CN109534510B

CN109534510B - Method for strengthening anaerobic ammonia oxidation denitrification process by chemical method

Info

Publication number: CN109534510B
Application number: CN201910026816.4A
Authority: CN
Inventors: 孙亮; 胡德皓; 张子昱; 邓晓燕
Original assignee: Qingdao University of Science and Technology
Current assignee: Qingdao University of Science and Technology
Priority date: 2019-01-11
Filing date: 2019-01-11
Publication date: 2022-09-02
Anticipated expiration: 2039-01-11
Also published as: CN109534510A

Abstract

The invention relates to an anaerobic ammonia oxidation denitrification process, in particular to a method for strengthening the anaerobic ammonia oxidation denitrification process by a chemical method, and belongs to the technical field of sewage treatment and regeneration. A method for strengthening an anaerobic ammonia oxidation denitrification process by a chemical method is characterized in that a proper amount of graphene oxide and anaerobic ammonia oxidation sludge are added into an anaerobic ammonia oxidation reactor to be mixed to treat wastewater so as to shorten the starting period of the anaerobic ammonia oxidation process and realize the quick starting of the anaerobic ammonia oxidation; and after the anaerobic ammonia oxidation is successfully started, adding an oxidation-reduction medium into the inlet water to perform enhanced anaerobic ammonia oxidation treatment on the wastewater so as to enhance the denitrification effect of the anaerobic ammonia oxidation process.

Description

Method for strengthening anaerobic ammonia oxidation denitrification process by chemical method

Technical Field

The invention relates to an anaerobic ammonia oxidation denitrification process, in particular to a method for strengthening the anaerobic ammonia oxidation denitrification process by a chemical method, and belongs to the technical field of sewage treatment and regeneration.

Background

The traditional biological denitrification process takes nitrification and denitrification as the core. Nitrification, i.e., under aerobic conditions, Ammonia Oxidizing Bacteria (AOB) oxidize ammonia nitrogen to nitrite, and Nitrite Oxidizing Bacteria (NOB) oxidize nitrite to nitrate; denitrification, i.e. the reduction of nitrate or nitrite to nitrogen by denitrifying bacteria (denitrifying bacteria) under anoxic conditions. Thus, the conventional nitrification and denitrification processes are carried out in two separate reactors or alternatively aerobic and anoxic environments by time control in the same reactor. The traditional biological denitrification technology is widely applied to urban domestic sewage treatment and partial industrial wastewater treatment in China, and comprises an anoxic-aerobic combined process (AO, A2O, multistage A2O and the like), an SBR method, an oxidation ditch process and the like.

Despite the wide application and continuous technological improvements of the conventional nitrification-denitrification process, the conventional nitrification-denitrification process is limited by the denitrification mechanism, and has a plurality of inevitable disadvantages:

(1) the nitrification stage and the denitrification stage need different environments and need to be distributed at different time or space, so that the capital investment cost and the occupied area are increased;

(2) more acid is generated in the nitration stage, the influence on the ammoxidation rate is reduced, and alkali is added for supplementing the alkalinity, so that the cost is increased, and secondary pollution is brought to the environment;

(3) the sludge yield is high, and the sludge expansion is easy to occur;

(4) for low wastewater, a large amount of organic carbon sources need to be added in the denitrification process;

(5) the mass transfer efficiency of the oxygen in the aeration tank is low; the electric energy consumed by aeration accounts for more than 60% of the total electricity consumption of the sewage plant;

(6) the return of sludge and nitrifying liquid results in increased power consumption and running cost;

(7) the denitrification process generates non-negligible greenhouse gas emission, such as CO ₂ 、CH ₄ And N ₂ O, and the like.

Therefore, the research and development of novel economic and efficient biological denitrification technology become key points and hot points in the field of water pollution control.

ANAMMOX (ANAMMOX) refers to a denitrification process in which ANAMMOX bacteria (AAOB) directly convert ammonia nitrogen into nitrogen gas using ammonia nitrogen as an electron donor and nitrite as an electron acceptor under anaerobic conditions. Compared with the traditional nitrification and denitrification process, the process does not need an additional carbon source, reduces the power consumption by 60 percent and the floor area by 50 percent, and reduces CO ₂ The yield is reduced by 90 percent, the sludge production amount of the process is extremely low, the treatment cost is only 0.75 EUR/kg N, which is far lower than that of the traditional biological denitrification process (2-5 EUR/kg N), and the process has revolutionary technical advantages and wide application prospect and is more and more widely concerned by researchers.

