Method for improving biological power generation and sludge stabilization of residual sludge microbial fuel cell through pre-chlorination

Abstract

The invention belongs to the technical field of environmental engineering, and discloses a method for improving residual sludge microbial fuel cell biological power generation and sludge stabilization through pre-chlorination, and the method comprises the following steps: adding sodium hypochlorite into residual sludge, and uniformly mixing, so as to pre-chloridize the residual sludge; and then, adding the pre-chlorinated excess sludge into the sludge microbial fuel cell subjected to microbial acclimation, and continuously operating the sludge microbial fuel cell. According to the method disclosed by the invention, the residual sludge is pre-chlorinated by using the sodium hypochlorite, and the concentration of the sodium hypochlorite in the pre-chlorinated residual sludge is strictly controlled to be 0.2 mg / L, so that resource utilization and sludge stabilization of the residual sludge can be realized at normal temperature based on a microbial fuel cell technology. Through the sludge pre-chlorination means, the performance of the microbial fuel cell can be improved, and especially the biological power generation and sludge stabilization efficiency of the microbial fuel cell can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental engineering, and more specifically, relates to a method for pre-chlorination to enhance the bio-electricity production of excess sludge microbial fuel cells and sludge stabilization, which can effectively promote the treatment and resource utilization of excess sludge. Background Art

[0002] At present, common sludge disposal methods include open-air dumping, landfilling and incineration, etc. These methods often occupy a large area, cause secondary pollution and require high capital investment.

[0003] As an emerging technology, bioelectrochemical systems (BES) can achieve sustainable treatment and energy recovery of wastewater and sludge. Sludge microbial fuel cell (SMFC) is a type of BES. Its principle is that anode microorganisms use organic matter in sludge as carbon source and energy source to produce metabolites, protons (H + ) and electron (e - ), degrading sludge and generating electric current at the same time. Using MFC to treat municipal sludge is a new technology developed in recent years, and researchers have done a lot of research in this regard. For example, the patent with application number 201110445557.2 provides an enzyme-enhanced MFC power generation performance using excess sludge as fuel and a method for enhancing sludge reduction. 200mM NaCl is added to the excess sludge to enhance the conductivity of the solution, and neutral protease and α-amylase are added in a ratio of 1: (1-4). This method has a good removal effect on total chemical oxygen demand (TCOD), total suspended solids (TSS) and volatile suspended solids (VSS), reaching 87.29%, 91.75% and 95.01% respectively, but the enzyme has a high requirement for temperature, and the best enhancement effect is at 40°C.

[0004] The main components of the residual sludge from urban domestic sewage treatment plants are polysaccharides and proteins, but microorganisms cannot directly utilize these macromolecular organic substances. They can only be absorbed and utilized by microorganisms when the macromolecular substances are decomposed into small molecular sugars, peptides and amino acids. The treatment efficiency of the residual sludge MFC is affected by many factors, such as the complex structure in the sludge, the rate limit of cell lysis, the strong barrier formed by the penetration of extracellular polymers and bacterial cell walls / membranes to hydrolases. In order to overcome the above problems, we need to take a series of measures to pretreat the sludge before biological oxidation to improve the utilization efficiency of the sludge. Various pretreatment methods have been reported in the literature, such as photochemical, ozonation, thermal hydrolysis, ultrasound, enzyme lysis, acidification, alkaline hydrolysis and other methods. In addition, these pretreatments can also be applied to a variety of combinations to improve process efficiency, such as alkali-heat combination, hot H2O2 combination, microwave combined with alkali-heat pretreatment and ultrasound-coupled Fenton oxidation. Summary of the invention

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

[0006] To achieve the above object, according to one aspect of the present invention, a method for improving the performance of excess sludge microbial fuel cell by pre-chlorination is provided, characterized in that the method comprises adding sodium hypochlorite to the excess sludge and mixing evenly, thereby pre-chlorinating the excess sludge; then, adding the pre-chlorinated excess sludge to the sludge microbial fuel cell after microbial acclimation, and continuing to operate the sludge microbial fuel cell;

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

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

[0009] As a further preferred embodiment of the present invention, the static treatment is specifically static treatment for 2 hours.

[0010] As a further preferred embodiment of the present invention, the pre-chlorinated excess sludge can improve the electricity generation efficiency of the sludge microbial fuel cell compared to the excess sludge not pre-chlorinated.

[0011] As a further preferred embodiment of the present invention, the pre-chlorinated excess sludge can improve the sludge stabilization efficiency of the sludge microbial fuel cell compared to the excess sludge not pre-chlorinated.

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

[0013] Through the above technical solutions conceived by the present invention, compared with the prior art, the present invention provides a pre-chlorination method that is easy to operate and low-cost to strengthen the MFC treatment of excess sludge, which can promote the resource utilization of excess sludge in urban sewage treatment plants, and improve the bio-electricity performance of MFC while strengthening sludge stabilization. The present invention can improve the sludge stabilization efficiency of sludge microbial fuel cells, including reducing sludge concentration (mixed liquor suspended solids concentration and mixed liquor volatile suspended solids concentration), increasing the release of sludge soluble chemical oxygen demand, increasing the degradation rate of sludge extracellular polymers (polysaccharides and proteins), and reducing the compactness of sludge floc structure. Based on MFC, the present invention recovers clean energy while treating sludge, which not only treats waste, but also fully and effectively utilizes resources.

