A microbial fuel cell constructed wetland coupled photoelectrocatalysis sewage treatment system and method

Abstract

The application discloses a sewage treatment system combining a microbial fuel cell constructed wetland with photoelectrocatalysis, which comprises a microbial fuel cell constructed wetland unit, a photoelectrocatalysis unit and an external circuit, wherein the microbial fuel cell constructed wetland unit comprises a plurality of independent microbial fuel cell constructed wetland main bodies, each of which comprises, from bottom to top, a gravel water distribution layer, an anode layer, an intermediate gravel layer, a sandy soil layer, a cathode layer and aquatic plants; the anode layer and the cathode layer are connected with the external circuit through copper core wires; the photoelectrocatalysis unit comprises a reaction tank, an anode, a cathode and an ultraviolet lamp arranged in the reaction tank, and further comprises an air pump and a stirrer; the anode and the cathode are connected with the cathode layer and the anode layer of the microbial fuel cell constructed wetland unit respectively. Compared with the prior art, the system combines the microbial fuel cell constructed wetland with the photoelectrocatalysis technology, can realize the synchronous removal of domestic sewage and refractory wastewater, and has low energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to a microbial fuel cell constructed wetland coupled photoelectrocatalysis wastewater treatment system and method, and belongs to the technical field of wastewater treatment. BACKGROUND

[0002] Energy shortage and environmental pollution are important problems faced by modern society development. Traditional wastewater treatment technology often needs to consume a large amount of energy. Therefore, the recovery of resources and energy from wastewater has become a new trend of wastewater treatment.

[0003] The microbial fuel cell constructed wetland combines the advantages of microbial fuel cell and constructed wetland technologies, which can not only effectively treat wastewater, but also produce electricity using biomass energy in wastewater. For example, Chinese patent application numbers 201110187473.3, 201410437150.9 and 201610020185.1 introduce several different configurations of microbial fuel cell constructed wetland devices for wastewater treatment, which can produce electricity while treating wastewater, but the wastewater purification effect and electricity production efficiency are generally poor. At present, the research on microbial fuel cell constructed wetland systems mainly focuses on improving the pollutant removal efficiency and energy output, and there are few reports on collecting and utilizing the weak energy produced by microbial fuel cell constructed wetlands.

[0004] Chinese patent application number 201611240733.8 introduces a method for treating wastewater by using arrayed wetland microbial fuel cell powered electro-Fenton process, which sequentially passes wastewater through nano-iron carbon micro-electrolysis reaction zone, electro-Fenton reaction zone and arrayed wetland microbial fuel cell for treatment, and connects multiple wetland microbial fuel cells to form an arrayed wetland microbial fuel cell to power the electro-Fenton system, thereby improving the biodegradability of refractory organic matter. Although this method uses the electricity generated by the wetland microbial fuel cell to power the electro-Fenton system, the electricity production efficiency is generally poor, the pollutant degradation and conversion effect is not good, and it can only be used to treat single refractory wastewater.

[0005] Photoelectrocatalysis as a highly efficient water treatment technology has great potential, and the ·OH produced has strong oxidizing properties, so it is often used to treat refractory organic matter such as heavy metals, drugs, dyes and phenolic substances. However, this technology needs an external bias to achieve good treatment effect, which increases the risk of energy consumption. Collecting electricity produced by microbial fuel cell constructed wetlands and using it for photoelectrocatalysis can alleviate this limitation to some extent, but there is no related report on the combination of the two. SUMMARY

[0006] To solve the above problems, the present application aims to provide a microbial fuel cell constructed wetland coupled with photoelectrocatalysis wastewater treatment system, which collects electricity generated by microbial fuel cell constructed wetland and couples with photoelectrocatalysis system to realize the removal of pollutants, has high electricity generation efficiency, good pollutant degradation and conversion effect, and can realize the simultaneous treatment of live wastewater and refractory wastewater.

