AU2016388020A1

AU2016388020A1 - Composite membrane separation method applicable to desalting and recycling of sewage

Info

Publication number: AU2016388020A1
Application number: AU2016388020A
Authority: AU
Inventors: Zimeng LI; Jinxing Ma; Chen PAN; Qiaoying Wang; Xueye Wang; Zhiwei Wang; Zhichao WU; Hongguang YU; Junjian Zheng
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2016-01-22
Filing date: 2016-10-27
Publication date: 2018-08-09
Anticipated expiration: 2036-10-27
Also published as: JP6583868B2; CN105692817A; JP2019506292A; WO2017124798A1; AU2016388020B2; CN105692817B

Abstract

Disclosed is a composite membrane separation method applicable to desalting and recycling of sewage. The method achieves desalting of the sewage through a filtering and adsorbing effect of a conductive composite membrane reactor. The conductive composite membrane reactor consists of a water inlet system (1), a power source system (2), a membrane reactor (3), a water outlet control system (4) and a clean water tank (5). The membrane reactor (3) consists of a reaction tank, a composite membrane module (6) and a stirring system. The composite membrane module (6) has a flat sheet membrane configuration and consists of a cathode composite membrane (8), an anode composite membrane (9) and a separation layer (10), wherein the cathode composite membrane (8) is formed by adhering, using a polymeric material, a cathode electrode (12) with a cathode current collector (11) and the anode composite membrane (9) is formed by adhering, using a polymeric material, an anode electrode (13) with an anode current collector (14). The cathode composite membrane (8) and the anode composite membrane (9) are separated by the separation layer (10) to avoid a short circuit. The cathode current collector (11) is disposed on the same side as a water inlet, the anode current collector (14) is disposed on the same side as a water outlet. Influent water first flows through the cathode current collector (11) and the cathode electrode (12), then the separation layer (10), and then the anode electrode (13) and the anode current collector (14), and is discharged from the conductive composite membrane reactor in the form of membrane effluent water.

Description

Composite membrane separation method applicable to desalinating and recycling of sewage

TECHNICAL FIELD

The invention relates to a composite membrane separation method applicable to desalinating and recycling of sewage, and a use of coupling principle of membrane filtration and electric adsorption to remove ions in sewage and improve the quality of effluent, which belongs to the field of sewage (wastewater) treatment.

BACKGROUND

With the rapid development of the social economy, the environmental situation is aggravated. Among the many environmental problems, the shortage of water resources has become increasingly serious, which becomes a bottleneck restricting the sustainable development of the social economy. Under such circumstances, promoting water conservation is no longer sufficient to meet current water demand. The development and utilization of unconventional water sources, such as desalination of brackish water, recycling of industrial waste water, and deep treatment and reuse of municipal waste water, are urgently needed. However, there are higher concentrations of ions such as Cl', NO3", SO42', and various metal ions in the groundwater in some rural areas, domestic sewage mixed with seawater in coastal cities, and wastewater in industries such as chemical engineering, printing, dyeing, food processing, and so on. Improper handling may cause serious water pollution problems.

In addition, it will affect drinking water safety and damage human health if heavy metal ions enter the water. For example, lead may induce anemia, the accumulation of mercury may cause rickets, and cadmium may cause bone pain. Excessive intake of copper can damage the liver. The arsenic compounds are highly toxic and have carcinogenic effects. Therefore, it is necessary to carry out desalination treatment to realize the utilization of these unconventional water sources. It has become one of the current research hotspots to achieve the goal of high standard discharge or effective reuse.

In recent years, the electric adsorption technology has attracted widespread attention due to its unique advantages in removal efficiency and energy consumption. By applying low-voltage DC power supply, electric adsorption technology can remove contaminating ions to achieve wastewater purification.

