Preparation and application of sludge deep dehydration conditioner based on waste concrete
By preparing a sludge deep dewatering conditioner through acid and alkali leaching of waste concrete, the problem of low three-rate values of municipal sludge was solved, achieving efficient dewatering and resource utilization of sludge and increasing the amount of fuel added to cement kilns.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-04
- Publication Date
- 2026-03-31
AI Technical Summary
In existing technologies, the inorganic component ratio of municipal sludge is low, which limits its dosage in cement kilns and makes it difficult to utilize effectively. Furthermore, traditional conditioning agents may deviate further from the appropriate range, limiting their addition in cement kilns.
Waste concrete was treated with acid leaching and alkali leaching to extract elements such as calcium, iron, aluminum, and silicon. These elements were then mixed to prepare a waste concrete-based sludge deep dewatering conditioner, which was used together with filter residue B for deep dewatering of municipal sludge. The sludge was then treated by gradient pressure filtration.
It significantly reduces the moisture content of sludge, increases the three-rate values of sludge products, enhances its admixture in cement kiln fuel, and achieves zero discharge and resource utilization of waste.
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Figure CN121758049A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the preparation and application of a waste concrete-based sludge deep dewatering conditioner. Specifically, it involves mixing the acid and alkali leachates from the combined acid-alkali treatment of waste concrete and aging them under certain conditions to obtain a waste concrete-based sludge conditioner. Municipal sludge pretreated with this waste concrete-based sludge conditioner undergoes processes such as filter pressing, crushing, drying, and pulverizing to obtain a sludge product that can partially replace cement kiln fuel and effectively increase its content in the fuel. Background Technology
[0002] Municipal sludge is a byproduct of wastewater treatment plants, primarily composed of water, inorganic matter (CaO, SiO2, Al2O3, Fe2O3, and trace amounts of heavy metals), organic matter, pathogenic microorganisms, and nutrients. Due to its rich organic matter content, high ash content, and inorganic composition similar to cement raw materials, municipal sludge can be used as a raw material and auxiliary fuel for cement products in cement kilns. Cement kilns, characterized by high combustion temperatures and large material throughput, can effectively achieve the harmlessness, volume reduction, and resource utilization of sludge. However, as a co-processing component in cement kilns, sludge needs to have its calorific value increased by reducing its moisture content and the amount of conditioning agents used. Furthermore, its addition amount in the cement kiln is influenced by cement firing process parameters, namely the three ratios (water content, oxygen content, and fuel content). , Restrictions.
[0003] Deep dewatering of sludge often employs conditioners such as iron salts, aluminum salts, or calcium-containing compounds to improve the mechanical dewatering performance of the sludge. For example, iron ions can chemically react with organic matter in the sludge, destroying the cell walls and cell membrane structures, thereby achieving cell disruption. Aluminum ions interact electrostatically with anions in the sludge, neutralizing the charge on the cell surface and reducing the repulsive force between cells, thus promoting cell aggregation and precipitation. Calcium ions can react with phosphate ions or cell surface substances in the sludge to form insoluble calcium phosphate precipitates, affecting cell stability and making the sludge structure looser, which is beneficial for subsequent cell disruption treatment. According to the cement plant design code (GB50295-2016), cement batching design provides empirical ranges for the three ratios: lime saturation coefficient 0.88~0.93, silicate ratio 2.4~2.8, and aluminate ratio 1.4~1.9. Generally, the three ratios of inorganic components in municipal sludge are lower than the suitable range for cement clinker. Therefore, using iron or aluminum salts as sludge conditioners will only further deviate from the appropriate range of the three ratios of sludge fuel, thus limiting the amount of sludge fuel used in cement kilns.
