A method for electro-dialysis redox treatment of nitrogen and phosphorus elements in aquaculture wastewater

Abstract

The present invention provides a method for electro-dialysis redox treatment of nitrogen and phosphorus elements in aquaculture wastewater, which includes constructing an electrolytic redox system. The electrolytic redox system includes a power supply and a membrane reaction cell: the membrane reaction cell includes an anode plate, an anion exchange membrane, a cation exchange membrane, and a cathode plate arranged in sequence; and a denitrification chamber, a feed liquid chamber, and a dephosphorization chamber are sequentially formed between adjacent components in the direction from the anode plate to the cathode plate in the membrane reaction cell; seawater aquaculture wastewater is injected into the denitrification chamber and the dephosphorization chamber, and an acidic ferric chloride solution is used as the feed liquid in the feed liquid chamber; then an electric reaction is carried out. By this method, the nitrogen element and the phosphorus element in the aquaculture wastewater are removed simultaneously in one electrolysis, significantly improving the working efficiency and reducing the wastewater treatment cost.

Description

Technical Field

[0001] The present invention relates to the field of treating mariculture wastewater by electro-oxidation and reduction with an organic membrane, specifically, the research on denitrification and dephosphorization of mariculture wastewater by electrodialysis oxidation and reduction. Background Art

[0002] Mariculture is a very large industry in China. With the rapid development of China's economy and the increasing living standards of the people, the demand and consumption ability of Chinese residents for marine products are getting higher and higher, and the mariculture industry is growing day by day. However, mariculture will produce a large amount of wastewater, which contains a lot of metabolites, nutrient salts and drug residues. These substances contain a large amount of nitrogen and phosphorus elements, and direct discharge will cause great damage to the environment and also have a harmful impact on the survival of marine products.

[0003] Traditional methods for denitrification and dephosphorization of wastewater mainly include the oxidation ditch method, the AAO method, the SBR method, etc. These methods can remove nitrogen, phosphorus and other elements in wastewater to a certain extent, but these methods have a large floor area, high process energy consumption, the salinity affects the activities of denitrifying bacteria, polyphosphate-accumulating bacteria, etc., and the nitrogen-phosphorus ratio in mariculture wastewater cannot meet the requirements of their denitrification and dephosphorization, so they are not suitable for treating mariculture wastewater.

[0004] For the emerging electrolytic treatment technology for denitrification and dephosphorization of mariculture wastewater, generally, denitrification is carried out first, then the anode plate material is replaced and dephosphorization is carried out. The process is cumbersome, the raw materials are relatively expensive, the energy consumption is high, and the economy is low. Summary of the Invention

[0005] The present invention aims to provide a method for electro-denitrification and dephosphorization of mariculture wastewater, and treat elements such as nitrogen and phosphorus in mariculture wastewater by electrodialysis oxidation and reduction. This method can better remove nitrogen and phosphorus elements in mariculture wastewater and is economical and efficient.

[0006] The present invention provides a method for treating nitrogen and phosphorus elements in mariculture wastewater by electrodialysis oxidation and reduction, including the following steps

[0007] (1) Construct an electrolytic oxidation and reduction system, and the electrolytic oxidation and reduction system includes a power supply and a membrane reaction tank: the membrane reaction tank includes an anode plate, an anion exchange membrane, a cation exchange membrane, and a cathode plate arranged in sequence; and denitrification chambers, a feed liquid chamber, and a dephosphorization chamber are sequentially formed between adjacent components in the direction from the anode plate to the cathode plate of the membrane reaction tank.

[0008] (2) Inject mariculture wastewater into the denitrification chamber and the dephosphorization chamber, and the feed liquid chamber is filled with an acidic ferric chloride solution.

[0009] (3) Turn on the power supply, record the voltage, current and reaction time; measure the conductivity in the feed liquid chamber; measure the pH values of the liquids in the denitrification chamber and the dephosphorization chamber, and intermittently take samples to determine the nitrogen and phosphorus element contents of the liquids in the denitrification chamber and the dephosphorization chamber.

[0010] (4) After the conductivity of the feed liquid chamber gradually decreases to a stable state during the reaction, cut off the power supply.

[0011] During the reaction, Cl - enters the denitrification chamber through the anion exchange membrane, and Fe 3+ enters the dephosphorization chamber through the cation exchange membrane. Cl - loses electrons at the anode plate to generate chlorine gas, which dissolves in water to form hypochlorous acid, that is, effective residual chlorine. Ammonia nitrogen in water is oxidized to nitrogen gas and removed when contacting with the effective residual chlorine. The oxygen generated on the anode plate will oxidize nitrite to nitrate and precipitate. Fe 3+ entering the dephosphorization chamber reacts with phosphate ions in the aqueous solution to form a precipitate and is removed.

