Methods and applications for improving the biofilm enrichment rate at the anode of microbial electrolysis cells

Abstract

This invention belongs to the fields of bioengineering, environmental engineering, and clean energy technology, and discloses a method and its application for improving the enrichment rate of biofilm at the anode of a microbial electrolysis cell. The method includes the following steps: constructing a microbial electrolysis cell reactor; adding inoculum to the reactor; adding PBS buffer nutrient solution and acclimatization substrate to the reactor; purging the air from the reactor to induce an anaerobic state; applying a constant micro-voltage and connecting a resistor in series to the anode and cathode of the reactor; culturing microorganisms at a constant temperature of 25-35℃, monitoring the voltage across the series resistor in real time, and repeating steps S3-S7 when the output voltage drops below 20mV, with the proportion of acclimatization substrate gradually increasing in each cycle. This invention, through a gradient acclimatization scheme that gradually increases the proportion of acclimatization substrate, can enrich dominant bacterial communities, resulting in biofilms with complete bacterial structure and high abundance of functional bacteria.

Description

Technical Field

[0001] This invention belongs to the fields of bioengineering, environmental engineering and clean energy technology, and specifically relates to a method and application for improving the enrichment rate of biofilm at the anode of a microbial electrolysis cell. Background Technology

[0002] The petroleum industry generates large quantities of high-concentration, recalcitrant wastewater, known as oilfield wastewater, during extraction, gathering, transportation, and refining processes. The main characteristics of oilfield wastewater include: high concentrations of petroleum hydrocarbons, high mineralization, the presence of benzene compounds, polycyclic aromatic hydrocarbons, and other biotoxic organic compounds, as well as complex composition. These characteristics make traditional activated sludge and physicochemical treatment methods difficult to implement, resulting in inhibited microbial activity, inconsistent effluent quality, and high operating costs. Therefore, there is an urgent need to develop new treatment technologies that combine high efficiency and cost-effectiveness.

[0003] Bioelectrochemical systems are a type of technology platform that utilizes electrochemically active microorganisms as catalysts to oxidize organic substrates at the anode and output electrons to an external circuit. Currently, the most commonly used method for enriching anodic biofilms is the enrichment method based on the microbial fuel cell (MFC) model. However, this method has the following significant drawbacks when treating oilfield wastewater systems: Firstly, MFCs rely solely on the self-generated potential difference from microbial metabolism as their driving force, which is typically only 0.3~0.5V. This potential difference is small and fluctuates significantly with substrate concentration and microbial metabolic state. High salt content in oilfield wastewater reduces the fluidity of microbial cell membranes and affects osmotic pressure balance. Furthermore, benzene compounds and polycyclic aromatic hydrocarbons have a significant inhibitory effect on the metabolism of electroactive microorganisms. This weak and unstable driving force is insufficient to overcome the thermodynamic energy barrier of microbial colonization, resulting in system start-up cycles that often last for weeks or even months, severely restricting the feasibility of engineering applications.

[0004] Secondly, under low-potential passive driving conditions, non-electrogenic bacteria can non-specifically attach to the anode surface through ordinary adhesion, competing with functional electrogenic bacteria with extracellular electron transfer capabilities for anode surface attachment sites and organic substrates. This results in a relatively low abundance of functional electrogenic bacteria in mature biofilms, poor overall electron transfer efficiency of the biofilm, and consequently affects pollutant removal efficiency.

[0005] Third, MFCs typically use air cathodes, relying on the reduction reaction of oxygen on the cathode surface as an electron acceptor. However, the oxygen reduction reaction kinetics are sluggish and limited by mass transfer, resulting in high internal resistance in the entire MFC system. This further weakens the metabolic driving force of anodic microorganisms and hinders the rapid accumulation of electroactive microorganisms in highly toxic oilfield wastewater environments.

