ACO Marine has completed the installation and commissioning of a Clarimar MF-10 wastewater treatment plant supplied to Damen Verolme Rotterdam for installation to the Stena operated semi-submersible Stena Don.

The drilling rig’s existing wastewater treatment plant was heavily corroded and non-compliant with regulation MEPC 227(64), which entered into force in January 2016.

It was replaced with the biological-type Clarimar MF-10 black and grey water treatment unit as part of an extensive four-month refit.

Mark Beavis, Managing Director, ACO Marine said: “A key aspect of the refit was to increase POB capacity from 120 to 140 persons, which required a biological wastewater treatment system capable of treating up to 14kg BOD5 biological load and 18,900 litres hydraulic load per day. However, due to space and access limitations we delivered the MF-10 as a ‘flat-pack’, which is less complex to install.”

Once the equipment has been unpacked and in-situ, assembly is simple. Since ACO Marine’s Clarimar units are manufactured from the ACO Group’s proprietary Composite PPFR, no hot welding is required. Unlike coated steel, the Polymer PPFR material is lightweight and completely resistant to corrosion, abrasion and chemical attack and the tank material is guaranteed for life against corrosion.

The plates and other elements of the assembly are fused together by simply “ironing” a bead of polymer along the joints. Once assembled the tank is then pressure tested and bolted in position to the vessel’s structure.

In this particular installation ACO Marine’s installation team, working closely with both the yard and the owner’s team, identified a solution where the discharge pump and blower assemblies were located on the other side of a separating bulkhead with an access opening for the removal of the ACO-MF Bio Sword filtration technology. The ACO Bio Sword eliminates the requirement for settling and chlorination stages.

“This allowed us to install the treatment plant in a smaller area” said Beavis.

Petr Hajek, ACO Marine’s Service Manager, added: “Installation was very straight forward and relatively quick as it didn’t require the cutting and subsequent patching up of access holes and rigging up heavy lift equipment to manoeuvre a pre-assembled unit into place. It also reduced the welding requirement and, ultimately, helped reduce installation time and dry-docking costs.”

The Stena Don project marked the second in a series of Clarimar MF units ACO Marine has supplied as flat-packs. The experience gained from the 2016 installation of an almost identical solution to the DSV Bibby Polaris helped in reducing installation and assembly times considerably.

“Not only does a flat-packed Clarimar keep retrofit costs down to a minimum, but when assembled and operational it has the lowest running costs of any sewage treatment plant on the market, said Beavis.”

The 95.5m long, 67m wide Stena Don, a harsh environment drilling rig with dynamic positioning and capacity to drill to a depth of 650m, is now operational off the Shetland Islands.