[0007] The present application also aims to provide a method for treating wastewater by using the above wastewater treatment system.

[0008] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0009] A microbial fuel cell constructed wetland coupled with photoelectrocatalysis wastewater treatment system, comprising a microbial fuel cell constructed wetland unit, a photocatalysis unit and an external circuit, wherein the microbial fuel cell constructed wetland unit comprises a plurality of independent microbial fuel cell constructed wetland main bodies, each of which comprises, from bottom to top, a gravel water distribution layer, an anode layer, an intermediate gravel layer, a sandy soil layer, a cathode layer and aquatic plants; the lower part of one side of the microbial fuel cell constructed wetland main body is provided with a water inlet, and the upper part of the other side is provided with a water outlet; the anode layer and the cathode layer are connected with the external circuit through copper core wires, and an external resistor is connected in series on the external circuit.

[0010] The photocatalysis unit comprises a reaction tank and an anode, a cathode and a UV lamp arranged in the reaction tank, and further comprises an air pump and a stirrer, wherein the air pump is communicated with the bottom of the reaction tank through a gas conveying pipe; the anode and the cathode are connected with the cathode layer and the anode layer of the microbial fuel cell constructed wetland unit through wires, respectively.

[0011] Further, the anode layer is made of 4-20 mesh copper wire mesh wrapped around 4-8 mm mixed fillers, and the mixed fillers are mixed by pyrite and granular activated carbon in a volume ratio of 1:(1-3).

[0012] Further, the cathode layer comprises an upper layer, a conductive interlayer and a lower layer, wherein the upper layer and the lower layer are carbon felt layers, and the conductive interlayer is a 4-20 mesh copper wire mesh.

[0013] Further, the gravel water distribution layer is composed of gravel with a particle size of 6-9 mm.

[0014] Further, the intermediate gravel layer is composed of gravel with a particle size of 4-6 mm.

[0015] Further, the height ratio of the gravel water distribution layer, the anode layer, the intermediate gravel layer, the sandy soil layer and the cathode layer is (20-30):(3-7):(20-30):(2-5):(1-3).

[0016] Further, the anode of the photocatalytic unit is a TiO2 / Ti thin film electrode, and the cathode is a graphite electrode.

[0017] The method for treating sewage by using the sewage treatment system of microbial fuel cell constructed wetland coupled with photoelectrocatalysis comprises the following steps:

[0018] (1) domestic sewage is introduced into the water inlet of the main body of the microbial fuel cell constructed wetland, and the domestic sewage flows through the gravel distribution layer, the anode layer, the intermediate gravel layer, the sandy soil layer and the cathode layer in sequence, in the anode layer, microorganisms decompose organic matter to release electrons and protons, the electrons are conducted to the cathode layer through the external circuit to form an electric current, and the purified sewage flows out from the water outlet at the top of one side of the main body of the microbial fuel cell constructed wetland;

[0019] (2) the recalcitrant sewage is introduced into the reaction tank of the photocatalytic unit, the anode and the cathode of the photocatalytic unit are powered by the microbial fuel cell constructed wetland unit, the ultraviolet lamp and the stirrer are turned on, and the air pump is used for aeration to perform photocatalytic degradation treatment on the recalcitrant sewage.

[0020] The recalcitrant sewage is cationic dye wastewater, including rhodamine B, methylene blue and methyl orange.

[0021] Further, the air pump is used for aeration in the photoelectrocatalytic device, and the aeration rate is 0.8-1.6 L / min.

[0022] Compared with the prior art method, the present application has the following beneficial effects:

[0023] (1) the present application combines the microbial fuel cell constructed wetland with the photoelectrocatalytic technology, realizes the synchronous removal of domestic sewage and recalcitrant wastewater, provides a new direction for the energy production and application of the microbial fuel cell constructed wetland, and opens up a new process for the township sewage treatment plant receiving domestic and industrial sewage.