[0006] In contrast, the Microbial Electrolysis Cell (MEC) mode applies an auxiliary voltage to the external circuit that is lower than the theoretical voltage for water electrolysis. This compensates for the difference between the electromotive force generated by the spontaneous oxidation of organic matter by microorganisms and the potential required for the cathode reaction, thereby driving the entire electrochemical process in a directed manner. This active electrochemical regulation can significantly improve the anode microenvironment, accelerate the colonization and enrichment of electrochemically active microorganisms in the oilfield wastewater environment through the electric field screening effect, and effectively inhibit the growth of non-electrogenetic bacteria.

[0007] Therefore, developing a method to rapidly enrich anodic biofilms in oilfield wastewater by replacing the traditional MFC model with a MEC model and combining it with a targeted domestication strategy is of great scientific significance and engineering application value. Summary of the Invention

[0008] The purpose of this invention is to provide a method and application for improving the biofilm enrichment rate of the anode in a microbial electrolysis cell, in order to solve the problem that the anode biofilm enrichment method based on the MFC model has obvious limitations in three dimensions—start-up speed, functional bacteria enrichment efficiency, and biofilm activity—when treating high-difficulty systems such as oilfield wastewater, and cannot meet the actual needs of rapid engineering deployment.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: On the one hand, the present invention provides a method for improving the enrichment rate of biofilm at the anode of a microbial electrolysis cell.

[0010] Includes the following steps: S1. Constructing the MEC reactor: Using porous carbon material as the anode and inert noble metal electrodes as the cathode, a sealed microbial electrolysis reactor is constructed.

[0011] S2. Inoculation: Inoculate the MEC reactor to provide a diverse source of microorganisms for the formation of the anodic biofilm.

[0012] S3. Feeding: Add PBS buffer nutrient solution and acclimatization substrate to the MEC reactor.

[0013] S4. Anaerobic treatment: Introduce nitrogen into the MEC reactor for no less than 10 minutes to purge the air from the reactor and bring the system into an anaerobic state.

[0014] S5. Apply driving voltage: Connect the reactor with a wire and apply a constant external voltage in the range of 0.5~1V to the anode and cathode of the reactor.

[0015] S6. Series resistor: A resistor with a resistance of 10~100 Ω is connected in series in the external circuit of the reactor for current sampling and monitoring of the system's operating status.

[0016] S7. Constant Temperature Culture and Cycle Management: Cultivate microorganisms under constant temperature conditions of 25~35℃ and monitor the voltage across the series resistor in real time. When the output voltage is lower than 20mV, it is considered that one operating cycle has ended. Repeat the steps of feeding, anaerobic treatment, voltage application, series resistance monitoring and constant temperature culture. In each cycle, the proportion of PBS buffer nutrient solution is gradually reduced according to the principle of gradient increase, while the proportion of acclimatized substrate is increased at the same time. This allows the microbial community to complete adaptive succession in a gradually increasing substrate stress environment until it uses acclimatized substrate as the only feed and maintains stable operation.

[0017] Preferably, in S1, the porous carbon material is one or a combination of carbon felt, carbon cloth, carbon paper, and carbon brush; the inert noble metal electrode is one or a combination of platinum sheet, platinum mesh, and platinum wire.

[0018] Preferably, in S2, the inoculum is municipal sewage, which is directly sampled from the sewage treatment plant without any treatment.

[0019] Preferably, in S3, the PBS buffer solution includes: one of sodium dihydrogen phosphate or potassium dihydrogen phosphate, one of disodium hydrogen phosphate or dipotassium hydrogen phosphate, ammonium chloride, potassium chloride, calcium chloride dihydrate, and multivitamins, and the pH of the prepared PBS buffer solution is 6.8~7.2.

[0020] Preferably, in S3, the acclimatization substrate is oilfield wastewater, which has the characteristics of high oil content, high salinity, and complex composition.

[0021] Preferably, in step S4, nitrogen gas is introduced for at least 10 minutes to ensure the construction of an anaerobic environment.

[0022] Preferably, in S5, the micro voltage applied across the anode and cathode should be in the range of 0.5 V to 1 V.

