Is this your challenge?

There is a variety of methods to process nuclear waste. When it comes to sludges, flocks or liquids, these can start with treatment such as filtration, ion exchange/adsorption, evaporation or even reverse osmosis and usually end with encapsulation or solidification in cement, bitumen or glass, to immobilise the radioactive material.

To be disposed of, sludge-like materials do have to be treated: dry or granular material have the immense advantages to be easier to incorporate into a safe, stable and manageable form so it can be transported, stored and disposed.

Unsurprisingly, getting materials ready for disposal is also a theme largely explored outside of the nuclear industry. Indeed, restoration or decontamination of contaminated sediments, sludges (even sometimes effluents) do require effective and energy efficient dewatering solutions. 

Global dewatering equipment market is booming: dewatering equipment are indeed witnessing high demand, due to the rising demand for minimisation of water footprint and the requirement for faster, more energy-efficient methods. That said, new techniques arriving on the market only generally offer improved traditional methods instead of ground-breaking new stance… until now. An innovative solution we think has the potential to be transferred to a nuclear scenario.

inTechBrew’s insight

Siccum operates from Luleå in Sweden and has created a new way to dewater material. A dewatering solution than has many advantages compare to traditional methods and offering an energy efficient and sustainable solution with a modular design for accessible foot-print and process integration. Today, Siccum is active in water treatment, mining, restoration, decontamination industries and are part of various research projects.

The Siccum freeze dewatering modules do make it more efficient and environmentally friendly to dewater material. To put it simply, when water goes through a state change from liquid to ice it will behave in certain ways. With the right parameters, water pushes the solids away when it goes through its state change to ice. This behaviour is what the Siccum’s technology harnesses to control the controlled separation of water from the material and gain the ability to deliver targeted dry matter content of materials. Importantly, Siccum‘s technology also traps contaminant in the solid phase, leaving a liquid phase ready for release.

Yes, this is a technology that is not yet mainstream and certainly not found on nuclear sites. That said, the results offered by the Siccum technology are worth noticing for the treatment of sludges, flocks or any other pumpable material from a nuclear site.

We, at inTechBrew, think this modular solution certainly has the potential to efficiently tackle the treatment of large volume of pumpable materials but could also tackle the problematic treatment of small volumes of liquid legacy waste. It could even be another way forward for soil remediation.

Indeed, Siccum’s ability to extract contaminants (incl. heavy metals) from sludge-like materials and achieve separation between the water phase and impurities can certainly be applied to granular waste containing radioisotopes. Overall, it offers volume reduction with a smaller environmental footprint than current methods. It also can integrate existing processes or be used as a mobile unit.

User case 1 : Dewatering Capatibility

Karlshäll, Norbotten, Sweden, Winter 2021-22

Sweden is among the world leaders in the production of pulp and paper. During the years 1912–1962, around 50 years, abrasive pulp was manufactured on Karlshäll paper mill, near Luleå (Sweden). During a ten-year period, mercury was used in the process. Like hundreds of paper mills in Sweden, and many more worldwide, the wastewater it released created what are known as “fiber banks” — nutrient-rich accumulations of industrial and organic waste from the mill, mixed up with the river’s natural sediment. For ten years until its closure in 1962, the Karlshäll mill (picture below shows site in 1929) released what may have been 100 kilograms of mercury into the Lule River.

There is usually a great need for effective dewatering when remediating contaminated sediments. Above all, dewatering aims to make volumes more manageable for transport, disposal, or post-treatment work of contaminated sediments: great dewatering result gives a large reduction in volume of dredged sludges, reduced need for transport, and smaller quantities/volumes for disposal.

Traditional methods, such as sedimentation or dewatering in geotubes, gives an increased Dry Matter (DM) content, but even after reducing the water content, the overall weight is still relatively high. A higher DM content can in some cases be achieved by mechanical methods, but at a higher cost.

WSP Sweden AB (WSP) has, on behalf of Luleå municipality, implemented a project within the government interest to treat contaminated sludges (with high fibrous content) and produce better guidance for post-treatment work on contaminated sediments.