[0004] Waste concrete is a hardened composite building material waste, mainly composed of natural aggregates, cement hydration products, and a small amount of unhydrated cement in a hardened composite. Its main inorganic components are SiO2, CaO, Fe2O3, and Al2O3, similar to the inorganic components in sludge, and its three-element ratio (Fe, A, and Calcium) values are much higher than those in sludge. Preparing waste concrete into a conditioner for deep dewatering of sludge not only allows for the synergistic modification of sludge by iron, aluminum, and calcium ions, but also improves the three-element ratio of inorganic components in the dewatered sludge product. Summary of the Invention
[0005] This invention aims to provide the preparation and application of a sludge deep dewatering conditioner based on waste concrete. Applying the sludge deep dewatering conditioner prepared according to this invention to the deep dewatering of municipal sludge can reduce the sludge moisture content from 80% to 42.5%. After pretreatment with the waste concrete-based sludge conditioner, the municipal sludge undergoes processes such as filter pressing, crushing, drying, and pulverizing. The resulting sludge product can partially replace cement kiln fuel and effectively increase its content in the fuel.
[0006] This invention relates to a method for preparing a deep dewatering conditioner for waste concrete sludge. First, the waste concrete is subjected to acid leaching and alkali leaching treatments, respectively. The obtained acid leaching solution and alkali leaching solution are mixed and aged under certain conditions to obtain a liquid waste concrete-based deep dewatering conditioner for sludge.
[0007] Specifically, the steps include the following:
[0008] Step 1: Soak the waste concrete powder in hydrochloric acid solution at a certain liquid-to-solid ratio. After soaking for a period of time, filter to obtain acid leachate and filter residue A.
[0009] Step 2: After washing and drying, the filter residue A is ground and mixed with a certain proportion of NaOH solid, and then placed in a muffle furnace for heat treatment. After cooling, deionized water is added, and the mixture is stirred evenly and then filtered to obtain alkaline leaching solution and filter residue B.
[0010] Step 3: Slowly add the acidic leaching solution obtained in Step 1 to the alkaline leaching solution obtained in Step 2 while stirring continuously. After the addition is complete, adjust the pH of the system to 3.0 with 10% NaOH solution. Place the mixture in a certain temperature for aging to obtain a yellowish-brown transparent liquid waste concrete-based sludge deep dewatering conditioner.
[0011] In step 1, the particle size of the waste concrete powder is less than 400 mesh; the liquid-to-solid ratio, i.e., the mass ratio of hydrochloric acid solution to waste concrete powder, is 2~4:1.
[0012] In step 1, the concentration of the hydrochloric acid solution is 10-50%; the soaking time is 5-24 hours; and the soaking temperature is 30-80℃.
[0013] In step 2, the amount of NaOH solid used is 10-50% of the mass of filter residue A; the heat treatment time is 0.5-8 h, and the heat treatment temperature is 200-800℃; the amount of deionized water used is 2-4 times the mass of filter residue A.
[0014] In step 3, the aging temperature is 30~70℃ and the aging time is 5~24 h.
[0015] In step 3, the solid content of the liquid waste concrete-based sludge deep dewatering conditioner is 10-30%, and the pH is 2-3.
[0016] The present invention relates to the application of the waste concrete-based sludge deep dewatering conditioner in the deep dewatering of municipal sludge.
[0017] Specifically, the sludge deep dewatering conditioner of this invention, along with the corresponding byproduct filter residue B, is added to municipal sludge with a moisture content of 80%. After thorough mixing, a sludge cake with a thickness of 12 mm is formed and placed in a filter press frame. A gradient pressurization method is used to filter the sludge, increasing the pressure by 0.5 MPa every 1 minute. When the pressure reaches 5 MPa, it is held for 10-25 minutes, reducing the sludge moisture content from 80% to 42.5%.
[0018] The addition amount of the sludge deep dewatering conditioner is 5%, calculated as a percentage of the dry sludge mass. The addition amount of filter residue B is the amount of filter residue B generated when a certain amount of sludge deep dewatering conditioner is added.
[0019] The waste concrete-based sludge deep dewatering conditioner of this invention can be used for deep dewatering of municipal sludge and increase the amount of sludge used as fuel in cement kilns.
[0020] Compared with the prior art, the beneficial effects of the present invention are reflected in:
[0021] 1. This invention employs acid leaching and alkali leaching processes to extract elements such as calcium, iron, aluminum, and silicon from waste concrete. The acid leaching solution and alkali leaching solution are then mixed and aged under certain conditions. The resulting waste concrete-based sludge deep dewatering conditioner and filter residue B can both be used for deep dewatering of sludge. The entire preparation process achieves zero waste discharge.
