Application Study On Electrolytic Treatment Of Ships' Ballast Water

The introduction of invasive marine species into new environments by ships' ballast water, attached to ships' hulls and via other vectors has been identified by the GEF as one of the four greatest threats to the world's oceans. The other three are land-based sources of marine pollution, over exploitation of living marine resources and physical alteration/destruction of marine habitat.In order to reduce the transfer of invasive marine species in ballast water IMO has joined forces with the Global Environment Facility (GEF) and the United Nations Development Programme (UNDP) to execut an international GloBallast programme. Dalian was selected as one of the six demonstration sites standing for East Asia area. The GloBallast activities commenced in March 2000 and the programme closed in December 2004.The project studied in this dissertation was the Item 1B4C as part of China activities of GolBallast Programme and received a financial support from GolBallast Programme and another fund from COSCO. The objectives of this study lie in two aspects: one is to establish the mechanism of how the electrolytic treatment to sterilize the aquatic organisms, and another is to solve the applicable problems to apply electrolytic treatment to ocean-going ships.The mechanism of sterilizing the aquatic organisms has been analyzed in this thesis. And it points out that the mechanism is an combined actions by many produced particles such as HClO, O ? and OH ?. It makes the previous mis-unstanding very clear that the killing mechanism is not the only reaction by single oxygen atom produced by decomposing of HCIO, but combined actions by many particles and effect of electric field.Many of experiments have been carried out and the effectiveness of electrolysis was verified. The experiments include the electrolytic treatment of 1. natural seawater, 2. seawater containing Artemia salina, 3.raw seawater and seawater with individual alga(qualitative analysis), 4.raw seawater and seawater with individual alga (quantitative analysis). The analyzed items of the each sample include but not limit tothe following: live/dead-identification, mortality and chlorine residue in the samples.Based on the experimental data, the kinetic model of chlorine decay in electrolyzed ships' ballast water was found by means of Non-linear fitting. The model is a second order reaction model and can be expressed as y=a/(1+bt), where the parameter a is often slightly greater than the theoretical value.Kinetic model of two algae treated by electrolysis was established by experiments. As for Nitzschia closterum with a density of 33.3x107/l_, the model can be expressed as CA=32.66e"058txl07. For Dicrateria spp. with a density of 106 xlO6/L, the model can be expressed as CA=100.63xl06/(l+1.97t).In according with the national standard-Laboratory Uniform Corrosion Totally Immersed Testing Method for Metal Material, the effect of metal corrosion of ballast tank caused by electrolytic ballast water was studied. It was verified that if treated with an initial chlorine concentration of 5.0mg/L, the increment of corrosion rate is not more than 35% in the first 12 hours. The corrosion rate will decrease after that.Experiments have been carried out on If and how much the THMs can be formed during the electrolytic treatment of ships' ballast water. After that the environmental acceptability and changes of the treated seawater property were analyzed.After the effectiveness of the treatment was verified, a prototype of Ballast water treatment unit was designed for practical on-board purpose. The performance of the prototype was tested in the Lab.