Not every treatment system needs a filter to provide effective ballast water management
In the early days of ballast water management development, when the practical aspects of systems aboard ships had not been fully thought through, it was proposed that filtration on its own could provide a solution to species transfer without any other treatment methods.
But ballast management pioneers took a different approach, with most of the very earliest projects involving heat treatment alone. That fell out of favour over time, but has since been revived in the Danish maker Bawat’s system, and is being pursued by others, too.
It has become obvious in the intervening years that treating ballast water to meet IMO’s 2004 Ballast Water Management Convention (BWMC) standard is more complex than was once thought, and that success usually relies on combining treatment methods. Filtration plays an important part in that, and is a preliminary step in three out of every four systems being marketed or developed at the present time.
So although most system makers have opted to make filtration a preliminary to treatment, some have decided that filtration is unnecessary.
For example, in a statement in May 2017 announcing its intention to apply for US Coast Guard (USCG) type-approval, Norway-based Knutsen Ballast Water Systems stated that its KBAL system is the only system available on the market that neither uses any kind of chemicals nor any filters. That claim would be disputed by others. UK-based Coldharbour Marine also states that no filters are used, as does Denmark’s Bawat and many others.
South Korean maker Techcross does not list filtration as part of its Electro-Cleen System (the first system to gain IMO type-approval in 2008), but the system does include a T-strainer unit with a 3 mm mesh to block large organisms and debris from entering the treatment system. It is debatable whether a mesh of that type can be considered a filter, not least because all of the systems that use filtration as part of their treatment regime do so with a filter of at most 50 μm.
That size has been chosen because it will remove some of the organisms of the dimensions that are specifically mentioned in the D2 performance standards of the BWMC. In practice, an organism with a maximum dimension of 50 μm would most likely pass quite easily through such a filter screen because of its natural elasticity and because it would likely be smaller than that in one dimension.
For that reason, it is not uncommon to see makers use even finer mesh sizes in their systems, although rarely below 30 μm. Desmi Ocean Guard’s RayClean system, for example, lists a 30 μm wire mesh filter on its original IMO type-approval certificate. Boll & Kirch managing director Robert Jellinggaard told BWTT that the market trend is toward finer filter sizes and its new aquaBoll series can filter down to 20 μm (see box).
It is worth mentioning that the convention is not only concerned with ballast water but also specifically refers to sediment in its full title and in its text. Systems without fine filters may use another form of mechanical separation such as a hydrocyclone – even some of the filter systems use this technology as a precursor to filtration – to remove organisms and coarse sediment.
It is much harder to prevent fine sediment entering ballast tanks. Scientific studies have shown that fine sediment may consist of particles of 20 μm and smaller, meaning they will pass through most system treatment filters. Even in a hydrocyclone, the sediment’s specific gravity, especially if it has a high organic content, will be below that which the device can separate out.
Hydrocyclones are still a feature of some systems, such as the Erma First system, made by the company of the same name. Its USCG type-approved Erma First Fit option uses 40 μm backwashing filters. Other makers have dropped them or withdrawn from active development and commercialisation. Among those that started out using hydrocyclones was Optimarin (in the first generation of its system), but hydrocyclones are no longer used in the version that was the first to achieve USCG type-approval (Optimarin was the first manufacturer to achieve that status).
There is no doubt that filtration that removes any organisms from the remaining treatment process will probably make the later processes more effective and so aid in meeting the discharge standard, particularly in UV systems where exposure to the UV radiation is essential. Most UV system makers will argue that their system is highly effective in exposing all organisms to radiation. But others doubt whether this is the case, especially in particularly turbid waters, arguing that individual organisms will avoid lethal doses.
Most of the systems that do not have filters are intended for use on the largest vessel types: bulk carriers and tankers. These ships have a need for high ballasting rates and uninterrupted ballasting because they are usually obliged to leave the berth immediately after cargo operations have ceased. The makers of these systems point out that, in practice, filters can be very troublesome and require frequent backwashing in all but ideal conditions.
Although the makers of systems that do use filters will argue this is not the case, it is a view shared by some seafarers, according to a report written in 2016 by Goran Bakalar, who is affiliated to Croatia’s University of Zadar and to Split-based International Maritime Technology Consultancy.
His study, Comparisons of interdisciplinary ballast water treatment systems and operational experiences from ships, included interviews with ships’ crews. In one case, a bridge officer said that filters were “a constant problem” in a Brazilian port, making the system inoperable. Others echoed that experience. Mr Bakalar reported that all of the officers interviewed stated that “they by-passed the treatment system and continued the ballasting or de-ballasting process to avoid shutdowns.” (The report is available online via http://bit.ly/BWTT-Crewstudy.)
