A method for breaking the cell wall of excess sludge to enhance the release amount of carbon source

Abstract

The present invention discloses a method for enhancing the carbon source release amount by breaking the cell walls of excess sludge, which couples the treatment with sodium acetate during the alkali hydrolysis of excess sludge to promote the release of carbon source by breaking the cell walls of excess sludge. The present invention controls the sludge moisture content, reaction time, alkali dosage, and sodium acetate concentration, and detects the contents of COD, nitrogen, phosphorus, protein, polysaccharide, LDH (lactate dehydrogenase) in the lysate of excess sludge after the coupled treatment of sodium acetate and alkali hydrolysis, as well as the sludge sedimentation performance, to verify the effect of sludge cell wall breaking. The present invention effectively realizes sludge cell wall breaking at a low cost, efficiently and rapidly releases biodegradable carbon source, thereby improving the efficiency of sludge resource utilization.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection and energy conservation, and in particular relates to a method for breaking the wall of residual sludge to increase the release amount of carbon source. Background Art

[0002] With the rapid advancement of my country's urbanization process and the rapid development of economic living standards, the discharge and treatment volume of urban sewage has also increased year by year. In the new era of continuous improvement of urban sewage treatment capacity, sludge, as the end product of sewage treatment, has also been increasing in production. However, under the trend of continuous increase in sludge production, the improvement of my country's sludge treatment capacity is far lower than the increase in sludge production, which has gradually become the main environmental problem in my country's urban pollution control field.

[0003] Faced with the high standards of sludge treatment in the era, traditional sludge treatment methods such as sanitary landfill can no longer adapt to the development of the times, and sludge stabilization methods such as sludge digestion and composting also have problems such as long treatment cycle and low organic matter conversion rate. This is mainly because a large amount of organic matter in the sludge is difficult to release due to the restrictions of cell wall barriers and extracellular polymer barriers. Therefore, research on sludge wall breaking to enhance organic matter release has gradually become a hot topic in the field of sludge treatment and disposal. The sludge breaking effect can not only promote the hydrolysis of macromolecules in EPS, but also break the cell wall of sludge bacteria, so that the easily degradable substances in the sludge bacteria are released, and even degrade the extracellular macromolecules that are difficult to degrade and utilize into small molecules that are easy to utilize through physicochemical reactions, thereby increasing the sludge availability. At present, the methods for promoting residual sludge wall breaking at home and abroad mainly include thermal hydrolysis, ultrasound, advanced oxidation treatment, enzymatic hydrolysis, etc. Although the above methods can lead to sludge cracking, they all have problems such as high equipment requirements and high energy consumption. Therefore, in order to solve the problem of sludge wall breaking, it is urgent to explore a new treatment method.

[0004] Alkaline hydrolysis can promote the chemical degradation of sludge floc structure and lipid substances in cells, and has the advantages of convenient treatment and low cost. It is currently one of the most important sludge breaking methods in the world. However, due to the protection of floc structure and extracellular polymers in sludge, alkaline hydrolysis alone is slightly insufficient to destroy the remaining sludge, and the overall wall breaking effect is poor. Summary of the invention

[0005] In view of the shortcomings of the above-mentioned prior art, the present invention provides a method for breaking the wall of excess sludge to increase the release of carbon source, which effectively achieves sludge wall breaking at a relatively low cost through sodium acetate coupling alkaline hydrolysis of excess sludge, and releases biodegradable carbon source efficiently and quickly.

[0006] The method for increasing the carbon source release by breaking the wall of excess sludge of the present invention is to couple sodium acetate treatment during the process of alkaline hydrolysis of excess sludge to promote the excess sludge to break the wall and release the carbon source.

[0007] The excess sludge is produced by a sewage treatment plant in a chemical park, and the moisture content of the excess sludge is controlled to be 95% before the sodium acetate coupled alkaline hydrolysis treatment.

[0008] The alkaline hydrolysis process is based on adjusting the pH value of the excess sludge to 12 using NaOH, with an addition amount of 0.1-0.2 g NaOH / g VS and a reaction time of 1 h.

[0009] The dosage of sodium acetate in the sodium acetate coupled alkaline hydrolysis section is based on the sodium acetate concentration in the mud-water mixture reaching 10-30%, preferably 20-30%, and the reaction time is controlled to be 3h.

