Filtration is a natural starting point for ballast water treatment systems and has developed into a specialist sub-sector of the industry, but it is not a universal
Filtration is a natural starting point for ballast water treatment systems and has developed into a specialist sub-sector of the industry, but it is not a universal
It is estimated that between 10 and 12 billion tonnes of ballast water is transported around the globe each year, with the potential to carry bacteria, plankton, viruses, small fish, crabs or jellyfish into foreign ecological systems. In the early days of ballast water treatment it was assumed that a simple filter on the intake would prevent the majority of organisms entering the ballast tanks. But research showed the mesh required would have to be much finer, which leads to clogging unless highly sophisticated technology is employed. The BWM Convention D-2 performance standards specify an organism with a maximum dimension of 50 μm, which is a technological challenge compared with a simple mesh filter.
There is still a need to filter large matter at the intake stage, and the majority of the systems require automatic pre-filtration of the seawater taken on board. Therefore a fine filter is installed between a coarse separator and the chemical or physical disinfection units. The filter’s task is to remove animal and vegetable organisms, as well as sediment from the ballast water. It must operate in a marine environment while overcoming the following challenges:
The stipulation of the organism size does not take into account the flexibility of being able to squeeze through the regulatory filter opening, nor the tendency of scientific techniques to progress, revealing ever smaller and equally aggressive forms of life in ballast water.
Boll & Kirch Filterbau manufactures filters for a wide range of industries and supplies its Bollfilter brand into the ballast water treatment market. In 2017, Boll & Kirch launched the Bollfilter AquaBoll model, which has a filtration capability down to 20 μm. AquaBoll is an automatic backwash filter model and is said to significantly increase overall plant efficiency through optimised functionality and adaptability. It is based on a novel platform concept, which uses a multi-part housing that can be adapted to suit a range of installations, even in small spaces. Filter elements, variable connection-flange positions and different housing materials support its flexibility to match the filter to application-specific filtration requirements. The AquaBoll filter 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.
Boll & Kirch’s Bollfilter brands also include the Bollfilter 6.18.3, which has already received United States Coast Guard (USCG) approval. It is available with optional 30 µm, 40 µm or 50 µm filtration. Customers include SunRui and its BalClor ballast water treatment system, and the Norwegian ballast water management system provider Optimarin.
Optimarin was the first ballast water system manufacturer to achieve USCG type-approval, and its systems are now available with 40 µm filters from Bollfilter, Filtrex of Italy, and Filtersafe.
Alfa Laval reports promising results from using Filtrex filters in its PureBallast 3.1, in two separate papers. The first, conducted for dredging contractor Van Oord at Dutch research facility Marine Eco Analytics (MEA-nl), demonstrated the ability to handle 250 mg/L of sediment, which is equivalent to samples taken by the Van Oord in the very muddy waters of Mumbai. The second study, an onboard comparison performed on a large container ship, established that the Filtrex basket filter with enhanced cleaning has 10 times greater backflushing efficiency than a standard filter.
More recently, Greek company Erma First’s current USCG Certificate was amended with the series of FILTREX filters (Alternate filter under the USCG Regime) and all models of Erma First ballast water treatment system FIT will have options of Filtrex or Filtersafe filters as per its current IMO Type Approval.
Filtersafe filters were used in the first chemical injection treatment system to receive USCG Type Approval. This was the Ecochlor ballast water system, which was approved in 2017 for a range of maximum treatment rated capacities between 500 m3/h and 16,200 m3/h. At the time the USCG issued a statement stating: “DNV GL’s evaluation and recommendation that Ecochlor be approved for use with all filter models of the Filtersafe BS-series. Filtersafe Standard and Turbo BS-series filters may be used with no limitation to their associated treatment rated capacity.”
As well as Ecochlor, Filtersafe lists its partners in the ballast water treatment industry as:
Among the other manufacturers of filters, HYDAC of Germany is a provider of pre-filter systems for ballast water treatment systems, namely its Hysteam back filter. This has a filtration point of below 40 µm according to the manufacturer’s specifications.