[0024] (2) compared with the traditional photoelectrocatalytic device for treating sewage, the present application uses a multistage microbial fuel cell constructed wetland as an external power supply to reduce the consumption of traditional electric energy of the system.

[0025] (3) compared with other existing microbial fuel cell constructed wetlands, the present application uses copper wire mesh wrapped pyrite and granular activated carbon mixed filler as anode material. The metal and semiconductor properties of pyrite are conducive to electric conduction, in addition, the high porosity of activated carbon material can enhance the effective adhesion of microorganisms and the contact area with pyrite, so as to realize the power generation and the improvement of the pollutant removal efficiency of the microbial fuel cell constructed wetland. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1Structure diagram of wastewater treatment system of microbial fuel cell constructed wetland coupled with photoelectrocatalysis of Example 1;

[0027] Figure 2 Test results of power generation voltage of microbial fuel cell constructed wetland unit of wastewater treatment system of Example 1 under different influent COD cr concentrations;

[0028] Figure 3 Test results of open circuit voltage and maximum power density of microbial fuel cell constructed wetland unit of wastewater treatment system of Example 1 under different influent COD cr concentrations;

[0029] Figure 4 Test results of purification effect of photo catalytic unit of wastewater treatment system of Example 1 on rhodamine B under different applied bias;

[0030] Figure 5 Test results of purification effect of photo catalytic unit of wastewater treatment system of Example 1 on rhodamine B under different aeration speeds;

[0031] In the figure: 1-gravel water distribution layer; 2-anode layer; 3-intermediate gravel layer; 4-sand layer; 5-cathode layer; 6-aquatic plant; 7-external resistance; 8-magnetic stirrer; 9-air pump; 10-anode; 11-cathode; 12-ultraviolet lamp; 13-reaction tank. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are clearly and completely explained below in combination with the drawings and specific examples.

[0033] Example 1

[0034] As Figure 1As shown, a microbial fuel cell constructed wetland coupled with photoelectrocatalysis sewage treatment system, comprising a microbial fuel cell constructed wetland unit, a photoelectrocatalysis unit and an external circuit, the microbial fuel cell constructed wetland unit comprises four independent microbial fuel cell constructed wetland bodies (1# CW-MFC, 2# CW-MFC, 3# CW-MFC, 4# CW-MFC respectively), each microbial fuel cell constructed wetland body comprises, from bottom to top, a gravel water distribution layer 1, an anode layer 2, an intermediate gravel layer 3, a sandy soil layer 4, a cathode layer 5 and aquatic plants 6; the lower part of one side of the microbial fuel cell constructed wetland body is provided with a water inlet, and the upper part of the other side is provided with a water outlet; the anode layer 2 and the cathode layer 5 are connected with the external circuit through copper core wires, and an external resistor 7 is connected in series on the external circuit; the anode layer is made of 4-8 mm mixed fillers wrapped by 6 purpose copper wire mesh, the mixed fillers are mixed by pyrite and granular activated carbon with a volume ratio of 1:1; the cathode layer comprises an upper layer, a conductive interlayer and a lower layer, the upper layer and the lower layer are carbon felt layers, and the conductive interlayer is a 4-20 purpose copper wire mesh; the gravel water distribution layer 1 is composed of gravel with a particle size of 6-9 mm, and the intermediate gravel layer 3 is composed of gravel with a particle size of 4-6 mm; the aquatic plants 6 are reeds; the heights of the gravel water distribution layer, the anode layer, the intermediate gravel layer, the sandy soil layer and the cathode layer are 25 cm, 5 cm, 25 cm, 4 cm and 2 cm respectively.

