CN116002940A - A method for increasing methane production in anaerobic digestion of sludge containing heavy metals - Google Patents

Abstract

The invention discloses a method for increasing the methane output of anaerobic digestion of sludge containing heavy metals. The method utilizes cationic polyacrylamide or anionic polyacrylamide to increase the methane output in the process of anaerobic digestion of sludge containing heavy metals. In the method of the present invention, the cationic polyacrylamide/anionic polyacrylamide is introduced into the sludge digestion system for the first time, and the adsorption and bridging, flocculation and electrostatic adsorption of heavy metals by the cationic polyacrylamide/anionic polyacrylamide are used to realize the The limitation of sludge fluidity reduces the direct contact between heavy metals and microorganisms, thereby slowing down the toxic effect of heavy metals on microorganisms, thereby increasing the abundance of related microorganisms in the anaerobic digestion process and increasing the methane production of the anaerobic digestion system. The process is simple , convenient operation, low cost, high cost performance, high efficiency and other advantages, it has high use value and good application prospect in improving methane production by anaerobic digestion of sludge.

Description

A method for increasing methane production in anaerobic digestion of sludge containing heavy metals

technical field

The invention belongs to the technical field of environmental protection and relates to a method for increasing the methane output of anaerobic digestion of sludge containing heavy metals.

Background technique

Excess activated sludge is the main by-product of conventional activated sludge treatment in sewage treatment plants. If a large amount of sludge is not properly treated and disposed of, it will cause serious secondary pollution to surface and groundwater, soil and air. , but also endanger human health. Anaerobic digestion of sludge is a biochemical process in which sludge undergoes dissolution, hydrolysis, acidification, and methane production in sequence with the participation of anaerobic microorganisms. Because sludge has a strong adsorption capacity for most pollutants, a large amount of exogenous pollutants, such as heavy metals, including cadmium, chromium, copper, lead, zinc, etc., are usually enriched in sludge. Taking heavy metal cadmium as an example, if the sludge contains cadmium, the enrichment of cadmium will have adverse effects on the methane production in the sludge anaerobic digestion system. Therefore, how to effectively reduce the toxic effect of heavy metals on the anaerobic digestion system is of great significance for effectively increasing the methane production capacity of anaerobic digestion.

So far, some researchers have made related attempts. For example, some researchers have proposed a method to enhance the stabilization process of heavy metals in anaerobic digestion sludge. By adding an appropriate amount of modified sludge biochar in the acid production stage of anaerobic digestion of sludge, it can be obviously adsorbed and captured in the reactor. free heavy metals, which can enhance the stabilization effect of heavy metals in sludge. However, the addition of modified sludge biochar in this method has no obvious effect on sludge methane production and stabilization process, and the preparation and synthesis of modified biochar are comparatively Complicated and time-consuming, inconvenient to operate, and low cost performance. In addition, some researchers have proposed a conditioner for the stabilization of heavy metals in sludge anaerobic digestion, by introducing oxidants (at least one of sodium peroxide, calcium peroxide and chlorine dioxide) into the sludge anaerobic digestion system And buffering agent (sodium carbonate and sodium bicarbonate mixture), reduce the impact of heavy metals on anaerobic digestion, can increase the hydrolysis rate of sludge, however, the conditioner used in this method has strong oxidizing and weak corrosive, so this method The purchase and transportation of the conditioner requires a lot of manpower, material and financial resources, and there is a problem of high cost. At the same time, the conditioner used in this method has a strong toxic effect on microorganisms, which leads to the anaerobic digestion process. The abundance of related microorganisms in the anaerobic digestion process is relatively low, and the activity of these microorganisms is easily inhibited, so that the methane production in the anaerobic digestion process is still low. Therefore, finding a cheap, simple and effective method to alleviate the toxicity of heavy metals to the anaerobic digestive system has become a top priority.

Polyacrylamide is a commonly used agent in the field of water treatment, and is usually used to enhance solid-liquid separation and sludge dewatering. However, so far, it has not been seen that polyacrylamide is added to the anaerobic digestion process of sludge for conditioning Related reports on the toxicity of heavy metals in sludge.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for increasing the methane output of anaerobic digestion of heavy metal-containing sludge with simple process, convenient operation and low cost.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

The invention discloses a method for increasing the methane output of anaerobic digestion of heavy metal-containing sludge, the method is to use cationic polyacrylamide or anionic polyacrylamide to increase the methane output in the process of anaerobic digestion of heavy metal-containing sludge.

