What are the characteristics of sludge that make sludge treatment and its subsequent disposal and re

According to the definition of sludge, sludge is a solid precipitate produced by the water and sewage treatment process, and the so-called solid precipitate material does not include screening, scum and sediment, but refers to the semi-solid and solid material produced during the treatment process. It is a thick substance between liquid and solid and can be transported by pump, but it is difficult to separate solids from liquid by sedimentation.

The Water Pollution Prevention and Control Law stipulates that sludge refers to the (semi-solid) or (solid) substances produced in the sewage treatment process, excluding screening, scum and sediment. Sludge is a product of sewage treatment and is an extremely complex heterogeneous body composed of organic residues, bacterial bacteria, inorganic particles, colloids, etc. The main characteristics of sludge are high moisture content (up to 99% or more), high organic matter content, easy to decay and smell, and fine particles, small specific gravity, and gelatinous liquid.

Sludge refers to the solid or semi-solid waste generated in the treatment process of domestic sewage, industrial wastewater, etc. Sludge needs to be treated and disposed of, and here are a few common methods for final sludge disposal:

1.Composting: Biological sludge with high organic matter content is mixed with other organic matter and stacked, fermented and rotted by microorganisms and converted into organic fertilizer. The composting method of treating sludge not only reduces the amount of waste, but it can also be used for agricultural production.

2.Incineration: High-temperature oxidation technology is used to dry the sludge and incinerate it at high temperatures. In this way, harmful ingredients can be completely broken down, turning them into ashes or gases.

3.Soil improvement: Mixing specially treated sludge into the soil can not only reduce the content of heavy metals and other substances in the soil, but also play a certain role in improving the soil.

4.Compressed landfill: Thickened sludge is stuffed into a sealed container, and the air in it is pumped and discharged by a compressor to a completely sealed state. This can avoid secondary pollution caused by the waste being exposed to the atmosphere.

The above are several common sludge final disposal methods, and in actual situations, it is necessary to choose the appropriate disposal method according to different environmental requirements, economic conditions and technical constraints.

Reasons for the poor sedimentation of activated sludge system (sludge swelling): sludge swelling is divided into two types: filamentous swelling and non-filamentous swelling, and filamentous swelling is the most common.

1.Filamentous bacteria swell.

At present, people's understanding of filamentous bacteria swelling is not completely unified, and it is generally believed that the competitive advantages of filamentous bacteria and mycelial bacteria are manifested in the following aspects.

Water quality: Water quality is the most important cause of the swelling of sludge filamentous bacteria. When the content of soluble carbohydrates (low molecular weight sugars and organic acids, etc.) in sewage is high, it is conducive to the growth of filamentous bacteria and causes sludge to swell. When the sulfide content in the sewage is high, it is conducive to the growth of sulfide bacteria and sludge expansion. When the pH value of sewage is low (pH 6), sludge swelling is prone to occur; When the wastewater lacks nitrogen and phosphorus (C, N, and P ratios are out of balance), filamentous bacteria have a large specific surface area, compete with colloidal bacteria for nitrogen and phosphorus and grow dominantly, which also leads to sludge expansion.

Temperature: The optimal growth temperature of colloidal bacteria is 28-30, the growth temperature of Chlamydia planktonic is 15-30, and the optimal temperature is 25-30. If the water temperature is 25-28, it is easy to cause the dominant growth of C. planktonii, resulting in sludge expansion.

If the water temperature is lower than 15, sludge expansion generally does not occur.

Dissolved oxygen: The effects of dissolved oxygen are complex, and both too low and too high dissolved oxygen can cause sludge to swell. If the problem of sludge swelling cannot be solved after other factors are eliminated, it is treated by adjusting the aeration system to improve the dissolved oxygen content.

Organic load: When the organic load is low, nutrients are deficient, and filamentous bacteria grow dominantly in nutrient competition, resulting in sludge expansion; When the organic load is high, the dissolved oxygen concentration decreases rapidly, and the filamentous bacteria grow dominantly, causing the filamentous bacteria to swell. When the sludge load of municipal sewage is very low or high at room temperature, filamentous bacteria swell will occur.

Process method: It has been proved in practice that the complete mixed type is more prone to sludge expansion than the push-flow type; The intermittent activated sludge method is the least likely to cause sludge expansion; There is a grit tank, but there is no process with a primary sedimentation tank, which is not easy to cause sludge expansion; Impeller aeration is more prone to sludge expansion than blast aeration; Jet aeration can effectively avoid sludge swelling caused by floating jersey bacteria.

2.Non-filamentous swelling.

When the sedimentation of the activated sludge system is poor (sludge swelling), a large number of filamentous bacteria cannot be found in the microscopic examination, which is called nonfilamentous swelling portNonfilamentous bacterial swelling mainly occurs when the water temperature is low and the sludge load is high.

For details, please refer to:

Causes of poor sedimentation (sludge swelling) of activated sludge systems and treatment methods.

Temperature, pH, dissolved oxygen, nutrients, organic load, toxic substances, and much more.

Summary. There is a certain amount of organic components in the sludge, and the dehydrated and dried sludge can be incinerated. In Japan, this method accounts for more than 60 percent of the total sludge treatment volume, and in the European Union, more than 10 percent of the total sludge treatment.

In order to prevent the production of dioxins and other toxic gases during the incineration process, the incineration temperature should be higher than 850. The incineration ash produced by sludge incineration has water absorption and solidification, so it can be used for soil improvement, road construction, etc., and can also be used as a raw material for bricks and ceramics, and can also be used as a fine filler for concrete mixture. Turning sludge into a granular fuel that burns well, has a calorific value comparable to lignite, and releases harmful gases much less than the incineration process, and its residues can be used in the construction industry.