[0035] The photoelectrocatalysis unit comprises a reaction tank 13 and an anode 10, a cathode 11 and a 275-320 nm ultraviolet lamp 12 arranged in the reaction tank, the photoelectrocatalysis unit further comprises an air pump 9 and a stirrer 8 (magnetic stirrer in this embodiment, a stirring rod is correspondingly arranged in the reaction tank), the air pump 9 is communicated with the bottom of the reaction tank 13 through a gas conveying pipe; the anode 10 is a TiO2 / Ti thin film electrode, and the cathode 11 is a graphite electrode; the anode 10 and the cathode 11 are connected with the cathode layer 5 and the anode layer 2 of the microbial fuel cell constructed wetland unit through wires respectively.

[0036] Application test:

[0037] The microbial fuel cell constructed wetland coupled with photoelectrocatalysis sewage treatment system of Example 1 is used for sewage treatment, the removal efficiency of pollutants and the power generation effect of the microbial fuel cell constructed wetland unit of the sewage treatment system are tested, and the purification effect of the photoelectrocatalysis unit of the sewage treatment system on rhodamine B (RhB) is tested.

[0038] (1) Test of the removal efficiency of pollutants and the power generation effect of the microbial fuel cell constructed wetland unit of the sewage treatment system of Example 1

[0039] Experimental Method: The microbial fuel cell constructed wetland unit of the wastewater treatment system was started. Domestic wastewater (COD values ​​of 100, 200, 300, and 400 mg / L) was introduced into the inlet of the main body of the microbial fuel cell constructed wetland. The wastewater flowed sequentially through a gravel distribution layer, an anode layer, an intermediate gravel layer, a sand layer, and a cathode layer. In the anode layer, microorganisms decomposed organic matter, releasing electrons and protons. Electrons were conducted to the cathode layer through an external circuit, forming an electric current. After purification, the wastewater flowed out from the top outlet on one side of the main body of the microbial fuel cell constructed wetland. The COD values ​​of different influents were tested. cr COD at concentration and HRT=1d cr NH4 + The removal rates of -N, TN and TP were measured, and different influent COD values ​​were tested. cr The voltage generated at the concentration, the open-circuit voltage, and the maximum power density.

[0040] COD cr NH4 + Removal rate test results of -N, TN and TP: Influent COD cr The pollutant removal rate was best at a concentration of 200 mg / L, with COD... cr NH4 + The maximum removal rates of -N, TN, and TP reached 68.85%, 42.76%, 39.68%, and 18.80%, respectively. However, changing the influent COD... cr Concentration has little overall impact on the detergency performance of CW-MFC; compared to optimal detergency performance, the influent COD... cr Concentration fluctuations on COD cr NH4 + The decrease in removal rates of -N, TN, and TP were 4.23–9.84%, 0.40–3.48%, 1.04–4.44%, and 4.00–16.80%, respectively.

[0041] Figure 2 The microbial fuel cell constructed wetland unit of the wastewater treatment system in Example 1 was tested under different influent COD levels. cr The figure shows the test results of the power generation voltage at different concentrations. In the figure, 1#CW-MFC, 2#CW-MFC, 3#CW-MFC, and 4#CW-MFC correspond to four structurally and materially identical, independent microbial fuel cell constructed wetland units within the microbial fuel cell constructed wetland unit. Figure 2It can be seen that as the CODcr concentration in the influent gradually increases, the output voltage of the CW-MFC device first increases and then decreases after power generation stabilizes. The output voltage reaches its maximum value when the CODcr concentration reaches 200 mg / L, at which point the stable output voltage of the CW-MFC is 396–415 mV. Since the current generated by a single CW-MFC is relatively small, four CW-MFCs can be connected in parallel to provide a photocatalytic bias power supply.

