A method for treating residual sludge by using a manganese-calcium composite agent

Abstract

The application discloses a method for treating residual sludge by using a manganese-calcium composite agent, which comprises the following steps: using the manganese-calcium composite agent to condition the sludge at normal temperature, then adding sodium bisulfite solution to react, and finally performing dewatering treatment. Based on the multiple effects of potassium permanganate and calcium hydroxide in the manganese-calcium agent, the method comprises the following effects: Mn(III) ion advanced oxidation, construction of a manganese-calcium metal-doped grid structure in sludge flocs, compressed double electric layer and electric neutralization of manganese and calcium ions, alkaline hydrolysis and fermentation, and the like. The method not only effectively removes sludge organic matters, but also makes the sludge flocs more compact by forming free water channels, and improves sludge dewatering performance. After the treatment of the manganese-calcium composite agent at normal temperature, the specific resistance of the residual sludge is reduced by 33%, the removal rate of COD is 31%, and the removal rate of SS is 24%, so that the reduction, stabilization and harmlessness of the residual sludge are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a sewage treatment plant residual sludge treatment method, and particularly relates to a method for treating residual sludge by using a manganese-calcium composite agent under normal temperature conditions. BACKGROUND

[0002] With the advancement of urbanization process in China and the increasing perfection of sewage treatment facilities, the amount of urban sewage treated increases year by year. The urban sewage treatment plant mainly using biochemical treatment process produces a large amount of by-products, i.e. residual sludge, in the sewage treatment process. The residual sludge is composed of silt, fiber, colloid, organic matter, microorganisms and metal elements, and the direct discharge of untreated residual sludge will cause secondary pollution to the ecological environment.

[0003] The goal of sludge treatment is reduction, stabilization and harmlessness, and dewatering is an important treatment link to achieve the above goals. The residual sludge has a very high water content and the sludge floc is highly hydrophilic, which causes difficulties in dewatering treatment. Therefore, pretreatment is needed before sludge dewatering. At present, the sludge pretreatment methods mainly include physical method, chemical method, biological method and combined treatment method. The chemical method changes the dewatering performance of the sludge by adding chemical agents, and common methods include ozone oxidation method, alkali dissolution treatment method, thermal hydrolysis method, lime stabilization method, etc. When the lime dosage is not enough in the lime stabilization method, the pH value will decrease with the extension of the reaction time, and it is difficult to achieve the stabilization effect.

[0004] Advanced oxidation technology is a technology that uses highly oxidizing active radicals to oxidize pollutants. Common active radicals include hydroxyl radicals, sulfate radicals, etc. Advanced oxidation technology has the characteristics of low treatment cost, low energy consumption and simple operation, and can be used for sludge dewatering pretreatment: reducing the water content of residual sludge and removing sludge organic matter. The advanced oxidation technology based on Mn(III) ions (PM / BS technology) has a good oxidation effect on difficult-to-biodegrade benzene ring substances such as phenol, ciprofloxacin and methyl blue, and the reaction principle is that potassium permanganate (PM) and sodium bisulfite (BS) react in water to generate Mn(III) ions. Mn(III) ions are a kind of active radicals with extremely strong oxidation, and have a good oxidation effect on difficult-to-biodegrade benzene ring substances such as phenol, ciprofloxacin and methyl blue. SUMMARY

[0005] In order to overcome the shortcomings of traditional sludge treatment technology, the present application provides a method for treating residual sludge by using a manganese-calcium composite agent, so as to realize the reduction, stabilization and harmlessness of the sludge.

[0006] To solve the above technical problems, the present application adopts the following technical scheme:

[0007] A method for treating excess sludge using a manganese-calcium composite agent includes the following steps: At room temperature, freshly prepared manganese-calcium agent is thoroughly mixed with the excess sludge, followed by the addition of sodium bisulfite solution. These steps generate multiple reactions, including advanced oxidation, complexation, coagulation (coagulant aid), alkaline hydrolysis, and fermentation. These reactions exhibit antagonistic or synergistic effects. By controlling the agent formulation, addition sequence, dosage, and reaction time, a segmented oxidation regulation pathway of "potassium permanganate pre-oxidation + Mn(III) advanced oxidation" and a manganese-calcium metal-doped organic matter grid structure are constructed. This enhances the bidirectional synergistic relationship between dissolved organic matter and the coagulant, improving sludge dewatering performance. Finally, sludge dewatering is performed.

[0008] As a preferred embodiment, the sludge solids concentration in the step is 13.5-14.5 g / L, the manganese-calcium agent used is a mixture of potassium permanganate powder and calcium hydroxide powder (mass percentages of 65% and 35%), the dosage is 2.5 g per 1 L of sludge, the sodium bisulfite solution concentration is 250 g / L, and the dosage is 20 mL per 1 L of sludge.

