CN105800897B - A method of strengthening excess sludge and stalk fast solid-state anaerobic digestion using Zero-valent Iron - Google Patents

Abstract

The invention discloses a method for using zero-valent iron to strengthen rapid solid-state anaerobic digestion of excess sludge and straw, which is to add domesticated and mature seed sludge, excess sludge, straw and zero-valent iron in layers in an anaerobic reactor The mixture of powder, sealed and cultured at 55°C, and then stirred every 5 days, the duration of anaerobic digestion is about 15-25 days, the average methane content in biogas is about 55%, and it is volatilized in the remaining sludge and straw The degradation rate of non-toxic solids is 50%-60%, the gas production per VS is about 600mL/gVS, and the peak period of gas production is consistent with the peak period of methane production. The invention realizes resource utilization and energy utilization of excess sludge and crop stalks, and has the advantages of fast start-up of anaerobic digestion, stable digestion process, simple equipment and low cost.

Description

A rapid solid-state anaerobic digestion method for enhancing excess sludge and straw by using zero-valent iron method

1. Technical field

The invention relates to a treatment method for resource utilization and energy utilization of excess sludge and crop stalks in a sewage treatment plant, specifically a method for using zero-valent iron to strengthen solid-state anaerobic fermentation of excess sludge and crop stalks to produce biogas, which belongs to organic Waste treatment and energy utilization technology field.

2. Background technology

By the end of the third quarter of 2015, 3,662 urban sewage treatment plants had been built nationwide. The substantial increase in sewage treatment rate has led to a rapid increase in sludge production. In 2015, the annual output of wet sludge (with a moisture content of 80%) in urban sewage treatment plants reached 33.59 million tons, and the daily sludge output reached 92,000 tons. Since sludge contains a large amount of nutrients and pollutants such as organic matter, nitrogen and phosphorus, and pathogenic microorganisms, improper disposal can easily cause serious secondary pollution, reducing or offsetting the results of huge sewage treatment investment. Sludge disposal has become an important municipal and environmental problem. At present, the main disposal methods are sanitary landfill and sludge incineration. Landfill is subject to more and more restrictions due to the secondary pollution of the environment or land constraints. Residual sludge contains a large amount of organic matter and nutrients, and is considered to be a renewable resource. Anaerobic digestion of sludge can produce biogas, and at the same time reduce the volume of sludge, stabilize the properties of sludge, improve the dehydration effect of sludge, reduce the odor of sludge, and improve the sanitary quality of sludge. Biogas can provide heat or power generation. The biogas power generation generated by anaerobic digestion of sludge in sewage treatment plants can meet 60% of its own energy consumption. Currently, wet anaerobic digestion is commonly used, but wet digestion produces a large amount of biogas slurry, and the treatment of biogas slurry increases sludge anaerobic digestion. the cost of. High-temperature solid-state anaerobic digestion has the advantages of small reaction volume, no biogas slurry, killing pathogenic microorganisms in biogas residues, and passivating heavy metals. It is an effective technical means for municipal organic waste treatment, but it has a long start-up time and easy accumulation of volatile fatty acids , The system is not stable enough and other shortcomings.

The organic matter in excess sludge is mainly composed of microorganisms, with high protein content and low carbon-nitrogen ratio of excess sludge. After anaerobic treatment, a large amount of ammonia nitrogen is generated. Adjusting the carbon-nitrogen ratio can reduce the formation of ammonia nitrogen. Straw has high carbon content and low nitrogen content, which is just the opposite of sludge. The mixture of the two can adjust the carbon-nitrogen ratio, and achieve better gas production effect with less or no other auxiliary materials. The degradation rate of straw is higher during high-temperature anaerobic digestion, and the addition of straw can significantly improve the gas production efficiency of sludge, significantly increase the gas production, and the biogas residue after anaerobic digestion can also be used as fertilizer and returned to the field. The amount of straw resources that can be collected in my country is about 687 million tons, but the current utilization rate of straw in my country is only 30%. Most of the straw is discarded or burned, causing serious environmental problems and haze weather. Therefore, solid-state anaerobic digestion of straw is an effective way for straw resource utilization and energy utilization.

