A method for treating phenolic and nitrate composite wastewater by zero-valent iron-catalyzed ozone

Abstract

The present invention discloses a method for treating phenolic and nitrate composite wastewater by zero-valent iron-catalyzed ozone. It constructs an advanced oxidation system, using zero-valent iron as a catalyst and ozone as an oxidant to effectively treat the composite wastewater containing phenols and nitrates. In this wastewater treatment system, the wastewater treatment device is equipped with an external ozone generator to supply the required ozone. After ozone is adsorbed on the surface of zero-valent iron, through the interfacial interaction mechanism between the catalyst and ozone, reactive oxygen species are activated and generated. The reactive oxygen species first convert phenolic compounds into quinone intermediates that are easier to further process. Subsequently, the quinone intermediates utilize their reversible redox properties to effectively promote the reduction process of nitrate. The present invention not only improves the treatment efficiency, but also due to its heterogeneous catalytic characteristics, there is no need to adjust the pH value of the wastewater, simplifying the treatment process, and having high practical application value and promotion potential.

Description

Technical Field

[0001] The present invention relates to a method for treating phenolic and nitrate compound wastewater by using zero-valent iron to catalyze ozone, belonging to the field of environmental pollution treatment. Background Art

[0002] In recent years, various types of water pollution in China have become increasingly diversified and complex, mainly manifested as the coexistence of multiple types and forms of pollutants. According to statistics from relevant research institutions, the emission density of phenolic pollutants from industrial sources in the river and sea basins of China can reach up to 53 kg / km 2 , while at the same time, the nitrate concentration in this basin exceeds 90 mg / L, specifically showing obvious combined pollution of organic phenols and nitrates. This is because in the process of industrial production, industries such as petrochemical, pesticide, smelting, and coking generally use phenolic compounds and nitrogen-containing chemicals as raw materials or auxiliaries. The wastewater generated during the production process of these substances contains a large amount of phenols and nitrates. If not properly treated, they will enter the water environment, leading to serious ecological problems such as toxic algal blooms, black and odorous water bodies, and ecological imbalance, and further threatening public health. In response to this problem, China has emphasized the importance of pollution prevention and control in the ecological environment protection plan, especially proposing a new strategy for the coordinated control of multiple pollutants to promote the sustainable development of the industrial economy.

[0003] There are significant technical challenges in the coordinated control of combined pollution of phenols and nitrates. First, the types of target pollutants in the wastewater are heterogeneous, which makes it difficult for traditional wastewater treatment technologies to achieve normal effects. For example, flocculation and sedimentation technologies cannot effectively remove highly soluble nitrates; while adsorption methods are difficult to remove both phenols and nitrates due to the selectivity of adsorbents. In addition, these technologies may have high operating costs and may cause secondary pollution. Biological denitrification is a potential technology that can achieve the synchronous treatment of phenols and nitrates. In this method, phenolic compounds and nitrates serve as electron donors and acceptors respectively, and the removal of pollutants is achieved through the electron transfer process mediated by denitrifying bacteria. However, the effectiveness of this method is limited by various environmental factors, including pH value, dissolved oxygen, temperature, and carbon-nitrogen ratio. In particular, the toxicity of phenolic compounds may inhibit the physiological activity of denitrifying bacteria, thus affecting the treatment effect.

[0004] In view of the limitations of the existing technology, there is an urgent need to develop new wastewater treatment technologies. These new wastewater treatment technologies should have high reactivity, wide adaptability, and economy to adapt to different environmental conditions and effectively remove combined pollutants of phenols and nitrates. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for treating phenolic and nitrate composite wastewater by zero-valent iron-catalyzed ozone, which has high reactivity, wide adaptability and economy, so as to solve the deficiencies existing in the above-mentioned prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for treating phenolic and nitrate composite wastewater by zero-valent iron-catalyzed ozone, comprising the following steps:

[0008] Put the phenolic and nitrate composite wastewater with a pH value between 2 and 12 into zero-valent iron powder, then connect an ozone generator with an air source, introduce ozone into the wastewater, and react for more than 30 minutes.

[0009] Preferably, the phenolic compounds in the phenolic and nitrate composite wastewater are at least one of phenol, p-chlorophenol, and p-aminophenol, and the concentration converted to phenol is 100-1000 mg / L.

[0010] Preferably, the nitrate in the phenolic and nitrate composite wastewater is soluble nitrate, and the concentration of nitrate ion is 20-200 mg / L.

[0011] Preferably, the particle size of the zero-valent iron powder is 1 nm-500 μm.

[0012] Preferably, the dosage of the zero-valent iron powder is 0.1-1.0 g / L of wastewater.

[0013] Preferably, in the ozone generator, the current is set to 0.5-1.0 A, and the gas flow rate is set to 10-200 mL / min.

