Envirocleanse’s Giles Candy agrees with Erma First’s Konstantinos Stampadakis that poorly maintained filters can cause problems. Better to have no filters on your BWTS, he suggests
In a recent article in Ballast Water Treatment Technology, Erma First’s managing director Konstantinos Stampadakis wrote that incomplete mechanical separation or filtration could have a detrimental impact on not just the quality of the treatment but also on the mechanical parts of the ballast water treatment system. Giles Candy is the business development officer at Envirocleanse, a producer of the USCG type-approved InTank BWMS, and in response to the Erma First article explains why the company’s products do not need filters.
Is mechanical separation essential for ballast water treatment systems?
All BWTS use mechanical separation in the form of pre-filters (strainers) on the intake. All vessels have a mud box, T-strainer or similar in the sea chest to prevent larger invasive species such as fish/jellyfish and so on entering the tanks, regardless of any downstream ballast water treatment solution with or without a filter. The question posed by the ERMA First article surrounds the use of filters which are integral to the layout of type-approved BWTS. It is proposed that having no filters on the BWTS would mean significant extra build-up of solids in the ballast water tanks. This is not necessarily the case. Most (usually 90%+) of the solids at uptake of ballast water are sized less than 50 μm. Larger particles, stirred up during vessel movement, settle out or flow away very quickly leaving organic particles and fine inorganic materials suspended in the water. Most suspended solids are silt and clay size particles (4-63 μm) and it is rare that a 40 or 50 μm filter will remove more than 20% of solids by weight. Then there is the issue of volume: all inline systems face the problem of pushing huge volumes of port water through a 50 μm, or smaller filter.
Killing efficiency for larger invasive species
In my opinion, the argument here is misleading. While larger organisms can withstand short exposure to higher TRO doses, the concentration time* (CT) approach has proved lower doses for a longer time is completely effective for small and large critters alike. The Envirocleanse inTank BWTS passed all the most stringent USCG and IMO testing, consistently exceeding the discharge standards even with the highest biological loading, on the basis of CT treatment. CT is a metric used in the waste water industry and by municipalities ensuring safe drinking water.
*CT is measured as total residual oxidant [TRO ppm] x exposure time [HRS].
Envirocleanse has found that effective and complete treatment of ballast water is conservatively achieved using a CT constant which allows treatment over 24 to 60 hours, depending on the vessel’s requirements, to both produce the intensity/time exposure profile to achieve complete treatment. This method also adjusts for the quality of each ballast load – it is not a ’one shot and done’ approach. The CT approach ensures complete disinfection of tanks and piping independent from ballast water quality and composition.
A vessel using equipment sized to provide an average dose of TRO 5 ppm for 24 hours is sufficient to de-activate species. The length of treatment time is generally not a constraint – the dosage is administered during the voyage. A vessel with a longer voyage pattern can use smaller equipment treating over longer timeframes of three to five days or more.
Dosing time and line velocity
Filters are required downstream for side-stream systems due to the relatively short contact time with the species. In general, side-stream BWTS have a line velocity of 2.5 m/sec. Depending on the length of the electrocatalytic chamber, there may be less than one second of exposure. For this reason pre-filters are required to trap the larger species and meet D-2 standard.
Mechanical wear of electrolysis units due to unfiltered water
Is this an issue for BWTS using electrolysis? The evidence is unclear:
All inline systems have only a very short contact time. In our opinion, this is a very short time to monitor, control and validate if the applied dose of active substance is adequate. There is also the issue of the biological load of the intake water. Places like the Yangtze river have a far higher biological load than Trinidad & Tobago waters. Is there the same level of efficiency in both locations? With the inTank recirculation loop, used to ensure the CT of 120 is achieved, accounts for and specifically adjusts treatment to each specific type of ballast loaded. This circulation also allows a maintenance dose to be applied to a ballast tank in the case of extended time in ballast, controlling regrowth putting biological compliance in the vessel’s control even if it has been in ballast for weeks.
Envirocleanse feel that the above statement answers the case for no filters. The Envirocleanse inTank set-up prevents:
For the reasons mentioned above, Envirocleanse does not apply filters on the recirculation loop before the TRO analyser, it is not required. As Envirocleanse’s vice president sales and marketing noted during sea trials of various BWTS, “Watching testing of other BWTS aboard Golden Bear: it was the filters that caused issues during type-approval testing”.