Feature 3 | WATER TREATMENT SYSTEMS Upping the microbe kill rate


A new ballast water treatment system has been designed to measure the amount of UV light required, over the widest water surface area possible, to destroy invasive species


systems for hull maintenance, but the UK manufacturer has thrown its hat into the ballast water treatment (BWT) ring, having unveiled a prototype BWT system which relies on a combination of filtration and ultraviolet (UV) technology to eliminate marine organisms, in line with the requirements specified by the IMO Ballast Water Management Convention – which, at time of going to press, is still not ratified. Speaking to Offshore Marine Technology


C


at the SMM 2012 exhibition in Hamburg, a spokesperson for Cathelco said: “Tere has been little focus so far on the effects of long-term corrosion on BWT systems, but, having produced ICCP systems for the past 20 years, we can bring an anti-corrosive perspective to these system types.” Te units be made available for all sizes and scales of ships, Cathelco claims, with capacities ranging from 50m3 1,200m3


/hr to /hr. Cathelco is keen to stress that the BWT


system does not rely on chemicals in any form, but has instead incorporated three main features designed to keep corrosion to a minimum and the system running as efficiently as possible. The goal, according to the IMO


requirements, is to manage the ballast water in such a way that each tonne of post-treatment ballast water contains a) less than 10 living organisms larger than 50microns (μm), and b)


less


than 10 such organisms, of between 10-50μm, per millilitre of ballast water. To increase the ‘kill rate’, Cathelco’s BWT system incorporates a pipework lay-out which disperses the filtered water in a helix-shaped flow. Tis dispersal pattern exposes as much


surface area of the water as is possible to the UV lamps, to ensure that the bacteria is bombarded with UV light from a


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Light adjustment Te cleanliness of the ballast water also determines how much UV power is needed to effectively eliminate organisms within. To this end, Cathelco has included a set of UV sensors, which are positioned in front of the system’s reactor chamber. These sensors have been specially


designed to measure the rate of UV light transmittance through the water, which will obviously decrease the murkier water conditions are. When filthy or murky water is introduced and light transmittance becomes weaker, the sensors will automatically trigger the UV lamps into performing at a stronger pace. In this way, more power is generated when it is needed to kill off remaining bacteria; similarly, the cleaner the water happens to be, the sensors will automatically relay a message to the system that less lamp


athelco may be better known for its range of impressed current cathodic protection (ICCP)


The Cathelco BWT system uses foam rubber balls to clean the UV chambers and lamp lenses (left), while users can check lamp performance via a control panel, linked to light intensity meters in the UV chambers


number of angles in the relevant contact period. Additionally, the water flows along one side of the twin UV chamber, and then passes along the other, effectively doubling the exposure of the water to the lamps. As a result, Cathelco says, the group is able to manufacture the system with more compact UV lamps than is typical of many alternative BWT systems, thereby enabling it to design the systems to fit between narrow machine spaces.


power is needed, thereby conserving energy and prolonging each lamp’s shelf life. Additionally, each UV chamber is fitted with light intensity meters, which measure the performance of the lamps and indicate when refurbishment is required. Thirdly, to safeguard the UV lamps


and chambers against the effects of corrosion, and / or build-ups of muck, the system deploys a specially designed ‘ball’ cleaning system. When the BWT cycle begins, the UV chambers are isolated from the rest of the system, and a separate pump inserts a set of foam rubber balls into these chambers. Tese balls polish away any residue that may have collected on the UV lamp glass, as well as cleaning the inside of the UV chambers, to cut the risk of corrosion. Te soſt nature of the balls also eliminates the need for heavy cleaning equipment, which could damage the lamp lenses or system components. Since the system was profiled at SMM


2012, the system has been tested aboard the 23,235gt ro-ro vessel Eddystone, operated by Andrew Weir Ship Management, and has also undergone land tests at the Netherlands-based NIOZ research facility. Cathelco says that it hopes to obtain IMO approval for the system by the end of Q2 2013. OMT


Offshore Marine Technology 1st Quarter 2013


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