A method for enhancing dewatering of digested sludge by recycling flocculants

Abstract

The present invention discloses a method for strengthening the dehydration of digested sludge by recycling flocculants, and relates to the technical field of urban sludge treatment. The method comprises the following steps: identifying and utilizing the recyclable flocculant PAC in the residual sludge, adding CaO2 to the residual sludge containing PAC, mixing evenly, and adjusting the pH value; sending the treated residual sludge into an anaerobic digestion reactor, monitoring the methane production and daily gas production until the gas is exhausted, that is, the anaerobic digestion is completed; dehydrating the digested sludge obtained after the anaerobic digestion is completed, so as to achieve enhanced dehydration of the digested sludge. The present invention is conducive to reducing the moisture content of the digested sludge, effectively improving the dehydration efficiency and resource recycling rate of the digested sludge; and polyaluminum chloride is used as a recycled flocculant to effectively break up the digested sludge particles, which can not only ensure the effective discharge of water between the digested sludge particles, but also optimize the fluidity and compressibility of the digested sludge, which is convenient for subsequent transportation and treatment.

Description

Technical Field

[0001] The invention relates to the technical field of urban sludge treatment, and in particular to a method for strengthening the dehydration of digested sludge by recycling flocculants. Background Art

[0002] Sludge, as a byproduct of sewage treatment, contains toxic and hazardous substances such as pathogens, heavy metals and persistent organic matter. If not properly treated and disposed of, it can easily lead to secondary pollution of groundwater and soil, thereby weakening the environmental benefits of sewage treatment facilities.

[0003] At present, technologies such as sludge incineration, blending, gasification, anaerobic digestion and alkaline thermal hydrolysis have made certain progress in the resource utilization of sludge. Among them, anaerobic digestion technology can not only effectively stabilize perishable organic matter and significantly reduce the number of pathogens, but also significantly reduce the volume of sludge, thus becoming the mainstream technology for sludge stabilization treatment at home and abroad. However, the application of anaerobic digestion technology has also brought new challenges, namely the substantial increase in the output of digested sludge, so efficient treatment and disposal of digested sludge is particularly important.

[0004] The treatment and disposal of digested sludge is a complex process, in which dehydration is one of the key links. Dehydration can reduce the volume and mass of sludge, making it easier to dispose of it later. The dehydration effect also directly affects the overall efficiency of sludge treatment. If too much water remains in the sludge, it will increase the difficulty and cost of sludge treatment and disposal. Compared with residual sludge, digested sludge particles are fine and have a large specific surface area, which enhances the interaction forces between sludge particles and between particles and water molecules (such as van der Waals forces, surface tension, etc.). Fine particles tend to form aggregates, trapping water inside and making it difficult to separate by conventional methods. Digested sludge also contains a large number of microbial cells, organic matter (such as proteins, polysaccharides, etc.), inorganic matter (such as metal ions, etc.) and colloidal substances. The interweaving of these components makes the sludge structure complex and dehydration more difficult.

[0005] In the process of sludge dewatering, sludge conditioning with chemicals is crucial. Through conditioning, the colloidal structure of the sludge can be destroyed, the hydrophilicity of the sludge can be reduced, and the interaction force between the sludge particles and water molecules can be reduced, making the sludge easier to dehydrate. A common method is to add specific cationic polymer coagulants for charge neutralization and adsorption bridging to improve the sludge dewatering effect. However, the use of external chemicals will increase the economic and environmental costs of sludge treatment and disposal, which is not conducive to sustainable development. Therefore, while solving the problem of digested sludge dewatering, how to balance energy and resource consumption to achieve the dual goals of improving digested sludge dewatering performance and reducing energy consumption is an important topic that urgently needs in-depth research and expansion. Summary of the invention

[0006] In order to solve the dehydration problem caused by the refractory organic matter and stable colloidal structure in the digested sludge, and at the same time improve the treatment efficiency of the digested sludge and reduce the treatment cost, the present invention provides a method for strengthening the dehydration of the digested sludge by recycling flocculants.