Compared with other water treatment technologies, electric adsorption technology is simple to operate and maintain, and has long service life time, low energy consumption, no secondary pollution. It also has a good removal rate of soluble pollutants. However, traditional electric adsorption processes are more sensitive to particulate pollutants. The introduction of particulate not only reduces the desalination efficiency, but also plugs the electrode, which increases the equipment maintenance costs. Therefore, it is necessary to set up a pretreatment process at the front end of the electric adsorption process to intercept particulates in treating of saline sewage containing particulate pollutants. Thereby, the footprint of the electric adsorption process, equipment costs, and operating steps were increased.

On the other hand, the membrane separation method is widely used in the field of sewage treatment because of its excellent solid-liquid separation efficiency. Membrane separation technology is an effective way to effectively solve the problem of particle pollution in the electric adsorption process. The main problem in the development of the membrane separation process is membrane fouling. Applying a DC electric field, the surface of the membrane is negatively charged and repels the negatively charged particulate pollutants in wastewater, to control membrane fouling.

Through coupling electric adsorption and membrane separation process, a new type of conductive composite membrane electric adsorption desalination process may be formed, which will achieve particle interception and ion removal simultaneously. This may develop new ideas for the treatment of saline sewage.

However, the existing research results and literature reports mainly focus on the optimization of the electric adsorption process. The results concerning desalination in domestic patents are also concentrated on the conditions of membrane separation and electric adsorption independently, such as Kiuchi Takafumi (“Membrane separation apparatus and membrane separation method”, Invention Patent Publication No. CN103052437A), Chang zheng (“Method for selectively removing Fe2+ and/or Fe3+ from industrial waste water through electric adsorption technology”, invention patent publication number CN104609518A). The processes coupling of membrane separation and electric adsorption are rarely reported. There is only a few of processes combining the two, such as Zhang Hongtao (“Membrane-electric adsorption device for a desalination system”, invention patent publication number CN103693718A). Zhang used ion-exchange membranes in combination with an electric adsorption process to desalt wastewater. The cation exchange membrane and the anion exchange membrane increase the selective permeability of cations and anions, respectively. However, the ion exchange membrane cannot act as a sewage filter. Secondly, the system still cannot resolve the damage of the particulate pollutants to the device itself. The cost of the ion exchange membrane is high, and operation and maintenance are troublesome.

This invention combines membrane separation with electric adsorption, and simultaneously realizes the functions of filtration separation and electric adsorption deionization of sewage, which effectively traps particulate in the sewage, avoids damage to the adsorption material, and simultaneously removes contaminating ions in the sewage, avoids secondary pollution, saves energy, and reduces costs.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a membrane separation technology to simultaneously accomplish solid-liquid separation and desalination in sewage treatment. This membrane separation technology is coupling membrane separation and electric adsorption processes, to complete filtration separation and electro-desorption deionization of sewage at the same time. The membrane separation technology can effectively intercept particulates, adsorb ionic contaminants in wastewater, and improve the efficiency of desalination, with no secondary pollution, simple operation, and low energy consumption. Hence, the membrane separation technology is suitable for the treatment of low-concentration saline wastewater.

The invention provides a composite membrane separation method for desalinization and recycling of sewage. The said separation method adopts a conductive composite membrane reactor to desalinate sewage, while the conductive composite membrane reactor consisting of a water inlet system 1, a power source system 2, a membrane reactor 3, a water outlet control system 4 and clear water tank 5;

The said water inlet system 1 composes a water inlet tank and a water flow regulating device, regulating the inflow flow according to the process requirements. The water flow regulating device is fixed at the inlet of the inlet tank, and the outlet of the water inlet tank is connected with the membrane reactor by a pipeline. The membrane reactor composes a reaction tank, a composite membrane module 6 and a stirring system. Several composite membrane modules 6 which are located in the reaction tank are connected by the conductive wire 7 with the anode and the cathode of the power source system 2 respectively. The membrane reactor is arranged in an immersed manner, while the agitator is fixed in the reaction tank, to mix the reaction liquid in the reaction tank. The outlet of the reaction tank in the membrane reactor is connected with the outlet system by the pipeline.

