Sludge Treatment

Accumulation of residues is called sludge in sewage treatment plant. Sewage sludge is a solid or slurry residue produced in the process of wastewater treatment. This residue is divided into primary sludge and secondary sludge. Primary sludge is produced by chemical precipitation, precipitation, and other primary processes, while secondary sludge is active waste biomass from biological treatment.

Sewage sludge treatment and disposal is an important factor in all the sewage treatment plant design and operation. Two basic objectives of treating sludge prior to final disposal are to reduce its volume and stabilize organic materials. Stable sludge does not smell bad and can be treated without causing nuisance or health hazards, while the smaller sludge volume reduces the cost of pumping and storage. Therefore, proper disposal of such sludge to minimize its impact on the environment is extremely important.

Sludge treatment process

The treatment of sewage sludge includes: thickening, digestion, dewatering and disposal processes.

Step 1 – Sludge thickening

Thickening is usually the first step in sludge treatment. In this step, sewage sludge is thickened in a gravity thickener to reduce its total volume to less than half, thus making the sludge easy to handle. Dissolved air flotation is another alternative method that can be used to effectively thicken sludge by using air bubbles to float solids to the top.

Step 2 – Sludge digestion

Sludge digestion is a biological process in which organic solids are broken down into stable material, this process also helps to reduce the total mass of the solids while destroying pathogens for dewatering or drying.

Large wastewater treatment plants typically use a second-stage digestion system in which organic matter is metabolized anaerobically by bacteria (in the absence of oxygen). In the first stage, the dried solid sludge is heated and mixed in a closed tank to allow anaerobic digestion by acid producing bacteria. These bacteria hydrolyze the large proteins and lipids present in the sludge and break them down into smaller water-soluble molecules, which are then fermented into various fatty acids. The sludge then flows into a second tank where it is converted by other bacteria into carbon dioxide (CO2) and methane, which is then collected and reused to power the digestion tank and generate electricity (depending on the amount recovered).

Sludge digestion can also be performed under aerobic conditions – i.e. in the presence of oxygen. The sludge is vigorously aerated in open tanks for about 21 days. No methane gas is formed during this process. Although aerobic systems are easier to operate than anaerobic systems, they are typically more expensive to operate due to the energy required for aeration. Aerobic digestion is often combined with small extended aeration or contact stabilization systems.

Aerobic and conventional anaerobic digestion converts about half of the organic sludge solids into liquid and gas. Thermal hydrolysis and anaerobic digestion can convert about 60 to 70 percent of the solids into liquid and gas. Not only is the amount of solids produced smaller compared to conventional digestion, but the increased biogas production can make some wastewater treatment plants self-sufficient in energy.

Step 3 – Sludge dewatering

Digested sludge is usually dewatered prior to disposal. The dewatered sludge still contains a significant amount of water – often up to 75% – but even with this moisture content, the sludge no longer behaves as a liquid and can be disposed of as a solid material. Therefore, it is important to dewater and dry the sludge beforehand. While using a sludge drying bed is the most common method of performing this process, it is very time consuming and can take several weeks to complete the process. To expedite these processes, waste management programs also employ solid-liquid separation units to perform this process.

Alternatives to sludge drying beds include rotary drum vacuum filters, filter presses, centrifuges, and screw presses. These mechanical systems require less space than sludge drying beds, and they offer a greater degree of operational control and the ability to process solid waste more easily in less time and at a lower cost. However, they must usually be preceded by a step called sludge conditioning, in which chemicals are added to the liquid sludge to coagulate solids and improve drainability.

Step 4 – Disposal

Once the sludge has been effectively dewatered, it can be buried underground in a sanitary landfill or used as a fertilizer, depending on its chemical composition. If the sludge is too toxic to reuse or bury, the sludge can simply be incinerated and converted to ash.

While sewage sludge is usually treated using a standard action plan, it is very important to consider the source of the effluent, the treatment process used to reduce the effluent to sludge, and the possible by-products that can be recovered from the effluent. before selecting a sludge treatment plan for further use. This will not only help you optimize your overall output, but also help you reduce costs by recovering useful materials for secondary use prior to final disposal.


Common sludge removal methods are sludge anaerobic digestion or sludge aerobic digestion processes.

Anaerobic sludge digestion system is widely used due to relatively low investment and operating costs, stable process conditions (sludge temperature), energy recovery (comprehensive use of sludge gas), and small footprint; however, the process is more dangerous.