[0022] 2. The present invention uses the prepared conditioning agent together with filter residue B for deep dewatering of municipal sludge. It can achieve the synergistic effect of multiple mechanisms such as cell disruption, neutralization of surface charge, alteration of sludge structure, and skeleton support of various elements in waste concrete on sludge, effectively reducing sludge moisture content and controlling the pH value of the effluent after sludge dewatering.
[0023] 3. Compared with traditional sludge conditioners, the sludge conditioner of this invention does not contain any added iron or aluminum salts. The three ratios of the sludge product after pressure filtration are closer to the suitable range, which can increase the amount of sludge product in cement kilns to a greater extent, thereby improving the treatment efficiency of municipal sludge. Attached Figure Description
[0024] Figure 1 Under the conditions of Example 1, the effect of conditioner dosage on the moisture content of dewatered sludge was investigated. It can be seen that the addition of the waste concrete-based sludge conditioner of this invention significantly reduces the moisture content of the dewatered sludge, and the moisture content decreases with increasing dosage. When the conditioner dosage reaches 5% of the sludge dry weight, the moisture content of the sludge after filter pressing reaches 65%. Further increasing the dosage may lead to a reversal of the surface charge of the colloidal particles, preventing further reduction of the sludge moisture content.
[0025] Figure 2 Under the conditions of Example 2, the effect of pressure on the moisture content of the sludge after filter pressing was investigated. It can be seen that the higher the pressure, the lower the moisture content of the dewatered sludge. When the pressure reached 5 MPa, the moisture content of the sludge after filter pressing reached 53.5%. Further increasing the pressure did not significantly decrease the moisture content of the sludge.
[0026] Figure 3 This study examines the effect of single-layer thickness of the sludge cake on the moisture content of the dewatered sludge under the conditions described in Example 2. It can be seen that, with the same total sludge cake thickness, a thinner single-layer thickness results in a lower moisture content of the dewatered sludge. When the single-layer thickness is 3 mm, further reduction in single-layer thickness does not significantly decrease the moisture content of the sludge after filter pressing.
[0027] Figure 4 Under the conditions of Example 2, the effect of filtration time on the moisture content of the dewatered sludge was investigated. It can be seen that the longer the filtration time, the lower the moisture content of the dewatered sludge. After reaching 25 minutes, further extending the filtration time did not significantly reduce the moisture content of the sludge after filtration.
[0028] Figure 5 Under the conditions of Example 3, the conditioner of the present invention is compared with traditional polyferric sulfate, polyaluminum chloride, and waste concrete, etc. It can be seen that, with the same amount of conditioner added, the method of the present invention has better dewatering performance for sludge, and the addition of filter cake B, due to its skeletal support effect, can further reduce the moisture content of the sludge after filter pressing. Detailed Implementation
[0029] The embodiments of the present invention are described in detail below with reference to some technical solutions.
[0030] In the following examples, the initial grade of the waste concrete is C30 and the particle size is less than 400 mesh.
[0031] The sludge used in the following examples was taken from the sludge well of the Chengbei Wastewater Treatment Plant in Lu'an City. The original sludge had a moisture content of 80.5%, a pH of 7.8, and an organic matter content of 60%.
[0032] Example 1:
[0033] Waste concrete powder was added to a 50% hydrochloric acid solution at a liquid-to-solid ratio of 2:1. The solution was then acid-leached in a 60°C water bath shaker for 5 hours, followed by filtration to obtain an acid leachate and filter residue A. 10% by weight of NaOH solid was added to the washed and dried filter residue A. After grinding and mixing, the mixture was heat-treated in a muffle furnace at 200°C for 8 hours. After cooling, 200% by weight of deionized water was added to the filter residue A. After stirring, the mixture was filtered to obtain an alkaline leachate and filter residue B. The acid leachate was slowly added dropwise to the alkaline leachate while continuously stirring. After the addition was complete, the pH was adjusted to 3.0, and the mixture was aged in an oven at 30°C for 24 hours to obtain a yellowish-brown, transparent liquid waste concrete-based sludge deep dewatering conditioner.
