What is Sludge Dewatering?

To clean dirty water means to remove impurities other than water (H₂O) from the sewage. Biotreatment (biological treatment) processes are widely used to remove contaminants dissolved in water. Biotreatment is a process of separating water contaminants using enzyme reactions of microorganisms. Simply put, contaminants in the water become food for these microorganisms, which then eat the food to separate the water and impurities.

The portion other than water (H₂O) separated by this biotreatment is “sludge,” which in this case consists of microorganisms and their carcasses and metabolites. Microorganisms are essential for cleaning water, but as a byproduct, the cleaner the water, the more sludge is generated. Sludge should be disposed of as industrial waste, and thus the law requires that it be disposed of properly.

Normally, more than 99% of the excess sludge generated in biotreatment is water. Incineration or landfill disposal of the sludge without any pre-treatment would cost a great deal of money. The major role of sludge thickeners and sludge dewatering presses is to reduce disposal costs and environmental load by thickening and dewatering this sludge as much as possible and reducing its volume.

Sludge dewatering presses not only reduce the volume of sludge by solid-liquid separation, but also produce the sludge in a cake-like form, which facilitates the easy transport, handling, and disposal of the sludge after dewatering.

The role of sludge thickeners is basically the same, but the sludge after bulk reduction is liquid, which is useful when the liquid is easier to handle after treatment. Water separated by sludge thickening and dewatering is returned to the wastewater treatment process, treated, and then discharged into rivers and other bodies of water so that it can be returned to its natural cycle.

On the other hand, sludge is often ultimately disposed of in landfills or by incineration, so it is extremely important from the standpoint of environmental protection and the
realization of a sustainable society to properly reduce the volume of sludge by
sludge thickeners and sludge dewatering presses. Generally, the
volume reduction rate of excess sludge is approximately 88% or more
by sludge thickeners and 95% or more by sludge dewatering presses.

Sludge is industrial waste generated from all wastewater treatment sites. For this reason, sludge dewatering machines are widely used not only in public sewage treatment plants but also in factories and farms that discharge wastewater above a certain volume as required by the laws of each country.

There are different types of technologies for sludge dewatering, which can be divided into several basic types:

• Filter Press (Plate and Frame Press) – works on the principle of filtration, where sludge is pressed between filter plates. It works sequentially, not continuously, and in its operation can be compared to the bellows of an accordion.
• Belt Presses – operate on the principle of pressing sludge between a permeable “endless” belt and rollers.
• Centrifuges – operate on the principle of separating solid and liquid sludge components by centrifugal forces at high speed.
• Screw Presses – operate on the mechanical principle whereby a screw presses the sludge through a cylinder whose perforated surface forms a filter element to separate the solids from the water.

Our VOLUTE™ dewatering presses are classified as screw-presses. Their design is exceptional in that the filter element of the dewatering cylinder is not a sieve (perforated surface), but a combination of fixed and moving rings, with the gaps between them forming the filter element. The moving rings are in constant motion due to contact with the screw flights, which provides the VOLUTE™ dewatering presses with a self-cleaning function. The surface of the dewatering cylinder does not have to be cleaned with pressurized water or mechanically, unlike other screw presses. VOLUTE™ dewatering presses are suitable for continuous operation and can directly dewater sludge with very low concentrations of suspended solids.

In particular, a mechanism that mechanically prevents clogging in the filtration zone has greatly improved energy efficiency and maintainability compared to conventional systems. In addition, by realizing an ultra-compact design, which was difficult to achieve with conventional systems, municipalities of a size that could not find an economic rationale for the introduction of sludge dewatering presses are now able to introduce our dewatering presses.

For example, in Europe, it is standard practice for municipalities with a population of 5,000 or less to arrange for a mobile dewatering truck to dewater once a week or so. Or, conventional products with excessive throughput are unavoidably introduced and perform dewatering once a week. In these cases, however, the amount of nitrogen that is contained in the dewatered filtrate being returned to the wastewater treatment could become so large as it is treated all at once.

As a result, the balance with the microorganisms would worsen, and the maintenance efficiency would deteriorate. Since these municipalities that manage sewage treatment plants with such problems are small in scale, this has not been recognized as a social problem. However, with the introduction of the VOLUTE™ ultra-small dewatering machine, users can now dewater the sludge on the spot as it is generated, instead of storing it unnecessarily, enabling stable wastewater treatment maintenance and cost reduction.

The ultra-compact models are rare in the world, and this is one of the advantages of the VOLUTE™ Dewatering Press.