UV radiation, as an effective method for bacteria inactivation, has been applied popularly on ballast water treatment. However, the inactivation efficiencies of UV radiation greatly depend on the UV intensity which distributed unevenly in water and can be deeply affected by the suspending particles in water. For better understanding of the spatial distribution of UV radiation, a 16W UVC lamp was measured underwater to detect the radiant intensity over horizontal and vertical distance. The distribution tendency of UV radiant intensity was probed behind large amounts of experimental data. In addition, four types of different water including tap water, clean seawater, seawater mixed with suspending substances (SS), and seawater mixed with typical algae, were studied to identity the influence of water environment on UV transmission. The impacting significances were compared among different water quality, to optimize the ballast water treatment methods combining with UV radiation.
Ballast water has been detected to be a great threat to marine ecosystem and human beings for threatens from biological invasion. Filtration is a kind of optimising primary method in ballast water treatment. However, so far no suitable filter has been applied considering effectiveness, economy, and resistance. A novel wall-flow structure porous ceramic filter (PCF) was adopted to combine with UV radiation. To evaluate the PCF, three types of indicator algae were filtered at different flow rates and initial alga densities. The results showed that up to 100% removal effciencies can be obtained on alga greater than 10µm and less than 50µm at the pointed alga density. The mechanism behind high removal efficiencies and high velocity were revealed as well.
For urgent requirement of onboard ballast water treatment, a combination method of wall-flow structure porous ceramic filtration (PCF) and UV radiation has been prompted and studied systematically in the lab. The paper mainly forcuses on the material selection for PCF in order to obtain a more effective, operational, durable and economic treatment. Hence four types of ceramic materials were compared, and a series of experiments were arranged to test alga removal efficiency, durability and differential pressure of the filters. A fuzzy comprehensive evaluation system was set up to assess filter performance from five aspects. The normalization results show that oxide ceramic wins carbide ceramic at three major fators: resistance, durability and cost.
UVA is seldom applied in UV inactivation or disinfection, however, it may be more suitable for underwater photo-catalysis treatment. Since the wavelength of UVA is longer than UVC, the former has higher transmission ability and encounter less disturbance of suspending substances in water. Also, the exciting wavelength of UVA is between 365nm and 413nm which coincides with the wavelength of UVA. Hence, the spatial distribution of UVA radiation is studied for a 15W UVA lamp. The decaying tendencies of UVA radiation intensity were probed over horizontal and vertical distance, behind large amounts of experimental data. Optimal radiation conditions plan to be detected based on the research to guide the UVA treatment.
In light of urgent requirement of onboard ballast water treatment, this paper presents a laboratory study of an application of a novel wall-flow structure porous ceramic filter (PCF), with employment of UV light. It has been found that, for onboard treatment, the operational conditions may significantly affect the filter performance. To obtain optimal operational conditions and high filtration efficiencies on plankton, PCF was studied systematically though computational prediction and mathematical analysis. According to the strict criteria of International Maritime Organization (IMO) on ballast water treatment, high density of indicator algae were mixed into simulated ballast water as processing targets, and nearly 100% removal efficiencies are expected. Flow rate, algal density and algal size were chosen as three key operational conditions, was investigated on a 6L PCF. Response surface methodology (RSM) was used to evaluate the significance of the three factors on the response values of algae removal efficiencies.
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