Fluorescence measurement technology represents the state-of-the-art for oil content metres used in bilge water management technology. “Now there is an oil-in-water monitor that actually measures oil in water,” said Gary Bartman, president of Turner Designs Hydrocarbon Instruments, in November 2008 when that company shipped its first order of the new TD-107 monitors to its distributor, NAG Marine, in the US. This is claimed to be the first ever production run of MEPC 107 (49) certified fluorescence-based oil content meters.
Fluorescent molecules emit light energy at a longer wavelength than they absorb it, and the fluorescence signature of oil can be used to determine its concentration, even in emulsion. As other particles such as soot and iron oxide do not fluoresce in the same way, this technique does not confound these different sources of bilge water contamination.
The most widely used oil content meter (OCM) technology is based on light scattering. Oil deflects light so light attenuation across a measurement chamber and its reflection on to an area otherwise obscured from direct light, gives a measure of turbidity and therefore oil content. According to Turner Designs, existing light scattering technology is not sensitive enough to detect low concentrations of oil. “The limit of detection is 5-15 ppm, depending on the application. The accuracy specification that equipment is built to is plus or minus 5 ppm! Does this make sense?”
Both MEPC 60 (33) compliant light scattering models and the newer emulsion-detecting MEPC 107 (49) models employ the same underlying principle of operation; the later are better calibrated and employ a variety of wavelengths to increase their sensitivity. However, sometimes fine iron particles, biological detritus and solvent emulsions may be detected as oil.
The Society of Naval Architects & Marine Engineers in the US has identified that a lack of understanding of present day contaminants and effective bilge water management practices is a major reason why oily water separators (OWS) are forced into recirculation so often that equipment failure and crew frustration become a problem. This may contribute to the incidence of illegal discharges.
Commander Bruce Russell, who has retired from the US Coast Guard and is co-chair of the technical and research committee on oily waste and bilge water, believes that manuals provided by equipment manufacturers do not provide an overall approach to managing systems. This leads to a ‘fix it’ approach rather than addressing the root causes of problems. “From a human factors point of view, it needs to be understood that while the oily water separator is running as advertised there is little incentive for ships’ crews to delve into theory and troubleshooting methods.
“Only when the separator is malfunctioning will the crew have the motivation to perform investigations into the source of the problem and, at that stage, they have the need for guidance that responds directly to what they observe in the engineroom.” The committee has prepared a diagnostic guide which has been submitted to IMO as a proposed MEPC circular. It describes contaminant identification techniques, troubleshooting options, recommendations for preventative and corrective measures and background theory.
As of 1 January 2005, newbuilding equipment and total replacements on existing ships are required to be in compliance with MEPC 107 (49); however, the US has proposed to IMO that MEPC 60 (33) equipment should be actively phased out, either through upgrade or replacement. That country estimates that mid-range equipment could cost between US$22,000 and US$57,500, depending on vessel size.
Balanced against savings in port discharge fees if no separation was done, this could lead to annual savings of between US$18,000 and US$360,000. US authorities believe it would be possible to achieve a complete phase-out of MEPC 60 (33) equipment by around 2016.
The US also believes that upgrades must include an MEPC 107 (49) compliant OCM. Older OCMs are only required to read distillate oil in the presence of 10 ppm cleaner test dust and they are not expected to detect emulsions. In contrast, MEPC 107 (49) OCMs must also read heavy oil and test fluids with cleaner test dust concentrations of 50 and 100 ppm. The required response time for MEPC 107 (49) OCMs is five seconds (rather than 20 seconds) and meters are required to be tamper resistant and to prevent discharge while flush water is being fed through.
The International Chamber of Shipping (ICS) has submitted a paper to IMO disagreeing with the active phase-out of equipment which, it says, may be functioning acceptably, especially when the industry still has issues with the reliability and functioning of MEPC 107 (49) equipment. “It is unwarranted,” says David Tongue, marine manager for ICS. Mr Tongue says that emulsions come from the use of cleaning additives when heavy fuel oils are used and that the industry’s future adoption of distillate fuels has not been considered.
The details of how upgraded equipment should be tested are being debated. The US believes that a full system, not just add-ons, should be type tested because fluid properties such as droplet size, back pressure and velocity can be affected by existing equipment and therefore have an impact on the performance of the new equipment.
For Mr Tongue, this is just active phase-out coming in through the back door. “It has to be recognised that the same equipment may operate differently on different ships and it depends on how the ship itself is operated.” He cites the Japanese Integrated Bilge System concept, where different waste streams are collected and managed separately, as an excellent alternative way of meeting environmental standards.
Many manufacturers offer units suitable for upgrading MEPC 60 (33) systems by providing additional pre- or post-OWS add-ons. Wave International of the UK, for example, offers its Wavestream 4Stand polishing units. These systems have a small footprint and are easy to install, says the company, and a set of four cartridges lasts from two to six months. This means that the cost of maintenance and bilge water disposal caused by a poorly operating OWS on a large ship can be reduced by at least 95 per cent.
David Burroughs, director of sales and marketing at EnSolve, believes that many OWS technologies are unable to deal with contaminants such as soot, rust and degreasers. He believes that coupling a filtration system to a MEPC 60 (33) coalescer will not necessarily achieve the results required for MEPC 107 (49). “Every certified MEPC 60 (33) system is different in performance, even if the technologies are similar; therefore, we believe that any older systems upgraded to MEPC 107 (49) requirements should have to pass the same testing requirements as new MEPC 107 (49) approved systems in its entirety. Otherwise, a shipowner is at significant risk in achieving the desired effluent quality stipulated under law.”