The above method is further improved. When cationic polyacrylamide is used to increase the methane production in the anaerobic digestion process of sludge containing heavy metals, the mass ratio of the cationic polyacrylamide to the volatile suspended matter in sludge containing heavy metals is 0.001 ~0.004:1.

The above method is further improved, the mass ratio of the cationic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.0015-0.0035:1.

The above method is further improved, the mass ratio of the cationic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.0015-0.003:1.

The above method is further improved, the mass ratio of the cationic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.002:1.

The above method is further improved. When using anionic polyacrylamide to increase the methane production in the anaerobic digestion process of heavy metal-containing sludge, the mass ratio of the anionic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.0005 ~0.003:1.

The above method is further improved, the mass ratio of the anionic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.0006-0.002:1.

The above method is further improved, the mass ratio of the anionic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.0007-0.001:1.

The above method is further improved, the mass ratio of the anionic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.00075:1.

The above-mentioned method, further improved, comprises the following steps:

S1, mixing cationic polyacrylamide with heavy metal-containing sludge to obtain a mud-water mixture;

S2. Perform anaerobic digestion on the mud-water mixture obtained in step S1 to complete the treatment of heavy metal-containing sludge.

The above method is further improved. In step S1, the cationic polyacrylamide is added into the heavy metal-containing sludge in the form of a solution; the mass volume concentration of the cationic polyacrylamide in the cationic polyacrylamide solution is 0.5%.

The above method is further improved, in step S1, the initial concentration of heavy metals in the heavy metal-containing sludge is ≥ 2.5mg/g VSS; the heavy metals in the heavy metal-containing sludge include cadmium, chromium, copper, lead, and zinc at least one of .

The above method is further improved. In step S1, the initial concentration of volatile suspended matter in the heavy metal-containing sludge is 29.1 g/L.

The above method is further improved, in step S2, the temperature is controlled to be 35° C. to 37° C. during the anaerobic digestion process; the time for the anaerobic digestion is 30 days to 45 days.

The above-mentioned method, further improved, comprises the following steps:

S1, mixing anionic polyacrylamide with heavy metal-containing sludge to obtain a mud-water mixture;

S2. Perform anaerobic digestion on the mud-water mixture obtained in step S1 to complete the treatment of heavy metals.

The above method is further improved. In step S1, the anionic polyacrylamide is added to the heavy metal-containing sludge in the form of a solution; the mass volume concentration of the anionic polyacrylamide in the anionic polyacrylamide solution is 0.5%.

The above method is further improved, in step S1, the initial concentration of heavy metals in the heavy metal-containing sludge is ≥ 2.5mg/g VSS; the heavy metals in the heavy metal-containing sludge include cadmium, chromium, copper, lead, and zinc at least one of .

The above method is further improved. In step S1, the initial concentration of volatile suspended matter in the heavy metal-containing sludge is 29.1 g/L.

The above method is further improved, in step S2, the temperature is controlled to be 35° C. to 37° C. during the anaerobic digestion process; the time for the anaerobic digestion is 30 days to 45 days.

Compared with the prior art, the present invention has the advantages of:

(1) The present invention provides a method for improving the methane yield of anaerobic digestion of heavy metal-containing sludge. For the first time, cationic polyacrylamide/anionic polyacrylamide is introduced into the sludge digestion system to alleviate the adverse effects of heavy metals on anaerobic digestion Influence, thereby increasing methane production in the anaerobic digestion process, specifically, using cationic polyacrylamide/anionic polyacrylamide to adsorb and bridging heavy metals, flocculation to limit sludge fluidity, reduce heavy metals and microorganisms The direct contact of heavy metals can slow down the toxic effect of heavy metals on microorganisms, which is beneficial to increase the abundance of related microorganisms in the anaerobic digestion process and increase the methane production of the anaerobic digestion system. In addition, for anionic polyacrylamide, in addition to restricting the fluidity of sludge, it also has an electrostatic adsorption effect for adsorbing heavy metals. Therefore, through the coordinated regulation of the above-mentioned multiple modes of action, sludge can be more effectively increased. Methane production during anaerobic digestion. Compared with the conventional method, the method of the present invention for improving the methane production of anaerobic digestion of heavy metal-containing sludge has the advantages of simple process, convenient operation, low cost, high cost performance, and high efficiency. High use value and good application prospect.