[0042] Figure 3 The microbial fuel cell constructed wetland unit of the wastewater treatment system in Example 1 was tested under different influent COD levels. cr The test results of open-circuit voltage and maximum power density at different concentrations show that when the influent COD... cr At a concentration of 100 mg / L, the open-circuit voltage, maximum power density, maximum current density, and system internal resistance of CW-MFC are 440 mV, 106.09 mW / m, and 106.09 mW / m, respectively. 3 918.37mA / m 3 436.20Ω; when the CODcr concentration is 200mg / L, the open-circuit voltage, maximum power density, maximum current density, and system internal resistance of the CW-MFC are 589mV, 204.31mW / mΩ, and 436.20Ω, respectively. 3 1428.57mA / m 3 405.20Ω; when the CODcr concentration is 300mg / L, the open-circuit voltage, maximum power density, maximum current density, and system internal resistance of the CW-MFC are 565mV, 190.13mW / mΩ, and 405.20Ω, respectively. 3 1326.53mA / m 3 408.10Ω; when the CODcr concentration is 400mg / L, the open-circuit voltage, maximum power density, maximum current density, and system internal resistance of the CW-MFC are 503mV, 135.85mW / mΩ, and 408.10Ω, respectively. 3 1122.45mA / m 3 423.60Ω.

[0043] The experimental results above show that the COD of the influent... cr The CW-MFC exhibits optimal power generation performance at a concentration of 200 mg / L, where its output voltage with an external 1000Ω resistor ranges from 386 to 447 mV, its open-circuit voltage from 571 to 594 mV, and its maximum power density from 193.15 to 257.97 mW / m³. 3 The maximum current density is 1428.57–1734.69 mA / m. 3 Too low influent COD cr The lack of organic nutrients affects power generation, while excessive COD... crThe decrease of dissolved oxygen in the wetland will lead to the decrease of power generation efficiency.

[0044] (2) The purification effect of the photocatalytic unit of the wastewater treatment system of Test Example 1 on Rhodamine B (RhB)

[0045] Experimental Method One: After the microbial fuel cell constructed wetland unit was operated stably, 25 mg / L of Rhodamine B solution (electrolyte Na2SO4 concentration 0.05 mol / L, pH = 3.0) was introduced into the reaction tank of the photocatalytic unit, the photocatalytic unit was connected, the anode and cathode of the photocatalytic unit were powered by the microbial fuel cell constructed wetland unit, the ultraviolet lamp and the stirrer were turned on, and the air pump was used for aeration, the aeration rate was controlled at 1.2 L / min, the resistance value of the external resistance 7 (variable resistance box) was adjusted, the output voltage was adjusted to 0V, 0.2V, 0.4V and 0.6V respectively, and the degradation efficiency of Rhodamine B solution under different positive bias was tested.

[0046] Figure 4 The purification effect test results of the photocatalytic unit of the wastewater treatment system of Test Example 1 on Rhodamine B (RhB) under different applied bias can be seen that the microbial fuel cell constructed wetland coupled with photoelectrocatalysis wastewater treatment system of Test Example 1 can remove more than 90% of RhB within 3h, and the RhB degradation rate increases with the increase of the applied positive bias.

[0047] Experimental Method Two: After the microbial fuel cell constructed wetland unit was operated stably, 25 mg / L of Rhodamine B solution (electrolyte Na2SO4 concentration 0.05 mol / L, pH = 3.0) was introduced into the reaction tank of the photocatalytic unit, the photocatalytic unit was connected, the anode and cathode of the photocatalytic unit were powered by the microbial fuel cell constructed wetland unit, the resistance value of the external resistance 7 (variable resistance box) was adjusted to maintain the applied bias at 0.6V, the ultraviolet lamp and the stirrer were turned on, and the air pump was used for aeration, the air pump gate was adjusted to make the aeration rate 0L / min, 0.4L / min, 0.8L / min, 1.2L / min and 1.6L / min respectively, and the degradation efficiency of Rhodamine B solution under different aeration rates was tested.

[0048] Figure 5 The purification effect test results of the photocatalytic unit of the wastewater treatment system of Test Example 1 on Rhodamine B under different aeration rates can be seen that within the range of 0-1.2 L / min of aeration rate, the degradation rate of RhB of the microbial fuel cell constructed wetland coupled with photoelectrocatalysis wastewater treatment system of Test Example 1 showed an upward trend with the increase of aeration rate, and then the degradation rate of RhB gradually decreased.

