial carbon sources (glucose) to stimulate the activity of microorganisms in the sludge system, improve the utilization rate of carbon sources in rice and corn fermentation broths by microorganisms; optimize the anaerobic fermentation conditions of rice and corn straws, improve the carbon source release rate, utilize the complexity of the carbon source composition in the fermentation broth, increase the diversity of microorganisms, avoid excessive reproduction of microorganisms, and improve the biological denitrification ability. This technology is conducive to the resource utilization of agricultural waste, reduces the cost of biological denitrification of low-carbon-nitrogen ratio sewage, and promotes the green and low-carbon development of sewage treatment. Description of the Drawings

[0012] Figure 1 Comparison chart of the effluent water quality with different carbon source additions in the examples and comparative examples; Figure 2 Comparison chart of the abundance of denitrifying genes with different carbon source additions in the examples and comparative examples. Detailed Embodiments

[0013] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Embodiment

[0014] The following steps are adopted: A method for improving the denitrifying performance of carbon sources in the fermentation of corn or rice straw by using glucose, comprising the following steps: Step (1): Pretreat corn or rice straw. Dry the corn or rice straw and then crush it through a 100-mesh sieve. Step (2): Add calcium peroxide to the pretreated straw at a ratio of 0.06 g / g, add water to submerge the straw, and soak for 24 h. Then mix the straw and anaerobic sludge at a mass ratio of 1:4, add 3 g / L of zero-valent iron, adjust the pH value to 6.5 - 7.5, and ferment under anaerobic conditions with nitrogen gas purging. The fermentation temperature is 34 - 36 °C, and the fermentation time is 10 days to obtain the fermentation broth. The anaerobic sludge is selected from the anoxic tank of the A2 / O process. When taking it, wash it with tap water and store it at -4 °C before use. Step (3): Add industrial glucose to the corn or rice straw fermentation broth obtained in step (2) at a mass ratio of 10 - 30% and adjust the carbon-nitrogen ratio of the mixed solution to 8 - 12 to obtain the denitrification carbon source (denoted as carbon source 4 after rice straw fermentation and carbon source 5 after corn straw fermentation). Step (4): Dilute the denitrification carbon source obtained in step (3) to a COD of 3000 mg / L, add it to the SBR reactor, control the dissolved oxygen concentration in the anoxic section of the reactor to be < 0.5 mg / L and the dissolved oxygen concentration in the aerobic section to be > 2.0 mg / L. The total hydraulic retention time is 24 h, each cycle is 12 h, and the reactor drainage ratio is 0.5. The addition of the denitrification carbon source in step (4) is determined based on the C / N of the wastewater treated in the SBR reactor, and the C / N in the SBR reactor is controlled to be 4 - 6. In this example, it is controlled to be 5.

[0015] Comparative Example 1 Directly use glucose as the denitrification carbon source (denoted as carbon source 1), and the SBR treatment steps are the same as those in Example 1.

[0016] Comparative Example 2 Directly use the straw anaerobic fermentation broth as the denitrification carbon source as in Example 1 (the rice straw fermentation broth is denoted as carbon source 2, and the corn fermentation broth is denoted as carbon source 3), and the SBR treatment steps are the same as those in Example 1.

[0017] Comparison of biological nitrogen removal effects The effluent quality of the SBR reactor during operation was measured. After 7 days of acclimation with simulated wastewater influent, the NH4+-N removal rates of the 5 reactors reached over 95%, and the nitrification in the reactors was complete. No carbon source was added in the first 7 days, and the average TN removal rate of the 5 reactors was only 16.04% ± 1.39%. Starting from the 8th day, a carbon source was added to adjust the C / N to about 5, and the effluent quality tended to be stable from the 18th day to the 22nd day. The effluent concentrations from low to high were carbon source 4 (0.95 ± 0.39 mg / L), carbon source 5 (1.00 ± 0.96 mg / L), carbon source 1 (3.56 ± 1.06 mg / L), carbon source 3 (5.61 ± 1.27 mg / L), and carbon source 2 (8.76 ± 2.64 mg / L). The TN removal rates from high to low were carbon source 4 (98.09% ± 0.79%), carbon source 5 (97.99% ± 1.91%), carbon source 1 (92.83% ± 2.11%), carbon source 3 (88.76% ± 2.53%), and carbon source 2 (82.47 ± 5.28%). It can be seen that the TN removal rate of the composite carbon source was significantly higher than that of the treatment groups using glucose and agricultural waste fermentation broth alone (P < 0.05). It could complete the denitrification process in the reactor and achieve satisfactory results. The effluent TN mainly existed in the form of NO3--N. Similarly, the effluent NO3--N and NO2--N of the two groups of composite carbon sources (carbon source 4 and 5) were lower than those of other treatment groups, and their effluent quality was better. In addition, the COD removal rates of all 5 treatment groups reached over 85%, and the effluent COD concentrations were all lower than 50 mg / L, indicating that the composite carbon source was easily utilized by microorganisms, and reasonable setting of the dosing amount would not cause the effluent COD to exceed the standard. By comparing the concentrations of TN, NO3--N, NO2--N, and COD in the effluents of the 5 reactors, it was observed that the effluent quality of the composite carbon source treatment groups (carbon source 4 and 5) was better than that of using glucose and fermentation broth alone. Therefore, the composite carbon source composed of fermentation broth and glucose is a highly potential external carbon source for denitrification. As Figure 1 shown

