Composite conditioning method for improving sedimentation and dehydration performance of sludge
By adding tannic acid and cationic polyacrylamide in stages, the problem of insufficient sludge settling and dewatering performance was solved, resulting in a significant improvement in sludge settling performance, reduction in reagent volume, optimization of floc structure, controllable cost, and simple and environmentally friendly operation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGDONG GDH WATER
- Filing Date
- 2026-03-17
- Publication Date
- 2026-05-08
AI Technical Summary
In existing technologies, when CPAM is used alone to treat sludge, there are problems such as insufficient EPS destruction, insufficient floc density, limited settling performance, and failure when TA and PAM are directly mixed.
A stepwise dosing strategy was adopted, first adding tannic acid (TA) and then adding cationic polyacrylamide (CPAM). The optimal dosing range and ratio were determined through experiments to ensure the synergistic effect of TA and CPAM.
It significantly improves the settling performance of sludge, reduces CPAM dosage by 20% to 50%, keeps reagent costs under control, produces denser flocs, and achieves better settling performance than using CPAM alone. It is also simple and environmentally friendly to operate.
Smart Images
Figure CN121990753A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for improving sludge settling and dewatering performance. Background Technology
[0002] The high water content and difficulty in dewatering of residual sludge generated by urban wastewater treatment plants are among the major challenges in wastewater treatment. Extracellular polymeric substances (EPS) in the sludge contain a large amount of protein and polysaccharides, forming a stable three-dimensional network structure that encapsulates a large amount of bound water, resulting in poor sludge settling performance and difficulty in dewatering.
[0003] Currently, adding flocculants is a common method to improve sludge settling and dewatering performance. Polyacrylamide (PAM) is widely used due to its excellent bridging flocculation properties. Cationic PAM (CPAM) combines with negatively charged sludge particles through charge neutralization and bridging to form flocs. However, using CPAM alone has limitations such as limited ability to disrupt EPS structure, difficulty in releasing bound water, insufficient floc density, relatively large volume after settling, increased cost at higher dosages, and the potential for loose flocs due to excessive CPAM dosage.
[0004] Tannic acid (TA) is a natural plant polyphenol with good complexing ability and hydrophilicity, capable of disrupting EPS structure and releasing bound water. However, existing studies have shown that direct mixing of TA and PAM in concentrated solutions immediately forms an insoluble complex precipitate, completely losing its flocculation activity. Therefore, how to achieve effective synergy between TA and PAM is a pressing technical problem to be solved in this field. Summary of the Invention
[0005] The present invention aims to solve the technical problems existing in the prior art when using CPAM alone to treat sludge, such as insufficient EPS destruction, insufficient floc density, limited settling performance, and failure of direct mixing of TA and PAM. The invention provides a composite conditioning method to improve the settling and dewatering performance of sludge.
[0006] The composite conditioning method for improving sludge settling and dewatering performance of the present invention is carried out according to the following steps: a step-by-step addition method is adopted: tannic acid is added to the sludge first, and cationic polyacrylamide is added after the reaction is complete.
[0007] The inventive point of this invention is:
[0008] 1. Step-by-step addition strategy: Add TA first, then add CPAM. This avoids the formation of ineffective complexes by directly mixing the two, while giving full play to the EPS destruction effect of TA and the bridging flocculation effect of CPAM, which significantly improves sludge settling and dewatering performance.
[0009] 2. Synergistic effect ratio: Through a large number of experiments, the optimal dosage range and ratio of TA and CPAM were determined. The synergistic effect was strongest and the settling performance was optimal when the mass ratio of TA:CPAM was 25:1.
[0010] 3. Low dosage and high efficiency: When the dosage of CPAM is reduced by 20% to 50% compared to using it alone, the sedimentation performance is improved, achieving a balance between reducing the amount of agent and optimizing the effect.
[0011] Compared with the prior art, the present invention has the following beneficial effects:
[0012] ① Settling performance is significantly improved
[0013] SV30 (30-minute sedimentation ratio): Under the optimal ratio (TA=20mg / L, CPAM=0.8mg / L), SV30 can be reduced to 43%, which is 52.2% lower than the control group (90%), and further reduced than the optimal dose of CPAM alone (1.2mg / L, SV30=44%).
[0014] SV60 (60-minute settlement ratio): can be reduced to 35%, the lowest value in the entire test, indicating the most thorough settlement.
[0015] ② Quantitative characterization of synergistic effects
[0016] To objectively evaluate the synergistic effect of the compounding method described in this invention, the synergistic enhancement factor (SEC) is defined as follows:
[0017]
[0018] In the formula, SV30 is the sludge settling ratio (%) after 30 minutes, SEC>0 indicates that the compound system has a positive synergistic effect, and the larger the value, the more significant the synergistic effect.