[0007] The present invention discloses the influence of residual exogenous pollutants or additives in sludge on the dewatering performance of digested sludge. In multiple links of sewage treatment plants, such as water inlet, primary sedimentation tank, biochemical tank, secondary sedimentation tank and sludge thickening tank, the addition of flocculants is a common phenomenon. In view of the widespread use of flocculants in multiple industries, it is inevitable that flocculants are released in large quantities in the environment and eventually enter the sewage treatment system. Therefore, in the sewage treatment process, it is inevitable that flocculants are enriched in sludge and participate in the anaerobic digestion process. Based on this, the present invention actively recycles the flocculants and combines them with conditioning aids to achieve the purpose of improving the dewatering effect of digested sludge.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A method for enhancing the dewatering of digested sludge by recycling flocculants, combining the recyclable flocculants in the residual sludge with conditioning aids to participate in the anaerobic digestion process, specifically comprising the following steps:

[0010] S1. Identify and utilize the recyclable flocculant polyaluminium chloride (PAC) in the excess sludge, add inorganic skeleton building agent calcium peroxide (CaO2) to the excess sludge containing the flocculant polyaluminium chloride, mix well, and adjust the pH value;

[0011] S2. The remaining sludge after treatment in step S1 is fed into the anaerobic digestion reactor, and the methane production and daily gas production are monitored until the gas is exhausted, i.e., the anaerobic digestion is completed;

[0012] S3. Dehydrating the digested sludge obtained after step S2 to achieve enhanced dehydration of the digested sludge.

[0013] Furthermore, in step S1, the moisture content of the excess sludge is greater than 95wt%, preferably 98wt% to 99wt%.

[0014] Furthermore, in step S1, the concentration of PAC is 10-40 mg Al / g TSS (ie, milligrams of aluminum contained in each gram of total suspended solids), preferably 20-30 mg Al / g TSS.

[0015] Furthermore, in step S1, the CaO2 concentration is 10-30 mg / TSS, preferably 20-30 mg / TSS, and further preferably 20 mg / TSS.

[0016] Furthermore, in step S1, the pH value is 6 to 7, preferably 7.

[0017] Furthermore, in step S3, the dehydration treatment is specifically: using a sludge specific resistance meter to perform suction filtration and dehydration for 5 to 30 minutes (preferably 10 to 15 minutes) at a pressure of 0.6 to 1.2 MPa (preferably 0.6 to 0.8 MPa) to obtain a filter cake.

[0018] Glossary:

[0019] Digested sludge: refers to sludge that has undergone anaerobic digestion treatment.

[0020] Residual sludge: refers to the sludge produced during the activated sludge treatment process.

[0021] The inventor discovered during the research process that the flocculant polyaluminium chloride (PAC) remaining in the sludge itself is actively utilized and creatively combined with calcium peroxide (CaO2) to promote the completion of the anaerobic digestion process. The prior art shows that the role of calcium peroxide CaO2 is mainly to provide oxygen to the water body, improve the anoxic environment of the water body, thereby promoting the rapid reproduction of aerobic microorganisms and further oxidizing organic matter, such as Chinese invention CN 112592013 A. However, the present invention creatively combines calcium peroxide (CaO2) with the flocculant polyaluminium chloride (PAC) to promote the completion of the anaerobic digestion process. Through the action of calcium peroxide, the intracellular organic matter and bound water in the sludge are efficiently released, and the structure of the extracellular high molecular polymer is effectively disintegrated, thereby providing good dehydration conditions for the dehydration of the digested sludge, thereby enhancing the dehydration effect of the digested sludge.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention utilizes the residual flocculants in the sludge. These flocculants are anaerobic digested with the sludge to achieve effective dehydration of the digested sludge. This method not only reduces the dependence on external flocculants, but also opens up a new way to recycle flocculants, significantly improving the utilization efficiency of resources.