Due to the high concentration of organic matter, solid-state anaerobic digestion is prone to high volatile fatty acid inhibition, resulting in a longer reaction start-up time, and high solid content also reduces the efficiency of electron transfer. In addition, the voids of straw contain a large amount of air, and the oxygen in it can easily lead to the poisoning of methanogens, both of which increase the start-up time and instability of solid-state anaerobic digestion. Reducing the startup time of solid-state anaerobic digestion and improving the stability of solid-state anaerobic digestion can significantly improve the efficiency of solid-state anaerobic digestion. Zero-valent iron is easy to oxidize. During the oxidation process, it can quickly consume the oxygen in the surrounding environment, and at the same time, it can provide electrons and accelerate electron transfer, so as to promote the activity of autotrophic methanogens and homoacetogens and the production of methane. Zero-valent iron acts as a reducing agent to react with toxic pollutants in sludge, reducing the toxicity of pollutants and reducing their inhibitory effect on methanogens. Therefore, adding trace amounts of zero-valent iron powder to the solid anaerobic digestion system can strengthen the solid-state anaerobic digestion and degradation of organic matter.

To sum up, the solid-state anaerobic digestion of excess sludge and straw is a method of resource utilization and energy utilization of organic waste, but it often has the characteristics of unstable operation. By adding zero-valent iron and using layered inoculation technology, the present invention realizes rapid startup, stable operation and increased biogas production, which is also the innovation of the present invention. In addition, it also has the advantages of biogas residue utilization, no biogas slurry, and sludge reduction.

3. Contents of the invention

The invention aims to provide a method for using zero-valent iron to strengthen rapid solid-state anaerobic digestion of excess sludge and straw. By adding zero-valent iron, the oxygen brought in by the straw is quickly removed, and some electrons are provided to accelerate the electron transfer in the process of organic matter degradation and methane generation. By inoculating seed sludge in layers, the inhibition of volatile fatty acids produced by rapid acidification of excess sludge is avoided, the start-up time of solid-state anaerobic digestion is reduced, and the stability of solid-state anaerobic digestion is improved. Through the mixing of sludge, straw and zero-valent iron powder, layered inoculation of seed sludge, and high-temperature solid-state anaerobic digestion, the remaining sludge and straw are rapidly anaerobically converted into biogas.

The present invention uses zero-valent iron to strengthen the method for rapid solid-state anaerobic digestion of surplus sludge and straw, comprising the following steps:

1. Raw material preparation: crush the elemental iron to obtain 80-200 mesh zero-valent iron powder for use; obtain the dehydrated residual sludge with a water content of 75-85% from the sewage treatment plant, and measure the volatile organic matter and nitrogen in it The content is used for standby; the straw is crushed to a size of 1-3 cm, and then three times the volume of water is added to the straw for soaking for 5 days, and the straw is set aside.

2. Seed sludge cultivation: put ordinary anaerobic methanogenic sludge accounting for 20% of the reactor volume in the anaerobic reactor, and then add the mixture of remaining sludge and soaked straw accounting for 40% of the reactor volume, Stir evenly; place the reactor in a constant temperature incubator, and incubate at a constant temperature of 35°C for 10 days, and then increase the temperature by 1°C every 3 days until it reaches 55°C. During the cultivating period, the mixture of remaining sludge and soaked stalks is supplemented every 5 days, stirred evenly, and the water content of the reaction mixture in the reactor is kept at 75-85%. When the daily biogas production is more than five times the effective reactor volume and lasts for more than 10 days, it indicates that the domestication of the seed sludge is completed, and the domesticated and mature seed sludge is obtained.

The dry matter mass ratio of the remaining sludge in the mixture of the excess sludge and the soaked straw initially added in step 2 and the soaked straw is 1:1; The dry matter mass ratio of mud and soaked straw is 1:1, and the dry matter mass in the mixture of supplemented excess sludge and soaked straw accounts for 3% of the dry matter mass in the reactor.

3. Raw material mixing: mix the remaining sludge and soaked straw according to the carbon-to-nitrogen ratio of 25-30:1, and then add zero price in proportion to 0.01-0.1% of the dry matter of the remaining sludge and soaked straw Iron powder, mixed evenly to obtain a mixture, heated to 55°C, and set aside.