[0014] Theoretical analysis:

[0015] In the present invention, zero-valent iron catalyzes ozone, and reactive oxygen species are generated through the interface interaction mechanism between the two. First, phenolic compounds are converted into quinone intermediates, and the reversible redox characteristics of quinone intermediates are used to mediate the efficient reduction of nitrate, realizing the synergistic treatment of phenolic compounds and nitrate.

[0016] Zero-valent iron (ZVI) presents a typical core-shell structure. The inner core of zero-valent iron (Fe 0 ) as an electron storage library is wrapped by an outer iron oxide shell layer, and is in a stable state and can already be industrially produced. Iron elements have the advantages of high crustal abundance, environmental friendliness, and strong power supply, and are widely used in various wastewater treatments. However, in some cases, the reaction effect is not ideal enough.

[0017] The inner iron core of zero-valent iron is wrapped by an iron oxide shell layer, and the surface oxide layer is composed of FeO, Fe3 O 4 , Fe 2 O 3 , FeOOH and other forms of iron oxides, which can provide sites for the adsorption and activation of ozone in this reaction, and the electrons in the iron core can also be transferred to the surface through the oxide layer to react with the adsorbed ozone molecules.

[0018] Zero-valent iron catalyzes ozone to produce reactive oxygen species (ROS) in two main pathways: ozone adsorption induced by hydroxyl groups on the surface of zero-valent iron and activation ( Figure 1 ), avoiding the strong base dependence of the traditional homogeneous ozone catalytic process (pKa = 11.8); the other is the zero-valent iron surface-bound ferrous iron electron-donating driven surface adsorbed ozone reduction activation ( Figure 2 ). Therefore, from the perspective of the reaction pathway, in addition to the ring-opening and deep oxidation to small molecules, the most likely oxidation products of phenolic compounds induced by ROS are quinone compounds ( Figure 3 ). Quinone redox electron mediators have the ability to drive low-barrier, kinetically favorable nitrate reduction reactions.

[0019] The present invention uses zero-valent iron to catalyze ozone to generate ROS to reduce phenolic compounds and convert them into quinone intermediates, which are used as redox electron mediators to reduce and remove nitrates, thereby achieving the coordinated removal of phenolic compounds and nitrates, solving the problem that traditional wastewater treatment methods cannot treat two types of pollutants at the same time. Moreover, the heterogeneous catalytic reaction has a wide pH application range and is highly adaptable to actual pollution scenarios.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] (1) The efficient synergistic removal of phenolic compounds and nitrate ions is achieved through zero-valent iron catalyzed ozone. The applicable pH range is wide and no additional adjustment is required. The raw materials used are economical, environmentally friendly, easy to operate, and do not produce secondary pollution.

[0022] (2) The ability of phenolic compounds to transform intermediates, quinones, to mediate redox electron transfer is utilized to accelerate electron transfer between zero-valent iron and nitrate. This is the first time this technical route has been proposed in this field and is extremely innovative.

[0023] (3) The present invention is applicable to various industrial, agricultural, and medical sewage treatment fields, has industrial application prospects, and has good application prospects in the field of environmental governance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the principle of hydroxyl-induced ozone catalysis in the oxide layer on the surface of zero-valent iron.

[0025] Figure 2Schematic diagram of zero-valent iron-catalyzed ozone generation of ROS with surface ferrous as the active site.

[0026] Figure 3 Schematic diagram of ROS oxidizing phenol to quinone (taking phenol as an example). Detailed implementation manners

[0027] The technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only used to illustrate the technical solutions of the present invention and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts are still within the protection scope of the present invention.

[0028] Example 1: Treatment of simulated phenol and nitrate composite wastewater by zero-valent iron-catalyzed ozone

[0029] Prepare the raw liquid for the simulated wastewater: the concentration of phenol is 500 mg / L, and the concentration of nitrate in the soluble nitrate solution is 100 mg / L; compound phenol (500 mg / L) - nitrate (100 mg / L) to simulate phenolic and nitrate composite wastewater. The initial pH value of this composite wastewater is adjusted to 7.4.

[0030] Add industrial iron powder (particle size 150 - 500 μm) at a ratio of 1 g / L to 100 mL of phenolic and nitrate composite wastewater, connect an ozone generator with an air source, set the current of the ozone generator to 0.5 A, and control the flow rate to be 10 mL / min to introduce ozone into the reaction pool. Start the reaction, take samples every 5 minutes, use high-performance liquid chromatography to test the concentrations of phenol and benzoquinone, and use ion chromatography to test the nitrate concentration. The whole reaction lasts for 1 hour.

[0031] As a control, set a single phenol simulated wastewater treatment control group, where the wastewater does not contain nitrate, and keep the same material dosage and ozone flow rate, and react for 1 hour.

[0032] As a control, set a single nitrate simulated wastewater treatment control group, where the wastewater does not contain phenol, and keep the same material dosage and ozone flow rate, and react for 1 hour.

