CN104478183A - Method for processing municipal sludge by combining energy grass with anaerobic fermentation technology - Google Patents

Abstract

The invention discloses a method for processing municipal sludge by combining energy grass with an anaerobic fermentation technology. Different processing methods are adopted according to the properties of primary sludge and active sludge, and the active sludge with high content of organic matters and fresh energy grass are mixed and undergo anaerobic fermentation stable treatment; and the primary sludge with high content of inorganic matters and biogas residues are mixed and are stabilized by a plant (energy grass) land system, so the method adapts to different sludge characteristics, solves the problems of low anaerobic fermentation system utilization efficiency caused by much mud sands in sludge, difficult finding of the carbon source required by fermentation and the like, overcomes the disadvantages of difficult recycling of traditional sludge processing methods, and simultaneously realizes municipal sludge processing and energy regeneration and recycling comprehensive utilization; and a soil conditioner is prepared through a plant stabilizing technology, so a way is found to finally process sludge, and the utilization value of sludge is maximized.

Description

A method of joint treatment of municipal sludge using energy grass and anaerobic fermentation technology

Technical field:

The invention relates to the technical field of waste resource utilization, in particular to a method for jointly treating municipal sludge by using energy grass and anaerobic fermentation technology.

Background technique:

With the development of the economy and the acceleration of the urbanization process, the sewage treatment rate in our country is increasing day by day, and the output of municipal sludge as an inevitable subsidiary product of sewage treatment is also increasing day by day. At present, there are more than 3,000 sewage treatment plants in the country, with a daily sewage treatment capacity of 140 million tons, and a sludge production volume (based on a moisture content of 80%) of more than 140,000 tons per day. Sludge contains toxic and harmful substances such as pathogens, heavy metals and persistent organic compounds. Without effective treatment and disposal, it will easily cause secondary pollution to groundwater and soil, directly threatening environmental safety and public health.

Municipal sludge mainly comes from primary sedimentation tanks, secondary sedimentation tanks and other process links, and is mainly divided into primary sludge and activated sludge (surplus sludge). Primary sludge refers to the sludge that has been settled and discharged from the primary sedimentation tank, and its water content is usually 97% to 98%; activated sludge refers to the remaining sludge discharged from biological treatment systems such as traditional activated sludge processes, and its water content is The rate is usually 99.2% to 99.8%. Sludge properties are an important basis for selecting sludge treatment and disposal processes. The indicators to measure sludge properties mainly include moisture content, volatile matter, and plant nutrients. Volatile matter is the most important chemical property of sludge. In general, the proportion of volatile solids in primary sludge is 50% to 60%, and that in activated sludge is 60% to 85%. The overall status of plant nutrients in sludge from sewage treatment plants in my country is shown in the table below:

sludge type Total Nitrogen (TN) Phosphorus (P ₂ O ₅ ) Potassium (K) Primary sludge 2.0～3.4 1.0～3.0 0.1～0.3 activated sludge 3.5～7.2 3.3～5.0 0.2～0.4

Because municipal sludge has the characteristics of high organic matter content and rich plant nutrients, the World Water Environment Organization (The WaterEnvironment Federation, WEF) has changed the name of sludge to bio-organic solids (biosolids). At present, sludge disposal mainly includes methods such as sanitary landfill, incineration, land utilization and manufacturing of building materials. In view of the above-mentioned characteristics of municipal sludge and my country's national conditions, resource utilization will be the main direction of sludge treatment and disposal.