[0018] Denitrification performance comparison Within 18 d - 22 d, monitor the changes in the concentrations of NO3--N, NO2--N, and COD in a cycle in the reactor. As shown in the following table, the denitrification kinetic indexes (denitrification rate VDN, denitrification potential PDN, and microbial growth factor YH) are calculated from the NOX removal curve. In the exogenous denitrification (EXD) stage, the denitrification rate VDN shows that carbon source 3 (5.78) > carbon source 2 (5.41) > carbon source 4 (5.48) > carbon source 5 (5.33) > carbon source 1 (4.87); in the endogenous denitrification stage, VDN shows that carbon source 5 (0.24) > carbon source 4 (0.23), carbon source 1 (0.23) > carbon source 2 (0.22), carbon source 3 (0.22); YH is used to describe the amount of COD consumed by the growth of the bacterial community or estimate the amount of biological sludge produced by denitrification. The microbial growth factor YH from large to small is: carbon source 2 (0.29) > carbon source 4 (0.27) > carbon source 1 (0.26) > carbon source 3 (0.25), carbon source 5 (0.25). This indicates that most of the COD content of carbon source 5 is used for nitrogen removal rather than for microbial growth, which is beneficial to preventing sludge bulking. Short - cut denitrification (PDN) has the advantages of fast reaction rate, less carbon source addition, low sludge production, and stable operation. It is found that carbon source 2 shows a lower PDN value, indicating that the use of rice fermentation broth alone is not conducive to the stable performance of biological nitrogen removal. Generally speaking, the composite carbon sources (carbon sources 4 and 5) are beneficial to promoting the biological denitrification process, and the denitrification performance is more excellent.

[0019] Table Denitrification Kinetic Indexes Comparison of Denitrification Functional Genes Nitrite reductase (Nir) and nitrous oxide reductase (Nos) are the key enzymes that catalyze the rate - limiting steps of denitrification, NO2-→NO and N2O→N2, respectively. The abundance of functional genes reflects the microbial nitrogen conversion ability to a certain extent. The results show that compared with carbon sources 2 and 3, carbon sources 1, 4, and 5 all have higher abundances of nirK, nirS, and nosZ gene abundances. It shows that compared with the carbon sources of rice (carbon source 2) and corn (carbon source 3) straw fermentation broth, the composite carbon sources (carbon sources 4 and 5) can significantly enhance the denitrification potential of organisms, as specifically shown in Figure 2 shown.

[0020] The above - mentioned preferred embodiments of the present patent have been described in detail, but the present patent is not limited to the above - mentioned embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the purpose of the present patent.

Claims

1. A method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose, which is characterized in that: It includes the following steps: Step (1): Pretreat corn or rice straw. After drying and crushing the corn or rice straw, it is sieved through a 100-mesh sieve. Step (2): Add calcium peroxide to the pretreated straw at a ratio of 0.06 - 0.2 g / g, add water to submerge the straw for soaking treatment for 24 h, then mix the straw and anaerobic sludge according to a mass ratio of 1:4, add 3 - 10 g / L of zero-valent iron, adjust the pH value to 6.5 - 7.5, and carry out fermentation under anaerobic conditions with nitrogen purging. The fermentation temperature is 34 - 36 °C, and the fermentation time is 5 - 15 days to obtain a fermentation broth. Step (3): Add industrial glucose to the corn or rice straw fermentation broth obtained in Step 2, and adjust the carbon-nitrogen ratio of the mixed solution to 8 - 12 to obtain a denitrification carbon source. Step (4): Dilute the denitrification carbon source obtained in Step (3) to a COD of 3000 mg / L, and add it to the SBR reactor. Control the dissolved oxygen concentration in the anoxic section of the reactor to be <0.5 mg / L and the dissolved oxygen concentration in the aerobic section to be >2.0 mg / L. The total hydraulic retention time is 24 h, each cycle is 12 h, and the reactor drainage ratio is 0.

5.

2. A method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose according to claim 1, characterized in that: The anaerobic sludge in Step (2) is selected from the anoxic tank of the A2O process and is stored at -4 °C after being washed with tap water when taken.

3. A method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose according to claim 1, characterized in that: In Step (2), the addition amount of zero-valent iron is 5 g / L, and the fermentation time is 9 days.

4. A method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose according to claim 1, characterized in that: In Step (3), the addition amount of industrial glucose calculated by COD is 10 - 30% of the COD of the corn or rice straw fermentation broth.

5. A method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose according to claim 1, characterized in that: In Step (4), the addition of the denitrification carbon source is determined based on the C / N of the wastewater treated in the SBR reactor, and the C / N in the SBR reactor is controlled to be 4 - 6.

6. A method for improving the denitrification performance of corn or rice straw fermentation carbon source by using glucose according to claim 5, characterized in that: Control the C / N in the SBR reactor to be 5.

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