[0010] The specific steps include:

[0011] S1: The standard water produced after the secondary sedimentation tank treatment in the sewage treatment plant enters the next water treatment structure process, and the residual sludge produced is collected;

[0012] S2: The excess sludge collected in step S1 is concentrated or diluted to adjust the moisture content to a specific level, and then sent to the alkaline hydrolysis section;

[0013] S3: After the excess sludge enters the alkaline hydrolysis reaction stage, the alkali dosage and reaction time are controlled to produce a mud-water mixture;

[0014] S4: adding sodium acetate to the mud-water mixture in step S3, and controlling the amount of sodium acetate added and the reaction time.

[0015] The present invention combines the high-concentration sodium acetate required by the sewage plant itself with the treatment of excess sludge, and controls the pH to inhibit the consumption of sodium acetate and promote the death of sludge, thereby improving the sludge wall breaking effect. On the one hand, the method releases valuable components such as organic matter in the excess sludge, and on the other hand, releases bound water in the sludge, thereby improving the sludge settling performance, achieving sludge reduction and resource utilization.

[0016] Technical effects and advantages of the present invention:

[0017] 1. The method for breaking the wall of residual sludge to enhance the release of carbon sources proposed in the present invention effectively achieves sludge wall breaking at a relatively low cost by coupling high-concentration sodium acetate with alkaline hydrolysis, thereby releasing the organic matter inside the sludge particles, thereby breaking the limitation of sludge resource utilization to a large extent.

[0018] 2. The sludge treatment method proposed in the present invention can effectively inactivate pathogenic microorganisms and parasite eggs in sludge under the action of high concentrations of sodium acetate and alkali, which is more stable and harmless than traditional sludge treatment and disposal methods. In addition, this method of breaking the wall of residual sludge to enhance the release of carbon sources also greatly achieves the reduction and resource utilization of sludge.

[0019] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 Schematic diagram of the volume and pH of the lysate;

[0022] Figure 2 Schematic diagram of ammonia nitrogen content in lysate;

[0023] Figure 3 Schematic diagram of total phosphorus content in lysate;

[0024] Figure 4 Schematic diagram of protein and polysaccharide contents in lysate;

[0025] Figure 5 This is a schematic diagram of the relative release of LDH from excess sludge (based on untreated sludge as a control);

[0026] Figure 6 This is a schematic diagram of the release of carbon sources from residual sludge;

[0027] Figure 7 It is a schematic diagram of the moisture content of dewatered sludge and VS / TS;

[0028] Figure 8 Schematic diagram of SV and SVI of residual sludge. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Implementation Cases:

[0031] Different concentrations of sodium acetate were used to couple the alkaline hydrolysis of the residual sludge to obtain a sludge mixture, which was then centrifuged to obtain a lysate and dehydrated sludge. The lysate and dehydrated sludge were used as carbon sources for denitrification experiments to analyze their actual availability. The specific experimental methods are as follows:

[0032] (1) Detect the moisture content and VS ratio of the residual sludge to be treated and adjust it to 95% moisture content;

[0033] (2) Each group took 100mL of 95% water content excess sludge and placed it in a beaker. 0.12gNaOH / g VS was added to the excess sludge of each group to adjust the pH to 12. After standing for 1 hour, different doses of sodium acetate were added and stirred evenly. After standing for 3 hours, part of the sludge was centrifuged at 8000r / min for 6 minutes to obtain lysis solution and dehydrated sludge. The dosage of each group of reagents is shown in the following table;

[0034]

[0035] (3) The lysate obtained from each group was taken to test the volume, pH, COD, ammonia nitrogen, total phosphorus, protein, polysaccharide, and lactate dehydrogenase (LDH) release, and the moisture content and VS / TS of the dehydrated sludge of each group were tested;

[0036] (4) Take part of the residual sludge that has been treated with sodium acetate coupled alkaline hydrolysis but not centrifuged in step (2) to test SV and SVI.