[0012] Preferably, the measurement of the nitrogen element content in the step (3) includes the determination of total nitrogen by alkaline potassium persulfate ultraviolet spectrophotometry and the determination of nitrate nitrogen by zinc-chromium reduction method. The measurement of the phosphorus element content in the step (3) includes the determination of total phosphorus by potassium sulfate oxidation method.

[0013] Preferably, a pipeline and an internal circulation pump are provided between the denitrification chamber and the dephosphorization chamber and are conducted through them. It is intermittently opened during the reaction, and the overall denitrification and dephosphorization effect can be achieved.

[0014] Preferably, the anion exchange membrane is CJMA-2 and the cation exchange membrane is CJMC-2.

[0015] Preferably, the cathode plate and the anode plate are made of graphite electrodes. Since the ferric chloride solution used in this method can provide chloride ions and ferric ions that can participate in denitrification and dephosphorization respectively, there is no need to use iron electrodes to generate ferric ions, which can reduce the electrode cost.

[0016] Preferably, the mass fraction of ferric chloride in the acidic ferric chloride solution is 45% and the mass fraction of hydrochloric acid is 5%.

[0017] Preferably, the voltage is maintained at 20 - 40V.

[0018] Preferably, the pH values of the denitrification chamber and the dephosphorization chamber should be maintained at 7.

[0019] Preferably, the current density is 20 - 40 mA / cm 2 .

[0020] The method provided by the present invention has a simple process flow, a small footprint of the process equipment, low energy consumption, good economy, and greatly reduces the treatment cost. Moreover, this method constructs an efficient electrodialysis reaction system for electrolytic treatment of aquaculture wastewater. And by using acidic ferric chloride as a reagent, nitrogen and phosphorus elements in the wastewater can be removed simultaneously during a single electrolysis process, significantly improving the working efficiency and reducing the wastewater treatment cost. The experimental results show that the removal rates of nitrogen and phosphorus elements in the seafood aquaculture wastewater are 92% and 85% respectively. In a relatively wide current density range, the current efficiency can reach over 70%. And under the optimal experimental conditions, the energy consumption is 1.2585 kWh / kg. During the exploration of the reaction system efficiency, it is found that maintaining the pH of the wastewater at 7 can keep the effect of the reaction system at a relatively high level, laying an important theoretical foundation for the industrial treatment of aquaculture wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of the electrodialysis redox reaction cell adopted by the present invention.

[0022] Figure 2 It is the current change under different voltage conditions.

[0023] Figure 3 It is the removal rates of total nitrogen and total phosphorus under different voltage conditions.

[0024] Figure 4 It is the removal rates of total nitrogen and total phosphorus under different pH conditions of the wastewater.

[0025] Figure 5 It is the energy consumption and current efficiency under different ferric chloride concentrations.

[0026] Figure 6 It is the energy consumption and current efficiency under different current density conditions.

[0027] Figure 7 It is the removal rates of total nitrogen and total phosphorus under different current density conditions.

[0028] Figure 8 It is the removal rate of nitrate nitrogen under different current density conditions. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention provides a method for electrodialysis redox treatment of nitrogen and phosphorus elements in aquaculture wastewater, including the following steps: (1) constructing an electrolytic redox system, and the electrolytic redox system includes a power supply and a membrane reaction cell: the membrane stack includes an anode plate, an anion exchange membrane, a cation exchange membrane, and a cathode plate arranged in sequence; and between adjacent components in the direction from the anode plate to the cathode plate of the membrane reaction cell, a denitrification chamber, a feed liquid chamber, and a dephosphorization chamber are formed in sequence.

[0030] (2) The liquid chamber contains acidic ferric chloride solution.

[0031] (3) Total nitrogen is determined by the alkaline potassium persulfate ultraviolet spectrophotometry method, nitrate nitrogen is determined by the zinc-chromium reduction method, and total phosphorus is determined by the potassium sulfate oxidation method.

[0032] (4) Turn on the power supply, record the voltage, current, pH of the wastewater, and conductivity of the liquid. Take intermittent samples for measurement until the conductivity of the liquid chamber is stable, then cut off the power supply, and the denitrification and dephosphorization of the mariculture wastewater are completed.

