Method for enhancing biological electricity generation and sludge stabilization of excess sludge microbial fuel cell by pre-chlorination

Abstract

The present application belongs to the field of environmental engineering technology, and discloses a method for improving biological electricity generation and sludge stabilization of residual sludge in a microbial fuel cell by pre-chlorination, which comprises adding sodium hypochlorite to the residual sludge and mixing uniformly to pre-chlorinate the residual sludge; then, adding the pre-chlorinated residual sludge to a sludge microbial fuel cell after sludge domestication, and continuing to operate the sludge microbial fuel cell. By using sodium hypochlorite to pre-chlorinate the residual sludge and strictly controlling the concentration of sodium hypochlorite in the pre-chlorinated residual sludge to be 0.2 mg / L, the present application can realize the resource utilization and sludge stabilization of the residual sludge at room temperature based on the microbial fuel cell technology. By the sludge pre-chlorination method, the performance of the microbial fuel cell can be improved, and the biological electricity generation and sludge stabilization efficiency of the microbial fuel cell can be improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental engineering, and more particularly relates to a method for improving biological electricity generation and sludge stabilization of residual sludge by pre-chlorination, which can effectively promote the treatment and resource utilization of residual sludge. BACKGROUND

[0002] The common sludge disposal methods at present include open-air stacking, landfilling and incineration, etc. These methods often have the characteristics of large land occupation, secondary pollution and high capital investment.

[0003] Bioelectrochemical systems (BES) can realize the sustainable treatment and energy recovery of wastewater and sludge at the same time as a new technology. Sludge microbial fuel cell (SMFC) as a kind of BES, its principle is that anodic microorganisms use organic matter in sludge as carbon source and energy, produce metabolic products, protons (H + ) and electrons (e - ) through anaerobic metabolism, degrade sludge and form current at the same time. The treatment of municipal sludge by MFC is a new technology developed in recent years, and researchers have done a lot of research in this field. For example, the patent with the application number 201110445557.2 provides a method for enhancing the electricity generation performance of MFC using residual sludge as fuel and for enhancing sludge reduction. 200 mM NaCl is added to the residual sludge to enhance the conductivity of the solution, and neutral protease and alpha-amylase are added in a ratio of 1:(1-4). This method has good removal effect on total chemical oxygen demand (TCOD), total suspended solids (TSS) and volatile suspended solids (VSS), which reaches 87.29%, 91.75% and 95.01% respectively, but the enzyme has high requirement for temperature, and the best enhancement effect is at 40℃.

[0004] The main components of the residual sludge in municipal sewage treatment plant are polysaccharides and proteins. Microorganisms cannot directly utilize these macromolecular organic matters, and only when the macromolecular substances are decomposed into small molecular sugars, polypeptides and amino acids can they be absorbed and utilized by microorganisms. The treatment efficiency of residual sludge MFC is affected by various factors, such as the complex structure of sludge, cell lysis rate limiting, extracellular polymeric substances and bacterial cell wall / membrane forming a strong barrier to hydrolytic enzymes. In order to overcome the above problems, we need to take a series of measures to pretreat the sludge before biological oxidation, so as to improve the utilization efficiency of sludge. Various pretreatment methods are reported in the literature, such as photochemical, ozonation, thermal hydrolysis, ultrasonic, enzymatic lysis, acidification, alkaline hydrolysis and other methods. In addition, these pretreatments can be applied in various combinations to improve process efficiency, such as alkaline heat combination, heat H2O2 combination, microwave combined with alkaline heat pretreatment and ultrasonic coupled with Fenton oxidation. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the purpose of the present application is to provide a method for improving the performance of residual sludge microbial fuel cell by pre-chlorination, which can realize the resource utilization and sludge stabilization of residual sludge at room temperature based on microbial fuel cell technology by using sodium hypochlorite to pre-chlorinate residual sludge and strictly controlling the concentration of sodium hypochlorite in the pre-chlorinated residual sludge to be 0.2 mg / L. Through the sludge pre-chlorination method of the present application, the performance of microbial fuel cell can be improved, especially the biological power generation and sludge stabilization efficiency of microbial fuel cell.