Sludge incineration can obtain surplus energy from exhaust gases, which can be used to generate electricity. Additives such as ignition agent, catalyst, loosening agent and sulfur fixing agent are added to the dewatered sludge to make synthetic fuel, which can be used in industrial and domestic pots, with stable combustion, good thermal and environmental protection tests, and is an ideal way for the effective utilization of sludge.

Hold on. There is a certain amount of organic components in the sludge, and the dehydrated and dried sludge can be incinerated. In Japan, this method accounts for more than 60 percent of the total sludge treatment volume, and in the European Union, more than 10 percent of the total sludge treatment.

In order to prevent the production of dioxins and other toxic gases during the incineration process, the incineration temperature should be higher than 850. The incineration ash produced by sludge incineration has water absorption and solidification, so it can be used for soil improvement, road construction, etc., and can also be used as a raw material for bricks and ceramics, and can also be used as a fine filler for concrete mixture. Turning sludge into a granular fuel that burns well, has a calorific value comparable to lignite, and releases harmful gases much less than the incineration process, and its residues can be used in the construction industry.

Sludge incineration can obtain surplus energy from exhaust gases, which can be used to generate electricity. Additives such as ignition agent, catalyst, loosening agent and sulfur fixing agent are added to the dewatered sludge to make synthetic fuel, which can be used in industrial and domestic pots, with stable combustion, good thermal and environmental protection tests, and is an ideal way for the effective utilization of sludge.

1.Temperature requirements.

Temperature is one of the environmental factors of shadow sludge acclimation, all kinds of microorganisms grow in a specific range of temperature, sludge acclimation temperature range is 10 40, the optimal temperature is 20 30. Therefore, it is recommended that the first operation of the system should not be carried out in winter.

The pH value is also one of the influencing factors. During sludge acclimation and subsequent normal operation, the influent pH of the system should be controlled between 6 and 9.

3.Nutrient requirements.

Good nutritional conditions are the prerequisite for the metabolism and growth of microflora. In the process of sludge acclimation, the nutrient parameters should be controlled at about 100:5:1 Bod:N:P, so as to provide good growth conditions for sludge acclimation.

4.Dissolved oxygen (DO) requirements.

DO is the main control index in the process of sludge acclimation, and the scope of DO should be controlled in the process of sludge acclimation. (The dissolved oxygen concentration is measured at a meter downstream of the water of the rotary disc aerator). DO can be detected by dissolved oxygen analyzer or manually detected to understand the change law of DO in the pool.

5.Mixed Suspended Solids Concentration (MLSS) requirements.

Organisms are the active part of sludge and the main body of organic matter metabolism, which plays a major role in the biological treatment process, and the value of the mixed liquid sludge concentration MLSS can relatively represent the amount of the biological part. The concentration of activated sludge should be controlled at 2 4g l.

6.Biophase microscopy requirements for sludge.

Activated sludge is in different stages of growth, and various microorganisms also show different proportions. Bacteria are responsible for the basic and basic metabolic role of breaking down organic matter, while protozoa, including metazoa, devour free bacteria. Normally functioning activated sludge contains bell worms, rotifers, ciliates, colloids, etc.

When the colloidal clump is large. Bell insects are active and numerous, and when rotifers and nematodes appear, the sludge is mature and has good properties.

7.Sludge 30-minute sedimentation ratio (SV) requirements.

When activated sludge is operating normally, the sludge sedimentation ratio should be controlled between 15% and 30% in 30 minutes.

1. Sanitary landfill: the advantages of sanitary landfill are the investment province, the implementation is fast, the method is simple, the treatment scale is large, the disadvantage is that the soil mechanical properties of the sludge are higher, the need for a large area of site and a large number of transportation degrees, the foundation needs to be treated with anti-seepage treatment to prevent groundwater pollution, etc. Landfill is still one of the important methods of sludge disposal in China, but in the long run, conventional landfill is an ultimate disposal method that cannot be recycled, requiring a large area of land, and its application proportion will gradually decrease.

2. Sludge composting: an important aspect of sludge composting in agriculture, it is the process of using microorganisms in sludge for fermentation. As early as the beginning of the 20th century, this technology was developed and researched in Europe, and was only used for the treatment of municipal waste at first, and later this method was introduced to sludge treatment and application of farmland.

3. Land use (sludge agriculture): China is a big agricultural country, whether it is from economic factors or from the factors of fertilizer efficiency, sludge land use is in line with China's national conditions disposal method. Sludge agricultural use is the most feasible and realistic disposal plan from the detailed situation in China.

Sludge can be used in agriculture to dispose of sludge in large quantities, and in principle, only sludge can be used for farmland when it reaches the relevant national standards; Sludge intervenes in the natural material recycling process of farmland, and the nitrogen, phosphorus, potassium, organic matter and trace elements in sludge are good agricultural fertilizers, which have a role in increasing crop yield. The organic matter and humus in the sludge can improve the soil structure and are good soil amendments. The agricultural utilization of sludge reduces the production rate, which is suitable for the current economic development of China.

4. Sludge incineration: After sludge incineration, the amount is greatly reduced. In addition, the heavy metals contained in the sludge are oxidized into non-chaotic oxides at high temperatures, making them an excellent material for the manufacture of ceramsite, ceramic tiles, and other products.

In recent years, the incineration method has been greatly developed, compared with other methods, the incineration method has the following convex advantages: it greatly reduces the volume and weight of the sludge, so the final substance that needs to be treated is very small, and sometimes the incineration ash can be made into useful products; The sludge treatment speed is fast and does not need to be stored for a long time; Sludge can be incinerated on site without long intervals; Energy can be used for electricity and heat.