[0023] Preferably, in S6, the resistance value of the series resistor is in the range of 10 Ω to 100 Ω.

[0024] Preferably, the initial ratio of inoculum, PBS buffered nutrient solution and acclimatization substrate in S2 and S3 is 1:3:1. A higher proportion of PBS is used to provide nutrition in the early stage of acclimatization. As the cycle progresses, the amount of PBS buffered nutrient solution and inoculum is gradually reduced until only acclimatization substrate is added in the final feeding, so as to achieve targeted screening of oil-tolerant and salt-tolerant microorganisms.

[0025] Preferably, the volume ratios of inoculum, PBS buffered nutrient solution, and acclimatization substrate in the first, second, and third cycles are 1:3:1, 1:2:2, and 0:1:1, respectively; and in the fourth cycle and thereafter, the ratio of inoculum, PBS buffered nutrient solution, and acclimatization substrate is 0:0:1.

[0026] On the other hand, the present invention provides a method for improving the enrichment rate of biofilm at the anode of a microbial electrolysis cell, which is applied to the treatment of oilfield wastewater.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention adopts the MEC active drive mode, which uses an external constant voltage to build a strong and stable anode electron outflow channel, effectively overcoming the inhibition of microbial metabolism by the high salt and high toxicity environment of oilfield wastewater. The system start-up time can be shortened to about 2 days, which greatly improves efficiency compared to the start-up cycle of several weeks to several months of the traditional MFC mode.

[0028] 2. This invention provides an external electric field to form a stable anodic oxidation driving force, which selectively promotes electroactive microorganisms with extracellular electron transfer capabilities, while inhibiting the attachment and competition of non-electrogenic bacteria that cannot utilize this electrochemical driving force. This results in a significantly higher relative abundance of functional electrogenic bacteria in mature biofilms compared to the MFC mode, thereby improving the overall electron transfer efficiency and pollutant degradation capacity of the biofilm.

[0029] 3. This invention employs a gradient acclimatization scheme that gradually increases the proportion of acclimatization substrate and decreases the proportion of buffer solution. Under the synergistic effect of MEC electrochemical screening, the microbial community is forced to undergo adaptive succession in a gradually increasing acclimatization substrate stress environment, ultimately resulting in the directional enrichment of dominant bacterial groups. The obtained biofilm microbial community has a complete structure and high abundance of functional bacteria.

[0030] 4. The present invention features a simple process and low cost. It eliminates the need for complex bacterial isolation and purification procedures; all electrode materials used are commercially available products; and the overall process is concise and suitable for engineering application. Attached Figure Description

[0031] Figure 1 The internal resistance fitting diagram and equivalent circuit diagram of the MEC reactor in Embodiment 1 of the present invention are shown. Figure 2 The bar chart shows the COD removal rate and coulombic efficiency of the MEC reactor after 5 and 10 days of cultivation in Example 1 of this invention. Figure 3 The current-time curves for the start-up and enrichment processes of the MEC reactor in Example 1 of this invention are shown. Figure 4 The results are the relative abundance analysis of the bacterial community in the anolyte biofilm in Example 1 of this invention; Figure 5 This is a SEM image of the microbial film enriched on the surface of the carbon brush anode in Example 1 of the present invention; Figure 6 The images show TEM images and elemental mapping distribution diagrams of the Geobacteraceae family enriched in the MEC reactor in Example 1 of this invention. Figure 7 The images shown are transmission electron microscopy (TEM) images and elemental mapping distribution diagrams of Thaurea bacteria enriched in the MEC reactor in Example 1 of this invention. Figure 8 This is a comparison chart of the relative abundance of dominant functional bacteria in the anolyte biofilm under MEC mode and MFC mode in Embodiment 1 of the present invention. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present application, the technical solutions in specific embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by those skilled in the art.

[0033] Those skilled in the art should understand that, unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional materials in the art and can be obtained through commercial channels.

[0034] Example 1 This embodiment illustrates the application of a method for increasing the enrichment rate of biofilm at the anode of a microbial electrolysis cell in the treatment of oilfield wastewater.

