CN104617322A - Microbial capacitive desalination fuel cell technology - Google Patents

Abstract

The invention discloses a microbial capacitive desalination fuel cell technology, which uses microorganisms to treat sewage to generate electric energy to supply power for a capacitive deionization unit, and relates to the technical fields of sewage biological treatment, microbial power generation, and capacitive deionization and deionization. The desalination technology consists of a microbial fuel cell and a capacitive deionization unit. It is characterized in that two cation exchange membranes and two active carbon cloth electrodes are placed between the anode chamber and the cathode chamber of the microbial fuel cell to form a desalination chamber. The problem in the prior art is that microorganisms oxidize organic pollutants to release protons, which accumulate and cause the pH of the anode chamber to drop, affecting production capacity and desalination. The invention uses two cationic membranes and activated carbon cloth electrodes to divide the anode chamber, the desalination chamber and the cathode chamber, so that protons can be freely transferred among the three chambers through the cationic membrane and the activated carbon cloth, and the pH of each chamber is stabilized. The invention aims to provide a method for long-term operation of microbial capacitance desalination fuel cells, maintain the activity of electrogenic bacteria, and improve electricity production capacity and desalination efficiency.

Description

A microbial capacitive desalination fuel cell technology

technical field

The invention relates to the technical fields of sewage biological treatment, microbial power generation, and capacitive deionization and desalination, and is a green and energy-saving environmental protection technology.

Background technique

Producing clean water in a safe, economical and energy-saving way is an important technical challenge faced by human society. Among them, desalination is a key technology for converting brackish water, seawater or sewage into human-usable water. Currently, the desalination methods widely used mainly include reverse osmosis, distillation, electrodialysis and ion exchange. These methods generally have the disadvantages of high energy consumption, low water yield, cumbersome maintenance, and secondary pollution to the environment.

Capacitive deionization desalination is a new type of water treatment method developed in recent years. It is a pair of electrodes with large specific surface area and large specific capacity (often using porous carbon materials, such as carbon aerogel, activated carbon, carbon fiber, etc.) , carbon nanotubes, etc.) apply a low-voltage DC electric field. When water flows between the electrodes, the charged ions in the water move to the oppositely charged electrode under the action of the electric field and adsorb on the electrode, thereby achieving the effect of desalination. When the adsorption capacity of the electrode reaches saturation, the electrode is short-circuited or a reverse electric field is applied, and the adsorbed ions return to the water to form concentrated water to be drained away, and the electrode is regenerated at the same time. Compared with other desalination methods, capacitive deionization has the advantages of low energy consumption, no need to consume chemicals, no secondary pollution, and simple operation and maintenance. Therefore, it is expected to be used in brackish water treatment, seawater desalination, reclaimed water reuse, drinking water It has been widely used in deep purification, heavy metal recovery and other fields.

There are several ways to provide DC power to capacitive deionization desalination equipment. It can be powered by adjusting the voltage of 220V commercial power and transforming it into DC, or it can be powered by batteries or accumulators. Solar energy, wind power, combined heat and power, etc. can also be used for power supply outdoors. Since the electrodes used in capacitive deionization and desalination equipment have the ability to store electricity as capacitors, it is also possible to connect a plurality of capacitors and use the stored electricity in mutual interaction as a power supply. Capacitive deionization has no special restrictions on the voltage of the DC power supply. Since the standard electrode potential of water is 1.23V, in order to prevent hydrolysis, it can generally be operated with a low voltage of no more than 1.2V.

Microbial fuel cell, as an emerging environmental protection technology, can generate electricity while treating sewage, and its open circuit voltage can meet the voltage requirements of capacitive deionization. Therefore, it is a method with great development potential to seamlessly combine microbial fuel cells and capacitive deionization, so that it can degrade organic matter, generate electricity, and desalinize three functions.

The principle of the dual-chamber microbial fuel cell in the prior art is shown in Fig. 1 . It uses microorganisms attached to the anode as a catalyst to degrade organic matter to produce electrons and protons. The generated electrons are transferred to the anode, and then to the cathode through an external circuit, thereby generating an external current. The generated protons reach the cathode either through the separation material (membrane or salt bridge) or directly through the electrolyte, where they undergo reduction reactions with electrons and oxides (such as oxygen, etc.) to complete the transfer of internal charges in the battery.