At present, the use of anaerobic digestion technology to stabilize sludge can not only recover energy in the form of anaerobic fermentation, but also use land in the form of fermentation residues, realizing cascade utilization of resources and avoiding disposal such as incineration The potential threat of secondary pollution of the method. However, the traditional sludge anaerobic fermentation has the following problems:

(1) The optimal carbon-to-nitrogen ratio for anaerobic fermentation is 25-30, while the carbon-to-nitrogen ratio of sludge is low (10-20), the fermentation gas production is unstable, and carbon sources often need to be added, and it is difficult to find a suitable carbon source ;

(2) Primary sludge (with large sand content and many inorganic substances) and activated sludge are not treated differently, resulting in a high content of inorganic substances such as mud and sand in the fermentation material, which not only occupies the reactor volume, but also affects the anaerobic fermentation effect;

(3) Sludge often contains trace amounts of heavy metals, and only anaerobic digestion cannot reduce the content of heavy metals;

(4) The gas production is small and the energy recovery rate is low.

Energy grass generally has the characteristics of well-developed root system, strong adaptability, fast growth, tall plants, high biomass, and low soil requirements. In addition to being used in greening barren hills, water and soil conservation, and improving soil structure, it has gradually become a new crop. Biomass energy raw material.

Invention content:

The purpose of the present invention is to provide a method for joint treatment of municipal sludge using energy grass and anaerobic fermentation technology.

The present invention is achieved through the following technical solutions:

A method for jointly treating municipal sludge by using energy grass and anaerobic fermentation technology, comprising the following steps:

a. After concentrating the activated sludge in the municipal sludge to a water content of 97% to 98%, it is mixed with fresh energy grass at a mass ratio of 1:1 to 2:1 for anaerobic fermentation, and the generated biogas is used for power generation or production Biological natural gas; solid-liquid separation is carried out on the fermentation residue to obtain biogas residue and biogas slurry; the biogas slurry is returned to the sewage plant for further treatment; waste heat generated by biogas power generation or bio-natural gas is used to dry energy grass, and the moisture content is obtained 20% to 30% dry energy grass;

b. Dewater the primary sludge in the municipal sludge to a moisture content of 80% to 85%, mix it with the biogas residue obtained in step a at a mass ratio of 2:1 to 3:1, and add the moisture content obtained in step a Adjust the water content to 50% to 60% for 20% to 30% dry energy grass, and perform aerobic composting for 5 to 8 days; the sludge after composting is applied to the land treatment system planted with energy grass, and the application thickness is controlled At 30-50 cm, the energy grass is mowed every 3-4 months, and the surface sludge of 15-25 cm is collected after mowing as a soil conditioner.

The energy grass is selected from any one of Jujungrass, Hybrid Pennisetum, Switchgrass, Miscanthus, Elephant Grass and the like.

The activated sludge in the municipal sludge refers to the sludge discharged from the secondary sedimentation tank.

The primary sludge in the municipal sludge is selected from sludge settled and discharged from grit chambers or primary sedimentation tanks.

In the above steps, the anaerobic fermentation adopts medium-temperature anaerobic fermentation (35°C-37°C), the solid-liquid separation of the fermentation residue adopts filter press, the biogas power generation uses a gas-fired internal combustion engine, and the stack retting adopts normal temperature stack retting.

Compared with prior art, the advantage of the present invention is:

(1) According to the different properties of primary sludge and activated sludge, different treatment methods are adopted. For activated sludge with high organic content, it is mixed with fresh energy grass for anaerobic fermentation stabilization treatment; for high inorganic content The primary sludge is mixed with the biogas residue produced by fermentation and then stabilized with the plant (energy grass) land system, which not only fully adapts to the characteristics of different sludges, but also effectively prevents a large amount of organic matter such as sediment from entering the waste water. Oxygen fermentation system improves the utilization efficiency of the system;

(2) The energy grass planted in the above-mentioned land system is an excellent carbon source for sludge anaerobic fermentation, which solves the problem of finding a carbon source; the mixed anaerobic fermentation of the planted energy grass and activated sludge makes up for the sludge alone Anaerobic fermentation has the disadvantages of low carbon-to-nitrogen ratio and insufficient carbon source, which can greatly increase biogas production; the biogas produced by anaerobic fermentation is used for power generation or bio-natural gas, providing energy for sewage and sludge treatment, which can greatly reduce sewage and sludge The treatment cost; the sludge stabilized by energy grass can be used as a soil improver for land use, realizing the cascade utilization of resources;