Despite the great advantages that the traditional nitrification-denitrification process has to be compared with, the anaerobic ammonia oxidation and the derivative process thereof still cannot be popularized in the global scope, because the anaerobic ammonia oxidation bacteria have some defects which prevent the large-scale application of the anaerobic ammonia oxidation bacteria due to the characteristics of the anaerobic ammonia oxidation bacteria. The multiplication time of the anammox bacteria is as long as 11-20 days, and the anammox process has almost no activity under the condition of extremely small number of floras, so that the starting period of the anammox process is very long, and new technologies and new means need to be developed to improve the activity of the anammox bacteria, accelerate the growth rate of the anammox bacteria, shorten the post-moving period of the anammox process, and finally realize the large-scale application of the anammox process. There are many documents currently investigating the control factors of the anammox process, such as temperature, pH, dissolved oxygen, nitrogen composition, organics, etc. In the prior art, the treatment effect of the anaerobic ammonia oxidation process is enhanced mainly by optimizing the reactor configuration, adding fillers, inoculating different types of inoculated sludge, optimizing operation parameters, applying a magnetic field and the like, but the prior anaerobic ammonia oxidation process still has the problems of long starting time and low total nitrogen removal efficiency.

The graphene oxide is formed by layering various epoxide, carboxyl and hydroxyl groups on the position plane and the edge of graphene. Graphene oxide has many characteristics, such as a large specific surface area, low biotoxicity, and the like. Compared with graphene, a large number of functional groups on the surface of graphene oxide have better affinity to microorganisms, in addition, the graphene oxide also has good biological adhesiveness and very good conductivity, and anammox bacteria can be attached to the surface of the graphene oxide to enhance the activity of the anammox bacteria, so that the rapid start of an anammox process is realized.

The biochemical reaction of the organism is essentially to achieve the purpose of oxidation or reduction through the transfer and transfer of electrons, thereby completing the conversion of substances. In the organism, the coenzyme is used as a carrier of electron transfer, participates in biochemical reaction and plays an important role. The coenzymes participating in the reaction mostly belong to quinone compounds, which are determined by the chemical characteristics of the quinone compounds, and the quinone compounds contain carbon-carbon double bonds and can perform electrophilic addition; contains carbonyl, can perform nucleophilic addition with a carbonyl reagent, is a conjugated system, and can perform 1, 4-addition reaction; it is essential that the quinone compound can reversibly react between an oxidized state and a reduced state by electron transfer. Based on the chemical properties of quinone compounds, it is theoretically feasible to use compounds with quinone structures as redox mediators to accelerate the degradation of pollutants by microorganisms. In recent years, researches of scholars at home and abroad prove that the quinone compounds have the function of accelerating the degradation of pollutants by microorganisms under proper conditions, and the degradation rate of the pollutants can be improved by one to several orders of magnitude. Based on this, we developed a chemical-based method to enhance the anammox denitrification process.

Disclosure of Invention

The invention provides a method for strengthening an anaerobic ammonia oxidation denitrification process by a chemical method, aiming at the problems of long starting period and low denitrification efficiency of the anaerobic ammonia oxidation process in the prior art.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a method for strengthening an anaerobic ammonia oxidation denitrification process by a chemical method is characterized in that a proper amount of graphene oxide and anaerobic ammonia oxidation sludge are added into an anaerobic ammonia oxidation reactor to be mixed to treat wastewater so as to shorten the starting period of the anaerobic ammonia oxidation process and realize the quick starting of the anaerobic ammonia oxidation; and after the anammox is started successfully, adding an oxidation-reduction medium into the inlet water to perform enhanced anammox treatment on the wastewater so as to enhance the denitrification effect of the anammox process.