Here, Siccum’s freeze dewatering was highlighted as a method providing control over the DM content and capable of achieving a large dewatering effect (high DM content) for the remediation of mercury-contaminated sludges outside Karlshäll. The dewatering technology offers the possibility of a large reduction of volume, which creates the conditions for a more cost-effective disposal of the residual. The freeze dewatering method is here considered to have a high potential for the treatment of, primarily, polluted sediments with a low DM content and a high content of organic material.

The sludge used in this work has been pumped directly from the bottom of the river, through suction dredging controlled by divers, into IBC tanks (1 m³) and then on to the freeze dewatering plant. The freeze dewatering plant was housed in a 40-foot container, where all steps from freezing, thawing and drying were carried out. The different steps involved in a freeze dewatering plant can also be dimensioned according to the desired production rate up to a maximum of 60 tons of material per day per unit (40-foot container).

The initial investigations showed that the DM content in the material after homogenisation was 2-7% of the wet weight, based on experience with DM content in pumpable material. The content of mercury in investigated sediments showed median levels of around 14 mg/kg DM (results from Luleå municipality, 2019).

Two air samples were taken inside the container where the experiment was carried out. Mercury measured in suspended dust (particulate matter) was captured by pumping air over a particulate filter and gaseous mercury was captured in dedicated carbon tubes placed after the particulate filter. Each sample were analysed for particulate bound mercury and for mercury in gaseous form. Particulate mercury was detected in both analysed samples but in concentrations below the Swedish Occupational Safety and Health Administration’s limit values. No mercury could be detected in samples of air (in the freeze container) that passed through the filters, showing that any unwanted release of mercury into the environment could be remedied by passing air through a particle filter before it is released.

Importantly, measurements have shown low levels of mercury (below legal requirements) in reject water that has undergone dewatering by freezing before analysis. Clearly demonstrating that Siccum’s freeze dewatering technology, in addition to separation between water and solids, also achieved separation between the water phase and impurities.

During this work, the energy consumption was between 43 and 45 kWh/ton of processed material, which is considered relatively low based on the achieved DM content (in a bench-scale experiment where another type of sediment, with DM content of 25%, was dewatered with an HTC (Hydrothermal carbonisation) method, an energy consumption of around 550 kWh/tonne DM (Sweco, 2021) was needed to achieve a DM content in the residual of 70-80%.).

The freeze dewatering plant used in this work is contained in a container and can therefore be adapted to be stationary or mobile, which can potentially provide advantages in areas where available surfaces are limited. The freeze dewatering process can also be automated and, through the application of alarm levels for the various steps in the process, monitoring can take place online, which means relatively little investment in terms of time for operating personnel during production itself.

Note: The limit value for mercury exposure during a working day is 20 µg/m³ (Arbetsmiljöverket, 2018) for both particulate bound and free mercury. All chemical analyses were performed by the accredited laboratory ALS Scandinavia.

User case 2 : Contaminants Extraction

Lulea, Norbotten Sweden, 2023

The sewage sludge from the area of contamination is heavily polluted with high levels of mercury, along with other toxic metals such as copper, zinc, lead, and cadmium, posing significant risks to both the environment and public health. This contamination largely stems from both industrial and municipal sources: notably, effluents from a decommissioned municipal treatment plant and discharges from nearby industrial laboratory activities in the 1960s. Minor pollution sources also include local dental services, primarily due to the utilisation of mercury in dental practices.

Two samples of rejected water were taken, one was filtered and one unfiltered. The results below clearly show that Siccum’s technology offers the ability to extract contaminants (incl. heavy metals) from sludge-like material and achieve separation between the water phase and impurities.