[0014] The present invention adopts sodium hypochlorite to carry out sludge pre-chlorination. On the one hand, sodium hypochlorite solution is low in price and very common in life; secondly, sodium hypochlorite is a strong oxidant, 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 in sludge, such as bacteria, viruses and parasites, thereby reducing the potential harm of sludge to the environment and human health; on the other hand, sodium hypochlorite also has a cell-breaking effect, which can destroy the floc structure of sludge, making it easier to be further treated and disposed by MFC.

[0015] The present invention particularly strictly controls the concentration of sodium hypochlorite in the pre-chlorinated excess sludge to 0.2 mg / L, which can effectively improve the performance of excess sludge microbial fuel cells. As illustrated in the following embodiments, compared with the unchlorinated group, the output voltage, redox potential, polarization current density, and volume power density of the MFC in the chlorinated group have been greatly improved; after MFC treatment, the concentration of mixed liquor volatile suspended solids (MLVSS) is significantly reduced, the release of soluble chemical oxygen demand (SCOD) is significantly increased, the degradation rate of polysaccharides and proteins in extracellular polymeric substances (EPS) is improved, and the stability of protein structure is also reduced.

[0016] In summary, the present invention uses sodium hypochlorite to pre-chlorinate the excess sludge and controls the concentration of sodium hypochlorite in the pre-chlorinated excess sludge to 0.2 mg / L, which can effectively improve the performance of MFC in treating excess sludge and promote the realization of resource utilization and stabilization goals. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a diagram of the MFC structure. In the figure: 1 is the main board, 2 is the cover plate without holes, 3 is the cover plate with holes, 4 is the nut, 5 is the gasket, 6 is the washer, 7 is the rubber plug, 8 is the stud, 9 is the air cathode, 10 is the carbon felt anode, 11 is the conductive titanium wire, 12 is the resistor, and 13 is the titanium wire hook.

[0018] Figure 2 This is the MFC startup process diagram.

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

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

[0021] Figure 5 This is a comparison of the polarization curve and power density curve of the control group and the 0.2mg / group MFC. Figure 5 (A) in the figure corresponds to the 4-stage polarization curve. Figure 5 (B) in the figure corresponds to the power density curve of the 4th stage.

[0022] Figure 6 It is the change chart of sludge MLSS and MLVSS.

[0023] Figure 7 It is the change of excess sludge SCOD.

[0024] Figure 8 This is a graph showing changes in EPS polysaccharide and protein content in residual sludge.

[0025] Fig. 9 It is a line graph of the stability of different protein structures predicted by infrared spectrum of residual sludge EPS.

[0026] in addition, Figure 6 , Figure 7 , Figure 8 , Fig. 9 The “Raw sludge” related performance data appearing in the test are all obtained by diluting the residual sludge originally collected from the thickening tank of Longwangzui Wastewater 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 purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Preparation, assembly and start-up of MFC: (1) Preparation of anode. Use scissors to make carbon felt into a rectangular block with a length of 2 cm, a width of 2 cm and a height of 1 cm. Put it into a beaker and pour acetone, anhydrous ethanol and ultrapure water in turn. After ultrasonic cleaning for 5 minutes, put it in a 50℃ oven to dry for 5 hours before use. (2) Preparation of cathode. The first step is to cut a 50-mesh (0.15mm wire diameter, 0.35mm aperture) steel wire mesh into a 3.8cm diameter round piece. Stack multiple round steel wire meshes and flatten them using a tablet press. Then clean the steel wire mesh in the same way as the anode. The second step is to weigh 5g of polyvinylidene difluoride (PVDF) powder on a scale, mix it with 50mL of N,N-dimethylacetamide solvent in a beaker, and heat it 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 oscillate, and put them in an oven at 80°C to remove moisture. Add 0.9-1.1mL of PVDF solution, stir and mix evenly, and transfer it all evenly to one side of the round stainless steel mesh. Then soak the cathode face down in ultrapure water for 15 minutes, then take it out and dry it naturally before use. (3) MFC assembly. Referring to the single-chamber cubic microbial fuel cell construction method known in the prior art, the single-chamber cubic microbial fuel cell reactor (size: 6cm×5cm×5cm, effective volume is 28mL) obtained in this embodiment is as follows Figure 1 As shown, it consists of four acrylic plates, four studs, eight nuts, three gaskets, and two washers. The anode and cathode are fixed on the reactor, and an external resistor with a resistance of 1000Ω is connected through a titanium wire. Then, the matrix solution (the formula is detailed at the end of this paragraph) is injected into the MFC single-chamber reactor to form a loop, so that the battery can generate electricity. (4) MFC startup. During the startup of the microbial fuel cell, the sludge from the sewage treatment plant is used as the inoculum to provide the electricity-generating bacteria. During the inoculation period, the sludge and the matrix are mixed in 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 inoculated 3 to 5 times; during the acclimation 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 continues to rise to a stable value (about 350mV), it can be considered that the startup is successful ( Figure 2 ). The formula for each 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: Collect the residual sludge in the thickening tank of the sewage treatment plant, dilute the sludge to a sedimentation ratio of 33%, then add sodium hypochlorite solution, set the sodium hypochlorite concentration to 0 mg / L, 0.2 mg / L, 0.5 mg / L and 1 mg / L, let it stand for 2 hours, then add the pre-chlorinated sludge into the MFC, replace it with new sludge after three days, and replace it seven times in a row for a total of 21 days (operating under normal temperature conditions).