[0035] S1, MEC reactor construction: Carbon brushes pretreated at 400℃ for 120 minutes were used as the bioanode. The purpose of this high-temperature pretreatment was to remove organic impurities and grease from the carbon brush surface, increase the hydrophilicity and oxygen-containing functional group density of the carbon fiber surface, thereby enhancing the initial adhesion ability of microorganisms to the anode surface. Carbon brushes, as the anode material, possess characteristics such as large specific surface area, excellent conductivity, high mechanical strength, and good biocompatibility, which are beneficial for biofilm formation and electron transfer between microorganisms and the anode. A platinum mesh was used as the cathode. As an inert noble metal electrode, the platinum mesh primarily acts as an electron conductor in the cathodic reduction reaction and does not participate in the biocatalytic process itself, ensuring the stability of the cathodic reaction. Strict sealing was implemented at the electrode connections to prevent air leakage and disruption of the anaerobic environment.

[0036] S2, vaccination Municipal wastewater was added to the pre-constructed MEC reactor. The municipal wastewater was taken directly from the influent of the wastewater treatment plant without any treatment. The reason for choosing municipal wastewater is that it contains a wide range of diverse microbial communities, including a certain proportion of electroactive microorganisms and facultative anaerobic microorganisms. It is an excellent natural source of bacteria for constructing the anodic biofilm, requiring no additional strain separation and purification operations, and is convenient and inexpensive.

[0037] S3, Feeding The feed consists of oilfield wastewater and PBS buffer nutrient solution. First, 30 mL of PBS buffer nutrient solution is prepared, with the following composition: sodium dihydrogen phosphate and disodium hydrogen phosphate form a phosphate buffer system, with sodium dihydrogen phosphate concentration of 15.4 mmol / L and disodium hydrogen phosphate concentration of 32.3 mmol / L; it also includes ammonium chloride at a concentration of 5.8 mmol / L as a nitrogen source for microbial growth; potassium chloride at a concentration of 1.7 mmol / L to maintain the ionic strength of the solution; calcium chloride dihydrate at a concentration of 10 mg / L as a divalent cationic nutrient element for microbial growth; and a 2 mL / L multivitamin solution to provide necessary growth factors for microorganisms. After thorough mixing of the above components, the pH of the prepared PBS buffer nutrient solution should be within the range of 6.8–7.2. This pH range coincides with the optimal metabolic pH of most electroactive microorganisms, which is beneficial for maintaining the normal physiological activities of anodic microorganisms.

[0038] In the initial stage, the volume ratio of municipal wastewater inoculum, PBS buffer nutrient solution, and oilfield wastewater was controlled at approximately 1:3:1. The main purpose of the high proportion of PBS in this stage was to provide sufficient and balanced nutrition for microorganisms, helping electroactive microorganisms to successfully colonize the anode surface in the early stage before they adapted to the toxicity of oilfield wastewater; at the same time, the introduction of a lower proportion of oilfield wastewater as a functional substrate allowed the microorganisms to gradually be exposed to the stressful environment of oilfield wastewater.

[0039] S4. Construct an anaerobic environment: High-purity nitrogen (≥99.9% purity) was continuously introduced into the sealed MEC reactor for at least 10 minutes. The establishment of an anaerobic environment is crucial for the enrichment of the anolyte biofilm. Electroactive microorganisms (such as Geobacteraceae) are strict or facultative anaerobic microorganisms; the presence of oxygen causes them to preferentially use oxygen as the electron acceptor rather than the anolyte for aerobic respiration, thus losing their electrochemical activity. Simultaneously, the anaerobic environment inhibits the growth of aerobic microorganisms, further increasing the selective pressure on electroactive anaerobic microorganisms. Introducing nitrogen for 10 minutes ensures that dissolved oxygen in the system drops to a negligible level, completing the construction of the anaerobic environment. After nitrogen introduction, the reactor was sealed and placed in a 25°C incubator for cultivation.