[0033] The method provided by the present invention has a simple process flow, a small footprint of the process device, low energy consumption, good economy, and greatly reduces the treatment cost. Moreover, this method combines various synergistic effects such as electrolysis, precipitation, flotation, oxidation-reduction, etc., with few secondary pollutants and easy treatment of the waste residue.

[0034] See Figure 1 , Figure 1 is a schematic structural diagram of the electrodialysis oxidation-reduction reaction cell adopted by the present invention. The reaction cell includes an anode plate, an anion exchange membrane, a cation exchange membrane, and a cathode plate arranged in sequence; and a denitrification chamber, a liquid chamber, and a dephosphorization chamber are successively formed between adjacent components in the direction from the anode plate to the cathode plate in the reaction cell. The CL - generated by the electrolysis of the ferric chloride solution in the liquid chamber enters the denitrification chamber through the anion exchange membrane, and Fe 3+ enters the dephosphorization chamber through the cation exchange membrane. Turn on the power supply, record the voltage, current, pH of the wastewater, and conductivity of the liquid. Take intermittent samples for measurement until the conductivity of the liquid chamber is stable, then cut off the power supply. At the beginning of the reaction, the conductivity of the liquid chamber drops rapidly, and the current also starts to drop with time. After a certain period of time, the current starts to rise.

[0035] Example 1: After loading the membrane stack according to the foregoing content, prepare a 35% ferric chloride solution containing 5% hydrochloric acid. Take 1 L of ferric chloride and introduce it into the liquid chamber, and take 2 L of mariculture wastewater and introduce it into the denitrification and dephosphorization chamber. Open the internal circulation system to make the solutions in the denitrification and dephosphorization chambers communicate with each other to achieve complete denitrification and dephosphorization. Connect the power supply, control the voltage at 10V, 20V, 30V, and 40V respectively, and record the time, voltage, current, pH in the denitrification and dephosphorization chamber, and conductivity of the liquid. Take intermittent samples for measurement until the conductivity of the liquid chamber is stable, then cut off the power supply. Maintain the pH in the denitrification and dephosphorization chamber at 7 throughout the process. As Figure 2 shows the change of current under different voltage conditions. It can be seen from the figure that the current decreases with time and will ultimately approach zero infinitely. This is because when the reaction proceeds to the later stage, the ion concentration in the liquid chamber is already very small, and the ions conducting electricity are the hydrogen ions electrolyzed from pure water. Attached Figure 2It can be seen that at the beginning, the currents of 10V and 20V increase first and then decrease. The reason is that at the very beginning, the voltage remains unchanged and the ion concentration in the liquid chamber is certain. When the power is first turned on, a buffering time is required, so the current is relatively small. The difference between 30V and 40V is not significant. Then, according to the appendix Figure 3 The removal rates of total nitrogen and total phosphorus under different voltages. It can be seen from the figure that the removal rate reaches over 90% at 30V. Considering the economic principle, the removal rates of total nitrogen and total phosphorus are relatively high when the voltage is between 20V and 40V, and the efficiency is the highest when 30V is selected.

[0036] Example 2: After loading the membrane stack according to the foregoing content, prepare a 35% ferric chloride solution containing 5% hydrochloric acid. Take 1L of ferric chloride and introduce it into the liquid chamber. Take 2L of mariculture wastewater and introduce it into the denitrification and dephosphorization chamber. Turn on the internal circulation system to make the solutions in the denitrification and dephosphorization chambers communicate with each other to achieve complete denitrification and dephosphorization. Connect the power supply, set the load voltage to 30V, record the time, voltage, current, pH in the denitrification and dephosphorization chamber, and the conductivity of the liquid. Take samples intermittently for measurement until the conductivity of the liquid chamber is stable, and then cut off the power supply. During the whole process, maintain the pH in the denitrification and dephosphorization chamber at 2, 5, 7, 9, and 11 respectively. As Figure 4 Shown is the removal rates of total nitrogen and total phosphorus of the wastewater under five pH conditions. It can be seen from the figure that when the pH of the wastewater is acidic or alkaline, the removal rate is very low, less than 50%. When the pH is 7, the removal rate of total nitrogen and total phosphorus can reach over 80%. Therefore, the optimal pH condition for the wastewater is 7.