[0006] To achieve the above purpose, according to one aspect of the present application, a method for improving the performance of residual sludge microbial fuel cell by pre-chlorination is provided, characterized in that the method is to add sodium hypochlorite to the residual sludge and mix uniformly, thereby pre-chlorinating the residual sludge; then, the pre-chlorinated residual sludge is added to the sludge microbial fuel cell after microbial domestication, and the sludge microbial fuel cell is continued to run.

[0007] Among them, the settling ratio of the pre-chlorinated residual sludge is controlled at 33%, and the concentration of sodium hypochlorite is 0.2 mg / L.

[0008] As a further preferred embodiment of the present application, the pre-chlorinated residual sludge is further subjected to a standing treatment before being added to the sludge microbial fuel cell after microbial domestication.

[0009] As a further preferred embodiment of the present application, the standing treatment is specifically standing for 2 h.

[0010] As a further preferred aspect of the present application, the pre-chlorinated excess sludge can improve the electricity generation efficiency of the sludge microbial fuel cell compared to the excess sludge without pre-chlorination.

[0011] As a further preferred aspect of the present application, the pre-chlorinated excess sludge can improve the sludge stabilization efficiency of the sludge microbial fuel cell compared to the excess sludge without pre-chlorination.

[0012] According to another aspect of the present application, there is provided a sludge microbial fuel cell using pre-chlorinated excess sludge obtained based on the above method.

[0013] Compared with the prior art, the present application provides a pre-chlorination means to strengthen MFC in treating excess sludge, which is convenient to operate and low in cost, can promote the resource utilization of excess sludge in municipal wastewater treatment plants, and improve the biological electricity generation performance of MFC while strengthening sludge stabilization. The present application can improve the sludge stabilization efficiency of the sludge microbial fuel cell, including reducing the sludge concentration (mixed liquor suspended solids concentration and mixed liquor volatile suspended solids concentration), improving the release of sludge soluble chemical oxygen demand, improving the degradation rate of sludge extracellular polymers (polysaccharides and proteins), and reducing the tightness of sludge floc structure. The present application is based on MFC, which not only treats waste, but also fully and effectively utilizes resources while treating sludge and recovering clean energy.

[0014] The present application uses sodium hypochlorite to pre-chlorinate sludge. On the one hand, sodium hypochlorite solution is low in price and very common in life. On the other hand, sodium hypochlorite is a strong oxidizing agent, which can oxidize macromolecular organic matter in sludge and decompose it into simple small molecules (this process can increase the bioavailability of sludge organic matter, thereby reducing the difficulty of subsequent biological treatment). At the same time, the oxidizing property of sodium hypochlorite also makes it an effective disinfectant, which can kill pathogenic microorganisms such as bacteria, viruses and parasites in sludge, thereby reducing the potential harm of sludge to the environment and human health. In addition, sodium hypochlorite also has a cytolysis effect, which can destroy the floc structure of sludge, making it more easily disposed of by MFC.

[0015] The application strictly controls the concentration of sodium hypochlorite in the pre-chlorinated residual sludge to be 0.2 mg / L, which can effectively improve the performance of the microbial fuel cell of the residual sludge. As shown in the examples below, compared with the non-chlorinated group, the output voltage, redox potential, polarization current density and volume power density of the MFC are greatly improved; after the MFC treatment, the mixed liquor volatile suspended solids (MLVSS) concentration is significantly reduced, the soluble chemical oxygen demand (SCOD) release is significantly improved, the polysaccharide and protein degradation rate in the extracellular polymeric substance (EPS) is improved, and the stability of the protein structure is also decreased.

