What are the factors that affect the poor dewatering effect of sludge?

A variety of chemicals can be used for sludge deep dewatering, and the following are the most common chemicals used for ordinary sludge dewatering:

Cationic polyacrylamide: This is a polymer flocculant, which can flocculate small particles in sludge into larger particles through adsorption and bridging, and improve the sedimentation performance and dewatering performance of sludge.

Polyaluminum chloride: This is an inorganic polymer coagulant, which can coagulate with impurities in the sludge to form an insoluble precipitate, so that the water in the sludge is separated.

Lime: Lime can neutralize with the acids in the sludge, adjust the pH value of the sludge, and promote the cohesion and settlement of the sludge.

Diatomaceous earth: Diatomaceous earth has the characteristics of porosity and high specific surface area, which can be used as a filter aid to improve the filtration performance and dewatering performance of sludge.

It should be noted that different kinds of agents are suitable for different sludge properties and treatment requirements, so it is necessary to choose the appropriate agent according to the specific situation in practical applications. For sludge with high organic matter, under the condition that lime is not allowed to be added in the process, it is necessary to customize the organic deep sludge dewatering agent, and adjust the corresponding process parameters to ensure the sludge treatment effect.

The main factors affecting the operation of the activated sludge method are:

1. BOD load and SS load: it is the design and operation of the aeration tank;

2. Hydraulic retention time (SRT) or sludge age: it is also an aeration tank;

3. Activity of activated sludge: the oxygen absorption and transfer rate of activated sludge has nothing to do with its moving height in the liquid. This contributes to the energy savings of the aeration system.

When I do not consider the difference of the dehydration machine.

The dewatering performance of sludge is mainly determined by the following aspects:

1. Sludge particle size and density.

According to the Stolke formula, the larger the particles, the denser they are, the faster they settle and the easier it is to dehydrate.

2. The viscosity of the sludge.

Sludge bacteria form colloidal bloms, which encapsulate the water and are difficult to separate by mechanical dewatering.

3. Dosage of pharmacy.

On the one hand, the flocculant can make the sludge particles bridge flocculation and easy to dehydrate, on the other hand, the viscosity of the sludge becomes larger, which makes the mud cake elastic and Q, and hinders the further dewatering of the sludge cake.

Sludge is usually pre-treated to improve dewatering performance before dewatering. The most common pretreatment method is the addition of inorganic salts or polymer coagulants. In addition, there are enameling methods and heat treatment methods.

Mechanical dehydration methods include filtration and centrifugation. Filtration is to filter the wet sludge with a filter layer (porous materials such as filter cloth and wire mesh) so that the water (filtrate) can penetrate the filter layer, and the dewatered sludge (filter cake) will be trapped on the filter layer. The centrifugal method is to achieve slurry-water separation by taking advantage of the different centrifugal tendencies generated by the difference between the solid and liquid specific gravity in the sludge.

The equipment used in the filtration method includes vacuum filters, plate and frame filter presses and belt filters. The vacuum filter continuously feeds and discharges mud, and runs smoothly, but there are many ancillary facilities. The plate and frame filter press is a common equipment in the chemical industry, with large filtration driving force, low moisture content of mud cake, intermittent mud inlet and mud outlet, and low productivity.

The manually operated plate and frame filter press is very labor-intensive, and now most of them are automatically operated by machinery. Belt filters are new types of filters with a variety of designs and different dehydration principles (gravity filtration, pressure filtration, capillary water absorption, granulation), but they all have rotary belts, which transport mud while dewatering, or only mud transport. They are similar in complexity and energy consumption.

The centrifugal method is commonly used in the horizontal high-speed sedimentation centrifugal dehydrator, which is composed of an inner and outer rotating drum, one end of the rotating drum is cylindrical, and the other end is conical. The speed is generally about 3000 rpm or higher, and there is a certain speed difference between the inner and outer bowls. The centrifugal dewatering machine has continuous production and automatic control, good sanitary conditions, and a small footprint, but the requirements for sludge pretreatment are higher.