The dual-chamber microbial fuel cell has no desalination function, and a three-chamber microbial desalination fuel cell is improved on the basis of it. The principle is shown in Figure 2: an anion exchange membrane and a cation exchange membrane are sequentially added between the anode and cathode in the microbial fuel cell to form an intermediate desalination chamber, and the desalination of the intermediate chamber is completed by using the potential difference between the cathode and anode on both sides of the battery. However, this process is irreversible and unsustainable, and the salt content of the electrolyte in the anode chamber and cathode chamber will increase, which will affect the subsequent utilization of the effluent. On the other hand, the accumulation of protons in the anode chamber leads to a drop in pH, which harms the activity of electrogenic bacteria, while the pH in the cathode chamber also increases, and this imbalance affects further production capacity and desalination efficiency.

Contents of the invention

The present invention proposes a new method for coupling microbial fuel cells and capacitive deionization and desalination, uses electric energy generated by microbial fuel cells to drive capacitive deionization and desalination, and overcomes the above two problems of existing microbial desalination fuel cells , so that the whole system can run stably.

The principle of this microbial capacitive desalination fuel cell is as follows: it consists of a microbial fuel cell and a capacitive deionization unit (as shown in Figure 3), including electricity-producing microorganisms, anodes, a cation exchange membrane, activated carbon cloth and conductive metal A capacitive electrode composed of a net, another cation exchange membrane, and an air cathode. The device is divided into three chambers, followed by an anode chamber, a desalination chamber and a cathode chamber. The positive and negative poles of the anode chamber and the cathode chamber are respectively connected to the adjacent activated carbon cloth capacitor electrodes in the desalination chamber, and the electrons are transferred to the activated carbon cloth capacitor electrodes through the external circuit, so that the capacitor electrodes have the same potential as the cathode and anode, and then the activated carbon An electric double layer is formed between the surface of the cloth and the solution, and ions are enriched on the surface of the electrode to reduce the concentration of ions in the solution in the desalination chamber.

The feature of this microbial capacitive desalination fuel cell is that it adopts the method of adding two cation exchange membranes in the microbial desalination fuel cell to replace an anion exchange membrane and a cation exchange membrane in the prior art, and will use activated carbon cloth The capacitive deionization unit as an electrode is coupled to separate the anode chamber and the cathode chamber, so that protons can freely transfer between the anode chamber, desalination chamber and cathode chamber through the cation exchange membrane and activated carbon cloth, and achieve the effect of stabilizing the pH of each chamber. The activity of the electrogenic bacteria in the anode chamber can be maintained, the electricity generation capacity and desalination efficiency can be improved, and the whole process can run stably for a long time.

The desalination process of this microbial capacitive desalination fuel cell is shown in Figure 4: the anode chamber processes organic sewage, and the electrogenic bacteria on the anode generate current and protons by oxidizing organic matter in the sewage, and the current is transmitted to the activated carbon cloth in the desalination chamber through an external circuit Capacitive electrodes, protons will not accumulate and cause the pH of the anode chamber to drop, but pass through two cation exchange membranes to the cathode chamber to complete the charge transfer inside the battery. Desalination chamber and cathode chamber can handle brine. Since the activated carbon cloth capacitor electrode has the same potential as the cathode and anode, the anions in the desalination chamber are adsorbed by the activated carbon cloth electrode near the anode chamber, and the cations are adsorbed by the activated carbon cloth electrode near the cathode chamber, so that the effluent can achieve desalination effect. Although the anions in the cathode chamber cannot pass through the cation exchange membrane and are adsorbed by the activated carbon cloth electrode in the desalination chamber, the cations inside can, so the cathode chamber also has a certain desalination effect. At this time, the protons coming from the anode chamber stabilize the cathode. The role of the pH of the chamber, so that the OH ⁱⁿ the cathode chamber will not accumulate and cause the pH to rise. In addition, using this method can also make the desalination chamber have a certain effect on the removal of organic matter, which is achieved through the adsorption of charged organic particles on activated carbon cloth, while the prior art microbial desalination fuel cells cannot do this. a little.