[0009] As a preferred option, after the manganese-calcium reagent is added, it is stirred and mixed at 50 rpm for 1 hour at room temperature.

[0010] As a preferred option, after adding sodium bisulfite solution, mix thoroughly, let stand at room temperature for 1 hour, and then carry out subsequent dehydration treatment.

[0011] The novel method for treating residual sludge according to claim 1 is characterized by achieving the reduction, stabilization, and harmlessness of residual sludge.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for treating residual sludge using a manganese-calcium composite agent provided by the present invention has the following advantages:

[0013] (1) To achieve the goals of reducing, stabilizing, and rendering harmless waste sludge, the main objectives are to remove organic matter and reduce the water content of the sludge. The former can be achieved through chemical oxidation or biochemical treatment, while the latter is primarily achieved through centrifugation or filter press dewatering. Sludge organic matter includes two types: extracellular organic matter (EPS) and intracellular organic matter. Biochemical treatment, mainly based on anaerobic fermentation, primarily degrades extracellular organic matter, but its removal effect on intracellular organic matter is poor, becoming a pressing problem for sludge stabilization. The concentration of organic matter in the sludge and the density of the flocs are key factors affecting the sludge dewatering effect.

[0014] The manganese-calcium composite agent is mixed with the excess sludge. The dissolved potassium permanganate pre-oxidizes some of the extracellular organic matter (extracellular polymers) in the sludge, breaking down the sludge flocs and allowing MnO4 to be released. - and Ca2+ Entering the extracellular polymeric substance (EPS) of sludge, the microorganisms come into full contact with the organic matter or microbial cells within the EPS. Through ionic bonds, van der Waals forces, hydrogen bonds, and complexation, they form a three-dimensional organic structure with a Mn and Ca backbone, resulting in a tight bond between the reactants and the sludge organic matter. This facilitates faster subsequent oxidation and coagulation reactions and improves dewatering efficiency. Simultaneously, after the manganese-calcium composite agent is added to the sludge, the pH of the sludge mixture exceeds 10, exhibiting strong alkalinity. Under alkaline conditions, the solid organic matter of the sludge (EPS and intracellular organic matter) undergoes hydrolysis and fermentation reactions. Specifically, the fermenting bacteria perform alkaline fermentation, breaking down the sludge flocs, releasing large amounts of EPS and intracellular organic matter, and converting large-chain organic molecules into short-chain organic matter and some monomeric substances. The aforementioned microbial action accelerates the dissolution of sludge solid matter, and the dissolved organic matter can further react with MnO4. - and Ca 2+ The combination of these elements creates a higher concentration of metal-doped three-dimensional organic matter structure, further improving sludge dewatering performance.

[0015] (2) When sodium bisulfite solution is added, an oxidation reaction occurs in the sludge. Potassium permanganate reacts with sodium bisulfite to generate Mn(III) ions. The reaction equation is as follows:

[0016]

[0017] (3) The Mn(III) ions produced by the reaction of potassium permanganate and sodium bisulfite in water have strong oxidizing properties and can oxidize organic matter in sludge. The reaction equation is as follows:

[0018] Mn(III) + organic matter → Mn 2+ +Product

[0019] Potassium permanganate is a commonly used strong oxidant, relying on its high-valence Mn(VII) ions to oxidize extracellular organic matter in sludge. However, another major class of organic matter in sludge—intrinsic organic matter—requires a very strong oxidant for dissolution / release due to the rigid structures of the sludge microbial cell walls and cell membranes; potassium permanganate cannot oxidize intracellular organic matter. Compared to potassium permanganate, Mn(III) ions have a higher redox potential and stronger oxidizing ability than Mn(VII) ions, and can simultaneously destroy and oxidize both extracellular and intracellular organic matter. Its mechanism of action is as follows: Mn(III) ions act on polysaccharides and proteins in the sludge flocs, leading to the rupture of sludge cells and the breakage of the EPS protein backbone. The breakage of the EPS protein backbone disrupts the dense and intact floc structure of the sludge, making the sludge more dispersed and porous, increasing the porosity of the sludge. Therefore, water can easily separate from the sludge, improving its dewatering performance. Furthermore, the rupture of microbial cells and the breakage of the EPS framework allow free water encapsulated within the cells and EPS to be released into the external environment of the sludge, thus reducing the free water content in the sludge and improving its dewatering performance. In addition, this invention utilizes the addition of framework constructs to the sludge flocs to further improve sludge dewatering performance. In an alkaline environment, the hydroxide framework formed by manganese and calcium ions disperses at the points of structural disruption in the sludge flocs, promoting dewatering. Simultaneously, many sludge organic materials possess electron-deficient structures that can complex / coordinate with calcium and manganese ions, forming a dual-metal interpenetrating organic network structure. That is, during the above reaction process, manganese and calcium ions continuously come into full contact with and react with the sludge organic materials dissolved using principles such as potassium permanganate oxidation, alkaline fermentation, and advanced oxidation of Mn(III) ions, continuously forming a metal-doped organic network structure. This network structure can effectively improve the sludge dewatering performance through adsorption bridging and the formation of free water channels.