The graphene oxide has many characteristics, such as large specific surface area, low biotoxicity and the like, in addition, the graphene oxide also has good biological adhesiveness and very good conductivity, and the anammox bacteria can be attached to the surface of the graphene oxide to enhance the activity of the anammox bacteria, so that the rapid start of the anammox process is realized. The biochemical reaction of the organism is essentially to achieve the purpose of oxidation or reduction through the transfer and transfer of electrons, thereby completing the conversion of substances. In organisms, the coenzyme is used as a carrier for electron transfer, participates in biochemical reaction and plays an important role. The coenzymes participating in the reaction mostly belong to quinone compounds, which are determined by the chemical characteristics of the quinone compounds, and the quinone compounds contain carbon-carbon double bonds and can perform electrophilic addition; contains carbonyl, can perform nucleophilic addition with a carbonyl reagent, is a conjugated system, and can perform 1, 4-addition reaction; it is essential that the quinone compound can reversibly react between an oxidized state and a reduced state by electron transfer. Based on the chemical properties of quinone compounds, it is theoretically feasible to use compounds with quinone structures as redox mediators to accelerate the degradation of pollutants by microorganisms. In recent years, researches of scholars at home and abroad prove that the quinone compounds have the function of accelerating the degradation of pollutants by microorganisms under proper conditions, and the degradation rate of the pollutants can be improved by one to several orders of magnitude. Based on the above, we developed an enhanced anammox denitrification process based on the characteristics of graphene oxide and quinones.

The main principle of the invention is that the biological adhesiveness and the conductivity of graphene oxide are utilized to enhance the activity of anaerobic ammonia oxidation bacteria and realize the quick start of the anaerobic ammonia oxidation process; the redox medium is used as the main function of an electron shuttle substance and an electron acceptor, the biochemical reaction of anaerobic ammonia oxidation bacteria is promoted to improve the reaction rate of the anaerobic ammonia oxidation reaction, the anaerobic ammonia oxidation process is strengthened, and the operation period of the anaerobic ammonia oxidation process is shortened.

Preferably, denitrification sludge in A2/O process of municipal sewage treatment plant is selected as sludge of anaerobic ammonia oxidation process, and K with pH 7.2 is used ₂ HPO ₄ /KH ₂ PO ₄ And flushing the denitrification sludge for multiple times by using a buffer solution so as to flush out ammonia nitrogen, organic matters, nitrite and nitrate in the denitrification sludge.

Preferably, the sludge concentration in the reactor is 10-12 g/L, and the sludge retention time is 15-40 d.

Preferably, the anaerobic ammoxidation reactor adopts a sequencing batch reactor, the dissolved oxygen is kept between 0.5 and 0.6mg/L, the reaction temperature is between 30 and 35 ℃, and the pH value is between 6.7 and 8.5.

Preferably, the graphene oxide is added in the first water feeding process, and the adding amount is 90-150 mg/L calculated by the volume of the reactor.

Preferably, the redox medium is added with the inlet water every time, so that the concentration of the redox medium in the anaerobic ammonia oxidation process is 0.1-0.3mmol/L of inlet water, and the optimal concentration is 0.2 mmol/L. Preferably, the redox mediator is one or more of 2, 6-disulfonic acid anthraquinone, 2-sulfonic acid anthraquinone, juglone, lawsone, menadione and riboflavin, and when there are more, the ratio is any ratio.

Preferably, the graphene oxide is prepared by a Hummers method.

Preferably, the method comprises a phase 1 and a phase 2, wherein the operation period of the phase 1 (day 1-45) is 48 hours, and the operation period of the phase two (day 46-60) is 24 hours.

Compared with the prior art, the activity of the anammox bacteria is improved by adding the graphene oxide and utilizing the biological adsorption property and the electrical conductivity of the graphene oxide, the starting time of the anammox process is shortened, the redox medium is added as an electron acceptor, the electron transfer in the anammox reaction process is accelerated, the reaction rate of the anammox and the total nitrogen removal efficiency are improved, and the running time of the anammox is reduced.