Of those systems in which filtration does not feature, two thirds have achieved type-approval under IMO’s regulations – but so far none has obtained USCG type-approval. That does not mean that unfiltered systems will not be given USCG type-approval and, at the time of writing in late March, some such systems have begun the process of undergoing the required testing regime.
Without exception, their manufacturers are confident that their systems – which use a variety of technologies including heat, deoxygenation and chemical treatment – will achieve the approval without any more difficulty than systems that do have filters.
Filtering out type-approval concerns
Most ballast water management systems (BWMSs) need filters. They are essential components of their operation and performance, so when a BWMS is assessed for type-approval its filter forms part of its type-approved system.
Some in the BWMS manufacturing sector have expressed frustration that because of this, if they want to offer a second filter option with their BWMS they have to resubmit the treatment equipment for a second type-approval.
In mid-March, one manufacturer that already has US Coast Guard (USCG) type-approval did exactly that and submitted an application for a second filter arrangement. At the time of writing in early April, the USCG had not finished assessing that application.
This applies if any modification is made, which prompted Hyde Marine executive director Chris Todd to say in January that the process discourages innovation and improvement “because if you spend US$4M to get the solution approved, you do not want to spend that again.”
But the company’s senior market manager for BWMS, Mark Riggio, understood why authorities take a rigorous approach. “The interaction of the filter and disinfection stage is very tricky to understand,” he told BWTT. “It is difficult to justify through testing that each stage of a treatment system is independent [of] the other stages.”
A related concern applies to the situation that would arise if a component, such as a filter, failed and a similar unit was not available – if the manufacturer had gone out of business, for example. The USCG has made its position clear, in postings on its online Maritime Commons blog. In September 2017, and again in October, it warned that “if the [BWMS] equipment fails to operate and parts from the original equipment manufacturer are no longer available then the equipment is no longer operating under its type-approval and must be replaced.”
One suggestion that a manufacturer put to BWTT is that components such as filters could be type-approved separately so that an equivalent or better unit could be substituted without affecting a BWMS’s type-approval status. BWTT contacted a number of leading manufacturers to ask their views on this proposal and received mixed reactions. Most did not wish to express a view.
One who did was Tom Perlich, chief executive of Ecochlor. He would support “any regulatory changes that allowed for the upgrade and improvement of a ballast water treatment system or the replacement of supporting components without further testing for type-approval or re-certification, as long as the BWMS manufacturer and/or parts supplier could demonstrate that their product is of equal or better quality and efficacy.”
But Coldharbour Marine chief executive Andrew Marshall urged caution. “People don’t seem to understand that for a BWMS that includes a filtration step, the filter not simply there as a standalone part,” he said.
The USCG has no plans to review its stance, if comments by the editor of its online blog, Maritime Commons, Lt Amy Midgett, are any guide. She told BWTT that the primary reason – of many – that its Marine Safety Center (MSC) does not approve individual components is because “the BWMS type-approval regulations are meant to evaluate the effectiveness of a BWMS system as a whole.” There is considerable variability in the arrangement and operation of these systems, she said, so “MSC must consider component changes on a case-by-case basis in order to determine the probable effects on system efficacy.”
New filter boasts flexible options for BWMS installations
Ballast water treatment systems will be a significant market for a range of automatic filters that Boll & Kirch unveiled during the Marintec exhibition in China in December 2017, describing its new aquaBoll series as “a new concept for fully automatic water filtration.”
Boll & Kirch managing director Robert Jellinggaard told BWTT that the filter has interchangeable components, which would be selected to suit the size, the required filtration efficiency and the degree of contamination of the process water. He highlighted one feature in particular that made the filter suitable for ballast water management systems (BWMSs): it can filter down to 20 μm, which matches market demand for finer filters.
AquaBoll is an automatic backwash filter. It is marketed under the company’s Bollfilter brand, and directly replaces its previous model. It is available in seven sizes, covering throughputs ranging from 50 m3/h to 1,250 m3/h. The smaller sizes have a cast pressure vessel, with its two halves bolted together, making it possible to orientate the inlet and outlet to suit the installation. For the larger sizes, the vessel is made from welded steel, because of the higher pressures involved, Mr Jellinggaard explained.
Because of its multi-part housing, filter elements, variable connection-flange positions and different housing materials, it can be adapted to suit a range of installations, even in small spaces, the company’s literature reports.
Bollfilter’s main customer is Optimarin, Mr Jellinggaard said, but it also does business with other BWMS makers. One of them – MMC Green Technology of Norway – was the first to fit the aquaBoll filter. Its sales and marketing director, Børge Gjelseth, told BWTT in January that it had four units even before Boll & Kirch had formally launched the device.
In June 2017 another Bollfilter customer, SunRui of China, obtained US Coast Guard type-approval for its system, which included a Bollfilter Automatic Type 6.18.3 filter.