[0040] S5. Apply driving voltage: The MEC reactor is connected by wires, and a constant DC voltage of 0.8 V is applied across the anode and cathode of the reactor via a DC regulated power supply. The applied voltage plays the following key roles: First, it provides a constant and strong driving force for anodic oxidation, stabilizing the anode potential within a range favorable for extracellular electron transfer by electroactive microorganisms. This allows microorganisms to continuously and efficiently export electrons generated by intracellular metabolism to the anode, overcoming the metabolic resistance caused by the high-salt, highly toxic oilfield wastewater environment. Second, it generates an electric field screening effect, meaning only electroactive microorganisms with extracellular electron transfer capabilities can directionally transfer electrons generated by metabolism to the anode, thereby gaining a competitive advantage over non-electrogenic bacteria on the anode surface biofilm and achieving the directional enrichment of functional bacteria. Third, it helps promote the directional migration of microorganisms to the anode surface, accelerating the initial biofilm attachment process.

[0041] Below 0.5V, the driving force generated by the applied voltage is insufficient to effectively overcome the thermodynamic energy barrier of microbial metabolism in oilfield wastewater environment; above 1V, the higher voltage may lead to excessively high anode potential, producing oxidative intermediate products that are harmful to microorganisms. At the same time, the electrolysis voltage close to that of water may cause a large amount of gas evolution (oxygen evolution), which will damage the integrity of the biofilm structure.

[0042] S6, Series resistor: A 10Ω resistor is connected in series in the reactor's external circuit. This resistor serves the following functions: by measuring the voltage across the resistor in real time and applying Ohm's law, the real-time current in the external circuit is calculated, thus reflecting the metabolic activity and electron output level of the anolyte biofilm; simultaneously, the small series resistor has minimal impact on the total impedance of the external circuit, and will not significantly alter the system's operating state, ensuring interference-free monitoring. A data logger is used to acquire and record the voltage across the resistor in real time, generating a complete current-time curve, which is used to determine the biofilm enrichment process and the end of the operating cycle.

[0043] S7. Constant Temperature Incubation and Cycle Management: The MEC reactor was incubated in a 25°C incubator. The purpose of this incubation was to provide stable temperature conditions for the growth and metabolism of the anodic microorganisms.

[0044] The output voltage across the series resistor is monitored in real time using a data logger. The variation in output voltage reflects the formation process of the anodic biofilm: in the initial inoculation stage, electroactive microorganisms have not yet effectively colonized the anode, resulting in a low output current; as the biofilm gradually forms and microbial metabolic activity increases, the output current gradually climbs to its peak, marking the biofilm's entry into maturity; subsequently, as organic matter in the oilfield wastewater is gradually consumed, microbial metabolism is limited by the substrate, and the output current gradually decreases.

[0045] When the output voltage across the series resistor drops below 20mV, it is determined that an operating cycle has ended, and the organic substrate is essentially depleted. At this point, fresh culture medium must be immediately replaced to maintain microbial activity, and the next operating cycle should begin. This cycle is repeated until acclimation is complete. In each cycle, the proportion of PBS buffer nutrient solution is gradually reduced according to a gradient increasing principle, while the proportion of oilfield wastewater is simultaneously increased. This allows the microbial community to complete adaptive succession under progressively increasing substrate stress until it can operate stably with oilfield wastewater as the sole feed source.

[0046] Specifically, the ratio of oilfield wastewater to the first cycle is 1:3:1; the ratio of the second cycle is 1:2:2; the ratio of the third cycle is 0:1:1; and the ratio of the fourth cycle and thereafter is 0:0:1, meaning only oilfield wastewater is added.

[0047] At the final stage of domestication, the only feed material was ultimately oilfield wastewater, enabling the targeted screening of functional bacteria. This process, through progressively intensified stress selection pressure, forced the elimination of non-functional bacteria in the microbial community that could not tolerate the high-salt and highly toxic environment of oilfield wastewater, while functional bacteria with petroleum hydrocarbon metabolism capabilities and high-salt tolerance (such as Geobacteraceae and Thaurea) were enriched, ultimately achieving the targeted reconstruction of the functional microbial community in the anolyte biofilm.