Drawings

FIG. 1 is a schematic structural view of an anaerobic reactor employed in the present invention;

fig. 2 is a flow chart of the preparation of graphene oxide in the present invention, wherein (a) the preparation of graphene oxide; (b) raw material proportion of graphene oxide;

FIG. 3 is a graph of the reactor nitrogen concentration during the start-up period;

FIG. 4 is an SEM photograph of example 1: (a) inoculating sludge; (b) control sludge (no graphene oxide added) on day 40; (c) adding test group sludge on the 40 th day;

FIG. 5 is a graph of the total nitrogen removal rate of a redox mediator (AQDS) added during one run (24h) of the process of the present invention;

FIG. 6 is a graph showing the activity of anaerobic ammonium oxidizing bacteria added to a redox mediator (AQDS) in accordance with the method of the present invention;

FIG. 7 is a graph showing the change in the amount of anammox functional gene (hzo gene) added to redox mediator (AQDS) in the method of the present invention.

Detailed Description

The technical solution of the present invention will be further specifically described below by way of specific examples. It is to be understood that the practice of the invention is not limited to the following examples, and that any variations and/or modifications may be made thereto without departing from the scope of the invention.

In the present invention, all parts and percentages are by weight, unless otherwise specified, and the equipment and materials used are commercially available or commonly used in the art. The methods in the following examples are conventional in the art unless otherwise specified.

Example 1

A method for strengthening anaerobic ammonia oxidation denitrification process by a chemical method is characterized in that a proper amount of graphene oxide and anaerobic ammonia oxidation sludge are added into an anaerobic ammonia oxidation reactor to be mixed for treating wastewater so as to shorten the starting period of the anaerobic ammonia oxidation process, and after the anaerobic ammonia oxidation is successfully started, 2, 6-disulfonic acid Anthraquinone (AQDS) which is an oxidation reduction medium is added every day for strengthening the anaerobic ammonia oxidation treatment of the wastewater.

Anammox sludge, which is obtained from denitrifying sludge obtained from A2/O process of a certain urban sewage plant in Qingdao city, and is treated with K with pH of 7.2 ₂ HPO ₄ /KH ₂ PO ₄ And flushing the denitrification sludge for multiple times by using a buffer solution so as to flush out ammonia nitrogen, organic matters, nitrite and nitrate in the denitrification sludge.

The water inflow of the embodiment adopts manual water distribution. The water quality of the influent water was adjusted to about 7 pH using 30% HCl or 20% NaOH solution as shown in tables 1 and 2.

TABLE 1 quality of influent water

Item	Concentration (mg/L)	Item	Concentration (mg/L)
				Sodium nitrite	70	Potassium bicarbonate	125
Ammonium sulfate	70	Calcium chloride dihydrate	5
				Potassium chloride	7	Magnesium sulfate heptahydrate	7
Sodium chloride	5	EDTA-Fe ²⁺	50
				Potassium dihydrogen phosphate	54	Solution of trace elements	1.25ml/L

TABLE 2 microelement composition

The anaerobic ammonium oxidation reactor described in this example was a sequencing batch reactor, and the effective volume was 0.5L, and the structure of the reactor is shown in fig. 1.

In order to compare the test effects, 3 reactors are provided in this example for comparative tests, wherein 2 reactors are used as test groups and are marked as R2; the third reactor served as a control and was run without graphene oxide and AQDS, designated R1. The test group and the control group were otherwise identical.

Graphene Oxide in the embodiment is prepared by a Hummers method, in references Hummers W S, Offeman R E.preparation of graphical Oxide [ J ]. J Am ChemSoc,1958,80(6):1339, wherein the dosage ratio of graphite, 98% concentrated sulfuric acid and potassium permanganate is 1 g: 50 ml: 5g, see FIG. 2 for the preparation method.

Firstly, adding the anaerobic ammonia oxidation sludge into an anaerobic ammonia oxidation reactor, so that the sludge concentration is 10g/L, and the sludge retention time is 20 d. And adding 50mg of graphene oxide into the test group reactor to ensure that the concentration of the graphene oxide is 100mg/L, and the running periods of the test group and the control group are both 48 h. The stirring speed is controlled at 70-90r/min, so that the dissolved oxygen in the reactor is kept at about 0.5mg/L, and the temperature in the reactor is ensured to be 30 ℃ by circulating hot water.

