PANASIA has developed and produced Ballast Water Treatment System for over 900 vessels in a combination of filtration and ultra violet technology. My presentation will focus on a study for higher disinfection efficacy of ultra violet technology to find better way to meet more stringent USCG standard. Recent rejection of USCG on MPN method became hot potato in this field, letting owners cast a doubt on UV technology. No one is easy to say if MPN is appropriate method or not but by focusing on the fact of rejection, the only means available now is FDA/CMFDA method.
As a company who has adopted FDA/CMFDA method from the beginning of G8 certificate, I believe it is worth of sharing what PANASIA did to find optimal resolution against FDA/CMFDA challenge. It is hard to consider all filtration and ultra violet combinations as just one technology with same efficacy because each manufacturer chooses slightly different design and technological specification as each one’s own way to meet the standard, thereby having inconsistent disinfection efficacy. Through my presentation today, I want to see dose value of ultra violet unit through CFD and to introduce three ways PANASIA mainly adopted for efficacy improvement.
UV light is the region of the electromagnetic spectrum that lies between X-rays and visible light. The UV spectrum is divided into four regions: vacuum UV, UV-C, UV-B, and UV-A. UV disinfection primarily occurs due to the germicidal action of UV-B and UV-C light on microorganisms. The germicidal action of UV-A light is small relative to UV-B light and UV-C light; therefore, very long exposure times are necessary for UV-A light to be effective as a disinfectant.
Although light in the vacuum UV range can disinfect microorganisms, vacuum UV light is impractical for water disinfection applications because it rapidly dissipates in water over very short distances. Therefore, the practical germicidal wavelength for UV light is defined as the range between 200 and 300nm. UV light plays a role in deforming DNV structure of microorganisms rendering them harmless but destroy of epidermal cells is also available by controlling output of UV light or augmenting total residence time of water in UV chamber. A combination of deformation of DNV structure and destruction of epidermal cells optimize disinfection efficacy of UV light.
UV dose value is commonly used to know sterilizing performance of UV light and it can be calculated by multiplying UV intensity and organisms’ residence time. Saying again, UV dose is the integral of UV intensity during the exposure period. If the UV intensity is constant over the exposure time, UV dose is defined as the product of the intensity and the exposure time.
With dose delivery in a continuous flow, UV reactor is considerably more complex than in a completely mixed batch reactor. Some microorganisms travel close to the UV lamps and experience a higher dose, while others that travel close to the reactor walls may experience a lower dose. Some microorganisms move through the reactor quickly, while others travel a more circuitous path. The result is that each microorganism passing the reactor receives a different UV dose. Accordingly, UV dose delivered to the microorganisms passing through the reactor is best described using a dose distribution.
The dose distribution a UV reactor delivers can be estimated using mathematical models based on computational fluid dynamics (CFD). CFD is used to predict the trajectories of microorganisms as they travel through the UV reactor. UV dose to each microorganism is calculated by integrating the UV intensity over the microorganism’s trajectory through the reactor.
- The first step is the 3D modeling: The thickness of the water layer between lamps, and between the lamps and the reactor wall influences dose delivery. If the water layer is too thin, the reactor wall and adjacent lamps will absorb UV light. If the water layer is too thick, water will pass through regions of lower UV intensity and experience a lower UV dose. The optimal spacing between lamps depends on the UVT of the water, the output of the lamp, and the hydraulic mixing within the reactor. Considering those points, draft 3D UV chamber model with lamp position is designed as its first step.
- As a second step, repositioned UV lamps’ intensity is calculated. As shown on the image below, nearest part of UV lamp has the strongest and highest UV intensity. The one in charge of designing UV chamber must take full of understanding on this.
- Third, velocity of flow: The flow through UV reactors is turbulent, rising different residence times. Through calculation of velocity, total time of microorganism’ residence inside UV chamber is acquired. And goal of velocity check is to calculate how residence time in UV chamber can be increased without disturbing delivery of UV dose.
- Finally, In order to gather dose distribution, 1,000 ~ 5,000 equal particles are flowed from inlet of UV chamber and routes of each particle is tracked to find which way it travels and how much UV dose it receives.
Through previous lines of CFD analysis on 1,000 ~ 5,000 particles, the number of particles on a certain UV dose sector is calculated.
- X axis indicates UV dose sector in which a certain amount of UV dose is exposed to particles.
- Y axis indicates the number of particles that is exposed to a certain amount of UV dose.
Through this graph, we can learn the amount of UV dose to each particle, and comparison on multi UV chamber is available.
To acquire higher disinfection efficacy, this study aims at decreasing the number of particles located at lower dose part and bringing the reduced group into upper part
Now, how can we do it? This is where experience counts.
There can be various cases of UV dose depending on which routes a particle travels.
Picture on left side shows the case with lowest UV dose exposure, and on right, the highest exposure.
Guide Vane is planned to be utilized to minimize the case with lower dose exposure by leading them to flow nearest to UV lamps. With this application, turbulence will occur inside UV chamber and turbulence must be controlled to the extent where residence time is not decreased.
By installing a Guide Vane there can be kind of high turbulence and we can extend total resistance time of each microorganism and the result is the following graph:
The blue line means before the Guide Vane and the red line means after the Guide Vane
By repositioning UV lamp there can be a case of microorganisms that can pass through the UV reactor without any exposure to the UV dose. We want to stop this kind of phenomenon so that we intentionally make a kind of repositioning of UV lamp and we can make a kind of the same turbulence effect inside the UV reactor.
In the following picture the green line is sample 1 and the red line is sample 2. You can see that the lowest UV part particles were moved to the upper part of the UV dose
Regarding UV Chamber Reformation, Sample 1 is using 24 quantities of UV Lamp and it can treat 750 cm3/h capacity. Sample 2 is using 22 quantities of UV Lamp but it can treat 1000 cm3/h capacity.
From sample 1 to sample 2 you can see that at the same field of the UV dose, the quantity of particles is increased without any change on its efficacy. This means that by increasing the capacity by 25% and allowing this extra 25% to be treated, you need less quantity of UV Lamp with the same efficacy level.
In conclusion, for higher disinfection efficacy technology we have introduced the Guide Vane, the UV Lamp Reposition and the UV Chamber Reformation. This is a kind of main improvement we did to our system. Here you can see our UV reactor:
Recently we got an award from the Korean government because this reactor is recognized as the world’s first UV disinfection unit with the largest capacity (1500 m3/h, with just one single module and by decreasing footprint to 44.5% and decreasing power consumption requirements by 44%). Actually, we want to break down the kind of stereotype that ‘technology cannot pass the USCG standard’ because there is also a way to pass it and we are currently successfully doing the land based test.
Above text is an edited article of Paul Jinhwa Kim presentation during the 2016 GREEN4SEA Conference & Awards
You may view his video presentation by clicking here
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The views presented hereabove are only those of the author and not necessarily those of GREEN4SEA and are for information sharing and discussion purposes only.
Paul Jinhwa Kim is the manager for International Sales and Marketing Division of PANASIA especially for Europe, mainly involved in marketing strategy. He joined PANASIA in 2014 after several year experiences in marine equipment business. He is an affiliated researcher for international regulations set by IMO & USCG on Ballast Water Management System. His role includes providing decision making support to customers with respect to Ballast Water Management System with a holistic view.