[0019] Synergistic effect (SEC) calculations show that at CPAM = 0.8 mg / L, the SEC reaches 15.7% (SV30 decreases from 51% to 43%); at CPAM = 0.5 mg / L, the SEC is 10.9% (SV30 decreases from 64% to 57%). This demonstrates a significant synergistic effect between TA and CPAM, rather than a simple additive effect.
[0020] ③ Reduction of drug dosage
[0021] The dosage of CPAM can be reduced from 1.2 mg / L when used alone to 0.8 mg / L, a reduction of 33%; with the synergistic effect of TA, the low dose of CPAM (0.8 mg / L) can achieve a better sedimentation effect than the high dose of CPAM (1.2 mg / L).
[0022] ④ Optimization of floc structure
[0023] The sedimentation kinetics study showed that although the initial sedimentation of the compound group was slightly slower than that of CPAM alone, it surpassed it after 20 minutes and the final sedimentation volume was lower, indicating that the flocs were denser and the structure was more stable; the supernatant was clearer and the mud-water interface was clearer.
[0024] ⑤ Easy to operate and cost controllable
[0025] It can be achieved using conventional sludge treatment equipment without additional investment; TA is a natural plant extract, which is environmentally friendly and poses no risk of secondary pollution; the total cost of the reagent is comparable to or slightly lower than that of using CPAM alone. Attached Figure Description
[0026] Figure 1 The curves showing the change of sludge settling ratio (SV%) over time (10~60 min) at different tannic acid (TA) dosages in beakers with concentrations of 0, 20, 40, 60, 80, and 100 mg / L are shown in Example 5.
[0027] Figure 2 The curves showing the change of sludge settling ratio (SV%) over time at different cationic polyacrylamide (CPAM) dosages in beakers of 0.2, 0.5, 0.8, 1, and 1.2 mg / L are shown in Example 6.
[0028] Figure 3 This is a bar chart comparing SV30 data for different TA dosages (i.e., concentrations in the beaker) when the CPAM concentration in the beaker was fixed at 0.2 mg / L in Example 7.
[0029] Figure 4 This is a graph showing the effect of TA dosage on SV30 at different CPAM doses in Example 8;
[0030] Figure 5 This is a contour plot showing the interaction between TA and CPAM dosage on SV30 in Example 9. Detailed Implementation
[0031] Specific implementation method one: This implementation method is a composite conditioning method to improve the settling and dewatering performance of sludge, which is carried out according to the following steps: adopting a step-by-step addition method: first add tannic acid to the sludge, and then add cationic polyacrylamide after the reaction is complete.
[0032] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the molecular weight of the cationic polyacrylamide is 8 million to 20 million. Everything else is the same as in Specific Implementation Method One.
[0033] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the molecular weight of the cationic polyacrylamide is 12 million. Everything else is the same as in Specific Implementation Method One or Two.
[0034] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: first, tannic acid is mixed with water to prepare an aqueous solution, and then evenly dripped or injected into the sludge, and reacted for 1 to 3 minutes under stirring conditions. Everything else is the same as in Specific Implementation Methods One to Three.
[0035] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the mass concentration of the tannic acid aqueous solution is 0.5%~2%. Everything else is the same as in Specific Implementation Method Four.
[0036] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that: CPAM is mixed with water to prepare an aqueous solution. After the tannic acid reaction is complete, the CPAM aqueous solution is added, and then stirred for 1-2 minutes to form dense flocs. Everything else is the same as in Specific Implementation Method Five.
[0037] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that it allows the mixture to settle after the CPAM reaction is complete, achieving mud-water separation. Everything else is the same as in Specific Implementation Method Six.
[0038] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the dosage of tannic acid is 0.1% to 1.5% of the dry sludge mass. Everything else is the same as in Specific Implementation Method Seven.
[0039] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the dosage of CPAM is 0.01% to 0.03% of the dry sludge mass, and the mass ratio of TA to CPAM is (10 to 40):1. Everything else is the same as in Specific Implementation Method Eight.
[0040] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the pH of the sludge is neutral to slightly acidic, specifically between 5.5 and 7.5. Everything else is the same as in Specific Implementation Method Nine.
[0041] The present invention is verified using the following examples:
[0042] Example 1: This example illustrates a composite conditioning method for improving sludge settling and dewatering performance. The sludge source is residual sludge from the secondary sedimentation tank of a municipal wastewater treatment plant, with MLSS = 3844 mg / L and pH = 7.2. Reagent preparation: Tannic acid (TA): Prepared as a 10 g / L stock solution (1% mass concentration, solvent is water); Cationic polyacrylamide (CPAM): The cationic polyacrylamide (CPAM) used in this example is an industrial-grade product with a molecular weight of 12 million, prepared as a 1 g / L stock solution, solvent is water.