[0016] In summary, by using sodium hypochlorite to pre-chlorinate the residual sludge and controlling the concentration of sodium hypochlorite in the pre-chlorinated residual sludge to be 0.2 mg / L, the performance of the MFC in treating the residual sludge can be effectively improved, and the realization of the resource utilization and stabilization goals can be promoted. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a structural diagram of the MFC. In the figure, 1 is a main plate, 2 is a non-porous cover plate, 3 is a porous cover plate, 4 is a nut, 5 is a gasket, 6 is a gasket, 7 is a rubber plug, 8 is a stud, 9 is an air cathode, 10 is a carbon felt anode, 11 is a conductive titanium wire, 12 is a resistor, and 13 is a titanium wire hook.

[0018] Figure 2 is a start-up process diagram of the MFC.

[0019] Figure 3 is an output voltage image of the MFC constructed by the residual sludge with different pre-chlorination degrees (i.e., different concentrations of sodium hypochlorite). Among them, Figure 3 (A) in corresponds to the 0 mg / L group (control group, i.e., without pre-chlorination), Figure 3 (B) in corresponds to the 0.2 mg / L group, Figure 3 (C) in corresponds to the 0.5 mg / L group, Figure 3 (D) in corresponds to the 1 mg / L group.

[0020] Figure 4 is a comparison diagram of CV curves of different MFC reactors.

[0021] Figure 5 is a comparison diagram of polarization curves and power density curves of the control group and the 0.2 mg / L group MFC. Among them, Figure 5 (A) in corresponds to the 4-stage polarization curve, Figure 5 (B) in corresponds to the 4-stage power density curve.

[0022] Figure 6 is a plot of sludge MLSS and MLVSS changes.

[0023] Figure 7 is a plot of residual sludge SCOD changes.

[0024] Figure 8 is a plot of residual sludge EPS polysaccharide and protein content changes.

[0025] Figure 9 is a plot of residual sludge EPS infrared spectrum predicting different protein structure stability.

[0026] In addition, Figure 6 , Figure 7 , Figure 8 , Figure 9 The "Raw sludge" related performance data appearing in the above table are all detected by diluting the residual sludge collected from the thickening tank of Longwangzui Sewage Treatment Plant to the same multiple (i.e., diluting the original residual sludge to a sludge settling ratio of 33%). DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0028] MFC fabrication, assembly, and startup: (1) Anode fabrication. Cut carbon felt into a cuboid 2cm long, 2cm wide, and 1cm high using scissors. Place it in a beaker and add acetone, anhydrous ethanol, and ultrapure water in sequence. Clean each with ultrasonic cleaning for 5 minutes and then dry in a 50℃ oven for 5 hours before use. (2) Cathode fabrication. First, cut 50-mesh (0.15mm wire diameter, 0.35mm aperture) steel wire mesh into circular pieces with a diameter of 3.8cm. Stack multiple circular steel wire meshes and then flatten them using a tablet press. Then clean the steel wire mesh using the same method as cleaning the anode. Second, weigh 5g of polyvinylidene fluoride (PVDF) powder using a balance and mix it with 50mL of N,N-dimethylacetamide solvent in a beaker. Heat at 80℃ for more than 4 hours until it becomes transparent and viscous. The third step is to weigh 0.3g of activated carbon and 0.03g of conductive carbon black, mix them in a beaker, vortex and shake, and dry them in an oven at 80℃ to remove moisture. Add 0.9-1.1mL of PVDF solution, stir and mix evenly, and transfer it evenly to one side of a circular stainless steel mesh. Then, immerse the cathode side down in ultrapure water for 15 minutes, and then take it out and let it air dry naturally before use. (3) MFC assembly. Referring to the known single-chamber cubic microbial fuel cell construction method in the prior art, the single-chamber cubic microbial fuel cell reactor (size: 6cm×5cm×5cm, effective volume of 28mL) obtained in this embodiment is as follows: Figure 1 As shown, it consists of four acrylic plates, four studs, eight nuts, three washers, and two gaskets. The anode and cathode are fixed on the reactor. An external resistor with a resistance of 1000Ω is connected by a titanium wire. Then, the matrix solution (see the end of this paragraph for the formula) is injected into the MFC single-chamber reactor to form a circuit, thereby generating electricity. (4) MFC start-up. During the start-up of the microbial fuel cell, sludge from the sewage treatment plant is used as the inoculum to provide the electricity-generating bacteria. During the inoculation period, the sludge and matrix are mixed at a volume ratio of 1:1 and injected into the microbial fuel cell chamber. The solution in the chamber is replaced every 72 hours, and the inoculation is repeated 3 to 5 times. During the acclimatization period, the matrix solution is injected into the microbial fuel cell chamber and the solution in the chamber is replaced every 48 hours. When the MFC output voltage rises to a stable value (about 350mV), the start-up can be considered successful. Figure 2 The formulation per liter of matrix includes 982.5 mL of phosphate-buffered saline (PBS), 12.5 mL of trace element solution, 5 mL of vitamin solution, and 1 g of sodium acetate (NaAc). PBS is prepared by dissolving 0.13 g of KCl, 0.31 g of NH4Cl, 4.576 g of Na2HPO4, and 2.772 g of NaH2PO4 in 1 L of deionized water.