[0024] (2) The present invention proposes an innovative sludge treatment method that combines a flocculant with a skeleton builder, aiming to significantly improve the dewatering efficiency of digested sludge, thereby effectively promoting the recycling of resources and achieving the goal of reducing environmental pollution through waste management. After in-depth research and precise chemical ratios, the two additives can work together to play a vital role in the dewatering process of digested sludge, greatly promoting the recycling of resources.

[0025] (3) The present invention not only improves the dewatering efficiency of digested sludge by recycling the flocculant in the sludge, but also significantly reduces the secondary pollution that may be caused during the treatment process. At the same time, it reduces the dependence on external flocculants, further reduces the treatment cost, and is conducive to the final disposal and resource utilization of dewatered water cake. In addition, the introduction of inorganic skeleton building agents optimizes the physical structure of the sludge, constructs a stable rigid framework inside the sludge, reduces the compressibility of the sludge, and opens up more internal channels for the dewatering process. The synergistic effect of flocculants and inorganic skeleton building agents further improves the dewatering efficiency and quality of digested sludge, creating favorable conditions for the subsequent treatment and resource utilization of dewatered water cake.

[0026] (4) The present invention fully demonstrates the potential for efficient utilization of existing waste resources. Through the synergistic effect of naturally residual flocculants and skeleton building agents in sludge, the true meaning of "using waste to treat pollution" is achieved, opening up a new path for environmental protection and resource conservation.

[0027] (5) Compared with the use of a single conditioning agent, the composite conditioning system formed by recycling flocculants and skeleton building agents in the present invention has a more significant effect on improving the dewatering performance of digested sludge under the same conditions. This composite conditioning method not only enhances the dewatering efficiency, but also improves the dewatering quality, providing more solid technical support for the subsequent treatment and resource utilization of digested sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The sludge resistance diagram of the original sludge and the sludge after anaerobic digestion treatment with different gradients of PAC provided in Example 1 of the present invention;

[0029] Figure 2 The graph of bound water content of the original sludge and the sludge after anaerobic digestion treatment with different gradients of PAC provided in Example 1 of the present invention;

[0030] Figure 3 This is a SEM image of the sludge after the original sludge sample provided in Example 1 of the present invention has been anaerobic digested;

[0031] Figure 4 This is a SEM image of the sludge after anaerobic digestion of 30 mg Al / g TSS PAC provided in Example 1 of the present invention;

[0032] Figure 5 The specific resistance diagram of the original sludge provided in Example 2 of the present invention and the sludge after anaerobic digestion treatment with 30 mg Al / g TSS PAC and different gradient CaO2;

[0033] Figure 6The graph of bound water content of the original sludge provided in Example 2 of the present invention and the sludge after anaerobic digestion treatment with 30 mg Al / g TSS PAC and different gradients of CaO2;

[0034] Figure 7 This is a SEM image of sludge treated with 30 mg Al / g TSS PAC and 20 mg / g TSS CaO2 after anaerobic digestion provided in Example 2 of the present invention;

[0035] Figure 8 This is the sludge resistance diagram of comparative example 1 of the present invention after anaerobic digestion is completed and 30 mg Al / g TSS PAC and 20 mg / g TSS CaO2 are added for coordinated treatment. DETAILED DESCRIPTION

[0036] In order to better understand the technical solution of the present invention, the present invention is described below with specific embodiments. It is necessary to point out that the embodiments are only used to further illustrate the present invention, and the applicable situations are not limited to the scope of the embodiments, and the present invention is not limited thereto in any way. Those skilled in the art in this field can make some non-essential improvements and adjustments based on the content of the above invention.

[0037] The contents not described in detail in the specification of the present invention belong to the known technologies of professionals in the field. Unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the field.

[0038] The present invention proposes a method for strengthening the dehydration of digested sludge by recycling flocculants. The conditioning agents used include recycled flocculants and conditioning aids. The recycled flocculants are inorganic polymer flocculants PAC, and the conditioning aids are inorganic skeleton building agents CaO2.