[0037] The implementation results are as follows Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8As shown. Free water in sludge can be removed by mechanical stress, but bound water is trapped in extracellular polymers (EPS) and cells and is not easily released. Therefore, when it is necessary to release bound water in cells, it is necessary to destroy EPS and sludge cell membranes. Under simple alkaline conditions, the volume of lysate after sludge centrifugation is 38.7 mL. After adding 5%, 10%, 20%, and 30% sodium acetate on the basis of alkaline conditions, the volume of lysate increased by 26.9%, 34.1%, 47.5%, and 53.5%, respectively. This also indirectly confirms the destructive effect of sodium acetate on the sludge floc structure and can promote the release of bound water in sludge. The pH of the remaining sludge dropped from 12 to 11.5 after alkaline hydrolysis alone, while the pH of the remaining sludge groups gradually stabilized at around 10.5 after sodium acetate was continued to be added. Sodium acetate is a strong base and a weak acid salt. Due to hydrolysis, the pH of the sludge group with a high sodium acetate concentration should be higher, but in fact, the pH of the sludge group containing sodium acetate is lower. This is because the cells contain acidic substances such as lysosomes, and the addition of sodium acetate promotes the lysis of sludge cells, releasing more intracellular substances, thereby causing the sludge pH to decrease. As the concentration of sodium acetate increases, sodium acetate and its hydrolysis products form a buffer system, causing the overall pH of the sludge to stabilize at around 10.5.

[0038] After sodium acetate coupled alkaline hydrolysis treatment, nitrogen-containing substances such as intracellular and extracellular proteins and nucleic acids in the residual sludge and phosphorus-containing substances are released into the liquid phase. Under simple alkaline conditions, the ammonia nitrogen content in the residual sludge lysate is 20.51±2.55mg / L, and the total phosphorus content is 20.42±1.54mg / L. This is because the alkali destroys the sludge floc structure, causing nitrogen and phosphorus release. Sludge cells contain high concentrations of nitrogen and phosphorus substances, and phosphorus is the basic component of cell membranes and cell walls. On the basis of alkali destroying the sludge floc structure and exposing sludge cells to the environment, the osmotic pressure difference caused by high concentrations of sodium acetate prompts the sludge cells to break, so the release of nitrogen and phosphorus increases with the increase of sodium acetate concentration. After 30% concentration sodium acetate coupled alkaline hydrolysis treatment of residual sludge, the ammonia nitrogen release increased by 165.85% compared with that under simple alkaline conditions, reaching 54.52±1.52mg / L, and the total phosphorus release also increased by 11.02%, reaching 43.4±2.55mg / L.

[0039] EPS is a complex biopolymer system composed of proteins, polysaccharides, humic acid and nucleic acids, which is affected by the influent water quality and the process selection of the sewage treatment plant. The EPS network structure around the microbial cells plays a protective role in adverse environments. The proteoglycan content in the sludge lysate is similar to that of ammonia nitrogen and total phosphorus, and increases with the increase of sodium acetate concentration. Under simple alkaline conditions, the protein and polysaccharide contents in the sludge lysate were 2176.04±91.15mg / L and 514.34±9.05mg / L, respectively. In comparison, under the conditions of 5%, 10%, 20%, and 30% sodium acetate coupled alkaline hydrolysis treatment, the total amount of proteoglycan in the sludge lysate increased by 21.88%, 37.35%, 59.11%, and 88.38%, respectively. The dissolution of proteoglycans increased significantly with the increase of sodium acetate concentration, indicating that the release of some proteoglycans under sodium acetate coupled alkaline hydrolysis conditions comes from the cracking of sludge cells.

[0040] LDH is expressed in all cytoplasms, and cell membrane rupture and increased cell permeability will lead to the release of LDH. Therefore, the extracellular LDH concentration can be used as an indicator of cell lysis. Taking the extracellular LDH content in untreated residual sludge as the basic control, the relative release of sludge LDH under different concentrations of sodium acetate coupled alkaline hydrolysis conditions was obtained. Under simple alkaline conditions, the relative release of sludge LDH reached 471%. On this basis, after adding sodium acetate, the relative release of sludge LDH also increased. When the sodium acetate dosage reached 30%, the relative release of LDH had increased to 827%. The results show that both alkali and sodium acetate can promote the rupture of sludge cell membranes.

[0041] The COD release of the residual sludge under simple alkaline conditions was 0.11 g / g VS. After adding 5%, 10%, 20%, and 30% sodium acetate, the COD release of the residual sludge in each group increased to 0.15, 0.24, 0.36, and 0.39 g / g VS, respectively. According to the divalent cation bridging (DCB) model, the negatively charged EPS combines with divalent cations to form a sludge matrix, while the multivalent cations in the sludge flocs can be absorbed by monovalent cations such as Na + Replacement, so when the sludge contains Na + In addition, due to the increase in osmotic pressure in the sludge after adding sodium acetate, the microbial cells will also undergo plasmolysis and autolysis, thereby releasing more carbon sources.