(3) Use energy grass to treat the mixture of primary sludge and biogas residue, not only to achieve the reduction of primary sludge and biogas residue, but also to use the plant transpiration of energy grass to reduce the content of heavy metals in the final product;

In a word, the present invention provides a method for joint treatment of municipal sludge using energy grass and anaerobic fermentation technology. The sludge in different process stages is treated separately, and while adapting to different sludge characteristics, it solves the problem of excessive mud and sand in the sludge causing annoyance. The problems of poor utilization efficiency of the oxygen fermentation system and difficulty in finding the carbon source required for fermentation make up for the shortcomings of traditional sludge treatment and disposal methods that are difficult to utilize as resources, and can realize comprehensive utilization of energy and resources while treating municipal sludge. The preparation of soil conditioner by plant stabilization method not only finds a way out for the final disposal of sludge, but also maximizes the utilization value of sludge.

Description of drawings:

Fig. 1 is a process flow diagram of the present invention.

Detailed ways:

The following is a further description of the present invention, rather than a limitation of the present invention.

In the following examples, the sludge concentration uses a conventional sludge thickener (centrifugal concentration and belt concentration), the anaerobic fermentation uses a medium-temperature anaerobic fermentation (35 ° C ~ 37 ° C), and the solid-liquid separation of the fermentation residue uses Belt filter press, gas-fired internal combustion engine for biogas power generation, conventional belt filter press for sludge dehydration, and normal temperature stack retting for stack retting.

Example 1: A method for joint treatment of municipal sludge using giant fungus grass and anaerobic fermentation technology

As shown in Figure 1, the method of joint treatment of municipal sludge using giant juncao and anaerobic fermentation technology includes the following steps:

a. After concentrating the activated sludge in the municipal sludge to a water content of 97% to 98%, it is mixed with fresh giant fungus at a mass ratio of 1:1 to 2:1 for medium temperature anaerobic fermentation, and the generated biogas is used for Power generation; solid-liquid separation of the fermentation residue to obtain biogas residue and biogas slurry; the biogas slurry is returned to the sewage plant for further treatment; the waste heat generated by the biogas power generation is used to dry giant fungus grass to obtain a moisture content of 20% Dried giant fungus grass;

b. Dewater the primary sludge in the municipal sludge to a moisture content of 80% to 85%, mix it with the biogas residue obtained in step a at a mass ratio of 2:1 to 3:1, and add the moisture content obtained in step a Adjust the moisture content to 50% for 20% dried giant fungus grass, aerobically stack retting for 5 days, and reduce the moisture content of the sludge and biogas residue mixture after composting to below 30%; apply the sludge after composting to seed For the land treatment system with Jujungrass, the application thickness is controlled at 30cm. Jujungrass is mowed every 3 months, and 15cm of surface sludge is collected after mowing as a soil conditioner.

The optimal carbon-nitrogen ratio for anaerobic fermentation is 25-30. In this example, the carbon-nitrogen ratio of the fresh giant fungus is about 40. After mixing with the sludge, the carbon-nitrogen ratio of the fermentation raw material can be adjusted to 30, so that the carbon-nitrogen ratio When anaerobic fermentation is carried out, the sludge gas production can be increased by about 15%, and the volume gas production rate of anaerobic fermentation can be increased from 1.0-1.1m ³ /(m ³ ·d) to 1.4-1.5m ³ /(m ³ ·d) , which greatly improves the production capacity of the equipment. Compared with separate fermentation, every thousand square tanks can produce 400-500m ³ more gas and 1000kwh more electricity per day; at the same time, the sludge stabilized by Jujuncao can be reduced by 50%. ~60%, the hay output per mu of Jujuncao can reach 3 tons; in addition, after using this method, the sand and stone and other inorganic substances in the anaerobic fermentation tank are greatly reduced, and the monthly sand discharge times of the fermentation tank can be reduced by about 20%.

