Efacec Povoa WTP (Portugal)

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EFACEC was contracted to design-supply and construct the complete plant process equipment and trusted in SIGMADAF to supply the DAF units. The WTP PÓVOA owned by AGUAS DO VALE DO TEJO has a capacity of 740 m3/h (54,000 PE) and features a treatment line with pre-ozonization, to oxidize the organic matter, algae and metals (Fe and Mn) in the raw water, lime dosing, coagulation/flocculation, dissolved air flotation (DAF), post-ozonization, activate carbon contact, sand bed filtration and final disinfection with chlorine.

SIGMADAF supplied to EFACEC the DAF system as part of the pre-treatment to remove algae, organic compounds and precipated metals after oxidation. The technology used is the LAMELLA PACK with counter and cross flow to optimize and assure an even laminar water flow distribution through the flotation tank with the water lateral outlets.

Prior to the DAF there is a physico-chemical treatment with chemicals (coagulant and polymer) dosing and mixing, this will help in the formation of larger size flocs which can be separated by flotation in the DAF tank.

Year construction 


Nº of units 


DAF model 




Pack lamelar 

Yes (GRP)

Water type 

 Surface water



Unitary flow 

600 m3/h

TSS in / out 

 350 / 10 ppm


 Photo of the Drinking Water Treatment Plant in Povoa (Portugal) in which SIGMADAF supplied two DAF-FPHF500 units as part of the water pre-treatment.

SIGMADAF FPHF Equipment Features 

The FPHF is a compact equipment especially effective for high water flow rates and high suspended solids content, using inclined plates settler (IPS) technology. The FPHF equipment utilises a combination of cross flow and counter-current flow, the heavier settling particles are separated with a relative high efficiency in the lamellas by the FPHF. 

High flows demand a better flow distribution in the flotation tank. The inflow surface of the lamella plates is equally divided against laminar flow proportionality within the system. In practice, it shows an attainable volume treatment above 100%, compared to conventional plate separators, which have mostly an overflow rate of at least 3 m/h. 

In this project the FPHF equipment is expected to remove algae and TSS. The suspended solids are aggregated in flocs in the flocculantion tank and they are make to float with the air-bubbles which enhance the buoyancy separation process. The use of micro-bubble flotation technology (30 to 50-micron range) increases the float efficiency, as smaller bubbles easily adhere to equal-sized or larger particles, boosting the overall effectiveness of the system. The SIGMADAF air aerator generates the required amount of air to be injected in small size bubbles in quantity and well distributed in the full tank volume.

Diagram of the water treatment process proposed by SIGMADAF Clarifiers for the Povoa Drinking Water Treatment Plant (WTP) in Portugal.

Unique system characteristics 

Detail photo of the DAF-FPHF500 equipment installed by SIGMA for water pretreatment at the Povoa Drinking Water Treatment Plant, in Portugal.

The FPHF is a high-performance system with a number of distinct features. 

• Efficient laminar water flow distribution, enhanced by the lamella pack and lateral pipe outlets along the tank length with adjustable outlet weirs to control the flow rates. 

• Skimer with a single movement separator, which rotates against the hydraulic flow of the water, helping to minimise the distance of the floated sludge and eliminating solids carry-over. Floated sludge is extracted into a collection hoper with a DS content 3 to 4 times greater than a conventional system. Dewatering or drying costs are then minimized. 

• Settled solids in the tank bottom are collected in the extraction auger with a shaftless screw device. The build-up and thickness of the solids is controlled with the operation time of the extraction screw and the pneumatic valve. The discharge cycle is self-cleaning and any particles adhered to the walls or sides of the system will loosen and follow their initial flow path. 

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