Of the 100 or so ballast water treatment systems currently in the Ballast Water Treatment Technology database, 70 use a form of standard filtration. Given that in some cases these ballast water treatment systems have been in development and production for 20 years, there are clearly many positives from using pre-filters and filters to protect and enhance ballast water treatment systems. But there are drawbacks, too. Nearly all filters used in ballast water treatment systems incorporate some form of cleaning regime, usually a backflushing process. This has been automated, but there is the underlying fear of filter clogging, real or otherwise.
This is one of the memes used in the marketing of ballast water systems without filters. The non-filter ballast water treatment systems use a variety of processes:
The above use a variety of process. De-oxygenation is achieved either by removing oxygen from the ballast water, such as in NEI Treatment System’s venturi stripping, or by adding inert gases from the ship’s engines or produced by a nitrogen generator in sufficient quantities to bring the oxygen content below that needed to support life, as in the Coldharbour Marine method. This method is particularly suited to tankers where inert gases are already used as a blanket in the tanks to prevent fire and explosions. The lack of oxygen in the ballast water will also help to inhibit corrosion in the ballast tanks, especially where the tanks have not been coated.
Cavitation will inflict shock damage to living organisms. This may kill the organism outright, but is designed in any case to inflict damage that will make subsequent treatment by other methods more effective.
Although not exactly making use of heat by direct application, the Knutsen KBAL system does make use of a low-pressure boiling phenomenon to achieve disinfection. Treatment in the type-approved KBAL system is a two-stage process that does not include any filtration. The first stage involves a pressure vacuum reactor working in combination with a vertical ballast water drop line to create a low-temperature boiling condition that eliminates the majority of the organisms. Any remaining bacteria are then eliminated by the UV chamber mounted downstream of the pressure vacuum reactor.
The Ferrate treatment is a unique process owned by Ferrate Treatment Technologies that uses a specialised molecule of iron in its plus-6 oxidation state and known as iron VI. The disinfection process employs oxidation and, although the end product is non-toxic, making the special iron molecule on board in a device called the ferrator involves the use of hazardous chemicals.
Using pre-treated water is an option that has been given a lot of thought but passed over mostly because of cost. However, Dutch dredging specialist Van Oord was given basic approval for its system at MEPC 65. Designed for ships such as dredgers with a minimal ballast capacity and which do not ballast regularly, the system makes use of potable water supplied from shore or generated on board. Such water would be free of organisms larger than 10 microns, but might need additional chlorine such that the maximum concentration of 5 mg chlorine per litre of ballast water is achieved.
The filterless Kurita ballast water treatment system from Japan is now going to be handled by TeamTec. Under a new distribution agreement, TeamTec will provide worldwide sales and marketing, as well as handling project execution, delivery and lifecycle service.
Kurita Water Industries of Japan, the developer of the system, is a company that supplies chemicals to produce industrially clean water for manufacturing processes. It is said to be unique in that it does not use filters but only water treatment chemicals (sodium hypochlorite) to eliminate aquatic organisms in the ballasting process and neutralise the ballast water in the deballasting process.
The configuration is simple: no filter, chemical storage tanks, equipment for feeding chemicals and controlling equipment. The system is IMO G8/G9 approved and currently is in the process of obtaining both revised G8 approval and USCG type-approval.
According to Kurita, the ballast water treatment system does not need large-scale reconstruction work. The system’s notable advantage is that it can be retrofitted during a regular inspection of the ship. TeamTec head of sales and projects Edvin Tunheim Tønnessen said: “from customers with older vessels we have seen an increasing demand for ballast water management systems that do not use filters and generally are easier to install. Kurita BWMS will enable us to offer a system with a very low system installation cost, as well as give us a good alternative for vessels with low ballast water-flow rates.”
TeamTec is a subsidiary of the IMS Group of Norway, which in 2017 purchased the rights to Oceansaver ballast water treatment system after the original company went bankrupt. The IMS Group continues to manufacture and support the Oceansaver BWMS, now sold under the name TeamTec Oceansaver ballast water treatment system.
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