[0043] Operating procedures: Place 1L of the above-mentioned sludge in a beaker and place it under a stirrer; first add 2mL of TA stock solution (equivalent to a TA concentration of 20mg / L in the beaker), and stir rapidly (250rpm) for 2min; then add 0.8mL of CPAM stock solution (equivalent to a CPAM concentration of 0.8mg / L in the beaker), and stir slowly (60rpm) for 1min; then pour the mixture into a 1L graduated cylinder, allow it to settle, and record the sludge volume at 10, 20, 30, 40, 50, and 60min. Experimental results: SV10=63%, SV20=50%, SV30=43%, SV40=40%, SV50=37%, SV60=35%; throughout the settling process, the supernatant was clear, the sludge-water interface was clear, and the flocs were dense.
[0044] Example 2: Comparison of different TA dosages. Procedure: The concentrations of TA in the beakers were set to 5, 10, 15, 20, 25, 30, 40, 60, 80, and 100 mg / L, with CPAM fixed at 0.8 mg / L; the remaining procedures were the same as in Example 1. Results: When TA was 10 mg / L, SV30 = 45%; when TA = 15 mg / L, SV30 = 53%; when TA = 20 mg / L, SV30 = 43% (optimal); when TA = 25 mg / L, SV30 = 49%; when TA ≥ 40 mg / L, SV30 > 60%, indicating a deterioration in effectiveness. This shows that the optimal dosage of TA is 10-20 mg / L.
[0045] Example 3: Comparison of different CPAM dosages. Procedure: The concentrations of CPAM in the beakers were set to 0.2, 0.5, 0.8, 1, and 1.2 mg / L, with TA fixed at 20 mg / L. The remaining procedures were the same as in Example 1. Results: When CPAM = 0.2 mg / L, SV30 = 86%; when CPAM = 0.5 mg / L, SV30 = 60%; when CPAM = 0.8 mg / L, SV30 = 43% (optimal); when CPAM = 1 mg / L, SV30 = 53%; when CPAM = 1.2 mg / L, SV30 = 45%. This indicates that the optimal dosage of CPAM is 0.8 mg / L.
[0046] Example 4: A separate control experiment was conducted, with a control group, a separate CPAM group, and a separate TA group.
[0047] Control group: No drugs were administered;
[0048] TA-only group: TA was added only, at a concentration of 20 mg / L in the beaker;
[0049] CPAM alone group: only CPAM was added, and the concentration in the beaker was 0.8 mg / L.
[0050] Experimental results: Control group: SV30=90%; TA alone group: SV30=89% (no improvement); CPAM alone group: SV30=51%; while the combination group (TA+CPAM): SV30=43% (see Example 1). This demonstrates that the combination has a synergistic effect.
[0051] Example 5: The effect of adding TA alone on sludge settling performance, i.e., without adding CPAM, the sludge source is the same as in Example 1. Figure 1 The graph shows the sludge settling ratio (SV%) as a function of time (10–60 min) at different tannic acid (TA) dosages in beakers with concentrations of 0, 20, 40, 60, 80, and 100 mg / L. As can be seen from the graph, the curves largely overlap. The SV30 of the control group (TA dosage of 0) and all dosage groups is between 88% and 92%, indicating that TA alone has no effect on improving sludge settling and only acts as a sludge conditioner.
[0052] Example 6: The effect of adding CPAM alone on sludge settling performance, i.e., without adding TA, the sludge source is the same as in Example 1. Figure 2 The graph shows the changes in sludge settling ratio (SV%) over time at different cationic polyacrylamide (CPAM) concentrations of 0.2, 0.5, 0.8, 1, and 1.2 mg / L in beakers. As can be seen from the graph, the settling performance gradually improves with increasing CPAM dosage, with SV30 decreasing from 78% (0.2 mg / L) to 44% (1.2 mg / L), indicating that CPAM is an effective flocculant. However, the increase in effect slows down at higher dosages.
[0053] Example 7: SV30 comparison of different TA dosages (i.e., concentrations in the beaker) with a fixed CPAM concentration of 0.2 mg / L in the beaker. The sludge source was the same as in Example 1. Figure 3The bar chart shows the 30-minute sludge settling ratio (SV30) at different TA dosages (5, 10, 15, 20, and 25 mg / L) when the CPAM dosage is fixed at 0.2 mg / L. The chart also marks the control group (SV30 = 90%) without any reagent and the CPAM-only group (0, SV30 = 78%) with only 0.2 mg / L CPAM as references. As can be seen from the chart, at low CPAM dosages, the SV30 after adding TA is higher than that of the CPAM-only group (82%–87%), and gradually increases with increasing TA, indicating that TA has no synergistic effect at this level and instead inhibits the flocculation effect of CPAM.
