Water treatment from river to demi – Portugal

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Project Description

Idroconsulting awarded Contract for water treatment package for a big power plant in Portugal.

A German join venture with Siemens as main partner has selected IDC to supply a complete turnkey package to obtain demi water from river water.

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The complete package consists of pre-treatment section for river water conditioning and a settling section for the removal of suspended solids; the sludge treatment with the aim to reduce the water content and to minimize the disposal and the final demineralization water treatment package to achieve the water characteristics as per final client request.


The water to be treated, after pH conditioning at the intake by means of NaOH and HCl dosing station, is fed into the pre-treatment section. The pre-treatment is performed by addition of ferric chloride, and polyelectrolyte as flocculation section and Sodium Hypochlorite solution with the purpose of sterilize the water to protect the whole plant from possible bacterial growth.

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The suspended solids are removed by settling tanks lamella type installed in parallel and by sand filters. The sludge coming from the settling tanks is sent to the dedicate plant section while the water is sent to the demineralization package.


This system is necessary to decrease the sludge water including a sludge thickener, a centrifuge, the centrifuge sludge feed pumps and the polyelectrolyte dosing pumps. To complete the package a screw conveyor is provided for sludge movement into containers.

The excess of water coming from the thickener is sent by overflow upstream the settling section.

This section has been designed for a capacity much higher than sludge production for more flexibility and with the aim to work discontinuously, only few hours per day.


The demineralisation system is the core of the whole supply and is mainly composed by:

  • Reverse osmosis
  • Stripping tower
  • Mixed bed polishing units
  • Neutralization system for mixed beds eluates

The pH is regulated by the hydrochloric acid dosage while the sodium bisulphite solution is dosed on the R.O. line feeding to eliminate the residual free chlorine and protect the membranes from chlorine oxidation. The chemical dosing system is completed by antiscalant that is added to mainly prevent calcium sulphate and barium sulphate scaling on the membrane. Any scaling on the membranes surface reduces the passage of the water through the membranes with consequent loss of plant performances. The correct and continuous dosing of antiscalant is fundamental to avoid irreversible damage of the membranes.

A gross filtration is performed by self-washing filters with a filtration degree of 25 microns while the cartridge filters operate as fine filtration to remove any impurities larger than 5 microns which could cause irreparable damage to the R.O. membrane surface.

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The water is sent to the Reverse Osmosis first step, then to the stripping tower to remove the excess of CO2 and then, if necessary, to the second R.O. step. The purpose of the section is to produce demineralised water (medium quality) to feed the final polishing Mixed bed units.

The mixed bed section provides to produce high quality water as required by power station. Normally one mixed bed is running while the other is in stand-by or under regeneration.

Project Details

  • Our goalThe modular approach in this project due to the variation of the water characteristics testifies to the adaptability of IDC despite the complexity of the whole supply. In this way the plant area is optimized and the performance achieved is significantly improved, allowing savings on energy costs and on the consumption of chemical products.
  • DetailsThe plant is located near the estuary of the Tejo river so the incoming water could be affected by the tidal cycles. In fact, three main scenarios have been identified: A) river water with no tidal influence (low TDS content and conductivity) B) river water with medium tidal influence C) river water with high tide influence The peculiarity of this plant is the flexibility in the management of flows with different flow rates and with variable characteristics.