EnSolve’s technology is distinctive because it uses both mechanical and biological treatment, and EnSolve claims no issues with false positives from OCMs coupled to its equipment. Microbes are used to convert hydrocarbons into CO2 and H2O, resulting in a system that has minimal filters or liquid wastes for disposal.
EnSolve launched an operating cost guarantee programme in September 2008. This allows ship operators to work to a predictable annual fee because EnSolve will charge them an annual fixed services and consumables fee, which covers all items required for normal operation of its PetroLiminator OWS, including nutrients, pH adjustment chemicals and replacement filter elements as well as a field service visit.
Coffin World Water Systems, based in the US, recommends pro-actively upgrading older equipment as new systems are more efficient and more effective at protecting the environment. Coffin World’s OWS guarantees an overboard discharge of 5 ppm or less continuously as a result of its Spir-O-Lator membrane which has a 0.01 micron pore structure. The system is compact and economical to run, and Coffin World offers an upgrade package to meet MEPC 107 (49) requirements. This package can, typically, be installed during short port stops or while underway.
Mahle Industriefiltration of Germany offers its pressure-type separation system that uses both gravity and coalescence. The MPEB-VT upgrade model consists of two units. The first is placed in the same location as the old OWS and the second can be placed anywhere in the engineroom. The system does not require backflushing, chemicals, adsorption or membrane filters.
EMS Ship Supply offers a vacuum-style, coalescing OWS that is small enough to be transported through existing doors and openings and has a cleaning grade of <5 ppm. The larger ClearWater model can be operated at 50 per cent capacity to achieve better cleaning results and has a cleaning grade of between 0.1 and 1ppm. Compared to other OWSs on the market, this system has very low filter consumption, says EMS.
Alfa Laval questions the adequacy of the type testing performed for MEPC 107 (49) systems since the manufacturer believes the test does not call for conditions simulating rough seas or the time and input that would lead to clogged filters. The company believes that the centrifugal separation technology that its new PureBilge unit employs is more efficient than chemical treatment, absorption filtration, membrane filtration and conventional coalscers.
These systems generally have large waste and back flush volumes, says Alfa Laval, and most, except membranes, lose efficiency in rough weather and when difficult emulsions are present. According to Pauli Kujala, business manager for waste oils at Alfa Laval: “If traditional static systems were to be tested with a realistic bilge water cocktail under conditions simulating a rough sea state around the clock for 20 days, they would be immediately eliminated.”
Alfa Laval claims that its system’s superior performance, even compared to other centrifugal separation systems, is due to the innovative XLrator laminar flow inlet device. The XLrator gently accelerates bilge water into the separator bowl with a minimum of shearing and foaming and this prevents the formation of further emulsions.
Andreas Rosebrock, sales area manager at RWO, believes that it is only physical-chemical flocculation/flotation systems that do not perform well in rough seas. RWO systems use an open porous coalescer with automatic backflushing, followed by an emulsion breaking oil and hydrocarbon polisher (SKIT/S-DEB OWS system pictured). “Our system, as well as others that have the same working principle, perform just perfectly, even in rough seas. We have never experienced any of kind of negative feedback from more than 10,000 separators installed on ships,” said Mr Rosebrock.
RWO’s systems have an automatic bypass for the separating system that extends the operating life of the demulsifier. The OCM periodically checks the water quality of the first stage separator and, if below 15 ppm, the demulsifier is bypassed until the 15 ppm alarm is activated. RWO offers a splitting and filtration unit (SFU) for pre-treatment of difficult bilge water. This is suitable for operation before any OWS, old or new, says RWO.
“It is a most efficient device for removing suspended substances and emulsified hydrocarbons upstream of the separator,” said Mr Rosebrock. “Installation on ships has shown that the SFU alone can remove greater than 90 per cent of suspended matter and hydrocarbons, providing effluent values less than 15 ppm for residual oil.”
Ola Larsson, managing director of Marinfloc, a company producing a system based on flocculation processing of emulsions, explains that in very rough weather the oil and water mixture in the bilge water tanks will be heavily stirred and a mechanical emulsion will be created. “If the heel is too large, all OWS systems will have difficulties, but in different ways. A membrane system will work for a short time and then the membrane filter will be clogged with oil particles and need an expensive filter replacement to continue running at 15 ppm,” he said.
“If the roll is greater than 22.5 deg, the Marinfloc system can have some difficulty in cleaning the bilge water but the problem is never the emulsion breaking. Instead, the problem is that the very heavy roll is creating a sub-optimal environment for one of our pumps. As soon as the roll is less, the Marinfloc will work at its defined capacity and will present cleaned water between 0-5 ppm – and no replacement of any parts is needed. If the roll is less than 22.5 deg, the Marinfloc system is an excellent emulsion breaker and bilge water cleaner, independent of the size of the emulsions.”
Marinfloc claims a significant security benefit with its White Box and Bridge Control monitoring system, which can be installed after any OWS. Inside the White Box is the OCM, flow switch, overboard flow counter, three-way valve and rinse water valve.
The White Box is enclosed in a lockable stainless steel cage that contains a door breaker mechanism that will trigger the three-way valve into the return position and register the action on the recorder. An optional bridge control unit enables bridge personnel to prevent discharge, based on the vessel’s position, and the digital recorder can be monitored from another computer or ashore, periodically or in real-time.