[0034] Weigh 100 g of sludge, add 5% (by weight) of waste concrete-based sludge deep dewatering conditioner, mix thoroughly, wrap with filter cloth to form a 12 mm thick sludge cake, and then place in a filter press frame. Apply pressure to the sludge cake using a gradient pressurization method, increasing the pressure by 0.5 MPa every 1 min. When the pressure reaches 5 MPa, maintain the pressure for 10 min. The resulting sludge has a moisture content of 65%, and the pH of the sludge filtrate is 6.7.
[0035] Based on the conditions of Example 1, the amount of deep dewatering conditioner added to waste concrete-based sludge was varied, and the effect of the change in the amount added on the moisture content of the sludge after dewatering was investigated. The results are shown in [Figure 1]. Figure 1 .from Figure 1 It can be seen that the addition of the waste concrete-based sludge conditioner of this invention can significantly reduce the moisture content of the dewatered sludge, and the moisture content of the sludge decreases with increasing dosage. When the dosage of the conditioner reaches 5% of the dry weight of the sludge, the moisture content of the sludge after filter pressing reaches 65%. Further increasing the dosage may lead to a reversal of the surface charge of the colloidal particles, thus failing to further reduce the moisture content of the sludge.
[0036] Example 2:
[0037] Waste concrete powder was added to a 30% hydrochloric acid solution at a liquid-to-solid ratio of 3:1 and leached in a 30°C water bath shaker for 8 hours. The mixture was then filtered to obtain an acid leachate and filter residue A. 30% by weight of solid NaOH was added to the washed and dried filter residue A. After grinding and mixing, the mixture was heat-treated in a muffle furnace at 400°C for 2 hours. After cooling, 300% by weight of deionized water was added to the filter residue A. After stirring, the mixture was filtered to obtain an alkaline leachate and filter residue B. The acid leachate was slowly added dropwise to the alkaline leachate while continuously stirring. After the addition was complete, the pH was adjusted to 3.0, and the mixture was aged in an oven at 50°C for 12 hours to obtain a yellowish-brown, transparent liquid waste concrete-based sludge deep dewatering conditioner.
[0038] Weigh 100 g of sludge, add 5% (by weight) of waste concrete-based sludge deep dewatering conditioner, mix thoroughly, wrap with filter cloth to form a 6 mm thick sludge cake, and then place in a filter press frame. Apply pressure to the sludge cake using a gradient pressurization method, increasing the pressure by 0.5 MPa every 1 min. When the pressure reaches 5 MPa, maintain constant pressure for 10 min. The resulting sludge has a moisture content of 53.5%, and the pH of the sludge filtrate is 6.8.
[0039] Based on the conditions of Example 2, the effects of changes in the filter press pressure, cake thickness, and filter press time on the moisture content of the sludge after dewatering were investigated.
[0040] Figure 2 Under the conditions of Example 2, the effect of pressure on the moisture content of the sludge after filter pressing was investigated. It can be seen that the higher the pressure, the lower the moisture content of the dewatered sludge. When the pressure reached 5 MPa, the moisture content of the sludge after filter pressing reached 53.5%. Further increasing the pressure did not significantly decrease the moisture content of the sludge.
[0041] Figure 3 Under the conditions of Example 2, the effect of the single-layer thickness of the sludge cake on the moisture content of the sludge after dewatering was investigated. It can be seen that the thinner the single-layer thickness of the sludge cake, the lower the moisture content of the sludge after dewatering. When the single-layer thickness was 3 mm, further reducing the single-layer thickness did not significantly reduce the moisture content of the sludge after filter pressing.
[0042] Figure 4 Under the conditions of Example 2, the effect of filtration time on the moisture content of the dewatered sludge was investigated. It can be seen that the longer the filtration time, the lower the moisture content of the dewatered sludge. After reaching 25 minutes, further extending the filtration time did not significantly reduce the moisture content of the sludge after filtration.