[0048] Test Example 1 This test case is a comprehensive characterization of the system performance after the MEC reactor in Example 1 has been running stably.

[0049] First, electrochemical impedance spectroscopy was performed on the system using an electrochemical workstation, and an equivalent circuit was fitted to evaluate the system's electron transfer performance. For example... Figure 1 As shown, in the equivalent circuit, Rs represents the ohmic impedance (including electrolyte resistance, electrode resistance, and contact resistance), and Rp represents the polarization impedance (reflecting the charge transfer resistance at the biofilm / electrode interface). The measured results show that the total internal resistance of the MEC reactor is 37.5Ω, indicating that the biofilm / anolyte interface has good electron transfer performance.

[0050] Next, reactor effluent was collected after 5 and 10 days of cultivation, and the chemical oxygen demand (COD) was determined according to the standard potassium dichromate method to calculate the COD removal rate. At the same time, the coulombic efficiency was calculated based on the measured charge and the theoretical power generation.

[0051] Experimental results are as follows Figure 2 As shown, the anodic biofilm enriched by this invention achieves a COD removal rate of over 87% and a coulombic efficiency of over 38% for real oilfield wastewater. The treatment effects of the 5-day and 10-day samples show little difference, indicating that a stable and mature biofilm structure has been successfully enriched on the anodic carbon brush, and the biofilm activity remains good.

[0052] During the cultivation process, the current values ​​were recorded during the enrichment process to obtain complete current-time curves for the MEC reactor start-up and enrichment process, such as... Figure 3 As shown, the results indicate that the MEC system exhibits a high peak output current around day 2 of operation and maintains a periodic current response in subsequent cycles, suggesting that the anolyte biofilm has successfully completed initial enrichment and entered the maturity stage. Compared with the traditional MFC mode, the start-up time of this invention is significantly shortened, confirming the strong promoting effect of applied voltage on the rapid colonization of electroactive microorganisms in oilfield wastewater environments.

[0053] Finally, total DNA was extracted from the biofilm on the surface of the anode carbon brush, and 16S rRNA gene high-throughput sequencing (V3~V4 region) was performed to analyze the community structure and composition of functional microorganisms.

[0054] like Figure 4 As shown, the relative abundance analysis results indicate that the anolyte biofilm enriched using the MEC model possesses rich microbial diversity, with a high concentration of functional bacteria: Geobacteraceae (a typical electrogenic bacterium with highly efficient extracellular electron transfer capabilities) and Thaurea (a specific degrading bacterium with petroleum hydrocarbon metabolism capabilities) are the most dominant bacterial groups. Compared with the biofilm enriched using the MFC model, the relative abundance of Geobacteraceae is significantly increased, verifying the targeted enrichment effect of the MEC electric field screening effect on electroactive functional bacteria. While metabolizing organic substrates, Geobacteraceae efficiently outputs electrons to the anode through extracellular electron transfer pathways such as cytochrome c-mediated direct contact electron transfer (DMET) and conductive nanowires, making it the core functional bacteria for electrogenic and organic matter degradation in the BES system. Thauera bacteria possess both aerobic and facultative anaerobic metabolic capabilities, enabling them to degrade petroleum hydrocarbon organic pollutants such as benzene series compounds and polycyclic aromatic hydrocarbons under anaerobic conditions. They are important functional bacteria in the biological treatment of oilfield wastewater. Their high abundance accumulation in biofilms is an important microbiological basis for the efficient oilfield wastewater degradation capability of the biofilm obtained in this invention.

[0055] like Figure 8 As shown, in the anolyte enriched by the MEC model, the relative abundances of Geobacteraceae and Thaurea were 50.17% and 25.81%, respectively; while in the control MFC model, the relative abundances were 45.43% and 23.72%, respectively. Compared with the MFC model, the relative abundances of Geobacteraceae and Thaurea increased by 4.74 percentage points and 2.09 percentage points, respectively, in the MEC model, indicating that the above functional microbial communities have a higher enrichment level in the MEC model.