4. Raw material inoculation: Lay the heated mixture and domesticated mature seed sludge into the reactor in the order of one layer of mixed material and one layer of domesticated mature seed sludge in a layered cross arrangement. The total volume of the mixture and domesticated mature seed sludge accounts for 4/5 of the volume of the reactor, and the volume of the laid domesticated mature seed sludge is 1/5 to 1/3 of the volume of the mixed material. The ratio of the volatile solid mass in the mud to the volatile solid mass in the mixture is 15-30:100, and the water content of the reaction mixture in the reactor is 75-85%.

5. Solid-state anaerobic digestion: After inoculation, seal the reactor, heat to 55°C, and carry out anaerobic digestion. Mix once every 5 days in the absence of air. Anaerobic digestion lasts for 15-25 hours at 55°C. Every day, the biogas is continuously collected for energy use, and the residue after digestion and degradation is collected for agricultural or forest use.

The concrete principle of processing method of the present invention is as follows:

Solid-state anaerobic digestion has the characteristics of high concentration of organic matter and low humidity, and it is easy to produce high concentrations of volatile fatty acids during anaerobic fermentation, resulting in severe acid inhibition and instability of the anaerobic process. During the inoculation process, it is easy to bring in air, leading to poisoning of strictly anaerobic methanogens. Low humidity also reduces the rate of electron transfer during organic matter degradation and methanogenesis, prolonging the treatment time for solid anaerobic digestion. By adding zero-valent iron powder, the oxygen in the surrounding environment is consumed, electrons are provided and electron transfer is accelerated, the degradation rate of organic matter is enhanced, and the activity of methanogens is promoted. The layered inoculation at the initial stage avoids the accumulation of volatile organic acids produced by the fermentation of easily degradable organic matter in the initial stage, accelerates the start of solid-state anaerobic digestion, and improves the stability and methane yield of anaerobic digestion.

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

1. The present invention uses zero-valent iron powder to strengthen the solid-state anaerobic digestion technology, quickly consumes residual oxygen, and accelerates the electron transfer in the process of organic matter degradation and methane generation, which is an important basis for improving the efficiency of solid-state anaerobic digestion.

2. The present invention adopts layered inoculation technology, through the layered distribution of inoculated seed sludge and sludge straw mixture in the initial stage, effectively controlling the concentration of volatile fatty acids around methanogenic microorganisms, realizing the rapid growth of methanogenic microorganisms, avoiding the Usually solid-state anaerobic digestion is an inherent defect of acid inhibition.

4. Description of drawings

Fig. 1 is a schematic diagram of mixed inoculation for solid-state anaerobic digestion of the present invention.

Fig. 2 is the methane production curve of solid-state anaerobic digestion of excess sludge and rice straw strengthened by zero-valent iron powder in Example 1. It can be seen from Fig. 2 that the addition of zero-valent iron shortened the stagnation period of anaerobic digestion and increased the biogas yield of residual sludge and rice straw by about 9%.

Fig. 3 is the methane production curve of solid-state anaerobic digestion of residual sludge and corn stalks enhanced by zero-valent iron powder in Example 2. It can be seen from Figure 3 that the addition of zero-valent iron shortened the stagnation period of anaerobic digestion of excess sludge and corn stalks, and increased the biogas yield of excess sludge and corn stalks by about 8%.

5. Specific implementation

The technical solution of the present invention will be further described by examples below.

Example 1: Solid-state anaerobic digestion treatment of excess sludge and rice straw in a sewage treatment plant

In this embodiment, the method of using zero-valent iron to strengthen the rapid solid-state anaerobic digestion of excess sludge and straw includes the following steps:

1. Raw material preparation: crush the elemental iron to obtain 120 meshes of zero-valent iron powder for use; obtain dehydrated residual sludge with a moisture content of 80% from the sewage treatment plant, measure the content of volatile organic matter and nitrogen therein, and use it for use; The straw is crushed to a size of 1-3 cm, then three times the volume of water is added to the straw and soaked for 5 days, and the straw is used for later use. The water content of the soaked straw is 80%.