According to the change of ammonia nitrogen of inlet and outlet water of the anaerobic ammonia oxidation reactor, the starting period of the anaerobic ammonia oxidation process is divided into 3 stages, namely a cell cracking stage (the ammonia nitrogen of outlet water is greater than that of inlet water), a starting lag phase (the ammonia nitrogen of outlet water is equivalent to that of inlet water), and a rapid growth stage (the ammonia nitrogen of outlet water and the nitrite nitrogen are rapidly reduced at the same time). At the initial stage of starting the anaerobic ammonia oxidation reactor, a large amount of microorganisms which are not suitable for the environment are cracked, so that a large amount of ammonia nitrogen is generated, and therefore the effluent of the reactor is even higher than the ammonia nitrogen concentration of the inlet water. As shown in figure 3, the highest ammonia nitrogen in effluent reaches 80mg/L in the initial startup period of the two reactors. Meanwhile, some organic matters can be generated due to the cracking of part of bacteria in the activated sludge during the period, so that the growth speed of heterotrophic denitrifying bacteria is far higher than that of autotrophic anammox bacteria. During the bacterial lysis phase, heterotrophic denitrifying bacteria dominate and cause a significant reduction in the effluent nitrite nitrogen concentration over this period of time. As shown in table 3, the bacterial lysis phase of R1 lasted for 20 days. However, the reactor only runs to day 15, the R2 reactor added with graphene almost finishes the cracking of bacteria, and the ammonia nitrogen concentration of the outlet water is higher than that of the inlet water. And then, starting the anaerobic ammonia oxidation process to enter a delay stage, wherein the ammonia nitrogen and nitrite nitrogen concentrations start to synchronously decrease although the removal rates are low, which means that the reactor starts to show the anaerobic ammonia oxidation activity. At this stage, it was found that the ammonia nitrogen concentration of the effluent water had some fluctuation, but the average value was lower than that of the feed water. The second phase of the R1 and R2 reactors lasted 16 days and 10 days, respectively.

TABLE 3 duration of the various phases of the reaction phase Start-Up phase

The successful start-up sign of the anaerobic ammonia oxidation process is that the removal rate of ammonia nitrogen and nitrite nitrogen by the reactor begins to increase rapidly at the same time. For example, the reactor R2 added with graphene runs for 25 to 45 days, the removal rate of ammonia nitrogen is increased from 28.57% to 88.57%, and the removal rate of nitrite nitrogen is increased from 54.28% to 78.57%. In contrast to R2, the normal anammox reactor was started to completion by the time the R1 reactor was run to day 60. The rapid increase in R1 and R2 lasted 24 days and 20 days, respectively. Through comparison of start-up periods of anaerobic ammonia oxidation reactors, it is found that the addition of graphene oxide shows a faster start-up speed in all 3 stages of the start-up of the reactors.

The anaerobic ammonium oxidation bacteria are regular or irregular spherical or ellipsoidal bacteria, and the size of the anaerobic ammonium oxidation bacteria is 0.8-1.1 mu m. Scanning electron microscope results (figure 4) show that the bacteria of the experimental group on day 38, inoculated with the sludge, are mainly brevibacterium, the particle size of the bacteria is between 0.5 and 1.0 mu m, which indicates that the bacteria are mainly denitrifying bacteria, after 40 days of culture, the spheroidicity bacteria are increased, the shape of the bacteria is consistent with that of typical anammox bacteria, and after the graphene oxide is added, irregular spherical or spheroidicity bacteria can be seen to be the main composition of the sludge, which indicates that anammox has been successfully started.

After two anaerobic ammonia oxidation reactors of an experimental group operate for 45 days, 2, 6-disulfonic acid Anthraquinone (AQDS) is added into the inlet water of one reactor, so that the concentration of the AQDS is 0.2mmol/L, the operation period is changed to 24 hours, namely the inlet water is replaced once a day, and the concentration of the AQDS in the inlet water every day is kept to be 0.2 mmol/L; the other reactor served as a control, with no AQDS added. The total nitrogen removal was compared between AQDS and non-AQDS added during one cycle, as shown in figure 5. After the AQDS is added, the total nitrogen removal rate is improved from 70% to 85% after 24h of reaction, which shows that the total nitrogen removal effect of the anaerobic ammonia oxidation is improved by adding the 2, 6-disulfonic acid Anthraquinone (AQDS) serving as the redox medium.