[0043] Example 3:
[0044] Waste concrete powder was added to a 10% hydrochloric acid solution at a liquid-to-solid ratio of 4:1 and leached in an 80°C water bath shaker for 24 hours. The mixture was then filtered to obtain an acid leachate and filter residue A. 50% by weight of NaOH solid was added to the washed and dried filter residue A. After grinding and mixing, the mixture was heat-treated in a muffle furnace at 800°C for 0.5 hours. After cooling, 400% by weight of deionized water was added to the filter residue A. After stirring, the mixture was filtered to obtain an alkaline leachate and filter residue B. The acid leachate was slowly added dropwise to the alkaline leachate while continuously stirring. After the addition was complete, the pH was adjusted to 3.0, and the mixture was aged in an oven at 70°C for 5 hours to obtain a yellowish-brown, transparent liquid waste concrete-based sludge deep dewatering conditioner.
[0045] Weigh 100 g of sludge, add 5% (by weight) of waste concrete-based sludge deep dewatering conditioner, mix thoroughly, wrap with filter cloth to form a 6 mm thick sludge cake, and then place in a filter press frame. Apply pressure to the sludge cake using a gradient pressurization method, increasing the pressure by 0.5 MPa every 1 min. When the pressure reaches 5 MPa, maintain the pressure for 25 min. The resulting sludge has a moisture content of 42.3%, and the pH of the sludge filtrate is 6.9.
[0046] Based on the conditions of Example 3, the added dewatering conditioner was changed, and the sludge dewatering effect was compared and investigated. The results are shown in […]. Figure 5 A comparison of the dewatering conditioner of this invention with traditional polyferric sulfate or polyaluminum chloride shows that, under the same dosage, the dewatering conditioner of this invention has better dewatering performance for sludge. Furthermore, the addition of filter residue B, due to its skeletal support effect, can further reduce the moisture content of the sludge after filter pressing.
Claims
1. A method for preparing a waste concrete-based sludge deep dewatering conditioner, characterized by The method comprises the following steps: Step 1: waste concrete powder is soaked in a hydrochloric acid solution, filtered after a period of time, and an acid leaching solution and residue A are obtained; Step 2: the residue A is washed, dried, and then mixed with NaOH solid by grinding, and then placed in a muffle furnace for heat treatment, and then deionized water is added after cooling, stirred uniformly, and filtered to obtain an alkali leaching solution and residue B; Step 3: the acid leaching solution obtained in step 1 is slowly added to the alkali leaching solution obtained in step 2 and continuously stirred, and then the pH of the system is adjusted to 3.0 by using a 10% NaOH solution, and the mixed solution is aged at a certain temperature to obtain a yellow-brown transparent liquid waste concrete-based sludge deep dewatering conditioner.
2. The preparation method according to claim 1, wherein: in step 1, the particle size of the waste concrete powder is less than 400 mesh; and the liquid-solid ratio, i.e. the mass ratio of the hydrochloric acid solution to the waste concrete powder, is 2-4:
1.
3. The preparation method according to claim 1, wherein: in step 1, the concentration of the hydrochloric acid solution is 10-50%; the soaking time is 5-24 h, and the soaking temperature is 30-80℃.
4. The preparation method according to claim 1, wherein: in step 2, the amount of NaOH solid is 10-50% of the mass of the residue A.
5. The preparation method according to claim 4, wherein: in step 2, the heat treatment time is 0.5-8 h, and the heat treatment temperature is 200-800℃.
6. The preparation method according to claim 1, wherein: in step 3, the aging temperature is 30-70℃, and the aging time is 5-24 h.
7. The preparation method according to claim 1, wherein: in step 3, the solid content of the liquid waste concrete-based sludge deep dewatering conditioner is 10-30%, and the pH is 2-3.
8. Application of the waste concrete-based sludge deep dewatering conditioner prepared by any one of the preparation methods of claims 1-7 in municipal sludge deep dewatering.
9. The application according to claim 8, wherein: the sludge deep dewatering conditioner and the corresponding by-product residue B are added to municipal sludge, mixed uniformly to form a sludge cake, and then placed in a filter press frame; and the sludge is subjected to filter pressing by using a gradient pressurization method, and the pressure is increased by 0.5 MPa every 1 min, and when the pressure reaches 5 MPa, the pressure is maintained for 10-25 min.
10. The application according to claim 9, wherein: the addition amount of the sludge deep dewatering conditioner is 5%, based on the mass percentage of the absolute dry sludge.