[0020] The manganese ions produced by the potassium permanganate / sodium bisulfite (PM / BS) reaction system are transition metals with low bacterial toxicity. Within a certain range, their addition can increase the total bacterial count and acid-producing bacteria in the sludge alkaline fermentation system. Therefore, the potassium permanganate / sodium bisulfite (PM / BS) system not only oxidizes and breaks down various dissolved and solid organic matter in the sludge and participates in the formation of the manganese-calcium doped network structure, but also promotes the acid-producing fermentation and proliferation of functional fermenting bacteria.

[0021] This invention proposes a segmented oxidation control pathway of "potassium permanganate pre-oxidation + Mn(III) advanced oxidation" to resolve the contradiction between organic matter concentration and coagulation effect. On the one hand, higher organic matter concentration indicates better sludge floc disintegration, allowing for the formation of a higher concentration of metal mesh structure and better dewatering effect. On the other hand, excessively high organic matter concentration in water leads to a poorer coagulation effect dominated by inorganic metal ions, weakening floc density and hindering dewatering performance. Therefore, this invention employs a two-stage oxidation method to resolve the above contradiction. Specifically, some organic matter is dissolved or removed through pre-oxidation, forming a mesh structure with metal; other organic matter can be removed through advanced oxidation, coagulation, or the formation of a metal-doped mesh structure, thus eliminating the limitation between the dissolution of high-concentration organic matter and its adverse effects on coagulation.

[0022] (4) Sludge particles are usually composed of negatively charged microbial flocs with a double-layer structure. Free Mn formed by the oxidation of Mn(III) in the sludge reaction system 2+ and the added Ca 2+ By compressing the double electric layer and neutralizing the charge through adsorption, the zeta potential on the surface of the bacterial floc particles can be reduced, promoting particle destabilization and facilitating aggregation into larger particles. This improves the solid-liquid separation effect of sludge, thereby enhancing sludge dewatering performance. At this point, the Ca in calcium hydroxide... 2+ It can compensate for the low concentration of free or divalent manganese ions generated by the advanced oxidation reaction of Mn(III), ensuring that there is an appropriate concentration of positively charged metal ions in the sludge reaction system, thereby ensuring the normal performance of coagulation.

[0023] (5) The novel advanced oxidation technology (PM / BS technology) is used to remove organic matter from the sludge, and the reaction produces a large amount of Mn. 2+ It reacts with oxygen in an alkaline environment to produce manganese hydroxide, as shown in the following reaction equation:

[0024] 2Mn 2+ +4OH 2- +O2→2MnO(OH)2

[0025] MnO(OH)2 and Ca 2+A novel manganese-calcium doped mesh structure can be formed within sludge flocs, replacing the original organic skeleton and serving as the main supporting structure. This novel manganese-calcium mesh structure exhibits excellent dispersibility and high mechanical strength, is uniformly dispersed within the sludge floc structure, and contains numerous free water channels, facilitating the removal of free water during dewatering and improving sludge dewatering efficiency. Simultaneously, free or individual manganese-calcium doped meshes can further form long-chain polymeric flocculants through hydrogen bonding, exhibiting excellent flocculation effects. These water-soluble chain-like polymeric flocculants can adsorb onto hydroxide colloids and active sites in suspended sludge, thereby bridging and linking the sludge flocs into larger flocs. Due to gravity settling, the dewatering performance of the sludge flocs is improved.

[0026] Sludge contains a wide variety of organic compounds, and the complexing ability of a single type of metal varies considerably for different organic compounds. To improve the stability of the metal-doped organic matter mesh structure and its complexing ability for a wider range of organic compounds, calcium and manganese were selected based on the principle of metal complexation. The study found that calcium doping can effectively modulate the electrical structure of the calcium-manganese-organic matter mesh system, optimizing its adsorption and complexing performance for different types of organic compounds.

[0027] (6) Adding calcium hydroxide to sludge can provide a large amount of calcium ions, promote sludge stability, and improve sludge dewatering capacity. At the same time, manganese salt ions that have not participated in the reaction in the sludge reaction system are removed from the sludge solution by forming manganese hydroxide precipitate with calcium hydroxide, thus ensuring the harmlessness of manganese salts in the sludge.

[0028] (7) Compared with other sludge treatment methods, this reaction is carried out at room temperature and has the advantages of good dewatering effect, low reaction temperature, low energy consumption, simple operation, safe treatment and easy control. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments.