[0039] This part of the residual sludge was taken from the secondary sedimentation tank of a sewage treatment plant. In order to simulate the residual PAC of different gradients in the residual sludge, no PAC was used in the treatment process of this sewage treatment plant. The recovered residual sludge was first sieved (1 mm) to remove impurities, and then placed at 4°C for 24 hours. After the supernatant was removed, it was placed for use. The inoculated sludge used in the experiment was taken from the anaerobic digestion reactor operated in the laboratory; calcium peroxide was a commercially available product. Example 1

[0040] Take the above simulated excess sludge, use different gradient recycling flocculant PAC to treat the excess sludge and enter the anaerobic digestion system. The specific steps are as follows:

[0041] (1) In an anaerobic digestion reactor with a working volume of 700 mL, 400 mL of excess sludge with a moisture content of 98 wt% was added, and then 0.1 mol / L PAC stock solution was added to achieve different PAC concentrations of 0 (original sludge sample), 10, 20, 30 and 40 mg Al / g TSS. After adding 100 mL of seed sludge, the pH was adjusted to about 7;

[0042] (2) The residual sludge after pretreatment was subjected to anaerobic digestion reaction until the gas was completely discharged, and digested sludge was obtained after the reaction was completed. Subsequently, the digested sludge was filtered and dehydrated for 10 min at a pressure of 0.8 MPa using a sludge specific resistance meter to obtain a filter cake, and the specific resistance of the original digested sludge sample and the digested sludge of different gradient PACs was calculated (e.g. Figure 1 As shown in Figure 2, sludge specific resistance (SRF) refers to the resistance generated by a unit mass of sludge on a unit filtration area when it is filtered under a certain pressure. The larger the SRF value, the worse the sludge filtration performance and dehydration performance.

[0043] The filter cake after filtration was subjected to differential scanning calorimetry (DSC) analysis, and the bound water content (e.g. Figure 2 The results show that when 30 mg Al / g TSS of PAC is added to the residual sludge involved in the anaerobic digestion process, the bound water content of the digested sludge is reduced, which is more conducive to the dehydration of the digested sludge.

[0044] The original mud sample after anaerobic digestion (such as Figure 3 ) and digested sludge containing 30 mg Al / g TSS (as shown Figure 4 SEM was performed to determine the Figure 3 and Figure 4 It can be seen that the digested sludge treated with the recyclable flocculant PAC is effectively broken up, the flocs present a smooth and dense surface, and have smaller gaps than the original sludge sample, which can provide more dehydration channels. Example 2

[0045] The above-mentioned simulated excess sludge is taken, and the flocculant PAC and the inorganic skeleton building agent CaO2 are used to treat the excess sludge and enter the anaerobic digestion system using different gradient cycles. The specific steps are as follows:

[0046] In an anaerobic digestion reactor with a working volume of 700 mL, 400 mL of excess sludge with a moisture content of 98 wt% was added. Then, 0.1 mol / L PAC stock solution was added to reach 30 mg Al / g TSS, and then 10, 20 and 30 mg / g TSS CaO2 were added respectively. Finally, 100 mL of seed sludge was added and the pH was adjusted to about 7;

[0047] The residual sludge after pretreatment was subjected to anaerobic digestion reaction until the gas was completely discharged, and digested sludge was obtained after the reaction was completed. Subsequently, the digested sludge was filtered and dehydrated for 10 minutes at a pressure of 0.8 MPa using a sludge specific resistance meter to obtain a filter cake. The specific resistance of the original digested sludge sample and the digested sludge synergistically reacted with polyaluminum chloride (PAC) added with 30 mg Al / g TSS and calcium peroxide (CaO2) of different gradients were obtained by calculation. The results are as follows: Figure 5 shown.

[0048] The filter cake obtained by filtration was subjected to differential scanning calorimetry (DSC) analysis, and the bound water content was calculated based on the thermal enthalpy change. The results are as follows: Figure 6 The results show that when 30 mg Al / g TSS of PAC and 20 mg / g TSS of CaO2 were added to the residual sludge in the anaerobic digestion process, the bound water content of the digested sludge was significantly reduced, which was more conducive to the dehydration process of the digested sludge.