(2) In the present invention, by optimizing the dosage of cationic polyacrylamide and anionic polyacrylamide, while effectively reducing the toxicity of heavy metals, it is guaranteed that polyacrylamide itself will not affect the anaerobic digestion system to the greatest extent, thereby more conducive to pollution The formation of slime micelles and the reproduction and expansion of microorganisms can more effectively increase the production of anaerobic digested methane.

(3) In the present invention, the mechanism of cationic/anionic polyacrylamide improving methane production in anaerobic digestion of sludge containing heavy metals has been analyzed. Through the measurement and analysis of the relevant steps of the sludge anaerobic digestion process, it is found that cationic polyacrylamide The addition of anionic polyacrylamide effectively improves the dissolution, hydrolysis and acidification process of anaerobic digestion of high-cadmium sludge, which in turn is beneficial to increase the production of methane. From the perspective of the toxicity source of heavy metals to microorganisms, it was found that the addition of cationic polyacrylamide/anionic polyacrylamide, on the one hand, effectively reduced the production of active oxygen species induced by heavy metals, and weakened the degree of oxidative damage to microbial cells; On the one hand, the activity of key enzymes (hydrolase, acid-producing enzyme and methanase) in the process of anaerobic digestion has been improved, and the process of anaerobic digestion has been promoted. At the same time, the determination and analysis of the microbial community related to the anaerobic digestion process showed that the introduction of cationic polyacrylamide/anionic polyacrylamide increased the abundance of related microorganisms in the anaerobic digestion process of heavy metal-containing sludge.

Detailed ways

The present invention will be further described below in conjunction with specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

The raw materials and instruments used in the following examples are all commercially available; the equipment and preparation processes used are conventional equipment and conventional processes unless otherwise specified.

Example 1

A method for increasing methane production in anaerobic digestion of sludge containing heavy metals, specifically using cationic polyacrylamide to increase methane production in anaerobic digestion of sludge containing cadmium, comprising the following steps:

(1) Take cadmium-containing sludge, the initial concentration of cadmium ions in the sludge is 2.5 mg/g VSS, that is, the mass ratio of cadmium ions in the sludge to volatile suspended solids (VSS) is 0.0025:1, and the The initial concentration of volatile suspended solids (VSS) in the sludge was 29.1g/L.

(2) Get cationic polyacrylamide, configure cationic polyacrylamide solution, the concentration of cationic polyacrylamide in this cationic polyacrylamide solution is 0.5% (w/v), join above-mentioned cationic polyacrylamide solution in the cadmium-containing sludge , control the mass ratio of the content of cationic polyacrylamide to the volatile suspended solids (VSS) of the sludge to be 0.002:1, mix evenly to obtain a mud-water mixture, the content of cationic polyacrylamide in the mud-water mixture is 2mg/g VSS.

(3) Fill nitrogen into the mud-water mixture, remove oxygen in each sludge system, control the sludge system to anaerobic conditions, and carry out anaerobic digestion at 35°C to 37°C for 40 days.

Blank group: Anaerobic digestion was performed on sludge without cadmium ions and cationic polyacrylamide, and other conditions were the same as in Example 1.

Control group: an equal amount of water was used to replace the cationic polyacrylamide solution, and other conditions were the same as in Example 1.

Simultaneously, the mass ratio of cationic polyacrylamide and volatile suspended solids (VSS) in the sludge was also investigated when the mass ratio was 0.001: 1 and 0.004: 1, respectively. same.

After testing, the methane production of different mud-water mixtures is shown in Table 1.

Table 1 Methane production corresponding to different mud-water mixtures

In Table 1, methane production is the relative content of methane compared with the blank group. According to the methane production of the blank group is 100%, then when the mass ratio of the control group, cationic polyacrylamide and volatile suspended matter VSS is 0.001:1, 0.002:1, 0.004:1, the corresponding methane production is respectively: 68% , 79%, 90% and 83%. It can be seen from Table 1 that compared with the control group, the addition of cationic polyacrylamide effectively restored the methane production. This is because in the present invention, by adding cationic polyacrylamide to the system with high concentration The flocculation of acrylamide reduces the direct contact between cadmium and microorganisms, effectively reduces the toxic effect of cadmium on microorganisms, increases the abundance of related microorganisms in the anaerobic digestion process, and promotes the production of methane in the anaerobic digestion system. It should be noted that compared with the control group, in the present invention, when the mass ratio of cationic polyacrylamide to volatile suspended matter in the sludge is 0.001-0.004:1, the anaerobic digestion methane production can be increased. In particular, when the mass ratio of cationic polyacrylamide to volatile suspended matter in the sludge is less than 0.001:1, the amount of cationic polyacrylamide is too low, it has basically no flocculation effect on sludge, and will not restrict the flow of heavy metals , which is not conducive to increasing the methane production of the anaerobic digestion system. However, when the mass ratio of cationic polyacrylamide to volatile suspended matter in the sludge is greater than 0.004:1, the flocculation effect is too strong, and the sludge flocs are excessively agglomerated, which is not conducive to the dissolution of sludge and hinders the process of anaerobic digestion; Secondly, the high concentration of cationic polyacrylamide itself has a certain toxic effect on anaerobic microorganisms, which is not conducive to the recovery of methane production. Therefore, by optimizing the mass ratio of cationic polyacrylamide to volatile suspended matter in sludge, it is more beneficial to increase the methane production of anaerobic digestion.

