By far, the most flexible sludge treatment process

Freese Dry Unit´s process is very flexible as a range of different dry solid contents can be achieved. It can also be used in different stages of the sludge treatment process. This flexible and natural process makes Freeze Dry Unit very safe, both at the workplace and the resulting final product. Hygienization can also be added to further secure the saftey of the final product. The flexibility of the process also comes in the form of mobility of the machine.

By far, the most flexible sludge treatment process

The process

The Freeze Dry Unit revolutionizes sludge dewatering and drying as the process can dry to above 95 percent dry solid content without the use of polymers. The dewatering and drying are achieved through a controlled process of freezing and drying. Liquid and solids are separated with the help of temperature and processing.

The Freeze Dry Unit can be used after or replace the dewatering step. If the Freeze Dry Unit is connected after the dewatering step, the use of polymers does not affect the process; but the Freeze Dry Unit does not require polymers to achieve a high degree of dryness.

With a low temperature, the Freeze Dry Unit dries the sludge to the desired dry substance between 30 and up to above 95 percent. The degree of dryness can be changed at any time if the need occurs.

Customers also have the option of a hygienization step.

The Freeze Dry Unit is also fully scalable and suits both small volumes of sludge as well as large volumes. The process is not restricted by volume.

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Material in and Material out

In Sweden, almost a million tonnes of sludge is treated every year. The Freeze Dry Unit works on most types of sludge from sewage waste to sludge from paper mills and nuclear waste. It also works on sludge from biogas production and the food industry.

The final product from the Freeze Dry Unit consists of two products, a dried sludge and reject water. In the process, separation between sludge particles and liquid are complete, this means that the reject water is particle free. Heavy metals and phosphorus are mostly bonded in the sludge and some nitrogen and trace materials end up in the reject water.

The Freeze Dry Unit dries the sludge to a desired dryness of above 95 percent. The high dry solid content opens for more applications, for example, nutrients from sewage sludge can be recycled. If the sludge is dry enough, it can be incinerated effectively and phosphorus can be extracted from the ashes. It can also be used as fuel in incinerators to produce energy.

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Drying temperatures

The Freeze Dry Unit is a low-temperature process, which greatly reduces the energy use. The low temperature ensures safety in the process as it decreases the risk of dust explosions, which is a problem in drying methods today.

The low temperature reduces the energy use of the process and compared to methods in use today, the Freeze Dry Unit only uses about a tenth of that energy. On average, the energy use in the sludge treatment processes in treatment plants is about ten percent of the whole plants’ energy use. Compared to a lot of sludge dryers today, the Freeze Dry Unit only uses about a tenth of that energy, considering the mass of removed water

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So that nutrients such as phosphorus and nitrogen can be utilized in a circular economy, for example, as a fertilizer, the sludge product must be hygienized so that no pathogens are released into nature  that could lead to harm to human health or crop infection.

The Freeze Dry Unit cleans the sludge by a form of pasteurization. The sludge is held in a temperature of above 70 degrees Celsius for a minimum of one hour. This can be achieved with low energy use.

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Sweden has a ban on deposition of organic material, which sludge consists of. A big part of the sludge in Sweden is distributed on arable land. The Swedish government is investigating a ban on sludge distribution because there is little knowledge of what happens with antibiotics remains and microplastics in the sludge.

If a ban of sewage sludge used in agriculture is introduced, a great need for new disposal ways are needed. These new ways of sludge disposal should encourage and enable nutrient recycling to create a circular economy. A sludge product with a high degree of dryness enable incineration for further extraction of phosphorus from the remaining ashes.

The Freeze Dry Unit is from different scenarios, future proof.  Because the dryness of dewatered and dried sludge can be changed at will, the method can be used to produce a variety of different final products that can be used in different areas such as fertilizer in agriculture or fuel in incineration chambers, whatever is necessary in the future. The customer can also choose the most effective dryness if pelleting is needed.

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A lot of today’s drying methods uses high temperatures to dry the sludge. Temperatures between 70 and 150 degrees Celsius are not uncommon in belt dryers. These high temperatures increase the risk of accidents, particularly dust explosions and spontaneous combustion.

The Freeze Dry Unit is a low-temperature process, which lowers the risk of dust explosions and spontaneous combustion. This makes it safe for all staff working around the process.


Mobility wise, the Freeze Dry Unit is unique. The method uses a plug-and-play solution, which means that the sludge flow can be connected before dewatering to be used to further dry the sludge, or completely replace it to dry the sludge.  A desired container for reject water connects after the process.

Customers do not have to get building permits or other complicated decisions to install the Freeze Dry Unit as the product is delivered in a container-concept. The Freeze Dry Unit can also be delivered as a mobile unit, to be stored on a truck to dry sludge on satellite treatment plants, vacation destinations where there is an increased demand seasonally or to treat sludge from privately owned wastewater.

The Freeze Dry Unit is as big as four containers and weighs around twelve metric tonnes. This means that they can be transported on normal trucks without restrictions

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