[0033] After the above groups react for 1 hour, test the concentrations of phenol and nitrate in the wastewater, and the removal results are shown in Table 1 below:

[0034] Table 1 Treatment of different wastewaters by zero-valent iron-catalyzed ozone

[0035]

[0036] Zero-valent iron-catalyzed ozonation was used to treat single-phenol, single-nitrate simulated wastewater and phenolic and nitrate composite wastewater for 1 hour throughout the process: the degradation amounts of phenol were 391.9 mg / L and 499.4 mg / L respectively, and benzoquinone was produced in both reactions. The concentration of benzoquinone first increased and then decreased; zero-valent iron-catalyzed ozonation was used to treat single nitrate and phenol-nitrate composite wastewater, and the nitrate removal amounts were 0.04 mg / L and 96.5 mg / L respectively. This indicates that the simultaneous presence of phenol and nitrate in the wastewater can be rapidly removed by the zero-valent iron-catalyzed ozonation technology.

[0037] Example 2

[0038] Prepare the raw material liquid for the simulated wastewater: the phenol concentration is 500 mg / L, and the nitrate concentration in the soluble nitrate solution is 100 mg / L; compound phenol (500 mg / L) - nitrate (100 mg / L) to simulate phenolic and nitrate composite wastewater. The initial pH value of this composite wastewater was adjusted to 7.4.

[0039] Industrial iron powder (particle sizes are 150 - 500 μm, 0.5 - 10 μm, 1 - 100 nm) with dosages of 0.1 g / L, 0.5 g / L, and 1.2 g / L respectively was added to 100 mL of phenolic and nitrate composite wastewater. An ozone generator with an external air source was used, and the current of the ozone generator was set to 0.5 A. Ozone was introduced into the reaction pool at a controlled flow rate of 10 mL / min. The reaction was started, and samples were taken every 5 minutes. High-performance liquid chromatography was used to test the concentrations of phenol and p-benzoquinone, and ion chromatography was used to test the nitrate concentration. The reaction lasted for 1 hour throughout the process.

[0040] After 1 hour of reaction for each group above, the concentrations of phenol, benzoquinone, and nitrate in the wastewater were tested, and the removal results are shown in Table 2 below: The reaction results of removing wastewater at different dosing concentrations of industrial iron powder (particle sizes are 150 - 500 μm, 0.5 - 10 μm, 1 - 100 nm):

[0041]

[0042] Example 3

[0043] Prepare the raw material liquid for the simulated wastewater: the concentrations of p-chlorophenol and p-aminophenol are 200 mg / L and 500 mg / L respectively, and the nitrate concentration in the soluble nitrate solution is 200 mg / L; compound them to simulate phenolic and nitrate composite wastewater. The initial pH values of this composite wastewater were adjusted to 2, 7.4, and 12 respectively.

[0044] Industrial iron powder (particle size 150 - 500 μm), with dosages of 0.5 g / L and 1.0 g / L respectively, was added into 100 mL of phenolic and nitrate composite wastewater. An ozone generator with an external air source was used, and the current of the ozone generator was set to 0.5 A. The ozone was introduced into the reaction tank at a flow rate of 50 mL / min. The reaction was started, samples were taken every 5 minutes, and the concentrations of phenols and benzoquinone were measured by high performance liquid chromatography, while the nitrate concentration was measured by ion chromatography. The whole reaction lasted for 1 hour.

[0045] After 1 hour of reaction for each group above, the concentrations of phenols and nitrate in the wastewater were measured, and the removal results are shown in the reaction results of Table 3 below:

[0046] Table 3 Results of removing wastewater at different dosing concentrations and pH values

[0047]

[0048] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating phenol and nitrate composite wastewater by zero-valent iron catalytic ozone, characterized in that: Add zero-valent iron powder into the composite wastewater containing phenols and nitrates, whose pH value is between 2 and 12, and then connect the ozone generator with air source to pass ozone into the wastewater for more than 30 minutes; The phenolic compound in the phenol and nitrate composite wastewater is at least one of phenol, p-chlorophenol and p-aminophenol, and the concentration converted into phenol is 100-1000 mg / L; The nitrate in the phenol and nitrate composite wastewater is a soluble nitrate, and the concentration of the nitrate ion is 20 to 200 mg / L; The particle size of the zero-valent iron powder is 1 nm to 500 μm.

2. The method for treating phenol and nitrate composite wastewater by zero-valent iron catalytic ozone as claimed in claim 1, characterized in that: The dosage of the zero-valent iron powder is 0.1-1.0 g / L of wastewater.

3. The method for treating phenol and nitrate composite wastewater by zero-valent iron catalytic ozone as claimed in claim 1, characterized in that: In the ozone generator, the current is set to 0.5-1.0A, and the gas flow rate is set to 10-200mL / min.

Images