Each group of composite membrane modules is a flat membrane structure, composed of a cathode composite membrane 8, an anode composite membrane 9 and a separation layer 10. Wherein, the cathode composite membrane is formed by adhering a cathode electrode 11 with a cathode current collector 12 by a polymer material.

An anode composite membrane is formed by adhering an anode electrode 13 with an anode current collector 14 by a polymer material, the said cathode composite membrane 8 and the said anode composite membrane 9 are separated by the separation layer 10 to avoid a short circuit.

The cathode current collector is located on the same side as a water inlet, and the anode current collector is located on the same side as a water outlet. Influent water first flows through the cathode current collector and the cathode electrode, then passes through the separation layer, after that passes through the anode electrode and the anode collector, discharges from the conductive composite membrane reactor in the form of membrane effluent water.

Specific steps are as follows:

Influent water that meets the process requirements flows to the water inlet tank, and the inflow flow rate is adjusted by the water flow regulating device. Expelled water from the water inlet tank flows to the conductive composite membrane reactor, operating in a constant flow or constant pressure mode. Influent water first flows through the cathode current collector and the cathode electrode, passes through the separation layer, then passes through the anode electrode and the anode current collector, and discharges from the conductive composite membrane reactor in the form of membrane effluent water. The membrane flux is controlled in the range of 8 - 50 L/(m2 h) and the transmembrane pressure difference is ranged from 0.4 - 20 kPa. When the power turns on, membrane reactor is activated, ionic contaminants in salty wastewater are adsorbed.

In the present invention, the inlet water concentration of the water inlet tank is controlled to be less than 5000 mg/L (calculated as TDS).

In the present invention, the applied direct current voltage is in the range of 0.4-2.0 V.

In the present invention, the power source system is powered by a regulated direct current power supply for the electric adsorption process. The cathode composite membrane is attached to the negative electrode of the power supply, and the anode composite membrane is attached to positive electrode of the power supply. A current monitoring device is configured in the circuit between the power supply system and the cathode or anode to monitor current conditions in real time.

In the present invention, a mesh material with good conductivity is used as the current collectors. The said material is selected from the group consisting of titanium material, titanium alloy material or stainless steel material. The cathode electrode or the anode electrode is a carbon-based material, and is selected from the group consisting of carbon cloth, carbon nanotube, activated carbon powder or fiber, carbon aerogel, graphene, or carbon black. The polymer is a high-molecular polymer. Specifically, the high-molecular polymer is selected from the group consisting of polyvinylidene fluoride, polyether sulfone, polytetrafluoroethylene or polyacrylonitrile.

In the present invention, a material with good water permeability is used as the separation layer. Specifically, the material is selected from the group consisting of nylon net, non-woven fabric or polypropylene material.

In the present invention, the cathode composite membrane and the anode composite membrane employ different electrode materials and current collector materials.

The principle of the invention is as follows: In the form of a flat membrane electrode, coupling membrane separation and electric adsorption process, the separation layer traps particulate pollutants at a suitable membrane flux, to realize the solid-liquid separation of wastewater. Applied appropriate voltage at the cathode and anode electrodes, the ionic pollutants in sewage were adsorbed to achieve the purpose of desalination of the sewage. When the electrode adsorption is saturated, desorption is started by applied additional power and the electrode is regenerated. Through adsorption-desorption cycles, membrane modules can be reused, operating costs can be reduced.

Compared with the prior art, the present invention has the following advantages: (1) The present invention adopts a membrane module form of a flat membrane, coupling membrane separation and electric adsorption technology method, which can adsorb ionic contaminants and separate solid-liquid at the same time. It breaks through limitations of existing membrane separation and electric adsorption processes, improves the desalination efficiency. The energy consumption of this technology is low, and the operation and management are convenient. (2) In the present invention, the outer side of the conductive composite membrane has a function of trapping particulate, which can reduce the ineffective adsorption and the abrasion of the inner adsorption material. After the “ adsorption-desorption” process, the recycling of the adsorption material is realized, the efficiency of electrode material is improved, and equipment maintenance costs is reduced. (3) Applying a DC electric field, the surface of the membrane is negatively charged and repelled the negatively charged pollutants, such as particles and colloids, in wastewater, to control membrane fouling. The membrane cleaning cycle and membrane service life is extended, energy consumption of membrane cleaning is reduced, and operating costs is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of a desalination process of coupling membrane separation and electric adsorption technology;