2. Seed sludge cultivation: add ordinary anaerobic methanogenic sludge to the reactor in the constant temperature incubator to 20% of the reactor volume, and the reaction volume of the reactor is 10L; add 40% of the reactor volume to the reactor % of the mixture of excess sludge and soaked stalks, stir evenly, and the dry matter mass ratio of excess sludge and soaked stalks in the mixture of excess sludge and soaked stalks is 1:1; the reactor is set at 35 Cultivate at a constant temperature for 10 days, then increase the temperature by 1°C every 3 days until 55°C, replenish the mixture of remaining sludge and soaked straw every 5 days during the cultivation period, stir evenly, and keep the reaction in the reactor The water content of the mixture is 75-85%, the dry matter mass ratio of the excess sludge and the soaked straw in the mixture of supplemented surplus sludge and soaked straw is 1:1, and the supplemented surplus sludge and soaked straw The dry matter mass in the straw mixture accounts for 3% of the dry matter mass in the reactor. When the daily biogas production is 5 times the volume of the effective reactor and maintained for more than 10 days, it indicates that the domestication of the seed sludge is completed, and the domesticated and mature seed sludge is obtained.

3. Mixing of raw materials: mix the remaining sludge and soaked straw with a carbon-to-nitrogen ratio of 25-30:1, and then add zero-valent iron powder in a proportion of 0.05% of the dry matter of the remaining sludge and soaked straw , mixed evenly to obtain a mixture, heated to 55°C, and set aside.

4. Inoculation of raw materials: Lay the heated mixture and domesticated mature seed sludge into the reactor in the order of one layer of mixed material and one layer of domesticated mature seed sludge in a layered cross arrangement. Layers, three layers of acclimated mature seed sludge. The total volume of the mixture and domesticated mature seed sludge accounts for 4/5 of the volume of the reactor, and the volume of the laid domesticated mature seed sludge is 1/3 of the volume of the mixed material, so as to control the volatility of the domesticated mature seed sludge The ratio of solid mass to volatile solid mass in the mixture is 30:100, and the water content of the reaction mixture in the reactor is 75-85%.

5. Solid-state anaerobic digestion: After inoculation, seal the reactor and move it to a constant temperature incubator preheated to 55°C for anaerobic digestion. During the anaerobic digestion process, do not open the anaerobic reactor every 5 days , fully shaken and mixed once, anaerobic digestion lasts for 21 days, and biogas is collected. The yield of methane obtained was 520mL/g VS reaction substrate, and methane generation is shown in Figure 2. After solid-state anaerobic digestion, the remaining sludge can be stabilized, reduced, harmless and resourceful.

Example 2:

In this embodiment, the method of using zero-valent iron to strengthen the rapid solid-state anaerobic digestion of excess sludge and corn stalks includes the following steps:

1. Raw material preparation: crush the elemental iron to obtain 80-mesh zero-valent iron powder for later use; obtain dehydrated residual sludge with a moisture content of 80% from the sewage treatment plant, measure the content of volatile organic matter and nitrogen therein, and use it for later use; Crush the corn stalks to a size of 1-3 cm, then add 4 times the volume of water to the corn stalks and soak for 5 days, and set aside for later use. The water content of the soaked stalks is 80%.

2. Seed sludge cultivation: add ordinary anaerobic methanogenic sludge to the reactor in the constant temperature incubator to 20% of the reactor volume, and the reaction volume of the reactor is 10L; add 40% of the reactor volume to the reactor % of the mixture of excess sludge and soaked corn stalks, stir evenly, the dry matter mass ratio of excess sludge and soaked corn stalks in the mixture of excess sludge and soaked corn stalks is 1:1; Cultivate at a constant temperature of 35°C for 10 days, and then increase the temperature by 1°C every 3 days until it reaches 55°C. During the cultivation period, supplement the mixture of residual sludge and soaked corn stalks every 5 days, stir evenly, and keep The water content of the reaction mixture in the reactor is 75-85%. The dry matter mass ratio of the excess sludge and soaked corn stalks in the mixture of supplemented excess sludge and soaked corn stalks is 1:1, and the supplemented remaining The dry matter mass in the mixture of sludge and soaked corn stalks accounted for 3% of the dry matter mass in the reactor. When the daily biogas production is 5 times the volume of the effective reactor and maintained for more than 10 days, it indicates that the domestication of the seed sludge is completed, and the domesticated and mature seed sludge is obtained.

3. Mixing of raw materials: mix the excess sludge and soaked corn stalks at a ratio of 25 to 30:1 carbon to nitrogen, and then add zero price in proportion to 0.1% of the mass of the remaining sludge and soaked corn stalks Iron powder, mixed evenly to obtain a mixture, heated to 55°C, and set aside.

