Impact of Mechanical Dewatering Advances on Wastewater Sludge Treatment

There are many types of mechanical dewatering devices on the market today. Some are more efficient than others. However, a properly designed mechanical dewatering device cannot guarantee high efficacy. The sludge’s chemical composition and structure can also affect its efficiency.


Electro-dewatering is a technique in mechanical dewatering wastewater that is used to actively remove ionic compounds. This method has several advantages over other dewatering processes. It can decrease energy consumption and dewater the wastewater faster. Electrodewatering can be adjusted to match the desired DS content, dewatering time, and power requirements.

Electro-dewatering can reduce the water content of sludge to about 60% wt% in five to twenty minutes. However, there are limits to its dewatering ability. The water content should be lower than 20 wt% for profound dehydration. In contrast, low-temperature drying methods can achieve profound dehydration in a fraction of the time.

There are three stages to the electro-dewatering process. The first stage is known as limit dewatering. There is almost no filtrate at this stage. As the electric field strength increases, the water content of the sludge decreases. This reduction of water content in the sludge allows for higher dewatering efficiency.

The electro-dewatering process reduces the volume of wastewater and improves its permeability. An electric field is applied to the wastewater to enhance the dewatering rate. This method is more effective when the feed is thickened, and the pH is neutral.

The electro-dewatering process enhanced dewatering performance compared to other dewatering methods. Besides reducing the volume of wastewater, it also increased the DS content. In pressure-driven electro-dewatering, the DS content in the sludge was up to 40%. This is a considerable improvement over other dewatering techniques. Moreover, electro-dewatering is energy-efficient, using less energy than thermal drying.

Sludge Conditioning

Many advances have been made in wastewater mechanical dewatering. These include a combination of thermal, mechanical, and electric effects. Microwaves and ultrasonic fields are also being developed to aid the dewatering process. Advances in this technology have led to the use of dewatering processes that can combine the kinetics of dewatering and shear forces.

Mechanical dewatering systems are often designed as screw presses. However, they can also be formed from conventional dewatering devices such as chamber filter presses, belt sieve presses, centrifuges, or decanters. The primary advantage of mechanical systems is that they take up less space and offer better operational control. These machines also require sludge conditioning, which involves adding chemicals to the sludge to thicken the solids and improve drainability.

The model is used to calculate optimal conditions for sludge dewatering. The resulting sludge cake is then modeled to achieve a moisture content of 63 percent. This method can reduce sludge volume by as much as 50 percent.

A mechanical dewatering system may include a flocculation tank that separates the liquid from the sludge. This tank may be connected to a drainage device or pipeline. The system may also include a recirculation system in which a gas (L) is introduced into the sludge. This helps to increase the efficiency of subsequent sludge dewatering processes.

Toxic Materials in Sludge

There are several ways to treat the toxic materials in wastewater sludge. One method is to use a chemical called quick lime. It is available in dry granular or pebble form and as a hydrated lime powder. Both forms increase the porosity of the sludge and reduce odors. Hydrated lime has the added benefit of reducing the amount of hydrogen sulfide ions, which are nonvolatile in water.

Sewage sludge is a complex mixture of organic materials and microorganisms. It is also made up of a small percentage of solids. These solids have hard-to-degrade biopolymers, polysaccharides, and peptidoglycan. Toxic materials are often found in the sludge, so it is essential to treat it before disposal. The appropriate treatment techniques can remove harmful components and recover valuable materials.

Freezing and thawing of sludge is another way to treat wastewater sludge. Freezing and thawing naturally occur in cold climates. The process enhances the dewaterability of the sludge and reduces its specific resistance, making mechanical dewatering more efficient. In addition, freezing and thawing decrease the reagents required to perform coagulation.

Thermal treatment processes also contribute to sludge decomposition. Depending on the initial chemical composition of sludge, up to 75 percent of its volatile solids dissolve in water. The resultant decomposed sludge contains approximately 2000 to 6000 mg/L solids. This decomposition increases the loading of the treatment plant by 10 to 25%.