Example 2:

A method for increasing the methane output of anaerobic digestion of heavy metal-containing sludge, specifically using anionic polyacrylamide to increase the methane output of anaerobic digestion of cadmium-containing sludge, comprising the following steps:

(1) Take cadmium-containing sludge, the initial concentration of cadmium ions in the sludge is 2.5 mg/g VSS, that is, the mass ratio of cadmium ions in the sludge to volatile suspended solids (VSS) is 0.0025:1, and the The initial concentration of volatile suspended solids (VSS) in the sludge was 29.1g/L.

(2) Take anionic polyacrylamide and configure it into an anionic polyacrylamide solution. The concentration of anionic polyacrylamide in this anionic polyacrylamide solution is 0.5% (w/v), and the above-mentioned anionic polyacrylamide solution is added to the solution containing In the cadmium sludge, control the mass ratio of the content of anionic polyacrylamide to the volatile suspended solids (VSS) of the sludge to be 0.0015:1, and mix evenly to obtain a mud-water mixture, the content of anion polyacrylamide in the mud-water mixture is 1.5 mg/g VSS.

(3) Fill nitrogen into the mud-water mixture, remove oxygen in each sludge system, control the sludge system to anaerobic conditions, and carry out anaerobic digestion at 35°C to 37°C for 40 days.

Blank group: Anaerobic digestion was performed on the sludge not containing cadmium ions and anionic polyacrylamide, and other conditions were the same as in Example 2.

Control group: an equivalent amount of water was used to replace the anionic polyacrylamide solution, and other conditions were the same as in Example 2.

Simultaneously, the mass ratio of the volatile suspended matter (VSS) in the anionic polyacrylamide and the sludge was also investigated when the mass ratio was respectively 0.00075: 1, 0.003: 1. The impact on the output of anaerobic digestion methane, other conditions and embodiment 2 same.

After testing, the methane production of different mud-water mixtures is shown in Table 2.

Table 2 Methane production corresponding to different mud-water mixtures

In Table 2, methane production is the relative content of methane compared with the blank group. When the methane production of the blank group is 100%, when the mass ratios of the control group, anionic polyacrylamide and volatile suspended matter VSS are 0.00075:1, 0.0015:1, and 0.003:1, the corresponding methane production is respectively: 68% , 93%, 86% and 79%. As can be seen from Table 2, compared with the control group, the addition of anionic polyacrylamide effectively restored the methane production, this is because the present invention adds anionic polyacrylamide to the system containing high cadmium sludge, through Adsorption bridging, flocculation and electrostatic adsorption of cadmium reduce the direct contact between cadmium and microorganisms, effectively reduce the toxicity of cadmium to microorganisms, increase the abundance of related microorganisms in the anaerobic digestion process, and promote anaerobic digestion. Digestive system methane production. It should be noted that, compared with the control group, in the present invention, the mass ratio of anionic polyacrylamide to volatile suspended matter in the sludge is 0.00075-0.003:1, both of which can increase the methane production of anaerobic digestion. In particular, when the mass ratio of anionic polyacrylamide to volatile suspended matter in sludge is less than 0.00075:1, the amount of anionic polyacrylamide is too low, and it has basically no flocculation effect on sludge and will not restrict the flow of heavy metals , will not increase the methane production of the anaerobic digestion system; and when the mass ratio of anionic polyacrylamide to volatile suspended matter in the sludge is greater than 0.003:1, the flocculation is too strong, and the sludge flocs are excessively agglomerated, which is not conducive to The dissolution of sludge hinders the process of anaerobic digestion; secondly, the high concentration of anionic polyacrylamide itself has a certain toxic effect on anaerobic microorganisms, which is not conducive to the recovery of methane production. Therefore, by optimizing the mass ratio of anionic polyacrylamide to volatile suspended matter in sludge, it is more conducive to improving the methane production of anaerobic digestion. In addition, compared with cationic polyacrylamide, the addition amount of anionic polyacrylamide is smaller, so methane production can be increased at a lower cost.