4. Inoculation of raw materials: Lay the heated mixture and domesticated mature seed sludge into the reactor in the order of one layer of mixed material and one layer of domesticated mature seed sludge in a layered cross arrangement. Layers, three layers of acclimated mature seed sludge. The total volume of the mixture and domesticated mature seed sludge accounts for 4/5 of the volume of the reactor, and the volume of the laid domesticated mature seed sludge is 1/4 of the volume of the mixed material, so as to control the volatility of the domesticated mature seed sludge The ratio of solid mass to volatile solid mass in the mixture is 20:100, and the water content of the reaction mixture in the reactor is 75-85%.

5. Solid-state anaerobic digestion: After inoculation, seal the reactor and move it to a constant temperature incubator preheated to 55°C for anaerobic digestion. During the anaerobic digestion process, do not open the anaerobic reactor every 5 days , fully shaken and mixed once, anaerobic digestion lasts for 21 days, and biogas is collected. The yield of methane was 650mL/g VS reaction substrate, and methane generation is shown in Figure 3. After solid-state anaerobic digestion, the remaining sludge can be stabilized, reduced, harmless and resourceful.

Claims (5)

1. A method for utilizing zero-valent iron to strengthen excess sludge and stalk fast solid-state anaerobic digestion, is characterized in that comprising the steps: (1) Raw material preparation: crush the elemental iron to obtain 80-200 mesh zero-valent iron powder for future use; obtain the dehydrated residual sludge with a water content of 75-85% from the sewage treatment plant, and measure the volatile organic matter and nitrogen therein The content of the straw is set aside; the straw is crushed to a size of 1-3cm, and then three times the volume of water is added to the straw and soaked for 5 days, set aside; (2) Seed sludge cultivation: put ordinary anaerobic methanogenic sludge accounting for 20% of the reactor volume into the anaerobic reactor, and then add the mixture of remaining sludge and soaked straw accounting for 40% of the reactor volume , stir evenly; place the reactor in a constant temperature incubator, and cultivate it at a constant temperature of 35°C for 10 days, and then increase the temperature by 1°C every 3 days until it reaches 55°C; during the cultivation period, replenish the remaining sludge and Stir the soaked straw mixture evenly, and keep the moisture content of the reaction mixture in the reactor at 75-85%; when the daily biogas production is more than five times the effective reactor volume and lasts for more than 10 days, it indicates that the seed pollution Mud domestication is completed, and domesticated mature seed sludge is obtained; (3) Mixing of raw materials: mix the excess sludge and soaked straw with a carbon-to-nitrogen ratio of 25-30:1, and then add zero valence iron powder, mix evenly to obtain a mixture, heat to 55°C, and set aside; (4) Raw material inoculation: Lay the heated mixture and domesticated and matured seed sludge into the reactor in the order of one layer of mixed material and one layer of domesticated and matured seed sludge in a layered cross arrangement; The total volume of domesticated mature seed sludge accounts for 4/5 of the reactor volume; (5) Solid-state anaerobic digestion: After the inoculation, seal the reactor, heat it to 55°C, and carry out anaerobic digestion. Mix once every 5 days in the absence of air. The anaerobic digestion lasts for 15- For 25 days, the biogas is collected continuously for energy use, and the residue after digestion and degradation is collected for agricultural or forest use. 2. The method according to claim 1, characterized in that: The dry matter mass ratio of excess sludge and soaked straw in the mixture of excess sludge initially added in step (2) and soaked straw is 1:1. 3. The method according to claim 1, characterized in that: In step (2), the dry matter mass ratio of the remaining sludge and the soaked stalk in the mixture of the remaining sludge supplemented during the cultivation period and the soaked straw is 1:1, and the ratio of the supplemented surplus sludge and the soaked straw is 1:1. The mass of dry matter in the mixture accounts for 3% of the mass of dry matter in the reactor. 4. The method according to claim 1, characterized in that: The volume of the domesticated mature seed sludge laid in the step (4) is 1/5～1/3 of the volume of the mixture, and the ratio of the volatile solid mass in the domesticated mature seed sludge to the volatile solid mass in the mixture is controlled For 15-30:100. 5. The method according to claim 1, characterized in that: In step (4), the moisture content of the reaction mixture in the reactor is controlled to 75-85%.