Label in the drawing: 1 is the water inlet system, 2 is the power source system, 3 is the membrane reactor, 4 is the water outlet control system, 5 is the clear water tank, 6 is the composite membrane module, 7 is the conductive wire, 8 is the cathode composite membrane, 9 is the anode composite membrane, 10 is the separation layer;

Figure 2 is a schematic diagram of a monolithic composite membrane module in detail;

Label in the drawing: 7 is the conductive wire, 8 is the cathode composite membrane, 9 is the anode composite membrane, 10 is the separation layer, 11 is the cathode current collector, 12 is the cathode electrode, 13 is the anode electrode, and 14 is the anode current collector.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention will be further illustrated by the following examples with reference to the accompanying drawings.

Example 1:

Using the process device shown in Figure 1, the water inlet system 1 was composed of a water inlet tank and a water flow regulating device. After the pretreatment to meet the process requirements, brackish water composing of NaCl was introduced into the water inlet tank. The concentration of salts present in the inlet water was 1200 mg/L (measured by TDS), and the influent flow was adjusted to control the flux to 10 L/m2 h. The outlet of the water inlet tank was connected to the membrane reactor through a pipeline. Effluent of the water inlet tank flows to the conductive composite membrane reactor. The membrane reactor was composed of a reaction tank, a composite membrane module 6 and a stirring system. The composite membrane module was shown in Figure 2. Wherein, the anode composite membrane was manufactured by adhering PVDF with titanium mesh and carbon cloth. The cathode composite membrane was adhered by PVDF with stainless steel mesh and carbon cloth, and the separation layer was non-woven fabric. The cathode composite membrane module was connected to the negative electrode of the power source system 2 through a conductive wire 7 with good conductivity. The anode composite membrane was connected to the positive electrode of the power supply through a conductive wire. The membrane reactor was arranged in an immersed manner, and the agitator was disposed in the reaction tank to mix the reaction liquid in the reaction tank. The membrane reactor was operated in a constant flow mode. When power turned on with 2.0 V operating voltage, the membrane reactor was started. The hydraulic retention time was 1 h, and the operation was 6 h. During the operation, the transmembrane pressure was stable at 0.7 kPa. The outlet of the reaction tank in the membrane reactor was connected with the outlet system by the pipeline. The water flow was controlled by the water outlet control system 4. The desalination rate of system was 65-72%.

Example 2

Using the process device shown in Figure 1, the water intake system 1 was composed of a water inlet tank and a water flow regulating device. The cold rolling wastewater was pretreated to meet the process requirements. Then, cold rolling wastewater was accessed into the water tank after biological treatment. The concentration of salts present in the inlet water was 1000 mg/L (measured by TDS), the suspended solids concentration was 50 mg/L and the influent flow was adjusted to control the flux to 40 L/m2 h. The outlet of the water inlet tank was connected to the membrane reactor through a pipeline, and the outlet of the water inlet tank flows into the membrane reactor. The membrane reactor was composed of a reaction tank, a composite membrane module 6 and a stirring system. The composite membrane module shown in Figure 2 was adopted. Both the anode composite membrane and the cathode composite membrane are manufactured by adhering titanium mesh and carbon cloth together through PAN, and the separator was a nylon mesh. The cathode composite membrane module was connected to the negative electrode of the power source system 2 through the conductive wire 7 with good conductivity. The cathode composite membrane module was connected to the negative pole of the power source system 2 through a conductive wire 7 with good conductivity. The anode composite membrane was connected to the positive electrode of the power supply through a conductive wire. The membrane reactor was arranged in an immersed manner, and the agitator was disposed in the reaction tank to mix the reaction liquid in the reaction tank. The membrane reactor was operated in a constant flow mode. When power turned on with 1.6 V operating voltage, the membrane reactor was started. The hydraulic retention time was 15 min, and the operation was 4 h. During the operation, the transmembrane pressure was stable at 2.3 kPa. The outlet of the reaction tank in the membrane reactor was connected with the outlet system by the pipeline. The water flow was controlled by the water outlet control system 4. The desalination rate of system was 60-70 %, and the concentration of suspended solids in the water was below the detection limit.

