Reverse osmosis desalinated water also cuts out Legionella
Water treatment specialist Enwa is supplying two large water treatment plants to Consafe’s accommodation rigSafe Astoria.The units, with combined capacity of 75 tons per day, are due for delivery next month.
Another offshore customer is National Iranian Oil Co. Enwa has supplied two 40 tonne per day systems to NIOC’s newbuild semisubSadra, and in August delivered a 35 ton-per-day unit for installation on a crane-barge. Earlier this summer it also completed delivery and commissioning of two 25 ton-per-day systems to the Korabel yard in Astrakhan for the Caspian Princess flotel.
North Sea-based platform supply vessel operators and subsea installation contractors on the company’s reference list include Farstad Shipping, Solstad Shipping, Stolt Offshore and Subsea 7.
Enwa uses the reverse osmosis process to treat water. Two streams are produced from untreated feed water: brine, which is discharged, and desalinated, purified water. The purified water then passes through a remineralization filter to achieve the correct acidity value. Of the feed water, 30-40% ends up as purified water, with the rest as brine.
Recent outbreaks of Legionnaire’s disease in Norway have brought the issue of safe drinking water to the industry’s attention. Offshore rigs and vessels can use Enwa’s systems to produce drinking water with sea water as feed - in this way there is no danger of the water being contaminated by Legionella bacteria, says marine segment manager Ingela Ivarsson.
Producing drinking water on board as required is safer than buying bunkered water, which must be stored and possibly treated to guard against contamination. And whereas bunkered water can cost $5 per cu m (much more in certain remote regions such as West Africa), an Enwa unit has an operating and maintenance cost of only around 71 cents per cu m.
The company can also supply a 100 ton-per-day system built into a 20-ft container. “You just plug it in,” says Ivarsson. Two containerized systems were delivered to Dolphin Drilling in 2003.
The equipment is delivered already tailored to the conditions of the sea water used as feed. Important variables are the salt content - productivity falls as salinity rises - and temperature, which has the opposite effect. If the rig moves to an area where the sea water conditions are different, the equipment can be easily adjusted by the customer to give optimal performance.
Reverse osmosis technology has come a long way since the early days when controls tended to be complicated and frequent maintenance was required. “We make every effort to keep things simple,” says Ivarsson. “The systems are easy to operate and need a minimum of maintenance.”•
For further information contact Ingela Ivarsson, Enwa. Tel +46 31 742 9263, fax +46 31 742 9260, [email protected], www.enwa.se