[0030] The physicochemical properties of the excess sludge are shown in the table below:

[0031]

[0032] A method for treating residual sludge using a manganese-calcium composite agent includes the following steps:

[0033] (1) First, add manganese-calcium agent to the remaining sludge and mix it with a stirrer at 50 rpm for 1 hour. The manganese-calcium agent is a mixture of potassium permanganate powder and calcium hydroxide powder prepared on the spot (the mass percentage composition of each component is 65% and 35%), and the dosage is 2.5g per 1L of sludge.

[0034] (2) Then add sodium bisulfite solution to the sludge, mix well, and let it stand at room temperature for 1 hour. The concentration of sodium bisulfite solution is 250 g / L, and the dosage is 20 mL per 1 L of sludge.

[0035] (3) The reacted material enters the solid-liquid separation device to obtain filtrate and filter residue.

[0036] Experiment 1: Verifying the effect of the mass ratio of each component in the manganese-calcium reagent on the experimental results.

[0037] The results of Experiment 1 are shown in the table below:

[0038]

[0039] In experiments 1-3, under optimal conditions, the CST reduction rate of the residual sludge was 31%, the COD removal rate was 29.4%, and the SS removal rate was 19.1%. Through multiple mechanisms including potassium permanganate oxidation, alkaline fermentation, and advanced oxidation by Mn(III) ions, sludge cell rupture and EPS organic matter skeleton breakage occurred, leading to the dissolution of intracellular substances from the bacterial flocs, thus reducing the SS value. Similarly, in the above reaction process, large organic molecules can be oxidized into small soluble organic molecules, while some organic matter is mineralized, thus reducing the COD value. Experiments showed that an excessively high potassium permanganate mass ratio did not improve the ability to mineralize organic matter or dewatering performance, and it also increased the production cost of manganese-calcium reagents; therefore, the appropriate potassium permanganate mass ratio is 65%. The addition of calcium hydroxide provides a large amount of Ca. 2+ In the sludge thickening and dewatering process, Ca 2+ It acts as a bridging agent in the formation of filter cake, which can improve the dewatering effect of sludge, while Ca... 2+ It is beneficial for improving soil fertility and facilitating subsequent treatment of sludge filter residue. However, if the mass ratio of calcium hydroxide is too high, the decrease in the mass ratio of potassium permanganate will weaken the oxidation capacity of the composite agent and reduce the dewatering performance of the sludge. Therefore, the appropriate mass ratio of calcium hydroxide is 35%.

[0040] Experiment 2: Effect of sodium bisulfite solution concentration on experimental results

[0041] The results of Experiment 2 are shown in the table below:

[0042]

[0043] In experiments 5-9, the CST reduction rate of the residual sludge under optimal conditions was 34.9%. When the sodium bisulfite solution concentration was too low, the amount of Mn(III) ions generated in the PM / BS system reaction was insufficient, resulting in inadequate mineralization of organic matter by the reagent and limited improvement in sludge dewatering performance. Conversely, when the sodium bisulfite solution concentration was too high, the reagent treatment cost was excessively high. Therefore, the suitable concentration of sodium bisulfite solution was 250 g / L.

[0044] The above description only illustrates the embodiments, advantages, and technical principles of the present invention. Those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating excess sludge using a manganese-calcium composite agent, comprising the following steps: Under normal temperature conditions, manganese-calcium composite agents are used to condition the remaining sludge; The manganese-calcium composite agent is a freshly prepared solid mixture, composed of potassium permanganate powder and calcium hydroxide powder, with the potassium permanganate component and calcium hydroxide component accounting for 65% and 35% by mass, respectively. When the manganese-calcium composite agent is mixed with excess sludge, the dissolved potassium permanganate pre-oxidizes some of the extracellular polymeric substances (EPS) in the sludge, breaking down the sludge flocs and allowing MnO4 to be released. - and Ca 2+ The material enters the sludge EPS and comes into full contact with the organic matter or microbial cells in the EPS to form a metal-doped three-dimensional organic structure containing a Mn and Ca framework. Then, a sodium bisulfite solution with a concentration of 250 g / L is added to carry out the reaction. Finally, dewatering is performed.

2. The method for treating residual sludge using a manganese-calcium composite agent according to claim 1, characterized in that: The solids concentration of the remaining sludge is 13.5-14.5 g / L, and the dosage of manganese-calcium composite agent is 2.5 g per 1 L of sludge. The mixture is stirred at 50 rpm for 1 hour at room temperature.

3. The method for treating excess sludge using a manganese-calcium composite agent according to claim 1, characterized in that: The dosage of sodium bisulfite solution is 20 mL per 1 L of sludge.

4. The method for treating residual sludge using a manganese-calcium composite agent according to claim 1, characterized in that: After adding sodium bisulfite, mix well, let stand at room temperature for 1 hour, and finally dehydrate.

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