Example 3:

Using the process device shown in Figure 1, the water inlet system 1 was composed of a water inlet tank and a water flow regulating device. Certain fertilizer production industrial wastewater composing of nitrate was pretreated to meet the process requirements. Then, fertilizer production industrial wastewater was accessed into the water inlet tank. The concentration of salts present in the inlet water was 900 mg/L (measured by TDS), and the influent flow was adjusted to control the flux to 10 L/m2 h. The outlet of the water inlet tank was connected to the membrane reactor through a pipeline, the outlet of the water inlet tank flows into the membrane reactor. The membrane reactor was composed of a reaction tank, a composite membrane module 6 and a stirring system. The composite membrane module shown in Figure 2 was adopted. Both the anode composite membrane and the cathode composite membrane are manufactured by titanium mesh and carbon nanotube, and the separator was a nylon mesh. The cathode composite membrane module was connected to the negative electrode of the power source system 2 through the conductive wire 7 with good conductivity. The anode composite membrane was connected to the positive electrode of the power supply through a conductive wire. The membrane reactor was arranged in an immersed manner, and the agitator was disposed in the reaction tank to mix the reaction liquid in the reaction tank. The membrane reactor was operated in a constant flow mode. When power turned on with 2.0 V operating voltage, the membrane reactor was started. The hydraulic retention time was 1 h, and the operation was 4 h. During the operation, the transmembrane pressure was stable at 2.4 kPa. The outlet of the reaction tank in the membrane reactor was connected with the outlet system by the pipeline. The water flow was controlled by the water outlet control system 4. The desalination rate of system was 57-68 %.

Example 4:

Using the process device shown in Figure 1, the water intake system 1 was composed of a water inlet tank and a water flow regulating device. Copper-containing waste water was pretreated to meet the process requirements. Then, copper-containing waste water was accessed into the water tank. The concentration of salts present in the inlet water was 500 mg/L (measured by TDS), and the influent flow was adjusted to control the flux to 25 L/m2 h. The outlet of the water inlet tank was connected to the membrane reactor through a pipeline, and the outlet of the water inlet tank flows into the membrane reactor. The membrane reactor was composed of a reaction tank, a composite membrane module 6 and a stirring system. The composite membrane module shown in Figure 2 was adopted. Both the anode composite membrane and the cathode composite membrane are manufactured by titanium mesh and carbon nanotube, and the separator was a nylon mesh. The cathode composite membrane module was connected to the negative electrode of the power source system 2 through the conductive wire 7 with good conductivity. The anode composite membrane was connected to the positive electrode of the power supply through a conductive wire. The membrane reactor was arranged in an immersed manner, and the agitator was disposed in the reaction tank, to mix the reaction liquid in the reaction tank. The membrane reactor was operated in a constant flow mode. When power turned on with 1.6 V operating voltage, the membrane reactor was started. The hydraulic retention time was 24 min, and the operation was 3 h. During the operation, the transmembrane pressure was stable at 1.5 kPa. The outlet of the reaction tank in the membrane reactor was connected with the outlet system by the pipeline. The water flow was controlled by the water outlet control system 4. The desalination rate of system was 45-58 %.