[0042] The moisture content of the residual sludge after centrifugal dehydration under simple alkaline conditions is 92.3%. With the increase of sodium acetate concentration, the moisture content of the dehydrated sludge decreases significantly. After adding 5%, 10%, 20%, and 30% sodium acetate, the moisture content of the centrifugal sludge is 85.3%, 80.1%, 72.0%, and 64.6%, respectively. After sodium acetate coupled alkaline hydrolysis treatment, part of the bound water in the sludge is converted into free water due to the decomposition of EPS. In addition, the dehydrated sludge contains residual sodium acetate, which is also the reason for the sharp decrease in its moisture content. In the process of determining the VS content of the sludge, the temperature needs to be raised to 605℃, and the boiling point of sodium acetate is 400℃, so the residual sodium acetate will be recorded in the VS part. In theory, the more sodium acetate residue, the higher the VS / TS. In the actual measured values ​​of each group, VS / TS decreases with the increase of sodium acetate concentration. This is because sodium acetate promotes the lysis of sludge cells, resulting in a decrease in VS in centrifugal sludge, and the reduction in organic matter covers the effect of sodium acetate residue.

[0043] The sludge settling ratio (SV) refers to the percentage of the volume of the precipitated sludge formed after the mixed liquid has been allowed to stand in the measuring cylinder for 30 minutes to the volume of the original mixed liquid, that is, the volume fraction of the settled sludge. The sludge volume index (SVI) refers to the volume of the settled sludge occupied by each gram of dry sludge, and its unit is mL / g. SV and SVI can reflect the sludge coagulation and precipitation performance, and can also indirectly reflect the degree of sludge dehydration. Compared with the simple alkaline treatment, the SV and SVI of the residual sludge after sodium acetate coupled alkaline hydrolysis treatment are lower, and the higher the sodium acetate concentration, the more obvious the reduction. Compared with the simple alkaline hydrolysis treatment, the SV and SVI of the sludge decreased by 3.56% after 30% sodium acetate coupled alkaline hydrolysis treatment. A large number of literatures have shown that alkaline agents can promote the breakup of sludge floc structure, and high concentrations of Na + The addition of alkaline agents will cause sludge cells to lyse due to excessive osmotic pressure difference. The destruction of EPS caused by alkaline agents exposes microbial cells to high concentrations of Na + environment, which may further promote Na + Induce sludge cell lysis. At the same time, microbial cell lysis also increases the EPS content, weakens the binding stability of EPS, and accelerates EPS disintegration. The dual destruction mechanism of alkali and sodium acetate on sludge destroys the floc structure and releases the bound water in the sludge particles, converting it into free water that dissolves in the liquid phase. Therefore, the treated sludge can separate more free water and has better sedimentation performance and dehydration degree.

[0044] Although the present invention has been described in detail with reference to implementation cases, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned implementation cases, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the implementation cases of the present invention.

Claims

1. A method for enhancing the carbon source release by breaking the cell walls of excess sludge, characterized in that: during the alkali hydrolysis of excess sludge, sodium acetate treatment is coupled to promote the breaking of the cell walls of excess sludge and the release of carbon source, including the following steps: S1: The qualified water produced after being treated by the secondary sedimentation tank in the sewage treatment plant enters the next water treatment structure process, and the generated excess sludge is collected; S2: The excess sludge collected in step S1 is adjusted to a specific moisture content by concentration or dilution, and then sent to the alkali hydrolysis section; S3: After the excess sludge enters the alkali hydrolysis reaction stage, the alkali dosage and reaction time are controlled. The dosage is 0.1 - 0.2 g NaOH / g VS, and a mud-water mixture is produced; S4: Sodium acetate is added to the mud-water mixture in step S3. The dosage of sodium acetate is 20 - 30% based on the concentration of sodium acetate in the mud-water mixture, and the reaction time is controlled for 3 h.

2. The method according to claim 1, characterized in that: in S2, the moisture content of the excess sludge is controlled to 95%.

3. The method according to claim 1, characterized in that: in S3, NaOH is used to adjust the pH value of the excess sludge to 12, and the reaction time is controlled for 1 h.

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