Embodiment 2: Utilize switchgrass and the method for anaerobic fermentation technology joint treatment municipal sludge

a. After concentrating the activated sludge in the municipal sludge to a moisture content of 97% to 98%, it is mixed with fresh switchgrass at a mass ratio of 1:1 to 2:1 for mesophilic anaerobic fermentation, and the generated biogas is used for power generation; Solid-liquid separation of the fermentation residue to obtain biogas residue and biogas slurry; the biogas slurry is returned to the sewage plant for further processing; the waste heat generated by the biogas power generation is used to dry switchgrass to obtain dry switchgrass with a moisture content of 30%;

b. Dewater the primary sludge in the municipal sludge to a moisture content of 80% to 85%, mix it with the biogas residue obtained in step a at a mass ratio of 2:1 to 3:1, and add the moisture content obtained in step a Adjust the moisture content to 60% for 30% dry switchgrass, aerobically stack retting for 8 days, and reduce the moisture content of the sludge and biogas residue mixture after composting to below 30%; the sludge after composting is applied to switchgrass The land treatment system, the application thickness is controlled at 50cm, the switchgrass is mowed every 4 months, and 25cm of surface sludge is collected after mowing as a soil conditioner.

Embodiment 3: Utilize the method of elephant grass and anaerobic fermentation technology to jointly process municipal sludge

a. After concentrating the activated sludge in the municipal sludge to a water content of 97% to 98%, it is mixed with fresh elephant grass in a mass ratio of 1:1 to 2:1 for medium-temperature anaerobic fermentation, and the biogas produced is used to prepare bio-natural gas; Solid-liquid separation is carried out on the fermentation residue to obtain biogas residue and biogas slurry; the biogas slurry is returned to the sewage plant for further processing; the waste heat generated by the preparation of bio-natural gas is used to dry elephant grass to obtain dry elephant grass with a moisture content of 25%;

b. Dewater the primary sludge in the municipal sludge to a water content of 80% to 85%, mix it with the biogas residue obtained in step a at a mass ratio of 3:1, and add the water content obtained in step a to 25% Adjust the moisture content of dry elephant grass to 55%, aerobic stack retting for 7 days, and the moisture content of the sludge and biogas residue mixture after composting and retting will be reduced to below 30%; the sludge after composting and retting is applied to the land where elephant grass is planted For the treatment system, the application thickness is controlled at 40cm. Elephant grass is mowed every 4 months, and 20cm of surface sludge is collected after mowing as a soil conditioner.

Claims (2)

1. A method utilizing energy grass and anaerobic fermentation technology to jointly process municipal sludge is characterized in that, comprising the following steps: a. After concentrating the activated sludge in the municipal sludge to a water content of 97% to 98%, it is mixed with fresh energy grass at a mass ratio of 1:1 to 2:1 for anaerobic fermentation, and the generated biogas is used for power generation or production Biological natural gas; solid-liquid separation is carried out on the fermentation residue to obtain biogas residue and biogas slurry; the biogas slurry is returned to the sewage plant for further treatment; waste heat generated by biogas power generation or bio-natural gas is used to dry energy grass, and the moisture content is obtained 20% to 30% dry energy grass; b. Dewater the primary sludge in the municipal sludge to a moisture content of 80% to 85%, mix it with the biogas residue obtained in step a at a mass ratio of 2:1 to 3:1, and add the moisture content obtained in step a Adjust the water content to 50% to 60% for 20% to 30% dry energy grass, and perform aerobic composting for 5 to 8 days; the sludge after composting is applied to the land treatment system planted with energy grass, and the application thickness is controlled At 30-50 cm, the energy grass is mowed every 3-4 months, and the surface sludge of 15-25 cm is collected after mowing as a soil conditioner. 2. The method of utilizing energy grass and anaerobic fermentation technology to jointly treat municipal sludge according to claim 1, wherein said energy grass is selected from giant fungus grass, hybrid pennisetum, switchgrass, miscanthus, elephant grass any of the.