[0049] The digested sludge containing 30 mg Al / g TSS PAC and 20 mg / g TSS CaO2 after anaerobic digestion (such as Figure 7 The scanning electron microscope (SEM) was used to determine the Figure 7 As shown. Figure 7 It can be seen that the digested sludge treated with the recyclable flocculant PAC and the skeleton building agent CaO2 has more obvious gaps and more and more complete drainage channels than Example 1 using only the flocculant PAC, which is more conducive to the dehydration of the digested sludge. Under the same conditions, the sludge specific resistance of the obtained filter cake is significantly smaller, that is, the dehydration performance is better.

[0050] Comparative Example 1

[0051] The digested sludge obtained after the untreated excess sludge participates in the anaerobic digestion process is then added with 30 mg Al / g TSS PAC and 20 mg / g TSS CaO2. The specific steps are as follows:

[0052] The residual sludge without pre-treatment is anaerobic digested to obtain blank digested sludge;

[0053] 30 mg Al / g TSS PAC and 20 mg / g TSS CaO2 were added to the blank digested sludge and mixed thoroughly. The treated digested sludge was filtered and dehydrated for 10 min at a pressure of 0.8 MPa using a sludge specific resistance meter to obtain a filter cake, and the digested sludge specific resistance was calculated.

[0054] After anaerobic digestion, the digested sludge with 30 mg Al / g TSS PAC and 20 mg / g TSS CaO2 added was used to calculate the sludge specific resistance. The comparison of sludge specific resistance before and after the addition of PAC and CaO2 in anaerobic digestion is shown in the figure below. Figure 8 As shown by Figure 8 It can be seen that the recycled flocculants and skeleton building agents enter the anaerobic digestion system together with the residual sludge, and the dewatering performance of the digested sludge obtained is significantly better.

[0055] The above experimental results show that the synergistic use of polyaluminium chloride (PAC) and calcium peroxide (CaO2) significantly improves the dehydration efficiency of digested sludge, and the use of polyaluminium chloride (PAC) and calcium peroxide (CaO2) in the anaerobic digestion reaction stage can improve the dehydration effect of digested sludge more significantly than using them after the anaerobic digestion reaction.

Claims

1. A method for enhancing the dewatering of digested sludge by recycling flocculants, characterized in that: The steps include: S1. Identify and utilize the recyclable flocculant polyaluminium chloride (PAC) in the excess sludge, add the inorganic skeleton building agent calcium peroxide (CaO2) to the excess sludge containing the flocculant polyaluminium chloride, the concentration of the PAC is 10-40 mg Al / gTSS; the concentration of the CaO2 is 10-30 mg / TSS, mix well, and adjust the pH value to 6-7; S2. The remaining sludge after treatment in step S1 is fed into the anaerobic digestion reactor, and the methane production and daily gas production are monitored until the gas is exhausted, i.e., the anaerobic digestion is completed; S3. Dehydrating the digested sludge obtained after step S2 to achieve enhanced dehydration of the digested sludge.

2. The method for enhancing dewatering of digested sludge by recycling flocculants according to claim 1, characterized in that: In step S1, the concentration of PAC is 20-30 mg Al / g TSS; the concentration of CaO2 is 20-30 mg / TSS.

3. The method for enhancing dehydration of digested sludge by recycling flocculants according to claim 1 or 2, characterized in that: In step S1, the moisture content of the excess sludge is greater than 95wt%.

4. The method for enhancing dehydration of digested sludge by recycling flocculants according to claim 1 or 2, characterized in that: In step S1, the moisture content of the excess sludge is 98wt% to 99wt%.

5. The method for enhancing dehydration of digested sludge by recycling flocculants according to claim 1 or 2, characterized in that: In step S3, the dehydration treatment is specifically: using a sludge specific resistance meter to perform suction filtration and dehydration for 5 to 30 minutes at a pressure of 0.6 to 1.2 MPa to obtain a filter cake.

6. The method for enhancing dewatering of digested sludge by recycling flocculants according to claim 5, characterized in that: The pressure is 0.6~0.8Mpa and the dehydration time is 10~15min.

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