Claims

1. A microbial fuel cell constructed wetland coupled photoelectrocatalytic wastewater treatment system, characterized in that, The application relates to a microbial fuel cell constructed wetland unit, a photocatalytic unit and an external circuit, wherein the microbial fuel cell constructed wetland unit comprises a plurality of independent microbial fuel cell constructed wetland bodies, each of which comprises, from bottom to top, a gravel water distribution layer, an anode layer, an intermediate gravel layer, a sandy soil layer, a cathode layer and aquatic plants; one side of the lower part of the microbial fuel cell constructed wetland body is provided with a water inlet, and the other side of the top is provided with a water outlet; the anode layer and the cathode layer are connected with the external circuit through copper core wires, and an external resistor is connected in series with the external circuit. The anode layer is made of 4-20 mesh copper wire mesh wrapping 4-8 mm mixed filler, and the mixed filler is mixed by pyrite and granular activated carbon with a volume ratio of 1: (1-3). The cathode layer comprises an upper layer, a conductive interlayer and a lower layer, the upper layer and the lower layer are carbon felt layers, and the conductive interlayer is 4-20 mesh copper wire mesh. The photocatalytic unit comprises a reaction tank, an anode, a cathode and a ultraviolet lamp arranged in the reaction tank, and further comprises an air pump and a stirrer, the air pump is communicated with the bottom of the reaction tank through a gas conveying pipe; the anode and the cathode are connected with the cathode layer and the anode layer of the microbial fuel cell constructed wetland unit through wires respectively.

2. The microbial fuel cell constructed wetland coupled photoelectrocatalytic wastewater treatment system according to claim 1, wherein, The gravel water distribution layer is composed of gravel with a particle size of 6-9 mm.

3. The microbial fuel cell constructed wetland coupled photoelectrocatalytic wastewater treatment system according to claim 1, wherein, The intermediate gravel layer is composed of gravel with a particle size of 4-6 mm.

4. The microbial fuel cell constructed wetland coupled with photoelectrocatalysis wastewater treatment system according to claim 1, wherein, The height ratio of the gravel water distribution layer, the anode layer, the intermediate gravel layer, the sandy soil layer and the cathode layer is (20-30):(3-7):(20-30):(2-5):(1-3).

5. The microbial fuel cell constructed wetland coupled photoelectrocatalytic wastewater treatment system according to any one of claims 1 to 4, wherein, The anode of the photocatalytic unit is a TiO2 / Ti thin film electrode, and the cathode is a graphite electrode.

6. A method for wastewater treatment using the wastewater treatment system of coupling photoelectrocatalysis with microbial fuel cell constructed wetland according to any one of claims 1 to 5, characterized in that, The application further discloses a treatment method of the microbial fuel cell constructed wetland unit. (1) domestic sewage is introduced into the water inlet of the microbial fuel cell constructed wetland body, and the domestic sewage flows through the gravel water distribution layer, the anode layer, the intermediate gravel layer, the sandy soil layer and the cathode layer in sequence, in the anode layer, microorganisms decompose organic matters to release electrons and protons, the electrons are conducted to the cathode layer through the external circuit to form an electric current, and the purified sewage flows out from the water outlet at the top of one side of the microbial fuel cell constructed wetland body; (2) the refractory sewage is introduced into the reaction tank of the photocatalytic unit, the anode and the cathode of the photocatalytic unit are powered by the microbial fuel cell constructed wetland unit, the ultraviolet lamp and the stirrer are turned on, and the air pump is used for aeration, so that the refractory sewage is subjected to photocatalytic degradation treatment.

7. The method of claim 6, wherein, In the step (2), the aeration rate is 0.8-1.6 L / min.

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