[0029] Sludge pre-chlorination and MFC treatment process: The residual sludge in the concentration tank of the wastewater treatment plant was collected, diluted to a settling ratio of 33%, and then sodium hypochlorite solution was added. The concentration of sodium hypochlorite was set to 0 mg / L, 0.2 mg / L, 0.5 mg / L and 1 mg / L, and the pre-chlorination was carried out for 2 hours. Then the pre-chlorinated sludge was added to the MFC, and new sludge was replaced after three days. The replacement was carried out for seven times, and the total time was 21 days (operated at room temperature).

[0030] In this embodiment, the mud-water mixture from the anoxic section of Wuhan Longwangzui Wastewater Treatment Plant was used as the bacteria solution, and the MFC reactor was successfully started. Figure 2 The residual sludge in the concentration tank of Longwangzui Wastewater Treatment Plant was collected for pre-chlorination treatment, and then added to the MFC for biological oxidation treatment. The specific treatment effect is shown as follows:

[0031] (1) Pre-chlorination improves the electricity generation performance of microbial fuel cell for treating residual sludge

[0032] The output voltage, CV (cyclic voltammetry) curve, polarization curve and power density were used as indicators to explore the change of resource production performance of sludge MFC under different doses of pre-chlorination. As shown in Figure 3 , the output voltage of the MFC in the 0.2 mg / L group increased significantly after 6 days and even reached about 600 mV, which was higher than the 400 mV of the substrate solution after domestication (as shown in Figure 2 , the output voltage of the MFC after domestication was about 400 mV), and the voltage values of the control group and the 0.5 mg / L and 1 mg / L groups were very low, indicating that appropriate pre-chlorination could promote the resource production of MFC for treating residual sludge. As shown in Figure 4 , in the CV curve, the redox potential of the 0.2 mg / L group increased significantly, which was 5 times higher than that of the control group (the highest peak of the curve represents the oxidation peak, the lowest peak represents the reduction peak, and the difference between them is equal to the redox potential). As shown in Figure 5 , the polarization curve and power density curve of the 0.2 mg / L group were significantly higher than those of the control group, and the maximum polarization current density and maximum power density increased by 8% and 15.6%, respectively, which directly reflected that pre-chlorination could reduce the voltage loss of MFC and increase the power density.

[0033] (2) Pre-chlorination improves the stability of microbial fuel cell for treating residual sludge

[0034] The influence of pre-chlorination on the stability of MFC for treating residual sludge was analyzed from several aspects such as mixed liquid suspended solids (MLSS), MLVSS, SCOD and EPS components. As shown in Figure 6As shown, the MLSS and MLVSS of the control group sludge were significantly reduced by 38.13% and 44.68%, respectively, after MFC treatment. This indicates that MFC can effectively reduce the sludge concentration. Pre-chlorination further promotes the reduction of sludge, especially the organic part (MLVSS). For example, when the sludge pre-chlorination dosage is 0.2 mg / L, the MLSS and MLVSS of the sludge in the MFC are reduced by 39.19% and 57.42%, respectively.

