5ppm certification for bilge water separators

31 May 2012
Alfa Laval’s PureBilge is certified by DNV to 5ppm under the Clean Design notation

Alfa Laval’s PureBilge is certified by DNV to 5ppm under the Clean Design notation

Alfa Laval says that shipowners seeking Clean Design class notation can now specify a bilge water treatment system that is certified according to DNV’s new 5ppm type approval process.

According to Alfa Laval, the DNV Clean Design class notation is a voluntary newbuilding specification which covers most aspects of ship design and operation. For bilge water, Clean Design stipulates a maximum 5ppm of oil remaining in the water after treatment, prior to pumping overboard. MARPOL regulations stipulate 15ppm. Alfa Laval’s PureBilge is the first system to obtain the latest DNV type approval certificate. The system has also been granted the US Coastguard Certificate of Approval.

The company says that previously, shipowners specifying 5 ppm have had to take the word of the equipment supplier that the system really does meet the limit, but this has not always been the case, with some systems unable to reach the 15ppm standard under real life conditions.

Some suppliers simply adjust the oil-in-water monitor down from 15ppm to 5ppm so that it functions as an oily water alarm with automatic stop, says the company. In such cases, the equipment is not removing the oil down to 5ppm; iIt simply prevents it from being discharged overboard. The bilge water then goes into recirculation and fills up the bilge water tank. When this is full it is pumped to the waste oil tank and when that has no more capacity the ship has a problem. It is in situations like these that environmental infringements may occur.

The PureBilge system was tested according to the DNV 5 ppm type approval programme No. 771.60 for oily water separators (OWS) and in December 2011 Alfa Laval obtained type approval certificate P-13965 for PureBilge 2005 and 5005 (2.5m3/h and 5.0m3/h). The company says this was not a great step; since its launch in June 2009, PureBilge had been tested at sea under real life conditions and consistently achieved results below 5ppm.

DNV Clean notation stipulates that the vessel must be designed and operated in accordance with current and future regulations for protection of the environment. Technical and management processes and procedures for collection, transfer and storage of waste must also be adopted. The Clean Design notation is based on the same Clean goals but is stricter. It stipulates that the constructional design and operation of vessels should be such that it minimises their impact on the environment.

Clean and Clean Design class notations are voluntary environmental newbuilding specifications. An important driver is the oil majors’ environmental policies, which are becoming increasingly stringent following a number of environmental disasters. As cargo owners and charterers, the oil companies typically demand higher than normal environmental compliance from the ship owners transporting their cargoes, such as tanker owners and owners of offshore supply vessels. The same applies to owners building LNG carriers and car carriers and, to some extent, to cruise lines, as environmental awareness grows among passengers.

DNV points out that the image of the individual ship owner and operator will clearly improve with customers and authorities, “since the notation demonstrates that the company’s policy is to be environmentally proactive in order to prevent accidental pollution as well”.

By adopting the Clean Design notation, owners clearly demonstrate that they have acted to limit emissions and operational and accidental pollution by taking proactive steps and responsibility.

The Clean Design notation stipulates requirements for controlling and limiting operational emissions and discharges. These requirements cover the most important environmental aspects, including fuel tanks’ protection from grounding damage, handling of sewage and garbage, environmentally friendly antifouling, NOx and Sox emissions, use of refrigerants; Green Passport Inventory for recycling the ship, handling of ballast water, handling of fuel oil, and handling of bilge water.

As stated in DNV’s Guidance for the Environmental Class Notations Clean and Clean Design, “for Clean Design the vessel must have bilge water holding tanks as required for the Class Notation OPP-F, which means that they must have required capacities dependent on the engine rating. The machinery space bilges must not be discharged to sea, but be discharged to shore. Clean Design requires oil content of bilge water to be less than 5ppm.”

However, Alfa Laval says that meeting DNV’s Clean Design requirements for bilge water takes more than setting the oil-in-water monitor - the treatment system must actually achieve 5 ppm.

In reaction to increasing environmental awareness, future legislation is expected to be more stringent, requiring the limit to be reduced to 5ppm from the current MARPOL 15ppm limit. For the Great Lakes it is already 5 ppm.

IMO resolution MEPC 107(49), for type approval of bilge water separators for 15ppm, specifies that, in addition to the removal of oil from bilge water, bilge water separators must be tested with a stable emulsion (including fine particles and a surfactant chemical). The DNV 5ppm testing process is basically the same as IMO with one important difference. DNV states: “the 5 ppm bilge water separator must be designed to operate in each plane that forms an angle of 22.5° with the plane of its normal operating position.”

This simulates a ship listing 22.5°. Thus, this testing process has gone some way towards simulating real life operating conditions at sea. Although Alfa Laval believes that it could have gone even further and simulated sea heave, the company sees this as confirmation of its assertion that centrifugal separation is the only effective technology for bilge water treatment onboard ships.

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