	Dry Residue (after Siccum)			Unfiltered Rejected Water
Analyte	Unit	Result	Error margin	Unit	Result	Error margin
Dry Substance	%	93.3	10%
Benzene	mg/kg Ts	< 0,0035	30%	mg/l	< 0,00050	30%
Toluene	mg/kg Ts	< 0,10	35%	mg/l	< 0,0010	35%
Ethylbenzene	mg/kg Ts	< 0,10	30%	mg/l	< 0,0010	30%
m/p/o-Xylenes	mg/kg Ts	< 0,10	35%	mg/l	< 0,0010	35%
Total TEX	mg/kg Ts	< 0,20	30%	mg/l	< 0,0020
Aliphatics >C5-C8	mg/kg Ts	< 5,0	35%	mg/l	< 0,020	35%
Aliphatics >C8-C10	mg/kg Ts	< 3,0	35%	mg/l	< 0,020	35%
Aliphatics >C10-C12	mg/kg Ts	33	30%	mg/l	< 0,020	20%
Aliphatics >C5-C12				mg/l	< 0,030
Aliphatics >C12-C16	mg/kg Ts	160	30%	mg/l	0.068	20%
Aliphatics >C16-C35	mg/kg Ts	2700	30%	mg/l	0.65	25%
Aliphatics >C12-C35				mg/l	0.72
Aromatics >C8-C10	mg/kg Ts	< 4,0	40%	mg/l	< 0,010	40%
Aromatics >C10-C16	mg/kg Ts	21	35%	mg/l	< 0,050	20%
Aromatics Total >C16-C35	mg/kg Ts	6.7	25%	mg/l	< 0,025	25%
Benzo(a)anthracene	mg/kg Ts	1.3	30%	µg/l	0.21	35%
Chrysene	mg/kg Ts	1.5	35%	µg/l	0.25	35%
Benzo(b,k)fluoranthene	mg/kg Ts	2.4	40%	µg/l	0.61	35%
Benzo(a)pyrene	mg/kg Ts	1	35%	µg/l	0.33	40%
Indeno(1,2,3-cd)pyrene	mg/kg Ts	0.79	35%	µg/l	0.21	45%
Dibenz(a,h)anthracene	mg/kg Ts	0.16	30%	µg/l	< 0,050	40%
Naphthalene	mg/kg Ts	0.91	30%	µg/l	< 0,10	30%
Acenaphthylene	mg/kg Ts	0.16	50%	µg/l	< 0,050	25%
Acenaphthene	mg/kg Ts	0.21	40%	µg/l	< 0,050	25%
Fluorene	mg/kg Ts	0.46	35%	µg/l	< 0,050	25%
Phenanthrene	mg/kg Ts	4.2	30%	µg/l	0.093	30%
Anthracene	mg/kg Ts	0.82	30%	µg/l	< 0,050	30%
Fluoranthene	mg/kg Ts	4.7	30%	µg/l	0.23	25%
Pyrene	mg/kg Ts	4.1	25%	µg/l	1.3	25%
Benzo(g,h,i)perylene	mg/kg Ts	0.78	40%	µg/l	0.15	45%
Total Low Molecular Weight PAHs	mg/kg Ts	1.3		µg/l	< 0,20
Total Medium Molecular Weight PAHs	mg/kg Ts	14		µg/l	1.7
Total High Molecular Weight PAHs	mg/kg Ts	7.9		µg/l	1.8
Total Carcinogenic PAHs	mg/kg Ts	7.2		µg/l	1.6
Total Other PAHs	mg/kg Ts	16		µg/l	1.9
Total PAH16	mg/kg Ts	23

	Dry Residue (after Siccum)			Unfiltered Rejected Water			Filtered Rejected Water
Analyte	Unit	Result	Error margin	Unit	Result	Error margin	Unit	Result	Error margin
Arsenic As (filtered)	mg/kg Ts	6.4	25%	mg/l	0.0026	30%	mg/l	0.00044	20%
Barium Ba (filtered)	mg/kg Ts	1000	25%	mg/l	0.3	25%	mg/l	0.14	25%
Lead Pb (filtered)	mg/kg Ts	270	25%	mg/l	0.12	20%	mg/l	0.00026	20%
Cadmium Cd (filtered)	mg/kg Ts	4.7	25%	mg/l	0.0018	25%	mg/l	0.00012	20%
Cobalt Co (filtered)	mg/kg Ts	21	30%	mg/l	0.0036	25%	mg/l	0.00074	20%
Copper Cu (filtered)	mg/kg Ts	660	25%	mg/l	0.13	25%	mg/l	0.0035	25%
Chromium Cr (filtered)	mg/kg Ts	410	25%	mg/l	0.016	25%	mg/l	0.000093	20%
Mercury Hg (filtered)	mg/kg Ts	27	35%	mg/l	0.013	25%	mg/l	< 0,00010	25%
Nickel Ni (filtered)	mg/kg Ts	56	25%	mg/l	0.014	25%	mg/l	0.0027	20%
Vanadium V (filtered)	mg/kg Ts	60	25%	mg/l	0.025	25%	mg/l	0.0025	20%
Zinc Zn (filtered)	mg/kg Ts	4700	25%	mg/l	1.9	25%	mg/l	0.43	25%