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

[0031] (1) Pre-chlorination improves the electricity production performance of microbial fuel cells in treating waste sludge

[0032] The present invention uses output voltage, CV (cyclic voltammetry) curve, polarization curve and power density as indicators to explore the changes in the resource-based power generation performance of sludge MFC under different doses of pre-chlorination conditions. Figure 3 As shown in Figure 2, the MFC output voltage of the 0.2 mg / L group increased significantly after 6 days and even reached about 600 mV, exceeding the 400 mV of the matrix solution after acclimation (e.g. Figure 2 As shown in the figure, the output voltage of the MFC after acclimation is around 400mV), while the voltage values ​​of the control group and the 0.5mg / L and 1mg / L groups are very low, indicating that appropriate pre-chlorination can promote the resource-based electricity generation of MFC in treating excess sludge. Figure 4 As shown in the CV curve, the redox potential of the 0.2 mg / L group increased significantly, 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 is equal to the redox potential). Figure 5 As shown, 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 intuitively reflected that pre-chlorination can reduce MFC voltage loss and increase power density.

[0033] (2) Pre-chlorination improves the stabilization performance of residual sludge in microbial fuel cells

[0034] The present invention analyzes the effect of pre-chlorination on the stabilization performance of excess sludge treated by MFC from several aspects such as mixed liquid suspended solids concentration (MLSS), MLVSS, SCOD and EPS components. Figure 6As shown in the figure, after MFC treatment, the MLSS and MLVSS of the control sludge were significantly reduced by 38.13% and 44.68%, respectively. This shows that MFC can effectively reduce sludge concentration. Pre-chlorination further promoted the reduction of sludge, especially for the organic part (MLVSS). For example, when the sludge pre-chlorination dose was 0.2 mg / L, the MLSS and MLVSS of the sludge in MFC were reduced by 39.19% and 57.42%, respectively.

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

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

[0037] 1600-1700cm in infrared spectrum -1 The amide I region is usually used to identify and analyze the structure of protein compounds. The peak differentiation analysis of the amide I region determined the secondary structure of the extracellular proteins in the sludge EPS (i.e., α-helix, β-sheet, β-turn, and random coil). The ratio of α-helix / (β-sheet + random coil) is used to evaluate the compactness of the sludge extracellular proteins. The higher the value, the tighter the protein structure. Fig. 9 As shown, compared with the control group, the amide I region of the infrared spectrum functional group involved in the protein part, the structural stability of the sludge EPS protein after chlorination at a dose of 0.2 mg / L was significantly reduced by 50% compared with the control group, which is beneficial to the biological oxidation utilization of MFC.

[0038] It can be seen that the SMFC operation results show that compared with the chlorinated group and the unchlorinated group, the output voltage, redox potential, polarization current density and volume power density of MFC have been greatly improved; after MFC treatment, the volatile suspended solids concentration MLVSS of the sludge mixed liquor decreased significantly, the release of sludge SCOD increased significantly, the degradation rate of polysaccharides and proteins in the extracellular polymer EPS increased, and the stability of the protein structure also decreased.

[0039] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the performance of excess sludge microbial fuel cells by pre-chlorination, characterized in that: The method comprises adding sodium hypochlorite to the residual sludge and mixing the mixture evenly, thereby pre-chlorinating the residual sludge; Then, the pre-chlorinated excess sludge is added to the sludge microbial fuel cell after the microorganisms are domesticated, and the sludge microbial fuel cell is continued to operate; Wherein, in the pre-chlorinated excess sludge, the sludge settling ratio is controlled at 33%, and the concentration of sodium hypochlorite is 0.2 mg / L.

2. The method according to claim 1, characterized in that: The pre-chlorinated excess sludge is also subjected to a static treatment before being added to the sludge microbial fuel cell after microbial acclimation.

3. The method according to claim 2, characterized in that: The static treatment is specifically to stand for 2 hours.

4. The method according to claim 1, characterized in that: Compared with the residual sludge that has not been pre-chlorinated, the pre-chlorinated residual sludge can improve the electricity generation efficiency of the sludge microbial fuel cell.

5. The method according to claim 1, characterized in that: Compared with the residual sludge not subjected to 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 excess sludge obtained by the method according to any one of claims 1 to 5.

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