[0054] Example 8: Effect of TA dosage on SV30 under different CPAM doses. Figure 4 This is a data graph, consisting of four subgraphs: a, b, c, and d, which correspond to the SV30 column comparison at different TA dosages when the CPAM dosage is 0.5, 0.8, 1, and 1.2 mg / L, respectively. Each subgraph also includes a control group (SV30≈90%) without any drug and a CPAM-only group at the corresponding dosage as references.
[0055] Figure (a) shows the TA dosage range of 5–100 mg / L for CPAM = 0.5 mg / L. The optimal TA dosage was 15 mg / L, with an SV30 of 57%, which was superior to CPAM alone (64%). TA showed synergistic effects in the range of 5–20 mg / L (SV30 ≤ 62%). SV30 gradually increased after TA dosage exceeded 25 mg / L, and excessive TA led to a deterioration in efficacy.
[0056] Figure (b) shows that for CPAM = 0.8 mg / L, the TA dosage ranges from 5 to 100 mg / L. The optimal TA dosage is 20 mg / L, with an SV30 of 43%, which is the best value overall and is 8 percentage points lower than that of CPAM alone (51%). The synergistic effect of TA is significant in the range of 10–20 mg / L (SV30 ≤ 45%). When the TA dosage exceeds 30 mg / L, the SV30 increases sharply, and the excess TA completely negates the effect of CPAM.
[0057] Figure (c) shows the dosage of TA at CPAM = 1 mg / L, ranging from 5 to 25 mg / L. When TA was at 5 mg / L, the SV30 (47%) was slightly better than that of CPAM alone (48%). When TA was ≥10 mg / L, the SV30 was higher than that of CPAM alone (49%~60%), indicating that the synergistic window of TA at high CPAM doses was extremely narrow, and that excessive doses would produce negative effects.
[0058] Figure (d) shows the dosage of TA at CPAM = 1.2 mg / L, ranging from 5 to 25 mg / L. The optimal TA dosage is 5 mg / L, with an SV30 of 40%, which is superior to CPAM alone (44%). When TA = 10 to 15 mg / L, the SV30 is comparable to that of CPAM alone (42% to 43%). When TA ≥ 20 mg / L, the SV30 increases, and the synergistic effect disappears.
[0059] Figure 4 This study comprehensively revealed the regulatory mechanism of TA dosage on sludge settling performance under different CPAM dosages. The strongest synergistic effect was observed in the range of CPAM = 0.5~0.8 mg / L and TA = 10~20 mg / L, at which point SV30 could be reduced to 43%~57%, a decrease of 33%~52% compared to the control group, and a further improvement of 2~8 percentage points compared to CPAM alone.
[0060] Example 9: The interaction effect of TA and CPAM dosage on SV30 Figure 5 Contour plot showing the interaction between TA and CPAM dosage on SV30. Figure 5 The optimal synergistic range is clearly indicated as: TA = 10~20 mg / L, CPAM = 0.5~0.8 mg / L.
Claims
1. A composite conditioning method for improving sludge settling and dewatering performance, characterized in that... The method is carried out in the following steps: a step-by-step addition method is adopted: tannic acid is first added to the sludge, and cationic polyacrylamide is added after the reaction is complete.
2. The composite conditioning method for improving sludge settling and dewatering performance according to claim 1, characterized in that... The cationic polyacrylamide has a molecular weight of 8 million to 20 million.
3. The composite conditioning method for improving sludge settling and dewatering performance according to claim 2, characterized in that... The cationic polyacrylamide has a molecular weight of 12 million.
4. The composite conditioning method for improving sludge settling and dewatering performance according to claim 1, characterized in that... First, mix tannic acid with water to prepare an aqueous solution, then evenly drip or inject it into the sludge, and react for 1 to 3 minutes under stirring.
5. The composite conditioning method for improving sludge settling and dewatering performance according to claim 4, characterized in that... The mass concentration of tannic acid aqueous solution is 0.5%~2%.
6. The composite conditioning method for improving sludge settling and dewatering performance according to claim 5, characterized in that... CPAM is mixed with water to prepare an aqueous solution. After the tannic acid reaction is complete, the CPAM aqueous solution is added and then stirred for 1 to 2 minutes to form a dense floc.
7. The composite conditioning method for improving sludge settling and dewatering performance according to claim 6, characterized in that... After the CPAM reaction is completed, the mixture is allowed to settle to achieve mud-water separation.
8. The composite conditioning method for improving sludge settling and dewatering performance according to claim 1, characterized in that... The dosage of tannic acid is 0.1% to 1.5% of the dry sludge mass.
9. The composite conditioning method for improving sludge settling and dewatering performance according to claim 8, characterized in that... The dosage of CPAM is 0.01% to 0.03% of the dry sludge mass, and the mass ratio of TA to CPAM is (10 to 40):
1.
10. The composite conditioning method for improving sludge settling and dewatering performance according to claim 1, characterized in that... The pH of the sludge is neutral to slightly acidic, specifically between 5.5 and 7.5.