In conclusion, the present invention improves the methane yield of anaerobic digestion of sludge containing heavy metals. For the first time, cationic polyacrylamide/anionic polyacrylamide is introduced into the sludge digestion system to alleviate the adverse effects of heavy metals on anaerobic digestion. This improves the methane production in the anaerobic digestion process. Specifically, the use of cationic polyacrylamide/anionic polyacrylamide to adsorb and bridge heavy metals, and flocculation to limit the fluidity of sludge and reduce direct contact between heavy metals and microorganisms , and then slow down the toxic effect of heavy metals on microorganisms, which is conducive to increasing the abundance of related microorganisms in the anaerobic digestion process and increasing the methane production of the anaerobic digestion system. In addition, for anionic polyacrylamide, in addition to restricting the fluidity of sludge, it also has an electrostatic adsorption effect on heavy metals. Therefore, through the coordinated regulation of the above-mentioned multiple modes of action, it can more effectively increase sludge repellency. Methane production during oxygen digestion. Compared with the conventional method, the method of the present invention for improving the methane production of anaerobic digestion of heavy metal-containing sludge has the advantages of simple process, convenient operation, low cost, high cost performance, and high efficiency. It has high use value and good application prospect.

The above examples are only preferred implementations of the present invention, and the scope of protection of the present invention is not limited to the above examples. All technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims (10)

1. A method for improving methane production in anaerobic digestion of sludge containing heavy metals, characterized in that the method is to utilize cationic polyacrylamide or anionic polyacrylamide to promote the production of methane in the anaerobic digestion of sludge containing heavy metals. 2. The method according to claim 1, characterized in that, the mass ratio of the cationic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.001 to 0.004: 1; the anionic polyacrylamide and the heavy metal-containing sludge The mass ratio of volatile suspended matter in heavy metal sludge is 0.0005-0.003:1. 3. The method according to claim 2, characterized in that the mass ratio of the cationic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.0015 to 0.0035: 1; the anionic polyacrylamide and the heavy metal-containing sludge The mass ratio of volatile suspended matter in heavy metal sludge is 0.0006-0.002:1. 4. The method according to claim 3, characterized in that the mass ratio of the cationic polyacrylamide to the volatile suspended matter in the heavy metal-containing sludge is 0.0015 to 0.003:1; the anionic polyacrylamide and the heavy metal-containing sludge The mass ratio of volatile suspended matter in heavy metal sludge is 0.0007-0.001:1. 5. The method according to claim 4, characterized in that, the mass ratio of the cationic polyacrylamide to the volatile suspended matter in the heavy metal sludge is 0.002: 1; the anionic polyacrylamide to the heavy metal sludge The mass ratio of volatile suspended matter in mud is 0.00075:1. 6. The method according to any one of claims 1 to 5, comprising the following steps: S1, mixing cationic polyacrylamide or anionic polyacrylamide with heavy metal-containing sludge to obtain a mud-water mixture; S2. Perform anaerobic digestion on the mud-water mixture obtained in step S1 to complete the treatment of heavy metal-containing sludge. 7. The method according to claim 6, characterized in that, in step S1, the cationic polyacrylamide and the anionic polyacrylamide are added to the heavy metal-containing sludge in the form of a solution; in the cationic polyacrylamide solution The mass volume concentration of the cationic polyacrylamide is 0.5%; the mass volume concentration of the anionic polyacrylamide in the anion polyacrylamide solution is 0.5%. 8. The method according to claim 7, characterized in that, in step S1, the initial concentration of heavy metals in the heavy metal-containing sludge ≥ 2.5mg/g VSS; the heavy metals in the heavy-metal sludge include cadmium, chromium , copper, lead, zinc at least one. 9. The method according to claim 7, characterized in that, in step S1, the initial concentration of volatile suspended matter in the heavy metal-containing sludge is 29.1 g/L. 10 . The method according to claim 6 , characterized in that, in step S2 , the controlled temperature during the anaerobic digestion process is 35° C. to 37° C.; the time for the anaerobic digestion is 30 days to 45 days. 11 .