Large-Scale Testing of Treatment Processes as Alternatives to Ballast Exchange

摘要

Large-scale dockside experiments were conducted to evaluate the treatment efficiency of commercially available unit processes for preventing the transfer of unwanted species via ships' ballast water. The project was conducted at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science on Virginia Key, Florida. Test system water with natural assemblages of organisms was pumped from Biscayne Bay, Florida, at a flow of approximately 5.7 cu m /min (1,500 gpm). Unit processes included a hydrocyclone, a self-cleaning 50 micrometer screen, and a UV treatment unit. In addition to these unit processes, a mixing and injection system was fabricated to add suspended solids or dissolved coloring agents to the water stream to explore the effect of increased suspended solids (turbidity) or water color on UV treatment efficacy. The results showed that screening of the test water at 50 micrometers was effective at removing most of the zooplankton and a small percentage of the microphytoplankton. In contrast, hydrocyclonic separation was not effective for treatment. Initially, UV treatment was able to reduce the count of viable microorganisms to an undetectable level; however, significant regrowth of bacteria was observed. The impact of increased turbidity on all unit processes was considered negligible. hence, if UV treatment units are to be utilized, removal of suspended solids prior to irradiation may not be necessary if initial design dosage is high enough. At relatively low UV doses, as would be seen in waters of high color, however, the dose was insufficient to inactivate natural assemblages of microorganisms.