Alexandroupolis - Nordic Water

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Three of our products used to treat water in Alexandroupolis.

In 2004, plans were drawn up for a new water purification plant in the Greek port city of Alexandroupoli. The challenge was to produce drinking water by treating surface water from reservoirs. We used several of our water treatment products to fulfil this task and the water purification plant was completed four years later.

Alexandroupolis Case

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The challenge
To build a new water purification plant in Alexandroupoli.

The solution
Raw water from a nearby river is collected into reservoirs and then pumped to the water purification plant. When it reaches the plant, the water is chlorinated and then runs through a channel, where our self-cleaning MevaScreen RS step screen clears away any solid particles. MevaScreen RS was the ideal solution in this case thanks to its low flow resistance, which leads to low levels of water impoundment. This is a major advantage if it is installed in gravity-controlled channels. It also boasts the highest relative capacity of all screen types available on the market.

Once the water has passed through the step screen, it is divided into two equally sized flows, each of which is channelled into two flocculation tanks with mixers. In the first tank, the water is mixed with the flocculant AlCl (approx. 35 g/m3) and in the second tank it is mixed with a polyelectrolyte (0.5-1 ppm).

Lamella and Zickert
The next stage after the two flocculation tanks with mixers involves three further flocculation tanks. These are equipped with our Lamella plate pack, which is designed to maximise sedimentation over the smallest possible area. Our Zickert bottom sludge scrapers are installed at the bottom of the tanks, continuously moving away sludge while also acting as thickeners. With the help of gravity, siphons raise the sludge to the surface and then on to a common sludge treatment tank.

The water is then passed through our world-leading DynaSand sand filter for final polishing. After it has been filtered, the water runs into a clean water tank, where sodium hydroxide is added in a final pH adjustment process. The last stage involves chlorinating the water before it is distributed to residents in the Alexandroupoli area.

The wash water from the DynaSand filters is processed in sludge tanks, which feature two Lamella plate packs equipped with a circular bottom sludge scraper. The overflow from the sludge tanks is pumped back into the flocculation tanks with mixers. Once a week, the thickened sludge is pumped into two Noxon centrifuges. The centrifuged sludge is then carried away via a conveyor belt and collected in a sludge collecting tank ready to be transported away by lorry.

The result
Operational information from 2008:

Normal turbidity, mg/l:1 – 27 NTU
Maximum turbidity, mg/l: 200 NTU
Algal residue, mg/l:-
Outflow from DynaSand
Normal turbidity, mg/l: 0.08 (0,06) NTU
Maximum turbidity, mg/l:0,06 NTU
Algal residue, mg/l:0,08 mg/l

Technical data
Project specifications for Lamella plate packs for pre-treatment

Materials and design
Supporting beam: galvanised steel plate
Lamella plates: EN1.4301 stainless steel, 55-degree slope
Size of primary sedimentation area: 760 m2
Number of tanks: 2
Number of plate packs: 4
Number of plate packs per tank:2
Design flow rate: 800 m3/h
Design overflow rate: 1,05 m/h

Project specifications for Lamella plate packs for sludge

Materials and design
Supporting beam:galvanised steel plate
Lamella plates:EN1.4301 stainless steel, 55-degree slope
Bottom scraper: circular
Size of primary sedimentation area:100 m2
Number of tanks:1
Number of plate packs: 2
Design flow rate: 100 m3/h
Design overflow rate: 1,0 m/h

Project specifications for DynaSand filters

Materials and design
Supporting beam:galvanised steel plate
Lamella plates:EN1.4301 stainless steel
Tank: concrete
Number of filters: 16
Number of tanks/lines:2
Filter bed depth: 1,5 m
Design flow rate:800 m3/h
Design overflow rate:8,3 m/h

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