Monday, 18th of April 2016
Visit of the Ashkelon desalinization plant
After 30minutes walking next to the Tel Aviv highway, 40 minutes of train, 45 minutes trying to understand hebraic at the Ashkelon bus station, we finally found a kind person who indicated to a taxi our direction and we arrived in the middle of the industrial zone, in front of the huge desalinization plant. By the way we understood the necessity of desalinization, crossing only arid landscapes during the train journey.
Half impressed, half disoriented, and totally out of breath, we met the ADOM-Ashkelon Desalinization plant manager. Little propaganda film as introduction, to sing Veolia Water and IDE ‘s praises, and then we were launched into the subject : year 2000, the missing rain, the water dependency of Israel, the hostile neighborhood, the lack of budget and skills locally…etc
And so the idea of the desalinization plant and the BOT (Build Operate Transfer) system with Veolia Water and IDE appear. It is in this way that first cubic meters were produced in 2005.
In few words and numbers, Ashkelon plant it’s :
One of the biggest desalinization plant in the world (the biggest up to very short time)
One of the 5 big plants of Israel, which are sufficient on their own to produce up to 70 % of the country drinking water
The first plant of this stature to run on reverse osmosis principle
800 000 cubic meters pumped a day
40 filters of pre-treatment with a sand layer and an anthracite layer
120 millions meters cubic of drinking water produced a year
40 000 membranes
~0,74 euros the meter cubic sold to the consumer
Every drop pumped go out of the plant 30min later, ready to be consumed
An ingenious energy recovery system
Quick point about reverse osmosis:
The natural phenomenon is Osmosis : if we have two solutions with different concentrations, separated by a semi-permeable membrane, concentrations will tend to be equal by passing water flow to the side with an higher concentration. Reverse Osmosis is the inverse phenomenon, imposed by an important pressure on the solution with an higher concentration. In the case of desalinization the solution with an higher concentration is sea water and the other fresh water.
The hard step of a desalinization plant is to impose an high pressure without wasting too much energy.
1st step : the pre-treatment
Pumping and passing through filters composed of a layer of 80cm of sand and a layer of 80cm of anthracite.
Passing through micro-filters.
2nd step : PRESSURIZATION
40% of the pumped water is bring from 1 to 70 bar thanks to pumps.
60% of the pumped water is only bring up to 2,6 bar to be re-direct to the energy recovery system where it will be bring up to 70 bar.
3rd step : 1st stage of membranes and energy recovery system
Each tube of the foto, contains 8 cylinders which are membranes rolled up. Sea water is injected in tubes under high pressure (70 bar), it passes trough an unique membrane, and then is collected by a central tube to be evacuated.
The remaining water continues to go trough the tube and passes trough other membrane. This water is more and more salted as and when it moves forward because it get all the salt of the sea water filtered by the first cylinders of membranes. And so when it arrives to the last cylinder, it’s too salty to be purified in one step. So one time it passed trough the membrane it’s collected by an other pipe to be filtered an other time by stage 2 and 3 of membranes. 60% of the produced water is concerned by this second step of filtration.
During this first step of filtration, 60% of the sea water initially pumped is rejected, it’s so a water very salty under high pressure. To not waste this energy, it’s sent in pistons, where it delivers the energy to a part of the pumped water, to bring its pressure from 2,6 to 70 bar.
4th step : 2nd and 3rd stage of filtration
Water filtrated by last cylinders of the tube is collected and sent to a new waterfall of membranes for brackish water.
5th step : minerals
Water produced by this process is too pure for human consumption, so they must add minerals.