The technology: Siccum’s freeze dewatering

Water & Ice

Water in materials can be separated into four different categories: free water (cavity water), interstitial water (capillary water, also called pore water), surface water (adsorption water, should not be confused with a lake or stream) and bound water (bound to particles).

Free water is the water that is not incorporated into the material matrix and can in principle run off a material and can be removed by traditional dewatering. Interstitial water is the water that exists between particles in the material structure and is retained in the material by capillary forces. The capillary forces can be broken by mechanical dewatering and can be removed using, for example, a belt filter press or a dewatering centrifuge. Surface water is the water associated with particle surfaces and (weakly) bound/adsorbed to the material structure. Surface water is difficult to separate out using mechanical dewatering techniques. Bound water is chemically bound in the material structure.

The free and interstitial water can typically be removed with mechanical methods. To remove surface and bound water other methods are needed. The most common method is to use oil burners to force the water to evaporate and is extremely energy demanding.

Freeze Dewatering

An energy efficient and cutting-edge solution is Siccum’s freeze dewatering modules, where the material is undergoing a controlled freeze process to allow the separation of the surface and bound water from the material.

When water goes through a state change from liquid to ice it will behave in certain ways. The water molecules are arranged in a strict formation which does not allow space for other atoms, molecules or particles, whereupon particles and contaminating substances are separated from the ice structure.

When water goes through its state change to ice, it pushes particles away. As such, under the right conditions, water molecules attract other water molecules, creating a flow towards the freezing front where the particles are ejected and clumped together. As the process continues, surface water and bound water also begin to move towards the freezing front. Through this process, where freezing and subsequent thawing takes place, the water that was previously bound to the material matrix is released as free water. The surface water is also released as free water.

It is important that the freezing process takes place in such a way that the bound water is drawn out of the solid and not encapsulated by ice. Siccum harnesses these properties to control the separation of water from the material and deliver targeted dry matter content of materials. The mineral grains, organic material and contaminants remain as the solid part of sediment.

Dewatering module

Siccum designs bespoke modules that can be configured for both continues process integration or for remote campaigning. In industrial context, this means the module is engineered to desired capacity to keep up a constant and set flow of material. The output is pre-set to targeted dry matter content to suit the next step of your material handling process. Operations can even be made mobile. Importantly, to ascertain the right solution for your dewatering needs, the first step will always be to consider the properties of your material and engage in a material evaluation to ascertain the right pre-sets requirements.

Once online, the material to be dewatered is pumped to the cooling unit. The controlled freezing, with respect to temperature and time, takes place with a continuous flow of dredged material. The freezing of material takes only a few minutes. Following this, a controlled thawing, with respect to temperature, air flow and time, completes the process to reach the desired DM content in the solid.

Overall advantages

• Control over dry matter % output ready for next process step,
• Typical module size 20 – 40ft HC dimensions,
• Can be installed as part of a continuous process or as stand-alone campaign facility,
• Flexible integrations,
• Fully automated operations,
• Remote process monitoring,
• Automated safety features,
• Low energy consumption: up to 20x lower energy consumption than traditional methods (filtration, centrifugation, drying…),
• Low environmental foot-print: no use of fossil fuels, no polymer/chemical needed, contributes to the green transition,
• Siccum dewatering solution enables contaminant’s extraction as part of the remaining solid/dry part,
• The Siccum dewatering solution has the potential to process large volume of sludge but can also be suitable as a mobile solution to treat small volume.

Any questions ? Interested in material dewatering ? Do not hesitate to contact us directly, we will help you find a fit-for-purpose and cost-efficient solution in material dewatering to answer your challenge.