DAF FT-25 By ESMIL Supports The Thickening Of Floatables From Primary Clarifiers At The Vilnius WWTP

As part of the modernisation of the municipal wastewater treatment plant in Vilnius, Prodeko-Ełk, a part of Esmil Group, supplied equipment for several key process stages.

One of these stages involved the treatment of floatable fractions generated during primary sedimentation. For this purpose, we delivered a DAF-25 dissolved air flotation unit with a nominal capacity of 30 m³/h.

Floatables are discharged from primary clarifiers as highly diluted liquid containing suspended solids, fats, oils, and petroleum-derived compounds. Due to their large volume and low dry solids content, this stream is difficult to transport and further process, for example in co-dewatering with primary sludge or in digestion. In practice, such material often accumulates in the primary clarifier zone.

DAF systems are typically installed at industrial plants for pre-treatment of process wastewater. In this case, the unit was applied in a different role – for the separation and thickening of floatables originating from primary clarifiers.

Process description
Float-rich sludge separated in the primary clarifiers is pumped to an equalisation tank and then fed to the flotation unit. Inside the system, the liquid stream is saturated with air, and the resulting microbubbles lift fats and suspended solids to the surface, forming a layer of floated sludge.

The floated sludge is removed by a skimming mechanism. The clarified water is directed to further treatment, while the thickened fatty slurry can be transferred for further handling.

The process operates without the use of chemical reagents, which supports both operational efficiency and reduced operating costs. As a result, a concentrated material with approximately 50% dry solids is obtained, and under favourable conditions 65–80%. At this level of thickening, the material can be sent for incineration at specialised facilities or used as a high-calorific additive prior to digestion (after heating).

Benefits of dissolved air flotation:

• reduction of floatable volume and thickening into a form suitable for transport, facilitating further management
• the concentrated mass can be used as a high-calorific additive before methanisation or sent for incineration
• effective removal of suspended solids, fats, oils, and petroleum-derived compounds, reducing the risk of pipeline clogging and equipment failures in downstream treatment stages

Comprehensive delivery with ESMIL involvement
As part of this modernisation project, we supplied not only the flotation unit but also:

• ZGRwt-54 radial clarifier scrapers equipped with the Probig floating sludge extraction system, responsible for the removal of sludge and floatables from the primary clarifiers
• 20 penstocks of various types, ensuring precise flow control within individual process lines

We would like to thank the general contractor, UAB Arginta, for placing their trust in our solutions and selecting ESMIL as the equipment supplier for this project.