[0037] Example 3: After loading the membrane stack according to the foregoing content, prepare ferric chloride solutions of 15%, 25%, 35%, 45%, and 55% respectively, each containing 5% hydrochloric acid. Take 1L of ferric chloride and introduce it into the liquid chamber. Take 2L of mariculture wastewater and introduce it into the denitrification and dephosphorization chamber. Turn on the internal circulation system to make the solutions in the denitrification and dephosphorization chambers communicate with each other to achieve complete denitrification and dephosphorization. Connect the power supply, set the load voltage to 30V, record the time, voltage, current, pH in the denitrification and dephosphorization chamber, and the conductivity of the liquid. Take samples intermittently for measurement until the conductivity of the liquid chamber is stable, and then cut off the power supply. The appendix Figure 5 Shows the current efficiency and energy consumption of ferric chloride solutions with different concentrations. It can be seen from the figure that as the concentration increases, the current efficiency gradually decreases and the energy consumption gradually increases. The energy consumption is 1.2382 kw·h / kg at a 45% ferric chloride concentration, and the current efficiency also reaches 65%. According to the economic principle, this is selected as the optimal concentration.

[0038] Example 4: After the membrane stack is loaded according to the foregoing content, a 45% ferric chloride solution containing 5% hydrochloric acid is prepared. 1 L of ferric chloride is introduced into the feed liquid chamber, and 2 L of mariculture wastewater is introduced into the denitrification and dephosphorization chamber. The internal circulation system is turned on to allow the solutions in the denitrification and dephosphorization chambers to communicate with each other until complete denitrification and dephosphorization are achieved. The power supply is connected, the load voltage is set to 30 V, and the time, voltage, current, pH in the denitrification and dephosphorization chamber, and the conductivity of the feed liquid are recorded. Samples are taken intermittently for measurement until the conductivity of the feed liquid chamber is stable, and then the power supply is cut off. During the whole process, the current density is set to 10 mA / cm 2 , 20 mA / cm 2 , 30 mA / cm 2 , 40 mA / cm 2 , 50 mA / cm 2 Appendix Figure 6 shows the energy consumption and current efficiency under different current density conditions. It can be seen from the figure that within the current density range of 20 - 40 mA / cm 2 , there are good current efficiency and low energy consumption. Figures 7-8 shows the removal rates of total nitrogen, total phosphorus, and nitrate nitrogen under different current density conditions. Combining the energy consumption and current efficiency, the optimal current density is 20 - 40 mA / cm 2 .

[0039] The above is only the preferred embodiment of the present invention. For those of ordinary skill in the art, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for electro-dialysis redox treatment of nitrogen and phosphorus elements in aquaculture wastewater, characterized in that, it comprises the following steps (1) Construct an electrolytic redox system, and the electrolytic redox system includes a power supply and a membrane reaction cell: The membrane reaction cell includes an anode plate, an anion exchange membrane, a cation exchange membrane, and a cathode plate arranged in sequence; and a denitrification chamber, a feed liquid chamber, and a dephosphorization chamber are sequentially formed between adjacent components in the direction from the anode plate to the cathode plate in the membrane reaction cell; (2) Inject mariculture wastewater into the denitrification chamber and the dephosphorization chamber, and the feed liquid chamber is an acidic ferric chloride solution; (3) Turn on the power supply, record the voltage, current, and reaction time; measure the conductivity in the feed liquid chamber; measure the pH values of the liquids in the denitrification chamber and the dephosphorization chamber, and intermittently sample to determine the nitrogen element and phosphorus element contents of the liquids in the denitrification chamber and the dephosphorization chamber; (4) After the conductivity in the feed liquid chamber gradually decreases to a stable state during the reaction, cut off the power supply.

2. The method according to claim 1, characterized in that, the measurement of the nitrogen element content in the step (3) includes the determination of total nitrogen by alkaline potassium persulfate ultraviolet spectrophotometry and the determination of nitrate nitrogen by zinc-chromium reduction method, and the measurement of the phosphorus element content in the step (3) includes the determination of total phosphorus by potassium sulfate oxidation method.

3. The method according to claim 1, characterized in that, A pipeline and an internal circulation pump are provided between the denitrification chamber and the dephosphorization chamber and are conducted through, and are intermittently opened during the reaction.

4. The method according to claim 1, characterized in that, The anion exchange membrane is CJMA-2, and the cation exchange membrane is CJMC-2.

5. The method according to claim 1, characterized in that, The materials of the cathode plate and the anode plate are graphite electrodes.

6. The method according to claim 1, characterized in that, The mass fraction of ferric chloride in the acidic ferric chloride solution is 45%, and the mass fraction of hydrochloric acid is 5%.

7. The method according to claim 1, characterized in that, The voltage is maintained at 20 - 40V.

8. The method according to claim 1, characterized in that, The pH values of the denitrification chamber and the dephosphorization chamber should be maintained at 7.

9. The method according to claim 1, characterized in that, The current density is maintained at 20 - 40 mA / cm 2 .

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