Aerobic sludge digestion system is less used due to relatively high investment and operation cost, larger land area, fluctuation of process conditions (sludge temperature) with temperature change, poor operation effect in winter, and high energy consumption; however, aerobic digestion process has the advantages of higher organic removal rate, good quality of treated sludge, better environmental condition of treatment site, and no danger in the process. After aerobic digestion of sludge, the removal rate of nitrogen can be up to 60% and phosphorus can be up to 90%, and the supernatant flow back to the wastewater treatment system will not increase the load of wastewater denitrification and phosphorus removal.

Generally, aerobic digestion process can be used in small sewage treatment plants with less sludge volume or when it is difficult to perform anaerobic digestion of sludge due to the influence of industrial wastewater.

Sludge is a solid sediment material produced by water and wastewater treatment processes.

Sludge is a product of wastewater treatment and is an extremely complex non-homogeneous body consisting of organic debris, bacterial organisms, inorganic particles, colloids, etc.

The precipitated material produced in the wastewater treatment process, including solids, suspended material, colloidal material contained in the wastewater and the sludge separated from the water, is collectively referred to as sludge.

Water that has lost its original function of use is referred to as sewage. Sewage is the result of new substances added to the water or changes in external conditions that cause the water to deteriorate and not continue to maintain its original function.

The composition and nature of sludge depends mainly on the composition and nature of the treatment not and the treatment process. According to different classification standards, there are various ways to classify sludge, which are briefly described as follows.

  1. According to the source of sludge, it can be roughly divided into three categories: feed water sludge, domestic sewage sludge and industrial wastewater sludge.
  2. According to the process of sludge separation from water, it can be divided into sedimentation sludge (including physical sedimentation sludge, coagulation sludge and chemical sludge) and biological treatment sludge (referring to the sludge produced by sewage in the secondary treatment process). Most of the modern sewage treatment plant sludge is a mixture of precipitation sludge and biological treatment sludge.
  3. According to the composition and nature of sludge, it can be divided into organic sludge and inorganic sludge. Organic sludge with organic matter as the main component can be referred to as sludge. Organic sludge is hydrophilic sludge. Domestic sewage sludge or mixed sewage sludge are organic sludge. Inorganic sludge with inorganic matter as the main component is often called sludge, and sediment in water treatment sedimentation ponds and certain industrial wastewater physical and chemical treatment processes are sludge, and inorganic sludge is generally hydrophobic sludge.
  4. Named according to the classification of sludge in different treatment stages, there are raw sludge, thickened sludge, digested sludge, dewatered and dried sludge, dried sludge and sludge incineration ash. This method is the more commonly used sludge classification method.
  1. Gravitational sedimentation method. That is, using the gravity of the suspended solids in the wastewater itself, natural settlement, so that the supernatant is purified. Gravity sedimentation facilities include level flow sedimentation tanks, vertical flow sedimentation tanks, and spoke flow sedimentation tanks. The use of inclined plate or inclined pipe sedimentation, will greatly reduce the footprint
  2. Mechanical filtration method. There are many types of filtration equipment and media used in the month of January, such as: plate and frame filter presses, chamber filter presses, membrane filter presses, belt filter presses, sand core filters, sand filters and microporous filters, etc. Various types of grids and screens are also part of the mechanical filtration method. The media used over the pool in addition to the filter cloth, screen, but also diatomaceous earth, quartz sand, fly ash, furnace ash slag, etc..
  3. Centrifugal separation method. Centrifugal separation method can separate the solids suspended in the wastewater, and also can separate the 2 kinds of liquid with different densities. Centrifugal machine has vertical, horizontal, continuous inlet and outlet solid-liquid separator.

Sewer sludge is too much, the use of baking soda and vinegar can not be cleaned and dredged. Because most of the components of the sludge is composed of fine sand, and the main component of fine sand is silica, and baking soda and vinegar are unable to chemical reaction with silica, so the use of baking soda and vinegar is not to unclog the sewer sludge.

Clean up sewer sludge method.

  • The use of high-pressure water truck to high-pressure water gun into the sewer, the use of high pressure water gun dilution sewer sludge, and with the machinery constantly stirring sludge until the sludge dilution to the water, to remove the sludge dredging sewer purpose.
  • Find professional pipeline dredging personnel to solve the silt in the sewer with a pipe dredging machine, pipe dredging machine has the function of breaking stones and sucking silt.
  • A hole in the sewer mud at the site, after the water chiseled by the silt blockage, and then break the cement block, the use of suction truck, the suction reach into the sewer, the sewer mud pumping clean.

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