The electrode regeneration process of this microbial capacitor desalination fuel cell is shown in Figure 5: after the capacitor is saturated, the capacitor is disconnected from the anode and cathode, and the two capacitor electrodes are connected with an external wire to make a short circuit. The cloth loses its polarity, the ions adsorbed on the electric double layer desorb from the carbon cloth, and the ions with opposite charges attract each other and transfer to the solution. Another method is to exchange the connection between the capacitor electrode and the cathode and anode, and apply a potential opposite to that of the desalination stage between the activated carbon cloth electrodes (the control circuit is shown in Figure 6, if the switches K1 and K2 are in the downward position at the same time in the desalination state , then turn to the desorption state and turn both to the upward position at the same time), the ions adsorbed on the capacitor are desorbed under the action of same-sex repulsion. The desalination chamber is flushed with rinse water to remove physically adsorbed ions to form concentrated water.

In addition to permeating protons, general cation exchange membranes can also permeate many other salt ions (such as Na ⁺ , K ⁺ , NH ₄ ⁺ , Ca ²⁺ , etc.). The reason for the anion exchange membrane in the prior art is mainly to enable protons to flow freely between the three chambers, therefore, the proton exchange membrane can also be used to replace the anion exchange membrane in the prior art to achieve the same purpose of proton transfer.

In addition, the method of spraying cation exchange membrane on the surface of activated carbon cloth capacitor electrode can also be used to make membrane electrode to achieve the same purpose of proton transfer. Since the formed ion exchange membrane is covered on the surface of the electrode by pressure, the permeability of ions will be deteriorated, and the resistance of the electrode and the membrane will be increased. The integrated membrane electrode made by the spraying method has thin thickness and low resistance, which can improve the operating efficiency of the device while realizing proton transfer.

Description of drawings

Figure 1: Schematic diagram of the prior art microbial fuel cell.

Figure 2: Schematic diagram of the prior art microbial desalination fuel cell.

Figure 3: Schematic diagram of the principle of the microbial capacitive desalination fuel cell in the present invention.

Figure 4: Schematic diagram of the desalination process of the microbial capacitive desalination fuel cell in the present invention.

Figure 5: Schematic diagram of the electrode regeneration process of the microbial capacitive desalination fuel cell in the present invention.

Fig. 6: A schematic diagram of a control circuit of the microbial capacitive desalination fuel cell in the present invention.

Detailed ways

Example 1:

The structure of the microbial capacitive desalination fuel cell as shown in FIG. 3 is adopted. The desalination chamber is separated by two cation exchange membranes and two activated carbon cloth electrodes. The activated carbon cloth electrode is composed of a layer of conductive metal mesh and activated carbon cloth (FM10 Activated Carbon Cloth, ^Chemviron Carbon, UK). . The carbon brush used as the anode of the battery is attached with active and stable electricity-producing microorganisms by inoculation operation. The contact surface of the air cathode and the solution is loaded with a platinum catalyst, and the other side is connected to the air and coated with a PTFE waterproof layer. The wastewater treated in the anode chamber, desalination chamber, and cathode chamber is composed of simulated components, with a pH value of 7.0 ± 0.2. After a round of operation, the pH values of each chamber change in sequence as -0.2, 0.1, and 1.5. The control group adopted the method in which an anion exchange membrane and a cation exchange membrane in the prior art separate the desalination chamber (its structure is shown in Figure 2). Times are -0.5, 0.1, 4.5. The results show that the method of the present invention has a good effect on stabilizing the pH value of each chamber, and is beneficial to the long-term stable operation of the system.

Claims (3)

1. a microbe capacitive desalination fuel cell technology, the method using two cation-exchange membranes to replace employing anion-exchange membrane of prior aries and cation-exchange membrane to combine separates anode chamber and cathode chamber, make proton can in anode chamber, desalting chamber, cathode chamber three freely shift between Room, stablizes each room pH.

2. method according to claim 1, utilization proton exchange membrane reaches the object that same proton freely shifts.

3. method according to claim 1, the method being used in positive and negative capacitive electrode surface spraying cation exchange coating reaches the object that same proton freely shifts.