The mechanical dewatering method is mainly used for primary sedimentation tank sludge and digested sludge. The moisture content of dewatered sludge is related to the properties of the sludge and the dewatering method. Under normal circumstances, the moisture content of vacuum filtered mud cake is 60 to 80 percent, plate and frame press filtration is 45 to 80 percent, and centrifugal dehydration is 80 to 85 percent.

On the basis of engineering commissioning, the sludge dewatering performance has a lot to do with the deterioration of PAM. Although foreign ones are expensive, the effect is immediate!

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.

Answer]: The moisture content of the sludge is very high, and it needs to be thickened before sludge treatment to reduce the moisture content of its source to reduce the volume of treatment equipment and treatment cost. Sludge dewatering is a sludge treatment method that removes water from the fluidized primary, concentrated or digested sludge and converts it into semi-solid or solid sludge blocks.

Sludge dewatering is done to reduce the volume of sludge for easy transportation, storage and disposal. The dewatering performance of sludge is related to the nature of sludge, conditioning methods and conditions, etc., and is also related to the type of dewatering machinery.

Sludge should be harmless, reduced and recycled, and high-level dewatering is the primary condition. What is the role of dewatering sludge to a moisture content of 60% or even below 50% here?

1. The volume of sludge is greatly reduced after high-level dewatering. For example, the water content of the sludge produced by the sewage treatment plant is more than 99%, and the sludge with a moisture content of 95% can be formed after adding a concentration reagent, and the sludge volume is reduced by 4 times. The sludge with a moisture content of 95% is treated by an ordinary sludge filter press to form a mud cake with a moisture content of 80%, and the volume is reduced by 3 times; After being treated with Tianyuan Environmental Protection Super Sludge Dryer, a mud cake with a moisture content of 50% is formed, and the volume is reduced by 9 times.

For industrial sludge, the difference in moisture content before and after treatment is higher, and the sludge volume reduction effect is more obvious.

2. The sludge is mostly liquid or viscous before high-level dewatering, which is very difficult to control whether it is transported or temporarily stored, and the pollution is easy to diffuse, and the treatment cost is high. The sludge treated by Tianyuan environmental protection sludge dryer has become a dry and hard mud cake, and the volume has been greatly reduced, which has reduced the sludge transportation volume and transportation cost, and the mud cake transportation is no longer difficult: in the past, a professional transport vehicle with very good sealing was needed for sludge transportation, but now ordinary vehicles can be used for sludge cake transportation.

3. Sludge disposal should be recycled, mainly referring to the utilization of sludge cake resources. If the sludge is to be sent to the fluidized bed for combustion after treatment, the moisture content of the mud cake is low, and the high-level dewatering treatment of the sludge is particularly important. For example, the moisture content of the sludge treated by the ordinary sludge filter press is more than 60%, which does not meet the standard of direct entry into the fluidized bed, while the water content of the municipal sludge after treatment by the Tianyuan environmental protection sludge dryer is as low as 40%, and the moisture content of the industrial sludge treatment mud cake is as low as 14%, which can be directly sent to the fluidized bed, or combined with other raw materials to produce cement, bricks, etc., so as to reduce the sludge resource disposal process and reduce the sludge disposal cost.

Nowadays, sludge treatment equipment has become an indispensable equipment for sewage treatment plants, paper mills, printing and dyeing factories and other industrial enterprises and municipal units.

Yes. Generally speaking, the moisture content of the primary sludge is about 95% to 97%, and the moisture content of the remaining activated sludge is also as high as 90%.

Answer: C

The sludge specific resistance can be used to measure the difficulty of sludge deshaping and backwater, and the smaller the specific resistance value, the easier it is to dewater. The degree of difficulty of dewatering is (from difficult to easy): activated sludge, digested sludge, primary sedimentation sludge, and putrid code sensitive sludge.