[0035] MFC has the function of sludge decomposition, especially for the organic components, which is verified by the increase of sludge SCOD from 10.53 mg / L to 42.41 mg / L after treatment of the control group Figure 7 ). The particulate COD (such as EPS) is first oxidized and decomposed into SCOD (such as soluble EPS) in the MFC by microorganisms, and then the SCOD is absorbed by the electricity-producing bacteria and converted into electrical energy and metabolites. Through sludge pre-chlorination, the release of SCOD is greatly enhanced. In particular, in the 0.2 mg / L dosage group, the SCOD reaches 127.11 mg / L, which is more than 11 times higher. Therefore, these results show that pre-chlorination promotes the stabilization of sludge by promoting the decomposition of microbial oxidation of the organic part of the sludge in the MFC.

[0036] EPS is an important component of the organic components of sludge. As shown in Figure 8 , the contents of polysaccharides and proteins in sludge EPS are significantly reduced during the treatment of residual sludge in the MFC, and the pre-chlorination at a dosage of 0.2 mg / L increases the degradation rate of polysaccharides and proteins in EPS by 18.6% and 16.3%, respectively, compared with the control group.

[0037] The amide I region of 1600-1700 cm -1 in the infrared spectrum is usually used to identify and analyze the structure of protein compounds. Peak differentiation analysis of the amide I region determines the secondary structure of extracellular proteins in sludge EPS (i.e. alpha-helix, beta-sheet, beta-turn and random coil). The ratio of alpha-helix / (beta-sheet+random coil) is used to assess the tightness of the sludge extracellular protein, and the higher the value, the more compact the protein structure. As shown in Figure 9 , compared with the control group, the part of the protein involved in the amide I region of the infrared spectrum functional group of the pre-chlorination group and the control group, the stability of the protein structure of the sludge EPS after chlorination at a dosage of 0.2 mg / L is significantly reduced by 50% compared with the control group, which is conducive to the biological oxidation and utilization of MFC.

[0038] It can be seen that the SMFC operation results show that compared with the non-chlorinated group, the output voltage, redox potential, polarization current density and volume power density of the MFC are greatly improved; after MFC treatment, the volatile suspended solid concentration MLVSS of the sludge mixed liquor is significantly reduced, the release of sludge SCOD is significantly improved, the degradation rate of polysaccharide and protein in extracellular polymeric substance EPS is improved, and the stability of protein structure also decreases.

[0039] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for enhancing the performance of the output voltage of a microbial fuel cell using excess sludge by pre-chlorination, characterized in that, The method is to add sodium hypochlorite into the residual sludge and mix uniformly, so as to pre-chlorinate the residual sludge; Then, the pre-chlorinated residual sludge is added into the sludge microbial fuel cell after the sludge is domesticated, and the sludge microbial fuel cell is continuously operated. In the pre-chlorinated residual sludge, the sludge settling ratio is controlled at 33%, and the concentration of sodium hypochlorite is 0.2 mg / L.

2. The method of claim 1, wherein, The pre-chlorinated residual sludge is further subjected to a standing treatment before being added into the sludge microbial fuel cell after the sludge is domesticated.

3. The method of claim 2, wherein, The standing treatment is specifically standing for 2 h.

4. The method of claim 1, wherein, Compared with the residual sludge without pre-chlorination, the pre-chlorinated residual sludge can improve the electricity generation efficiency of the sludge microbial fuel cell.

5. The method of claim 1, wherein, Compared with the residual sludge without pre-chlorination, the pre-chlorinated residual sludge can improve the sludge stabilization efficiency of the sludge microbial fuel cell.

6. A sludge microbial fuel cell using pre-chlorinated residual sludge obtained based on the method according to any one of claims 1-5.

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