[0056] Figure 5 SEM images of the biofilm enriched on the surface of carbon fibers in carbon brush anodes are presented. The images clearly show that the carbon fiber surface is tightly covered by a dense and complex microbial film, with various microbial morphologies coexisting and diverse bacterial community morphologies, indicating that the biofilm structure is intact and the three-dimensional network is well developed.

[0057] Figure 6 and Figure 7 TEM images and elemental mapping distributions of *Geobacteraceae* and *Thauera* bacteria in the biofilm are presented. TEM characterization results show that rod-shaped bacteria, approximately 1.5 μm long and 500 nm wide, exhibit morphological characteristics highly consistent with *Geobacteraceae*; while spherical bacteria, approximately 500 nm in diameter, match the morphological characteristics of *Thauera*. Elemental mapping analysis further validated the cellular structural characteristics of these bacterial species, corroborating the 16S rRNA sequencing results, jointly confirming the successful enrichment of these two types of functional bacteria in the anolyte biofilm.

[0058] Finally, it should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. Those skilled in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents; that is, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for improving the biofilm enrichment rate at the anode of a microbial electrolysis cell, characterized in that, Includes the following steps: S1. Construct a microbial electrolysis cell reactor; S2. Add inoculum to the microbial electrolysis reactor; S3. Add PBS buffer nutrient solution and acclimatization substrate to the microbial electrolysis cell reactor; S4. Expel the air from the microbial electrolysis cell reactor to allow it to enter an anaerobic state; S5. Apply a constant micro voltage of 0.5~1V across the anode and cathode of the microbial electrolysis cell reactor; S6. Connect a resistor in series in the external circuit of the microbial electrolysis cell reactor; S7. Cultivate microorganisms under constant temperature conditions of 25~35℃, and monitor the voltage across the series resistor in real time. When the voltage across the series resistor is lower than 20mV, repeat S3~S7, and reduce the proportion of PBS buffer nutrient solution in each cycle while increasing the proportion of acclimatization substrate. Specifically, the volume ratio of inoculum, PBS buffer nutrient solution and acclimatization substrate in the first, second and third cycles are 1:3:1, 1:2:2 and 0:1:1, respectively; in the fourth cycle and thereafter, the ratio of inoculum, PBS buffer nutrient solution and acclimatization substrate is 0:0:1, so that the microbial community completes adaptive succession in the substrate stress environment that increases in each cycle until it uses acclimatization substrate as the only feed and maintains operation.

2. The method according to claim 1, characterized in that, In the S1 microbial electrolysis reactor, the anode is a porous carbon material, and the cathode is an inert noble metal electrode.

3. The method according to claim 2, characterized in that, The porous carbon material is one of carbon felt, carbon cloth, carbon paper, or carbon brush; the inert noble metal electrode is one of platinum sheet, platinum mesh, or platinum wire.

4. The method according to claim 1, characterized in that, S3 contains PBS buffered nutrient solution, which includes sodium or potassium dihydrogen phosphate, disodium or potassium hydrogen phosphate, ammonium chloride, potassium chloride, calcium chloride dihydrate, and a multivitamin solution.

5. The method according to claim 4, characterized in that, The PBS buffered nutrient solution in S3 includes: 15.4 mmol / L sodium dihydrogen phosphate, 32.3 mmol / L disodium hydrogen phosphate, 5.8 mmol / L ammonium chloride, 1.7 mmol / L potassium chloride, 10 mg / L calcium chloride dihydrate, and 2 mL / L multivitamin solution.

6. The method according to claim 1, characterized in that, The constant micro voltage in S5 is 0.8 V.

7. The method according to claim 1, characterized in that, The resistance value of the series resistor in S6 ranges from 10 to 100 Ω.

8. The application of the method as described in any one of claims 1-7 in the treatment of oilfield wastewater.

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