Claims

Claims

1. A composite membrane separation method for desalinization and recycling of sewage, wherein the said separation method adopts a conductive composite membrane reactor to desalinate sewage, while the conductive composite membrane reactor consisting of a water inlet system (1), a power source system (2), a membrane reactor (3), a water outlet control system (4) and clear water tank (5); the said water inlet system (1) composing of a water inlet tank and a water flow regulating device, regulating the inflow flow according to the process requirements, the water flow regulating device disposed at the inlet of the inlet tank, and the outlet of the water inlet tank connected with the membrane reactor by the pipeline; the membrane reactor composing of a reaction tank, a composite membrane module (6) and a stirring system, several composite membrane modules (6) located in the reaction tank connected by the conductive wire (7) with the anode and the cathode of the power source system (2) respectively, the membrane reactor arranged in an immersed manner, the agitator disposed in the reaction tank to mix the reaction liquid in the reaction tank, and the outlet of the reaction tank in the membrane reactor connected with the outlet system by the pipeline; each group of composite membrane modules having a flat membrane structure and composing of a cathode composite membrane (8), an anode composite membrane (9) and a separation layer (10), wherein, the cathode composite membrane is formed by adhering a cathode electrode (11) with a cathode current collector (12) by a polymer material, an anode composite membrane is formed by adhering an anode electrode (13) with an anode current collector (14) by a polymer material, the said cathode composite membrane (8) and the said anode composite membrane (9) are separated by the separation layer (10) to avoid a short circuit; the cathode current collector located on the same side as a water inlet, and the anode current collector located on the same side as a water outlet, the influent water flowing first through the cathode current collector and the cathode electrode, then the separation layer, after that the anode electrode and the anode collector, discharged from the conductive composite membrane reactor in the form of membrane effluent water; specific steps as follows: flowing the influent water that meets the process requirements to the water inlet tank, adjusting the inlet flow rate by the water flow regulating device, flowing the effluent from the water inlet tank to the conductive composite membrane reactor, operating in a constant flow or constant pressure mode, flowing the influent water through the cathode current collector and the cathode electrode first, passing through the separation layer, then through the anode electrode and the anode current collector, discharging from the conductive composite membrane reactor in the form of membrane effluent water, the flux of the membrane controlled to 8-50 L/(m2h), the transmembrane pressure 0.4-20 kPa, power turns on, membrane reactor is activated, ionic pollutants in salty wastewater are adsorbed.
2. The composite membrane separation method for desalinization and recycling of sewage according to claim 1, wherein the inlet water concentration of the water inlet tank is controlled to be less than 5000 mg/L (calculated as TDS)..
3. The composite membrane separation method for desalinization and recycling of sewage according to claim 1, wherein the applied direct current voltage range is 0.4 - 2.0 V.
4. The composite membrane separation method for desalinization and recycling of sewage according to claim 1, wherein the power source system is powered by a regulated direct current power supply for the electric adsorption process, the cathode composite membrane is attached to the negative electrode of the power supply, and the anode composite membrane is attached to positive electrode of the power supply, a current monitoring device is configured in the circuit between the power supply system and the cathode or anode to monitor current conditions in real time.
5. The composite membrane separation method for desalinization and recycling of sewage according to claim 1, wherein the cathode current collector or the anode current collector uses a mesh material with good conductivity, the said material is selected from the group consisting of titanium material, titanium alloy material or stainless steel material, the cathode electrode or the anode electrode is a carbon-based material, and is selected from the group consisting of carbon cloth, carbon nanotube, activated carbon powder or fiber, carbon aerogel, graphene, or carbon black, the polymer is a high-molecular polymer, specifically the high-molecular polymer is selected from the group consisting of polyvinylidene fluoride, polyether sulfone, polytetrafluoroethylene or polyacrylonitrile.
6. The composite membrane separation method for desalinization and recycling of sewage according to claim 5, wherein the cathode composite membrane and the anode composite membrane employ different electrode materials and current collector materials.
7. The composite membrane separation method for desalinization and recycling of sewage according to claim 1, wherein the separation layer uses a material with good water permeability, specifically the material is selected from the group consisting of nylon net, nonwoven fabric or polypropylene material.