The activity of the anammox bacteria is another effective index for measuring the denitrification effect. As shown in FIG. 6, after the reactor was stably operated for 50 days, the activity of anammox bacteria was 0.1 g/(L) without adding graphene oxide and AQDS control group ² D) Activity of anammox bacteria in the graphene oxide-added test group of 0.25 g/(L) ² D) is improved by 2.5 times compared with a control group without adding graphene oxide and AQDS, and the activity of the anaerobic ammonium oxidation bacteria of the test group with graphene oxide and AQDS is 0.4 g/(L) ² D), the activity of the anaerobic ammonium oxidation bacteria can be greatly promoted by adding a redox medium, and the denitrification effect of the anaerobic ammonium oxidation process is enhanced by 1.6 times compared with a test group without adding AQDS and 4 times compared with a control group without adding graphene oxide and AQDS.

The denitrification capability of the anaerobic ammonia oxidation process can also be reflected by the change of the number of the hzo genes encoding key enzymes in the metabolic process of the anaerobic ammonia oxidation bacteria. The qPCR analysis (FIG. 7) showed that the number of hzo genes in the control group was 1.6X 10 in the reactor operated for 50 days ⁸ copies·g ^-1 (in terms of MLSS), the increase in the number of hzo genes after addition of graphene oxide was 8.5X 10 ⁸ copies·g ^-1 (in terms of MLSS), the number of hzo genes after addition of AQDS was 8.9X 10 ⁸ copies·g ^-1 The ratio (measured as MLSS) was 5.31 times and 5.56 times higher than that of the control group, which is consistent with the results of denitrification effect and anammox activity.

The application of the graphene oxide and the redox medium overcomes the problems of long start-up period, low activity of anaerobic ammonium oxidation bacteria and low total nitrogen removal rate of the anaerobic ammonium oxidation process, and provides a new idea for efficiently degrading nitrogen-containing pollutants.

The above-described embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way, and other variations and modifications may be made without departing from the spirit of the invention as set forth in the claims.

Claims

1. A method for strengthening anaerobic ammonia oxidation denitrification process by a chemical method is characterized by comprising the following steps: the method comprises the steps of adding a proper amount of graphene oxide and anaerobic ammonium oxidation sludge into an anaerobic ammonium oxidation reactor to be mixed to treat wastewater so as to shorten the starting period of an anaerobic ammonium oxidation process and realize the quick starting of anaerobic ammonium oxidation;

the method comprises a stage 1 and a stage 2, wherein the operation period of the stage 1 is 48h, and the operation period of the stage 2 is 24 h; when the anaerobic ammonia oxidation is successfully started, entering a stage 2, adding 2, 6-disulfonic acid anthraquinone into inlet water, and performing enhanced anaerobic ammonia oxidation treatment on the wastewater;

denitrifying sludge in A2/O process of municipal sewage treatment plant is selected as sludge in anaerobic ammonia oxidation process, and K with pH 7.2 is used ₂ HPO ₄ /KH ₂ PO ₄ Flushing the denitrification sludge for multiple times by using a buffer solution to flush out ammonia nitrogen, organic matters, nitrite and nitrate in the denitrification sludge;

the anaerobic ammonia oxidation reactor adopts a sequencing batch reactor, the dissolved oxygen is kept at 0.5-0.6mg/L, the reaction temperature is 30-35 ℃, and the pH value is 6.7-8.5; the sludge concentration in the reactor is 10-12 g/L, and the sludge retention time is 15-40 d;

the graphene oxide is added in the first water inlet, and the adding amount is 90-150 mg/L calculated by the volume of the reactor; the graphene oxide is prepared by a Hummers method, wherein the use amount ratio of graphite to 98% concentrated sulfuric acid to potassium permanganate is 1 g: 50 ml: 5g of the total weight of the mixture;

the 2, 6-disulfonic acid anthraquinone is added with the inlet water every time, so that the concentration of the 2, 6-disulfonic acid anthraquinone in the anaerobic ammonia oxidation process is 0.2mmol/L of inlet water.